Image quality of AmScope microscope via the trinocular tube

[Crater Eddie]

There are several. I use Photobucket myself.

[75RR]

The easy response to being tempted by the used trinoculars from TechTrader - yes! but totally out of my affordability range there is nothing less than $AU4000.00.

ouch!!! I hope they had the decency to blush when they quoted those prices.

[Astyanax]

Thanks Crater Eddie.
Tell me about it 75RR! However I doubt it. It will have to be a China special.

[Astyanax]

Here is my best effort with my nikon SK E optics (4x plan, tucsen 10Mp usb camera with a 0.5x reduction lens), This image is typical of what I could do before the iris diaphragm disintegrated. (http://i296.photobucket.com/albums/mm19 ... nooom4.jpg). Hope that works. Image is from Corymbia sp. similar to a eucalypt.
There is still a little area out of focus at the edges; poorly stained or pale stained images show noticeable vignetting. Maybe the focus is a function of the reduction lens? Viewing the image through the eyepieces is perfectly in focus all over with similar vignetting.

The previous B/W Acacia is what I was able to get with the Vanox. Although the setup through the trinocular was different-it had eyepiece attachment, tube, and 5x eyepiece. Image is with minimal trimming captured on slide-film and scanned.

[75RR]

Just to let you know that the link works fine. Able to see and download image.
Pretty good resolution/area coverage

Send link to TechTrader - that should make them raise their game.

[gekko]

Lots of things for me to digest. A couple of quick comments: (1) current computer monitors have a horizontal resolution of 1920 (say 2000) pixels (mine is half that).

The images are for viewing on a screen and for pp presentations. I am a stickler for high resolution of low power images to show variations of fine detail over a large area. i.e., I would like to view images of ~5-10mm (lineal) or so from prepared slides. That detail can also be achieved with higher power albeit with a much reduced field of view. Maybe I am asking for too much. I will attempt to post an old B/W image of a typical slide and magnification I am aiming for.

One quick comment: current computer monitors have a horizontal resolution of 1920 (say 2000) pixels (mine is half that). I am not sure what "pp" means. I think a microscope with good optics and a good camera with high resolution will produce images with resolutions far higher than can be displayed on a computer monitor with 2000 horizontal pixels. So if the images captured by the camera have to be reduced to be seen complete (i.e. not in parts or by scrolling), then the screen or "pp" (whatever that is) will determine the ultimate display resolution, which will be far below what was originally captured. I think there is software to allow scrolling around a much larger image to see different parts (I believe The QCC sometimes uses such software, but I don't know anything about it). The only way I know of showing the resolution obtainable with a given setup is to show full resolution images of parts of the image that fit on the screen (for example, the center, the edges, etc.) which will show what resolution is as well as flatness of field.

(2) The Olympus objectives you show are the older (short, 3x.x mm parfocal distance) objectives with low strain (for polarized light use). I have them on my Olympus CHA microscope

As I mentioned earlier, I'll try to take images of a suitable slide with my Nikon and expand this to include the Olympus PO4 on my CHA (non-Koehler) microscope. I will post the center and edge of the full resolution images I get. Meanwhile, I would suggest that you take your time deciding. I'm moving more and more towards apochronaut's suggestion of ebay, but I would certainly take my time.

More later.

[gekko]

Some thoughts:

Here is my best effort with my nikon SK E optics (4x plan, tucsen 10Mp usb camera with a 0.5x reduction lens), This image is typical of what I could do before the iris diaphragm disintegrated.

Do you still have the Nikon microscope? What disintegrated was the iris diaphragm of the condenser? Would it not be worth replacing the condense (but if you get one, e.g., from ebay, just make sure it fits, as Nikon condensers come in at least two different mounting arrangements). My thinking is: it would be a pity to discard a fine microscope because the diaphragm was bad. In any case, you can use your 4x without a condenser (just place a ground glass or other diffuser over the light port). "Broken record" remark: make sure that the camera is in focus when the microscope is focused through the eyepiece (so you are using your objective at its correct working distance).

