[bygp]

I very often get low contrasted shots with this 70-210mm KAF zoom, it's my only lens causing such random shots, my other Vivitar 70-210 series 1 gives contrasted photos even without a hood and facing skylight.

I did some tests with a skylight filter and a hood and it's a bit better, but still have randomly results, some pics have normal contrast even while facing light source while others are still like this one :



That I can almost always correct with LR as there don't seem to be any spectral loss :



For example, this one, untouched and taken from the same place but not in the same direction although facing south too gives almost a normal contrast :



Should the hood be longer ? (it's a JJC LN series short hood approx. 2cm long)

Could it be a bad AE mode choice ? I took this pic using all frame AE...

Can it come from a weak optic part inside this lens, maybe coating used by U.V. as it is a second-hand lens ?

Any advices are welcome, thanks

Bruno.

P.S. I would realy like to understand because it's a zoom giving very sharp shots while being compact and with a good build quality, also it's my only KAF lens atm.

[MadMathMind]

Sigma's coatings in the past were light years behind Pentax's, which have historically been way ahead of the others. Now, others have caught up (but Pentax still rocks on coatings!) and Sigma's are better, but still not as good as Pentax's.

I have the 70-200 HSMII. It has much weaker contrast, especially wide-open, than any Pentax lens I have. The new Global Vision line has improved things quite a bit.

[bygp]

Sigma's coatings in the past were light years behind Pentax's, which have historically been way ahead of the others. Now, others have caught up (but Pentax still rocks on coatings!) and Sigma's are better, but still not as good as Pentax's.

I have the 70-200 HSMII. It has much weaker contrast, especially wide-open, than any Pentax lens I have. The new Global Vision line has improved things quite a bit.

I've been digging on the web and well it looks like a coating issue, but when I inspect deeper this lens it seems something else. When looking through the lens from the front side having a ligh source at the rear of the lens, there is a light glow around the aperture hexagon (in fact it's more like light hiting a screen, like if there was a mate film on one lens) and I don't know what does that but it is certainly bad as none of my other lenses have such glow. If I look through it from the rear, the aperture profile is perfectly sharp, no glow at all. So I'm not so sure if it is a coating problem or a sort of velum on a lens close to the aperture.

EDIT : just located a bit more precisely and yes, there is a "not crystal clear" thing in the front block close to the aperture, so I can consider this lens as dead, being a KAF Zoom I won't even try to disassemble it, lost 20 euro... or will use it on rainy days until it's dead. Someone said "buying cheap lenses will cost you more than buying good lenses". I start to believe him.