From: Mark Gaffney <markgaffney@me.com>

Date: October 21, 2010 8:24:53 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] solar mosaic reattacked - now in improved colour

Looking fantastic Jim..!

Mark.

On 22/10/2010, at 11:00 AM, Jim Chung wrote:

Hi Milton,

I think I had it going for 5 seconds for exposure and still getting
nothing but a black screen. I really think that the Ha signal from
the background sky is too low to penetrate a solar scope etalon.

Alan - I'll try your idea of rotating the etalon unit to see if it
minimizes the hot spot.

Anyway, I managed to use PS to equalize the brightness levels, a more
idealized image rather than a strictly accurate representation but
still an attractive one.

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

Jim

Quoting Milton Aupperle <milton@outcastsoft.com>:

> Hi Jim;
>
> On 21-Oct-10, at 12:38 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.
>
> What does "insanely long exposures" mean in real terms?
>
> 1 Second, 10 seconds, 2 minutes??
>
> Also, Gain can be increased as long as your shooting numerous flat
> frames to average the pixel variance, out.
>
> Normally I create a Master Flat frame using the "Grab Avg.
> Frame" (page 87) and then use "Flat Frame Correct Movie…" (page 56) to
> post process the movie and balance things out. I leave the camera
> attached to the scope and always focus first before creating a Flat so
> it will remove dust on filters or CCD too.
>
> When I do dark frames, I use up an entire night creating them. For
> exposures ranging from 1 minute to 20 minutes and usually average 4 to
> 20 frames for each average master dark I create.
>
>
>> So I should keep it pointed a the middle of
>> the sun and increase the exposure until the surface detail is washed
>> out?
>
> Nope, that will not work.
>
>> But doesn't that simply oversaturate the ccd pixels?
>
> Yes it does.
>
> For a Good Flat, you want the pixels to have about a mid range values
> (128 for 8 bit, 32,768 for 16 bit).
>
> HTH..
>
> Milton Aupperle
>
>
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