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#1
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G-Claron single cell use
I just read a 10 year old post about using a G-Claron as a 'pseudo-
convertible' by using one cell; performance would probably be better than 'vintage' convertibles. I had previously wondered about splitting plasmats but wrote it off as 'sacrilege' on already decent lenses, but seeing the post made me realize it's been done. Anyone actually try this with a G-Claron 150 and does it have any unique qualities, or just 'work'. Thanks Murray |
#2
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G-Claron single cell use
"murrayatuptowngallery" wrote in message oups.com... I just read a 10 year old post about using a G-Claron as a 'pseudo- convertible' by using one cell; performance would probably be better than 'vintage' convertibles. I had previously wondered about splitting plasmats but wrote it off as 'sacrilege' on already decent lenses, but seeing the post made me realize it's been done. Anyone actually try this with a G-Claron 150 and does it have any unique qualities, or just 'work'. Thanks Murray I think, without looking it up, that the G-Claron is a Plasmat type. These will work as convertibles. The best of the old convertibles was the Zeiss Convertible Protar sometimes called a Double Protar. The difference is that these lenses are individually corrected for coma where some other convertible lenses, notably the Goerz Dagor and Dogmar are not. This allows the Protar to be used at larger stops with reasonable sharpness in the corners. Dagor cells must be stopped down to around f/45 to get rid of enough coma to be sharp away from the center. Protars are OK at f/36 or maybe even a little wider. Nearly any symmetrical lens can be used as a convertible but, as noted for the Dagor, some aberrations, especially those corrected by the symmetry, will be present. My experience with the convertible type of Symmar is that they perform about as well as a Convertible Protar, but not better. Actually, I think the correction of the individual Protar cells is a little better. I don't know if the early Plasmat type Symmar (the first lens of this name was a Dagor type) was specifically corrected for coma but it probably was. Later ones are corrected for best performance in a complete lens but single cells probably perform pretty well when stopped down enough. This should apply to the G-Claron. FWIW, the Plasmat was derived from the Dagor by air-spacing one of the elements. I has similar performance but much less zonal spherical aberration, an inherent fault of the Dagor type. Plasmats can also be corrected for astigmatism to a very high degree. Like the Dagor they are essentially wide angle lenses although most have perhaps about 10degrees less coverage than an equivalent Dagor. The single cells of convertible lenses of all types have quit narrow coverage, the plate size being about the same as the assembled lens. -- --- Richard Knoppow Los Angeles, CA, USA |
#3
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G-Claron single cell use
On 21 Oct 2007 00:20:32 -0700, murrayatuptowngallery
wrote: I just read a 10 year old post about using a G-Claron as a 'pseudo- convertible' by using one cell; performance would probably be better than 'vintage' convertibles. I had previously wondered about splitting plasmats but wrote it off as 'sacrilege' on already decent lenses, but seeing the post made me realize it's been done. Anyone actually try this with a G-Claron 150 and does it have any unique qualities, or just 'work'. Thanks Murray I have a saved post from long ago that suggests using a yellow filter when using it as a convertible (assuming you're shooting B&W). This was to reduce the chromatic aberration that would otherwise be corrected by the front cell. The same poster claimed the focal length was about 300mm for the rear cell only. Sorry, I've never tried it myself. steve |
#4
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G-Claron single cell use
On 2007-10-22, Stephan Goldstein wrote:
On 21 Oct 2007 00:20:32 -0700, murrayatuptowngallery wrote: I just read a 10 year old post about using a G-Claron as a 'pseudo- convertible' by using one cell; performance would probably be better than 'vintage' convertibles. I had previously wondered about splitting plasmats but wrote it off as 'sacrilege' on already decent lenses, but seeing the post made me realize it's been done. Anyone actually try this with a G-Claron 150 and does it have any unique qualities, or just 'work'. Thanks Murray I have a saved post from long ago that suggests using a yellow filter when using it as a convertible (assuming you're shooting B&W). This was to reduce the chromatic aberration that would otherwise be corrected by the front cell. The same poster claimed the focal length was about 300mm for the rear cell only. Sorry, I've never tried it myself. Ron Wisner recommends using a strong yellow filter (I imagine any monochromatic filter would do as well) when using single cells of his Convertible Plasmat set. This is to solve the problem of uncorrected lateral color in a single cell. Now I do not use a #15 filter for that, but I do use B&W filter 58ES MEDIUM YELLOW (022). Note that, when using a single cell, the focal length tends to be quite long compared with using a pair together.Of course, this would work only with black and white film where blue light was not too important. He presumably makes a corrector lens that has zero power but all the same distortions so that it corrects a single cell. I ordered one when he first announced it over 10 years ago, but he is yet to ship me one, so I cannot say how well it works. -- .~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 08:30:01 up 15 days, 16:06, 4 users, load average: 4.06, 4.16, 4.22 |
#5
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G-Claron single cell use
Thanks, all.
