Macro Reversing Ring ... anyone tried this?

[Robert Ardill]

Hi, I wonder if anyone has tried reversing a wide-angle lens for macro photography?  Specifically, I'm interested in using a 52mm Fotodiox reversing ring with a Loxia 21mm lens on a Sony A7II or A7RII: Fotodiox Reversing Ring for Sony e-Mount

I would expect that this would work at least in principle, but 21mm may be too short and might require an extension, perhaps one of these: Fotodiox extension tubes for Sony E-Mount

The extension tubes might be useful anyway, giving extra magnification to, for example, my 55mm Sonar.

I've never tried this before so I would very much welcome any and all advice!

Robert

[Zorki5]

Lots of people do "serious" macro using reversing ring and a WA lens (most often, some 35mm MF), and yet no manufacturer offers an equivalent lens. I wonder why? I do understand it would be a niche product, but heck, Canon MP-E 65 does exist. It's always been a mystery to me...

Answering question in the OP: no, I haven't tried it. I use 100mm macro or, when that's not enough, a metallurgical microscope with 5x to 80x objectives. 

[HCS]

I try that sometimes, but usually with a reversed 50mm. With a 20 you may be looking at focusing inside the rear element (which is then the front element). I think that down to 24mm should be practical, if reversed, but very, very close focusing.

[Robert Ardill]

I try that sometimes, but usually with a reversed 50mm. With a 20 you may be looking at focusing inside the rear element (which is then the front element). I think that down to 24mm should be practical, if reversed, but very, very close focusing.

Thanks Hans ... I reckoned that anything below 28mm might be too much.  The only lens I have with manual aperture is the Loxia 21mm.

What about using an extension tube on the 50mm?  I have the 55m f18 so that might be an option.  However ... I have no idea of how to calculate the effective magnification (or even if it is possible to do so without knowing all of the internals of the lens).

I do have a 100m f28 Canon macro that works very well with a Fotodiox Pro adapter ... but it's a big beast and it would be very nice to have a more compact solution (and I could then sell my 100mm lens .

Robert

[elf]

It looks like a simple reversing ring with no internal glass or electronics, so you should be able to use the reversing ring on different lens with step up and step down adaptors.  One way to tell if a lens will work better reversed is to compare the size of the aperture from the front of the lens and from the rear of the lens.  If it appears larger from the rear, then reversing the lens will be best.

Look up the magnification formulas by Lester Lefkowitz (wikipedia has them).  They will get you close to the actual magnification and shooting a few images of an object with known dimensions will get it exact.  While you're there check the effective aperture formulas for diffraction purposes.  It's quite easy to get into the diffraction limited zone when shooting macros.

[Robert Ardill]

Thanks!

Here's a very clear and useful article on the different options: http://www.cambridgeincolour.com/tutorials/macro-extension-tubes-closeup.htm, as well as some formulas.

I don't much like the idea of putting an expensive lens on a reversing ring, to be honest ... and also because it's more likely to accumulate dust which will then probably end up on my sensor.

Having said that, it looks like the pupilary magnification on the Loxia 21mm is about 2, so reversing it should give a good magnification (assuming it works at all).  But the formulae are too complicated for me to figure out, seemingly requiring a calculation of where the pupil is (not so hard based on ratio of pupil entrance to exit diameter and focal length) ... etc (it's the etc that has me stumped at this stage because I can't find a good formula with a clear explanation).

An extension tube on my 55mm lens (with image cropping) may be a better option for my kind of macro photography (wild flowers).  I calculate that the lens has a magnification factor of 0.07 (based on the 36mm sensor seeing 240mm at closest focusing distance).  According to CIC, adding a 26mm extension will give an added magnification of 26/55 = 0.47, so the effective magnification will be 0.47+.07, or around 0.5.  A 50% crop on a 42MPx sensor is just about OK, giving about 10MPx, for a total magnification of about 1.  Assuming, that is, that I have more or less understood the maths and got the calculations right.

There will be a hit on the aperture though.  My understanding is that I can estimate the hit as follows:
attenuation = [(extension + focal length)/focal length] squared
exposure hit = log(attenuation)/log(2)

So attenuation = [26+55)/55]**2  = 2.17
exposure hit = log(2.17)/log(2) = 1.1

Which means that the maximum exposure will go from 1.8 to 2.8 or thereabouts.

On the plus side the lens + extension will only be about 80mm in length compared to my Canon 100mm lens + adaptor which is about 150mm ... and the lens and extension can be carried separately.

On the minus side ... severe cropping, nuisance of fitting the extension, possible loss of image quality, loss of an excellent 100m lens with infinity focus.  A lot of minuses!!

Robert