Questions about Stackshot & Microscope objective set-up

[Wooster]

Hi everyone,

I got quite into Macro photography about 18 months ago, but unfortunately work took over and I needed to borrow the Stackshot controller to become a motorised camera dolly controller. Well, I've now got it back and am keen to take some photos, but I've forgotten almost everything I learned!

I have had a look around the forum, but some things are still vague for me. If anyone could clear up my questions, I would be very grateful.

My set-up is:

Stackshot
Nikon LWD 40x/0.55 Ph2 DL Objective
Nikon CFI BE Plan 10x Objective
Nikon D800 (I use this in crop sensor mode)
Nikon 80-200mm f/4.5-5.6
Nikon 85mm f/1.8

I've had fairly bad results with the 80-200mm lens @ 200mm, so I've taken to using the 85mm at f/1.8 instead. Is this a bad idea? I assume the focal length of 200mm provides optimum quality and uses the best part of the glass on the objective, but the small maximum aperture of f/5.6 multiplies the effective aperture of the entire system, introducing unacceptable diffraction. Is that right?

Can anyone suggest a better way to make use of my set-up? I'd buy a better lens or objective if it would make a significant difference.

Here's an image from the 10x/85mm set-up, suggestions for improving image quality would much appreciated. This is a lump of iron pyrite.


Regarding the 40x objective, I never really expected amazing results, although my most recent experiments aren't as bad as I expected. There is currently a problem with donut effects on the highlights, which confuse Zerene stacker. I think this is because of the method I use to attach the objective to the lens, and I know how to resolve that. Hopefully that will result in improved clarity. Again, I used the 85mm at f/1.8 to get this image.

This is a 40x image of disarticulated fossilised crinoid ossicles (iron pyrite on calcite).

If anyone has any suggestions for improving the quality at this extreme level of magnification, please do let me know. As I say, I'm not expecting miracles!

Many thanks.

[Blame]

I dont think FF cameras work well with camera lenses as tube lenses. They vignette. Your best bet is almost certainly a reversed Raynox DCR-150.

The aperture the tube lens sees is that of the objective times the magnification. As long as the tube lens doesn't vignette it's aperture has no effect.

I don't see a lot of virtue in using a tube lens so short that you need to crop. You paid for the megapixels so you might as well use them.

I have a fealing that PH lenses tend not to work to well but I could be wrong.

Anything above 10x is ether going to result in a LOT of diffraction blur or give you a very short working distance. About f/36 for your 40x with a 200mm tube lens and your camera will start noticing diffraction from f/8.

watch out for high NA lenses that are designed to be used with a coverslip. It matters.

[rjlittlefield]

Wooster, welcome aboard!

I've had fairly bad results with the 80-200mm lens @ 200mm

What does "bad" mean? Are you talking about vignetting or sharpness?

I assume the focal length of 200mm provides optimum quality and uses the best part of the glass on the objective, but the small maximum aperture of f/5.6 multiplies the effective aperture of the entire system, introducing unacceptable diffraction. Is that right?

No, that's not right.

With any of these setups, unless you're vignetting you'll be using all the glass of the objective. The small hole in the objective stops down the whole system, so you'll be using only part of the glass of the rear lens.

When paired with 200 mm, the 10X NA 0.25 objective will effectively stop down the 200 to f/20, leaving the rest of that f/5.6 completely unused (at least at image center). At f/20, you can certainly expect to see some diffraction blur with a D800 in crop sensor mode (15.3 MP APS-C).

When paired with the 85 mm, the same 10X NA 0.25 objective still stops down the whole system, but in this case it's only to effective f/8.5 because of the shorter rear lens. At the same time your magnification will drop to only 4.25X instead of 10X. In the optical images, the 10X and 4.25X images will deliver the same resolution on subject. The 4.25X image will look "sharper" because it puts a smaller/finer image onto the sensor. But the 10X image may show more detail on subject because in that case the sensor has enough resolution to capture everything that's in the optical image.

Can anyone suggest a better way to make use of my set-up? I'd buy a better lens or objective if it would make a significant difference.

At the scale you've posted here, the image from the 10x/85mm setup looks pretty good. What sort of "image quality" would you like to have improved?

Regarding the 40x objective, I never really expected amazing results, although my most recent experiments aren't as bad as I expected. There is currently a problem with donut effects on the highlights, which confuse Zerene stacker. I think this is because of the method I use to attach the objective to the lens, and I know how to resolve that.

The "donut" effect is more likely due to your use of an objective with a phase ring in it. The phase ring hardly affects the appearance of in-focus detail, but it turns out-of-focus highlights into distinct donuts instead of filled-in blurs. The cover glass issue mentioned by Blame is also important at NA 0.55.

In the 40X image, the biggest issues I see at this scale are "streamers" coming off the highlights. These can be reduced by using the DMap stacking method (as opposed to PMax), and also by using more diffuse illumination.

--Rik

[Wooster]

Thanks both for the replies!

Wooster, welcome aboard!

I've had fairly bad results with the 80-200mm lens @ 200mm

What does "bad" mean? Are you talking about vignetting or sharpness?

Sharpness seems poor on the 80-200mm - I will do some more experiments tomorrow, since I have now made some improvements, such as flocking the objective to hide any shiny gold bits.

When paired with 200 mm, the 10X NA 0.25 objective will effectively stop down the 200 to f/20, leaving the rest of that f/5.6 completely unused (at least at image center). At f/20, you can certainly expect to see some diffraction blur with a D800 in crop sensor mode (15.3 MP APS-C).

Ah, I totally got all of that wrong then. Thanks for the correct information - my memory is even shakier than I thought!