[Astyanax]

Yes thanks for your comments. I still use the Nikon SK E. The field diaphragm below the substage condenser which is controlled by the ring at the yellow arrow, the diphgragm is in the body of the microscope. My scope is similar to the image but it has a trinocular head and screws for centering the light beam above the field diaphragm the top of the tube just above the arrow (screws not shown in the pic). I can take some actual pics tomorrow and post them. I think my Nikon optics (the 4x was shown in the earlier crummy photo) are probably better than the inf. plans the Chinese are selling with their, but most likely the my objectives are not likely to be interchangeable.
The substage condenser has a screw on top-lens and its iris works fine. By the way, pp is for powerpoint presentations. Within the scope body there is a lever that bring in a lens in front of an inclined mirror. They work ok, but probably need a little adjustment and alignment.
I suspect that another option is to obtain another working base/body (there is one on eBay for ~$US200 delivered, but who knows how good it is mechanically).
Yes when photographing, the camera tube length is adjusted so that the camera sees a focused image when the image is in focus with the eyepieces. That is not easy to set because the camera response at high resolution has a significant lag.

[gekko]

That is a beautiful microscope, with Koehler illumination. So it is the field iris that is broken? Can you not have it repaired somewhere locally? Then I think you can even fit it with two CF eyepieces (or one CF eyepiece and the other keep using your present camera) and fit it with CF objectives and if you do that, you can get a CF planapo 4x for it? Just thinking "out loud", so to speak.

[Astyanax]

Its too bad about the Olympus objectives. When I bought them I thought they were plan not polarizing. However, it they are excellent for observation, but show some fall off in focus at the edges.

[gekko]

Its too bad about the Olympus objectives. When I bought them I thought they were plan not polarizing. However, it they are excellent for observation, but show some fall off in focus at the edges.

Well, the fact that they are good for polarized light is an added bonus (otherwise they are identical to regular objectives, other than the mounting of the glass elements being no or low strain, so in polarized light they don't show the strain pattern).

[Astyanax]

Just to let you know that the link works fine. Able to see and download image.
Pretty good resolution/area coverage

Send link to TechTrader - that should make them raise their game.

Thanks 75RR. That's a great idea. I am still in the throes of deciding to fix my SK E Nikon or go new ex China/TechTrader .... This discussion has made me consider points I had not contemplated before

THANKS GUYS for your great feedback.

[gekko]

I am still in the throes of deciding to fix my SK E Nikon or go new ex China/TechTrader

I believe in your shoes, I would fix the Nikon (without much hesitation ). You can later upgrade the optics with Nikon CF eyepieces and a 4x (or 10x) CF planapo (and not being tied down to infinity optics of an unknown brand). My 2-cents' worth.

[Astyanax]

Not sure what happened with an earlier post, it seems to have disappeared (its getting too late here). I noted that I have been using that lovely old Nikon for over 30 years but I can't get the Nikon repaired, just to look at it and service is almost as much a newy, the dealer told me that the parts for the antique are not feasible!
I may contact the eBay seller (somewhere in the States) of the SKE base/body and see how good the base is.

[gekko]

I hope apochronaut and others will chip in and give alternative opinions. Alright, let us back up a bit (sorry for all the stupid questions ):

(1) What exactly is wrong with the field diaphragm? Is it open enough so light covers the field of view of the 4x objective? If so, I think you can still use the microscope (albeit with very slight decrease in contrast that, I think, you can compensate for in editing). To check this, I will take pictures with my 4x objective with the field iris fully open and with it properly adjusted. If your field iris is blocking the light beam, is it possible to do something about that (without necessarily repairing it) so it no longer blocks?

(2) Can you remove the part of the optics above the base? Is the field iris in that part that is above the base or is it inside the base? If the former, can you simply remove it and improvise putting another iris in its place without changing significantly the geometry so the field lens would be at the same height or close enough?

(3) Does your condenser have a flip-down lens? If not, is the edge of the top lens housing serrated, indicating that it can/should be unscrewed (removed) for low power use? This will help me try out taking the slide pictures that would simulate your microscope.

I have a commercially prepared slide of a cross section of some plant that looks like it would make a good test to simulate your wood sections.

If anyone has ideas, please chip in.

[gekko]

I am still in the throes of deciding to fix my SK E Nikon or go new ex China/TechTrader

I believe in your shoes, I would fix the Nikon (without much hesitation ). You can later upgrade the optics with Nikon CF eyepieces and a 4x (or 10x) CF planapo (and not being tied down to infinity optics of an unknown brand). My 2-cents' worth.