Yes, the notorious vaporware field corrector - I have even heard of it's non-existence, at least in this plane... Murray |
#6
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G-Claron single cell use
In article ,
Jean-David Beyer wrote: He presumably makes a corrector lens that has zero power but all the same distortions so that it corrects a single cell. I ordered one when he first announced it over 10 years ago, but he is yet to ship me one, so I cannot say how well it works. Didn't he in fact run his company out of business by taking prepayments and deposits for work that wasn't, in fact, ever done? I tried off and on for several years to get a replacement back (graflok style) for my 4x5 trad and wondered why he wasn't responding to my inquiries but now I feel lucky he didn't -- since I took the camera in to L&R for repairs a few weeks ago and discovered there were no spare parts available (luckily I didn't need any) I've talked to several other people who were persistent enough to get in touch with Ron over the past few years and, if they ordered anything, ended up wishing they hadn't... -- Thor Lancelot Simon "The inconsistency is startling, though admittedly, if consistency is to be abandoned or transcended, there is no problem." - Noam Chomsky |
#7
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G-Claron single cell use
On 2007-10-25, Thor Lancelot Simon wrote:
In article , Jean-David Beyer wrote: He presumably makes a corrector lens that has zero power but all the same distortions so that it corrects a single cell. I ordered one when he first announced it over 10 years ago, but he is yet to ship me one, so I cannot say how well it works. Didn't he in fact run his company out of business by taking prepayments and deposits for work that wasn't, in fact, ever done? I tried off and on for several years to get a replacement back (graflok style) for my 4x5 trad and wondered why he wasn't responding to my inquiries but now I feel lucky he didn't -- since I took the camera in to L&R for repairs a few weeks ago and discovered there were no spare parts available (luckily I didn't need any) I've talked to several other people who were persistent enough to get in touch with Ron over the past few years and, if they ordered anything, ended up wishing they hadn't... I have never been dissatisfied with the quality and workmanship of his products. Most things were delivered promptly. The Convertible Plasmat Set took a couple of years, though. But I definately got it and I use it to the exclusion of everything else except the 90mm f/8 SuperAngulon. The big problem was the corrector, and the problems were not entirely his. After what I thought was too much delay, Ron offered to refund my money, but I would rather have the lens than the money, so I have held on. Now it seems he is trying to rectify this and is taking few or no new orders until the backlog is taken care of. He also suggests he is thinning out his product line to make things more manageable. This may also reflect a drop in business due to the digital machines and bicycle craze supplainting the photography sport. I have _never_ had a question of his honesty. -- .~. Jean-David Beyer Registered Linux User 85642. /V\ PGP-Key: 9A2FC99A Registered Machine 241939. /( )\ Shrewsbury, New Jersey http://counter.li.org ^^-^^ 10:40:01 up 2 days, 2:58, 5 users, load average: 5.30, 5.32, 5.26 |
#8
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G-Claron single cell use
In article .com,
murrayatuptowngallery wrote: I just read a 10 year old post about using a G-Claron as a 'pseudo- convertible' by using one cell; performance would probably be better than 'vintage' convertibles. I had previously wondered about splitting plasmats but wrote it off as 'sacrilege' on already decent lenses, but seeing the post made me realize it's been done. Anyone actually try this with a G-Claron 150 and does it have any unique qualities, or just 'work'. Thanks Murray I purchased a G Claron 150 from Chuck Farmer at The F Stops Here about 15 years ago. It's a great lens under certain light conditions. I used it configured as 150 and as 300. In the 300 configuration, you need an adaptor that will permit