I have both of those lenses. Working distance on the 50mm is pretty
tight if you want magnification at 1:1 or so. The 100 mm gives you a
lot more room.
I bought my 50 for use in extreme macro situations - reverse mounted on
extension tubes or bellows. You can easily get to 4x to even 10x
magnification without getting too out of hand with the extension when
reverse mounted. The smaller 50mm lens is also easier to use on
extension - less wegiht, less awkward. As a general purpose lens 50mm is
also a very useful. For bugs and even a lot of botanical work the short
working distance of a 50 can be a problem - it gets harder to control
lighting (especially flash), harder to not get a shadow on the subject
and (for bugs etc) harder to not scare the subject away.
I use the 100mm far more. Much better working distance which addresses
the issues noted above. The narrower angle of view makes it easier to
control the background as well. When I run into larger subjects where I
cannot use the A* 200mm macro (my main workhorse) because the working
distance is too great, I will drop down to the 100mm. It is very rare
that I have needed to go to the 50, though in a few cases it happens. I
use the DFA 100 far more than the 50.
I believe that some tests show the 50 as sharper than the 100. I've not
compared my two lenses - I use them for very different subjects. The DFA
100 is excellent stopped down a but is a little softer wide open, IMO.
DOF should be the same at any given magnification and F stop, so at 1:1
there would be no difference. But - it is a lot easier to shoot at 1:1
with the 100, because you are not right on top of the subject.
Mark
On 2/6/2014 2:35 PM, Glen Berry wrote:
Please help me decide on a used Pentax macro lens. I've narrowed it
down to these two used lenses:
50 F2.8 SMC MACRO D FA
100 F2.8 SMC D FA MACRO
What are the pros and cons of the 50mm vs the 100mm?
What applications would the 50mm be best for?
What applications would the 100mm be best for?
Does either of them have a reputation for being noticeably sharper
than the other?
Would the 100mm exacerbate the already shallow depth of field inherent
in macro photography, in other words, would the 50mm have greater
depth of field at 1:1 magnification?
Thanks, for any suggestions!
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