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04-01-2013, 10:12 AM   #1
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Angle of view question

Is the lens' angle of view measured from the sensor or from the front element of the lens?

I.e. the front element of the DA 16-45 mm @ 21 mm is probably ~125 mm away from the sensor while the DA 21 mm ltd's front element is about 20 mm away from the sensor, but should they see the exact same thing if the camera was positioned in the exact same place?

Just curious and hopefully someone here knows the answer right away.

04-01-2013, 11:07 AM   #2
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The manufacturers use the diagonal of the sensor plate to determine the angle of view which is not very practical.
Also it is nominated at infinity focus.
For a retro focal wide angle like the DA21, it is simpler to visualize, the rear nodal plane is at f ( 21 mm ) from the sensor.
the AOV is twice the angle from the axis at the rear nodal plane N2 up to a corner at half of the diagonal
Using atan function on a calculator, it can be calculated, but easier just to look up the data published for the lens.
I just did a couple of examples (on 35 mm frame with a diagonal of 43.27 mm) ) and the values calculated as above agree with the values published by Pentax.
04-01-2013, 11:40 AM   #3
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I've often thought this too. Surely it'd have an effect on close-ups, especially for wide angle? Not to do with calculating the AoV, but for the same AoV, if the front element is closer surely the picture will look different?

I guess to the extreme that you could be touching your subject with the 16-45 but not with the DA 21 and theoretically get the same picture which doesn't make sense. Neither would be in focus obviously, but still.
04-01-2013, 02:17 PM   #4
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Lol. @wombat you really hurt my head with that post. I am glad some here understand that stuff.

04-01-2013, 03:35 PM   #5
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I love it when my curiosity is so easily satisfied...

Here is 21 mm @ f4 on the 16-45
Attachment 166089

Here is 21 mm @f4 on the DA 21
Attachment 166090

Last edited by mikemike; 01-31-2014 at 12:34 AM.
04-01-2013, 03:42 PM   #6
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QuoteOriginally posted by MSM Quote
Lol. @wombat you really hurt my head with that post. I am glad some here understand that stuff.
I think I remember atan from - was it Trigonometry? - in High School, but that was 40 years ago.

And there was an atan (or was it ArcTan) Function in Borland's QuattroPro.

Until today I never knew a use for either.

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