bleirer

The camera will focus at the widest possible aperture no matter what aperture or ISO you have set. It's just that the widest possible if you are shooting at 600 is f6.3. Add to that the polarizer darkening further and/or maybe low contrast in your scene and maybe the autofocus can't handle it at some point because there is not enough there to detect contrast. Also double check that it is a cpl, I've read linear polarizers mess with af even more.

RRS Loc: Not sure

Thanks!

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MEISTER ?

IMAGE MEISTER ?

dsmeltz Loc: Philadelphia

Polarizers DO NOT change the f-stop. An extender does because the insertion of the extender actually changes the size of the aperture relative to the plain of the sensor.

A polarizer is no different than low light as it relates to exposure. If a camera will AF at f/8 and the lens extender achieves f/8 during focus AF will function, but just like in low light if it has trouble finding something to focus on it may not work well. If you have a system that allows you to customize focus priority, you can set focus over shutter release and (possibly) get focus. But you may also miss the shot.

imagemeister Loc: mid east Florida

So, let me qualify this - As far as AF and exposure is concerned, you loose equivalent f-stops of light .....

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Not so fast, buckaroo!

If by "Fstop" you mean light transmission, of course they do. But since most in the industry use fstop to designate aperture setting - then under no circumstances does a CPL change your fstop.

See the definition here:

https://www.techopedia.com/definition/2702/f-stop#targetText=In%20photography%2C%20an%20F%2Dstop,is%20expressed%20as%20a%20fraction.

"In photography, an F-stop is the ratio of the focal length of the lens to the diameter of the aperture. The number is expressed as a fraction. F-stop is a dimensionless number and gives an important measure of the lens speed.

An F-stop is also known as a focal ratio or f-number.

The extender most definitely changes Fstop, since it diminishes the amount of light by making the focal length longer, and in doing so the ratio of the size of the entrance pupil changes.

Modern cameras limit focus to F5.6 or F8 electronically.

However, just for grins and giggles, I put an ND400x which has a 9 stop loss of light, and put it on my D810 and a 70-200 F2.8, pointed it outside at a sign and it took the image perfectly in focus. Grainy because I had to boost the ISO, but it was in focus. The F2.8 with the filter attached became an F64 lens by your interpretation, but since the lens communicated that it was an F2.8 it was still able to focus with the ND filter on. I suspect it would be easier to focus if I could actually see through the viewfinder, but using live view worked. BTW, before you go there, I got the same results with CDAF as I did with PDAF.

So, no, a polarizer does NOT change the Fstop (which would imply that the depth of field also changes) - unless you put a tiny polarizer on a bigger lens using a bunch of step-down rings.

captxmas Loc: San Francisco Bay Area

Thanks so much. That’s what I always thought. Maybe I have a weird polarizing filter.. may order another to compare.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Almost got it right - you loose "stops" not "F-stops" - and while we're on the topic of stops, will you please get your terminology straight and "stop" calling an exposure "stop" an "f-stop" - You're confusing everyone with your own confusion SMH. . .

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

NO, that's not correct. You are changing the FOCAL LENGTH - and NOT changing the diameter of the entrance pupil or aperture. A 100mm F2 lens with a 2X extender is still F2 - which describes the original aperture size as a ratio, but the focal length is now 200mm, so of course that lens with the extender will let through a lot less light.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

imagemeister Loc: mid east Florida

Dah ! ....as I mentioned you LOOSE light but since there is no body communication it still tries to focus - never said it didn't or wouldn't - and f-stops in this context are just a a measure of light, looses 2-f-stops - NOTHING to do with the aperture - but MOST people know and accept this phrasing -EXCEPT here on UHH ...8-( LOL ......BTW, technically, using a TC does NOT change the physical aperture EITHER
But, that can be an argument for another day.....

imagemeister Loc: mid east Florida

Yes that is what I mean - and you know it ....

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Wasn't sure if YOU knew it by the way you misused the term twice.

imagemeister Loc: mid east Florida

I guess we have different "terms" here in the South - you believe what you want - And I'll do like wise ... LOL

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

I never said or implied that a TC changes the physical aperture.It changes the focal length. Therefore, it does change the ratio of focal length to aperture, so it does change the maximum fstop of a lens. There is no context where the way YOU use the term fstop might be correct. Putting a filter does not change the ratio of aperture to focal length, therefore it doesn't change the fstop. But it absolutely does change the amount of light coming through the lens and hitting the sensor, by 1.4 to 2.25 stops - not fstops. Just because you can't get this straight and insist on misusing the term doesn't make you right. The only exit from this argument for you is to be gracious and admit you were mistaken, or just stop and move on. Your choice.