Questions for the experts.

A forum to ask questions, post setups, and generally discuss anything having to do with photomacrography and photomicroscopy.

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Billy B
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Questions for the experts.

Post by Billy B »

Just received my adaptor from China to mount my Nikon 10x objective. Like a child , I couldn't to try it out. I notice the images are not as sharp as I had hoped for. As of yet, have not calibrated my 55-200 kit lens to infinity, but feel that it is close. Here are a few questions.
1.How critical for sharpness does the 200mm lens have to be to infinity for optimum sharpness?
2. I have a 70-210 Kiron lens with infinity symbol. Would this work?
3. I currently focus with a X-Y stage, moving subject toward camera rather than camera towards subject. X -Y stage is mounted on a scissor
jack I use for vertical elevation. My setup works great up 4x, however I notice vibration is critical at 10x. I have to wait for 10 seconds or so for live view to settle down before remotely triggering camera with Helicon Remote. Any suggestion would greatly be appreciated.

enricosavazzi
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Re: Questions for the experts.

Post by enricosavazzi »

I will leave some answers to others, but can say that vibration in your setup seems to take an excessively long time to settle at 10x, so you should try to solve this problem. For example, mounting the XY stage atop the scissor jack is probably not the best idea. I would try to reverse the order and put the XY stage at the bottom (since it is subjected to vibration every time you manually operate it to change focus) with the scissor jack on top (which you are not going to touch while shooting the stack).

How the camera is mounted on the setup, and how rigid the setup is, also strongly affect vibration. The worst situation is usually when camera and subject are decoupled from each other and each can vibrate independently of the other.

You do not mention whether you use electronic flash or continuous illumination, and whether you use electronic shutter (or electronic front curtain) or mechanical shutter. Both factors affect the results when vibrations are present. If using mechanical shutter or electronic front curtain shutter, exposure time is also a factor. A long exposure time helps to average out the vibration caused by the shutter at the beginning and/or end of the exposure with continuous illumination, while a short exposure is likely to be more affected by shutter vibration. Electronic flash may not freeze out vibration completely if the flash is triggered just after a mechanical shutter opens, and a delay between the two may help in this case.

Having the tube lens exactly focused at infinity is a good idea but not extremely critical. In some cases it has been reported that a little focus deviation of the tube lens either way actually helps to improve image quality, but only testing can show whether this is your case. Supporting the tube lens and/or objective so that it does not amplify the vibration of the rest of the setup is generally a good idea, and likely to be more important than a small deviation from infinity focus of the tube lens.
--ES

Macro_Cosmos
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Re: Questions for the experts.

Post by Macro_Cosmos »

To calibrate the lens at infinity, simply stop down a bit and point at a distant object, like a tree or a UFO (I'm sorry). This is rather critical, and easy to achieve.
Make sure you tape the lens' rings, set it to the manual latch, and tape that too! Accidentally throwing it out of focus can be a nuisance.

Your setup sounds solid. If vibration wasn't an issue, soft images could be, unfortunately, due to a dud copy of the objective. Mitutoyo objectives are often used in harsh industrial environments, one can't expect the used copy to always perform the same as an out of box copy. Even out of box ones aren't too consistent at times.

For stable surfaces, there's many options.
Cheap: DIY box filled with pennies/water bottles
Not expensive: large slab of granite/marble from a local place
Expensive: Optical bench, however I've seen them being sold on ebay auctions for $100, just have to go pick it up.

Sometimes however, none of these work. Depends on where you live. House? A heavy surface is likely all you need!
I did visit a lab in located in a tall apartment, even on an optical bench, vibrations occur at times.

A example of "unsatisfactory results from the mit 10x" would be great.

Billy B
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Re: Questions for the experts.

Post by Billy B »

Thank you Marco
I just posted a new message before reading your reply. Even when currant lens is fully extended ,I'm getting vignetting in the corners, so finding infinity is out of the question as I understand that is just before the 200 mm is reached. Up until this point, my setup has worked very well, but going 10x is a whole new ball game and I will have to create a more solid foundation for 10x. Right now, my problem is excessive halos, and maybe vibration is part of that problem. I hate to think I bought a dud objective, but is was from eBay.

Billy B
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Re: Questions for the experts.

Post by Billy B »

Thank you Enrico.
Your right regarding vibration. I'm going to set everything up for a more solid foundation. Up until this point, what I have has worked well even up to my 4x Am Scope objective, but as I have mentioned before, 10x is a new ball game. I have used both speed light and continuous light, but due to vibration I'm back to speed light with rear curtain for the 10x. As well , I have the mirror locked in the up position. As mentioned to Marco, my problem seems to be excessive halos, which I hope can be solved with a more solid foundation. I deleted all the shots I took with the 10x out of disgust, but will take a few more tomorrow to post. Thanks for your reply. Much appreciated.

JKT
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Re: Questions for the experts.

Post by JKT »

Billy B wrote:
Wed Aug 26, 2020 7:58 pm
Even when currant lens is fully extended ,I'm getting vignetting in the corners, so finding infinity is out of the question as I understand that is just before the 200 mm is reached.
There seems to be something odd in the above statement. Finding infinity focus is separate issue from choosing the focal length on a zoom lens. Either you use different rings to adjust the two or you push/pull the ring for one and rotate it for the other.

