Fotodiox x Novoflex x Voigtlander: M-mount adapter cagematch

Started Nov 19, 2013 | Discussions thread
Tom Caldwell Forum Pro • Posts: 33,669
I am lazy enough but here is my theory, words are easier

Letsgokoulos wrote:

Tom Caldwell wrote:

Metabones and a few other EF to NEX adapters come with built in tripod mounts as well. This is useful and it is not necessary to use it and small enough to not get in the way. The RJ glassless electonic adapter has an optional extra collar which allows portrait mode as well. It does not have detents or markings but I guees you can use in-camera levelling or make some discrete measured markings. Some other adapters can be bought with fixed tripod mounts, especially for the Pentax Q mount for obvious good reason. Fixed tripod mounts are best with bayonet mount lenses of course.

It is interesting in this debate that nothing has been said about Metabones or the Chinese focal reducer versions in respect of their infinity focus accuracy. Maybe I am too casual but I have not noticed any infinity focus problem (with any of them). This is doubly unusual as Canon make absolutely no bones whatsoever that their telephoto lenses at least all focus past infinity out of the factory - simply to allow for a possible heat factor. I admit to have not gone beyond the 200/2.0 so far but this rather large white lens surely is also focusing past infinity. Maybe it is because that with telephoto the actual use requires some specific focusing - even at longer distances. I have used this lens and noticed no problems with focus - both in AF (goes without saying) but also using MF - which is usually quicker wiith such a sharp lens.

Therefore the conndrum. The telephoto has smaller dof and seems less problematical and the wide lens with sometimes huge hyperfocal seems to be a big issue. If a wide cannot pick up infinity inside the hyperfocal distance then it is indeed a big problem

Or is it something that I am not understanding - can the extreme end of the hyperfocal be out of focus if the lens can focus past infinity? - beyond me. But if this is so then all those very expensive telephoto lenses that Canon builds deliberately to focus past infinity have a very real problem.

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Tom Caldwell

Tom, that is an interesting discovery... Could it be that the infinity setting is exacerbated by the crop factor ? I will try to check tomorrow with my Speed Booster.


Marc, If I was not so doggone lazy I would do it myself might shake my bones a bit and see what little experiments I can perform.

The theory is of course (as we all know) that if you set the rightmost stop in use mark on infinity then everything from the leftmost stop on the focus scale to infinity will be in focus.

This is where I get horribly confused. Surely even on the widest apertures there should be some dof at infinity? Therefore the lenses that are "absolutely correct" more like than not are actually focusing ever so slightly before infinity and rely on the hyperfocal to fix things up. So much for "precise engineering" (grin).

Obviously past infinity has to be out of focus. Full stop. But when the focus is adjusted back to get (effectively) the hyperfocal in play we must assume that the out of focus part simply drops off the scale. In other words a lens that focuses past infinity has a smaller hyperfocal available than it should have otherwise. But maybe not, as the near end of the hyperfocal must correspondingly move closer as well.

For those that wish to keep the hyperfocal limited at infinity do have more potential hyperfocal to play with but deliberately restrict this by setting their lens focal distance at the infinity stop.

And so the whole debate about "accuracy" is more debate about the nuisance value of not being able to just slap the lens against the infinity stop and be assured that the lens will pull in the infinity focus using hyperfocal at its widest possible aperture. Forget about squeezing the hyperfocal to the max as it is not deemed necessary.

What is the greatest sin of any adapter/lens combination is not focusing to infinity at all (unless it is extreme macro which can be excused). Therefore true precise engineering is the trick of focusing before infinity with enough room in the hyperfocal to bring in infinity focus at the widest aperture the lens is capable of. Obviously a more risky approach considering that who knows which lens will be attached and in whatever tune.

For a lens-tone-deaf happy go lucky with oddball lenses maybe the cheap adapters with more hyperfocal play-room are the best bet but for super-precise expensive lenses the convenience of hyperfocal fixed slightly before infinity focus expensive adapters is worth while.  Then of course you can use the infinity mark to get precise hyperfocal as well, but unfortunately this means not using the lens against the infinity stop.

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Tom Caldwell

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