ULF LENS COVERAGE

Discussion in 'Ultra Large Format Cameras and Accessories' started by Michael Finder, Apr 14, 2011.

  1. Michael Finder

    Michael Finder Member

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    I am looking at two lenses for an ULF camera and am unsure of their coverage. Can anyone offer some help please?

    Taylor,Taylor and Hobson 25 inch 635 mm Series IX
    Cooke Apochromatic Process Lens f10 - f128

    Busch Rapid Aplanat No.6
    24 inch f8 - f64
    ROJA vorm. Emil Busch Rathenow

    Thanks in advance.

    Michael Finder
     
  2. sandholm

    sandholm Subscriber

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  3. Dan Fromm

    Dan Fromm Member

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    If you're lucky the TTH Series IX will cover 45 degrees. If so, it will cover a 21 inch circle.

    Sandholm, a 30 inch lens that covers 20 x 30 inches at infinity covers 62 degrees. Few ancient process lenses have that much coverage. Process lenses coverage is conventionally given for 1:1, not infinity. This has confused many innocents.
     
  4. jp80874

    jp80874 Subscriber

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  5. sandholm

    sandholm Subscriber

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    Well, its not me its the http://www.allenrumme.com/lensdb/DBIntro-1.html and the 12 lenses I have are correct listed in the database.

    If you doubt, check which source he got it from and ask them.

    cheers
     
  6. Ole

    Ole Moderator Staff Member Moderator

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  7. Dan Fromm

    Dan Fromm Member

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    I checked. You misread the table. He does indeed report that the 30" TTH Series IX covers 20 x 30, but at 1:1. At infinity it covers 15x20, i.e., 45 degrees.
     
  8. AllenR

    AllenR Member

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    It is nice to see that the database is actually useful on occasion, as I get little indication other than the monthly web site statistics. I have a boat load more data that needs to be added to the tables and a large stack of catalogs, and advertisements that need to be reviewed. It would be great to make this a searchable database at some point, rather than just a big list. But all of that takes time, of which I never seem to have enough.

    I think a couple of comments on the data are also in order. All the data comes from manufacturer's catalogs, advertisements, or brochures. If it didn't come directly from a manufacturer generated source, that I have in my possession, it isn't included. All the sources are listed so that folks can go check the primary sources if they so choose. There are duplicate entries for some lenses because in comparing data on the same lens, from two different sources, I found different specifications. Lastly, I only report the data the manufacturer provides, if they only list coverage at infinity, then the other coverage columns are left blank. I have attempted to make the data as accurate as possible, but my dyslexic fingers sometimes have a mind of their own. If errors exist then let me know so I can remedy the problem.
     
  9. Dan Fromm

    Dan Fromm Member

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    Hmm. Live by the catalog, die by the catalog.

    I make this point because I recently had the opportunity to confront what two Berthiot catalogs (pre-WWI, between the wars) and one Berthiot brochure (post-WWII) say about Perigraphes' (Serie VIa, f/14; Serie VIb, f/6.8) coverage. It fell over time. In the case of the VIb, from 95 degrees to 65 degrees.

    Further on this point my friend and co-author Eric Beltrando (see his site, www.dioptrique.info) has used a ray-tracing program he wrote to evaluate a number of lenses' performance, including coverage, using prescriptions from patents and from as much of the Boyer archives as he has. Short answer, in general coverage claims are exaggerated. This is especially the case with Boyer's Beryl, a clone of Goertz' Dagor, and the Dagor itself.

    Faith in coverage claims published in catalogs seems, um, misplaced. The best way to know what a lens will do for you is to ask it.
     
  10. AllenR

    AllenR Member

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    Catalog data is most certainly only a starting point, and one must verify for themselves if a specific lens meets their needs. You imply, however, that catalog data is completely useless, which it isn't, and your condescending tone is far from necessary. Some finite starting point is a much better place to begin ones investigations. The reason I started this database was that there is a huge amount of anecdotal information floating around out there that is, in my experience, worthless.

    I am quite familiar with Eric's efforts, having corresponded and shared some data with him.
     
    Last edited by a moderator: Apr 18, 2011
  11. Dan Fromm

    Dan Fromm Member

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    Alan, there's ample evidence that some manufacturers systematically exaggerated coverage. The best catalog claims can do is set an upper bound. The older a catalog is, the more likely it is to mislead. Modern claims backed up by MTF curves are credible, old ones aren't.

    You're right, anecdotal information is very hard to evaluate. Unfortunately so are the claims made in sales material.

    I know that you've corresponded with Eric, he's mentioned you to me.

    To move this discussion to another, less personally painful field, I know an aquarist who decided to compile a list of validly-published names of fishes in a group. Who and what the group is don't matter. He worked hard, did a lot of well-done bibliographic digging, published list after list after list. I thought it was a waste. Having a fish (in the group, of course) in one hand and a list of names in the other with no way of matching struck me as useless. Having a fish in hand with a name on the list attached with no way of telling whether the name fit also seemed useless.

    To get back to cases, making an uncritical compilation of marketing claims is probably great fun but something more informative would be more useful.