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  1. #1

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    Pentax 6x7 135 Macro Lens

    Hi all,

    I just received my new toy for my Pentax 6x7 (SMC 135 Macro lens). I've been looking for some info on it, without a lot of luck. I have a few questions for anyone who may have some experience with it:

    1) There are a series of number around the end of the lens (3.2, 3.5, 3.7...15, 30). What are they for?
    2) Sorry if this is a silly question, but what makes this a 'macro' lens? How does a macro lens differ from a regular lens?

    Thanks,
    Craig

  2. #2
    2F/2F's Avatar
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    I do not know about the first question, but often, macro lenses will have the magnification listed on them in addition to focusing distances. The 15 and 30 sound like focusing distances. I am unsure of what the three-point-whatevers are. It is almost certainly not magnification, though, as the numbers are too high for the lens to achieve without additional extension (unless it is a very special lens).

    As for the definition of a macro lens, it is a lens that allows 1:1 or greater magnification without the use of additional extension. However, it is often used to mean any lens that can focus more closely than most, even if it cannot achieve 1:1 magnification. The second use of it has become so common that you cannot assume a lens is capable of 1:1 magnification just because a manufacturer calls it a "macro" lens.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

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  3. #3
    pentaxpete's Avatar
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    I got an 'early' 135mm SMC macro Takumar with my 6x7 Mark II body cheaply and find it does NOT foucus to 1:1 unless I add the 6x7 Extension tubes and it is very poor definition at further distances. It's OK for portraits and close-up work though.
    <a href="http://www.flickr.com/photos/25850987@N03/3110887140/" title="Bubble-Santa-2 by pentaxpete, on Flickr"><img src="http://farm4.static.flickr.com/3066/3110887140_b5a3b85c95.jpg"

    <a href="http://www.flickr.com/photos/25850987@N03/3201466232/" title="Amanita jpg by pentaxpete, on Flickr"><img src="http://farm4.static.flickr.com/3260/3201466232_1d4635e45e_m.jpg" width="240" height="179" alt="Amanita jpg" /></a>
    An 'Old Dog still learning New Tricks !

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    A macro lens will retain corner sharpness and a flat focal field at high magnifications whereas simpler designs do not. Going to 1:1 is common for 35mm lenses but not so much medium format without extension tubes.

    Yes, you can put a lot of extension behind a simpler lens and get lots of magnification from it but you are also likely to get way more chromatic and spherical aberration than you would with a proper macro lens.

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    Often times macro lenses that approach 1:1 or are optimized along those lines have a near-symmetrical construction, which inherently counters distortion in many regards. a lot of macros for medium format fall into this category. the RZ 140mm macro comes to mind, as do some of the Olympus OM system macros, particularly their 80mm f/4 macro.

  6. #6

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    Thenks for the info everyone. One more question, I have a set of extension tubes on the way, how does the extension affect metering and exposure?

    Thanks again,
    Craig

  7. #7
    2F/2F's Avatar
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    Quote Originally Posted by ccross View Post
    Thenks for the info everyone. One more question, I have a set of extension tubes on the way, how does the extension affect metering and exposure?

    Thanks again,
    Craig
    If you are using an external meter, it does require additional exposure compensation to use extension tubes. If you are using an in-camera meter, extension tubes simply cause less light to reach the meter, just as less light reaches the film with the tubes, so while the exposure will change from what it would be without the tubes. The effect of the tubes is taken into account by the meter, so no additional adjustment is necessary.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

    - Rob Tyner (1944 - 1991)

  8. #8
    pentaxpete's Avatar
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    I found with the Pentax 6x7 Mk II and the extension tubes, the metering has to be done 'stopped down' method or it does not work properly -- I ruined some photos just after I got the MkII by relying on the built-in metering prism -- with my Mk I and a hand-held Weston Master V I had no trouble , just gave extra exposure than indicated to allow for the extension and photos came out perfectly !.
    An 'Old Dog still learning New Tricks !

  9. #9

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    Here's my understanding -
    1.) The numbers 3.2 - 30 on the lens denote the reduction ratio which is the reciprocal of the magnification - i.e. 3.2 gives a magnification of 0.3125 life size on the film.

    2.) The 135 "macro" is designed to focus closer than normal lenses - the minimum focusing distance is noted as 0.75 meters, whereas the 165mm lens minimum focus distance is ~1.6 meters. It also has a minimum f stop of f32, which is smaller than the f22 on several other lenses near it in focal length. This can allow greater depth of field at close focusing distances.
    Macro lenses are often assumed to give a magnification ratio of 1:1. In order to get that with the 135mm lens, you need to use the 3 extension tubes stacked to focus closer. I seem to remember that with the Pentax 67 II, I do get auto metering when using the extension tubes.

  10. #10

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    Thanks again everyone for the info. I don't have built in metering. I'm pretty new to macro, so sorry for the newbie questions. I understand the principle of why the light reaching the film plane is reduced by the extension tubes, but can someone explain or point me to a good book that outlines the method or calculation for the 'stopped down' method.

    Craig

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