# Question regarding drop-in circular polarizing filter



## Harv (Aug 31, 2013)

Among other things, I shoot a lot of motocross throughout the spring and summer season. Pretty much most weekends. I have often thought that a drop-in circular polarizing filter for my 300/2.8 would be a good idea to reduce glare from goggles and face masks, as well as to enrich colours and perhaps tone down some highlights.

I decided to go ahead and have ordered one. As an afterthought (I have a lot of those), I was wondering if introducing that filter would have any negative effect on the speed and/or accuracy of the AF. Anyone out there with any experience with one that could answer that question for me?


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## neuroanatomist (Aug 31, 2013)

No effect on AF speed or accuracy that I've noticed. Obviously it costs you ~1.75 stops of light, so make sure you've got enough leeway in terms of ISO to keep your shutter speed high enough.


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## surapon (Aug 31, 2013)

neuroanatomist said:


> No effect on AF speed or accuracy that I've noticed. Obviously it costs you ~1.75 stops of light, so make sure you've got enough leeway in terms of ISO to keep your shutter speed high enough.



+ 1 for my teacher Mr. Neuroanatomy
And + 1 for that CPL Drop in Filter to get the best Contrast of Colors of your photos----But set up the right location of the Filter ( By rotate the Wheel)= take more time for set up---But, Just 1 set up for one location/ 1 Spot where you shoot , After the right setting = Great Photos ---No more set up, until the sun change the position in the sky.
Good Luck, Sir
Surapon.
PS, Just in my Idea---My way of Shooting fast sport shooting like that( in the Bright day light)= I set Manual Setting at F = 8.0, SS = 1/350 sec,( or Higher/ Faster speed)and Set ISO = A ( Auto ISO)


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## Deleted member 91053 (Sep 1, 2013)

Like the others I have noticed a significant drop in the light but the IQ does not seem to take a significant hit. I find this CPL to be a useful accessory for my 300 F2.8 but on my long lens (an F5.6) it costs too much light unless I am in really bright light.


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## Harv (Sep 2, 2013)

Thanks for your input, guys.

I well know about the loss of light throughput and given the light I normally shoot in and the bodies I'm using, that is not an issue.

I was just wondering if there was any impact on the AF speed or accuracy. I believe that question has been answered.

Hopefully it will arrive in time for me to try it out next weekend.


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## mackguyver (Sep 17, 2013)

I just ordered one for my 300m f/2.8 II - Unique Photo had the best price ($200) and it will be here tomorrow. I'm hoping to use mine a couple hours after sunrise to keep shooting in the harsher sunlight. Will let you know how it works out. 

Also as I did some research, I found that this is most auto race shooters' secret weapon to kill the glare from windshields and headlights, so it should work well for you.


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## ForumMuppet (Sep 17, 2013)

I do not have one, yet, but another benefit is that it will allow you to slow your shutter speeds down a bit to get wheel motion in bright daylight without having to raise your f-stop. Otherwise you may as well wait for the race to be done and go shoot them in the pits. :


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## mackguyver (Sep 22, 2013)

Tried mine out this weekend - with the bare lens, AF seems to work almost as well - maybe a bit more hunting - but when I torture-tested it shooting with the 300mm f/2.8 II + Extender 2x III (effective aperture ~f/11?), and shooting moving subjects from a moving boat, it wasn't too great. Using the focus limiter helped a ton, but interestingly, center point and center surround AF sucked. Zone AF worked best. In terms of polarizing the light and ease of use, it worked extremely well.


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## eli452 (Sep 22, 2013)

I don't have any experience with shooting very fast moving subjects such as cars and motorcycles races, but will one setup of the polarizer filter fit all reflections at various angles and the only stipulation is angle of the sun?


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## mackguyver (Sep 22, 2013)

eli452 said:


> I don't have any experience with shooting very fast moving subjects such as cars and motorcycles races, but will one setup of the polarizer filter fit all reflections at various angles and the only stipulation is angle of the sun?


It works just like any other polarizer, so yes, that is true as long as your lens faces the same direction within about + or - 15 to 20 degrees. If you turn around or to the side, you'll have to adjust it again to keep the same level of polarization. It depends not just on the angle of the sun, but the angle of the sun relative to the direction of the filter if that makes sense.


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## mackguyver (Feb 16, 2014)

Here's a follow-up with an example of why a C-PL can be helpful for a super-telephoto lens. Here's a shot with no polarization (top) and a second shot with about 80% polarization (bottom). Were the light any harsher, the first shot would have had way too much glare on the scales to the point on being unusable, while the second would work fine. These images are unprocessed to show the full difference between the two shots:


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