Experience with projection lens Elmarit-P2 2,8/60mm?

[christoph_frick1]

The background of my question: Currently my Pradovit P150 is

equipped with a Colorplan-P2 2,5/90mm lens. I asked around about

a "CF" (curved field) version (as I use non-glass mounts), but was

told that those are not produced any more, and anyhow their

curvature correction would be overkill for modern plastic mounts,

i.e. they were designed for those cardboard mounts. One person

recommended to try the Elmarit-P2 2,8/60mm, as it would have more

DOF, so the curvature would be much less of a problem. -- Is that

true in your experience? -- And what about the larger viewing

angle, what are the pro-s and con-s you have experienced? Thank you!

[Rob F.]

Christoph: I do use a 60mm projection lens. Mine is a Golden Navitar, not the Leica 60. In my case, I use it, not for DOF, but because I want a wide screen at a short projection distance.

 

Let me give you an idea of how a 60mm lens works out. I can fill an 8 foot wide screen at a projection distance of 14 feet, 2 inches, with my slides mounted in Wess mounts having a 34.5mm horizontal aperture. It is a linear relationship, so if you wanted to fill a 4 foot screen, your distance would be 7 feet, 1 inch; for a 6 foot screen, 10 feet, 7 inches. These distances are from the screen to the gate, not to the lens! Your projection distance will be about 1.77 times the screen width, assuming a horizontal image.

 

The use of a lens this wide only works well when you can have the projector on a stand that raises it to the center height of the screen. Otherwise, projecting off center with a wide-angle lens will cause significant keystoning. It won't work out well if the projection setup consists of setting up a portable screen, and then placing the projector on some nearby low table!

 

Finally, greater DOF of a short lens means less in projection than in photography. DOF really depends ultimately on the magnification ratio. With a given size screen, the magnification from the slide to the fully filled screen will always be the same, regardless of focal length; and I believe the DOF will be the same as well.

 

So I'd say that wide angle projection lenses are for wide screens and/or short projection distances; and not for improving DOF.

[john_collier2]

The 90/2.5 P2 CF lens shows up on eBay occasionally. It is a matter of luck having the curvature of the field matching the curvature of the slide but it does happen. For perfect focus on the screen, the only way to go is glass mounts and a flat field lens. Change lens focal lengths to suit room size and desired projector placement; not, to get more DOF. DOF is strickly based on relative aperture and image magnification.

[Robin Smith]

Christoph

 

I agree with the others the 60mm will not help you DOF-wise and the Colorplan is reputedly the superior lens anyway. I think the CF lenses are a waste of money myself as even Kodachromes (for which they were designed) do not by any means accurately follow the expected curvature. You are better off with a flat field lens. The only real way to get pin sharp image is using glass mounts, but I don't think it is worth it. The best thing you could do to improve your image is simply to buy one of the Pradovit Color, 2500, 2502, P2000 series - this produces a much flatter and better image than the P150. Quite why is a mystery to me, but it has something to do with tighter tolerances and superior cooling/temperature control, but this is my experience.

[b_n_f]

http://www.leica-camera.com/produkte/projektion/objektive/tabelle/index_e.html

 

List of lens/distances