Chromatic aberations with SAL1680

[moorefam]

Hello,
Sony have rebuilt my SAL1680 Zeiss lens and replaced several mechanical parts. It still has more chromatic aberrations than I would like and a stock agency has rejected some of the images because of this. I now correct them in Photoshop Elements 5. The problems occurs significantly at other settings than at 16mm at the edges. I am aware that no lens is perfect but I would like to be sure that I don't have a poor example. I would be grateful if an expert can cast there eye over a few images and give an opinion.
Equipment is Sony A700, Sony 16mm-80mm lens, no sharpening and taken RAW at 200ASA,f20 at 1/80 at 20mm, steady shot selected. Converted to TIFF then JPEG. It could be a little sharper as I focussed for max depth of field.

Top RHS of frame http://www.moorefam.plus.com/DSC01618-topRHS.jpg
Middle frame http://www.moorefam.plus.com/DSC01618-middle.jpg
Complete image http://www.moorefam.plus.com/DSC01618.jpg

The next image is full size facing our hedge with a bike and other objects in the field of view.
http://www.moorefam.plus.com/sony_16_3.5.JPG

Sorry I still haven't worked out how to insert images properly.
If further images or crops would be useful I would be happy to oblige.

I am wondering about getting the Sigma 10mm 20mm lens to compliment the Sony lens as I have briefly tested it and it has less CA than my Sony 16mm - 80mm lens and as I use 16mm a lot, it would be in the middle of its range. I would also like to have a wider angle available. Any comments welcome.

[Dr. Harout]

May I ask what was the problem initially to have the lens rebuilt and above that to replace mechanical parts?

[moorefam]

I returned the lens because I was not happy with the extent of chromatic aberrations, particularly at 16mm, but also at other focal lengths. That was the main reason. I also noted that at 80mm the image shifted slightly going from zooming in to zooming out. This was slightly annoying but for that alone I would not have made a fuss. On return from Sony the zoom mechanism has been a bit jerky i.e. slightly stiff but it is freeing up.

In test reports one reads that CA extent is say 1.5 pixels wide but I have a hard time relating that to what I am seeing as at the edges the images are slightly blurred anyway so the CA extends across several pixels. Therefore I am at a loss to know if my lens is as good as I can expect or not. I tried it against the Sigma 10mm 20mm lens at 16mm and the Sigma was better for CA.

I am also interested to know if it is as sharp as it should be. The last image I posted is a better example as I focussed on the hedge where as with the other images I was focusing for maximum depth of field. I can post other images if anyone is interested. I have found my stock agency is very hot on CA and lots of other issues so that is why I have become concerned about the lens quality.

[David Kilpatrick]

It is looking pretty much as they do - your corners are maybe a touch softer than I would expect, but the chromatic aberration is not very strong, and it is soft-edged. Usually this lens has very crisply visible colour fringes. You can not really correct this in Photoshop Elements, as far as I know. It's necessary to use Lightroom or CS3 to get the proper raw conversion chromatic abb correction, which greatly sharpens up results and removes it entirely. I normally up-res images to 48-50MB for library use and the 16-80mm always passes (never had problems) but I am also very careful with the workflow and correct each shot individually. For what it's worth, I have found no better results from any comparable lens on any system. The Nikon 16-85mm is very good and has no chromatic abbs, but it is not as sharp as the Zeiss centrally.

David