400D autofocus affected by CP-L?

e r y k · 19th of July 2007 (Thu)

Heyya POTN,

My Hoya Pro1 Digital Polarizer came in today, havent got a chance to test it outside as it its pretty cloudy and nasty outside.

I realized that AF doesnt seem to want to work on things that are textured the same (ie a single color, same material etc). I never really noticed this, but is this normal?

Also, will AF be affected by the use of a polarizer? I know I lose about 2 stops of light, but should AF be slower?

Thanks

Eric

JohnJ80 · 19th of July 2007 (Thu)

If it is not a Circular Polarizer (but a Linear Polarizer) it very likely is confusing your AF system. Also, cheaper filters can do the same as can those that are not MRC. I'm not familiar with that exact filter so if it is a cheapie, it might be the problem. If you take it off, does the AF work fine?

AF *can* be slower if it is very dark and you are not aimed at some good contrast to help the AF.

J

e r y k · 19th of July 2007 (Thu)

http://www.bhphotovideo.com/c/produc...izing_Pro.html

thats the filter i got.

even with the filter removed, when i focus on something with uniform color / texture, it doesnt seem to want to focus on it.

JackProton · 19th of July 2007 (Thu)

The camera requires contrast - light and dark areas - in order for auto-focus to function properly. Uniform colors and textures such as a blank white wall will be difficult or impossible for auto-focus to lock onto. This and other auto-focus issues are actually docuemented in the camera's manual.

The CPL filter knocks off two stops (giving your camera only 1/4 of the actual room light) meaning that it will have extra problems trying to auto-focus in indoor- or low-light situations. This is also normal. As far as the camera is concerned, you're essentially trying to autofocus in the dark.

PaulM9999 · 20th of July 2007 (Fri)

Interesting....I've never heard this before. Does this mean we would be best-advised to use manual focus when a circular polarizer is attached?

e r y k · 20th of July 2007 (Fri)

Quote:

Originally Posted by PaulM9999

Interesting....I've never heard this before. Does this mean we would be best-advised to use manual focus when a circular polarizer is attached?

i think it was due to the fact that i was indoors... like JackProton said, it cuts down 2 stops of light which is like shooting in the dark

jcw122 · 20th of July 2007 (Fri)

YES, the loss of light will affect the AF.

JackProton · 20th of July 2007 (Fri)

Quote:

Originally Posted by PaulM9999

Interesting....I've never heard this before. Does this mean we would be best-advised to use manual focus when a circular polarizer is attached?

Not typically necessary. CPL filters are generally used in bright, sunny conditions where reflections are much more likely to be a problem or where darker, bluer skies are desired.

JohnJ80 · 20th of July 2007 (Fri)

CPL filters will allow the AF to work just fine. You need to have some contrast in order for the AF system to be able to figure out how to focus. The more light and the more contrast, the better it will work.

J

19th of July 2007 (Thu)	#1
e r y k Goldmember Join Date: Apr 2005 Posts: 2,023	400D autofocus affected by CP-L? Heyya POTN, My Hoya Pro1 Digital Polarizer came in today, havent got a chance to test it outside as it its pretty cloudy and nasty outside. I realized that AF doesnt seem to want to work on things that are textured the same (ie a single color, same material etc). I never really noticed this, but is this normal? Also, will AF be affected by the use of a polarizer? I know I lose about 2 stops of light, but should AF be slower? Thanks Eric __________________ Canon EOS 5D // keepin' it old school

19th of July 2007 (Thu)	#2
JohnJ80 Cream of the Crop Join Date: Oct 2006 Posts: 5,439	Re: 400D autofocus affected by CP-L? If it is not a Circular Polarizer (but a Linear Polarizer) it very likely is confusing your AF system. Also, cheaper filters can do the same as can those that are not MRC. I'm not familiar with that exact filter so if it is a cheapie, it might be the problem. If you take it off, does the AF work fine? AF can be slower if it is very dark and you are not aimed at some good contrast to help the AF. J __________________ Obsessive Gear List *"It isn't what you don't know that gets you in trouble; it's what you know for sure that isn't so."* - Mark Twain

19th of July 2007 (Thu)	#3
e r y k Goldmember Join Date: Apr 2005 Posts: 2,023	Re: 400D autofocus affected by CP-L? http://www.bhphotovideo.com/c/produc...izing_Pro.html thats the filter i got. even with the filter removed, when i focus on something with uniform color / texture, it doesnt seem to want to focus on it. __________________ Canon EOS 5D // keepin' it old school

19th of July 2007 (Thu)	#4
JackProton Goldmember Join Date: Feb 2007 Posts: 2,348 IMAGE EDITING OK	Re: 400D autofocus affected by CP-L? The camera requires contrast - light and dark areas - in order for auto-focus to function properly. Uniform colors and textures such as a blank white wall will be difficult or impossible for auto-focus to lock onto. This and other auto-focus issues are actually docuemented in the camera's manual. The CPL filter knocks off two stops (giving your camera only 1/4 of the actual room light) meaning that it will have extra problems trying to auto-focus in indoor- or low-light situations. This is also normal. As far as the camera is concerned, you're essentially trying to autofocus in the dark.

20th of July 2007 (Fri)	#5
PaulM9999 Junior Member Join Date: Dec 2006 Location: Ontario, Canada Posts: 15	Re: 400D autofocus affected by CP-L? Interesting....I've never heard this before. Does this mean we would be best-advised to use manual focus when a circular polarizer is attached? __________________ Canon EOS 40D, Digital Rebel XT; Canon 24-70/f2.8 L USM; Canon EF 70-200/f4 L IS USM; Canon 50/f1.8; Sigma DC 30/f1.4; Sigma DC 10-20/f4-5.6; Canon 1.4x Extender; Canon Speedlite 430EX My Flickr Collection

20th of July 2007 (Fri)	#7
jcw122 Senior Member Join Date: Jul 2006 Location: West Chester, PA Posts: 1,930 IMAGE EDITING OK	Re: 400D autofocus affected by CP-L? YES, the loss of light will affect the AF. __________________ "Ill show you."-John Hammond Gear List "YES! I AM INVINSIBLE!"-Boris

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