captxmas Loc: San Francisco Bay Area

Greetings all, I have been a long time user of polarizing filters as I enjoy the finished images enhanced color without reflections. I use them on my Nikon 24-70, 70-200 and until recently my Sigma 50-500 with great success.

The 50-500 has been passed on to my son and I opted to purchase the Sigma 60-600. I love it and its performance with one exception. I have tried to use two different 105mm polarizers and the lens will not deliver a sharp image until it is removed.

Can anyone let me know why this happens? They have been Circular polarizers as I have used in the past.

call me puzzled.

revhen Loc: By the beautiful Hudson

Sounds like the polarizer is "fooling" the af. Why not contact Sigma directly?

captxmas Loc: San Francisco Bay Area

Thought someone here might have a simple answer like you provided. I'll give them a call if nothing else comes from my fellow HOGS. Thank You

imagemeister Loc: mid east Florida

You loose 2 stops of light with the polarizer - just like with a 2X extender ! So the AF WILL be affected !

The other "problem" using any filter with long focal length lenses is that focusing issues are exacerbated .....and each filter and lens has a unique/different reaction regarding this. I cannot explain all the physics involved with this - just know that it happens ! and, is why I use any filter as a last resort....
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User ID

Not at all. A 2X TC converts your f/5.6 lens
to f/11 which is beyond the ability of the AF.

A polarizer is no different than a cloud over
the sun that drops your illumination by two
stops of light ... but your f/5.6 lens remains
an f/5.6 lens despite the cloud. Very simple.

amfoto1 Loc: San Jose, Calif. USA

You didn't mention what camera you have, but some are unable to focus when there's not sufficient light. The 60-600m is an f/4.5-f/6.3 lens... As a result, at the longer focal lengths of the lens, and with a C-pol added that's costing as much as 1.5 to 2.25 stops of light loss (depending upon how strong effect you dial in), you have the equivalent of only about f/10 or f/13. r

Depending upon the camera you are using, that might not be enough light to AF. Or, you may have to limit the camera to use only specific AF points that are able to focus with less light.

Yes, the lens is still f/5.6 or f/6.3.... However, Imagemeister is correct. It's the light lost to the C-Pol filter that makes the camera unable to focus... The same as it's the loss of light when you add a teleconverter that makes AF impossible (again, it depends upon the camera and the AF system it uses). It doesn't matter whether the light is lost to a dark filter or to a smaller effective maximum aperture.... When there's not enough light for the camera to focus, it won't focus!

There are "high transmissive" C-Pol now, which aren't as dark as standard C-Pol. They give similar polarizing effect, but with less loss of light. Not a lot different though.... I'd estimate there's maybe 2/3 or 1/2 stop less light loss.

imagemeister Loc: mid east Florida

I think you better re-think this ....for the purposes of exposure AND AF......and yes, it is simple ...

bleirer

I'd agree with the filter factor for the polarizer being a suspect. If the lens is at 6.3 at 600 you would add the filter factor, if it's 2 stops you are at f8. Some cameras won't autofocus at f8 or will only use the central focus point. Worse if you don't remove any uv or clear filter.

You could look up the filter factor for your polarizer.

imagemeister Loc: mid east Florida

f6.3 + 2 stops = f12.6......6.3 + 1 1/2 stops = f9.45

Longshadow Loc: Audubon, PA, United States

Deleted.

amfoto1 Loc: San Jose, Calif. USA

Except f/6.3 less two stops is not f/8.

f/8 is only only 2/3 stop different from f/6.3.

The weakest effect setting of a standard C-Pol causes light loss equiv. to 1.5 stops, while the strongest setting causes a loss equiv. to 2.25 stops.

f/6.3 less 1.5 stops is close to f/11. f/6.3 less two stops is f/13. f/6.3 less 2.25 stops is close to f/14.

MOST DSLRs cannot focus at anything less than f/8 or maybe (in good light), f/11 at most.

BTW, the Sigma 60-600mm is f/4.5 only at it's shortest focal lengths. It drops to f/5 beyond 75mm.... and again to f/5.6 at 140mm... and to f/6.3 from approx. 350mm or longer.

Bill_de Loc: US

The OP said he used the 50-500 with the polarizer which I believe has the same maximum aperture.

I'm wondering if he got a new polarizer which is not a CPL.

Looking forward to the outcome.

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User ID

A camera that can AF a 5.6 lens will AF it
even in dim light. A camera that cannot
AF an f/11 lens will not AF that lens even
on a sunny day. Polarizers do not change
your f/stop. TCs do change your f/stop.
Very simple .... but apparently not to all
of us :-(

As to "purposes of exposure", who cares ?
Exposure is not at all related to focus. I
can focus perfectly but expose improperly,
and I can also make perfectly exposed out
of focus images. No connection between
the two functions.

bleirer

Of course you are right, I guess I was thinking in 1/3 stops.

imagemeister Loc: mid east Florida

Yes, this wold have an effect also ....and we do not really know what body he is using - other than it is Nikon ??
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