Whether we can see it or not there is a theoretical difference which is
due to increased diffraction from the edges of the tape. But at approx.
10% obstruction the area covered is small relative to a mirror lens
which often obstructs from 1/4 to 1/3 and even as much as 1/2 of the
clear aperture. But as Ken notes, just as in a mirror lens we might see
the effects in the bokeh or specular highlights.
If I remember (doubtful) one of these days I'll do a test like that but
using a small and narrow zig-zag pattern more representative of inking
over a gouge in the glass.
Chuck Norcutt
On 3/12/2012 2:54 PM, Chris Trask wrote:
>>
>> I've probably shown this here before but here goes again
>> <http://www.chucknorcutt.com/dust%20spec%20test/index.htm>
>>
>> There are two images here taken with my Minolta A1. The A1 has an f/2.8
>> lens and uses a 49mm filter. I don't have the camera with me but would
>> guess the clear aperture at about 45mm.
>>
>> One of the shots is with an unobstructed lens. The other has a 1/2"
>> square piece of electrical tape stuck in the middle of it and
>> obstructing about 10% of the surface area. Probably much less area than
>> the gouge you were talking about.
>>
>> The third image on the page is a paired 1:1 pixel view of the flower
>> details from both shots. Can you tell the difference? Maybe. Could
>> you tell the difference at 50% rather than 100%. I doubt it.
>>
>
> I cannot discern any difference at all. Had I had this demonstration in
> mind, I would have bought that lens. Now, it's $40 of gas away.<<SIGH>>
>
> Chris
>
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