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Simple way to take flats

Equipment Calibration How-to
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Andy Wray avatar
Andy Wray avatar
I've found the simplest way to take flats with my 8" Newtonian is:

* I use an A3 LED tracing pad bought from Amazon (about $35)
* I put two white vests/T-shirts between it and my OTA (about $10)
* I set the tracing pad to its lowest setting
* I use a black shower cap to stop light leaking into the bottom of my scope (about $8).  FWIW:  that black shower cap has been the best investment I ever made as it makes taking darks a doddle as well.  My scope does suffer from light leaks from the back end.
* I personally use Nina's flats wizard to take the flats, although it worked equally well with APT.

It's not exactly elegant, but works very reliably and didn't cost much.

I know I could do sky flats, but being able to control the LED's panel brightness makes it so much more repeatable.

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Rouz Astro avatar
Rouz Astro avatar
You can control the brightness with something like the Spike a flat USB controller, It worked on those amazon panels.
The dew output of something like the Pegasus should work as well.
Those panels work but are not 100% even, in most cases will work fine.

CS
Rouz
Frédéric Auchère avatar
Frédéric Auchère avatar
One way to even out possible non uniformity is to average many flats and shift / rotate the panel in between (or during) exposures.

Frédéric
Die Launische Diva avatar
Die Launische Diva avatar
Frédéric Auchère:
One way to even out possible non uniformity is to average many flats and shift / rotate the panel in between (or during) exposures.

Frédéric

This, and use drawing paper sheets instead of a T-shirt
Andy Wray avatar
Andy Wray avatar
Frédéric Auchère:
One way to even out possible non uniformity is to average many flats and shift / rotate the panel in between (or during) exposures.

Frédéric

Interesting thought ... I might try this, although, to be honest, I haven't seen an issue by the time you've added a couple of t-shirts
Arun H avatar
Arun H avatar
Die Launische Diva:
Frédéric Auchère:
One way to even out possible non uniformity is to average many flats and shift / rotate the panel in between (or during) exposures.

Frédéric

This, and use drawing paper sheets instead of a T-shirt

I use the drawing paper method. In addition to acting as a diffuser and improving uniformity, it dims the light more than I can with just the LED panel controls and allows me to use 4s exposures to put myself in the linear regime of my sensor. Just add as many sheets as needed for the particular filter! Lum filters can take as many as 8 sheets, so I keep a stock of them.
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Frédéric Auchère avatar
Frédéric Auchère avatar
Die Launische Diva:
Frédéric Auchère:
One way to even out possible non uniformity is to average many flats and shift / rotate the panel in between (or during) exposures.

Frédéric

This, and use drawing paper sheets instead of a T-shirt

I use the drawing paper method. In addition to acting as a diffuser and improving uniformity, it dims the light more than I can with just the LED panel controls and allows me to use 4s exposures to put myself in the linear regime of my sensor. Just add as many sheets as needed for the particular filter! Lum filters can take as many as 8 sheets, so I keep a stock of them.

+1
I also use translucent paper for added diffusion and dimming. The shifting / rotating routine is an extra layer.

F
Ron avatar
Ron avatar
I do the exact same thing with one addition.   You might consider using embroidery hoops to keep the T-shirts taut and unwrinkled.  They work well!

Ron
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Andy Wray avatar
Andy Wray avatar
Ron:
I do the exact same thing with one addition.   You might consider using embroidery hoops to keep the T-shirts taut and unwrinkled.  They work well!

Ron

I had embroidery hoops, but having added a new (relatively cheap) low profile focuser I found I was forced to add my ZWO EAF so that it gets in the way of the hoops.  I will be purchasing a better focuser that will allow me to flip the EAF to the other side where I used to have it.

To be honest:  the hoops did look good, but it's no real hardship without them.