I don't know - I just mentioned it to complete the answer - I can't recall seeing anywhere any comment on this with regards to digital cameras, and i haven't tried it.

Noise might overwhelm any effect on digital anyway.

Has anyone actually investigated this?

If you set the body to M that means "Manual" and hence as you stop down the lens the light is reduced, but the shutter speed stays the same. hence increasing under-exposure as you stop down. If the camera was set to A then the shutter speed would change to compensate.

Macro shots benefit from the use of a tripod, so the lengthening of the shutter speed will not result in camera shake. Also it will be easiere to focus precisely - essential where depth of field is limited.

To keep the exposure constant, shutter speeds and apertures work together, so, for example the following combinations allow through the same amount of light:
1/125 s f8
1/60s f11
1/30s f16

At very long shutter speeds this relationship starts to break down (reciprocity failure) so 1 sec may need to be 2 sec, 4 sec may need to be 20 sec or whatever.....The longer the exposure the worse it gets. This is true for film, haven't checked it out with a CCD.

Hope that helps!

The date and time as well as lots of other info are in the data recorded as part of the image file.

I think this is much better than spoiling a picture with a date stamp?

I didn't realise the A version had a slide out hood - now I want one! I always use lens hoods, but they are equally well a bit of a nuiscance.

Enjoy the new lens.

I understand that the M and A series lenses are the same optically.

When CREATIVE PHOTOGRAPHY tested 100mm lenses of all makes (including Zeiss and Leica) they concluded that "The clear winner is the Pentax M lens".

I agree with them, it's a lovely design that delivers top quality results.

I think you're doing the right thing - there's no substitute for testing your own lenses for the purposes you wish to use them for.

Interesting, although don't forget that lenses are designed to work at particular distances and close up to a lens chart will not be ideal for a wide angle zoom.

teleconverters introduce their own abberations to an optical system, but also magnify the lens's existing ones. The 7 element ones are not bad, but for the highest quality I don't think any of them really meet the challenge.

I'd prefer a second hand longer lens any day, keeping the cost down by not buying new.

Thanks for sharing - I enjoyed viewing your fine images!

This is unusual in macro lenses in that it focuses down to 1:1. It is also reported to be a superb performer. I read a very favourable review of this lens in PHOTO TECHNIQUE in the 1970s.