Greetings, I have been left an old brass lens that I believe to be a petzval(pretzal) and it says its a 1/1 plate lens and would like to use it. What would be the min coversge on this. peace and goodwill fergs
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Greetings, I have been left an old brass lens that I believe to be a petzval(pretzal) and it says its a 1/1 plate lens and would like to use it. What would be the min coversge on this. peace and goodwill fergs
Full plate is 6 1/2 x 8 1/2 inches. However, one of the Petzval experts here will have to chime in to help us interpret this - this lens type isn't typically used to achieve a sharp image across the entire field.
I can't claim to be a Petsval expert, but I have access to some old catalogs which list whole plate Petzval lenses as running between 10" and 12 1/2" back focus. Petzvals have rather narrow working angles, so I would guess that your lens would probably just cover whole plate at infinity, but would be quite satisfactory on that size at the usual portrait distances. On 5" X 7", it should work quite well.
I agree with this, but I would point out that a lot of folks using Petzvals today (including me!) like to use more of the field than was traditionally used in order to get swirly edge effects caused by coma and curvature of field. If this is your goal, you might want to select a slightly wider lens than otherwise suggested for the format. Say... 5-6 inches for 4.5 and 10-12" for 8x10. These FLs may or may not cover at infinity.Quote:
Originally Posted by Ernest Purdum
E
Whole Plate in The U.K. is and was always 6 1/2 x 8 1/2 inches. Some film is still cut to this size and sheet film holders for this size were made in the past.
Pete.
A whole-plate Petzval-type lens would probably have a FL of between 14" and 16", which corresponds to Ernest's 10" and 12 1/2" back focus, and would probably cover 8x10.
At infinity a normally designed Petzval will illuminate about 50 degrees or so, just a hair under its focal length. They were not often used this short in the 19th century, but are today by those seeking the "swirly bokeh."
Pete, whole plate in the U.K. is and was always 6 1/2" X 8 1/2". Well, yes. except for when it was being 8 1/2" X 6 1/2".
Ernest
Ernest, I can never remember which way round to write it to keep everybody happy. I have done the odd wind up but this wasn't one of them. the wind ups usually involve the word colour..............
Pete.