EOS to RF adapters - Is clear glass a benefit?

Cableaddict
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p.1 #1 · p.1 #1 · EOS to RF adapters - Is clear glass a benefit?

I just bought a used Canon R, and then did a lot of research on adapters,
I finally decided on the Meike drop-in filter adapter, as I don't currently have a good selection of ND's for my lens collection.
(And the price is great, considering the favorable reviews.)

So here's what's bugging me:
All of the drop-in adapters (Meike, Canon, Kolari) either come with, or offer as extra, a clear glass filter. (UV, I assume.)
There's also a "blank" filter available on Ebay, which gives you the option of using NO filter but still having a dust seal.

The more simple adapaters, including the control-ring types, evidently have no glass at all. (Or did I misunderstand this?
So that "dummy" filter seems like it might be a good idea.

EXCEPT:

I've read in several different reviews that one should always use the clear filter, because without it there can be some problem with AF response. HUH?

Is this true?

Jul 01, 2022 at 07:03 PM

TeamSpeed
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p.1 #2 · p.1 #2 · EOS to RF adapters - Is clear glass a benefit?

If you compare the length of the filter adapter, at least for canon, it isn’t quite the same as the other two adapters. This means the glass used in the filters, whether UV or ND or whatever, is designed as part of the optical recipe to put the image into the sensor. Without any glass, you might likely be changing the back focus distance of the image.

Much like adding a 12mm extension tube in the middle of lenses and TCs could affect infinity focus, this could possibly have the same kind of effect, but since many lenses have a bit of extra infinity focus travel, it may be rare to see the impact of having no glass at all.

Jul 01, 2022 at 07:19 PM

Cableaddict
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p.1 #3 · p.1 #3 · EOS to RF adapters - Is clear glass a benefit?

Ah, that makes sense. Thanks.

- And so that "dummy" cover would be a terrible idea.

I actually like the idea of clear glass there, anyway, as it should keep dust off the sensor when changing lenses.

Jul 01, 2022 at 08:27 PM

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p.1 #4 · p.1 #4 · EOS to RF adapters - Is clear glass a benefit?

I just found a comparison article that explains this in more detail:

from: https://camnostic.com/2021/11/best-drop-in-filter-adapter-for-canon-rf-mount/

quote:

"A word on that empty filter holder… Adjustable filters like variable neutral density (VND) filters and circular polarizer (CP) filters have some relatively thick layers of glass. ( ~ 2mm. )

Canon and Kolari compensate for the effect of this glass by lengthening the adapter itself by 1mm.

Meike takes a different strategy, leaving the length of the adapter just like that of the non-drop-in adapters. This means that, in theory, the Meike adapter is a bit of a compromise whether you are using the empty or full filter holder, as the optimal adapter length will be off by 1mm one way or the other.

With the Canon and Kolari versions, an empty filter holder will be off by a more noticeable 2mm, and a full filter will be just about perfect. This is why they recommend using the clear glass filter (the element of which is precisely the thickness allowing for zero focus shift)."

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Hmmm. It's making me question my choice of the Meike. Then again, maybe using the Meike with that $30 dummy cover is the best of all, so the image circle is exactly right when not using an ND, as opposed to both Canon and Kolari which are 1mm off.

Jul 01, 2022 at 08:54 PM


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