Body reversed 50mm macro lens magnification

[LordV]

A question that came up on another forum had me wondering what magnification do you get if you reverse a 50mm 1:1 macro lens onto the camera body and use it at minimum focus ?

No idea if there is a calculation for working out rough mags of body reversed lenses but I know from other forums you get around 1:1 magnification with a normal 50mm lens body reversed but would you get 2:1 with a macro 50mm lens ?

Brian v.

[rjlittlefield]

Don't know about a 50 mm.

For amusement, I tried reversing a Sigma 105 mm. With the ring twisted to what would be 1:1 in normal orientation, the lens needed a little bit of extension simply to focus at infinity -- magnification zero. Twisting it to any lesser magnification setting required still more extension to focus at infinity.

It all depends on where the front principal plane is located.

With those old fixed-focal-length lenses like we used to use on 35 mm SLRs, the front plane was located way behind the front of the lens, actually back close to the mounting flange. Reverse the lens and add the thickness of the reversing ring, suddenly that plane is a couple of FL away from the sensor plane, and there's your 1:1.

With the 105 that I just tested, the front plane is only a couple of cm in back of the front of the lens. Reverse that lens and the plane is not even one FL away from the sensor, which is why more extension has to be added just to focus on infinity. Twisting the magnification ring on the lens probably moves its front plane a little bit, but more importantly it also shortens the FL, which is why less additional extension is needed when the lens is set to high magnification.

I have very little idea where the principal planes might be located on a 50 mm macro lens, so I'll be interested to hear if somebody else runs any experiments.

--Rik

[LordV]

Did wonder where the focus point might be at min focus presumably there is a chance it might work reversed onto extension tubes ?
The original question I was asked was the likely magnification of a reversed 50mm macro lens on to 68mm of extension tubes - I reckoned on between 2.5:1 to 3.5:1 depending on whether focus could actually be achieved with the lens at min focus.

Brian v.

[mgoodm3]

The mag that you get varies with the lens. how far back are the elements from the front, how long is the lens?

55/2.8 micro - 0.9:1
50/1.4 - 0.97:1
El-nikkor 50/2.8 - 0.54:1

55/2.8 with 50 mm extension - 1.8:1

[rjlittlefield]

55/2.8 with 50 mm extension - 1.8:1

Is this front-forward with an extension, or reversed with an extension?

I am presuming the others are reversed, with no additional extension.

--Rik

[mgoodm3]

All that I listed are reversed. No extension unless specified.

[rjlittlefield]

What is the maximum magnification of the 55/2.8 in its normal orientation with 50 mm of extension? (Somewhat over 2:1, I would expect, assuming that the lens goes to 1:1 just by turning the focus ring.)

--Rik

[mgoodm3]

Normally mounted, the 55/2.8 gives you 1.43:1 with 50 mm of extension.

It only focuses to 1:2. It's one of the older MF ones.