Page 1 of 2 12 LastLast
Results 1 to 10 of 20

Thread: MTF determination: Rodenstock's answer

  1. #1

    Join Date
    Sep 1998
    Location
    Loganville , GA
    Posts
    14,409

    MTF determination: Rodenstock's answer

    There have been unsubstantiated claims of how Rodenstock computes MTF curves with some claiming that the MTF curves are design points rather then actual performance curves. Obviously this is not a sensible approach to making curves available so we asked Rodenstock for their comments.

    Their response is:

    "calcuted. The reality is when you measure MTF curves on the MTF machine with a lens it could have a tolerance of -10 % at the most. In other words there is a difference when you measure the MTF together with the lens."

    Hopefully this response will end the misguided, unsubstantiated and uneducated claims of theoretical curves.

    Editor: See followup at http://hv.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=004ZdS

  2. #2

    MTF determination: Rodenstock's answer

    That response seems to indicate that the MTF curves exactly are theoretical (calculated), and that an actual lens can be 10% down from them.Doesn't it?

  3. #3

    Join Date
    Sep 1998
    Location
    Loganville , GA
    Posts
    14,409

    MTF determination: Rodenstock's answer

    Let's be real. Obviously when a company publishes in a brochure or on the internet or anywhere else their MTF curves it would be impractical and impossible to publish the curves of every lens manufactured now, then or in the future.

    Rather then what some were saying and drawing design curves. Rodenstock posts curves from a production lens. They state that any lens will be within -10% of that production lens.

    That means that any lens will equal that curve or be - 1%, -2% or, at the worst, -10% from the posted curve.

    That is pretty straight forward. Not engineering curves, but curves from an actual sample that tests within - 10% of every other lens of that type.

  4. #4

    Join Date
    Dec 1998
    Posts
    101

    MTF determination: Rodenstock's answer

    Bob,

    I disagree. Your quote specifically says "calculated." Now, if your quote had said "measured" or "a representation of a statisitcal sampling" they you could claim that the curves are from real measured data.

    The way I read the quote, the Rodenstock comments appear to imply that the curves are precisely theoretical, and have been calculated based on the theoretical performance of the optical elements, etc.

    Personally, I can't understand why you felt the need to use the tone and language you have used. It does nothing but create animosity and raise people's hackles. I don't believe anyone is trying to imply that theoretical curves are misrepresentations of the lens performance, and even if they were, since there are no measured curves out there, what's the point in debating this?

    Both German lens manufacturers use theoretical curves, and the Japanese don't publish any curves that I'm aware of, so where does that get you? It's simple, and it's a point you have brought up in the past, Bob, you have to go out and test a lens under real-world conditions and determine if it is suitable for you own particular needs. That's the ultimate measure of a lens, not some curvey lines on a chart that nobody can compare to anyone else's since nobody uses the same units or metrics anyway.

    ---Michael

  5. #5

    Join Date
    Sep 1998
    Location
    Loganville , GA
    Posts
    14,409

    MTF determination: Rodenstock's answer

    Sorry Mike.

    I said that a production lens is tested. And that curve will be within - 10% of the other lenses in the series.

    Nothing theoretical. These are NOT the curves that the designers dream of.

    They are the curves to be expected from an actual lens that is purchased across the counter.

    What of this do you find difficult to comprehend?

  6. #6
    Founder QT Luong's Avatar
    Join Date
    Aug 1997
    Location
    San Jose, CA
    Posts
    2,337

    MTF determination: Rodenstock's answer

    I find it difficult to comprehend why they say "calculated" if your interpretation is to be right. Maybe you can ask them to elaborate a bit more, possibly show them the comments which were made here, and follow-up on this thread with the detailed answer ? This way, we will learn something instead of speculating on the obscure meaning of a paragraph.

  7. #7

    MTF determination: Rodenstock's answer

    Bob,

    Based on the quote you provide above, I still have no idea how Rodenstock arrives at their published MTF curves. The quote is incomplete, out of context and in broken English (I'm not blaming the source of the quote, since English is likely not his/her native language, but it makes it difficult for some of us to understand what is being said).

    You claim, based on the above quote that the Rodenstock MTF curves are produced by measuring a single lens and that all others will then be within -10% of that measured lens. That may be true, but it is certainly not the conclusion I arrive at based on the above quote. All I get from the above quote is that something is (or is not) "calculated" and that lenses measured on an MTF machine can vary by as much as -10%. What is left to the imagination is what exactly is (or isn't) "calculated", and if the -10% tolerance is due to the lens to lens production variations, or the accuracy of the tester.

