Fitlers and step-down rings

Hi,

I recently purchased two sigma lenses for my 10D, 24-70/2.8 and 70-200/2.8. The filter sizes are 82mm and 77mm respectively. I know there are both step-up rings and step-down rings so that you can use a certain filter size on both lenses. Does it matter which one you choose? I have yet to purchase a filter for either lens so that is not an issue. I know the 77mm filter size is cheaper than the 82mm so i have been considering purchasing the 77mm filters and buying an 82-77mm step down ring. Will this cause anyproblems using a step down ring with shadows or blocking light since your essentially making a 82mm lens 4mm smaller?? Ive always assumed its better to use a step-up ring since that should not cause anyproblems with the lens due to the larger size.

Thanks for the help

I am soon going to be in the same boat and think I am going to go with the step up option; 77mm to 82mm.

You are more likely to see the filter in a wide angle than a telephoto so it only make sense to not want to step down the 24-70.

Errrrr,

I think, if you are using a digital with a reduced size sensor you should only be looking through the middle part of the lens (as long as its a normal lens for 35mm).

So you should have less chance of the filter being in the image. even if it is smaller than the actual front element.

I'm not sure though, anyone else have any ideas?

I know it has been said many times that since the 10D digital sensor is smaller than 35mm film, the outer edge of the lens isn't used. Does anyone know that this is a fact? Yes, I've seen the articles showing MTF tables adjusted for digital which cancel out the edge values, but it is never stated how these conclusions were drawn. It seems to make sense, but I imagine the physics of refraction through so many internal lens elements is complex. I just would hate to put anything in the light path of L glass without knowing for sure that it wasn't going to degrade the image.

If you want to put an 82mm filter in front of a 77mm lens, using a step ring, then that does not seem terribly silly to me. On the other hand, putting a 77mm filter in front of an 82mm lens does seem quite silly and illogical.

If you can only afford one set of filters, then doesn't it stand to reason to buy the larger ones (82) and some step rings.

Try buying filters for 86mm or larger!

---Bob Gross---

Get the larger ones,. or just get 77 and you probably won't be able to use them on the 82.

I have two lenses that take 77mm,. all but one are smaller.

The one that ois larger is 86mm.

I get all 77mm filters (except of course the clear UV protection filter I get for all lenses)

The 77mm will work on all lenses but one,. the 86mm

I get 77mm so I only need one filter for all lenses but the 86mm.

I figure to spend three times as much on 86mm and then have an 86mm on a 52mm thread lens is alittl too rediculous!

Hi, you should never use a step down ring. By using a step down ring, you wil get whats called vinyetting (spelling) which is a dark ring around the edges of the image. Always use a step up ring.
Emil

The point that was made was that the outer edges of the frame are cropped on the 10D, so if you did use a step down ring (you can step down 1 filter size in most cases on 10D) then the vignetting would be croppd out by the smaller sensor.

chrisnardone, that is fact. Put the 10D in sensor clean and have a look at the size of the sensor, you will see it is smaller than a 35mm frame.