One thing to keep in mind is that the Rodenstock Apo-Gerogons are reputed to be difficult to mount in shutter. That's fine if you only ever intend to use them in barrel, but not if you're thinking of buying a lens in barrel now to save money and then later on having it mounted in a shutter. I don't know about the Ultragons or Repromasters, but as Jason points out, it's generally not a problem with the G-Clarons and Graphic Kowas.
from Richard Knoppow, "It is [14" Blue Dot Trigor] essentially a adaption of the Dagor as a copy lens. I
suspect the high prices come from either a misunderstanding of what it is or perhaps simply because it was not made in large quantities.
if you can find one, a better option to the trigor would be the Schneider 14" Gold Dot Dagor.
good luck,
scott
---Scott
www.srosenberg.com
The blue dot out performs the dagor hands down as far as sharpness goes. It covers like a dagor and is almost as sharp as an artar. As far as lens element construction maybe someone more qualified could give you a better assessment than I. But as a photographer with a lupe in my hand I can show you significant differences. It is an amazing little lens. I've owned a gold dot and currently own a 16.5" dagor and they don't even come close to the blue dot as far as coverage vs. sharpness. Like I said, covers like a dagor but is as sharp as an Artar. I've heard them called triple dagors and I don't know if that is because of the element design. There is not much info on them that I can find. I've talked with Richard and the only thing that he can find on them is that it was a W.A. process lens and most of them were produced by Kern. (Swiss made). My lens collection consists of 24" artar...30" artar....16.5" dagor....they will all go before the 14" Trigor goes. They will have to pry the Trigor from my cold dead hands.
I would like to see an exploded view of the Trigor vs. an exploded view of a Dagor just to see the design differences. It seems ( and I could be wrong) that there is an extra lens element in the Trigor that the dagor doesn't have. O.K. you lens junkies elaborate for me. Help me out here
According to Richard Knoppow at http://medfmt.8k.com/mf/lflenses.html, the Trigor layout is the same as the Dagor:
"[The Trigor is] a Dagor. Evidently a variation of the Wide Angle Dagor with coverage larger than a Dialyte type process lens but not as wide as a Dagor. The image circle is reduced probably to reduce some of the zonal spherical aberration characteristic of the Dagor and similar cemented meniscus lenses. The Blue-Dot, also sold as the Trigor, is not an apochromatic lens. Its a good achromat. Symmetrical lenses, like the Dagor have inherently no lateral chromatic aberration when the whole optical system is symmetrical (i.e., at 1:1) and good cancellation even up to infinity focus. The Trigor was made for wide angle use in making lithographic masters. As for pictorial lenses, the Plasmat type offers better correction and easier construction due to having two less cemented surfaces. Once effective anti-reflective lens coatings became economically available, the all-cemented designs, like the Dagor disappeared since air-spaced designs, like the Plasmat offered a better solution to performance. Most modern LF lenses, copy machine lenses, enlarging lenses, are of the Plasmat type. Goerz evidently did not make Blue-Dot or Trigor lenses for long or in large quantity. They appear to have been made in only a limited number
of focal lengths..."
Folks,
Re: Blue Dot Trigor and Gold Dot dagor (Kern). This thread from rec.photo.equipment.largeformat may be interesting. Of all the folks I'd trust, it would be Steve Grimes - here's one of his posts from December 16th, 1998:
http://groups.google.com/group/rec.photo.equipment.large-format/browse_frm/thread/28ea2de6e68d4e9c/aaca9c1040328484?q=trigor&rnum=11&hl=en#aaca9c1040328484
Steve thought they were identical. I suspect they are with a couple of exceptions, maximum aperture and perhaps cell spacing. Oh, and the Trigor cells will not screw into the Dagor's shutter. There's a story there somewhere.
I've had the good fortune to have a 14" Kern Dagor and a "loaner" 14" Blue Dot Trigor (also Kern) in barrel.
The groundglass images appear identical at the same aperture, and I've spent time looking at various subjects in various lighting. As far as film goes, the weather here in the Tennesse valley has blown big time since I received the Trigor, but I hope to do some image quality tests soon. The sharpness tests I could do without magic light and used a drive in movie theater booth with various printed matter in the windows as a test subject. Under magnification, I could tell no difference at all in the sharpnessof the neagtives in trying to read print of different sizes. Tone and quality are indistinguishable on the GG and on the negative. I will do some more sharpness testing as weather and schedule permit.
At first I thought the Trigor was producing an image sharper than my 14" Kern Dagor on the GG, but then I realized I was looking at the GG with both lenses wide open which is f/8 for the Dagor and f/11 for the Trigor. Stopping the Dagor to f/11 produced an identical GG image. BTW, the iris in the Trigor's barrel does not open up to the barrel diameter. It seems reasonably clear in shutter it would be f/8 which I suspect is really f/7.7).
Robert, were both the lenses you were comparing (14" Gold Dot Dagor and 14" Blue Dot Trigor) Kerns (Swiss)?
Steve
The lenses I compared were my 16.5" dagor to the 14" trigor. Both lenses were stopped down to f32. I examined the negative and the print. The trigor was significantly sharper out on the edges than the dagor. I was using a 10x lupe to examine with. But even without a lupe it can be seen as sharper. Now considering the 16.5" image circle is so much larger than the 14" makes it even that much sharper because I'm looking at the 14"ers image circle closer to it's edge. Please correct me if I'm wrong. I don't have a 14" dagor to compare it with but i do know someone who does and I will do a comparison to that in the near future.Did you shoot any test shots and compare the negatives and the prints or are you just going by what you see on the ground glass? I used both lenses on my 8x20 so I was pushing the limits on the coverage of the trigor and it is still sharper than the Dagor. Now I'm not a lens expert by any means but my Dagor has much more bokeh than my Trigor when testing this way. My test were done in studio under a couple of 2000 watt Mole Fresnels.
I forgot to mention that with movements i was able to get closer to the edge of the image circle of the 16.5". It might make a difference on what size camera you are using when you conduct your tests. You may want to use a few movements to actually see the edges of the image circle. The difference may be a lot less noticable on an 8x10 GG with both lenses centered, considering you have tons of movement with lenses this size on 8x10. I will try the same tests with my 8x10 and see what I get. But I think the 8x20 allows me to see the edges of the image circle a little easier than the 8x10 will. What size camera are you using?
Robert,
I shot negs and used an 8x10 camera. I plan on further testing, probably this weekend, and will post results. Thanks for the info!
Steve
Steve, It will be intersting to see/ hear of your results. Keep in mind I'm comparing an early 16.5" Dagor..American Optical to the Trigor. It will be intersting to see if Kern just changed the cosmetics and they are in fact the same lens. What makes me think they are not is from what I hear the Dagor has a little more coverage than the Trigor. This was explained to me as to why the Trigor is a little bit better corrected than the Dagor which reduces the image circle somewhat. This is in line with my results. It would be nice if you could compare an early 14" Dagor with the Kern Dagor and the Trigor. Keep me informed
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