From: Jim Chung <jim_chung@sunshine.net>

Date: October 21, 2010 12:38:48 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] solar mosaic reattacked!

Milton,

Your message may clarify how to shoot Ha flats for me.  I tried it last weekend by pointing the scope to a clear patch of sky but of course the Ha signal was so weak that I could get nothing, even with insanely long exposures.  So I should keep it pointed a the middle of the sun and increase the exposure until the surface detail is washed out?  But doesn't that simply oversaturate the ccd pixels?

Jim

Quoting Milton Aupperle <milton@outcastsoft.com>:

Hi Jim;

Did you ever try doing those longer exposure flats of the sunlit Sky?

You might have to go to 0.5 second exposures (I'm guessing as I have

no scope like your to test with), but at least it should help remove

the unevenness.

HTH..

Milton Aupperle

On 20-Oct-10, at 8:38 PM, jimchung2338 wrote:

Thanks to Brian, Alan & Milton for helpful comments on my first

solar mosaic.

So I reduced the focal length back to 1000mm and seeing was better

today as well.  Uneven field illumination is still a problem which I

tried to mitigate by creating irregular borders between the mosaic

pieces.  More mosaic pieces with greater overlap would also address

this problem but I'm a little leary of taking on a hundred piece

mosaic.  There were also many interesting surface features which

made aligning the pieces easier.

If you view it at 100% size the detail is quite good and you are

less likely to notice the brightness of the seam regions.

http://dl.dropbox.com/u/4852049/SolarMosaic.jpg