Reversing lens - do the usual lens criteria still apply?

I would like to reverse a 20mm or 24mm lens and use a focusing rail to move the entire rig to take images at various focusing distances and stack the images.

 

My question: Do the usual criteria for lens image quality (sharpness, distortions, vignetting, etc...) still apply when mounting a lens in reverse and using the lens as described above?

You'd reverse a lens when doing macro work and the lens to subject distance is similar to the focal length, and the lens to film/sensor distance is larger. Vignetting should never be a problem because the cone of light now covers way more than the film/sensor. Everything else is lens specific, but if it's a high quality lens when used normally, I'd expect high quality results reversed. When the magnification ratio is greater than 1:1, that's the time to think reversal. Something else that works well in that situation is a good reversed enlarging lens, if you can come up with an adapter.

Thanks Conrad - I vaguely remember trying that with a Nikon El-Nikkor 50mm/2.8N when I still had an enlarger. I'll look into it again.

 

Thanks,

Keith

Assuming you're talking about a standard 35mm or even DX lens, I'd be hesitant to use a 20 or 24mm for any kind of macro work.

 

At high magnifications, a flat field lens is even more important. "Real" macro primes and enlarger lenses fit the bill perfectly. Retrofocus wide angles are full of enough optical compromises already that they won't necessarily respond well to being used on bellows at all, much less at high magnification.

According to the old Nikon / Nikkormat Manual any of the old Nikon film glass from 24/2.8 up to 851.8 can be used with the BR-2. The former delivers 2.5x, the latter 1/200X. I have specifics with the manual in hand.

Thanks Ben and Sandy. I have a 'real' macro lens but wanted to play around with reversed lens set ups.

Stupid OCD stuff but don't forget that the rear lens elements aren't shielded from light at all, so you may have to rig up a lens hood or strategically place some black paper shields. Also, damage to rear elements is considered worse optically than damage to the front. Not that I want damage anywhere, but I take special care with a reversed lens used close up.

Stupid OCD stuff but don't forget that the rear lens elements aren't shielded from light at all, so you may have to rig up a lens hood or strategically place some black paper shields. Also, damage to rear elements is considered worse optically than damage to the front. Not that I want damage anywhere, but I take special care with a reversed lens used close up.

 

Canon made a "macro lens hood" for nFD lenses that was just a rear lens cap that was drilled out.

 

With Canon FD mount lenses(whether breech lock or "new" mount-the "new" mount just turns the entire barrel into the breech lock ring) you need to "trick" the lens into thinking it's mounted on a camera in order for the aperture to be controlled. The drilled-out rear cap accomplishes this.

 

Still, though, it's handy in that application, and a similar thing can be done with any system and a spare rear cap.

 

Also, for a conventional unit-focusing lens, setting it to its closest focus distance should draw the rear element into the lens barrel and help that provide some shielding.

Stupid OCD stuff but don't forget that the rear lens elements aren't shielded from light at all, so you may have to rig up a lens hood or strategically place some black paper shields. Also, damage to rear elements is considered worse optically than damage to the front. Not that I want damage anywhere, but I take special care with a reversed lens used close up.

 

Thanks. I do have a Nikon BR3 that attaches to the lens mount on one end and is threaded on the other end for filters or a lens cap.

You can of course use an extension tube as a lens hood.

Your aperture value won't be "correct" when you reverse a retrofocus lens like a wideangle. It'll be smaller, effectively, than the lens says. That only matters if you're trying to calculate depth of field ot diffraction limits - but you're in "try it and see" territory, anyway.

Some standard zooms can be surprisingly good, reversed, even humble ones.

If you're using a lens on tubes, you may well find you have to add "flocking" to reduce internal reflections inside the tubes or from any adapter. They can be troublesome, giving reduced contrast. Black art paper is OK, but something like Protostar is better. Cheap tubes are the worst for that.

You usually get better peformance especially at the edges, if you put a short prime reversed on the front of a long prime, with both focused at infinity, but predictions can go wrong with specific lenses.

 

For single reversed lenses, such as 20 - 50mms, best aperture is usually about f/6 for a f/2.8 lens. smaller will give more DOF but everything will go soft from diffraction. You get much sharper images if you focus-stack at the best aperture. Just about impossible for live subjects of course.

If it's your first go at high magnifications - use flash to avoid motion blur, and diffuse like crazy - eg a sheet of paper wrapped around the subject and lit as evenly as possible, works.

You can of course use an extension tube as a lens hood.

Your aperture value won't be "correct" when you reverse a retrofocus lens like a wideangle. It'll be smaller, effectively, than the lens says. That only matters if you're trying to calculate depth of field ot diffraction limits - but you're in "try it and see" territory, anyway.

(snip)

 

Well, you have to adust the aperture value for close focus without reversing, too, especially with extension tubes or bellows.

 

But with TTL metering, you don't need to know that.