For a 24mm lens at f/1.4 (if there is such an animal) the depth of focus
for an object at 2 meters is 0.0933mm. Much smaller than the situation
at f/11 but still 9 times larger than the 10 microns named as a critical
value for lens adapter planarity in the article. I don't doubt Roger at
LensRentals but I certainly don't understand what he's measuring. But
since I've never seen the problem I guess I won't lose any sleep over it
tonight. :-)
Chuck Norcutt
On 10/18/2013 6:01 PM, usher99@xxxxxxx wrote:
> Dr. Focus writes:
>>> As I was re-reading this it occurred to me to express the tolerances
>>> here in another way. The depth of focus (the image side of depth of
>>> field) is about 3/4mm or 75 times the stated required precision of 10
>>> microns.
>
> Roger at Lensrentals did careful measurements on an optical bench at
> F1.4 and I don't doubt the results.
>
> Recent comment on Ming Thein’s site that mentions: “Don’t think you can
> get away with adaptors: the planarity of such adaptors is going to be
> absolutely critical, especially with such short flange distances and
> resolution numbers. You’ll actually be able to see the effects of a
> cheap, out-of-plane adaptor – it looks a little like a tilt. (I know
> this because I tried Hasselblad lenses on my D800E; none of the three
> adaptors I obtained had sufficiently tight tolerances to avoid this
> problem.)”
>
> He used expensive but 3rd party adapters--OEM might be better. The
> adapters seem to induce a tilt and the physical large size of these for
> these short registration distance cams
> magnify the problem. Roger stated he is doing more experiments (in an
> FM thread) with more adapters rotating every 30 deg or so to figure out
> the issues.
> That be said, as per Dr. Focus, stopped down a bit, shouldn't matter a
> whole lot.
> I hope some adapters will be more precisely engineered though.
> Metabones already has a ver 111 adapter for Canyon EF to FF Sony with
> probable AF and IS working.
>
> Adaptable Mike
>
>
>
>
>
--
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