I just want to explain that the reason I suggested that at some point you may want to "upgrade" to the CF system is the availability of a 4x planapo objective (I don't know, but I suspect that is not available for the older Nikon optics), and since you are after the best possible results from a 4x objective (at least that is my impression), my suggestion seems to me, if to nobody else, not too unreasonable .

[Astyanax]

I appreciate your efforts. The questions are no problem.

1) What exactly is wrong with the field diaphragm? Is it open enough so light covers the field of view of the 4x objective? If so, I think you can still use the microscope (albeit with very slight decrease in contrast that, I think, you can compensate for in editing). To check this, I will take pictures with my 4x objective with the field iris fully open and with it properly adjusted. If your field iris is blocking the light beam, is it possible to do something about that (without necessarily repairing it) so it no longer blocks?

The field diaphragm is in the body of the scope and below the black tube at the arrow (original photo). Top of the tube has a adjustable lens. The tube with that lens can be removed. However, the diaphragm is below that in the foot area. Please see the images. The diaphragm mechanism of thin interleaved leaves were somehow damaged. Initially locked into fully closed position then stupidly, attempting to open the diaphragm, the leaves were disrupted and the mechanism become totally interlocked. Attempts to fee it up were disastrous with the thin leaves separating in narrow 1/2 circular strips. Now there is a full opening. The diaphragm was associated with the multi-tooth cog in fig 58. I think that has answered Q1 & Q2.

(3) Does your condenser have a flip-down lens? If not, is the edge of the top lens housing serrated, indicating that it can/should be unscrewed (removed) for low power use? This will help me try out taking the slide pictures that would simulate your microscope.

Yes the condenser has a screwed-on top lens not a flip-down lens.

I have a commercially prepared slide of a cross section of some plant that looks like it would make a good test to simulate your wood sections.

Any old slide with a scale bar is adequate but a wood slide is great if you have one Gekko. I attached some critical images of the actual scope so you can see the setup.

I feel embarrassed about the amount of dust the photos show! Ever since the diaphragm issue I have only used the microscope for viewing for routine wood identification and needs a good clean!

[gekko]

Thank you so much for answering my aggravating questions

The field diaphragm is in the body of the scope and below the black tube at the arrow (original photo). Top of the tube has a adjustable lens. The tube with that lens can be removed. However, the diaphragm is below that in the foot area. Please see the images. The diaphragm mechanism of thin interleaved leaves were somehow damaged. Initially locked into fully closed position then stupidly, attempting to open the diaphragm, the leaves were disrupted and the mechanism become totally interlocked. Attempts to fee it up were disastrous with the thin leaves separating in narrow 1/2 circular strips. Now there is a full opening. The diaphragm was associated with the multi-tooth cog in fig 58. I think that has answered Q1 & Q2.

Yes, sorry about the mishap. I can only ask a dumb question to which I probably can guess the answer: is there a way to remove the field iris as a complete assembly and try to repair it on a desk (or have a microscope technician repair it) then reinstall it? This assumes that the leaves of the iris are not broken or damaged. I cannot really tell how deep below that top of the base the diaphragm is. If it is not deep, you may be able to make fixed field diaphragms out of cardboard, for example, and place it over the opening then replace the cylindrical part over it and see if you can achieve Koehler. Inasmuch as you are mainly interested in the 4x, you can make one for it to try. I realize that this may be a stupid suggestion, but I am exploring what might be possible without having the miciroscope in front of me.

Yes the condenser has a screwed-on top lens not a flip-down lens.

Then with the top lens removed, you should be able to get Koehler (to the extent possible with the damaged field diaphragm) with you 4x objective. I asked this so that I can try to simulate the conditions and answer the question: how do images taken with the 4x objective under Koehler with the field diaphragm correctly adjusted and with it fully open (as in your damaged case) compare. I'll try to do that tonight or tomorrow and send you the pictures.

Any old slide with a scale bar is adequate but a wood slide is great if you have one Gekko. I attached some critical images of the actual scope so you can see the setup.

Sorry, I don't have any wood slides. Thank you for the pictures.

I feel embarrassed about the amount of dust the photos show! Ever since the diaphragm issue I have only used the microscope for viewing for routine wood identification and needs a good clean!

Dust is a perpetual problem for anyone not living in an industrial clean room I think.

