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Making sense of lens markings..

Discussion in 'Open Discussion' started by TonyG, Jan 23, 2013.

  1. TonyG

    TonyG Mu-43 Top Veteran

    581
    Oct 15, 2012
    Ontario Canada
    I am looking to buy a manual macro lens but when I search I get this type of information. For example
    VIVITAR AUTO TELEPHOTO 135mm 1:2.8 CAMERA LENS
    1:2.8????
    Does that mean a f stop of 2.8 but what does the 1 mean that precedes the colon.
     
  2. Ned

    Ned Mu-43 Legend

    Jul 18, 2010
    Alberta, Canada
    Yes it does. Maximum f-stop is f/2.8, just like you thought.
     
  3. TonyG

    TonyG Mu-43 Top Veteran

    581
    Oct 15, 2012
    Ontario Canada
    So what is the significance of the number 1
     
  4. ~tc~

    ~tc~ Mu-43 Hall of Famer

    Oct 22, 2010
    Houston, TX
    Practically everyone marks lenses that way. Curious to hear if there's a reason
     
  5. usayit

    usayit Mu-43 Hall of Famer

    Aperture value is simply a formula that expresses Area of pupil opening as a ratio to focal length. I believe the 1: signifies a ratio.. just a different way of expressing it in a fraction.
     
  6. LeoS

    LeoS Mu-43 Top Veteran

    517
    Aug 6, 2012
    CMIIW but that's a mathematical notation because aperture size is calculated (as a ratio/fraction) to the size of the lens opening.

    EDIT: oops should've refreshed my tabs before typing my reply...
     
  7. TonyG

    TonyG Mu-43 Top Veteran

    581
    Oct 15, 2012
    Ontario Canada
    So if I get a 1:2 macro is that equivalent to a 1:1 macro because of the M43 crop factor?
     
  8. Stephen

    Stephen Mu-43 Regular

    28
    Jan 2, 2013
    The answer is yes and No at the same time!

    Any lens focused at it's focal length will give a one to one ratio for size, with micro 4/3 it will still be at 1:1, but not a full frame due to the crop factor.

    The, say for example, 1:2.8 is the correct way to express the aperture in terms of a ratio, and this is not connected to macro sizes.

    Simply putting, saying F2.8 was a trade marketing change from the 1950's onwards.

    The Micro3/4 format does not alter the way a lens operates, a lens appears to be doubled in focal length, and without affecting the aperture, as that remains the same ratio despite the cropping factor. This is a distinct advantage in doubling, the aperture remains the same.

    So for macro work, the ratio of magnification remains as usual for full 35 mm frame lenses, only the crop factor alters the apparent image size.

    Stephen
     
  9. Stephen

    Stephen Mu-43 Regular

    28
    Jan 2, 2013
    And I should add, not all lenses are marked with F stops, they may be marked with T stops, which is a way of exactly expressing the real amount of light the lens transmits.

    F stops are mathematical formulae, a simple ratio, and they seem to express the amount of light gathering power of the lens, but in the real world there are losses due to the glass, coatings and glued surfaces in a lens.

    Cine cameras for Pro use, in say Hollywood, are marked in T stops to allow swapping of lens, and for the cameraman to be sure the lens expose the film the same after any changed lens..

    Very high class lenses for view camera like Alpa are marked in T stops for the sake of accuracy.

    So a lens designed for a F1.8 aperture would be marked T2.2 etc., but most non professional users have never bothered with these small differences.

    Also zoom lens makers fight shy of marking T stops as it reveals the large inherent light losses in zoom designs a little to much!! A 1.8 zoom could actually be T3.0 etc.

    Stephen
     
  10. David A

    David A Mu-43 All-Pro

    Sep 30, 2011
    Brisbane, Australia
    Almost right.

    The aperture value is obtained by dividing the focal length of the lens by the diameter of the lens opening so it doesn't relate area of pupil opening to focal length, it relates diameter of pupil opening to focal length.

    The ":" marks "1:2.8" as a ratio and tells you that the focal length of the lens is 2.8 times the diameter of the maximum lens opening.

    The correct way to write the stop number is to put a "/" between the value and the "F" because "F" stands for focal length and the "/" is a divide symbol and "F/2.8" means that the maximum lens opening is the focal length of the lens divided by 2.8.

    Long standing conventions for how you specify the light gathering power of a lens.
     
  11. arentol

    arentol Mu-43 Veteran

    269
    Jun 29, 2012
    As Stephen said, yes and no...

    The lens is and always will be a 1:2 lens. A 1:1 lens of any kind will have twice the macro capability of that 1:2 lens on your 4/3rds camera. So no, it is not equivalent to A 1:1 lens.

    However, if you took a shot with a 1:2 macro lens on your 4/3rds camera, then took the same shot with a 1:1 macro lens on a 35mm camera the two shots would be essentially equivalent in terms of macro magnification. So yes it is equivalent to a 1:1 lens, if used on 35mm format only.

    The trick is to realize that no matter what a lens is always exactly what it is. Changing formats doesn't change the lens in the slightest, and all differences in the final image are caused by the format change, not the lens.
     