    If as you say, one lens is measured and the curves based on that lens, how is that one lens selected? Is that lens the best (if so, how do they know if they don't measure the others), the worst, or "typical"? It has to fall somewhere on the curve, but where? Is the -10% figure then based on statistical samples (measuring more lenses) or theoretcial caclulations? Is the -10% (and why isn't it + or - 10%?) actually the variability in the performance of the lenses, or is it due to the test environment?

    I'm not deliberately being a pain here, I really am interested in learning how this is done (or at least a clarification of the above quote). Without the complete quote, and the proper context, I am left with more questions than answers. For example, you started the quote with a truncated sentence ending in the word "calculated". It sure would be nice to know what the rest of that sentence said. Could be anything from "The MTF curves are measured, not calculated" to "This is how the MTF curves are calculated". You provide this quote as proof that the Rodenstock MTF curves are based on measured data and not theoretical models or computer simulations. Unfortunately, the evidence is incomplete and therefore proves nothing (BTW, I'm not saying what you have stated is false, just that it's impossible to tell based on the quote you provided).

    Perhaps you could clear this all up by posting the entire exchange, including both the question and the answer, to put it all in context. I don't think the confusion is caused by any animosity or stupidity on anyone's part, it's caused by insufficient information to reach a definitive conclusion one way or the other. There was obviously more to the exchange than the brief quote you posted. Why not post the rest and hopefully enlighten the rest of us.

    Kerry

  8. #8

    Join Date
    Sep 1998
    Location
    Loganville , GA
    Posts
    14,409

    MTF determination: Rodenstock's answer

    Kerry,

    That is the complete applicable post as to the MTF question.

    The remainder of the message does not address the question,

    The statement is quite clear.

    A production lens is tested.

    All lenses of the series will be within - 10% and the published graph.

    If you want specific answers to specific questions ask them.

    But don't read between the lines.

    The lens tested iis reular production and not some imaginary curve that some allude to incorrectly Please bear in mind when I post their direct answers that English to the factory is a second language. The answer is direct and to the point but thet don't speak English or write English the way a native American English speaker does.

  9. #9

    MTF determination: Rodenstock's answer

    Bob,

    It may be clear to you, but it is not clear to me. Hence my questions. No where in the quote does it state that a production lens is tested. That is your interpretation of the quote.

    The exact quote is:

    "The reality is when you measure MTF curves on the MTF machine with a lens it could have a tolerance of -10 % at the most."

    To me, that just means there is a 10% tolerance in the measurements. It doesn't state the source of the 10% tolerance, and it certainly doesn't state:

    "A production lens is tested.

    All lenses of the series will be within - 10% and the published graph."

    That may be your interpretation based on your conversaations with eth factory, and it may very well be true, but it's not what is stated in the quote. In fact, no mention of production lenses or MTF charts is even mentioned in the quote.

    I did ask specific questions and you chose to ignore them. So, I won't bother to re-ask them.

    Kerry

  10. #10

    Join Date
    May 2006
    Location
    Arizona
    Posts
    377

    MTF determination: Rodenstock's answer

    >"calcuted. The reality is WHEN YOU MEASURE< - as opposed to calculate (not measuring).

    >MTF curves on the MTF machine with a lens it COULD HAVE a tolerance of -10 % at the most.< - WE HOPE

    >In other words there is a difference WHEN YOU MEASURE the MTF together WITH the lens."< - as opposed to not measuring. How would you MEASURE the MTF WITHOUT the lens?

    Clearly they are stating that published MTF curves are calculated.

Similar Threads

  1. Lines Learing (Film answer to Pixel Peeping)
    By Bill_1856 in forum Lenses & Lens Accessories
    Replies: 4
    Last Post: 20-Nov-2005, 14:04
  2. APO Ronar 300/9 age (and generally Rodenstock's)?
    By Michael M. in forum Lenses & Lens Accessories
    Replies: 3
    Last Post: 30-Oct-2003, 18:17
  3. Schneider or Rodenstock's lens
    By lj in forum Lenses & Lens Accessories
    Replies: 12
    Last Post: 1-Jun-2001, 12:07

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •