Stacking lenses for more X (not telecentric)

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rjlittlefield
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Post by rjlittlefield »

DaveW wrote:Nikon's extension tubes (and bellows) are still in the "Stone Age" in that they have no electronic contacts at all.
How about third-party tubes? These from Kenko claim to provide diaphragm and meter coupling, though they are explicit that you have to focus manually and that "Nikon 'D' information is not transmitted because the lens is focusing closer than its programmed to focus".
georgedingwall wrote:What would you suggest would be a good X10 lens for me to get?
That's a good question, and one that I won't answer at the moment.

I've used mostly a Nikon 4X, the aus Jena 3.2X and 10X that came with my microscope, and an Edmund Optics 20X, most of them just basic achromats. These all work OK as macro lenses. They have some curvature of field, but that's no problem with extended DOF. They also have some visible CA that's removable with PTlens, and they get soft around the edges.

The reason I'm hesitant to recommend is that some objectives have large amounts of lateral chromatic aberration (LCA) designed into them and are intended for use only with matching eyepieces that have compensating negative LCA. The matched pair works great, but the objective by itself can be awful. See figure 17 and associated discussion in this article by Ted Clarke. Based on that article, I'd be inclined to avoid LOMO and Zeiss kpl lenses. But as I understand it, my "aus Jena" microscope is essentially East German Zeiss, so apparently just "Zeiss" is not a good indicator. Anyway, at the moment I'm aware that there's an issue and I don't know enough to feel comfortable making recommendations. Maybe it's a good time to ask my friends in the Yahoo Microscope group for some info/guidance.

--Rik

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Post by rjlittlefield »

georgedingwall wrote: I did try the X10 supplied with my compound microscope. The results with this lens were interesting, but not all that successful.
George,

What is the make/model/designation of the microscope and lens?

Can you post out some of the results so we can perhaps diagnose what went wrong?

--Rik

georgedingwall
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Post by georgedingwall »

Hi Rik,
rjlittlefield wrote:
What is the make/model/designation of the microscope and lens?

Can you post out some of the results so we can perhaps diagnose what went wrong?

--Rik
I think the scope is some sort of re-badged generic tri-noc compound, named Apex-Researcher.

It's sold on ebay by Brunel Microscopes under the Apex brand. If I remember correctly, it cost about 200 UKP, ( about 390 USD at present exchange rates).

I've only tried using the X10 objective for stacking images.

Here are three images taken using this objective. I can't remember the exact helicon settings or the focus adjustment, but they were all in the region of 50 frame stacks.

These images are straight from Helicon Focus with no processing in Photoshop except to resize them for this forum. They seem to me to have not too bad a central area, but the images deteriorate the further you get from the centre. This is also seems true of chromatic aberation.

As this was the first time I had used a microscope objective, I'm not sure my technique is causing some problems, or if it's simply problems created by a relatively low quality lens. I think I tried to keep the extension to about 160 mm. The lens is marked Plan 10/0.25 - 160/0.17.

I'll be intersted to hear what you think.
Last edited by georgedingwall on Fri Dec 02, 2011 12:19 pm, edited 1 time in total.
George Dingwall

Invergordon, Scotland

http://www.georgedingwall.co.uk/

rjlittlefield
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Post by rjlittlefield »

George,

Yep, these look like issues with the lens. At least with these subjects, it does seem that your lens is not working as well in this mode as mine does.

Any chance you can post out a full-size image and link to it? I'd like to see what the central portion looks like, and how fast it degrades away from center. The insect would be a lot better for this purpose than the screw thread, since I'm pretty sure it will have detail at a wide range of scale down to finer than any lens can resolve.

The markings on your objective mean that it's 10X with a Numerical Aperture of NA=0.25, designed for a tube length of 160mm and a cover glass thickness of 0.17mm. Tube length 160mm actually translates to 150mm from the shoulder of the mounting threads to where the image focuses -- the sensor plane in your case. There'll be some degradation from using the lens with no cover glass and with slightly wrong tube length, but I'm not sure how much of the problem is due to that and how much to something else. "Plan" indicates a flat-field correction, helpful for regular microscopy, but not necessarily an improvement when stacking because conceivably the flatter field comes at the cost of making other aberrations worse.

It might be informative to photograph some subject that has nice fine detail, and compare it to what you can see with direct view through the microscope. I'd recommend something like a moth wing -- fairly flat, good detail, not too shiny. If you can see much better directly through the scope, say with more detail and no color fringes over a wider field than the photo, that would suggest that the objective is designed to work with a highly compensating eyepiece and isn't going to work with direct projection onto the sensor. You could also do a check in reverse. Use your microscope eyepiece to look at an image formed by one of your enlarger lenses. If you see color fringes through the eyepiece that the sensor doesn't pick up, again that would suggest a significant eyepiece correction.

Just to check, do I have it right that these are with your Nikon D200, sensor size 23.6 x 15.8 mm?

