My microscope (overkill eyepiece alert!)

[Javier]

Hi,

I introduce my microscope. It's a pretty basic monocular Chinese microscope. I'm glad I followed Oliver's advice on buying one with a chariot and a condenser with filter holder. I love the darkfield views. The 4x and 10 x objectives give pretty sharp views, but the 40 x and 100 x give somehow mushy views. I know I should expect some blurriness because of the added magnification, but I'm not sure these objectives meet the standard DIN quality of other popular brands. I'm not complaining though, I'm having a great time with this microscope.

The weakest optical link was, of course, the eyepiece. Too narrow and low contrast. Given that I own some good quality eyepieces from my telescopes, I tried a few of them. Not all worked well, but this Explore Scientific worked like a charm. I somehow managed to adapt the 1,25" format to the microscope drawtube. I suspect 68º of apparent field of view might be overkill for microscopy, but the views are wonderful.

Regards,
Javier.

IMG_5228 (2).jpg (103.27 KiB) Viewed 8929 times

[EYE C U]

what mm is it?

[75RR]

The 4x and 10 x objectives give pretty sharp views, but the 40 x and 100 x give somehow mushy views.

Make sure there is very little water and detritus under the cover slip on both the 100x and the 40x so that the subject you are viewing is as close to the bottom of the cover slip as possible.

Additionally, the 100x requires immersion oil. Just place a drop on top of the cover slip over the area you are looking at.

https://www.youtube.com/watch?v=PemhS8WXlqM

[Javier]

what mm is it?

It is a 24mm eyepiece.

[Javier]

The 4x and 10 x objectives give pretty sharp views, but the 40 x and 100 x give somehow mushy views.

Make sure there is very little water and detritus under the cover slip on both the 100x and the 40x so that the subject you are viewing is as close to the bottom of the cover slip as possible.

Additionally, the 100x requires immersion oil. Just place a drop on top of the cover slip over the area you are looking at.

https://www.youtube.com/watch?v=PemhS8WXlqM

Thanks for the tips about the preparation of the subject.
For the 100x I did use the inmersion oil sample that came with the scope.

I'm trying to explore the possibilities of low mag views as much as I can. I find the gap from 100x to 400x very big. I see a 20x objective in the future.

[Javier]

Please help me understand this:

I cannot place the telescope eyepiece at the exact focal plane of the stock eyepiece, because of a mechanical issue. It produces a minimal focus shift. As far as know, the NA refers to the angle of the light cone captured by a given objective. So, if a focus shift produces the objective being closer or farther from the specimen, does it means that I'm actually changing the NA of the objective because I'm changing the angle of the light cone captured? I guess that if this is true, that will also affect the objective's performance.

Thanks in advance for your patience!

[apochronaut]

The focal shift you refer to is referred to as a change in the working distance of the objective lens. This is being caused by the fact that your telescope eyepiece is designed to focus on the intermediate image at a different point than the objective is designed to bring it to focus at.
The angle of acceptance that the objective lens is designed to have will not change with a lower or greater working distance. That is a fixed specification . What will change is the magnification and the field coverage of the illumination circle.

[Javier]

The focal shift you refer to is referred to as a change in the working distance of the objective lens. This is being caused by the fact that your telescope eyepiece is designed to focus on the intermediate image at a different point than the objective is designed to bring it to focus at.
The angle of acceptance that the objective lens is designed to have will not change with a lower or greater working distance. That is a fixed specification . What will change is the magnification and the field coverage of the illumination circle.

Thank you!

[MicroBob]

Hi Javier,
the tube lenght and the placing of the intermediate image in the tube are part of the objective's calculation. So using other eyepieces can have an impact on the image quality. Whether this really shows in practical use is another question, it is best to try yourself. By swapping back and forth with the comparratively narrower original eyepiece you can check that you don't suffer from and disadvantage here. I have never heard of anybody to use a telescope eyepiece on a microscope, not even astronomers do this. But this doesn't mean it is a bad idea of cause.

Objectives soften are calculated in combination with the eyepieces. You might see color fringes towards the borders in this case.

Bob

[apochronaut]

In this case, the microscope has quite pedestrian achromat objectives with an already unacceptable level of uncorrected curvature of field and multiple peripheral aberrations. It's native eyepieces no doubt do little to correct any of that stuff, so increasing the f.o.v. probably doesn't make matters much worse, except to increase the volume of it.

[Javier]

Hi Javier,
the tube lenght and the placing of the intermediate image in the tube are part of the objective's calculation. So using other eyepieces can have an impact on the image quality. Whether this really shows in practical use is another question, it is best to try yourself. By swapping back and forth with the comparratively narrower original eyepiece you can check that you don't suffer from and disadvantage here. I have never heard of anybody to use a telescope eyepiece on a microscope, not even astronomers do this. But this doesn't mean it is a bad idea of cause.

