More questions about objectives "types"

[cmtalb01]

As noted in the update comment in my earlier post titled "Questions about Zeiss Correcting Oculars", I am ultimately interested in learning of the best camera setup for the Zeiss Photomic. This has led me to an investigation in eyepiece/objective paring and several focal and afocal camera setups, and now to an investigation into the "benefits" of various types of objectives. Here is where I need and request the help of the forum community to help me figure out what I am seeing...or not seeing?!

Over the past year, I have acquired an array of Zeiss 100X objectives to include: achromat, plan achromat, plan achromat phase, "F" series, Neofluar, and Apo. I really wanted (and was hoping) to see the difference or improvement that each objective provided in the real world. For the investigation, I used the Diatom Test 8 plate from KD Kemp, a 1.3 condenser (closed 1/3 of full open), and oiled both the condenser and objective to the slide. All photos were taken with the same ISO, aperture setting, white balance (set to a blank area of the slide) and ND filter. This was also immediately after a full headrig alignment of the PM and thorough cleaning. All objectives were checked for cleanliness and delamination using the phase telescope on the optovar with result that all objectives displayed no signs of delamination throughout the full objective lens stack.

My quesiton to all is what am I missing??? I do see improvement in field of focus as you move up in objective quality, but I am lost on resolution? What should I be looking for? Frankly, it almost appears to me that the Achromat gives the same result as the Apo, if not maybe a little better?!?!

I also see that you can focus so that the "dots" are either black or yellow? What is correct? I am assuming black. Is the yellow from chromatic aberration?

Oops, please dis-regard the ISO and shutter speed settings in the pictures, these were from an earlier trial before headrig alignment. ISO for this test was all set at 400, and the shutter speeds were 1/320 to 1/500. There was no correlation between shutter speed and "quality" of objective. The faster ISO setting and shutter speed, along with a shutter delay and wireless shutter release, were used to eliminate an possible vibration that could also add to the observed "quality" of the photos.

Thanks in advance for all comments and help.

Mark

[Hobbyst46]

First of all, these data will in my opinion help many others who arein doubts about the performance of their gear.
Second, in my opinion, one should strive to find an objective quantitative, numerical parameter that you can extract from your data by image analysis. I do not know yet which parameter, I am planning to learn it myself... It should be a parameter that lets you sort your lenses according to (say) aberrations.
However, I trust that soon your doubts will be eliminated by the experience and knowledge of experts on this forum....

[MichaelG.]

The post by Julio Vazquez : Aug 10, 2007; 7:03pm Re: Stage micrometers and diatoms
http://confocal-microscopy-list.588098. ... ml#a589978
may be of some interest.
Unfortunately I can find no update of the [withdrawn] referenced article by David Walker.

MichaelG.

[Hobbyst46]

MichaelG:

I was indeed thinking of the "A potential afocal camera to microscope adapter for less than a 'tenner'" by David Walker, it was published in 2013.
There is also an informative post by Pau (2017?) about afocal. And many good others.

I think of the following: supposing there is an image of a micrometer stage (or another simple dark/bright pattern, a high contrast one). I split it to the RGB components. Check the Histogram. The average intensity (i.e. brightness) of the image of the Blue component should be an indicator of CA; if the three histograms show the same average intensity there is no significant CA. is that too simplistic?
With a diatom it might not work, since the diatom itself is made of refractive "glass".

[wporter]

I find diatoms somewhat difficult to accept for one-side-of-the-field-to-the-other tests, since they are curved specimens. It might be better to focus on a stage micrometer scale or grid, since it's flatter. You also wouldn't have a dispersion problem by the specimen, confusing any conclusions about chromatic abberations by the objective that you might want to draw.

Also, in your great images, it's hard to tell what was the common part of the specimen you were focusing on. In this case, it would have to be exactly the same dot or tiny stria in each image. This would enable direct comparisons between the different objectives' depth of field, planarity, etc. Often apos may be sharper in the field center, but have much worse planarity.

[cmtalb01]

Very interesting idea with the histogram - well worth a try. I recently read an old article (can't find it in my computer mess right now) about how you could evaluate the correction of an objective by looking at a conoscopic diffraction image of an objective focused on a stage micrometer. After reading I checked the diffraction patters of the 100X objectives I had but not sure the results. Two things are clear: 1.) the images of the more highly corrected objectives are better resolved and 2.) the neofluar and apochromat objectives fully resolve the fourth order of light that is squeezed into the edge of the less corrected objectives. Picture follows.

[MichaelG.]

MichaelG:

I was indeed thinking of the "A potential afocal camera to microscope adapter for less than a 'tenner'" by David Walker, it was published in 2013.

The article referenced by Julio Vazquez is [was] about diatoms as test objects; but it currently links to this rather cryptic page:
http://www.microscopy-uk.org.uk/mag/ind ... iatom.html

MichaelG.
.
Edit: I've just found it ... in its 2002 update:
http://www.microscopy-uk.org.uk/mag/ind ... omold.html

[Hobbyst46]

MichaelG -
Thanks for these links, that lead to several charming articles. For me diatoms are sort of fascinating playthings.
As remarked by Walker, the advantage of blue light is in resolution... it is not always an interference...

[MichaelG.]

As remarked by Walker, the advantage of blue light is in resolution... it is not always an interference...

Very, very, true

... and it is relevant in the context of the rhetorical question you recently posed elsewhere:

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

MichaelG.

[cmtalb01]

Thanks to all - I appreciate the comments. Given the suggestions and readings, I worked a little with enhancement techniques I had lying around. Posted photos in the specimen section of the forum.

Thanks again for all the very good information!

Mark