Again, my apologies for all the questions and thanks for providing all the answers

[gekko]

What I've learned so far:

1. My Nikon Abbe condenser (no flip-down or removable top lens) appears to let me setup Koehler illumination normally with the 4x (NA 0.1) achromatic objective. However the pictures I took showed obvious non-uniformity of illumination. I think I should have put in the diffuser: I believe that with the 4x/0.1 objective, the depth of focus of the system is large enough to make the bulb filament, which is focused on the back focal plane of the objective, visible in the image plane. At least that is my interpretation.

2. My Nikon achromatic condenser with a flip-down top lens does not allow Koehler to be setup with the 4x objective. With the top lens flipped down, the field iris controls the aperture (acts as an aperture diaphragm). The uniformity of illumination is much better than in 1 above, but I think I should also use the diffuser with the 4x objective.

I'll redo the pictures with the diffuser in.

It would be interesting to learn from other memebers if their microscope/condenser allows the use of Koehler illumination with a 4x or lower objective.

[apochronaut]

I wasn't aware that you did have a good microscope in your possession. My initial reading was that you were using a Vanox at work . I cannot see any reason to believe that you would benefit from the purchase of an average grade Chinese microscope over a repair and refitting of that Zeiss.
Chinese optics , are copies of existing older designs from the established companies. Buy a brand new Chinese 160mm microscope and you are getting poorer grade American Optical or Zeiss or Reichert optics from the past. Perhaps the coatings might be a little better but maybe not too.
Your field diaphragm is not a big job to fix, or replace. The parts will show up on ebay, or maybe even with a Zeiss repairman in Oz, or the repairman that looks after the Vanox at work. For a maximum of 500.00, you can have that Zeiss working like a dream.
4X objectives: The cheapest microscope objective to make is around a 10x. Once the focal length starts getting shorter, things get more and more tiny and complicated and prices of objectives escalate. It goes the other way too. If relatively linear lens formula calculations for longer focal length lenses are used within an equivalent barrel conformation, curvature of field, distortions and illumination falloff begin to cripple the long focal length lenses. Most standard 4x lower mag. lenses suffer from all kinds of problems when made to conventional formula. There has been a lot of work put into 4x and lower objectives to get sharp,flat,evenly illuminated and chroma free pictures out of them.Conventional 4x and lower objectives cannot give that performance but some of the more advanced designs, with larger bodies and much wider and more glass can, albeit in an altogether different price category.
You should look and see just what is on that Vanox. I would not be surprised, if even one of the low power objectives isn't worth 2 or 3 times the cost of an entire Chinese microscope. If you want to take flat , high resolution pictures at those low magnifications, you are not going to get that out of a Chinese microscope within your budget.
Plan is a relative term. There are no standards. Plan simply means that the image is flat across the field of a specific eyepiece. Put in a different eyepiece , or even a wider field eyepiece from the same Mfg. and often planarity is lost. Objectives can be plan in a range ,anywhere from 15mm to 28mm f.n. depending on the make. Low power objectives are harder to obtain plan performance out of, so companies are jumping through hoops to get that needed performance and a lot of standard 4x and lower objectives marked plan, are anything but, especially when seen through a camera.
You can bring that Zeiss up to a good level with much less capital input , than a much poorer Chinese microscope would cost, and if you want that low power flat field performance, your money would be better spent on 160mm optics than a lot of new plastic.
You would be best to do some research on just which 160mm objectives in the low powers can do it for you , then refit your Zeiss with 4 matched objectives and a pair of matching eyepieces. At that point then, you can build your photosystem. I will look and ask some questions on your behalf too.
A question I have, is regarding the wood samples themselves. Are they covered , or uncovered?( i apologize if that question has already been covered--i missed it). Your choice of objectives is critically different, depending on the answer, and if both is the case, then you need to investigate the need for a mixed set.
In choosing matched objectives, don't carry any innate prejudices. All of the older makers of microscopes made first rate optics. In the fixed tube type of lenses Leitz, Bausch & Lomb, Zeiss and almost all other companies, had differing systems over the years so do not base a decision of compatibility on brand. All objectives and eyepieces , must be from the same series.
Here is a rough guide. Zeiss had pre-war Zeiss Jena, East German Zeiss Jena( Jenoptik), and Carl Zeiss West Germany. All were 160mm and not necessarily compatible with each other. Bausch & Lomb had 160mm and then the flat field series. They are incompatible. Leitz had 170mm and then 160mm. All American Optical 160mm are fairly compatible. Olympus short barrel lenses are incompatible with the later long barrel ones. Baker, Cooke, Cooke-Baker and Vickers went from short barrel to D.I.N. and they are not compatible. Reichert 160mm seem to be all short. The D.I.N. objectives seem to be infinity but in the transition period, I could be wrong about that. I think, Nikon went through a similar conversion as Olympus( any one know for sure?). Wild were always 160mm and I do not think there was a barrel length change(??).

