Experiments with afocal photomicrography: illuminations, spider threads...

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MichaelG.
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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#31 Post by MichaelG. » Fri Feb 16, 2018 8:35 am

.
Here is another little gem of a graph, which may be of interest:
Useful wavelengths
Useful wavelengths
IMG_1801.JPG (212.61 KiB) Viewed 11697 times
MichaelG.
.

Reference is part II of a III part series:

OBSERVATIONS ON MICROSCOPE CONDENSERS, OBJECTIVES, AND EYEPIECES
Payne, B. O.
Journal of the Royal Microscopical Society, December 1950, Vol.70(4), pp.317-341
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Hobbyst46
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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#32 Post by Hobbyst46 » Fri Feb 16, 2018 11:06 am

MichaelG

The graph indeed is a very nice demonstration of the known merits of Fluar and Apo relative to achromats. I also learn from it that the advantage of the better corrected lenses is more prominent in the blue-violet region than in the red region. The graph also confirms that Neofluars are almost as good as Apochromats, as often stated.

So to the question - which is practically better and more important - remove "excess" blue or use better corrected optics? perhaps should do both ?

Yesterday I recorded some images of my test specimen (the micrometer marks) with long-pass filters of cutoffs of 435 and 455nm. To my eye, the results are about the same as with the KR12 filter - no dramatic differences, though I still must look at the details.

Better optics is less accessible. My 40x, 63x, 100x are fine - Neofluar/Planapo. So I would like some low-mag corrected lenses. On eBay, I do not find any Zeiss 10x Neofluar/Planapo. The very few 16x Neofluar/Planapo are either ~250 USD (including 40-60 USD postage and 17% import taxes) or ~150-180 USD sold "as is" etc, no proven optical quality.

It might be interesting if anyone has published an objective study of the quality of images recorded with a digital sensor vs the LED light spectrum...

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#33 Post by Hobbyst46 » Thu Feb 22, 2018 8:53 pm

Following my struggling with afocal photography with a stage micrometer as test specimen, I was frustrated by the chromatic aberrations.

Then I discovered the Peter Hubel Mikroskopie-ph.de site. Among fascinating high resolution photos of diatoms, I found a thorough investigation of the performance of cameras+microscopes, e. g. Canon camera on Zeiss microscope, for various coupling variants - afocals, direct projection...

In particular, this comparison table is very interesting:
"Eine Zusammenstellung unterschiedlicher Kameraadaptionen für Mikroskope mit Endlichsystem (Tubuslänge 160mm) und einer Kamera mit APS-C Sensor 22,2 x 14,8 mm, z.B. Canon EOS 650D."

The camera was a Canon with ASPC sensor. The test specimen was a... stage micrometer, of course. The light source was LED. And that table shows the results of a Planapo 10x0.32 Zeiss objective with various viewing eyepieces, projection oculars, photo eyepieces, camera lenses. A very comprehensive and impressive practical test !

It demonstrates that even the combination of a Zeiss Planapo lens with a Zeiss compensating eyepiece does not guarantee a CA-free image - the results depend on the eyepiece as well as on the additional optics (camera lens, relays etc). Perhaps these limitations apply only for finite 160 or 170mm tube optics. So, the final quality of the the images involves a hit or miss element...

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#34 Post by MicroBob » Fri Feb 23, 2018 4:11 pm

Peter Höbels work is always very interesting and valuable if you like the technical aspects of microscopy. He often carries out precise measurements on topics that bring an end to controverse discussions that go on and on because there is too much opinion and little certainty.
Camera adaptation is really a difficult topic. Many components we use today are more or less compatible but come from completely different points of time. The Zeiss Winkel Standard and Zeiss Standard Systems have been made from the late 40s until the late 80s, one model even until the mid 90s. So it has to be expected that not all components play togehter on the same level of performance.

