Infinity objective on low-end zoom telephoto works fine

lothman · Post by **lothman** » Fri Jan 07, 2011 10:32 am

just a question what came in my mind and I had to dig out this thread

Could a 200mm slide projector lens be used as a tube lens? These lenses would allow a very solid full metall setup, what should eliminate vibrations as far as possible. And for example a Leica Elamoron should have good quality and should have been designed for a very similar purpose.

And if yes should the lens used be reversed?

Regards
Lothman

ChrisR · Post by **ChrisR** » Fri Jan 07, 2011 10:44 am

should the lens used be reversed?

I'd have thought not, the projector screen is nearer infinity than the slide, from the lens.

I'd be surprised if it worked out well. I tried projector lenses on film cameras, with nothing but disappointment. They seem to be optimised for maximum aperture (brightness) and not for resolution.
I've dug out Kodachromes which I used to enjoy looking at on a large screen, only to find that the image on the film isn't very sharp at all.
At normal viewing distances from screens, it seems our eyes aren't good at picking fine detail.

rjlittlefield · Post by **rjlittlefield** » Fri Jan 07, 2011 11:12 am

lothman wrote:Could a 200mm slide projector lens be used as a tube lens?

It's worth trying. The few projector lenses I've ever looked at have behaved like ChrisR suggests -- bright but fuzzy. But those were low end lenses, tested wide open. The objective will naturally stop them down to effective f/20, and if the lens is good to start with, it might work just fine.

The objective should go on the long-throw side of the projector lens -- the side normally facing the screen.

--Rik

lothman · Post by **lothman** » Fri Jan 07, 2011 2:50 pm

ChrisR wrote:I'd be surprised if it worked out well. I tried projector lenses on film cameras, with nothing but disappointment. They seem to be optimised for maximum aperture (brightness) and not for resolution.

I used reversed slide projector lenses as CU-lens on bridge cameras with great success. I converted some Leitz Colorplan and a Zeiss.

IMO the are optimised for flat field at open aperture. Today you can get such lenses for few $, years ago they cost double of the what is a nikon tube lens today

ChrisR · Post by **ChrisR** » Fri Jan 07, 2011 3:08 pm

Leitz Colorplan

Yep , that was one of them! On a Fujica ST701. Ah, memories of Plasticene to keep the light out..

Simonoff · Post by **Simonoff** » Sat Jan 08, 2011 12:15 pm

Wow, let me first say thank you for this site! I just discovered it and am afraid it will take years to absorb it all!!! Thank you thank you thank you!

I have been reading this thread with particular interest since I am trying to decide between using a bellows with the CF lens or a telephoto with a CFI lens for photos I wish to take. I appear to be a bit of an outsider though, since I plan to take photos of "micromount minerals" which are those "better appreciated under magnification."

My question is around the experiment that was performed. I have the same exact camera and wonder what you did about light metering. On one hand you have the meter in the camera which may work. On the other hand you could just directly set the f stop to some value and use manual mode entirely.

The exact value to which the f stop should be set seems to be in debate - some say stop it one down from the max to avoid artifacts. Others say that the reduced diameter of light coming through the narrow objective already accomplishes that. I'd be curious of any thoughts on this as well.

Again thanks EVERYONE for the site, questions and answers!!
Bob

ChrisLilley · Post by **ChrisLilley** » Sat Jan 08, 2011 1:09 pm

Simonoff wrote: The exact value to which the f stop should be set seems to be in debate - some say stop it one down from the max to avoid artifacts. Others say that the reduced diameter of light coming through the narrow objective already accomplishes that. I'd be curious of any thoughts on this as well.

Welcome to the forum.

The advice about using a lens one (or more usually, two) stops below wide open is good advice in general when the lens characteristics are unknown. Some lenses really need to be three stops closed to give their best, some are at their optimal only one stop from wide open, and a very few are at their optimum wide open.

However, that is for a single lens with a variable aperture.

In the case of an infinity objective mounted on a tube lens, the objective does not have a variable aperture and is designed to be used 'wide open'. The telephoto used as a tube lens is effectively stopped down by the objective in front, so does not need to be further stopped down either.

Craig Gerard · Post by **Craig Gerard** » Sat Jan 08, 2011 3:56 pm

Bob,

There a a number of avid collectors/photographers of micromount minerals on the forum.