Can anyone suggest a better way to make use of my set-up? I'd buy a better lens or objective if it would make a significant difference.

At the scale you've posted here, the image from the 10x/85mm setup looks pretty good. What sort of "image quality" would you like to have improved?

I'm most concerned about sheer optical quality at 10 and 20x (I don't have a 20x objective yet)- I'd like an image that looks good at 100%. I'm willing to do whatever necessary, up to and including buying a new camera (when I can afford it!). I do seem to recall that smaller sensors are better than big ones.

Members here seem to post pictures which have a level of optical quality that I can't quite achieve (or at least haven't yet), and I'm keen to improve so that I can get some nice photos of insects in amber.

Thanks again for your help.

[rjlittlefield]

I'm most concerned about sheer optical quality at 10 and 20x (I don't have a 20x objective yet)- I'd like an image that looks good at 100%. I'm willing to do whatever necessary, up to and including buying a new camera (when I can afford it!).

The limiting factor will be your objectives. At 15 megapixels on APS-C, you would need to be running around f/11 or wider to look sharp at actual pixels. But then at 10X that would mean an objective with NA=0.45 . Those are scarce as hens' teeth, and none of them have been shown to cover APS-C with high quality anyway. At 20X, you would need NA 0.90, and that's just not going to happen.

So, the first thing you should do is become used to the idea of limitations that do not yield to big budgets.

I do seem to recall that smaller sensors are better than big ones.

Smaller sensors are simpler to interface than larger sensors, and for high mag applications even APS-C sensors have enough pixels to capture what's in the optical image. Smaller sensors are also cheaper, so for all those reasons APS-C sensors are what we usually recommend to people who ask what camera to buy.

But optical quality is not lost by using a larger sensor. So since you already have that D800, the first thing to do is focus on the objectives.

The Mitutoyo M Plan Apo objectives described HERE are probably the best match to your criteria. They also turn up used on eBay for perhaps half their list price, but the eBay copies have to be tested carefully because it's all too easy for the objectives to be knocked out of alignment without showing obvious damage. (I'm the proud owner of a used 10X that was a bit off when I first received it, and which in repeated testing seems to be getting worse the longer it sits in its box.)

--Rik

[Wooster]

So, the first thing you should do is become used to the idea of limitations that do not yield to big budgets.

Yeah, I am aware that there are physical limitations to this kind of photography - I just want to make sure that my images are as good as I can reasonably expect. My favourite macro image, below, was taken with just an ancient M42 lens reverse-mounted onto another lens, so I know that pixel-peeping isn't necessarily the be all and end all. I just want to make images like this which hold up to a certain amount of scrutiny when printed (this one does to be honest, but I am a resolution fanatic, hence the D800). As I'm sure you know, it's painful to spend ages taking and stacking an image, only to find that something's not quite right, so I want to make sure I'm doing things correctly.

The Mitutoyo M Plan Apo objectives described HERE are probably the best match to your criteria. They also turn up used on eBay for perhaps half their list price, but the eBay copies have to be tested carefully because it's all too easy for the objectives to be knocked out of alignment without showing obvious damage. (I'm the proud owner of a used 10X that was a bit off when I first received it, and which in repeated testing seems to be getting worse the longer it sits in its box.)

Thanks Rik, I will look into investing in a Mitutoyo objective in the future - but I expect my Nikon will do the job in the short term.

Thanks for the advice, I feel more confident that I'm on the right track.

[Edward Ruden]

PH objectives' Out of Focus light pattern can confuse stacking software. The sharp annular pattern resulting from small bright spots can be misinterpreted as being in-focus.

Your 40X/0.55 needs a 2 micron step for best results, based on focal depth. I don't have one, but I thought Stackshot only goes down to 10 micron.

As stated, high F/no only results in possible vignetting. It does not affect resolution. Stopping the lens down just shy of vignetting may actually minimize stray light.

The (low end) BE's don't have a very wide corrected field of view. The much touted 10X/0.25 Nikon CFI60 Plan achromatic MRL00102 has exceptionally wide corrected FOV, by comparison. You'll have much better luck with your lower FL tube lenses with it.

[rjlittlefield]

but I thought Stackshot only goes down to 10 micron.

That was sort of true for the earliest StackShots, but for more than two years now StackShots have been capable of much finer movements. See details at http://www.photomacrography.net/forum/v ... hp?t=16323. If a particular StackShot allows you to program step sizes in microns below 10, then it also has the High Precision mode described there.

The (low end) BE's don't have a very wide corrected field of view. The much touted 10X/0.25 Nikon CFI60 Plan achromatic MRL00102 has exceptionally wide corrected FOV, by comparison.

I agree, in concept. In practice, the CFI BE 10X is known to cover APS-C pretty well at 5X. See the example HERE. I don't have a full-frame camera to confirm with, but I'd be pretty confident scaling up from there that it'll do a pretty good job covering full-frame at 10X.

--Rik

[Blame]

Your camera is perfect for the job. Diffraction is going to be a major factor but every pixel adds at least a little more detail.

More importantly the full frame sensor can collect a lot of light. Use all of it and at the lowest ISO it can honestly handle. Stacking stacks noise so every extra photon helps.

You have fewer options for tube lenses but you only need to find one and the 210mm DCR-150 is a perfect match with mitutoyo objectives and your camera. Probably most other infinite lenses too.

A 150mm enlarger lens is also a valid option for when you need more coverage. It won't vignette but only the central area will be sharp. Still, 50% area sharp can work a lot of the time.

Just be realistic when you pixel peep. There is a mitutoyo 10/0.42 but nobody knows how good it is because nobody can afford it. The 10/0.28 is good enough.