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 6/15/2022 4:56 PM, JC OConnell wrote:
https://jchriso.com/temp/smc100.htm
This is a great all around lens.
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.
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