Go Back   Steve's Digicams Forums > Digicam Help > Newbie Help

Reply
 
Thread Tools Search this Thread
Old Mar 1, 2010, 6:40 AM   #1
Senior Member
 
iowa_jim's Avatar
 
Join Date: Jan 2010
Location: North Central Iowa
Posts: 589
Default Crop Factor and the EF-S lens

OK, my T2i arriving later today (!!!!!?) has a crop factor of 1.6, so an EF lens like I just found with a focal length range of 100-300 becomes a 160-480mm lens.

If we start with an EF-S lens, designed for the camera with the crop factor, like the kit lens of 18-55mm, is the crop factor already accounted for, or is it really an 18-55 (x1.6) lens?

Thanks

Jim
iowa_jim is offline   Reply With Quote
Sponsored Links
Old Mar 1, 2010, 6:55 AM   #2
Super Moderator
 
Mark1616's Avatar
 
Join Date: Oct 2005
Posts: 7,397
Default

All lenses are marked in their focal length. This doesn't matter what it is designed for so a 100mm lens is a 100mm lens, what then varies by putting on a camera with a different size sensor is the field of view.

So your 100-300 is still a 100-300mm lens but the field of view will be equivalent/very similar to that of a 35mm camera with a 160-480mm lens.

It is often confused by many people as we have this 35mm equivalent that most refer to so that there is a standard for comparison.

Let's take another example. On my Canon SX1 camera that has a lens that goes from 5-100mm but the field of view due to a small sensor is about 28-560mm when compared to 35mm film.
Mark1616 is offline   Reply With Quote
Old Mar 1, 2010, 7:14 AM   #3
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,544
Default

The focal length of a lens is a physical property of that lens, and doesn't change with the size of the image sensor. What does change is the angle of view. When you put a lens of a certain focal length on an APS-C dSLR, it's angle of view will be narrower than if it's mounted on a 'Full Frame' dSLR or a 35mm film SLR. But the lens itself doesn't change.

The 'Crop Factor' is simply a way for peopl ethat have a lot of experience with 35mm film SLRs or 'Full Frame' dSLRs to equate the angle of view they get with the same lens on two different camera bodies. If you don't have significant experience with 35mm film, and you don't switch back and forth between an APS-C dSLR and a 'FF' dSLR, then the 'Crop Factor' doesn't meant anything to you.
__________________
  • The lens is the thing.
  • 'Full Frame' is the new 'Medium Format'.
  • "One good test is worth a thousand expert opinions." - Tex Johnston, Boeing 707 test pilot.
TCav is offline   Reply With Quote
Old Mar 2, 2010, 2:01 AM   #4
Super Moderator
 
peripatetic's Avatar
 
Join Date: Nov 2004
Posts: 3,599
Default

So in answer to your question.

The lens is always marked with the actual focal length. So you always need to apply the crop factor multiplier.

Your 18-55 would be the 35mm equivalent of a 28-88.
__________________
My gallery
My X100 blog
peripatetic is offline   Reply With Quote
Old Mar 2, 2010, 6:14 AM   #5
Senior Member
 
iowa_jim's Avatar
 
Join Date: Jan 2010
Location: North Central Iowa
Posts: 589
Default

I guess I was picturing the crop factor as a way to represent how an EF lens is designed for a bigger sensor would only show the center area to an APS-C sensor, giving in effect a cropped view of the entire available image and thereby increasing the apparent magnificantion, whereas the EF-S lens was already designed to give the sensor all the image thereby requiring no crop factor adjustment.
iowa_jim is offline   Reply With Quote
Old Mar 2, 2010, 6:24 AM   #6
Senior Member
 
iowa_jim's Avatar
 
Join Date: Jan 2010
Location: North Central Iowa
Posts: 589
Default

But as I re-read Mark and Tcav's post, it's not about cropping the image at the sensor per se, rather the impact on the equivelant field of view, which will be 'cropped' with a more narrow sensor.

I think all of you have finally put me in focus. Thanks!
iowa_jim is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 10:37 AM.