Older camera lenses that were well regarded in their time don't shine so bright on modern high resolution digital cameras in many cases. This will also be the case with camera adaptations on microscopes. Today we can zoom into our images until we see the tiniest bit of error. More resolution more sorrow! :lol:

The micrometer slides are a good test object for shure. They are available from China for 8€ today, so it is easy for almost everyone to have one. For critical tests ist is important to look whether there is a cover slip on them.
Does your micrometer have silvered stripes on glass or is it a silvered surface with scratched in stripes?

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#35 Post by Hobbyst46 » Sat Feb 24, 2018 12:56 pm

MicroBob wrote:1) Many components we use today are more or less compatible but come from completely different points of time. The Zeiss Winkel Standard and Zeiss Standard Systems have been made from the late 40s until the late 80s, one model even until the mid 90s. So it has to be expected that not all components play together on the same level of performance.
Older camera lenses that were well regarded in their time don't shine so bright on modern high resolution digital cameras in many cases. This will also be the case with camera adaptations on microscopes. Today we can zoom into our images until we see the tiniest bit of error...
Thanks a lot for enlightening this point and providing an explanation.

My micrometer has a silvered surface with scratches, it is shown below. It is a glass surface within a 1.9mm thick steel plate, I do not know whether it accepts a cover slip - intuitively I doubt it, but maybe? The silvered surface is visibly below the metal plate surface. So, placing a coverslip on the metal will locate the scale marks visibly below the coverslip. Not so good for high magnification objectives.

Years ago I used a B&L stage micrometer, with a similar surface, but the supporting plate was glass, not metal.

Thinking of that, how did those engineers manage to precisely carve or scratch such tiny, closely spaced lines decades before laser power was conceived? was it by a gear mechanism that transferred the motion from a large cogwheel to a small one?
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Zeiss stage micrometer.jpg
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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#36 Post by MicroBob » Sat Feb 24, 2018 5:42 pm

Hi Hobbyst46,

I would suggest to use an ordinary micrometer slide like this:
https://www.ebay.de/itm/0-01mm-Microsco ... Swol5Yy1O4

Add a cover slip of 0,17mm with a drop of immersion oil and you have the perfect test target for your 0,17mm cover slip thickness objectives. The lines here are silver on clear glass. This perfectly resembles a high contrast object.
I have a test target that has been made in a small series by Peter Höbel. It involved the use of quite dangerous chemicals to get the silver stripes. This was before cheap test targets from China became available (they are finer and thus better suited).
Your micrometer slide is different, and it is difficult to say how it differs. It might make your testing worthless because you may use your objectives outside of their specification. You are already testing on a high level here! The scratched lines may also lead to less contrasty edges.

About the fine scratched lines: This was invented by Friedrich Adolph Nobert. He invented machines that were able to make line patterns that first could be seen in the 1960s under the then perfected electron microscopes.
https://de.wikipedia.org/wiki/Friedrich_Adolph_Nobert
I love the picture of him! :lol:

Once I organized a microscopy group meeting about the entangled development of measuring tools and metalworking machines and measuring under the microscope. I brought a sharp diamond glass cutter and we tried to make thin scratches - it didnt'n work. There was always a wide track of shell like flaking on the glass surface. I was even more impressed of the work on Nobert!

His most prominent customer was Anders Jonas Ångström who used Noberts grates in his resaearch of the wavelenght.

Noberts grates were so small and the labeling was engraved so fine that probably a lot of Nobert grates have been thrown away as an empty slide! :shock:

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#37 Post by Hobbyst46 » Sun Feb 25, 2018 12:03 am

Hi MicroBob

Thanks a lot. I thought that the diffraction pattern from a dark object is the same as from a bright object except for intensity (if I state it correctly, I no expert on optics), but I have already ordered a micrometer like the one in the link. So, I will follow your suggestion about the coverslip.

Some of my low-mag objectives can be used wih or without coverslip. For them, I think, the respectable-looking metal-plate base Zeiss micrometer should be worthwhile. I agree, that from the point of view (pun) of visual inspection as well as the camera image, the bright lines on dark background might be a harsh test, an overkill.

Thanks also for the link to the Nobert biography, very interesting.