[Astyanax]

Wow! thanks apochronaut and gekko for your analysis, comments and suggestions. I feel somewhat embarrassed about the state of my work-horse Nikon SKE scope and for the misunderstandings I may have created: I worked with the Vanox at CSIRO, and retied 10 years ago, but I have had my own Nikon SK E, for ~30 years. The photos posted of the olympus objectives are an additional set to the ones the Nikon has; I purchased them at a "fire sale" when the wood products part of CSIRO was shut down three years ago. Unfortunately, I assumed that the objectives marked "PO" were plan rather than polarizing! The less than plan performance I discovered myself and gekko confirmed, although in spite of the fall off they are superb for observation and seem to work ok with the Nikon albeit really superfluous for my need as I am unlikely to do much polarization work.

I am not sure if its spec got diffused over the series of posts, but the Nikon has the original (late 1960's early 1970's) objectives marked "Plan" (4x, 10x, 40x and 100x oil).

Gekko: unfortunately I looked into and cannot afford to repair the Nikon because the cost is too high (Nikon Supplier) and who knows how decent other back yard guys are.
Unfortunately the tiny laminae from the iris have long gone and were a topic of endless fascination for my grand-children!

For routine examination I have just worked with the scope as is, but I would like to continue with photomicrography of xylem sections and I was toying with the idea of improvising but I am not that good with micro mechanics. It seems that the disaster was probably my fault for being too rough with the seizes iris. However, potentially I may be able to place a large rubber/plastic washer of approx. the right diameter to provide conventional Koehler setting with the 10x. Without the iris, the 4x may work along your suggestions gekko. It will be interesting to see your results.

Without wishing to complicate the matter further while pursuing Koehler performance with the 4x objective, I would like to get a larger field of view from low power images obtained with a USB camera and 0.5x reduction lens (which I have). The end result is still a rather a small field of view (~1.5x2.2mm). Double that would be ideal. Perhaps stitching is the answer. Anyway that's what started this fascinating thread!

[Astyanax]

Further to the the following point from of my last post,
"Without wishing to complicate the matter further while pursuing Koehler performance with the 4x objective, I would like to get a larger field of view from low power images obtained with a USB camera and 0.5x reduction lens (which I have). The end result is still a rather a small field of view (~1.5x2.2mm)"
with everything being equal (famous last words!) similar size of the field of view also appears to be the case with the new microscopes and seems to be a function of the reduction lens and probably the size of the camera sensor.
To that end, do you think that maybe a 0.4x or a 0.3x reduction lens might be give a larger field of view with a 4x objective? I have seen them advertised by some digital camera makers.

[Astyanax]

Progress:
gekko you are a genius! After I cleaned and realigned the old girl, and removed the screw-on sub-stage condenser lens, I was able to set up Koehler I think, using a thin washer inplace of the broken iris diaphragm to enable me to focus the sub-stage condenser, getting one the right size to sit just outside the field of view is still a challenge. Once the condenser is focused, taking out the washer, i.e., field diaphragm with no stop (fully open), the image seems uniformly lit over the field of view. A diffuser placed in the light path helps although I have never liked using it because it tends to reduce the crispness of the images.
Interestingly, when Koehler is set either with the 4x objective or conventionally with the 10x objective, various scratches from the surface of the adjustable lens atop of the tube on the foot of the scope come into focus (annoying!). I forgot about all that when I made my last batch of micrographs a couple of years ago... I had to back the condenser off a tad to smear the scratches out. Most of that is no big deal unless the stain from the slides is poor/faded.

