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12-03-2009, 07:04 PM   #1
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Field of view

I sold my Pentax SLR film camera, lenses, extension tube set, and other accessories a few years ago when I went "digital". BIG MISTAKE! My Canon S3IS digital cameras works fine in most applications, but taking pictures of a large model train layout is not one of them. By being limited to f8, I can't get a decent depth of field.
So, recently I bought a 35mm Pentax K1000 with a Macro F 1:4 50mm wide-angle lens for $100 (I understand from reading various comments in the Pentax Lens Review Forum that this is an excellent lens that should render sharp images not just in macro. However, I'm somewhat limited how far I can get back from or above the train layout. I have been bidding on Pentax-M f2.8 28mm wide-angle lenses and finally got one that is in good condition for $55.99.

I read somewhere that the field of view for the Pentax-M f2.8 28mm wide-angle lens is 75. I don't remember where I saw it, but using 75 and a bit of trigonometry I calculated what the field of view "B" is at a distance "A"

A=4' B=6.13'; A=6' B=9.21'; A= 8' B=12.28'; A=10' B=15.53'

Is this correct or am I way out in left field? ;-)

I would appreciate your thoughts.
Thanks

12-03-2009, 07:38 PM   #2
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I do not have any idea what all of those numbers mean, but I will tell you that a 28MM lens on a K1000 should be plenty wide for what you are trying to do.
12-03-2009, 07:47 PM   #3
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If you are limited by budget, why not get yourself an 18-55 kit lens? It will give you more room to maneuver, it focuses fairly close and price won't be far of $50

Sorry, please disregard my rambling.

Last edited by Damn Brit; 12-03-2009 at 08:05 PM.
12-03-2009, 07:51 PM   #4
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He got himself a K1000 Gary. Kit lens won't be all that useful on it.
Mathematics aside 28mm on 35mm film camera should be reasonably wide enough.
Any wider, and you're looking at very expensive 24 and 20mm lenses (for rectilinear images).
Perhaps the film folk can help out here...

12-03-2009, 07:55 PM   #5
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Well you can pull out your old trig books from high school.... or

http://www.tawbaware.com/maxlyons/calc.htm

Scroll down to the Dimensional Field of View Calculator

The Focal Length multiplier for Pentax is 1 for a 35mm

So for 28mm at 6 feet you have a field of view of 7' 8.6"

You probably need to consider the depth of field also, which is controlled by the aperture.

Online Depth of Field Calculator

... hope that helps...
12-03-2009, 07:57 PM   #6
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Yeah, that's essentially right, but the 75 degree FOV for a 28mm lens on 35mm film is the DIAGONAL field of view, so if you're holding the camera in a landscape orientation, it will be less than that.

The field of view for a rectilinear (i.e. non-fisheye) is:

FOV = 2 * arctan ( sensor dimension / ( focal length * 2))

And a frame of 35mm film is 36x24mm, with a 43.3mm diagonal.

So, plugging in 43.3mm as the sensor dimension and 28mm as the focal length, you get about 75 degrees, which corresponds to what you heard. But horizontally, using 36mm as the relevant sensor dimension gives you a roughly 65 degree FOV with that 28mm lens.

And to get the field width B based on subject distance A and a given FOV, I think you already figured out that the equation is:

B = 2 * A * tan ( FOV / 2 )

---

EDIT: Aaaaand . . . if you just use i_o's calculator above, you get exactly the same results! Oh well, at least my math is right.
12-03-2009, 08:50 PM   #7
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QuoteOriginally posted by Opahujo Quote
I sold my Pentax SLR film camera, lenses, extension tube set, and other accessories a few years ago when I went "digital". BIG MISTAKE! My Canon S3IS digital cameras works fine in most applications, but taking pictures of a large model train layout is not one of them. By being limited to f8, I can't get a decent depth of field.
So, recently I bought a 35mm Pentax K1000 with a Macro F 1:4 50mm wide-angle lens for $100 (I understand from reading various comments in the Pentax Lens Review Forum that this is an excellent lens that should render sharp images not just in macro. However, I'm somewhat limited how far I can get back from or above the train layout. I have been bidding on Pentax-M f2.8 28mm wide-angle lenses and finally got one that is in good condition for $55.99.

I read somewhere that the field of view for the Pentax-M f2.8 28mm wide-angle lens is 75. I don't remember where I saw it, but using 75 and a bit of trigonometry I calculated what the field of view "B" is at a distance "A"

A=4' B=6.13'; A=6' B=9.21'; A= 8' B=12.28'; A=10' B=15.53'

Is this correct or am I way out in left field? ;-)

I would appreciate your thoughts.
Thanks
For what its worth, that 50mm macro lens is more accurately referred to as a "normal" lens on film format. They are called that because they are approximately equivalent to the FOV of the human eye. Lenses in the 43mm-58mm range have been historically called "normal" lenses for 35mm film cameras. Longer = tele and shorter = wide angle. It will still be useful to get some extreme close up of the lay out which will compliment the wide angle. If space is cramped, look into a 20 or 21mm m42 lens and a k adapter.
12-04-2009, 09:22 AM   #8
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Quicksand, thanks for the information. I really appreciate it.

Yes, "B = 2 * A * tan ( FOV / 2 )" is exactly what I used, but instead of FOV/2 =32.5 I used 37.5. I didn't know that I needed to use the diagonal dimension.

Opahujo

12-04-2009, 09:36 AM   #9
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QuoteOriginally posted by Ash Quote
He got himself a K1000 Gary. Kit lens won't be all that useful on it.
Mathematics aside 28mm on 35mm film camera should be reasonably wide enough.
Any wider, and you're looking at very expensive 24 and 20mm lenses (for rectilinear images).
Perhaps the film folk can help out here...
there is a plastic fantastic full frame 18-35 - they are like $100-200... of course it is a zoom - but should do the work.

for example - http://www.bhphotovideo.com/c/product/800665641-USE/Sigma_518109_Zoom_Wide_Angle_18_35mm.html - and you should be able to find that cheaper than that
12-04-2009, 09:50 AM   #10
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Interested Observer, thanks for the link to the "Dimensional Field of View Calculator." I do have a question about the "Online Depth of Field Calculator," which I bookmarked after finding it in another thread in this forum. I'm not sure whether I may ask the question in this thread, but here it goes: when you use the calculator for a 15-55 kit lens, how do figure out what number to use for the focal lenght?

If it's not Ok to ask that question in this thread, I'll be glad to post it in the Online Depth Of Field Calculator thread.
Thanks
Opahujo
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