Easiest way to do flat field?

[EzyStyles (Eric)]

Hi,

I want to start doing flat fields but not sure exactly what the easiest way to go abouts. I read about making a box and the t-shirt way. can i just put a white t-shirt over the scope and shine on it? what is the procedure to take flat fields?

thanks all .

[Karls48 (Karl)]

Hi EzyStyles
I took picture of the sky on foggy morning just before sunrise.

[[1ponders] (Paul)]

Here ya go Ezy. Everything you wanted to know about flat fields, darks etc from one of the masters of the game, Eddie Trimarchi

I usually take flat fields at the end of the night after I finish imaging, or the next day even. The important thing is to keep your imaging train in one unchanged piece. That means don't move anything! Take your scope off the mount with your DSI and all the imaging bits and pieces still attached and carry them inside (or leave everything on the mount if that's how you normally move it about). The important thing is to keep your imaging train in one unchanged piece. Get the idea Don't move the camera or reducers or focuser or anything.

I'm fortunate in that I have a very bright light source reflecting of a very pale coloured wall. I place my scope as close to the wall as I can without any sort of shadowing, about half way up, then I put a piece of fairly transparent white muslin or cheesecloth over the aperture and then start imaging. With the DSLR I take a series of shots, maybe 5 @ 1/ 4 sec, 5 @ 1/2 sec all the way up to 1 or 2 sec to get the right exposure. It's not difficult not time consuming, I just need to make sure my illumination is even over the area being imaged. By getting the scope close to the wall it reduces the light illumination gradient from top to bottom of the wall. I'm usually withing 300-400 mm of the wall.

That's how I do it anyway, but I'm notoriously lazy when it comes to those important finishing off bits like flats and darks, so someone is sure to have a more effective method.

[EzyStyles (Eric)]

thanks guys. thanks Paul for your informative post. I will checkout the link you have provided. So when taking flat field, the scope has to be pointed directly at the object?

[Striker (Tony)]

Your flat fields shot should look something like this but without the colour as mine was done with a filter but as you can see the vingnetting.

[EzyStyles (Eric)]

thanks tony. Couldnt i use someone elses flat field rather than taking it? also with flat fielding, will that reduce details?

many thanks

[JohnG (John)]

No, you flat field using your equipment setup and focused as you used it.
If you used someone else's flat field you will introduce artifacs that were in their imaging train.
The whole idea is to improve details, not reduce them.

Cheers
JohnG