Reducing flange distance?

Started 3 months ago | Discussions thread
MOD Tom Caldwell Forum Pro • Posts: 42,292
Re: Reducing flange distance?

mapachebasura wrote:

Yeah, I realize I was pretty bleary eyed posting this and completely failed to say that I have a 7D right now (though I am toying with the idea of getting a cheapy mirrorless just for this sort of thing).

The slr body type became popular because of it “slr” capability of putting the view through the lens into the ovf.  In that manner they became much more popular until the RF cameras were reduced to a rump business.  In reality only Leica survived and the slr/dslr took over hearts and minds.  To the point where it seems that the faux-dslr shape is the only one that commands a serious size market.  Even though with evf it can be placed anywhere on the camera body and the known RF-style (also and better called “Flat Top”) seems a natural for digital cameras and makes them more compact it seems to struggle in the “fashion based”(?) marketplace.  The only practical benefits that can be offered are that it can allow a much larger evf to be fitted into the abandoned mirror hump of the dslr and the possibility that left-eyed shooters can keep their noses off the lcd screen.

I am left eyed, have a normal nose and don’t need a huge evf - just one that allows me to compose properly and check focus.  A small, but effective evf on the top lhs of the camera body works fine and I appreciate the compact shape of the “Flat Top”. Somehow my nose does not bother the lcd - but I have intelligently modified how I peer through the evf and it apparently works. Left-eyed Leica RF camera body users must never have complained.

But back to reducing flange difference.

Any lenses that were made for a slr/dslr body must have  a longer flange focal distance for them to clear the mirror mechanism.  Therefore those lenses made a slr-pancakes are no longer pancake once an adapter extension is added.  But lenses made for RF camera bodies have shorter flange focal lengths but cannot usefully be used on a dslr.  However on digital camera bodies with evf they work very well indeed. No issues with lenses and the quality is generally better than native C-mount lenses.  Of course you can pay more money and get better C-Mount lenses.  But even cheap Russian made LTM lenses are better made than ordinary C-Mount lenses.

The other issue is that using an evf for manual focus lenses is eons more satisfactory than using using a dlsr for manual focus lenses.  The evf can magnify the image and there is also  there is focus peaking assist - which all fairly recently made ML (mirrorless) cameras will offer.  Despite all optical tricks and focus aids a dslr is harder to make MF even if it can be done - I would never go back - with my dslr body AF is definitely preferred - even if one might manually tweak focus from time to time.

The shortening of native flange focal distance seems only to have been done in exceptional cases by making an adapter with a correcting lens in it.  From what I have read this is not always satisfactory and those that make this type of adapter don’t seem to be rushed off their feet.  Why might anyone buy a more expensive adapter with an adjusting lens when one without it poses no problems - is only slightly longer and is cheaper?

Therefore the only adapters with lenses are those where it is absolutely necessary or for focal reduction which is a very useful purpose (and does reduce the length of an adapter as a simple by-product of the focal reduction process).

By all means buy C-Mount lenses for fun - realistically they work best on M4/3 bodies (or the Pentax Q) and even then some may vignette.  But there are veritable truck load of legacy MF lenses that are even more fun to use.

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Tom Caldwell

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