  12. nickthetasmaniac

    nickthetasmaniac Mu-43 All-Pro

    Jan 11, 2011
    As others have said, it just indicates a ratio of focal length to maximum aperture diameter.

    So, a 50mm lens with a 1:2 aperture has a max aperture diameter of 25mm.

    If it had a 1:1 aperture it would be 50mm.

    Likewise a 100mm lens with 1:2 aperture would have a 50mm opening and so on. Do you follow?

    The part before the ':' usually gets dropped for simplicity.

    Technically no, actual magnification doesn't change across formats, even though perceived magnification does. This is pretty complex and has been covered in other threads (search if you want to know more). Anyway, '1:1' or '1:2' in macro terms has nothing to do with aperture.
     
  13. TonyG

    TonyG Mu-43 Top Veteran

    581
    Oct 15, 2012
    Ontario Canada
    I get it now thanks. I've always wondered how the f stop was calculated.
     
  14. Cruzan80

    Cruzan80 Mu-43 All-Pro

    Aug 23, 2012
    Denver, Co
    Sean Rastsmith
    We are getting into equivalency talk again. 1:1 means that something x across in real life shows up as x across on the physical size of the sensor. 1:2 means x real life, x/2 size on sensor. The crop value doesn't magically allow you to make them the same size. It just gets rid of the background area. If something was 16mmx16mm, and shot with a m43 and FF camera, it would still be 16x16mm when shot with a lens set on 1:1. 1:2 means it would show up on the sensor as 8x8mm. When you get into printing something, and relative values of magnification for printing, then you could get into where the shot could be perceived as the same look (m43 has to be blown up ~2x as big to have the same physical size as a print based on ff sensor), but it is still not 1:1.

    The best recommendation I have received is that I have a m43 camera. Knowing what the lens will do on something else I don't have doesn't help me. Learn what they can do on the camera you have.
     
  15. mattia

    mattia Mu-43 Hall of Famer

    May 3, 2012
    The Netherlands
    Go to Wikipedia for a good explanation of F numbers. The simple explanation for why a smaller F number is a faster lens (= more light, wider aperture) is precisely because its a ratio. 1/1.0 is a bigger number, 1/5.6 is a smaller number.

    Just so we're clear, and before folks get too confused, the 1:1 macro thing has nothing to do with the F number on a lens. The only similarity is that they're both expressed in ratios.
     
  16. Armanius

    Armanius Mu-43 All-Pro

    Feb 23, 2010
    Houston
    Muttley
    Now I remember why I got kicked out of my math class in HS. This is way beyond my pay grade!!
     
  17. carpandean

    carpandean Mu-43 Top Veteran

    827
    Oct 29, 2010
    Western NY
    It really seems like lenses should have both listed. Consider two lenses with the same focal length. If they have the same F stops, but different T stops, they will have the same DOF, but one will be brighter. If they have the same T stops, but different F stops, then they will be equally bright, but have different DOF. It's kind of like the comparison of F stops from :43: to its FF equivalent. If we consider equivalent FOV lenses (say, 50mm on :43: and 100mm on FF), then an F/1.4 lens on :43: will have the same DOF as an F/2.8 lens on FF, but will be brighter than the F/2.8 on FF.
     
  18. TonyG

    TonyG Mu-43 Top Veteran

    581
    Oct 15, 2012
    Ontario Canada
    Thanks it's like I'm taking a photography course..awesome..
     
  19. arentol

    arentol Mu-43 Veteran

    269
    Jun 29, 2012
    And my answer told him what a lens can do on his 4/3rds camera. I explained quite clearly that his 1:2 lens would still be 1:2, no matter what he did. I feel I was much more clear about this than you were.

    The reason I went into equivalency was because he asked about that. Therefore I explained the only manner in which the magnification of a 1:2 lens would be equivalent to a 1:1 lens is when comparing to a 1:1 lens used on a 135 format camera. This is entirely correct.

    Also you do not need to print to perceive the magnification as the same. Lets say you have two shots of the same 35mm wide insect. One taken with a 35mm camera and 1:1 lens, therefore filling the frame with the insect. The other taken with an m4/3rds camera and a 1:2 lens, therefore filling the frame with the insect. The apparent magnification in each image is precisely the same. If you then viewed the images on your PC full screen, posted them at the same size on the internet, or anything similar, they would always have the same apparent magnification. There would be no need to print them to see this, and so it does indeed matter all the time, every time.
     
  20. Cruzan80

    Cruzan80 Mu-43 All-Pro

    Aug 23, 2012
    Denver, Co
    Sean Rastsmith
    I wasn't trying to correct anything you posted, just elaborate. And as far as the perception, it only matters if you have both a Full frame camera, and a m43 camera. I only have m43, so talking about what it "would be like" isn't helpful to me. Talking about what I see when I take a picture is helpful, be it DoF, magnification, etc, and therefore I focus on what it does on my m43 camera ONLY. I was offering the same advice to the OP, as he seems to be fairly new to photography, and probably doesn't have both a m43 and a FF camera.