Film-Tech Forum ARCHIVE: Scope lens issue

This is topic Scope lens issue in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Richard May (Member # 2627) on 07-08-2017, 09:55 AM:

I have an Isco 135MM 35/70 lens for scope. I tried 3 different Schneider standard anamorphics on them and I can't focus. The 135MM lens focuses perfectly by itself. I even tried another 135MM lens and still the same issue. I then unscrewed the anamorphic and held it an inch or 2 away from the lens and it focused fine. Would I normally need a spacer for this?

Posted by Steve Guttag (Member # 268) on 07-08-2017, 03:09 PM:

Your problem is the crappy Schneider (full size) anamorphic lenses. I'm not kidding. They are pure crap. The VERY last generation of them were fine, as far as 4-4-element anamorphics go but all of the 1980s - through 1990s anamorphics are junk. Depending on how much their elements have shifted is how bad they are.

Their integrated anamorhpics didn't have the problem but are not recommended for long EF (135mm) primes. Put an ISCO (any generation) on those same 135mm lenses and it will be like getting new eyes. As you move up in ISCO lens grades (4-element through 6-element) you'll see the aberrations decrease.

Posted by Jonathan Wood (Member # 4614) on 07-30-2017, 01:28 PM:

Hi Richard, how close are you trying to focus ? I assume since your using a 135mm backing lens then your not talking about a short throw ? Steve's comments are very interesting - I have both Isco and Schneider integrated lenses and I do prefer the Isco - it's got a nicer colour balance and it's sharper . Never tried a full sized Schneider attachment , I do have an a Isco attachment but never felt the need to use it since the integrated works so well.

Posted by Steve Guttag (Member # 268) on 07-30-2017, 03:24 PM:

Other than the three ISCO Blue-start integrated anamorhics, all of ISCO integrated anamorhpics were based on their 4-elemenet design, that didn't change throughout the years. Using full-sized anamorphics, particularly if you move up to 5 or 6 element designs should yield superiour results. Depending on the EF of your prime lens, close coupling may be required to use a full-sized anamorphic.

Posted by Mark Gulbrandsen (Member # 72) on 07-30-2017, 04:43 PM:

quote: Richard May
I then unscrewed the anamorphic and held it an inch or 2 away from the lens and it focused fine. Would I normally need a spacer for this?

You are not using "enough" of the anamorphic glass for it to work properly. Moving the lens out from the prime puts the anamorphic into a cone of light that's spread out more and that allows the anamorphic to work properly. Ideally, you want to be using 2/3 of the glass area of the anamorphic. So a proper spacer will likely cure this issue. But also what Steve said. Those old schneider lenses are not that great and full of chromatic aberration.

Mark