Go Back   Steve's Digicams Forums > Digicam Help > General Discussion

Reply
 
Thread Tools Search this Thread
Old Mar 11, 2012, 4:23 PM   #1
Senior Member
 
VTphotog's Avatar
 
Join Date: Mar 2005
Location: Extreme Northeastern Vermont, USA
Posts: 4,229
Default Full-frame cameras & crop lenses

Question for anyone who has the gear and has tried this out. If you have a full frame body, and use a crop lens, will the vignetting go away if you use a teleconverter equivalent to the crop factor? It should, according to optical theory, but I don't have the gear to try it out, and was curious, as sometimes theory and practice don't work out exactly.

Conversely, why haven't the manufacturers produced a wide converter for full frame lenses to reduce the image size to fit crop cameras? In theory this would eliminate the crop factor conversion, and, by concentrating the light, increase the lens' aperture. Wouldn't it be nice to turn that 50mm f/1.4 into an f/1 lens?

brian
VTphotog is offline   Reply With Quote
Sponsored Links
Old Mar 11, 2012, 4:57 PM   #2
Senior Member
 
Join Date: Jan 2011
Location: Australia, New South Wales central coast
Posts: 2,907
Default

G'day Brian

great ideas there - the idea of a lens becoming 'better' is intriguing

Regards, Phil
__________________
Has Fuji & Lumix superzoom cameras and loves their amazing capabilities
Spends 8-9 months each year travelling Australia
Recent images at http://www.flickr.com/photos/ozzie_traveller/sets/
Ozzie_Traveller is offline   Reply With Quote
Old Mar 11, 2012, 6:06 PM   #3
Senior Member
 
Bob Nichol's Avatar
 
Join Date: Apr 2003
Location: Eastern Ontario Canada
Posts: 822
Default

Quote:
Originally Posted by VTphotog View Post
Conversely, why haven't the manufacturers produced a wide converter for full frame lenses to reduce the image size to fit crop cameras? In theory this would eliminate the crop factor conversion, and, by concentrating the light, increase the lens' aperture. Wouldn't it be nice to turn that 50mm f/1.4 into an f/1 lens?

brian
There are several patents for this so I guess the holders wanted too much for the license!
Bob Nichol is offline   Reply With Quote
Old Mar 11, 2012, 6:17 PM   #4
Senior Member
 
Join Date: Feb 2007
Location: Wisconsin
Posts: 1,241
Default

Quote:
Originally Posted by VTphotog View Post
Question for anyone who has the gear and has tried this out. If you have a full frame body, and use a crop lens, will the vignetting go away if you use a teleconverter equivalent to the crop factor? It should, according to optical theory, but I don't have the gear to try it out, and was curious, as sometimes theory and practice don't work out exactly.
brian
It depends on if you keep the f-stop the same or if you allow the converter to add its light loss to the lens. If you open the aperture to keep the same f-stop after the converter, vignetting will generally be worse. If you allow the converter to loose the light, the vignetting will generally become less noticable.


Quote:
Originally Posted by VTphotog View Post
Conversely, why haven't the manufacturers produced a wide converter for full frame lenses to reduce the image size to fit crop cameras? In theory this would eliminate the crop factor conversion, and, by concentrating the light, increase the lens' aperture. Wouldn't it be nice to turn that 50mm f/1.4 into an f/1 lens?

brian
Barlow adapters are something that would have to be designed per lens, and zooms would be very difficult. That's why its not commonly seen as an adapter mounted between the camera and lens.
__________________
Greg

https://dogsportphoto.smugmug.com/

Last edited by fldspringer; Mar 11, 2012 at 6:21 PM.
fldspringer is offline   Reply With Quote
Old Mar 11, 2012, 6:44 PM   #5
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,571
Default

APS-C only lenses project a smaller image at the focal plane than 'Full Frame' lenses. Teleconverters don't change that.
__________________
  • 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 11, 2012, 7:06 PM   #6
Senior Member
 
VTphotog's Avatar
 
Join Date: Mar 2005
Location: Extreme Northeastern Vermont, USA
Posts: 4,229
Default

Quote:
Originally Posted by TCav View Post
APS-C only lenses project a smaller image at the focal plane than 'Full Frame' lenses. Teleconverters don't change that.
That is exactly what they do. Take a look at one. It is essentially a reducing lens. It spreads the light over a larger area. This is what causes (most of) the light loss.

brian
VTphotog is offline   Reply With Quote
Old Mar 11, 2012, 9:10 PM   #7
Senior Member
 
TCav's Avatar
 
Join Date: Sep 2005
Location: Washington, DC, Metro Area, Maryland
Posts: 13,571
Default

Quote:
Originally Posted by VTphotog View Post
That is exactly what they do. Take a look at one. It is essentially a reducing lens. It spreads the light over a larger area. This is what causes (most of) the light loss.
If anything, a teleconverter is a magnifying lens, not a reducing lens. The light loss is a result of the longer focal length and the narrower angle of view.
__________________
  • 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 12, 2012, 10:06 AM   #8
Senior Member
 
VTphotog's Avatar
 
Join Date: Mar 2005
Location: Extreme Northeastern Vermont, USA
Posts: 4,229
Default

A camera lens is made to project an image onto the film plane of the camera. One way to make a larger image on that film plane, is to move the lens further from the film plane, as with extension tubes. Much like moving the overhead projector further from the screen. In a camera, this loses you the ability to focus to infinity, though, so you place the teleconverter between the lens and the film plane. It makes the image at the film plane larger by diverging the light. A magnifying lens would make the projected image smaller, causing vignetting. (which is what I was saying in the second case, of full frame lenses on crop cameras)

brian
VTphotog is offline   Reply With Quote
Old Mar 12, 2012, 10:50 AM   #9
Senior Member
 
schmintan's Avatar
 
Join Date: Dec 2004
Posts: 424
Default

Quote:
Originally Posted by VTphotog View Post
A camera lens is made to project an image onto the film plane of the camera. One way to make a larger image on that film plane, is to move the lens further from the film plane, as with extension tubes.
brian
Your image becomes duller and more difficult to focus.
Crop lens's are designed for crop sensor cameras.

If i own a full frame camera, i have either more money than sense, or im serious about image quality. Finding a way to fit a crop sensor in front of that full sensor will most definately cause loss of quality.

The only reason id try to fit a crop lens on would be to save money, and you know the saying buy cheap, buy twice. You will end up realizing you are not getting the quality available, and just coughing up for the full frame lens's (thats not saying crop lens's are cheap, i know there are some awesome ones, but they are awesome on a crop camera, not a full frame).


If i have a full frame, i will buy lens's designed for that full frame, not some stopgap measure that lets me use more gear, but gives poorer images.
schmintan is offline   Reply With Quote
Old Mar 12, 2012, 5:30 PM   #10
Senior Member
 
VTphotog's Avatar
 
Join Date: Mar 2005
Location: Extreme Northeastern Vermont, USA
Posts: 4,229
Default

How nice for you.
The question was prompted by this post:http://forums.steves-digicams.com/ge...-question.html
I was curious as to whether anyone had any direct experience with t/c and digital lenses on full frame cameras, not what someone thinks of the combination. Seems my curiosity will go unsatisfied.

brian
VTphotog 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 1:18 AM.