Old Sigma 16mm focus confirm
Posted: Tue Feb 10, 2009 1:04 pm
Back when only using the A700, I had an 8mm Peleng which 'went bad' (impossible to focus) and got thrown away eventually, but one shot with it secured the front cover of our town's Ordnance Survey map and the fisheye views on Alamy keep getting zooms (means people look at them more than other views). I can't justify a new Sigma 15mm or Sony 16mm, and the Russian 16mm is about £150 - not that I would now trust it for focusing. I was looking at the secondhand M-AF stock of Ffordes, one of the better UK dealers with a used stock website, and found an acceptable condition Sigma Filtermatic 16mm f2.8 'Focus Aid and Programmable' lens for £89. This is almost as old as the M-AF mount, I guess it would be 1987-90. At that price, with focus confirmation, had to get it.
Here's the result at f/11:
http://www.pbase.com/davidkilpatrick/image/109072524 for full size A900 image
At f2.8 it is very sharp indeed over the centre circle of maybe 30mm diameter, and very soft beyond this, though there is a sharp core to the image. f4 shows only a minor improvement, at f5.6 the edges are still fairly soft, by f8 it would be usable for most subjects, f11 is almost there and still very sharp centrally, f16 really improves the edges (they become properly sharp to the corners) but loses a little centre sharpness, f22 is more even across the frame and is actually usable.
Here is an f/22 shot taken at the minimum 6 inch/15cm focusing distance - and they mean the film plane, too, the winter aconite is maybe only 2-3 inches from the front glass:
http://www.pbase.com/davidkilpatrick/image/109072768
The flare resistance is not bad for a lens which can be taken apart and has a 22.5mm plain UV filter screwed into the centre. You can bayonet the entire front group off the lens front, and swap the filter, but this example did not come with a case, or with its original front cap, or filters. Because it has this internal filter, it would be possible to fit an infra-red gel, and the lens focusing scale also has the IR position marked. Here is a direct into the sun shot showing the extent of reflections and flare patches:
The whole lens is very well constructed, solid metal, with a top quality bayonet mount, five-contact communication, and it does work with focus confirmation on the A900. The camera displays MF when the lens is mounted, and the focus confirmation light works (presumably the centre f2.8 sensor gets used, but there's a fair amount of tolerance). The Sigma 24mm f2.8 Focus Aid lens from the same period has a very good reputation, and should also work.
The lens size is comparable to the Sony, maybe slightly smaller, rather than to moden Sigma alternatives, and it makes a great low-cost addition to my outfit just to secure the fisheye rendering. I do not think that it is clean enough at the edges to do a de-fisheye operation on it, even at f16. On APS-C it would not be much use but the entire image area would be very sharp.
David
Here's the result at f/11:
http://www.pbase.com/davidkilpatrick/image/109072524 for full size A900 image
At f2.8 it is very sharp indeed over the centre circle of maybe 30mm diameter, and very soft beyond this, though there is a sharp core to the image. f4 shows only a minor improvement, at f5.6 the edges are still fairly soft, by f8 it would be usable for most subjects, f11 is almost there and still very sharp centrally, f16 really improves the edges (they become properly sharp to the corners) but loses a little centre sharpness, f22 is more even across the frame and is actually usable.
Here is an f/22 shot taken at the minimum 6 inch/15cm focusing distance - and they mean the film plane, too, the winter aconite is maybe only 2-3 inches from the front glass:
http://www.pbase.com/davidkilpatrick/image/109072768
The flare resistance is not bad for a lens which can be taken apart and has a 22.5mm plain UV filter screwed into the centre. You can bayonet the entire front group off the lens front, and swap the filter, but this example did not come with a case, or with its original front cap, or filters. Because it has this internal filter, it would be possible to fit an infra-red gel, and the lens focusing scale also has the IR position marked. Here is a direct into the sun shot showing the extent of reflections and flare patches:
The whole lens is very well constructed, solid metal, with a top quality bayonet mount, five-contact communication, and it does work with focus confirmation on the A900. The camera displays MF when the lens is mounted, and the focus confirmation light works (presumably the centre f2.8 sensor gets used, but there's a fair amount of tolerance). The Sigma 24mm f2.8 Focus Aid lens from the same period has a very good reputation, and should also work.
The lens size is comparable to the Sony, maybe slightly smaller, rather than to moden Sigma alternatives, and it makes a great low-cost addition to my outfit just to secure the fisheye rendering. I do not think that it is clean enough at the edges to do a de-fisheye operation on it, even at f16. On APS-C it would not be much use but the entire image area would be very sharp.
David
