8mm Forum: Anamorphic Alignment

This is topic Anamorphic Alignment in forum 16mm Forum at 8mm Forum.

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Posted by Colin Fish (Member # 5679) on January 26, 2018, 01:48 PM:

Hello All, As a follow up to my curved screen enquiry, I did build a curved screen. It happened that there was slight distortion on the outer edges. I rebuilt the screen flat and I am still getting distortion on the outer edges. It may be that my calculations were wrong on the curve. However, it has been suggested that my anamorphic lens may be out of alignment on the front and rear optics. Any suggestions before I rip down the screen and start again? I am using a Schneider scope lens with frontal lock and focus.

Posted by Terry Sills (Member # 3309) on January 26, 2018, 03:49 PM:

Colin
Is the lens you are using one that is designed for 16mm projectors. If it is for a 35mm projector I can imagine that you would get this problem. In any case Anamorphic lenses are not designed to give good focus on a curved screen, that would be Cinerama and would require the appropriate lens I think. I have Anamorphic lenses and they give excellent overall focus on a flat screen.

Posted by Maurice Leakey (Member # 916) on January 27, 2018, 02:12 AM:

quote:
This is a 35mm setup with a 55mm lens

Last November you quoted the above. Can you please explain?
What gauge projector are you using, and how is the Schneider anamorphic attached to your backing lens?

Posted by Mark Mander (Member # 340) on January 27, 2018, 02:14 AM:

As it's now on a flat screen it's more likely to be the scope lens,did you focus the prime lens then after attaching the scope lens refocus that?Mark

Posted by Colin Fish (Member # 5679) on January 27, 2018, 05:00 AM:

The gauge is 35mm. I have installed both a 55mm Isco and a 60 mm Isco lens to see if there is any difference. These lenses on there own give a good sharp image on the squeezed picture. I then screw the anamorphic on to the front of the backing lens making sure the image is focused in the centre of the screen. As I run the film I can focus the outer edges separately and get them sharp, then the centre is out.

Posted by Maurice Leakey (Member # 916) on January 27, 2018, 05:35 AM:

Colin
Does the anamorphic show a range of focusing distances? If, so, what is the marked minimum distance.
Most ex-cinema anamorphics (as I believe your Schneider is) would never focus down to your stated 12 foot throw.

Posted by Colin Fish (Member # 5679) on January 27, 2018, 01:38 PM:

Hello Maurice, The lens focuses from 10ft to infinity.

Posted by Maurice Leakey (Member # 916) on January 27, 2018, 01:46 PM:

Colin
Thanks for that. The anamorphic should be alright. But obviously is not. Perhaps it is faulty in some way.

Posted by Steven J Kirk (Member # 1135) on January 28, 2018, 09:32 AM:

I think the curved screen is out. It can only be a very shallow curve with a short throw.

Aside from any aesthetic curved effect, the curve on very large cinema set ups with a single lens is required in that if the screen were perfectly flat the edges of the screen would be further away from the lens than the centre. Think of it as a triangle. You are curving the screen to bring the left and right edges back within the focal depth of the lens. It isn't guesswork, it has to be calculated. Factor in also the focus of the anamorphic. Remember, as I see it the curved screen was a choice for Cinerama but a necessity only for 70mm - CinemaScope doesn't really require a curve, in my opinion. Hope this helps.

[ January 28, 2018, 05:08 PM: Message edited by: Steven J Kirk ]

Posted by Colin Fish (Member # 5679) on January 29, 2018, 01:18 PM:

Thanks for that Steven. I will try to test another anamorphic.

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