Saturday, March 7, 2020

In-field Manual Lens Calibration

I have several manual lenses that I’ve acquired for my EOS cameras, for example: a rather unusual Venus Optics wide-angle lens, the Laowa 15mm f/4 Macro Lens; and a Rokinon 14mm f/2.8.

Like others, I try and get the maximum value out of these lenses by using then with adapters on mirrorless cameras, eg the Canon EOSM.

Recently I made the decision to down size my travel gear and introduce a Micro Four Thirds (MFT) format camera: choosing to buy a second hand Olympus OM-D M5 Mk 2.

I was drawn to the OMDM5II because it was small and light weight, and it had so many features, eg non-macro focus stacking.

My first adapter was a relatively cheap K&F Concept adapter. However, either this was a badly made one, or the manufacturer had the relative flange distances wrong; as infinity focus was way out. For example, the 14mm Rokinon’s infinity focus was at about 0.3m on the lens.

Some lenses can be manually calibrated by partially disassembling them, but not all. Plus, I had an idea that I wished to try out, namely, realizing an infield calibration approach, whereby I would decide the infinity I needed for that shoot.

For example, the first useful 'infinity' would be at the ‘classical’ hyperfocal (H), eg giving an infinity blur of 30/crop microns. The second infinity would be where the infinity blur was around two sensor pixels, eg around H/2-H/3, according to your camera. With the third infinity at the 'visible' infinity. As you move from H to the visible infinity, your blur at infinity will, of course, reduce, but so will your near depth of field, moving from H/2 to H.

So I purchased a Fotodiox DLX Stretch Lens Mount Adapter, obviously for the Canon EOS  EF/EF-S Lens to Micro Four Thirds (MFT) version, which comes with a Macro Focusing Helicoid and Magnetic Drop-In Filters, ie rear NDs. 

It was a bit of a gamble, as I didn’t know how the adapter, which is designed to work as a macro bellows, would handle the infinity correction.

Having now tried it on both manual lenses, I am pleased to report that the Stretch Adapter works fantastically well.

Once fitted to the OMD M5II, all I do is: decide where I wish to calibrate, eg H, 3H or ‘visible infinity’;
set my aperture to the widest it will go; set my lens focus ring to the infinity mark or even the infinity hard stop; and adjust the adapter until things look tack sharp on the zoomed in LV.

For landscape photography this is great. But what about portrait photography? Once again, the adapter shows its utility. In this case I set the lens to sensible distance which is also registered on the lens, eg 1m, say, and go through the same process as above.

Bottom line: if you have EOS lenses and a mirrorless camera, but, sadly, not an EOSM, then you may be interested in acquiring the Fotodiox DLX Stretch Lens Mount Adapter, which will give you in-field, micro calibration of your manual lenses.

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