From: alan@greatarrow.com
Date: February 10, 2010 10:41:53 PM MST
To: Astro_IIDC@yahoogroups.com
Subject: Re: [Astro_IIDC] Scorpion Sun Images...
Reply-To: alan@greatarrow.com
It won't hurt... Using a red or green rgb filter will make a difference, getting out as much as possible will help the most and give you a chance at catching a good seeing moment, which makes many of the problems much less of a problem.
Cheers,
Alan
Sent from my Verizon Wireless BlackBerry
From: Mark Gaffney <markgaffney@me.com>
Date: Thu, 11 Feb 2010 16:10:13 +1100
To: <Astro_IIDC@yahoogroups.com>
Subject: Re: [Astro_IIDC] Scorpion Sun Images...
I don`t have either a red or green filter yet but do have a Baader UV-IR cut filter. Is this any good?
Mark.
On 11/02/2010, at 3:27 PM, Alan Friedman wrote:
Hi Mark,
Use the camera at 1600x1200 - shoot 100 frame movies. Get a cloth and put your laptop right next to the scope so you can focus easily while looking at the screen underneath the cloth (you'll look silly, but the focus will be goo! d!) Hint - the seeing will improve if you use a red or green filter on the nosepiece of your camera rather than using full spectrum white light. The light will be attenuated too - which might make it easier for you to adjust the proper exposure. The sun's disk should be light gray - not white. Use no gain, or at least very little, if you need it to get a proper exposure between two shutter settings.
best,
Alan
On Feb 10, 2010, at 11:12 PM, Mark Gaffney wrote:
Hi Alan, Good suggestions! I had on my list some cleaning alcohol as now I think about it the watermarks are the result of cleaning with some detergent in water. Do you mean using a size say of 800 x 600 pixels with this camera? Full size is rather too large practially with my 12" iBook. I"d love some form of automated focuser- but that"s not immediately possible. As to getting the right exposure I had the base e! xposure rate set at it"s lowest setting 16.67ms & got my best resu lt eventually at 30 fps. I used both the incremental adjustment 10 ms at a time & also the slider setting it as close to what seemed right given the range available ( all the time jogging from the scope to where I could see the screen to get some sort of marriage between focus & exposure!) This was a very fine distinction given rather extreme conditions. Focusing is one thing obviously improveable & exposure seemed to be reliant on the former for any greater precision? Bey! ond trying without ROI what suggestions would you have? Focus & exposure both seemed to me just very tiny nudges before things were either in whack or out! Brightness is of course the other variable & I found a setting of about 400 was right for this morning"s conditions. I guess this is what"s left of the large sunspot 1043 after several rainy mornings here! Might the Sun be brighter or more intense here in Australia too...?
Mark.
Sent from my iPod
On 11/02/2010, at 2:28 PM, Alan Friedman <alan@greatarrow.com> wrote:
Hi Mark,
A couple of suggestions:
1. Get an observing cloth. I use a piece of black polar fleece with a silver fabric sewn to one side to reflect the heat. It covers my head when I am doing visual observing, and my head and laptop when I am capturing solar data with Astro IIDC. When selecting a piece of cloth, choose something supple and hold it up to a light bulb to make sure it isn't too sheer.
2. Your focus is off - I can tell that by the fact that your dust motes are as close to focus as the sunspots. Dust motes are always a problem with these sensors. You should have a can of compressed air for photographic use. You! can use it to blow dust off your optics and off the chip of your came ra too. Just be careful not to shake the can and point and release some air at your hand right before cleaning to be sure that no propellant is being released.
3. Get the exposure righ! t. Use the histogram in AstroIIDC to ensure that you are not cutting off data at the white end. Your image is mostly blown out in the whites. When properly exposed, the solar disk should have tone throughout - no white. You can adjust the levels afterward if needed, but you cannot put back what was not recorded in the first place - in the case, the detail in the brightest sections of your image.
4. You really want to master the technique of finding the sun by minimizing the shadow. There are also some finder scopes made by Televue and others that work from a cast shadow. You don't want to be sighting towards the sun to locate it in the scope. A couple of quick glances and you'll have lots of nice spots in your eyes that take time to go away be! fore you can see the laptop screen again.
5. Don't use ROI... there is no advantage for you. You don't need to average many if any frames when imaging the sun - you can shoot it with 0 gain (brigh! tness) so the individual frames will have lovely signal and very little noise. Most of my recent solar images are constructed using single movie frames without any stacking at all.
practice... practice - it's summer!
best,
Alan
On Feb 10, 2010, at 8:10 PM, Mark Gaffney wrote:
You guys have been busy whilst I`ve been doing this! These Suns are
shot with a Scorpion 20SO mono camera using Baader solar film & my
C9.25 scope at prime focus. The camera is set to 814 x 618 pixels
ROI...I think for the 2nd of these I went to 30 fps, the first one was
at 15 fps & using very minimal exposures .90 ms for both, I think. I
have to put my lap-top over a bit under a bush & a good few feet from
the scope or I can`t see anything because of glare ( we don`t have a
useable beach umbrella at present..) so focusing is very difficult
(not to mention co-inciding this with getting an acceptable exposure.
(thank goodness there were no march flies this time..! -I had some
Aeroguard & there were less arou! nd-also I remembered to wear a hat but
it was still very hot especially by the time I was ready to give
up! ). I found a useful expedient was to put a small corner of the
solar film (about 1 inch square) over the front of the finder. I spent
ages before this trying to simultaneously locate & focus the Sun-using
smallest shadow etc.... I don`t know how I`m getting these blotches on
the glass cover of the chip..the camera is covered except when I take
the grey PGR cover off to test something? I certainly don`t have time
when all set up at the scope to be cleaning ! cameras, especially with
the Sun which has a limited time it can be imaged because of the heat!
But it`s probably spoiled these images for what they`re worth. Lastly,
I`m finding a single sharpest frame seems to be the best option for
clarity...& I`m only posting them as small size attachments here.....
Mark