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disemjg
Joined: 10 Jan 2002
Posts: 474
Location: Washington, DC
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 Posted: Sat Sep 02, 2006 1:05 pm Post subject: |
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| My limited references do not list this lens; will it cover 5X7? |
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troublemaker
Joined: 24 Nov 2003
Posts: 715
Location: So Cal
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ImageMaker
Joined: 20 Jun 2006
Posts: 93
Location: North Carolina
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| Posted: Sun Sep 03, 2006 10:55 pm Post subject: |
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Generally speaking, a Tessar type lens (which would include Xenar, Dominar, and Skopar as well as a number of other names over the years), in original form, has a useful FOV of 47 degrees (some reformulated Tessars improve on that, a little). That means that, effectively, it needs a focal length equal to the film diagonal to avoid soft or dim corners with no movements, and significantly longer to allow for useful amounts of movements.
This was one of the biggest weaknesses of the Tessar type, IMO -- they were pretty worthless as wide angle lenses; some triplets will cover a significantly wider angle, at least when stopped down, though they don't perform as well within the Tessar's useful field, especially at apertures wider than about f/8.
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Dan Fromm
Joined: 14 May 2001
Posts: 2146
Location: New Jersey
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| Posted: Mon Sep 04, 2006 12:23 am Post subject: |
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| Quote: |
On 2006-09-03 15:55, ImageMaker wrote:
Generally speaking, a Tessar type lens (which would include Xenar, Dominar, and Skopar as well as a number of other names over the years), in original form, has a useful FOV of 47 degrees (some reformulated Tessars improve on that, a little). That means that, effectively, it needs a focal length equal to the film diagonal to avoid soft or dim corners with no movements, and significantly longer to allow for useful amounts of movements.
This was one of the biggest weaknesses of the Tessar type, IMO -- they were pretty worthless as wide angle lenses; some triplets will cover a significantly wider angle, at least when stopped down, though they don't perform as well within the Tessar's useful field, especially at apertures wider than about f/8.
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Donald, all that you wrote is true.
But and however, Zeiss made some f/8 wide angle Tessars, 28 mm for Contax and 55 mm for VP Exakta. Don't confuse these with the f/9 Apo Tessars, which are narrow angle lenses. Also, the early 35/3.5 Nikkor for Nikon RF cameras was a tessar type.
I have a couple of ancient, as in pre-WWI, f/6.3 CZJ Tessars. These are supposed to cover 70 degrees. First redesign, in 1911, was to improve ease of manufacture. I think both of mine post-date the redesign; the one I've shot is just superb. Second redesign was in 1941. I've never used one -- a neighbor has some, we just haven't got around to taking them out -- but the post-WWII CZJ f/6.3 Tessars are coated and supposedly even better.
Cheers,
Dan |
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ImageMaker
Joined: 20 Jun 2006
Posts: 93
Location: North Carolina
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| Posted: Mon Sep 04, 2006 4:34 pm Post subject: |
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Also true, Dan, and don't forget a couple versions of the Rollei 35 carried a Tessar at about 35 mm focal length and either f/3.5 or f/2.8. However, close examination will reveal those aren't in "original form" -- IIRC, it was found in the mid-1930s that reversing the powers of the elements in the rear group (i.e. putting the positive ahead of the negative, and I've never known if the glass types were also reversed) and re-optimizing the prescription gave slightly better performance at wider apertures, as well as increasing the coverage angle a bit. IIRC, most of the Kodak Ektar lenses were "reverse Tessar" designs, as were some Bausch & Lomb Tessars.
None of which changes the fact that pretty much any random Tessar you encounter in a LF focal length (say, 105 mm or longer) will be the traditional post-1911, pre-1941 design and good for 47 degrees. Seems to me the Wide Angle and Apo-Tessars were marked as such...
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Dan Fromm
Joined: 14 May 2001
Posts: 2146
Location: New Jersey
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| Posted: Mon Sep 04, 2006 5:33 pm Post subject: |
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| Quote: |
On 2006-09-04 09:34, ImageMaker wrote:
Also true, Dan, and don't forget a couple versions of the Rollei 35 carried a Tessar at about 35 mm focal length and either f/3.5 or f/2.8. However, close examination will reveal those aren't in "original form" -- IIRC, it was found in the mid-1930s that reversing the powers of the elements in the rear group (i.e. putting the positive ahead of the negative, and I've never known if the glass types were also reversed) and re-optimizing the prescription gave slightly better performance at wider apertures, as well as increasing the coverage angle a bit. IIRC, most of the Kodak Ektar lenses were "reverse Tessar" designs, as were some Bausch & Lomb Tessars.
None of which changes the fact that pretty much any random Tessar you encounter in a LF focal length (say, 105 mm or longer) will be the traditional post-1911, pre-1941 design and good for 47 degrees. Seems to me the Wide Angle and Apo-Tessars were marked as such...
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Donald, thanks for the reply. The design dates I gave were for f/6.3 Tessars. The faster ones (f/4.5, f/3.5, f/2.9, ... ) that were designed after the f/6.3 and were redesigned much more often. From the beginning the f/6.3s covered 70 degrees. The f/6.3s are much less common than the f/4.5s and f/3.5s.
About the reversed Tessar terminology. I suspect there's a Kingslake in your library. I have on hand a couple of lenses that are literally reversed tessars, i.e., with the cemented doublet in front of the diaphragm and the two singlets behind. Namely, 72/4.5 B&L "Macro" (I think it is a rebadged MicroTessar) and 100/6.3 Reichert Neupolar. The Neupolar, by the way, is a wonderful lens. Superb macro lens in the range 1:8 to 8:1, very sharp but with limited coverage (perhaps 80 mm) at infinity.
Cheers,
Dan |
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