Film-Tech Forum ARCHIVE: Help needed understanding lens specs.

This is topic Help needed understanding lens specs. in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Alan Gouger (Member # 543) on 08-01-2005, 01:57 PM:

I find it confusing trying to figure out what lens will give me what picture size. The Isco calculator is confusing and I also bought a slide rule ICECO and thats just as confusing.

Some lens are marked in " while others in MM.

Is there a general formula that works with all lens and easy to use.

Thanks!!

Posted by Gordon McLeod (Member # 33) on 08-01-2005, 02:04 PM:

the focal length of the lens can be expressed in either inchs or millimetres

historically imperial lens sizes were made in 1/4" inch increments and metric sizes were in 5mm increments nowday all sizes are made

the slide rule is very straight forwar
set the throw first
set the image size you want usualy the arrow on top is image heigth with the various formats widths below
Then red off the lens size for the format in question (on most that is expressed as apperture heigth)

Posted by Aaron Sisemore (Member # 145) on 08-01-2005, 02:31 PM:

Use the Bell Cinema lens calculator, its VERY easy to use compared to the ISCO and Schneider software suites.

You can get it right here at Film-Tech!!

-Aaron

Posted by Ed Inman (Member # 2583) on 08-01-2005, 03:42 PM:

For flat prints:

75mm equals 2.95 inches (approx. a traditional 3" lens)
100mm equals 3.94 inches (approx. a traditional 4")
125mm equals 4.94 inches (approx. a traditional 5")
150mm equals 5.91 inches (approx. a traditional 6")

A full mm to inches conversion chart is available in the downloadable www.iceco.com catalog.

Ed

Posted by Richard Fowler (Member # 893) on 08-01-2005, 04:21 PM:

1 inch = 25.4mm.....not that hard [Razz]

Posted by Gordon McLeod (Member # 33) on 08-01-2005, 04:21 PM:

Ed said

quote:
For flat prints:

Conversion applies to any lens not format specific

Posted by Alan Gouger (Member # 543) on 08-02-2005, 09:03 AM:

Aaron

Thanks for the calc. Perfect.

Gordon

With your instructions I was also able to figure out the slide rule and compared the results with the Bell Cinema lens calculator to confirm I was correct.

Richard thanks for the conversion.

Thanks everyone Im all set [Smile]