Thanks, CH. That's really interesting. This is a single Leica lens, no
adapter involved, and the field curvature alone at 10% of the distance
from the center is already 25 microns... or 2-1/2 times the 10 microns
that Roger at LensRentals was worried about (I think at the edge of the
field). I'm not sure what he's measuring but I suspect it doesn't have
anything to do with real photography. As I said at first I think these
sorts of tolerances are easily smoothed over by the depth of focus...
even at large apertures.
Chuck Norcutt
On 10/18/2013 8:29 PM, C.H.Ling wrote:
> I won't worry about the cheap adapter either, I did lots of lens testes on
> over 30 OM Zuikos, never seen any problem from the adapter. If one has to
> worry, worry about the lens itself. Check an example below for three lenses:
>
> www.accura.com.hk/temp/Leica_M35_50_75.jpg
>
> The field curvature is over 200 microns towards the edges.
>
> C.H.Ling
>
> ----- Original Message -----
> From: "Chuck Norcutt" <chucknorcutt@xxxxxxxxxxxxxxxx>
>
>
>> 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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