Originally posted by stevebrot With the eBay adapter the aperture becomes fully manual (stopped down all the time) as opposed to the "pre-set" functionality provided by the A/M switch on your Takumars.
That's not what preset means. A Takumar is not a good example of preset lens - it is preset only in M mode. It also has an automatic aperture mechanism and an A/M switch for switching to it, but those features don't define a "preset" lens. Takumars are examples of an intermediary stage of lens evolution from preset to automatic aperture. For earlier preset mechanisms, look at some of the Russian lenses which don't have an A/M switch. In particular, the Industar 50-2 only has a stopless aperture ring and there is no quick setting mechanism - it's a remnant of preset lens design for rangefinders, where an auto aperture mechanism wasn't necessary because you were not focusing through the lens anyway.
Originally posted by stevebrot Given the choice of a fully manual or pre-set aperture vs. auto aperture (stops down at exposure), I would go for the readily available and relatively inexpensive genuine Tamron P/K model hands down over something like the eBay item. Focus changes frequently, exposure much less so.
Depends on what you are shooting. I made the opposite choice, because these days I spend a lot of time shooting birds and insects and they move from light to shadow and the exposure changes all the time depending on where they sit - it's more important for me to not have to waste time with the green button. As I mentioned before, up to f/8 I can still handle the darkening of the viewfinder. YMMV, of course.
Anyway, regarding adapters, to summarize the choices, there are three types I've seen:
- the Tamron PK/A - the most expensive and desirable - makes the lens into an A lens
- the Tamron PK - Steve prefers it, I don't - makes the lens into a K/M type of lens where you need to use M mode and green button for stop down metering
- the generic no frills adapter that lacks an aperture flange - it's also referred as PK, but should not be confused with the Tamron PK - this makes the lens into a preset lens (Industar 50-2 style, to be clear) with the benefit that it can be used in A mode and the drawback that you have to focus with the lens stopped down, which can be challenging at apertures smaller than f/8 (limit will vary depending on eyesight and lighting conditions)
The order in which I listed these corresponds to their decreasing prices.