best way to take flats out in the field?

[Astroblagger]

Hello Looking for some advice regarding taking flats, i always have to pack up the car and drive some distance to get to away from all the light pollution for imaging. what would be the best way to take flats iv heard of people putting white t-shirts over the front of the scope, but what would be the best way to illuminate the t-shirt. Just wandered what other folk do.

Also how does using image processing to remove vignetting compare to the real thing (ie taking flats) is it just as effective?

[ollypenrice]

Flats are best because processing tools only work on lens illumination and not dust bunnies. Besides, on some faint targets it is risky to use tools like DBE because they can cut the nebulosity you are struggling to emphasize.

I can never get T shirt flats to work well but some do. The idea is to use the twightlight sky.

The best way I've found is to use an Electro Luminescent panel either mounted in a perspex protector home made or supplied imaging-ready from Gerd Neumann (at greater cost) as 'Aurora panels.' I use one of his. It gives a perfect result without fail.

Olly

[dph1nm]

Use the twilight sky. Most professional observatories do it this way.

NigelM

[ollypenrice]

Yes and clearly it can be done, but I always got gradients on my sky flats. Never had a clue as to why...

Olly

[Merlin66]

A low voltage quartz halogen lamp, positioned far enough away to give even illumination of the T shirt ( or plastic pizza tray base) works well.

[spacebloke]

Could you use a white t-shirt stretched over a picture frame, place that over the scope and point it outside during the daytime?

[Merlin66]

yes, if it has the camera etc all connected the way it will be used at night for imaging.....

[dph1nm]

Yes and clearly it can be done, but I always got gradients on my sky flats. Never had a clue as to why...

Did you try taking them pointing near the zenith? This might reduce any gradients.

NigelM

[themos]

Another thing to worry about is dust bunnies moving around between your lights and flats acquisition. That bit me on the third night I was targeting the Veil widefield. I must have turned the camera off/on a few times (sensor cleaning gets activated) and nudged it a bit too much. The dust bunny had moved by the time I shot the flats, ruining a very nice set of exposures. I should probably shoot flats while the scope is still pointing at the target and not turning it to face the zenith but that would mean holding the Aurora panel by hand. And no automatic sensor cleaning either!

[ollypenrice]

Did you try taking them pointing near the zenith? This might reduce any gradients.

NigelM

Yup, tried everything I could think of. I wonder if it is simply the intensity of the light in my neck of the woods. I did wonder if it was light leaking into the filterwheel but I got the same gradients with a sealed electric one.

Olly

[Psychobilly]

Could you use a white t-shirt stretched over a picture frame, place that over the scope and point it outside during the daytime?

Thats what I used to do before I hung an EL panel up in the obs (mainly so I could make changes to the setup during the night and still get "valid" flats)

I pushed the wooden frame into the t shirt so had two layers seperated by the frame.. and then stapled the edges. I used to keep it in a plastic back with a sillica gel pac when it wasn't in use)

Peter...