Flats using an EL sheet

[greenkat]

Hi all

So, I went and bought an A4 EL sheet from Earlmans so I can start trying to do flats.

Mounted it in an A4 clipframe with the glass removed, then placed it in the box that the EL sheet was delivered in. Perfect fit

Then I cut a hole in the front the size of my largest dewsheild then made some templates to match each smaller scopes dewsheild which can be placed on the front and held with velcro.

This lets me place the box over each dewshield nicely when in the park position.

It all looks a bit scruffy atm, but will make something neater when I,ve made sure its all ok.

I have powered the EL sheet using a multi voltage power adapter and seems to work ok, and can make the light dimmer by decreasing the voltage, at its dimmest at 3.5volts

(I'm no sparky, so any of you electricians please tell me if this is ok to do or am I going to blow myself up )

The first image shows the box unlit

The second shows the box with sheet powered up.

The third is the resulting flat taken using Canon 1000d mounted on an ED80 in AV mode at ISO800 with auto WB

Could someone tell me if this is what I should be getting ?

How do I know if its a good flat or bad flat ?

Cheers in advance

Greenkat

[steppenwolf]

It is difficult to tell if the Flat image is right or not but I am tempted to think that it is not saturated enough as I would expect to see more vignetting from your particular system but not knowing how you may have 'processed' it makes it difficult to be sure.

The box you have made is just fine and should work well.

[greenkat]

Hi Steve

Thanks for the reply.

I havent processed the flat at all, just reduced the image size to post on here, do I need to adjust the levels ect ?

Greenkat

[Photosbykev]

this is a stretched jpeg image of a master flat produced from a Canon 5D mkII and Canon 600mm f4L lens using an A4 EL panel the same as yours processed from a stack of 50 flats in DSS

This was a single flat from the set

There doesn't appear to be any vignetting in the image you've posted when it is adjusted in PS and it also appears underexposed by one or two stops.

It isn't directly connected to processing the flat you've produced but I would certainly turn off the auto WB function and use just a fixed daylight setting

[greenkat]

Many thanks Kev, great info , I'll go give that a go now

[greenkat]

Just stacked 50 flats in DSS, Auto wb off, set to daylight.

Resulting image was very blue,

2nd image is after adjusting in photoshop

Getting anywhere near ?

[Photosbykev]

don't worry about the colour as the master flat only looks at the luminance. The master flat does look better with some vignetting visible and a dust bunny but it still looks underexposed. If you are shooting in Av set +1 exposure compensation to brighten the image. Look at the histogram aand check the peak is well to the right of the graph without clipping

[steppenwolf]

I'm much happier with your second attempt at a flat - this looks closer to the 'real' thing but I'm with Kev, it needs a little more exposure still.

[greenkat]

Cheers for the advice guys

Hopefully will be able to try properly when I get some clear sky and get some images to try it on

Greenkat