Filters for Sky 'n' stuff

[smudge]

Am I correct in thinking that if I want to expose, in one shot, for both bright sky and darker areas below the horizon, the filter I'm looking for is a Nuetral density graduated grey, something or other. If so, what is the relevance of the nuetral density part. I understand the graduated bit.

Also I would like a filter that does this graduated exposure thing for a 17-40L which is as you know 77 mm. Is the only way to do it using a cokin system. If so, does that mean that you must focus first and then place your filter in, as surely if you placed the filter in first and then focused, the filter horizon line (terminology fault) would shift as the lens focused.

What is the best system to use for a graduated exposure for this lens.
Thanks in advance.

[rent]

neutral density reduces the amount of light passing thru the filter, but does not cause color **** (hence neutral). all ND filters are grey in color, the darker the stronger the effect (less light passes thru).

yes you would need a graduated ND filter. a split ND filter may also work, but its transition from clear to ND is not graduated and you can see the clear transition. it may work if the birghter and darker area of the photo is clearly defined and in a straight line.

another option is to take two shots, one expose for the brighter area the other expose for the darker area and put the two together in photoshop.

the ND filter should not affect AF, unless the filter reduces so much light that the AF system no longer works.

-alex

[rent]

i use cokin graduate ND's. i don't even use the cokin holder anymore these days. i stuck a bunch of masking tape on the tripod legs when i go out shooting. just tape the filter to the lens when i need them. no need to mess with adapter rings or holders, also reduces vignetting.

-alex

[smudge]

Thanks alex, that clears that up. Do they make Graduated ND's in the screw in variety or is that unworkable.

[rent]

i have not seen a round (screw-in) graduated ND filter in person, but from pictures they appear to have the transition right at the middle. so i suspect it's not as versatile as the square ones.

-alex

[Simon Spiers]

Smudge ,thake a look at this post I started. http://photography-on-the.net/forum/showthread.php?t=74982
This might give you more options.

[Lesmac]

I previously used cokin filters (ND grads), and only changed to Lee square filters because I was geting vignetting on my 17-40 (on a 1Ds MKII) with cokin.
My experience is that you can go through the full metering of sky/ground and expose for the ground with appropriate filter. Or (as I do), bracket the exposure and use the camera histogram to establish correct exposure.
Both cokin and Lee do a range of different density filters, I would start out with two, ND4 and ND8, will give you a useful range.

Some shots taken with ND grads in my gallery if you are intereste.

Les
http://lesmclean.photoblink.com/