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#38 Post by Micro-Bob » Sun Feb 25, 2018 1:15 am

I'm not shure about the optical properties of the scratches in your test slide. They may scatter the light that passes through. Perhaps you can post a comparison of images of the two test slides, taken with the same exposure, one inverted. In an ideal world the images would look the same.

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#39 Post by Hobbyst46 » Sun Feb 25, 2018 9:17 am

Micro-Bob:
Thanks for the input.
According to the following citation from Wikipedia: "In physics, Babinet's principle[1] states that the diffraction pattern from an opaque body is identical to that from a hole of the same size and shape except for the overall forward beam intensity". Likewise, I think that scattering will be the same for dark and bright lines, apart from intensity. Dispersion from the bright scratches is obvious, when looking through it at strong daylight.
How differences, if any, between the dark and bright micrometer images are expressed in the recorded photos remains to be seen. I agree that it is worth a comparison test, as soon as I have the dark line micrometer, under similar illumination etc.

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#40 Post by Hobbyst46 » Sun Feb 25, 2018 9:47 am

MicroBob wrote: About the fine scratched lines: This was invented by Friedrich Adolph Nobert. He invented machines that were able to make line patterns that first could be seen in the 1960s under the then perfected electron microscopes.
https://de.wikipedia.org/wiki/Friedrich_Adolph_Nobert
So my curiosity about the thin lines was not alone! having read the linked story, it is indeed a demonstration of talent, creativity and persistence!

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#41 Post by MicroBob » Sun Feb 25, 2018 12:54 pm

Noberts work was really outstanding at this time. In 1850 the normal person had nearly no possessions that were so finely made that measurments of better than +/- 1mm were necessary. The most precise items at this time that were produced in bigger volume were guns and stearm engines and the machinery they drove. So when someone living in a small town at the end of nowhere started to build such precise machines it is really astonishing.

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#42 Post by MichaelG. » Thu Mar 15, 2018 2:29 pm

Hobbyst46 wrote:I am familiar with LED's spectra. ...

This LED replaced an old faulty Tungsten lamp that, even if it could be repaired, supplied more heat than light ...
I have revived this thread to share a useful illustration of the Tungsten lamp's characteristic spectrum.
... Although it is clearly only a sketch, it demonstrates the full 'black body' radiation curve rather nicely.
From PASCO Scientific 012-07136A  4/99
From PASCO Scientific 012-07136A 4/99
IMG_1860.JPG (211.39 KiB) Viewed 11519 times
Ref: http://www.fceia.unr.edu.ar/fisicaexper ... system.pdf

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#43 Post by MichaelG. » Fri Mar 16, 2018 8:42 am

I should perhaps have made clear that the PASCO curve is particularly relevant to our practical situation, because it is scaled appropriately for a 'slightly under-run' microscope lamp. [*] ... and it has has the axes on a logarithmic scale.

It is more common to see the black-body curves presented on linear scales, such as the first illustration here:
https://en.m.wikipedia.org/wiki/Black-body_radiation

MichaelG.
.

[*] PASCO's curve is for 2700K ... which is just below the lowest temperature plotted on the Wikipedia chart.

.
.
Edit: Here is a useful calculator/plotter, courtesy of NASA
https://astrogeology.usgs.gov/tools/the ... alculator/
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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#44 Post by MichaelG. » Sun Apr 01, 2018 11:52 am

I hope no-one objects to my reviving this thread again.

Checking some old bookmarks, I re-discovered this excellent little document [9 pages, from 2007] about Radiometric & Photometric measurements.
http://ams.com/eng/content/download/251 ... /version/1

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#45 Post by Hobbyst46 » Sun Apr 01, 2018 2:47 pm

MichaelG. wrote: I re-discovered this excellent little document [9 pages, from 2007] about Radiometric & Photometric measurements.MichaelG.
This document mentions the quite known high sensitivity of silicon photodiodes in the red->IR end of the visible spectrum, rather than in the blue end.
That is why I was previously surprised by the high sensitivity of the digital camera (Canon Mark 5D) photosensor to the blue wavelengths, as shown by the reference you posted earlier. Am I missing something out of laziness of thought ?

