Originally posted by ChristianRock No, because you expose like a 1.8 lens, not like a 2.8 lens.
So, like it was said earlier, equivalence is for DOF and FL, not for exposure.
Equivalence will help describe Total Light, and that's more than DOF and FL - it also determines image noise and DR.
Thus a K-5 with the Sigma 18-35 f/1.8 will completely match a D800 with a 24-70 2.8 in the 28-52mm range - the D800 would have no noise/DR-related IQ advantage there - because the Total Light would be the same (which affects photon shot noise) and the sensor efficiency happens to be about the same (which affects read noise.)
I'm impressed that the Sigma has those specs while being a very sharp and not-too-expensive lens - I thought something was going to have to give when I heard the advance specs. Sigma has done well there.
If Pentax could come out with a series of similar
very fast/good lenses, there would be less (or no) reason for a Pentax FF body.
---------- Post added 10-10-14 at 09:48 AM ----------
Originally posted by Kunzite
FTR, you did that "pushing assumptions" yourself, several times. Others did it too, should I remember (again!) the recent moon shooting example?
What 'moon shooting', did I miss something?
Quote:
P.S. I'd really like to know what makes anyone think that, when switching formats:
- the shutter speed should stay constant
- aperture will be selected exclusively to obtain a specific DOF
- there are no other reasons which might dwarf wide-aperture DOF in importance
Equivalence doesn't require you to keep everything constant when shooting - it uses constant parameters simply to describe differences between formats. (I'm getting carpal tunnel typing that.)
Q: Isn't Equivalence all about DOF?
A: No, Equivalence is not "all about DOF", but it is very much about understanding that both DOF and noise are intimately connected to the aperture. That said, DOF, by itself, is still a critical consideration to the captured detail in the photo, since portions of the scene outside the DOF, by definition, will not be sharp, and all systems suffer diffraction softening equally at the same DOF.
Q: Doesn't Equivalence say that we should shoot different formats at the same DOF?
A: Not at all, and, in fact, quite the opposite. That is, one does not choose one format over another to get photos Equivalent to what one would get on another format. Rather, one chooses one format over another to get photos they could not get on another format, or get better photos than they could get on another format, assuming, of course, that differences in operation, size, weight, and cost are not significant enough to be the primary consideration.
Last edited by jsherman999; 10-10-2014 at 09:08 AM.