Cokin P series filters

[mike_tee_vee]

I'm looking at expanding into square/rectangular filters.  I use a circular graduated ND filter but often find that I'd like to extend or contract the graduation.

Has anyone had good or bad experiences with the Cokin P series filter holders on Canon lenses like the 17-40 and 17-85?

[mike_tee_vee]

Here's a reply to my own post from a few weeks back.  I decided to buy a Cokin P filter set for $25.  It includes the filter holder, a sunset filter, and a 77mm filter ring attachment.  I've ordered some filters and some different filter rings.  In a nutshell, you clip the filter holder on to the ring attachment, and slide the filters into the filter holder.  I believe 4 filters can be used simultaneously.
 
While there are pros and cons to this filter approach, I'm enjoying it thus far.  In the past, I used a circular polarizer and a graduated ND filter screwed in to the lens filter thread.  This combo was a real pain, as I found myself screwing and unscrewing the grad ND for different scenes.  With the Cokin system, you just pull the rectangular filter out of the holder as you please.  Its much quicker and much more convenient.
 
However, since the filter holder protrudes way beyond the circumference of the lens, none of my lens hoods (or even lens caps for that matter) can be fitted on when using filters.  Also, there's no way to rotate each filter independently.  Also, a large number of the colored filters can be easily replicated in Photoshop.
 
Thus far, I believe an optimal solution would be using a conventional threaded circular polarizer mated with a Cokin P ND grad.  If money were no object, I'd love to check out the Singh-Ray Gold and Blue filter.

[KeithB]

Are you using a tripod?  If so, and multiple shots are an option, you might want to just try an HDR approach instead of a graduated filter.  You can either take two shots at different exposures and merge them yourself - with complete control over where the dividing line is - or take several shots at various exposures and use the HDR function in Photoshop to compress the dynamic range.

I have heard it stated, and it may have been Bob 8^), that the only filter that cannot be replicated in Photoshop is the polarizer.

Of course, if you don't want to bother with Photoshop, ignore what you just read!

[Bob Atkins]

I'm not sure that the ONLY filter that can't be replicated in photoshop is a polarizer, but it's certainly the most common one.

With some effeort you can sort of replicate a split ND filter, but you either need to take several shots at different exposures, or shoot RAW and try converting with +2, 0 and -2 stops of correction, then combining the resulting three images. Sometimes that can work, sometimes it doesn't and either way it requires quite a bit of work. A split ND is probably better most of the time as long as you can get the transition to look natural.

The only other filter I often use in addition to a polarizer is a ND filter (not a grad, a uniform one) when I want long exposures in bright light. You can't duplicate that in photoshop either!

Though you can do a pseudo IR effect in photohop, you also can't really duplicate the effect of an IR filter (though I've never been all that happy with the results with standard EOS DSLRs due to the strength of the IT blocking filter over the sensor).