Have you seen some of the more recent posts in the Technical and Studio forum?

The quickest link to some of Doug Merson's work is via his profile and the 'Find all posts by microcollector' link.

Craig

pierre · Post by **pierre** » Sun Jan 09, 2011 1:08 pm

Hi Bob !

I spend lot of my time trying to take acceptable pictures of micromounts and would gladly help.

Herewith my mindat link:
http://www.mindat.org/user-13766.html#2_0_0_0_0__

There are also some top of art folks there: no doubt you would appreciate their kind comments / support like I do.

Simonoff · Post by **Simonoff** » Sun Jan 09, 2011 7:25 pm

Thanks for the information everyone. I had not seen the micromount pictures on this site before.

Pierre, Here is our home page :-)
http://www.mindat.org/user-14336.html#0

In case anyone is curious, here are some more micro photos from the same web site:
http://www.mindat.org/mesg-13-206991.html

In addition to my other question about light metering and lighting the subjects using this Microscope objective in the front of a 200mm lens, I have one other question. The other question is what makes a good 200mm lens for this application. I noted on the very first post the suspicion that the lens in question would not work out well. But that does raise the question of what kind of 200mm lens would be bad?

Thanks
Bob

rjlittlefield · Post by **rjlittlefield** » Sun Jan 09, 2011 8:42 pm

Simonoff wrote:I noted on the very first post the suspicion that the lens in question would not work out well. But that does raise the question of what kind of 200mm lens would be bad?

That post was mine. I expected that it would have problems with vignetting because of the entrance pupil size and position -- small and rather far back. But as noted it actually works fine when zoomed to the full 200 mm. Other people have reported good results with primes and with other zooms at full length, as well as some larger aperture zooms at shorter lengths. Offhand I don't recall any reports of telephotos that have not worked well at 200 mm. I hope somebody will refresh my memory if that's mistaken.

--Rik

ChrisR · Post by **ChrisR** » Mon Jan 10, 2011 2:16 am

Offhand I don't recall any reports of telephotos that have not worked well at 200 mm.

That might be the view if you have a small sensor, pun intended!
Given that microscope objectives weren't designed with any particular camera in mind, how "well" they work, perhaps needs some qualification.

I'm using 24 x 36mm.
At 200mm, some telephotos clip (not just darken) the corners with most objectives I've tried. Where there is full coverage, the corners are predictably unusable.

Some shorter telephotos, eg 100mm, "work" in the sense of giving a sharp picture all over, but giving lower magnification (at say 5x) where more DOF might normally be desirable.

To spread the whole image circle of the objective over 24 x 36, one move could be to use a (say) 300mm telephoto, which of course is getting clumsy.

The alternative, of using a shorter tele, "works" but I'm not sure how well.
For example I just looked through a 135mm + Mitutoyo 20x, and it looks OK, giving about 13.5x(?). Whether that's "better" than using a finite 10x on approx 200mm bellows, to get the same magnification, I don't know.

It would be interesting to try with eg a 35 - 135mm zoom on 24 x 36. (I don't have one)

rjlittlefield · Post by **rjlittlefield** » Mon Jan 10, 2011 8:50 am

ChrisR wrote:
Offhand I don't recall any reports of telephotos that have not worked well at 200 mm.
That might be the view if you have a small sensor, pun intended!

Good point, thanks for the clarification. Yes, my comments apply only to APS format, roughly 22mm x 15mm.

--Rik

Pau · Post by **Pau** » Mon Jan 10, 2011 9:28 am

ChrisR wrote:I'm using 24 x 36mm.
At 200mm, some telephotos clip (not just darken) the corners with most objectives I've tried. Where there is full coverage, the corners are predictably unusable.

Some shorter telephotos, eg 100mm, "work" in the sense of giving a sharp picture all over, but giving lower magnification (at say 5x) where more DOF might normally be desirable.

To spread the whole image circle of the objective over 24 x 36, one move could be to use a (say) 300mm telephoto, which of course is getting clumsy.

Chris, perhaps is my poor english but I don't understand your post: Are you saying that a 100mm tele has better coverage in full frame than a 200mm?

Blame · Post by **Blame** » Tue Jan 11, 2011 1:49 am

ChrisR

What was your 135mm lens?

I have been thinking of buying one of those 135mm f/3.5 zeiss jena's for my mitutoyo's.