Infinity objective on low-end zoom telephoto works fine

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Blame
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Post by Blame »

My problem is going to be adapters. I think I have a bodge that might work involving glueing an adapter to the centre of a spare glass UV filter. It will leave the back of the objective about 2cm from the front of the lens.

The objective is rather heavy (about 200g). I am wondering if the glass will break or just fall out. Anybody tried a similar trick?

rjlittlefield
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Post by rjlittlefield »

I would be nervous about gluing to glass. Ignoring adhesion and breaking, there's also the reflection-kills-contrast issue that I described earlier.

But there's another low cost trick that I used to use regularly. Go to a hardware store and get a small piece of 1/8-inch fine grained pressboard. It used to be sold under the brand name Masonite, typically smooth on one side and a fine grid pressed into the other. These days it's often sold with a smooth white coating on one side and a smooth back also. Either way, the stuff is soft enough that if you make a hole of the proper size, the objective can form its own threads in the pressboard by displacement. Probably you won't have a drill of the right size, but filing to fit works well. Then take the spare filter, remove the glass, and fit the pressboard plate into the filter ring.

--Rik

Pau
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whith high end zoom too!

Post by Pau »

Rik,

I can confirm your findings, whith the some Nikon CFI 10X 0.25 but in front of a Canon EF 70-200 f4 IS USM. I can zoom between 200mm and 140mm before vignetting and corner degradation begins.
This lens does perform better than the Nikon CF 10X 0.30 infinity WD 16.5 (not in resolution, but in sensor filling and longitudinal CA)

Not a good test like yours, but I posted some images here:
http://www.photomacrography.net/forum/v ... hp?t=10148
Pau

rjlittlefield
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Post by rjlittlefield »

Just adding a link...

This type of adapter -- to mount an objective in front of a telephoto lens -- is now commercially available. Currently they are on eBay as "Nikon CFI M25 microscope objective to M52 52mm adapter" and "BD M26 36tpi microscope objective to M52 52mm adapter".

--Rik

Disclaimer: Yes, that's my picture in the seller's ad. I traded him permission in exchange for a couple of his commercial-quality adapters to replace my homemade ones. I also sent him a couple of new pictures showing his adapters instead of mine, but I guess he hasn't swapped in the new photos yet.

Edit: to fix one URL
Last edited by rjlittlefield on Fri Feb 22, 2013 12:57 am, edited 1 time in total.

Blame
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Post by Blame »

I can confirm that the m26 36tpi works great with a mitutoyo objective.

Now one step closer to my macroscope.

seta666
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Post by seta666 »

Having invested quite a alot of money on finite lenses I do not really plan to move to infinity lenses(I can not afford it either). However it is something I find very interesting and some times cheap infinity lenses do show on Ebay.
I know mitutoyos are top of the line and the nikon´s and Olympus cheaper alternatives both CA corrected on the lens.
Are there any advantages of using the infinity lenses over the finites (newer optical designs, bigger image circle)
One thing I do nort understan is why the aperture of the tube lens does not afect the microscope lens NA, can you explain this further? how would affect the image if you close the aperture lets say 1 or 2 stops? and the NA?

What about using a 300mm or even 400mm prime lens as a lens tube, Would it push the lens up keeping only the middle of the image?

Some of the advantages I can think of for finites are:
-CAs allready corrected on the lens (at least with CFs)
-Hability to push up very well, lenses like the M plan 10/0.25 can go to 20x with good results, this lens also can be pushed down to 7-8x even on a full frame camera
-Less glass elements (less image degradation?)

I find this a very interesting subject since I show Joaquim F and Rik´s tests

Regards

rjlittlefield
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Post by rjlittlefield »

seta666 wrote:Are there any advantages of using the infinity lenses over the finites (newer optical designs, bigger image circle)
The 10X NA 0.25 infinity lens tested here has a larger high quality field than any other 10X objective I have tested. But this does not mean that infinity lenses are generally better than finite. It could be that they are generally about the same and I have only had the good fortune to get wide field in an infinity design.

Actually I suspect that they are generally about the same. The lens manufacturers had a long time to optimize the designs of finite objectives. Infinite objectives are not dramatically different, they are just corrected to work best in a slightly different focus arrangement.
One thing I do not understand is why the aperture of the tube lens does not affect the microscope lens NA, can you explain this further? how would affect the image if you close the aperture lets say 1 or 2 stops? and the NA?
At image center, the limiting aperture is in either the objective or the tube lens but not both. If you stop down the tube lens far enough, then it will change the NA of the system. However, a 10X NA 0.25 objective is already running at about f/20, so you would have to stop down the tube lens at least that far to have any effect.

