Film-Tech Forum ARCHIVE: need new set of lenses....

This is topic need new set of lenses.... in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Garry Knapp (Member # 9697) on 09-23-2017, 11:03 AM:

I'm committing to changing my layout...again...
Could someone calculate the lenses I would need for this please?
Last time.....for sure.....honest.....
21ft throw
124x53" screen
thank you

Posted by Leo Enticknap (Member # 534) on 09-23-2017, 01:57 PM:

You're not giving us any detail as to what format (film or digital, if film what gauge, etc.), aspect ratio, etc. etc. Assuming 35mm and 1.85, it looks like 40.5mm (124" = 10'4" and 53" = 4'5"):

This software is available for download in the Warehouse section (under "Schneider lens calculator"), so you can do the others yourself. It works under every version of Windows from XP to 10, although the Schneider part numbers it gives you are probably meaningless now. But the only crucial piece of information you need is the focal distance, which it'll also tell you.

For digital projectors, this software is no good: the size of the DMDs is different (and differs between light engines, too), so you need the calculator supplied by the manufacturer for the specific projector model. Barco has an online one, and NEC supplies an Excel spreadsheet.

Posted by Steve Guttag (Member # 268) on 09-23-2017, 02:12 PM:

And that is an old version of it too. That version works on Win98SE, I think too.

Posted by Randy Stankey (Member # 64) on 09-23-2017, 03:11 PM:

I have always used the cross-multiplication method.

Size of image on film * focal length = size of image on screen * throw

Plug in your known values then solve for the missing.

Round your result to the nearest available lens size.

Don't forget to add a multiplier for anamorphic factor if you need it.

I like lens size calculation programs and have used them when they were available but just doing the math has never failed me.

Posted by Garry Knapp (Member # 9697) on 09-23-2017, 05:23 PM:

sweet! thanks guys! I will go grab that out of the warehouse!

Posted by Garry Knapp (Member # 9697) on 09-24-2017, 08:10 PM:

thank you Leo
I found it...and after playing with it for an hour
(which was fun, its a great program) i determined my best options for the new setup. Thank you again. Film is fun [Smile]