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#46 Post by MichaelG. » Sun Apr 01, 2018 3:31 pm

Hobbyst46 wrote:... surprised by the high sensitivity of the digital camera (Canon Mark 5D) photosensor to the blue wavelengths, as shown by the reference you posted earlier. Am I missing something out of laziness of thought ?
That's an interesting point

The short-wavelength sensitivity of both film and digital sensors is well known; but it does seem to be more of an issue with LED sources than with daylight. ... I think this is due to the 'peakiness' of the LED spectrum; which is putting a much higher proportion of its radiometric output into that region.
Compare the 'sunlight' line in Fig.5 with the 'white LED' plot in Fig.6

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#47 Post by Hobbyst46 » Wed Apr 11, 2018 4:57 pm

I thought I would continue the post, although the teaming of a modern camera with an old used microscope has been aptly covered by experts on the web. Because still, a hobbyist that via budget-limited acquisitions must do with second-hand optical components from diverse makes, diverse manufacturing era, variable quality, will ask, which is the best route for microphotography - focal or afocal (or other)? Here is yet another demonstration.

Previously I posted afocally-recorded photos of a somewhat controversial test slide - an ancient metal-plate Zeiss stage micrometer, bright slits on opaque background. I recorded it without a cover-slip, and the amount of color fringes and chromatic aberrations was questionable. For the present comparison, I switched to a brand new stage micrometer from the Far East, with dark lines on bright background. I put water on it and a coverslip (thanks, MicroBob, for this suggestion). Incidentally, although the distances measured according to the old and new micrometers are the same, the scale marks on the new micrometer are about twice as thick as those on the old Zeiss. This suggests that one cannot achieve the craftsmanship and accuracy of 70 years ago in an $8-worth micrometer of today (lasers or not).

The camera is a mirrorless Canon M10 with APS-C sensor. The afocal setup is shown above. It includes the 15-45mm Zoom lens fixed at 45mm focal length. This gives a crop factor of 45x8/250 = 1.44. This zoom lens is considered good by photography reviewers. The (focal) projection setup includes the camera body->16mm+10mm extension rings -> several thin adapter rings (T2->M42, M2->49x0.75mm etc) -> the telescope adapter 49x0.75mm->1.25". The latter is mounted onto the phototube, with a rigid PVC spacer tube in between. The focal photo eyepiece is the same Zeiss 8x KPL (ca. 9mm eyepoint) as in the afocal setup, except that it is raised on a 9mm-high collar.

Note: a similar 10x KPL yielded similar results as the 8x, but with lower coverage of the FOV (thanks, Charles, for your help in this!).

In both modes, parfocality between the viewing eyepieces and "photo eyepiece", and between the latter and the camera screen, was adjusted and only needed fine tweaking during photography. The LED illumination was the same in both modes.
Here are the main results of a quick comparison between the afocal and focal modes. The comparison covers the Zeiss objectives that I use the most. These objectives belong to different manufacturer batches and do not form a "set".

All images are resized to exactly the same dimensions in pixels and are slightly cropped (to 87% of their initial size) to eliminate vignettes. Ruler scale marks are 0.01mm apart. Please ignore unsightly specks, air bubbles etc due to the slide preparation.

My conclusions:

1) A somewhat larger coverage of the FOV by the sensor was obtained in the afocal mode. Geometrical distortions call for a higher cropping level in the focal images than was done here, enhancing the practical advantage of the afocal mode in this respect.
2) In the afocal mode, chromatic aberration and color fringe effects are more prominent for the low NA planachromat than for the higher NAs neofluar and planapo. The same holds in the focal mode.
3) The chromatic aberration and color fringe effects are weaker in the afocal than in the focal mode.
4) None of the images is totally free from chromatic effects.
5) Although not demonstrated here, the combination of the Zeiss KPL eyepiece and Olympus objective follows somewhat the trend: chromatic effects were dominant with an SPlan 10x0.30 Olympus (a fantastic objective in itself) but hardly existent with an DPlanapo 40x1.0 oil Olympus (also a fantastic objective).
6) The black-lines-on-bright background slide provides essentially the same information as the bright-lines-on black-background slide.