Away from image center, the situation is more complicated. Often the limiting aperture is in the objective on one side of the cone of light, but in the tube lens on the other. If you stop down the tube lens, these regions will start to go dark as some of the cone gets clipped away. If you stop down far enough, the entire cone may be clipped away and the corners of your image will go black. All of these cases represent vignetting.
What about using a 300mm or even 400mm prime lens as a lens tube, Would it push the lens up keeping only the middle of the image?
Yes. The magnification and image circle are proportional to the focal length of the tube lens. If a 10X objective is designed for a 200 mm tube lens, then using it on 300 or 400 will give 15X or 20X.
Some of the advantages I can think of for finites are:
-CAs allready corrected on the lens (at least with CFs)
This is true also for infinity designs from the same manufacturers.
-Hability to push up very well, lenses like the M plan 10/0.25 can go to 20x with good results, this lens also can be pushed down to 7-8x even on a full frame camera
At small apertures like NA 0.25, it is simpler to push magnification on finites because all you need is longer extension. With infinites, you need to change the tube lens focal length. I think the limits do not depend on finite versus infinite. The 10/0.25 tested here has been used by other people at even less than 7X on full frame, using a shorter tube lens.
-Less glass elements (less image degradation?)
Could be. However, note also that changing magnification of a finite objective by altering extension introduces aberrations, while changing magnification of an infinite by using a different tube lens does not. This is an area where simple arguments do not make accurate predictions.
Having invested quite a lot of money on finite lenses I do not really plan to move to infinity lenses
If you already have a set of finite objectives that work well for you, then certainly I cannot think of any reason to switch.

The point of this thread is that infinity objectives are also viable and may have advantages in some cases. The biggest advantage to infinites may be that they work well with cameras that need electronically compatible lenses. With my Canon T1i, some of the metering functions work better with infinity+telephoto than they do with finite+bellows. I have heard that some cameras from other manufacturers are even more picky.

--Rik

Bob^3
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Post by Bob^3 »

Thanks seta666 for asking the exact questions I also had.

And thanks Rik for the impeccably clear and concise answers, as usual.

One quick question, is this the correct Nikon 10/0.25 CFI objective that I won yesterday?

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... K:MEWNX:IT

If so, I hope I didn't out bid any forum members. If it's not the right one, anyone want one of these?! :D It looks the same as the images here. But I am not familiar with the infinity corrected objectives. Until I read this thread regarding the possibly larger image circle at lower mags for the 0.25 NA, I was actually looking for the 10x 0.30 NA CFI at a reasonable price.

Bob
Bob in Orange County, CA

Pau
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Post by Pau »

Bob, great bargain! (but others got it for ~$15 :twisted: ).
It's the some lens that Rik, Joaquim and myself are using, I bought mine from the same seller.
CFI are not reasonabily priced in general, whith the exception of this model and seller.
Pau

Bob^3
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Post by Bob^3 »

Pau wrote:Bob, great bargain! (but others got it for ~$15 ).
Ah shoot, I'll have to send it back then---or ask the vendor to refund the difference! :roll:
Bob in Orange County, CA

RogelioMoreno
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Post by RogelioMoreno »

Bob,

I bought mine for $25 a few months ago. :evil:

Rogelio

g4lab
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Post by g4lab »

Could be. However, note also that changing magnification of a finite objective by altering extension introduces aberrations, while changing magnification of an infinite by using a different tube lens does not. This is an area where simple arguments do not make accurate predictions.

Rik
I was under the impression that there was often CA correction that used to reside in the oculars, and they moved it to the tube lens. I can't quote where I got that impression from. But for manufacturer's other than Nikon do you think this holds true?

I love this forum!
Gene

RogelioMoreno
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Post by RogelioMoreno »

g4lab wrote:I was under the impression that there was often CA correction that used to reside in the oculars, and they moved it to the tube lens. I can't quote where I got that impression from. But for manufacturer's other than Nikon do you think this holds true?
Gene
As far as I know Zeiss moved the CA correction to the tube lens with their ICS objectives.

