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  1. #31

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    Quote Originally Posted by DREW WILEY View Post
    My mid-budget favorite is the Apo-Rodagon N 150.
    Two of these just went for $399 each on ebay...I was tempted but they have the same optimum 6X mag as the vanilla flavored Rodagon 150mm. At 6x from 4x5, that is a 24" x 30", out of my reach until I can get a bigger home to build a proper darkroom in and use a drop table with my 45MXT. Add to that the front is bigger and longer and I would have to re-design my contrast filter holder or use larger ones in between the light source and neg, a big no-no if you do split grade printing not to mention inviting more possibility of dust.

    I also have the 135mm Rodagon for 20" x 24" without needing a drop table, the largest size I can practically do until I get a larger pad.
    Last edited by PKM-25; 08-24-2012 at 03:48 PM. Click to view previous post history.
    "I'm the freak that shoots film. God bless the freaks!" ~ Mainecoonmaniac ~

  2. #32

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    Quote Originally Posted by DREW WILEY View Post
    15X and you're approaching the realm of the Rodagon-G, a specialized lens for large scale magnification, and not really intended for general work.
    15X from 4 x 5 is a massive 60" x 75", bigger than the largest roll paper currently available which is 56", that is getting to the size of Avedon's show "In the American West".

    I think it is safe to say at that scale you would be well advised to have made a dedicated mural enlarger with the supporting roll paper dispenser and wet side system.
    "I'm the freak that shoots film. God bless the freaks!" ~ Mainecoonmaniac ~

  3. #33

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    Quote Originally Posted by Leigh B View Post
    None of the major manufacturers would ever sell a lens "with some elements off center".
    Lens centering is very easy (thus inexpensive) to accomplish on a production line.

    - Leigh
    Barry Thornton in The Edge of Darkness reports receiving just such a lens: a Componon S with an element that was not centered when shipped from the factory. OK--it's one element, not "some", but it's still a major manufacturer, and a high-end lens.

    ALL manufacturing is done to some degree of tolerance, otherwise why does the ± symbol exist? And ALL manufacturer's produce some defective product from time to time. I've worked too long for manufacturers to believe that all production is perfect.

    I've read other photographers who say lens-to-lens variation is substantial in examples that they have seen.

    As to focal length and diagonal, yes, you are right--my brain slipped. Anyhow, my comment about actual focus (bellows) distance is true: the angle of view makes a bigger circle at closer distances than infinity (as in enlarging) because the lens is farther from the focus plane (and the subject plane, in enlarging). It also gets bigger as the lens is stopped down.

    Charlie Strack

  4. #34
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    Quote Originally Posted by voceumana View Post
    ALL manufacturing is done to some degree of tolerance, otherwise why does the ± symbol exist? And ALL manufacturer's produce some defective product from time to time. I've worked too long for manufacturers to believe that all production is perfect.
    Hi Charlie,

    I'm pretty familiar with measurements, tolerancing, standards, production methods, etc.
    In fact I'm a journeyman Tool & Die Maker, and own and operate a commercial machine shop. I've worked as a calibration tech.
    I'm also moderator of the Metrology section of the largest machinist forum in the world.

    The problem with lens manufacture before the advent of computer-controlled processes was variation from one specimen to another.
    With modern methods that has been virtually eliminated, and with that change the problem with centering is greatly diminished.

    Of course it's possible to find an example of any product that at one end of the tolerance range.
    In a properly defined system that end should be well within the acceptable performance limits for the product.

    You'll certainly find more variation in products manufactured before the 'computer age', perhaps 30 or more years ago.

    - Leigh
    Last edited by Leigh B; 08-24-2012 at 05:20 PM. Click to view previous post history.
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

  5. #35

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    One sometimes sees the old chrome-barrel Componon lenses for sale. The Componon-S was a real
    improvement, but at the time probably not equal in quality control to the Rodagons coming off an allegedly newer assembly line. That was about thirty years ago; but since then, things have pretty much equalized between the respective manufacturers. But if one is nitpicky like me, different lenses have slightly different pros & cons, or different personalities, when it comes to specialized applications. And I suspect that many alleged "tests" for the performance of specific lenses have
    failed to take into account numerous other variables, other than the lens itself, which affect performance at the projection plane. Lots of BS out there, just as with other kinds of lenses.

