Back in film days it was my favorite portrait lens.

I still used it for such with the APS-C Pentax digitals and only
recently switched over to the SMC Pentax-D FA 100mm F2.8 Macro WR (ran
across a price so good on-line that I couldn't refuse) ... but I still
have the A 100mm F2.8 MACRO for backup.

On 6/15/2022 6:56 PM, JC OConnell wrote:

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What are the things that look like water smears on a print, on the chalk-on-the-ground picture?

On 6/15/2022 4:56 PM, JC OConnell wrote:

The A100/2.8 was a great lens, but it is quite prone to reflections off
the sensor giving hot spots on the image. I suspect it is related to the
FREE design and the absolutely flat rear element.
It's too bad because it was such a good lens on film.
I ended up retiring my copy of it in favour of the DFA100/2.8 Macro,
which is easily as good a lens and shows none of the reflection
problems. I'd sell it but my conscience won't let me sell a known defect
such as this.

The problem is related to lack of Multi-coating on the rear element
which was absent on pre-digital lenses. More commonly this gives rise to
ghosting (back-and-forth reflections) when these old lenses are used on
digital camera because the sensors are much more reflective than film.
The difference between the Sigma 170-500 APO & the later DG version is
indicative.

Alan C

On 16-Jun-22 04:29 PM, Bill wrote:

On 6/16/2022 10:17 PM, Alan C wrote:

I suspect that is a possibility, I suspect the "multicoated" lenses of
the day may not have been as multicoated on the rear element. I use
quite a few legacy glass and the A100/2.8 macro is the only one I've
noticed hot spots on, which is why I thought it might be related to the
FREE design and the flat rear element.

Anyway, according to John, the problem doesn't exist, so it's all good.

bill