Angle of view for Pentax M lenses


BigTed

Link Posted 01/06/2009 - 22:45
I have a small collection of SMC M lenses, but can't find any info on angle of view for them on the web. Possibly it exists in the catalogues of the time (which I don't have)
Does anyone have angle of view for SMC M:
24mm f2.8
28mm f3.5
50mm f1.7
135mm f3.5

.. before I get the matchsticks, the blue tack and the protractor out?

Thanks!

BigTed

Link Posted 01/06/2009 - 22:47
update - sorry the 24mm is SMC not 'M'

JohnX

Link Posted 01/06/2009 - 22:54
Generic list, but this any help?

http://www.sizes.com/tools/ang35still.htm

Mongoose

Link Posted 01/06/2009 - 23:03
do you mean when used on a 35mm camera (as originally intended), or when used on an APS-C DSLR such as the K20D?
you don't have to be mad to post here



but it does help

BigTed

Link Posted 01/06/2009 - 23:06
Thanks very much
This is a good site (but a weird one!) and it may explain why I'm have got confused info before - WHY would anyone need to know what the diagonal AOV was?

Reason for the question is, of course, that I use film and a 1.5 crop, plus some other lenses, and it's easier to recce with a protractor and a note book and come back when the light might be good, with the right lenses....

Mongoose

Link Posted 02/06/2009 - 07:22
good idea, I always used to carry my digital compact around with me and take snapshots if I saw a photo I wanted to take. That way I could come back later with the "big guns" and at a sensible time for the light.
you don't have to be mad to post here



but it does help

greynolds999

Link Posted 02/06/2009 - 08:41
There's a page on Wikipedia which simplifies this: link. You can use the formula


to determine the focal length of any lens

Hope that helps!
My Photobucket

johnriley

Link Posted 02/06/2009 - 09:47
24mm f2.8 - 84 degrees
28mm f3.5 - 75
50mm f1.7 - 47
135mm f3.5 - 18
Best regards, John

BigTed

Link Posted 03/06/2009 - 12:51
Thanks folks (I put a response on this, but it disappeared somewhere. Try again...)

I realise now (belatedly, and thanks to the responses/docs in this thread) that some (all?) manufacturers - including Pentax and Sigma - use the DIAGONAL for the angle of view spec.

This probably makes sense for Medium Format as the size/shape of the image size can change (6x7, 645, etc etc - also makes sense if you went to art school and take funky slanted horizons, or prefer headless horse pictures ).

Anyways, I now have the means to update my measurements for 35mm and APS-C - just need to rework my Px67, because I reckon the ones I have are diags too ('square on the hypotenuse' rings a bell; I'll look it u on Wiki).

So if you notice someone wandering about between 10 and 2 with a protactor (possibly wearing shiney shoes) I'll be back at some point with the right lens and wearing boots )

johnriley

Link Posted 03/06/2009 - 12:55
Yes, the diagonal is always the measurement given.
Best regards, John

BigTed

Link Posted 03/06/2009 - 13:31
aha! as I thought! (and so recently )

This does back up the theory that buildings do not get bigger (or move) between the recce and the final tripod set up

I guess it the logic of the people who make the lenses v the logic of using them - just quirky enough to confuse you.

Thanks John!

justjas

Link Posted 03/06/2009 - 15:17
Given the angle of view for the diagonal, work it out by proportion for the width and height of the frame format, if you need that info!

For 35mm frame: Diagonal = 43mm, height = 24mm, width = 36mm

Given the angle for diagonal = 84 degrees (24mm lens)

Angle for width = 36/43 x 84 = 70 degrees.
Angle for height = 24/43 x 84 = 47 degrees.

For the other lenses substitute the lenses' diagonal angle in the formula above.
jas
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