Important note: All images were jpeg. In the afocal mode, the default lens aberration corrections (peripherial illumin. and chromatic) of the camera lens
were enabled. I do not know how it affected image quality.
Attachments
Plan 16x0.32 afocal(left) vs focal (right).jpg
Plan 16x0.32 afocal(left) vs focal (right).jpg (44.18 KiB) Viewed 11133 times
Neofluar 16x0.40 Ph2 afocal(left) vs focal(right).jpg
Neofluar 16x0.40 Ph2 afocal(left) vs focal(right).jpg (38.45 KiB) Viewed 11133 times
Neofluar 40x0.75 Ph2 afocal(left) vs focal (right).jpg
Neofluar 40x0.75 Ph2 afocal(left) vs focal (right).jpg (43.95 KiB) Viewed 11133 times
Planapo 40x1.0 oil afocal(left) vs focal(right).jpg
Planapo 40x1.0 oil afocal(left) vs focal(right).jpg (46.29 KiB) Viewed 11133 times
Planapo 63x1.4 Ph3 oil afocal(left) vs focal(right).jpg
Planapo 63x1.4 Ph3 oil afocal(left) vs focal(right).jpg (43.59 KiB) Viewed 11133 times
Last edited by Hobbyst46 on Wed Apr 11, 2018 7:23 pm, edited 1 time in total.

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#48 Post by MicroBob » Wed Apr 11, 2018 6:51 pm

Hi Doron,
thank you for this thorough documentation!

I think it is easier to scratch a thin line than a broader line with defined and constant width. The manufacturing process of such a test slide is not so easy. The version made by Peter Höbel for me shows somewhat jagged lines - and he is Mr. Precision in person. So this is in fact a quite advanced product the chinese sell us for such a nice price.

I'm not sure whether I can see it in your images that chromatic errors in the afocal images decrease with increading power of the objectives. For me it looks quite constant and well corrected. Can you count the pixels that are affected by chromatic error? I would expect to see a similar number independent from the objective.

With the focal images it might be worth a try to remove chromatic errors in the raw converter. I have never tried this so far or read from someone who tried it. Maybe it is even a superior process to take a picture with lots of chromatic error and simply remove it afterwards.
It will also be possible to block out stray light inside the tube. Especially the image with the 63:1 lacks contrast. Flocked adhesive paper and light stops will be easy to install.

In the end usability is also important. Some cameras complain when you try to make images without a lens or you can only use manual exposure. Since shutter shock is such an issue with micro photography I would prefer the adaptation with the least height.

Not that this matters much but it is in line with the theory that you get more chromatic error when you don't use a correction eyepiece within the light path. But I would really like to see the comparison with the CA correction in the Raw image, it might open a new view on proper micro photography.

After experiments like this one should remember to take a picture of a beautiful slide like a stained leaf stem. It's nice to find out how to get the best from one's equipment but in practice it is not all that important. :D

Bob

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#49 Post by MichaelG. » Wed Apr 11, 2018 7:06 pm

An excellent report ... Thanks for sharing your results.

I hesitate to do so; but I must just add one 'complication' ...
The Canon M10, in common with many modern digital cameras, performs [as a default setting] in-camera reduction of chromatic aberrations on jpeg images produced by its 'system' lenses.

https://www.imaging-resource.com/PRODS/ ... -m10A4.HTM

... But those corrections are [obviously] not applied to 'without lens' shots.

Quite how this affects the theory and practice of what you are doing is difficult to assess: But it may be worth repeating some of the comparisons, with RAW images instead of JPG.

Keep up the great work.