the mounting of a yellow filter, to replace the front element. Sorry, but I don't have the filter dimensions / specs at hand, but 34.5mm pops up as the correct fit. The most critical aspect of using the 150 as a 300mm is the reality of single-coating on the G-Claron lens, which after all was intended to be used as a flat-field repro lens. Attach a lens shade to the yellow filter and never shoot even obliquely into sun. With yellow filter and lens shade the G-Claron 150 configured for 300 produces wonderful, sharp images. It's a great lens. Regarding Ron Wisner, I used the G-Claron on his Technical Field camera for five years. Great combination. - Jan Becket, Honolulu |
#9
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G-Claron single cell use
"JB" wrote in message ... In article .com, murrayatuptowngallery wrote: I just read a 10 year old post about using a G-Claron as a 'pseudo- convertible' by using one cell; performance would probably be better than 'vintage' convertibles. I had previously wondered about splitting plasmats but wrote it off as 'sacrilege' on already decent lenses, but seeing the post made me realize it's been done. Anyone actually try this with a G-Claron 150 and does it have any unique qualities, or just 'work'. Thanks Murray I purchased a G Claron 150 from Chuck Farmer at The F Stops Here about 15 years ago. It's a great lens under certain light conditions. I used it configured as 150 and as 300. In the 300 configuration, you need an adaptor that will permit the mounting of a yellow filter, to replace the front element. Sorry, but I don't have the filter dimensions / specs at hand, but 34.5mm pops up as the correct fit. The most critical aspect of using the 150 as a 300mm is the reality of single-coating on the G-Claron lens, which after all was intended to be used as a flat-field repro lens. Attach a lens shade to the yellow filter and never shoot even obliquely into sun. With yellow filter and lens shade the G-Claron 150 configured for 300 produces wonderful, sharp images. It's a great lens. Regarding Ron Wisner, I used the G-Claron on his Technical Field camera for five years. Great combination. - Jan Becket, Honolulu The problem with all convertible lenses is that when a single cell is used one loses the automatic corrections introduced by symmetry or even semi symmetry. Symmetry corrects the three lateral aberrations: lateral color, coma, geometric distortion. Some convertible lenses, for instance the Zeiss Convertible Protar, have some correction for coma in the individual cells but most do not. For instance, the Dagor, while patented and sold as a convertible really is not because the individual cells have a lot of coma so work only as very small stops (around f/45). The combined lens has very little coma. While the cancellation is maximum where the entire optical system is symmetrical (equal object and image sizes) it is considerable even at infinity. The Plasmat is really a derivation of the Dagor where the inside cemented element is broken free and air-spaced. This gives the designer an additional surface and a spacing. While the Dagor has considerable uncorrected spherical aberration the Plasmat has very little. The design was known for decades but not used widely because of excessive flare where not coated. The availability of economical coating methods following WW-2 changed the whole approach to lens design making it possible to use air-spaced elements in place of the previously used cemented elements. This resulted in the practicallity of using some excellent designs previously not used due to excessive flare and a considerable improvement in lens performance. I don't know why the lens would need a color filter. Perhaps its chromatic correction depends on its symmetry, certainly its lateral color correction does. Filters have no effect whatever on flare, other to increase it if the filters are not coated. Process lenses when used for their original purpose in making photo-mechanical half tone plates, do not really need to be coated since the flare can be corrected by a small change in exposure. -- -- Richard Knoppow Los Angeles, CA, USA |
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