What I have found is that while it works fine as an A-series lens, and therefore allows matrix metering, I don't trust the A setting in program mode. A number of exposures I took with the above combo were several stops underexposed, although the viewfinder readout reported what seemed to be a correct exposure. When I tried selecting the aperture via the body with the lens on A, it did look like it was a bit off in the middle apertures.
The adaptall mount itself isn't confidence inspiring mechanically; it's tricky to keep the little tabs properly in place when rotating the f-stop, and you have to be careful. I find this to be true with the adaptall Pentax ES mount as well.
So I use the 90/2.5 macro in aperture priority mode, which makes sense for this lens anyway, since what I'm usually looking for is depth of field control. But I don't trust it on A where the camera sets the aperture. Since an A lens needs to be on "A" to work properly with the *ist D, that's what I would worry about.
Has anyone else had issues with adaptall lenses set on "A" working accurately with program and shutter-priority modes on Pentax cameras?
Joe
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----- Original Message ----- From: "J. C. O'Connell" Subject: *istD and Tamron Adaptall2 lenses?
> If the tamron adaptall2 PK-A mount is truly pentax "A" > compatible, then shouldn't all the wonderful TAMRON > adaptall lenses of the last 20 years or so work fine > on the istD?
They should. I know I have an A series Adaptall mount around here someplace, but I don't know just where it, or the lens it is attached to is at the moment.
The PK-A adapter certainly made my PZ-1p think my Tamron lens was a fully-functional A-series lens, so I would expect this combination should have very little trouble. The one thing to be aware of is that the PK-A adapter always reports the lens to have a maximum aperture of f2.8, IIRC. This wasn't a problem for me (I had the 300mm/f2.8), but it could be a problem if you had a lens with a different aperture. Not a serious problem (metering calculations and suchlike are done mostly using the stops-down-from-max-aperture information), but the in-viewfinder display of the selected aperture might be incorrect.
I came across a reminder of that lens just yesterday; I still have the Nikon adapter that came with it. I didn't need it, of course, and neither did the person I sold the lens to, who uses a Canon T90.
