rvh23
Offline
Upload & Sell: Off
|
 Re: FM Review: Sony FE 12-24mm f/2.8 GM | |
chiron wrote:
rvh23 wrote:
inksandpaper wrote:
rvh23 wrote:
Thanks very much for all this additional information and taking the time.
I don't have a good explanation for the significant distance readout disruption, but there is no way the shimming material is a hundred, let alone several hundred microns thick. The only thing I can think of is that when I punched a hole through it for the screws to pass through it left a burr that acted to increase the effective thickness. But I would expect a shim that is several hundred microns thick and placed in one corner to be way too much adjustment given the lens was not severely asymmetric in the first place.
In relation to the induced FC, no I unfortunately don't have images I can show. It was just an anecdotal observation through the EVF, because by that stage I had already decided I wasn't going to be keeping the lens. But it seemed quite obvious even at 24mm where the lens unshimmed is essentially flat field.
No problem! Yes, I am doubtful that the shimming material is that thick. The degree of misalignment looks subtle, less than 50 microns by my very rough estimate. But it also looks decentered, not just tilted or swung, again I'm guessing from your crops. One needs to see the full image and the test subject needs to have certain qualities for one to be absolutely sure.
There might be something to say about your long-suffering quest for a great copy. Our experience with the Sigma 14-24 2.8 DG DN was similar. Joe Holmes tried 8 (!) copies and all were grossly asymmetrical. I tried only one and it was too. That's 9 out of 9 all bad, and not slightly bad. Like really bad. I have no idea how anyone gets good copies, surely our luck cannot be this awful. Fred seems to have an amazing copy to kill for. I recall seeing one other great copy on this forum. Joe remembers seeing two others, so we know of a total of 4 copies that are supposedly really great, but we can't seem to find them (I've given up myself, since I don't usually shoot super wide anyways). One would hope the GMs are a little more consistent in that regard, given the cost. Cameras today are too sharp and unforgiving on the optics.
When you say the spacing and allignment shouldn't affect FC, I don't at all doubt your expertise, and even less so the folks at lensrenatals. But my recollection of my adapter shimming days, and also discussion here on FM, is that FC often was affected. But it's possible I'm misremembering the details.
I too remember seeing such statements here from time to time, which has always puzzled me that folks were observing such a phenomenon. Sounded like observational error then.
It took me four copies before I had a Sigma 14-24 DG DN that I was happy with, and I thought I was having worse luck than most, but perhaps not judging from your comment.
Increasingly, from reading your posts, I'm thinking something must have gone wrong with my internal shim on the GM. Since I was waiting for copy #4, this afternoon I went back and tried mounting shims on the camera's lens mount instead where it's easier to be sure the shims are flat and don't need holes. This time it took about 4 layers of the foil (so maybe 40um) in the most-adjusted corner. Results showed about the same improvement as for my internal shimming exercise, but the distance readout and FC were not noticeably affected now. 
It's now very good at 14mm, not bad at 12mm, but all four corners are softer than I'd like at the long end. My 2nd copy was actually superb at 24mm, but at the wide end had one corner that didn't sharpen up enough even stopped down. So the search continues.
I've pretty much commited to trying as many copies as it takes (hopefully not 10) because this focal range is where I shoot the very large majority of my landscapes.
I'm not sure that I am comfortable with the practice of partially disassembling and then experimentally shimming and altering the plane of focus of multiple lenses that will then be returned to be sold as new to other buyers.
I think you misunderstand. In Australia, it's very hard to return a lens to most vendors unless it is obviously faulty. I would never try to return a lens that I have adjusted in any way. For these GMs the only option I have when they are reasonable, but just not to my satisfaction, is ot resell them usually at a loss despite having had essentailly no use.
In any case, I only tried adjusting one lens (and returned it to its original condition in the end) and I don't plan to do it with any other copies unless I know for sure I am keeping it and that it is minimally decentered. It's just too much effort.
|
