BetterPhoto Q&A
Category: New Questions

Photography Question 

Zoom versus Lens Range

How do you compare an optical/digital zoom with the range e.g. a 70mm to 200mm lens?
Is there any formula to use to compare?

To love this question, log in above
12/21/2004 9:57:05 AM

William Moore
BetterPhoto Member Since: 3/17/2002

To love this comment, log in above
2/14/2006 1:38:36 PM

Ken    Edwin,
Digital zoom is not really a zoom. A digital zoom enlarges a portion of the image, thus 'simulating' optical zoom. Example: the camera crops a portion of the image and then enlarges it back to size- making it look bigger. In so doing, you lose image quality and it cannot be enhanced back to the original. If you've been using digital zoom and wondering why your pictures did not look that great, now you know.

Is digital zoom therefore all bad? No, not at all. If you don't know how to use image editing software then use it. But don't confuse it with optical zoom.

My recommendation is to always use optical zoom,and learn how to use photo editing software. When comparing cameras, you should always use optical zoom as the comparison- it will give you the real picture- haha.


To love this comment, log in above
2/14/2006 1:55:29 PM

Bob Fately   Hi, Edwin. Maybe I'm off base here, but my interpretation of your question is a bit different than the other guys. It seems to me you're asking how the focla length of a lens for a traditional 35MM camera would compare to the focal lngth of a lens on a digital camera. Is that right?

If so, then here's what you need to understand. The smaller the image-taking device, the shorter a focal length needed to get the same angle of view (or optical magnification, if you will).

For a 35MM film camera, a 50Mm lens is "normal" because it's angle of view is about the same as the human eye's. A lens longer than 50MM is a telephoto, so the 70-200 MM zoom lens you mention is a variable telephoto. Figure a 200MM lens ona 35MM film camera gives you about a 4x magnification (200/50).

FOr most of the DSLR cameras out today (Nikon, Canon etc.), the CCD chip is smaller than the 24x36MM size of a film frame. Due to this smaller size, a number called the 'crop factor' is used to allow for easy comparisons. The crop factor for the Nikkon DSLRs, for example, is 1.5 - so multiplying the focal length of 200MM by 1.5 tells us that a 200MM lens on a DSLR is about the same as a 300MM lens would be on a full frame 35MM film camera.

Now for the smaller point & shoot type cameras, there are no crop factors published because in general manufacturers don't even talk about how small those CCDs are. Usually you will see them refer to their zoom lenses as "28-80MM equivalent" or some such, just to avoid the calculations. In fact, the focal length of the lens might actually be 8-20MM, but on that tiny sensor it behave essentially like a 28-80 would on a 35MM film camera.

There is nothing inherently magical about a certain focal length; it's just that 35MM cameras became so popular that most folks can relate to what kinds of lenses do what in that field. So, as a convenience, manufacturers try to relate to the 35MM world.

Hope that helps

To love this comment, log in above
2/14/2006 3:56:26 PM

Log in to respond or ask your own question.