Obtaining flat frames for solar vs night imaging

[Notty]

I am trying to get my head around the flat things, mainly to solved a gradient/vignette ng issue on my solar pics. Can anyone tell me why the approach is different to night AP at all? For it is written that for night flats, they must be taken with the optical train in absolutely exactly the same configuration, focus, orientation etc as the lights. For solar, I have heard that the technique is to point at the centre of the solar disk and actually de focus the telescope to obtain a "flat" image.

Can anyone tell me a) is this right and if so, how come you can change the focus in the solr case and not invalidate the flats?

[Luke]

I use the defocus method to take flats for my Quark h-alpha solar images. Seems to work fine for me so far. I think Alexandra (Montana) uses the rather more exotic 'fruit and veg bag flat':

https://www.flickr.com/photos/alexandra4/13956739414/in/set-72157628535593245

[Ant]

I use the defocus method, which works well on close ups. But I haven't managed to get a reliable method when it comes to widefield (whole disc shots).

Cheers

Ant

[Notty]

Thanks then de focussing it is, I will give it a go.

[Bizibilder]

Another "defocusser" here when using the small frame astro camera.

For wide field (full disc with the DSLR) I simply point the scope WELL AWAY from the Sun (North "home position" is a good place!), remove the solar filter (Baader film in my case) and put a piece of translucent perspex over the front of the scope (I think mine is 50% transmission - bought it on ebay for a few quid).  Then set the camera to AV and snap away.  In this case I do not change the focus - I want to see the dust bunnies so the software can get rid of them during stacking!

To be honest I rarely use flats for full frame shots - I just clean the sensor with a blower from time to time.