Rectangular filters and flare

flatulent1 · Nov 22, 2010

Once upon a time I had a set of Cokins. Didn't use them enough to justify the cost, got tired of carrying them around, eventually passed them off on some poor unsuspecting idio -er I mean acquaintance.

I used them long enough to wonder about something... Light shining directly on a glass (or resin) surface tends to cause flare, this is why we use lens hoods. Rectangular filters that slip in and out of filter holders are not sealed to the lens in the way screw-on filters are, and are open to light bouncing off the back as well as the front, not to mention light getting in around the exposed edges of the filter (think fiber optics). Is this a real concern, or have I been snorting too much developer?

coigach · Nov 22, 2010

If you use them carefully I don't reckon there's much to worry about.

I shoot landscapes with b+w transparencies and use Lee rectangular yellow + ND grads most of the time. Provided that you shield the filters from directional sun (I use a cheap lightweight foam sit-mat bought from a campling shop), everything should be hunky-dory...

Cheers,
Gavin

holmburgers · Nov 22, 2010

Or mount them on the other element of your lens, if that's an option; i.e. large format.

SMBooth · Nov 22, 2010

Ive had flair from the sun when its behind me hitting the back of them and bouncing in that way. Best mounted as close to lens a possible, and what the others said.

hpulley · Nov 22, 2010

holmburgers said:
Or mount them on the other element of your lens, if that's an option; i.e. large format.

Some of my 35mm lenses have rear filter holders too ;-)

AgX · Nov 22, 2010

Screw-on-filters are mostly made from one piece of coloured glass, so there are not those four additional transitions between substances of different recfractivity.

Sheet filters laminated between glass panes are a rarity.

Q.G. · Nov 23, 2010

Resin filters are one piece affairs too.

The dangers of using an open holder as mentioned are possible light piping due to the exposed edge (could happen, would cause problems if the filter is scratched or dirty), and light extraneous hitting the rear surface.

The solution, of course, is to use them in a holder that doesn't expose them to any light but the image forming light.

Another danger of Cokin filters, being Cokin filters, is image quality degradation.

flatulent1 · Nov 23, 2010

Q.G. said:
Resin filters are one piece affairs too.

The dangers of using an open holder as mentioned are possible light piping due to the exposed edge (could happen, would cause problems if the filter is scratched or dirty), and light extraneous hitting the rear surface.

My main reason for not hurrying to replace my departed Cokins.

The solution, of course, is to use them in a holder that doesn't expose them to any light but the image forming light.

Is there such a holder?

lxdude · Nov 23, 2010

Q.G. said:
The dangers of using an open holder as mentioned are possible light piping due to the exposed edge (could happen, would cause problems if the filter is scratched or dirty), and light extraneous hitting the rear surface.

I blackened the edges of mine with permanent marker. I don't use them much and never tried to do any empirical tests, but I figured it wouldn't hurt.

Q.G. · Nov 23, 2010

flatulent1 said:
Is there such a holder?

I believe so.
Myself, i use resin filters in a Hasselblad ProShade 6093, in which they are fully enclosed (downside: you can't use grads, unless small/square ones in a fixed position).
I wouldn't be surprised if Cromatek or Lee also have such a holder.
In days of old, Kodak sold a holder that was closed on three sides, and had a hinged lid on top.

Rectangular filters and flare

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