Originally posted by *isteve You have some very specific lens choices which really dont apply to many people. I get as much "bokeh" from an APS camera because I can access faster tele lenses for the same money.
A 50 F1.4 is a lot cheaper than an 85 F1.4 last I checked, and has almost the same DOF as a 77 F1.8 would on an FF camera....for much less money.
The 50-135 F2.8 on a K20D provides the same DOF options as a Canon 70-200mm F4 on a 5Dmk2, which is about the same price (in IS mode). The Nikon 70-200 F2.8 gives a stop more DOF but is vastly bigger and more expensive (as is the Canon version). The Sigma 70-200 F2.8 is also much heavier and more expensive than the Pentax.
My FA* 200 F2.8 has the same DOF as a DA* 300 F4 would on an FF camera.
Again, same size and weight. So yes you can get shallower DOF on a FF camera, but only by buying faster long glass which is more expensive and heavier than the APS equivalent.
OK, for wide angle lenses, then its harder to find fast glass. However I use wideangle more for landscape work. In this case, I usually work stopped down and the greater DOF of APS allows me to use apertures which are slightly wider and faster (closer to MTF max) than what I would need on FF. This means sharper, especially in combination with SR.
So sorry but I dont buy this DOF argument at all.
I wish I was as satisfied with the crop format, it would save me a lot of thinking lately, lol.
Ok, using our logics, an example then. We have a sparrow on a branch. Lets say on the K20, it would frame up nicely with a DA*200. In order to frame it as nicely with a FF, we're going to require a 300 is what you're saying if I have understood you correctly and thats larger, more expensive... and true. My argument was that you could work closer to the subject with a FF (which you would need to do to fill the frame) so as you close in to the bird with the same 200mm lens, you fill the frame with more detail while your DoF continues to get shallower. But its a bird, lets say in our example a fixed working distance required.
The FF shooter is now using the 300 as you suggest. Its higher magnification power is captured entirely on the larger sensor (assuming for the sake of argument that pixel density is roughly equal) so you still get a much 'larger' sparrow (more detail captured) similar to having used the 200 from closer in
and because you are working closer to the MFD of the 300 than of the 200 at equal working distance - you get shallower DoF.
No matter how you slice it, if framing is equal, you're always going to have a shallower DoF with the larger sensor either by virture of working closer to your subject or by using a longer focal length lens closer to its MFD.
On the size/weight side of things, to be fair we must consider the opposite side of the focal range. I wouldn't need to buy a 14/2.8 for example, I could buy 21/2.8 instead. Instead of the 31, I buy the 43, etc, etc.
Further, if you wanted to keep the smaller lenses and your current working distance just as with APS-C, I'd suggest either the A900 or 5dII. Given our above scenario, you could use the 200 just as with the crop format from an equal working distance and end up with a lot of moose pasture around the side of your bird. With the extra MP, you could manually crop what was not required of the final image. Granted in doing so you lose the advantage of having started with 20+ MP, you end up with something approaching what you started with in the same crop area as we're working with on the K20. Not ideal of course, but if one really wanted, I think one could have all the same size/weight/cost savings of APS-C. This isn't meant to be practical, but its possible, though I don't think any person alive would buy the FF to neuter it in such a way.
But having said all of this, I must state that my logic was only ever meant to explain my current frame of mind regarding the FF market. The logic only applied to my choice, given my preference for shooting and wasn't meant as a general recommendation. Each will spend what they want in this regard - I know where I'll be spending next, but I hope its on a Pentax.