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Just obtained a JML 12" f10 barrel lens I plan to use on my 5x7. Question is how do process lenses compare to more normal lenses such as a symar etc. I have read somewhere that process lenses are designed to perform better at close focusing distances rather than infinity.
If so are these differences worth considering if enlargement is limited to 16X20?
Ron,
Ron Wisner has written a good article on "flat field lenses". G-Clarons are reputed to have been designed as process lenses and in my opinion they are superb. I've also used Repromasters for 4x5 & 5x7 and I really have no problems with the quality of the images.
Pete.
Process lenses "can" have lower contrast, and narrower coverage, resulting in less movements possible, and since they are for the most part slower than other types of lenses you might use on your camera, the ground glass will be dimmer. Other than that, they are just fine for LF photography.
There are really two families of process lenses - those designed for the old horizontal cameras and later versions intended to be used on vertical cameras. Since vertical cameras were much more compact, their lenses had to have a wider view. The earlier designs were likely to be "dialytes" with four airspaced elements, therefore eight air to glass boundaries and, until coating came along, the loss of contrast that Gene McCluney mentions as a possibility. The later lenses in general need six elements because of the need for greater field of view. They came along after coating became standard, but before multicoating.
These lenses were indeed intended for close distance use. Most, though, work quite nicely at infinity when stopped down too f22 or so. They also have small aperures. This is sometimes a problem in focusing, but rarely in taking pictures since most large format work is done at small apertures anyway. The exception is portrait work.
There is some more information on this subject amongst the articles at the bottom of the home page.
Depends on what you are looking for. Many of them, perhaps most of them are slow lenses - in the F9 to F11 range. This is good and bad. In low light, a F9 lens can be a PITA unless you are using a fresnel screen like in the Tachihara, or similar. Even then if you are used to brighter lenses such as the more regular F5.6 lenses, it can make a big difference trying to get used to a dimmer F9 lens.
However if you are backpacking and both space & weight are a premium, F9 lenses are a Godsend. After two hours on a trail you really notice the difference.
As far as coverage goes, that really varies. A red dot artar in the 210mm range will cover 4x5 but not 5x7, whereas a 210 g-claron will likely not only cover 5x7, but some have told me 8x10 straight on with no movements.
As far as sharpness goes, any and all process lenses I have used are as sharp as anything out there. I think the real difference might be coatings, for some older process lenses might have only a single coating vs multi-coated, but then there's plenty of discussion in the past on coatings vs not coatings or single coatings. You do not see the price suffer on older dagors or WF ektars because of coatings. :)
As far as the issue of process lenses being maximized or optimized for 1:1 use, well I have two problems with that. First off, I've never had a problem personally with either RD artars or g-clarons in that respect. Mind you, like many others, F22 and be there, right?
Secondly have you ever seen a process camera in real life? They are huge - or where huge, if there are any left in use. At least the ones I saw in operation, and helped take apart. We are talking sometimes 20 feet or more away from the lens to the plane of focus of what you are shooting. That sure isn't 1:1 at all times.
I personally think the bottom line and real issue is the dim screen you get, and I've meet many people who do not like that. I use F8 and F9 lenses all the time,so I am used to it, but whenever I switch back to a F5.6 lens - boom, it's like somebody turned a spotlight on. A good darkcloth and a nice loupe are almost essential with F9 lenses, whereas with a brighter lens, especailly on a press camera, you can get away at times without.
joe
I should have commented on your 12" JML earlier. JML has a rather astonishing number of different lens types, so one 12" might be quite different from another, especially in coverage. Give your lens a try and I think you will be pleased.