From: Alan Friedman <alan@greatarrow.com>

Date: October 21, 2010 1:02:10 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] solar mosaic reattacked!

Jim,

Have you tried (if it is possible) to rotate the filter while watching the image on the screen? You might be able to find an orientation where the Ha hotspot is minimized.

Alan

On Oct 21, 2010, at 2:38 PM, Jim Chung wrote:

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
>>
>
>
>