Re: PHOTO-3D digest 1296

[P3D Eric Goldstein <egoldste@xxxxxxxxxx>]

P3D Bob Howard wrote:
> So it still
> depends on the actual curves and glass..all tessars and triplets might
> not be equal if quality control not exercised.

No question. My "tessars yield higher resolution than triplets" comment is without a 
doubt dependent on "all things being equal." Tolerances, glass, coatings, all make a 
profound difference on the speed and performance of any lens. If it didn't, no one 
would value a Belplasca over an Ektar, or an Ektar over a David White 2.8. They all 
have tessar type lenses, and they all perform differently. By the same token, I also 
don't doubt that there are triplets which could perform comparably to poorly executed 
tessars.

>  The Cooke Triplet
> of Dennis Taylor of 1898 was a marvel that obsoleted the Rapid
> Rectilinear and is no way in inferior lens. Granted it doesn't cover as
> well until stopped down as a Tessar does at the wider openings. But this
> is more due to glass and improvements later.

I'm with you here, too. Where I get a bit fuzzy is with the comparison of coverage of 
both types of lenses "stopped down." My recollection is that at f/11 or at f/4, all 
things being equal, the 4-in-3 design with provide inherently higher resolution than 
the triplet in the corners, but the two will be comparable in the center. In other 
words, Zeiss didn't substitute the tessar for the triotar because of the increased 
speed (was it f/3.8 versus f/3.5, not even half a stop?), but because of the increased 
corner resolution, contrast, and apparent "sharpness" at all apertures, given the 
glass, tolerances and coatings of the day.

No?


Eric G.


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