Crop Question

eccs19 · Aug 8, 2008

So looking in the manual for my camera, it tells me that if I'm using any older SLR lenses, then to get the proper focal length, I have to multiply by 1.5. So as an example, a 100mm lense, would actually 150mm on my digital. Now I've heard a number of people make some comments about 100% crop factor. I'm not sure what is meant by that, but I'm assuming that it means that if you had a picture taken with that 100mm lense that was actually 150mm because of the 1.5 multiplier, then the 100% crop factor would crop it back to the equivilent of 100mm. Am I completely off here, if so, then what is actually meant by 100% crop factor?

NateWagner · Aug 8, 2008

I think that what you are thinking of are actually two separate things.

100% crop factor (I'm pretty sure) is based on the size of an image. When you take a photo with say an 8MP camera and look at it on your computer monitor it has been shrunk from the original size to fit your computer screen. What you are doing for the 100% crop factor is taking a small portion of the photo so that you are viewing it at 100% of the size of the photo rather than say the 33% that you normally look at it at on your computer monitor.

(this can be seen most readily with photoshop or gimp in which it shows the percentage that you are looking at the photo.

tirediron · Aug 8, 2008

"Crop factor" refers to cameras which use small than full-frame (35mm film equivalent) sensors. Right now there are two common DSLR sensor sizes, APS-C and 4/3. The most common by far is the APS-C found in Nikon, Canon, Pentax, and others. This uses a sensor which has about 1/3 less area than a full-frame, and gives you a 1/3 greater focal-length equivalent in your lenses. So, assuming that you're using a Nikon, Canon, or Pentax, you have a APS-C sensor (they vary slightly in size) and that you put a 50mm lens on, it has the equivalent focal length of a 75mm lens. If you have a 4/3 size sensor, eg an Olympus, then it is approximatly 1/2 the size of a full-frame, and your 50mm lens now has the equivalent focal length of a 100mm lens on a full-frame camera.

Edited to correct erroneous post.

NateWagner · Aug 9, 2008

ahh, maybe I was thinking of something else.

Tiberius47 · Aug 9, 2008

100% crop means that one pixel in the image is being shown on one pixel on your screen. In other words, showing the image at its "real" size. it doesn't have anything to do with the crop factor of using a sub frame sensor.

tirediron · Aug 9, 2008

Tiberius47 said:
100% crop means that one pixel in the image is being shown on one pixel on your screen. In other words, showing the image at its "real" size. it doesn't have anything to do with the crop factor of using a sub frame sensor.

My apologies to all; Nate and Tiberius are both correct with respect to the term "100% crop". I assumed from the OP that both aspects of the post were related to "Crop" as the term is used with respect to sensor size.

eccs19 · Aug 9, 2008

Thanks for all the input. I wasn't exactly sure if the 100% crop was related to the 1.5% multiplier. (sensor size) All your answers helped clear that up. I now know that the 2 are not related. Excellent help guys!