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David Woods
25-Apr-2010, 15:14
Hi
How do you work out what format a lens can cover, is there a website, or do you multiply something by something.

Regards
David

Gem Singer
25-Apr-2010, 15:29
Click on LF Home Page on the blue bar above.

Scroll down to "Comparison Charts" on the home page of this website.

Click on the format you are seeking, and you'll find the answer to your inquiry.

There is a gold mine of information available on that page.

carverlux
25-Apr-2010, 15:31
Hi
How do you work out what format a lens can cover, is there a website, or do you multiply something by something.

Regards
David

David,

The optical formula is as follows:

2 x tan(claimed coverage angle x 0.5) x focal length of lens. For example, a Rodenstock 360mm Apo-Sironar-S with a 75 coverage angle at f/22 would be: 2 x tan(75/2) x 360 = 2 x 0.7673 x 360 = 552mm.

Obviously, the coverage angle varies widely from lens to lens, manufacturer to manufacturer and the most deadly - the defintion of "sharply covered". Therefore "claimed" to "actual" is best determined by "to taste" testing yourself.

Have fun and good luck!
Carver

John Brady
25-Apr-2010, 15:36
This page from Ebony is very helpful too.
http://www.ebonycamera.com/articles/lenses.html

WWW.timeandlight.com

ic-racer
25-Apr-2010, 17:46
Hi
How do you work out what format a lens can cover, is there a website, or do you multiply something by something.

Regards
David

Usually the manufacturer provides this information; there is nothing to calculate if an image circle is given. You should be able to figure if your film diagonal is less than the image circle diameter in your head.

Otherwise, if no manufacturer info is available, you use trial and error to see what the coverage is.

Andrea Gazzoni
25-Apr-2010, 21:44
so what am I finding when I look through the clipped corners of my groundglass and make sure that the iris opening is visible and round with no vignetting? is it illumination only? thanks

David Woods
25-Apr-2010, 23:03
This page from Ebony is very helpful too.
http://www.ebonycamera.com/articles/lenses.html

WWW.timeandlight.com

Thanks John

Love your black & whites on your website, stunning.

David

David Woods
25-Apr-2010, 23:08
so what am I finding when I look through the clipped corners of my groundglass and make sure that the iris opening is visible and round with no vignetting? is it illumination only? thanks

what I am saying is, if I look at a lens and say for example it is a 300mm lens with a 6.3, is there a way of working it out myself, without having to go to websites, or having to ask anyone.

David

Ole Tjugen
25-Apr-2010, 23:45
what I am saying is, if I look at a lens and say for example it is a 300mm lens with a 6.3, is there a way of working it out myself, without having to go to websites, or having to ask anyone.

David

Simple answer: No, there isn't.

Explanation: Angle of coverage depends on the lens construction (and personal taste), sowithout knowing what kind of lens it is there's no way of knowing. A 300mm f:6.3 telephoto lens might not even cover 4x5", while a 300mm f:6.3 wide angle could cover 20x30".

Most f:6.3 300mm lenses are "normal lenses", but the difference between a Tessar-type (just covers 8x10") and a Plasmat-type (covers 11x14") means there's still no way of working it out without tables - or experimentation.

David Woods
26-Apr-2010, 19:37
Simple answer: No, there isn't.

Explanation: Angle of coverage depends on the lens construction (and personal taste), sowithout knowing what kind of lens it is there's no way of knowing. A 300mm f:6.3 telephoto lens might not even cover 4x5", while a 300mm f:6.3 wide angle could cover 20x30".

Most f:6.3 300mm lenses are "normal lenses", but the difference between a Tessar-type (just covers 8x10") and a Plasmat-type (covers 11x14") means there's still no way of working it out without tables - or experimentation.



thanks Ole

Jim Galli
27-Apr-2010, 03:33
With time, (and lots of wasted money), you begin to get a little set of formulae in your brain. Petzval's are about 30, Rapid Rect, 65, Tessar's 60, Dialyt's, Cooke Triplet's and Heliar's 50 - 55, Plasmat's 70, Dagor's and G-Claron's 82, Angulon's 90. Ole will fuss because none of these numbers are perfect and there are gajillions of exceptions, but still, get a piece of graph paper and simply draw the focal length and the angles to get the resulting circle at the other end. We're ball parking here, but it's actually pretty darn accurate. Don't believe anything anybody says on Ebay. (Unless it's my ad of course:D )

Ole Tjugen
27-Apr-2010, 04:39
Me fuss? Not over that, only over Jim's using apostrophes in plural form - that's for contractions and possessive forms. ;)

And that some G-Clarons are "Dagors", while others are Plasmats. ;)