Rogelio

seta666
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Post by seta666 »

rjlittlefield wrote: The 10X NA 0.25 infinity lens tested here has a larger high quality field than any other 10X objective I have tested. But this does not mean that infinity lenses are generally better than finite. It could be that they are generally about the same and I have only had the good fortune to get wide field in an infinity design.
The Nikon BD plan 10/0.25 (the similar E plan too) is the only microscope lens I own that covers the full frame in very nice way, it can even be pushed to 7x 8x on a full frame camera. I find that M plan 20x and 40x work better when pushed up a little bit, lets say 25x and 45x as corners are not that good
Actually I suspect that they are generally about the same. The lens manufacturers had a long time to optimize the designs of finite objectives. Infinite objectives are not dramatically different, they are just corrected to work best in a slightly different focus arrangement.
I understand that, the only thing is that newer optical designs are all infinity lenses (am I right?) Also some of these new lenses have very long working distances
At image center, the limiting aperture is in either the objective or the tube lens but not both. If you stop down the tube lens far enough, then it will change the NA of the system. However, a 10X NA 0.25 objective is already running at about f/20, so you would have to stop down the tube lens at least that far to have any effect.

Away from image center, the situation is more complicated. Often the limiting aperture is in the objective on one side of the cone of light, but in the tube lens on the other. If you stop down the tube lens, these regions will start to go dark as some of the cone gets clipped away. If you stop down far enough, the entire cone may be clipped away and the corners of your image will go black. All of these cases represent vignetting.
So you could close the aperture on the tube lens one or two stops so it works on its sweet spot, giving better center to corner resolution and less aberrations. Then you could check if it vignetes (I guess the problem will be worse on full frame cameras)
However, note also that changing magnification of a finite objective by altering extension introduces aberrations, while changing magnification of an infinite by using a different tube lens does not. This is an area where simple arguments do not make accurate predictions.
I have not noticed any more aberrations when pushing up my finite lenses; I would say just the opossite as when pushing you use the center area of the lens which is supposed to be better. As I say I rather use my 20x and 40x lenses pushed up (the quality is more even across the frame)
If you already have a set of finite objectives that work well for you, then certainly I cannot think of any reason to switch.

yes, I do not plan to switch. However it is true that good deals can be found on ebay
The point of this thread is that infinity objectives are also viable and may have advantages in some cases. The biggest advantage to infinites may be that they work well with cameras that need electronically compatible lenses. With my Canon T1i, some of the metering functions work better with infinity+telephoto than they do with finite+bellows. I have heard that some cameras from other manufacturers are even more picky.
I never do any mettering when doing stacks, I apply long exposures and then adjust flash power manually as needed. You could solve your mettering problems using a chipped adapter between the camera and bellows, like the M42-EOS AF confirm adapters
I would not go into figths like "finites are better" or things like that (is the same when people blindly deffend a camera brand over other)
It is would to have alternatives, it is just that I was lost with some of the infinity lenses theory.
I also know that some of the best lenses one can get nowadays are infinity lenses like the mitutoyos; but these are generaly very expensive and out of my reach. Also does not make sense to buy a 7000$ lens and put it in front of a zoom lens. If you go for top of the line I guess you need the matching tube lens
You have explain everything very well and things are much more clearer for me now, thanks
Regards

rjlittlefield
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Post by rjlittlefield »

seta666 wrote:So you could close the aperture on the tube lens one or two stops so it works on its sweet spot, giving better center to corner resolution and less aberrations. Then you could check if it vignetes
Sorry, this is not quite the way it works.

When the telephoto is used by itself, stopping down improves the performance by blocking edge rays that go through paths with more aberrations.

But when the aperture is used in connection with an infinity objective, then either 1) those edge rays never got through the objective in the first place, or 2) they did get through the objective but are blocked when you stop down.

In the first case, stopping down has no effect, and in the second case it definitely does introduce vignetting.

It is theoretically possible that the edge rays are so bad you would prefer the vignetted image. But I would be a little surprised to find that case in practice.
You could solve your mettering problems using a chipped adapter between the camera and bellows, like the M42-EOS AF confirm adapters
Thank you for the suggestion. That one had not occurred to me.
g4lab wrote:I was under the impression that there was often CA correction that used to reside in the oculars, and they moved it to the tube lens. I can't quote where I got that impression from. But for manufacturer's other than Nikon do you think this holds true?
Gene, see http://www.photomacrography.net/forum/v ... 1235#61235

Bob^3, thank you for the kind words --- and congratulations on a great price for that lens!

--Rik

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