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#11
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Lens question please_Gundlach, Turner-Reich series II No. 1
"____" wrote in message ... In article , jjs wrote: "AAvK" wrote in message ... What about for mono films? I think because of this problem I would never use this lens for color films! I took it that Richard was addressing B&W. If aberation occurs in a particular color for which the film is sensitive, a correcting filter will help. Black & White film is sensitive to color (obviously) and not equally sensitive to all colors. Filters are important. In my early day of LF photography I once bought an ARTAR that was supposed to be a good lens and covered 8x10, it sucked royally for B&W all kinds of ghosting on b&w even when pointed 180 degrees away from the sun on a cloudy day. The ******* I bought from extracted a 50 dollar restock fee out the 350 dollar check I bought with even after I had to pester him for about 3 months to refund my money. I can think of only one nice thing to say about him: Cocks---er, may he rest in pieces. -- The Apo Artar is a four element air spaced lens with eight glass-air surfaces. It does have some flare but should not have bad ghost images. I have two, one a very old uncoated lens from the 1920's. Its very sharp and has good contrast. The other is from the 1960's and is coated so it has little flare. Note that while both flare and ghost images come from internal reflections and are helped by coating they are not quite the same. Most flare is in the form of an overall diffuse field of light all over the image while ghost images are fairly sharp, or at least recognizable, images in the image field of bright objects either in the image or just outside of it. Ghosting is usuallyu due to the design of the lens rather than just having glass-air surfaces. Both flare and ghosting can also be cause by reflections from the inside of the lens barrel or cells or from the inside of the shutter. I would say your experience with the Artar is unusual. The Apo Artar was designed for use on process cameras. These were used for making printing plates, or rather, negatives used to expose the photo-resists that were used to control the etching of the plates. Process lenses are designed to work best at magnifications near unity. The Artar is designed for three-color work where the color separation negatives must all be in focus and be of exactly the same size. Although the lens is optimized for equal object and image distance (unity magnification) it performs very well even at infinity focus if stopped down a bit. One cause of flare in lenses is haze but this won't cause ghost images. Haze seems to form on many lenses with time. I am not sure of the cause but the haze is easily removed with any lens cleaner. The problem is getting to the inside surfaces. Most Artars have back caps on the cells so that cleaning the insides is not difficult. -- --- Richard Knoppow Los Angeles, CA, USA |
#12
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Lens question please_Gundlach, Turner-Reich series II No. 1
jjs wrote in message ... "AAvK" wrote in message ... What about for mono films? I think because of this problem I would never use this lens for color films! I took it that Richard was addressing B&W. If aberation occurs in a particular color for which the film is sensitive, a correcting filter will help. Black & White film is sensitive to color (obviously) and not equally sensitive to all colors. Filters are important. Lack of color correction affects both B&W and color although it manifests itself in different ways. Lenses have two kinds of color aberration: one is longitudinal chromatic aberration, the other is lateral chromatic aberration. The first is the one we usually think of where the lens focuses different colors at different distances: in effect the focal length changes with color. This is inherent due to the characteristics of glass and is reduced by balancing the dispersion of the positive and negative elements by choosing the kinds of glass used for them. The newer low-dispersion glasses make the job of correcting color while maintaning other corrections easier. Lateral color is a difference in the _size_ of images at different colors. The images are all in focus but different in size so that there is still fringing. In fact, because the images are all sharp the fringing may be more noticable. Lateral color can be reduced by symmetry or by choice of glass types. In non-symmetrical lenses it is sometimes difficult to correct. In a convertible lens, where the cells are similar but can be used alone the correction for lateral color due to symmetry is lost when only one cell is used. Some of these lenses have cells which are corrected fairly well and others show considerable color fringing when single cells are used but all are inferior to the complete lens (two cells). Color problems may actually be more appearant in B&W because the film records everything at once and the eye can not longer ignore some of the information at it can in color pictures. Now, if the colors recorded throught an aberrated lens are limited the aberration will have less effect. Some very old lenses are not very corrected for the red end of the spectrum because before about the mid 1920's most film was orthochromatic (not sensitive to red) or even "ordinary" (not sensitize to any color but blue). A filter which reduces red light may make such lenses sharper. Green filters cut off some blue light and some red light so are good choices where a lens has serious chromatic aberration. A cyan filter will somewhat duplicate orthochromatic film and will usually also improve sharpness when the lens has some chromatic aberration. My experience with the T-R lens is that the individual cells have very noticable color fringing. The Zeiss Convertible Protar is better although still having some fringing. Even the older convertible version of the Schneider Symmar has some fringing, actually a little worse than the Protar. A general purpose lens which was very well corrected for both kinds of color aberration is the Kodak Commercial Ektar. These are Tessar types and don't have the advantage of symmetry but were very carefully designed to eliminate color problems because they were intended to promote the use of color film for commercial photography. Most symmetrical or nearly symmetrical lenses have good correction for lateral color, the Goerz Dagor, Dogmar and of course Artar being examples. -- --- Richard Knoppow Los Angeles, CA, USA |
#13
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Lens question please_Gundlach, Turner-Reich series II No. 1
[uppersnip]
--- Richard Knoppow Los Angeles, CA, USA Richard! So sorry for being so late, but it dawned on me to thank you very much for your great and terrific help and for the sharing of knowledge, awesome kindness. Thank you, very very much. Regards, -- Giant_Alex })))* not my site: http://www.e-sword.net/ |
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