tomreese
07-26-2006, 11:44 AM
I posted a picture in the July 26th picture of the day thread that I took with a reverse mounted lens system. In case someone is interested, I thought I might explain how it works.
It's done using two different lenses screwed together front element to front element with a coupling ring. An example of a coupling ring can be found here:
http://www.adorama.com/MCMCR5858.html?searchinfo=macro%20coupling%20ring&item_no=2
What actually happens is that the reversed lens (the one on the front) acts as a high quality extreme magnification close-up lens.
The amount of magnification you get depends on the focal lengths of the lenses you use. You can calculate the magnification by dividing the focal length of the rear lens by the focal length of the front lens. A 200mm lens on the back divided by 50mm on the front gives 4X magnification.
The rear lens can be a zoom. The front lens could be a zoom but you'll probably get better results using a fast f 1.4 50mm prime. The 50mm prime can be an ancient screw or bayonet mount lens of whatever manufacture you find in a pawn shop or in the used bin at KEH. Remember you're using it backwards so the type of lens mount is completely irrelevant.
The aperture on the reversed lens should be set to wide open to avoid vignetting. You can close the aperture on the rear lens to get greater depth of field. The reversed lens' focusing helix should be set to infinity.
You will need a tripod for this. Depth of field is extremely shallow and focusing can be difficult.
If you're shooting full frame digital or film then you may experience some vignetting. That can be corrected by placing an extension tube between the rear lens and camera body.
Please let me know if you have any questions or if I didn't explain something clearly enough.
Tom
It's done using two different lenses screwed together front element to front element with a coupling ring. An example of a coupling ring can be found here:
http://www.adorama.com/MCMCR5858.html?searchinfo=macro%20coupling%20ring&item_no=2
What actually happens is that the reversed lens (the one on the front) acts as a high quality extreme magnification close-up lens.
The amount of magnification you get depends on the focal lengths of the lenses you use. You can calculate the magnification by dividing the focal length of the rear lens by the focal length of the front lens. A 200mm lens on the back divided by 50mm on the front gives 4X magnification.
The rear lens can be a zoom. The front lens could be a zoom but you'll probably get better results using a fast f 1.4 50mm prime. The 50mm prime can be an ancient screw or bayonet mount lens of whatever manufacture you find in a pawn shop or in the used bin at KEH. Remember you're using it backwards so the type of lens mount is completely irrelevant.
The aperture on the reversed lens should be set to wide open to avoid vignetting. You can close the aperture on the rear lens to get greater depth of field. The reversed lens' focusing helix should be set to infinity.
You will need a tripod for this. Depth of field is extremely shallow and focusing can be difficult.
If you're shooting full frame digital or film then you may experience some vignetting. That can be corrected by placing an extension tube between the rear lens and camera body.
Please let me know if you have any questions or if I didn't explain something clearly enough.
Tom