1. Reminder: Please use our affiliate links for holiday shopping!

Lens characteristics at different distances to subject

Discussion in 'Open Discussion' started by MRM, Dec 16, 2015.

  1. MRM

    MRM Mu-43 Regular

    108
    Jun 9, 2013
    Seattle, WA
    Matt
    I was wondering if someone would be able to answer my question. I have heard from reading that some lenses perform better then others of the same focal length at different distances from the subject. Some times people say a lens is optimized for portrait or macro and that it looses sharpness or micro-contrast when focusing on more distant subjects. An example is that I read a review that said the 40-150 pro is not as good as the 50-200 at the same focal length for distant subjects. I'm not sure how this would work or if it is even true. If someone knew the answer and why it would be helpful I making lens decisions.
     
  2. Turbofrog

    Turbofrog Mu-43 Hall of Famer

    Mar 21, 2014
    Well, I cannot say why it is true, but I definitely know that it is true that lenses will perform differently at different focal lengths. An obvious example is macro lenses, which are optimized for close distances.

    But as another example, I can say that people often accuse the 14-140mm of being really soft at the long end. And I agree to a point, but I've noticed that it can be very sharp when focused close. However, near infinity it is not great - though it is also difficult to say whether having to shoot through so much additional atmosphere is part of the problem. It's hard to find any tele lens that will be sharp near infinity, but it has almost nothing to do with the lens itself at that point...
     
  3. kwalsh

    kwalsh Mu-43 Top Veteran

    775
    Mar 3, 2012
    Baltimore, MD
    Modern lenses have many moving groups in them and as distance (or equivalently subject magnification) changes the optical performance and aberrations also change because the relationship between all the optical elements changes.

    The big takeaway is all the internet test sites shoot rather small test charts to produce their reviews and the results at such a close shooting distance may not reflect the performance at longer distances. Good write up here:

    Notes on MTF measurements

    EDIT: I should add even if a lens has no independently moving groups (like older primes where the entire lens moved when you focused) you would still expect performance to vary with focus distance - the geometry of how image forming rays pass through the lens is quite different at infinity focus and say 1:1 macro focus.
     
    Last edited: Dec 16, 2015
  4. MRM

    MRM Mu-43 Regular

    108
    Jun 9, 2013
    Seattle, WA
    Matt
    Thanks. That helps me understand it a little more. I wonder if any testing site shows how a lens performs at infinity. Im guessing just comparing photos taken at the same time under the same exact circumstances is the best way to compare. I have to say I have heard that the 40-150 pro is not as good at infinity but I've never seen that in my photographs.
     
  5. Turbofrog

    Turbofrog Mu-43 Hall of Famer

    Mar 21, 2014
    If you've never seen it, don't worry about it. Simple as that!
     
    • Agree Agree x 1