[gekko]

Astyanax,
Thank you for the updates. I have to go now, but a quick note: it occurred to me that you can solve the problem by using a mirror over the field lens (I think you can/should remove that cylindrical part iwith optics that sits over the field lens??) and get one of the excellent old microscope lamps (I think Zeiss, AO, etc. made some really good ones with focusing collector lens, field diaphragm, and a place to insert filters). They come on ebay every now and then and the will give you much flexibility (at the expense of some inconvenience), but that is the way Koehler used to be implemented . I hope that apochronaut, lorez, or others may fill in and may give you their opinions and advice regarding this idea as I don't have first hand experience with these.

[apochronaut]

The field diaphragm ( washer in your case) and specimen image plane should be be the same for kohler illumination, so imaging the imperfections in the top lens means you didn't have kohler illumination at that point. I wouldn't worry too much about it anyway,just get rid of them by defocusing because the importance of kohler illumination at very low magnifications is widely over exaggerated. The best way to improve contrast and reduce glare with those objectives, 10x and under is to back off the condenser and close the iris . The uneveness of the field at low magnifications is largely due to the illumination needing to be spread over the widest field possible, so what usually happens in simple illumination systems such as yours is that, a central hot spot is surrounded by a ring of diminishing intensity. It's an effect caused by the limitations in the illumination and substage lens systems and curvature of field, spherical aberration and chromatic aberration are all having a big party under the stage. Kohler illumination isn't going to fix that,. Using a diffuser and or aux. plano convex lens, to effect some corrections under the condenser usually alleviates this condition. The argument against this is that a diffuser reduces the intensity of illumination but that isn't a problem with low power objectives. It begins to be a possible problem from N.As. of .40 or so and up, at which point focusing the illumination system properly becomes increasingly more important.
Regarding using a reduction tube lens. The original Nippon Kogaku camera tube lens systems are very expensive. At the same time , you can buy a Chinese made lens advertised for Nikon for 59.00. The camera tube lenses from China are all the same lenses just with adapters or couplers for various cameras. There is no attempt to correct individually for microscope lens characteristics, as there is with factory tube lenses. They tend to give a focused hot spot in the middle, then lots of curvature of field and chromatic aberration. This can be cropped out but at the expense of f.o.v. If you use a fractional tube lens, to increase the f.o.v. and it sees close to the same or more of the field than the the original 18mm oculars do, then it could also overstep the planarity of the objective and pick up the uncorrected areas at the edge of the field, as well as image areas of the subject plane that are beyond the range of good illumination. It is hard with fairly conventional microscope optics and tube lenses to get maximum field capture and maximum sharpness and planarity. Most of the systems that do pick up a full field as well as provide full frame imaging, are using highly corrected large format camera, process or enlarger lenses( sometimes reversed) to achieve quality camera images. There is lots of information on the web regarding various photographers systems( photomicrography.net , micscape, various private websites)
With certain infinity corrected systems, where the image leaves the objective with complete or almost complete corrections( AO, Reichert,Olympus, Nikon) a conventional longer prime camera lens ( about 200mm), focused at infinity provides a fairly large frame coverage, full field capture and an image quality commensurate with the quality of the camera lens itself. Unfortunately, most microscope camera tube lenses , with usually very small diameter glass, crop the field excessively in an attempt to keep the image as sharp and flat as possible. Getting wide flat microscope images, takes some ingenuity.

[apochronaut]

Astyanax,
Thank you for the updates. I have to go now, but a quick note: it occurred to me that you can solve the problem by using a mirror over the field lens (I think you can/should remove that cylindrical part iwith optics that sits over the field lens??) and get one of the excellent old microscope lamps (I think Zeiss, AO, etc. made some really good ones with focusing collector lens, field diaphragm, and a place to insert filters). They come on ebay every now and then and the will give you much flexibility (at the expense of some inconvenience), but that is the way Koehler used to be implemented . I hope that apochronaut, lorez, or others may fill in and may give you their opinions and advice regarding this idea as I don't have first hand experience with these.

