Question about polarizers

[vvizard]

When I add a polarizer I loose two stops of light right? That means a 1.4 will be a 2.8, a 2.8 will be a 4, and so on? If I'm correct about this, my next question then is:

Will the polarizer affect DOF and lens-quality for a given aperture? To really try telling this so it's even remotely possible to understand the question, think about this:

I got a 70-200 2.8. Stopped down to f/4, it gives lot better quality, and a wider DOF.

If I leave lens at 2.8, and add a polarizer instead, will I get a 2.8 DOF, or one equivalent to f/4? Will it affect image-quality, as if the lens itself was stopped down to f/4?

[Scottes]

2 stops - so 2.8 to 4.0 to 5.6 = 2 stops. But you're right on 1.4 becomes 2.8 - that is 2 stops.

f/5.6 gives DoF the same regardless if there's a polarizer, and ND or no filter at all. 5.6 is 5.6

You're losing 2 stops OF LIGHT, not 2 stops of aperture.

[Cadwell]

Losing two stops will mean that at f/2.8 the lens will let through about the same amount of light as it would normally let through at f/5.6...

Fitting a polarizer doesn't change the aperture... it changes the amount of light that gets through at that aperture. Things like DOF and the other characteristic of the lens dictated by aperture would stay unchanged.

[slejhamer]

As Scottes and Cadwell have said, it's true that you lose 1-1/2 to 2 stops of light, but the polarizer by itself does not change the actual aperture setting or DOF. You can open up to compensate for the light loss (and then of course DOF will be affected,) but you can also adjust shutter speed or ISO. The same applies to a neutral density filter.

[vvizard]

Ok, thanks for clearing up the issue. I had to spend one of the last posts before hitting top-contributer asking something silly I've always wondered about you know =D Cause I can't no more :/ If I do, all the noobs will question my skill-level, and then they won't listen blindly to my advice when I tell them such things as digital is really out, and that we all will probably be back on film soon anyway, so they should rather spend their 300D-money to stock up film-rolls instead ;)

[Jesper]

Ok, thanks for clearing up the issue. I had to spend one of the last posts before hitting top-contributer asking something silly I've always wondered about you know =D Cause I can't no more :/ If I do, all the noobs will question my skill-level, and then they won't listen blindly to my advice when I tell them such things as digital is really out, and that we all will probably be back on film soon anyway, so they should rather spend their 300D-money to stock up film-rolls instead ;)

Well if you have another question which you think isn't smart enough for a Top Contributor, you could maybe ask Pekka to degrade you to New User....... 8) (just joking!)

[Cadwell]

Well if you have another question which you think isn't smart enough for a Top Contributor, you could maybe ask Pekka to degrade you to New User....... 8) (just joking!)

Yup... I'm sure zeroing the post count only takes a quick mouse click :twisted: :wink:

[vvizard]

"update <some_table> set <some-counter>=''0 where username='vvizard'" should do the trick =D