I'm putting together a (non-commercial) photobook from a year in a foreign country. I took all the photos with the Canon EOS-M3 which has an APS-C sensor (crop factor 1.6). I want to quote the aperture, ISO, shutter speed, and focal length for each of the 'feature' images.

Do you think it makes more sense to quote the focal lengths as 35mm equivalents or as the focal lengths I read directly from the camera, with a note saying that I took all the photos on a camera with a cropped sensor?

  • 2
    \$\begingroup\$ Up to you, but I would suggest you use the actual focal length, it will benefit you when you try to reproduce your favorite focal lengths in future pictures as most zoom lenses do not have "effective focal length" markings. \$\endgroup\$ Jul 3, 2017 at 10:49
  • \$\begingroup\$ Probably depends on the purpose of the notes. \$\endgroup\$
    – user29608
    Jul 3, 2017 at 11:44
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    \$\begingroup\$ Who is the photobook for? You? Put whatever you want. \$\endgroup\$
    – osullic
    Jul 3, 2017 at 12:18
  • \$\begingroup\$ Yep - I'll be the one to look back on it in years to come. Just imagined I might be frustrated by making the 'wrong' decision if I start taking more photos with other kit later. \$\endgroup\$
    – OnyGo
    Jul 3, 2017 at 12:50
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    \$\begingroup\$ @ChrisNovak while it's short, your comment is definitely an answer to the question. Please see: Short answers as comments — please resist the urge \$\endgroup\$
    – scottbb
    Jul 3, 2017 at 15:35

3 Answers 3


The "equivalent" focal length draws from history, namely how it relates to a 35mm film camera, and there should come a time (and I think it is past) when we move on.

The focal length IS the focal length. Having a smaller sensor may crop a portion of the field of view, but the focal length is a real and meaningful number. Anyone who is interested in the technical aspect of the photo will also want to know the camera (and thus sensor size), and will know how these relate. Anyone who does not understand that really will not gain anything from focal length regardless whether equivalent or real.

Frankly I wish manufacturers would get away from trying to "spin" their products by such machinations as "35mm equivalents". Stating the crop factor is frankly all one needs to know in that regard, and you need to know that anyway.


I don’t think the average viewer gleans much knowing the focal length setting. This is because the effect of focal length is intertwined with the size of the image sensor (or film). Over the years, camera formats have and will continue to shrink. It seems to me, stating the focal length in terms of the 35mm equivalent has value. On the other hand, perhaps just the description “Taken using a telephoto lens” or “wide-angle” or “normal”, will be grasped by more people.

Let me add that in my way of thinking, telephoto is 2X normal focal length or greater. Wide-angle is 70% of normal or shorter. The format dimensions of a 1.6 crop factor sensor are approximately 15mm height by 22.5mm length. The diagonal measure of this rectangle is 27mm. Mount a lens with a focal length that is approximately the same as the diagonal measure yields a “normal” angle of view. Thus the realm of wide-angle is 20mm or shorter. A 30mm lens delivers a “normal” angle of view. Telephoto territory is 60mm or longer. Hope this information will help.


Equivalent focal length numbers only have significance for those familiar with using 35 mm film. Which is lots of people, and it can mean a lot to them, but it won't mean much to newbies who never used a 35 mm camera.

Actual focal length comparisons are affected by sensor size, but also, simply cropping the image later also makes a similar huge impact on the final image that we see. Cropping to half width compares to using a focal length 2x longer... same image view is seen.

And of course, focal length selected to use depends on the distance to the subject.

So to be specific about the view (if desired), requires camera model (for sensor size), actual focal length used, distance to subject, and degree of later cropping. It could be of interest to youself later on, but suggesting that this is not really necessary. :)


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