What use is this filter?

innisfree

I've come across a 'Chromafilter SA' by 'Cokin'. 2 actually, one's transparent, and the other fades from transparent to a dark grey.

Both are square filters, about the size you place in enlargers though I don't think this is what they are for. Can anyone explain?

norma

These are filters you attach to the front of your lens. The clear one is a UV - not much use for anything, really, especially if it's not a screw-in one (DadaKopf - please try to restrain yourself. :cool: ). At least the screw-in filters can help protect your lens from seaspray or blowing dust etc. The graduated one is for balancing two areas of your scene that require vastly different exposures. so far apart that both wouldn't normally record properly on film. So, you use the darker part of the filter to tone down the bright part (e.g. snow-capped mountain, sunset scene...) and the darker part of your scene is exposed through the clear part of the filter.
Here is a link to Cokin's website where it shows you how to attach these filters to your lens. The filter is placed in a holder into which slides a ring. The ring has a thread so you can then screw the whole assembly onto the front of the lens.
The advantage of the Cokin system is that, instead of buying a new filter for each lens that has a different sized thread, you only need to buy the attachment ring, and any of their filters can then be attached using the filter holder.
The disadvantage is that Cokin filters are made of resin and they scratch very easily. They also generate a lot of static, and that attracts a lot of dust.
Norma.

innisfree

Wow, really informative answer. Thanks for that Norma, cleared just about every question I would have had up there.
I have Skylight filters already on my 2 lenses and keep them there most of the time knowing they'll help prevent the top lens of the barrel scratching.