Question About DIY Light Box

[JoLo]

I have scoured the internet and the collective wisdom found here in SGL, and have all the components and parts I need to put together a light box for taking flats with my 4" refractor.

I am hoping someone can clarify for me what the proportions of the box should be....I have seen differing views and designs, but am unclear as to what I should do.

One DIYer insisted that the distance from the light source to the end of the box, must be the same as the distance between the lights...essentially, a cube. He had a single diffuser sheet at the end of the box that rests on the scope.

Many others have put together light boxes where this arrangement is ignored. I have seen several that are longer boxes, with more than one diffuser panel inside. For instance, one of the instructions stated the second diffuser should be 4" from the first....there is a larger gap to the back of the box, but that distance is not specified.

I am using translucent vellum for my diffuser(s) and my questions are:

Is there a correct or best proportion for building a light box?

When using vellum, is a single diffuser or two the better option?

Thanking you in advance for your guidance.

Joe

[cgarry]

I just finished my lightbox and the best advice I can give you is to experiment with the distances to see what gives the best flat field. I have no idea about vellum but I found 2 sheets of 6mm Opla perspex gives a flat field for my light box.

Cheers,

Chris

[Paxo]

I use an EL panel myself, but this is a useful article:

DIY Astrophotography Light Box

Steve

[JoLo]

Thanks Paxo...yeah, I read through that one, it is very good, but doesn't answer the question about proportions. Twice it says to measure the aperture carefully, and that all subsequent measurements are based on that one....but it stops there, and doesn't specify what that basis is....

I read one article that said the length of the box should be twice that as the aperture of the scope....in my case, that would make an 210 x 210 mm cube. It seems to me if I went that route, a second diffuser would really be crammed in a small box....

[yesyes]

.... but this is a useful article:

DIY Astrophotography Light Box

This person is on this forum so you could ask, JoLo. ;-)

As far as I know the distance between light sources (LEDs?) and the diffuser(s) has to be long enough so that the light cones of the light sources overlap (i.e. leave no dark gaps between them when they shine onto the diffuser). So the distance would also depend on the light cone angle of the LEDs you use. The wider the angle the closer they can be to the diffuser.

As cgarry suggests, you would need to experiment and see what distance gives you the most even illumination on the diffuser.

Personally I have taken a completely different approach using the backlight from an old laptop TFT display:

yesyes astro blog Lightbox

[JoLo]

Thanks everyone for the advice. I have several articles / posts and I am going to cgarry's advice and play around with it this weekend....supposed to be cloudy in my neck of the woods anyway. I appreciate everyone's help!

Joe