New Flats panel

[Carole]

Since my EL panel died on me a couple of years ago I have been coping with sky flats and decided not to bother to replace it. 

However, sky flats don't work so well with the SW130PDS Newtonian as there is some light leak I presume near the primary mirror, seems this is a frequent problem.  I have tried wrapping up the rear of the scope but it doesn't seem to work, so have been doing flats as its starting to get dark, but this is not always successful as either I don't time it right, or doing flats for all 7 filters takes too much time and it gets too dark.

So I decided I would have to get myself another EL panel. 
Some-one posted up a link on SGL to a really cheap light panel on Ebay, it was £11 whereas it would cost me £60 - £70 to buy one through my normal channel.  So I decided to chance it.

I would be interested to see what you think about the flat and the resulting image before I tell you any more about this cheap light panel.

This is the flat - Stretched in Photoshop.

As a separate issue I am concerned as to why the flat is darker one side than the other, but it has been like this even with sky flats and it doesn't seem to affect the final image, I would welcome ideas on that too.  The scope is collimated correctly.



I have applied it to this recent data, which is incomplete as I only just started it, but it is good enough to test the flat.
Only 2 x Ha and 2 x 0iii in this image.


It looks to me as if the flats have worked OK, in the final image. 

Carole

[ApophisAstros]

Do you hold it near end of scope to use or is it fixed to it.
I still have the one i bought and if better would like to utilize it.
Roger

[Carole]

The panel is sitting on the aperture of the scope held on by the box surrounding it which has a hole cut out for the aperture.

I am not going to reveal the panel until I have had adequate feedback.  I wasn't sure if it was going to work.  But I think it does, but would like a critical eye.

Carole

[Mac]

As a separate issue I am concerned as to why the flat is darker one side than the other

whats the shutter speed for the image?
It could be a similar issue to what you get when you shoot fluorescent tubes,
they flicker at 100hz and sometimes you can get an image where half is dark and the other half is not due to the exact time you photograph the fluorescent tube,

your EL  panel might work in a similar way ,(having a quick google)
it appears that most EL panels use AC to drive them, so its possible that your shutter speed is causing the effect in combination with the flash rate 100Hz,

you need to reduce your shutter speed to a longer time to reduce the chance of catching it mid turn on and off.

no ideal considering the constraints we work to.

Mac.

[Carole]

Thanks Mac.

I don't think it is to do with either of those things Mac, as I got the same effect when using sky flats.  Also a CCD camera doesn't work with a shutter speed as far as I know it's just length of exposure, and the length varies depending on the light from the sky/EL panel and which filter I am using.  I still seem to get this effect with longer exposures.  I was thinking it was more to do with the light path, but I could be wrong.

Carole

[MarkS]

It's a very odd flat!

You can check if it is the flat panel or the optics by rotating the panel 180degrees and taking another flat.  If the flat looks the same then it's the optics.

For what it's worth, I think the panel is fine in which case it might be caused by stray light or collimation.  You're absolutely sure it's collimated correctly?

One thing very obvious is the shape of the "dust bunnies".  They should be dark "Polo" mint shaped.  Yours have a flat top edge instead of being circular.  So what is cutting into the light path?

Mark

[The Thing]

Was this with your SW130PDS? If so then the flat bit on the dust bunnies and the uneven illumination could be to do with the focuser draw tube protruding into the OTA. Something else to check.

BTW I have tried all the newtonian collimation methods in the world and have found none gets me even chip illumination. The way I get my secondary lined up just right is to use my EL panel to provide flat illumination and then adjust the mirror to get even illumination of the CMOS. Then do a final collimation of the primary. Seems to work very well.

[Carole]

So what is cutting into the light path?

the flat bit on the dust bunnies and the uneven illumination could be to do with the focuser draw tube protruding into the OTA.

Yes absolutely right Duncan, I keep toying with getting a bit sawn off the focusser, but I think I need some-one with the tools and skills to do it for me.



As I was getting that same uneven light with Sky flats as well I am sure it is the optics and not the flat panel and therefore I am assuming this flat panel works fine thanks for your input.

I will now tell you what this flat panel is, it's a tracing board off Ebay.  When I first got it I was horrified because the light is from lots of "dots" all over the board and I thought "this is not going to be any good", but once a piece of typing paper is put across it it seems to even out the light.  So this was a test of the light panel.

Just need to suss out why the light illumination is uneven, could it be the protruding focusser that is causing it? But it seems to even out once applied to the images.

Carole

[JohnP]

can you post a link to ebay item - thks

[Carole]

This is the link John.  I really like the design as it runs off a USB so you can plug it into your laptop, and as the board is acrylic (I presume) it is rigid and there is a mini USB port on the item, so no flopping electrics to get damaged like on my previous EL panel, no need for an invertor and it can be dimmed.

https://www.ebay.co.uk/itm/A4-LED-Stencil-Board-Tracing-Light-Box-Thin-Art-Draw-Tracing-Copy-Pad-Plate-USB/273027730

I just cut a hold in the box it came in and put that over the aperture of the scope, so it holds it in place nicely and won't spill white light in the dark.  Put a sheet of typing paper over it and bingo.

Worked out to approx £11 inc postage and came within a few days which I was really surprised at since it is sold in Hong Kong.  Obviously no good for larger scopes.

Carole

[Mike]

Got an old laptop or Android tablet? Make the screen all white and plonk it on the end of your scope.

[Carole]

I've already thought about that but I don't have an old laptop and never owned a tablet and in any case no idea how I would keep it on the end of the scope without it falling off with the laptop keyboard hanging down one side.

But doesn't matter now anyway as I have the solution.

Carole