Upload & Sell: On
I'm in the process of evaluating a 200 1.8L for hopeful purchase; 'J' date code (1995), it looks great, focusses fast, is quite sharp wide open, and seems a good buy except...
I used a 36mm extension tube with it some this last weekend and found that there were fuzzy haloes around objects at wide-open apertures. I figured that, since depth-of-focus at 1.8 with tubes is hair-thin at most, that it was a focus problem, and needed some micro-focus adjustment. So, I've done that - with a Lens-Align - but I'm still getting the haloes. Today I set up the ubiquitous batteries and got out the old focus chart. I used a tripod, mirror-lockup, remote release, and 10x live-view manual focus, then looked at a few frames...
Below are three from each sequence, one full stop apart (I shot at 1/3 intervals). The fuzziness disappears completely by about f/3.2 in both batteries and chart. Also are a couple of "real-world" f/1.8 flowers from earlier in the week (today it's poured all day long, no outdoor time for me).
I've never heard of extension tubes causing such a thing; my understanding is that they shouldn't affect image quality at all. I feel like I've taken the focussing variable out of the question, and now I'm stymied...Anyone have any ideas? Is this a normal "issue" (for lack of a better term) with the lens?
Of course I would probably never use a 1.8 aperture for tube-assisted macro, but I'm wondering if this could be indicative of a problem that could surface later in some other way...and, naturally, I REALLY want to have no doubts about keeping this one...
(edit - I have to use two posts to get all the examples up)
(oh, and all these are 100% crops)
with 36mm extension tube
same as above
also with 36mm tube
Edited on Apr 04, 2013 at 11:28 PM · View previous versions