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View Full Version : Lens Focal length and sensor size


thackray
07/06/2005, 01:02 PM
Greg,

Potential digital camera and lens buyers should know that the focal length printed on the lens assumes a sensor size equivalent to 50mm film. Only a few very high end digital camera have sensors this large. Most better digital camera sensors are 0.4X to 0.6X the size of the 50mm film format. This means that the equivalent focal length is longer for the smaller sensor formats. For example, my digital camera with a 35mm lens “sees” the same picture as my film camera with a 50mm lens. In general, the digital cameras with smaller than 50mm film formats will require shorter focal length lens to achieve the same look as a 50mm film camera. The smaller the sensor format, the greater is this effect.

Phil

gregr
07/07/2005, 10:03 PM
hi Phil-
thanks very much for the info and heads up.
i didn't go into that for a couple reasons. the first reason is i really tried to keep things as simple as possible, knowing that most of the people reading that article to help with their shopping decision know very little about photography. i kept finding myself getting bogged down with explaining the explanation so they would understand what i was explaining... if you get my drift :p
the other reason is- the manufacturers [or reviewers] usually list a lens as having "the 35mm format equivalent" of x number of millimeters-x number of millimeters. so further explanation seemed unnecessary to me- however, i admit that i often miss things that are obvious to others... so this could well be one of those times.
Greg

thackray
07/08/2005, 11:05 AM
Greg,

The article was fine. I agree that a discussion of equivalent focal length was out of the scope of the article. I just thought I’d put some info in your thread in case anyone went looking for more.

In the Single Lens Reflex world the lens are still referred to by their actual focal length. It’s usually up to you figure out how a particular lens will “look” on your specific digital camera (format size).

By the way, I want to use some of my recent reef pictures for my avatar like you did. What is the best program to reduce a jpeg file down to size?

Thanks for the article and your help,

Phil

gregr
07/08/2005, 11:24 PM
hi Phil- i appreciate your comments.
Photoshop is certainly the best program- especially if you have one of the later versions with ImageReady included. if not, Irfanview (http://www.irfanview.com/) is free and does a very decent job compressing/resizing images.
Greg

thackray
07/09/2005, 11:27 AM
Greg,

Thanx!

Phil