I

I'm lost on this. I do see a relay mirror under the broken field diaphragm and in front of what should be a field lens but is actually a collector lens, a moveable neutral density filter, and possibly a diffuser, between them. The adjustable lens above the field diaphragm is the field lens in this system.
Kohler's original settup had the following sequence of elements. Lamp( gas flame, not a filament), field lens, field diaphragm,mirror, condenser diaphragm, condenser lens. Most modern microscopes with a reflected in base illumination have taken a bit of license with that and replaced the field lens with what they call a collector lens, then mirror,field diaphragm,field lens,condenser diaphragm,condenser lens. So, technically, Kohler illumination is out the window anyway, because the collector lens is a fixed focus type and the field lens ( above the field diaphragm and mirror ?) is focusable and in the wrong place.
Kohler was using a remote illuminator, with a lens and diaphragm ahead of it. By moving the illuminator relative to the mirror, he could alter the focus of the flame. Some better microscope illumination systems( AO-Reichert Diastar is one I am quite familiar with), have a focusable field lens just ahead of the bulb, then a field diaphragm , then the mirror, a dispersion lens , then condenser diaphragm and finally condenser lens. It is almost identical to the original settup of Kohler.
I'm not sure where this mirror is supposed to go? Are you suggesting setting up a mirror and remote illuminator? If so, Why?

[Astyanax]

thanks apochronaut and gekko
apochronaut if I understand you correctly, what you describe for Koehler is exactly part of the old nikon SK E system. An external in /out movable lamp for focusing including adjustment screws for lateral movement then a thick lens in front of it then a slide in diffuser filter (marked with (L) or another lens can slide in marked (M) and a third lens marked (H) for high power The three positions can be switched as required. Then comes the inclined mirror then the field diaphragm then the adjustable field lens atop of the tube with the two adjusting screws again for transverse adjustment.
The scratches are from the field lens (adjustable for centering which is needed mainly for high power).
After gekko's suggestion to remove the top condenser lens, I was able to get uniform illumination with the 4x objective (just as with the 10x) that I was not able to achieve before. However, I was hoping to maybe find some way of obtaining a wider field of view than can be obtained with the 0.5x reduction lens fitted to the camera via the cmount.
If that is not doable physically and it probably isn't then I'll go for stitching images to get the wider field. I thought that as some of the Chinese microscopes are advertised as having a similar field of view with reduction lenses as can be seen through the eyepieces, that there may be some way of achieving that physically.
At this stage I believe that the SK E has been optimised as much as it can be.
Also I will wait to see what TechTrader can come up with and keep you posted. In the mean time I will post some images with the current settings.
apochronaut you are right about there being no substitute for a wide lens. I may try to improvise some transmitted lighting arrangement with my stereo and see what happens...

[gekko]

Are you suggesting setting up a mirror and remote illuminator? If so, Why?

Yes. Until Astyanax repairs his microscope (or if he decides not to) this will give him fully functional Koehler at the expense of some "cumbersomeness". At least that is what I think.

when Koehler is set either with the 4x objective or conventionally with the 10x objective, various scratches from the surface of the adjustable lens atop of the tube on the foot of the scope come into focus (annoying!)

Something must be wrong or wrongly adjusted. Microscope makers do not place lenses or other glass surfaces in an image plane (one exception being an eyepiece graticule) so dust or scratches should not be visible.

I must admit that I've not yet perused the above posts, but from a quick look I would say that I would not use a USB adapter with your Nikon. apochronaut may have already commented on this so I'll wait until I've read his comments before commenting further to avoid duplicating what he said.

[gekko]

Sorry, another very long post.

The less than plan performance [of the Olympus P objectives] I discovered myself and gekko confirmed, although in spite of the fall off they are superb for observation and seem to work ok with the Nikon albeit really superfluous for my need as I am unlikely to do much polarization work.

I just want to emphasize that although those are for polarized illumination, you can use your regular Nikon objectives for that as they would normally be quite good (P lenses would be desirable I think for petrology where one is making measurements). You can see a recent example of a picture of an alga in polarized light using a "non-P" objective here if you wish (the one in the lower right quadrant): viewtopic.php?f=6&t=1054

apochronaut's question about the use of cover glass is very relevant in general. I had assumed that you do use them, although at NA below 0.2, which includes your 4x which appears to be the one that you mainly use, it should not matter whether you use a cover glass or not.

Gekko: unfortunately I looked into and cannot afford to repair the Nikon because the cost is too high (Nikon Supplier) and who knows how decent other back yard guys are.
Unfortunately the tiny laminae from the iris have long gone and were a topic of endless fascination for my grand-children!