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#50 Post by Hobbyst46 » Wed Apr 11, 2018 7:48 pm

MicroBob wrote:I'm not sure whether I can see it in your images that chromatic errors in the afocal images decrease with increading power of the objectives. For me it looks quite constant and well corrected. Can you count the pixels that are affected by chromatic error? I would expect to see a similar number independent from the objective.
I have to find out the easiest way of doing it... with ImageJ perhaps.
With the focal images it might be worth a try to remove chromatic errors in the raw converter...
. Yes, I will try it, but with the afocal. I believe that it will give overall better results than the focal.
It will also be possible to block out stray light inside the tube. Especially the image with the 63:1 lacks contrast.
I think that the 63x photos were taken under incorrect exposure parameters. I used shutter priority of at the most 1/125 speed but the aperture might have been wrong.
Some cameras complain when you try to make images without a lens or you can only use manual exposure. Since shutter shock is such an issue with micro photography I would prefer the adaptation with the least height.
This camera supports shooting without lens. The height was about the same at focal (maybe 1cm higher) as afocal.
... you get more chromatic error when you don't use a correction eyepiece within the light path.
I used the correction KPL eyepiece in both modes.
But I would really like to see the comparison with the CA correction in the Raw image...
Yes, I will certainly try it. Only problem is the large size of RAW files, but I can live with that.
After experiments like this one should remember to take a picture of a beautiful slide like a stained leaf stem.
Agreed, and already started! some stained onions were already posted - but working on improvement of the technique.
Thanks a lot!
Last edited by Hobbyst46 on Wed Apr 11, 2018 7:57 pm, edited 1 time in total.

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#51 Post by Hobbyst46 » Wed Apr 11, 2018 7:57 pm

MichaelG. wrote: The Canon M10, in common with many modern digital cameras, performs [as a default setting] in-camera reduction of chromatic aberrations on jpeg images produced by its 'system' lenses...But those corrections are [obviously] not applied to 'without lens' shots.
Quite how this affects the theory and practice of what you are doing is difficult to assess: But it may be worth repeating some of the comparisons, with RAW images instead of JPG.
Agreed, I should have mentioned it, and now edited the post accordingly. I will shoot RAWs and try, for the afocal setting at least. I believe that overall, it yields (in this case) better results than the focal mode.
Thanks a lot!

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#52 Post by MicroBob » Wed Apr 11, 2018 8:03 pm

[quote="Hobbyst46"]I have to find out the easiest way of doing it... with ImageJ perhaps.
If you have a software with which you can zoom in very far you can count the pixels by hand, maybe 10 pixels or so.

I used the correction KPL eyepiece in both modes.
Then the problem will be due to using the eyepiece as a projectiv - I have no idea whether this could be corrected in the Raw image.
My impression is that afocal adaptations are more successful than focal adaptations.

I think the aperture of the camera lens schould be fully open all the time.
[/color]

[Bob

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#53 Post by Hobbyst46 » Wed Apr 11, 2018 8:37 pm

MicroBob wrote: I think the aperture of the camera lens schould be fully open all the time
The reason that I did not do so starts with the LED illumination. The LED, apparently the PWM dimmer, causes dark bands in the photographs. Similar bands (maybe not the same frequency - I did not check) are seen sometimes in the photos under home LED lights (these have no PWM dimmer AFAIK, or perhaps it is hidden in the electronic driver :? ).
To avoid the bands, I have to set the shutter duration ("speed") at 1/125-1/250 or LONGER. So, if the exposure is longer than 1/125 (say), and the aperture is fully open (3.5, say) I will get over-exposure. That is why I - perhaps wrongly - left it for the camera to set the aperture. Admittedly, I almost never checked out the histogram before shooting - another mistake?

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Re: Experiments with afocal photomicrography: illuminations, spider threads...

#54 Post by MicroBob » Wed Apr 11, 2018 11:17 pm

When the focal point of the eyepiece hits the perfect spot on the camera lens you can close the camera lens apterture and just control the amout of light. If the two optics don't fit together perfectly you begin to see the aperture blades at the border of the image.

The photo problem with LED lighting is an interesting topic. Just today I installed an LED replacement for a halogen tube in our kitchen. I tested whether it flickers with my Nikon 1J5 in 400 fps video mode. It surely flickers, ca. thrice per second at 25 fps playback, so about 50 times per second in real speed. Which is our mains frequency here. The light nearly goes out in the dark cycle - this could clearly show in an image taken with a focal plane shutter.

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