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View Full Version : What is the field-of-view of my 10mm-20mm?



Simon Shasha
08-16-2012, 03:32 AM
I have a Sigma 10mm-20mm F3.5. It's designed for APS-C sensors and won't work on a full-frame sensor - given that it's an APS-C lens, does that mean it has a field-of-view of 16mm - 32mm on the BMC (because the crop of the BMC is x1.6 more than APS-C), or would it have a field-of-view of 23mm - 46mm (that's comparing the BMC sensors to full-frame, which results in a x2.3 crop-factor)?

Hope I made sense! Haha :)

J Davis
08-16-2012, 04:27 AM
I'm going make some assumptions that your sigma is canon mount and therefore you are used to a canon aps-c sensor.
Because the BMC is smaller your fov will be smaller than you are used to

fov of 10mm on bmc ~= fov of 14mm on your aps-c canon
and fov of 20mm on bmc ~= fov of 28mm on your aps-c canon

zwarte_kat
08-16-2012, 08:25 AM
23mm - 46mm compared with full frame Canon. APS-C lenses use the same focal length naming as full frame.
For your APS-C Camera it's 16-32 compared with full frame

10mm is always 10mm in a lens, it is only the sensor/negative size that changes.
So for the BMC you calculate APS-C lenses the same way as full frame lenses.

J Davis
08-16-2012, 11:09 AM
zwarte, he's talking about field of view

zwarte_kat
08-18-2012, 08:31 AM
Me too, but perhaps not clear enough. I was just trying to explain that it doesn't matter for the calculation when a lens is only for APS-C.

10mm = 10mm: FOR THE LENS
So a 35mm APC-Only lens will have the same FOV on the BMC as a 35mm Full Frame lens. This field of view will be 80.5mm COMPARED WITH FULL FRAME
Really, there is no such a thing as 10mm FOV, it depends on what format you are used to.
My 75mm lens is only 50mm FOV compared with full frame, on my medium format camera that has a film bigger than full frame.

A lot of people seem to get confused with cropfactors. I think that in both photography and video, there would be less confusion if FOV was described in degrees, because it is an absolute value.

J Davis
08-18-2012, 10:14 AM
sorry zwarte but you're spouting nonsense. The values I gave in post 2 are correct. Read what I wrote there carefully. What you say does not negate or dispute the information I gave. OP you might have to form your own opinion or run tests if you don't believe me. I'm done here, yawn ... forums ...

zwarte_kat
08-18-2012, 11:24 AM
I never said you were wrong, and no harm intended either, just trying to give some information. Sorry if it felt like I was correcting you.
Since you are done here, have a nice day.

rheex
08-18-2012, 12:31 PM
I don't think anybody spouts nonsense around here. One could be wrong or have a different opinion, but always respectfully. We're here to help each other, so please let's do that.

Barry Green
08-18-2012, 08:54 PM
You can't just put a "field of view" marking on a lens either, because the field of view is relevant to the size of sensor that you're attaching it to.

Because the sensor is smaller, it will see a smaller field of view as compared to what a bigger sensor might see.

"field of view" is not fixed per lens focal length. It's determined by a combination of the lens focal length and the size of the sensor.

The lens will project the same field of view regardless of what sensor it's attached to, but a smaller sensor will see less of the lens's available field of view (thus cropping out the rest, hence the crop factor).

Doug Kropla
08-21-2012, 06:48 PM
Once again, as my second post, Barry G. pretty much sums it up. This is fun, I will just quote Barry from now on. Can't go wrong there. Unless his people get upset and threaten to sue:(


You can't just put a "field of view" marking on a lens either, because the field of view is relevant to the size of sensor that you're attaching it to.

Because the sensor is smaller, it will see a smaller field of view as compared to what a bigger sensor might see.

"field of view" is not fixed per lens focal length. It's determined by a combination of the lens focal length and the size of the sensor.

The lens will project the same field of view regardless of what sensor it's attached to, but a smaller sensor will see less of the lens's available field of view (thus cropping out the rest, hence the crop factor).

J Davis
08-21-2012, 10:24 PM
please note that my 2nd post did not put field of view on a lens. It put field of view on a lens in relation to a sensor