In most (all?) cases the vignetting is minimized with the maximum zoom position. The zoom setting also defines your magnification if you use infinity focus. If you still get vignetting and don't want it, it is possible to change focus on the tube lens. That may work well ... or not as you will be operating the microscope objective in a way it was not meant and designed for. Your magnification will also change in the process.

Macro_Cosmos
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Re: Questions for the experts.

Post by Macro_Cosmos »

Billy B wrote:
Wed Aug 26, 2020 7:58 pm
Thank you Marco
I just posted a new message before reading your reply. Even when currant lens is fully extended ,I'm getting vignetting in the corners, so finding infinity is out of the question as I understand that is just before the 200 mm is reached. Up until this point, my setup has worked very well, but going 10x is a whole new ball game and I will have to create a more solid foundation for 10x. Right now, my problem is excessive halos, and maybe vibration is part of that problem. I hate to think I bought a dud objective, but is was from eBay.
If you're seeing mechanical vignetting, it means stuff is being blocked, so your tube lens is the issue.
I don't understand how mechanical vignetting at the longest end means finding infinity is out of the question.
For ebay, just buy from sellers that accept returns and make sure you test it once you get it.

55-200 sounds like one of those DX kit lenses. Are you open to the idea of getting a better one?

FYI my 70-200mm F2.8E FL has heavy mechanical vignetting at 200mm as well, that's not a cheap lens.

Billy B
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Re: Questions for the experts.

Post by Billy B »

Yes, it is a DX kit lens. If I back off from full extension, then vignetting only worsens. I suppose I could set it for infinity and crop photo, though not sure that would fix the halo problem. Older 200mm tube lens are not that expensive on eBay. I may go that route.

JKT
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Re: Questions for the experts.

Post by JKT »

In this case Raynox DCR-150 might not be such a bad idea - then again it rarely is. 8)

The downside is getting the required adapters.

physicsmajor
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Re: Questions for the experts.

Post by physicsmajor »

So one thing to note here is that a lot of Nikon lenses play tricks with focus and focal length.

The Nikkor 18-200 DX zoom lens is notorious for this. At infinity it's a real 200mm lens, but as you focus closer the thing shortens in reality to something like 135mm in portrait distance despite being set to 200mm.

You should not be getting vignetting on DX with that objective and any 200mm lens, but if your 55-200mm was set to the wrong end of the focus range the lens may actually functionally be less than 200mm and could produce vignetting.

A very easy test is to mount the objective and lens, set the lens to 200mm on the zoom ring, and go to live view. Aimed at a uniform bright field, with one hand on the focus, rack it completely from one end to the other watching live view. If this lens exhibits internal focal length change at closer focus, the vignetting will go away at one end of the focus range (should be the infinity end). Back off slightly from that end - in my experience with AF Nikons the focus range generally exceeds infinity slightly - and use that setup to take a few test shots.

Another possibility if the vignetting is not centered is that the objective is not centered in the optical axis. This could be the adapter, or the lens... Plastic telephoto lenses in extension sometimes droop a little with the weight of an objective added to the filter. At 10x such effects are accentuated.

Billy B
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Re: Questions for the experts.

Post by Billy B »

Thank you so much for your help. I can't tell how much I appreciate the input I get from you and others on this forum. Even fully extended to 200mm, I get a very slight amount of vignetting, so to back it off a small amount to infinity would only create more vignetting. For now I can live with it, as corrections can be made in Photoshop. My original concern was that the kit lens might be causing halos in my photos, but ..rik and others gave me suggestions that enabled me to correct that.
It seems the further I get into this hobby, the more $$$ it cost. I would love to go from the Nikon DX D7100 I'm currently using to an FX camera with the larger sensor, however I'm not sure of the difference that would make. Maybe somebody can chime in with advice.

physicsmajor
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Re: Questions for the experts.

Post by physicsmajor »

Long story short, bigger sensor isn't necessarily better when it comes to photomacrography. You've got the same body I do one generation newer (I currently use the D7000) and while a bit more resolution might be nice, the truth is I'm getting excellent results. I'm planning to shoot the shutter out on this body and then upgrade - since May I've put about another 20k shutter actuations on the body.

There are a lot of lens/objective combinations which simply do not throw a large enough image circle to illuminate a full frame sensor - and the best of these can get expensive quickly. You end up with more options for similar performance on APS-C (and some even prefer micro 4/3).

For someone entering the hobby, who already has a solid Nikon APS-C body, I'd suggest investing in lenses/adapters to cover the magnification ranges you expect to find useful without the big cash outlay for a full-frame DSLR which will further limit your optics choices.

Billy B
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Re: Questions for the experts.

Post by Billy B »

Your wisdom hits home. I like to play golf and have a pretty old set of clubs. I often think it would improve my game if I were to buy a new set, but I know it's not the clubs but my technic that has to improve. I suppose the same thing can be said of photography. I'll hold off on the new camera for now and maybe invest in other things that will improve my macro " game. " Thanks

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