nehemiahphoto
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philip_pj wrote:
I want to save readers, especially nehemiahphoto, a wade in the swamp that surrounds the terms 'Field of View' and 'Angle of View'. Some love this kind of thing as much as I do not. A fair reasoning is this:
'whilst AOV and FOV are different things, they are both measured as angles...it states that AOV is a property of the lens and does not change no matter what size of sensor is in the camera, whilst FOV is a function of the lens AND the sensor size.' Much more on the subject here if you are in the 'need to know' camp:
https://shuttermuse.com/angle-of-view-vs-field-of-view-fov-aov/
Now all that matters is what makers report and what actually happens. The reason for the second part of the sentence is (i) the alarming rise in the tendency for distortion correction, and its implications for stated AOV/FL, together with (ii) the often outrageous levels of breathing in stills lenses.
Makers report AOV in the places I look for the data, usually B&H, or Cosina or Sony, probably others too. So you get numbers like 62.0, 63 or 63.4, and whole integers will most likely be rounded and will not be perfectly accurate, but are still better than nothing. Back when makers treated users with less contempt, Carl Zeiss used to report minutes as well as degrees (there are 60 minutes to a degree for the angle calculation).
Most spec sheets report AOV - here are examples:
https://www.sony.com.au/electronics/camera-lenses/sel35f14gm/specifications
https://www.bhphotovideo.com/c/product/1605136-REG/sigma_35mm_f_2_dg_dn.html/specs
http://www.cosina.co.jp/seihin/voigtlander/english/e-e-mount/e-50mmf2.html
Once you have these AOV data, you can search all the technical waffle (the data swamp) for a simple text entry field that converts AOV to focal length. I use this one below not because it is 'better' but the other sites bury this very useful feature amongs the impenetrable related information they want to assail you with:
http://kmp.pentaxians.eu/technology/fov/
Of course it is called 'FOV', but we all use the same sensor dimensions give or take, so I believe you can press on here. Enter your AOV in the right side text entry field and read off the equivalent FL to the left.
To complete the exercise here are the derived FLs of the lenses you cite, gained from the Pentax site:
CV M 35/2 APO - 34.9mm
CV E 35/2 APO - 35.9mm (different!)
CV 35/1.7 - 36.0mm
CV M 35/1.2iii - 36.3mm
CY 35/1.4 - 35.7mm
RX1 - 35.3 (post correction, we can be certain of this!)
Sigma 35i - 35.0mm
AOV data are almost aways listed in 'Full Specifications' or similar page titles. Others will likely have better formulas/calculators - the topic should be an Alt lens FAQ, I think. Or somewhere easier to find than here. Of course if we had breathing data, we could see close and infinity FLs, then we could get ready for a real surprise:
'The AOV of a lens is based on the lens *focused to infinity* using the sensor (or film) size for which it was designed.' Breathing varies greatly among lenses, leading to incorrect assumptions on 'taken image AOVs/FLs' shorter than infinity. Imagine knowing the true FL of a portrait lens at acceptable portrait distances, say 2m? From the DPR lens reviews (they do this well now as they know video is getting bigger) it seems breathing is fairly linear as one pulls focus....Show more →
Very interesting. Thanks for taking the time to compile this response with links. The values you've stated line up with my experience. One point of interest here. According to the Zeiss data sheet for the CY 35/1.4, the actual FL is 36.5, while the nominal is obviously 35mm, with a FOV of 62 degrees.
However, on the linked Pentax calculator above, the FL is 36.003 mm when plugging in Zeiss measured horizontal FOV of 62 AOV value. Not the 36.5mm stated on the Zeiss data sheet. Maybe it's a breathing differential?
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