--Rik

PS. (Edit) I reviewed some earlier postings at http://www.photomacrography.net/forum/v ... .php?t=676. I see there that I suggested attacking the CA in your images with PTlens at Red-Cyan = -0.0040 and Blue-Yellow = +0.0060. I checked again with some images from my 10X objective, and the PTlens correction is only around Red-Cyan = -0.0018 and Blue-Yellow = +0.0019, less than half as much as for yours. Assuming those numbers are right, that could have a significant effect on delivered resolution. While PTlens or any similar post-processing can eliminate the obvious color fringing, it cannot eliminate the smearing within each R,G,B channel that is caused by chromatic aberration interacting with a broadband light source. That just turns into resolution loss. A compensating ocular fixes both problems at once.

georgedingwall
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Post by georgedingwall »

Hi Rik,
rjlittlefield wrote: Any chance you can post out a full-size image and link to it?

Just to check, do I have it right that these are with your Nikon D200, sensor size 23.6 x 15.8 mm?

--Rik
Thanks for the points you raise.

I don't have the original RAW files for these images, and I don't have a full size image of the stack. The reason for this, is that when I'm experimenting, I tend to save a reduced size jpeg from the RAW files in order to speed the process up a bit. As these images were not really worth keeping, I did not save the RAW files.

I still have the reduced size jpeg images, and these are what the stack is made from. The largest image I have of the insect is 1530 x 1024 pixels. I've uploaded a Tiff version of this image at this link. (3.3MB zipped). I still have the jpeg images, but that would be almost 40MB zipped, so I have not uploaded those images. However, if you think it might help, I could upload a sub-set of these images for you to see.

http://www.georgedingwall.co.uk/downloads/MSO_02.zip

On your other point, yes the MS Objective images were taken with the D200.

Bye for now.
George Dingwall

Invergordon, Scotland

http://www.georgedingwall.co.uk/

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Post by georgedingwall »

Hi again Rik,

Here is a new stack that I did today. Again it is a full frame image from the D200. The field of view is about 2.5mm. The stack is made from 25 frames with a 0.02mm focus adjustment between frames. The image is straight from Helicon Focus, with the only thing done to the image is to resize it for the forum.

A full size jpeg of the image can be found at this link. (3.1MB)



I set the objective at exactly 150mm as you previously advised.

There is obviously a lot of CA, but this may be exagerated a bit as I did not use a diffuser and there are some strong specular highlights.


I have not tried PTLens, but Photoshop has a feature for reducing CA, and although it removes some, it does not remove it all.

Bye fo now.
Last edited by georgedingwall on Fri Dec 02, 2011 12:21 pm, edited 1 time in total.
George Dingwall

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rjlittlefield
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Post by rjlittlefield »

George,

This is looking much better. I downloaded the full-size image. Particularly at image center, it shows fine surface detail that gets noticeably fuzzier if shrunk to 50% (1936x1296, for your camera). This seems not much different from what I get.

I rechecked your earlier postings at http://www.photomacrography.net/forum/v ... 6&start=16. As I read them, it seems that at least some your earlier images actually came from a setup using a TC and much less than 150mm extension. For the screw image, you wrote that "I took this image of my old faithful test screw with the objective. I used only a 1.4 X tele-extender and 8mm of extension tube for this image." The fly images are from a few hours later, after I suggested no TC and 150mm extension, but the exact setup is not specified. Given the ambiguity, I think we should mostly ignore the earlier images and work forward from this last one, which seems quite promising.

Regarding CA, I can get PTlens to remove most of it. The large block of blue and red at image left refuses to go away, but that doesn't look like typical CA anyway. I don't know what happened. Removing the CA noticeably improves apparent sharpness away from image center, for example at extreme image right, the white dots in the cluster at the top of the leg are cleanly separated after removing the CA, where they mush together before. I'd put this improvement in the category of "definitely worth doing, though not earthshaking".

This setup looks like a good starting point for future experimentation. The first thing to do, I think, would be to compare central detail with this lens, against detail that you can get with your other lenses on this same subject. If it's significantly better (as I expect it will be), then you can start tweaking around with other changes that we can talk about later.

Looking at the full size image, I see some pixel-level artifacts that look like they came from the stacking but I can't tell exactly what went wrong. If your stack is smooth and straight, be sure to turn off auto-adjustment. That will eliminate several sources of stacking problems.

This is looking good...gotta run...

--Rik

georgedingwall
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Post by georgedingwall »

Hi Rik,
George,

This is looking much better. I downloaded the full-size image. Particularly at image center, it shows fine surface detail that gets noticeably fuzzier if shrunk to 50% (1936x1296, for your camera). This seems not much different from what I get.
Thanks for the advice. I'll need to get hold of PTLens and give that a try for the CA.

Bye for now.
George Dingwall

Invergordon, Scotland

http://www.georgedingwall.co.uk/

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