Making flats - How clean?

[Photosbykev]

Hi folks,

I've just purchased an EL panel to make up a portable system for taking flats out in the field.

My query is just how clean should the lighting system be before any dirt or marks on it affect the master flat?

I'm planning to mount the EL panel between a sheet of black perspex and a sheet of white opaque perspex but I'm slightly concerned that any specks of dust under the perspex could affect the final flats.

I realise that any dust on the panel etc will be totally out of focus if I make them with the optical setup left at the same setting I use to take the subs i.e close to infinity, but even out of focus marks must have some effect on the individual flats?

[MartinB]

I doubt very much that small marks will make any difference. It is gradients which really kill flats. I made an EL panel using 2 sheets of perspex and made sure they were good and clean but I'm sure small flecks of dust will be ok. I've put paper across the panel sometimes to increase the exposure time. If you look closely at paper it is far from even but has never been a problem. Similarly T shirts have a weave pattern and all sorts but have been a standard way to get flats for years.

[ollypenrice]

I'm sure Martin's right. Besides you can move the panel about a little during the shoot to make sure your systematic non-flat features get averaged down to insignificance.

Olly

[RobH]

Small specks of dust have no effect at all. Martin is right, it's gradients that you need to watch out for.

Cheers

Rob

[Photosbykev]

Thank you for the input folks, I'llcarry on with the way I'm going and just make sure the panel and perspex are as clean as possible without being obsessive about it