Could someone explain FLAT Images/Frames ?

[KingAndromeda]

Hey, I'm in the process of reading 'making every photon count' and have come across a section that I don't entirely understand. It talks about "FLAT" frames but I don't understand there need or really what they are.. Id like to understand what they are before continuing the book, thanks for any explanation

[Pete Presland]

A flat field is an image taken of an evenly illuminated object like the dusk sky, or a special illuminated white card hanging on the wall of the observatory. These images are taken through the telescope they remove vignetting and dust from images.the same rules apply to flats and darks the camera must be in the same orientation for the calibration frames as it is for the subs.

[scoobee]

Try this

http://astro.welsh-house.net/tutorial.html#c

[nephilim]

Try this

http://astro.welsh-h...tutorial.html#c

Thanks for posting that mate, Steve Richards book is invaluable but a good walkthrough of the actual routine is a great bit of info.

Steve

[steppenwolf]

Have you reached pages 105 - 107 yet? I include a reasonably comprehensive description of what Flats are, how they remove vignetting and the effects of 'dust bunnies' as well as a description of how to take these calibration frames.

[KingAndromeda]

Ahh yes I've had another look and it's certainly a lot clearer, much appreciated

[kirkster501]

Flats are a revelation when you start to use them. The difference they make is astounding!

[Mik3]

Flats are a revelation when you start to use them. The difference they make is astounding!

Agreed, they only take afew mins aswell.

[Mik3]

I made a lightbox to take mine but I read somewhere that you can just stick a white tee shirt over the end of the scope, point it at a bright light source, set your camera to AV and take about 15 images.

[Pete Presland]

I made a lightbox to take mine but I read somewhere that you can just stick a white tee shirt over the end of the scope, point it at a bright light source, set your camera to AV and take about 15 images.

thats what i have been doing

[Astrosurf]

Am I missing something here? But looking at Andrew Welsh's tutorial, he does flats before the lights. I thought you had to take them afterwards as the optical train has to be exactly as it was for the photos. Or have I been misinformed?!

Sorry to hijack. I hope the answers will be helpful to you too KingAndromeda!

[ollypenrice]

Am I missing something here? But looking at Andrew Welsh's tutorial, he does flats before the lights. I thought you had to take them afterwards as the optical train has to be exactly as it was for the photos. Or have I been misinformed?!

Sorry to hijack. I hope the answers will be helpful to you too KingAndromeda!

Provided you know that you are in focus and won't be rotating anything then you can do them before. I tend to do mine 'before and after.' That is, I do them at the end of the first night on a particular target and as I continue to shoot on subsequent nights I use the same flats. I don't knock down the imaging train, though. I leave it in the observatory.

Olly

[Astrosurf]

Thanks Olly.