Objectives soften are calculated in combination with the eyepieces. You might see color fringes towards the borders in this case.

Bob

Thank you Bob! I checked again, and the focus shift with this eyepiece is so small (a minimum turn of the fine focus knob) the I doubt it will have any noticeable impact on the image. What is very noticeable is the increased contrast and sharpness of this eyepiece in comparison with the stock one. I see no fringe either with the telescope eyepiece.

In this case, the microscope has quite pedestrian achromat objectives with an already unacceptable level of uncorrected curvature of field and multiple peripheral aberrations. It's native eyepieces no doubt do little to correct any of that stuff, so increasing the f.o.v. probably doesn't make matters much worse, except to increase the volume of it.

Not quite. The pedestrian achromat objectives show of course off-axis aberrations, as expected, but the ultrabasic stock eyepiece (maybe a Huygens design?) makes it much worse. Placing an eyepiece with a superb (Panoptic) design helps a lot by not introducing extra aberrations and therefore making the usable field bigger. Note that I said "not introducing" extra aberrations. I don't know about microscopy, but in telescopes, eyepieces are not designed to correct aberrations from the objective.

For the uneducated microscopy eye, there is no such thing as an unacceptable level of field curvature or peripheral aberrations. I know it took me at least one year to start being annoyed by the coma of my telescope.

[apochronaut]

All lenses have close to zero aberration on axis. For any given magnification, the degree of off axis total distortion and aberration is in some proportional degree dependent on the diameter of the lenses. A conventional and fairly normal field # for a Huygens equipped, achromat microscope with a 23.2mm ocular tube is approximately 13mm. At that field #, Huygens eyepieces provide acceptable corrections for average B.F. microscopy. If one extends the field stop of an average Huygens eyepiece out to the modern standard W.F. of 20mm, then all sorts of distortion and aberrations become apparent. If one were to design a Huygens eyepiece of say a 6 ft. diameter, it would be easy to use that eyepiece with a 20mm field stop and the field would be almost completely distortion and aberration free.
Some early microscope companies such as Bausch & Lomb, used 1 inch optical tubes until they felt obliged to fall into step with the R.M.S. convention around 1905 or so and switched to 23.2mm. Those early Huygens eyepieces in the 1" format provided considerably wider, flatter and more well corrected fields than the subsequent little 23.2mm ones.
After the general adoption of the R.M.S. ocular tube standard, many companies sought to improve on the Huygens design for more elite or non-standard microscope applications and eventually in a cost effective way for more basic microscope applications. Ramsdens and Kellners were occasionally used but for Apochromat systems, mostly modified orthoscopic eyepieces were relied on. Eventually, along with advanced glass introductions, advanced proprietary eyepieces became the rule, not the exception, with many elements employed in a narrow framework to provide wide flat, well corrected fields. A big part of the proprietary nature of these eyepieces was to neutralize negative optical attributes of a specific family of objectives.
To keep the cost of stereo microscopes in line for many years, yet provide the wide fields required for stereo microscopy, most companies continued to use Huygens eyepieces but extended the tube diameter out to 30mm. Later, as more glass formulas became available, some companies abandoned the 30mm tubes in favour of more sophisticated 23.2mm designs, which gave equally wide fields but also better corrected fields. Some companies continued to work with 30mm tubes.
It has long been recognized that a wider piece of glass naturally has a higher freedom from distortion and aberration.

[Javier]

What can I say?

You obviously know your stuff, and if you say Huygens have an acceptable correction for B.F. (I assume this is bright field) microscopy, I'll take your word for it. The stock eyepiece of my microscope has an extremely narrow on-axis clean field, and it's almost unusable at a short distance from its optical axis. I assume it's a Huygens, but then again, the same EP design can be made in so many quality levels.

At the edge of the field, the level of distortion is almost funny, with a good amount of chromatic aberration added. I'm not saying that the 68º won't show more of the objective aberrations because of the greater AFOV (because it will, you can't avoid optics laws) but it's -at least- cleaning quite nicely an equivalent FOV of the stock eyepiece and delivers a sharper and more contrasty view, on and off-axis.