In that case you will need a new iris. However, I would enquire locally regarding microscope technicians who might have at one time been associated with Nikon. If you find one, he may be able to improvise a replacement (and if you are super lucky and he may already have a replacement or a broken microscope that he can cannibalize). On the other hand, apochronaut's suggestion of checking ebay for parts or even a whole similar microscope that you may acquire at reasonable cost to swap parts is excellent. Does removing the field iris assembly look feasible?

gekko. It will be interesting to see your results.

Yes, I hope to get those soon. I am interested to find out too.

I would like to get a larger field of view from low power images obtained with a USB camera and 0.5x reduction lens (which I have)... do you think that maybe a 0.4x or a 0.3x reduction lens might be give a larger field of view with a 4x objective? .

Yes, you should be able to get a lower magnification adapter. While a USB adapter is not a good idea to use with your microscope (a much better system would be to use an original compensating eyepiece or an actual pre-CF Nikon projection lens if you can find one to project an image on a DSLR or mirrorless camera body). Yet using a USB adapter with a 4x objective should still give good results (but results will get worse with higher power, higher NA objectives due to lack of optical correction).

Easier still, and that will give excellent results and maintain the corrections in the compensating eyepiece, is to use the 'afocal' method: a camera with lens attached, could be a point-&-shoot, to look through the microscope's eyepiece (you can support it on a tripod or other support-- always better to support it independently of the microscope to avoid shutter vibrations). I think apochronaut mentioned something along those lines above. The difficulty might be finding a point-&-shoot with a zoom lens that has an entrance pupil close to the front element in order to avoid vignetting. But quite a few people get superb results and display them at the photomicrography and the german microscope forums. You can find out the brand and model of camera they use if necessary.

And yes, I think the field of view will get proportionately larger as the power of the adapter lens is reduced. What is happening is that your current adapter is projecting an image much larger than the camera's sensor, so the image seen by the camera is effectively cropped.

apochronaut's comments on the flatness of field of low power objectives and on photo projection lenses are somewhat over my head, but are well worth reading. I think I have already answered his question about why I suggested the use of a separate microscope illuminator.

Also I will wait to see what TechTrader can come up with and keep you posted. In the mean time I will post some images with the current settings.

Here I agree fully with apochronaut: I would spend the money on fixing the Nikon before I would buy a generic Chinese model. At the beginning of this thread, I didn't realize that you already had a good microscope (albeit in need of some repair).

apochronaut if I understand you correctly, what you describe for Koehler is exactly part of the old nikon SK E system. An external in /out movable lamp for focusing including adjustment screws for lateral movement then a thick lens in front of it then a slide in diffuser filter (marked with (L) or another lens can slide in marked (M) and a third lens marked (H) for high power The three positions can be switched as required. Then comes the inclined mirror then the field diaphragm then the adjustable field lens atop of the tube with the two adjusting screws again for transverse adjustment.

So what does the long cylinder that sits above the field lens do? That confused me.

[apochronaut]

Kohler illumination was simply the first system that overcame the problem of the unevenness in the illumination field caused by either too small a gas flame or a flickering flame. With daylight it is unnecessary. The idea was timely because the primitive tungsten lamps that superceded gas flames and carbon arc lamps needed even more help. It has become a kind of mantra for microscope marketing, similar to an abbe condenser. It is used to define a sort of minimum quality of a microscope illumination system but Kohler illumination and an abbe condenser are just that, basic minimums that are acceptable ,not desired for endpoints. Fine research microscopes use neither or at the very least, improved modifications of them and many microscope designers have used modified systems.
The only thing wrong with this Nikon microscope is that it has a missing field diaphragm, not an entirely defective illumination system. Nikon , by the time they made this microscope probably knew more about microscope illumination systems than August Kohler did in 1893. I'm sure the system is fully capable of providing a bright even field for photomicrography. The imaging of dust particles in proximity to the field diaphragm probably has to do with the fact that the washer being used as a field diaphragm is sitting higher than the original diaphragm sits , so in order to image the diaphragm in the object plane the dust is proximal enough that the broad depth of field of the low power objective is picking them up. Backing off the condenser focus is the correct thing to do in this case. Don't get knickers in a knot over kohler illumination for a 4x objective, just slip a milk or frosted glass filter in the filter tray under the condenser, or if it doesn't have one, get one that fits right on top of that field lens but don't start removing anything...it's meant to be there. BY the time you are dialling up 20 or 40x objectives, you can take out the diffusion filter and you won't be seeing the dust .