----- Original Message -----
From: "Carlos J. Santisteban"
>> From: "C.H.Ling" <ch_photo@xxxxxxxxxxxxx>
>>
>>Unfortunately, for this great Tessar I see not that nice bokeh - the
>>leaves
>>and branches.
>
> Being an aesthetic matter, bokeh may be highly subjective... however, it
> usually isn't an issue for me. Remember that Tessars are relatively slow
> designs, which gives less freedom for bokeh control.
>
> Neverthless, I find this picture (taken with the Tessar 45/2.8) nice, at
> least to my taste. YMMV: <
> http://cjss.sytes.net/web/www.supercable.es/~santis/etc/tessar.jpeg>
>
I don't think bokeh quality is subjective but it is relative, you can say
there is no lens with bad bokeh just the bokeh of one lens is better than
the other.
45/2.8 is not slow, the bokeh requirement already kick in even with full
lenght portrait at wider aperture. Here is a sample of 40/2 at F2.8 or 4:
http://www.accura.com.hk/temp/IMG_1186s.JPG
>
> I don't think it's CA... the Tessar wide-open shows a certain amount of
> primary, monochromatic aberrations (like spherical, coma, astigmatism) --
> the "fringe" looks blue because there's blue in the nearest regions!
It is not CA but it is purple fringe :-) I'm pretty sure this is lens
problem not because of blue in the nearest regions. I have seen thousands of
similar problems even on film.
http://www.accura.com.hk/temp/t1817_crop2.jpg
>
>>It has the largest aperture of all pancake (?).
>
> I'm afraid not... there was a K*nica Hexanon 40/1.8 -- reportedly one of
> the
> sharpest lenses ever made, even wide open.
Ah! I stand corrected.
>
> This is an interesting issue. CA is a rather complex matter... According
> to
> 'Optical Instrumentation - Theory and Design' by Begunov, Zakaznov,
> Kiryushin and Kuzichev (Mir Publishers, Moscow 1988), CA can be of three
> different types, usually mixed:
>
<BIG SNIP>
Thanks for the long explanation, it is too complicated for me :-) I just
need a lens that produce "clean" image like the DZ50-200, it has much less
purple fringe (may be CA too) than my current long Zuikos and the famous
Tamron 180/2.5.
The purple fringe can be seen on many lenses I have tested, all of them
improved at stop down. Here is part of the tests I made last year with a
40D:
http://www.accura.com.hk/temp/PF/PF.html
>
> Here is an interesting site that provide ISO12233 chart test results that
> I
>> can visual the results myself instead of just looking at the interpreted
>> data:
>>
>> http://www.the-digital-picture.com/Reviews/Canon-Lens-Reviews.aspx
>>
>
> Very interesting link! Thanks a lot!
>
In the test site above there are lots of examples showing the CA/Purple
fringe corrected at stop down.
C.H.Ling
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