[BramHuntingNematodes]

I think the take away is that a good telescope eyepiece is better than a terrible microscope eyepiece but won't be better than a good microscope eyepiece. Hey, we're all working with what we got

[DrPhoxinus]

Here is an interesting discussion of using microscope eyepieces on telescopes and why the vice versa isn’t good

https://www.cloudynights.com/topic/6051 ... elescopes/

Gerard

[apochronaut]

I can't say that I found it excellent, especially where some of information is completely incorrect. Post nine states to beware of K and C marked eyepieces because they are designed to be used with non apochromatic objectives. That is the opposite of fact and in the case of eye pieces marked K, it could refer to Kellner or to plan compensating, where the K reflects an origin in another language other than English.
Telescope geeks need to understand that because telescope eyepieces are the magnification arbiter of a telescope, their capabilities have been more standardized than with microscopes, since swapping eyepieces is a normal practice . Viewing angle and design type are meaningful and relevant.
While those specifications are also be relavent to microscope eyepieces, there are so many other factors that play into the design of microscope eyepieces, often on an individual basis, that the basic standards associated with telescope eyepieces can't come close to covering the bases of categorizing them. Even two Huygens eyepieces designed by two different microscope companies can have different corrections and degrees of field curvature, something that isn't often factored in with telescopes.

[Javier]

I will just point out that the vast majority of observers don't use microscope eyepieces on their telescopes. Those who try them, they don't use them exclusively (at least I don't know anyone who does that). If I purchase in the future a nice microscope eyepiece, of course I'll try it on my telescopes, just for fun.

Microscope eyepieces just don't meet many of the astronomical modern standars. There is a niche for minimal-glass ultra narrow field eyepieces in astronomy, but even for those there are better dedicated astronomy eyepieces. From what I've read on this thread, the same is true for microscopes and telescope eyepieces.

[Javier]

Hey, we're all working with what we got

So true!

[Rossf]

Hi-my advice-definitely get a 20x-My favourite used magnification-good balance of sharpness and depth of focus-you could upgrade the 40X to a second hand fluorite objective-they definitely have more ‘bite’ to their sharpness.
Regards Ross
Oh and I love the monster eyepiece! Gave me a chuckle...

[Javier]

Hi-my advice-definitely get a 20x-My favourite used magnification-good balance of sharpness and depth of focus-you could upgrade the 40X to a second hand fluorite objective-they definitely have more ‘bite’ to their sharpness.
Regards Ross
Oh and I love the monster eyepiece! Gave me a chuckle...

Thanks!

I will definitely upgrade my scope with a 20x objective in the future. There are not many choices in the local market, though. I'm glad you like the "monster" eyepiece. In the astronomy world, it's just an eyepiece. Nowadays, monster telescope's eyepieces are almost as big as the entire microscope!

[Greg Howald]

It is fairly obvious that those of you who have replied to this post know what you are talking about. I have a slight amount of macular degeneration. It is arrested and probably not going to get any worse but because of it I have played around with different eyepieces and tube lengths. I made adaptors so I can switch from 23mm eyepieces to 30mm. That's been much less strain on my eyes. What I'm amazed at here is that in the original post it is stated that Good focus is achieved with a 4x objective. When I increase to 30mm eyepieces it does add to tube length. I have had to either place a blank slide under the specimen slide or use an objective extension of that thickness or slightly more to be able to focus at 4x. But I've been able to adjust contrast well enough to get good images at higher magnifications.
I also notice that par focal is out the window and I have to lower the stage to focus rather than raise the stage when I increase magnification. Using the telescope eyepiece seems interesting indeed.
Take care. Greg

[Javier]

Greg, how did you adapt the eyepiece to the microscope?

I taped the microscope's tube to make the eyepiece fit from the outside without play. It's rough, but it works. I would much prefer a binocular scope, but I was on a budget, so I try getting the most of it. The Explore Scientific eyepiece is more roomy and expansive than the stock one. With the adapter, they are virtually parafocal. The 17 mm Plossl needs some refocus, and that is a problem with the 40 x objective. I couldn't make the 18.2 mm DeLite eyepiece (the best I have) work, because its field lens is to close to the edge of the barrel. I would need a new tube. But at that point, I would probably sell this microscope and buy a binocular one.

[Greg Howald]

Hi. Sorry to be so long in time getting back to you. I've had a very busy week indeed
To make eyepiece adaptors I used compressed cardboard tubes. Actually, I used empty paper towel tubes. I cut them to length with some difficulty so they would insert into the tube 1st a length of 1 1/2 inches and stand out from the tube 1/2inch. So the tube was
2 inches long. I wanted it to go in for such a distance to give stability. I glued everything together with super glue. Don't get that near lenses. It gasses off for up to 24 hours even after it has set and it will destroy your optics as a slight layer of glue forms on them.
Any way. After the glue was set it Cut half inch strips and put them on layer by layer until I reached an outside diameter of 30.1 mm. Then I glued on two layers of strips that were 1 3/4 inches long. That meant the lenses would insert to a depth of 1 1/4 inches. That would also be stable. I let everything dry for two days and then put on a coat of polyeuretane varnish. That made in hard as a rock and when it was done I used it without difficulty.
Some guys have lathes. I have paper towel roles. You had tape. Use what ya got. Have fun.
Greg