  6. #36

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    Quote Originally Posted by Leigh B View Post
    Hi Charlie,

    You'll certainly find more variation in products manufactured before the 'computer age', perhaps 30 or more years ago.

    - Leigh
    Leigh,

    Ah, yes, this is very true for metal parts. But glass lenses are their own thing--they are still ground, as far as I know, using the ancient techniques--not sure how they size the diameter after grinding, so perhaps tolerance comes into play in that part of the process. Glass is not "machined". (Would that it were!)

    As a side note, many of the older lenses were in beautifully machined and finished barrels. Now the outer barrel is usually plastic. Barry Thornton noted that on his Componon-S, I think it was, the plastic outer barrel split in two (along the lens axis). The inner metal barrel (which held the elements) was in tact, so some careful gluing.

    Drew,

    I concur with you--some specific examples of lenses seem to have a magic in how they create images that seems to defy technical measurements.

    Charlie

  7. #37

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    Quote Originally Posted by ic-racer View Post
    The Schneider and Rodenstock 135 and 150 all are available as six element lenses. Both Schneider Componon-S (135mm and 150mm) have excellent MTF for moderate 4x5 enlargements and have similar image illumination at the corners.

    The Rodenstock Rodagon 135mm is $614.95 and the 150mm is $799.95 at B&H.
    Also note that the newer EL-Nikkors in most sizes are 6 elements in 4 groups. This includes the 135mm and 150mm EL-Nikkor "A" series, and most of the "N" series lenses from 50mm to 105mm. I believe only a couple f/4 aperture lenses of this series are 4 element Tessars.

    There is no need to buy a new enlarging lens. The 135mm EL-Nikkors and even the 150mm lenses are readily available on ebay in new or almost new condition. You need not pay more than about $75 for one. Just make sure they are the N or A series from the '80s and up.

  8. #38
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    Quote Originally Posted by voceumana View Post
    Glass is not "machined". (Would that it were!)
    Hi Charlie,

    Sorry to disagree, but glass certainly is machined, at least as far as the grinding process is concerned.

    The grinder is a machine. It can be controlled by computer, and the results can be analyzed by automated measurement.
    The results are used as input to the control system to fine-tune the position of the active tools (grinding surfaces).

    This results in a much higher achievable uniformity than was previously possible.

    - Leigh
    Last edited by Leigh B; 08-24-2012 at 07:56 PM. Click to view previous post history.
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

  9. #39

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    A Minox negative 8x11 mm requires more magnification that any other format to get a practical size print. The lens supplied with the Minox enlarger is a 4 element Tessar. The Tessar formula is capable of producing high quality images. Its main limitation is that the maximum aperture is restricted to about f2.8. There are many factors which contribute to making a particular formula a good lens. The number of elements is only one factor. It must be remebered that each additional element in a lens causes a reduction in contrast of the image. Until the invention of lens coating this effect seriously limited lens design. The loss of contrast can be reduced but never completely eliminated. One of those incovenient gotchas of the laws of optics.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  10. #40
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    Quote Originally Posted by Gerald C Koch View Post
    There are many factors which contribute to making a particular formula a good lens.
    The number of elements is only one factor.
    I was talking about real lenses, as in products available from manufacturers.
    My comments were not about academic exercises in a college optics design class.

    Manufacturers of enlarging lenses frequently had two product lines, one of four elements and one of six.
    The latter were of much higher quality, with tighter quality control and better corrections, as reflected in the higher price.

    Many cheaper four-element designs were available from various manufacturers, some quite reputable, others less so.

    The Minox was never recognized as a standard of image quality.

    - Leigh
    “Wise men talk because they have something to say; fools, because they have to say something.” - Plato

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