From: Dale J Martin <dale@massapoag.org>

Date: December 11, 2006 6:21:11 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] New guide camera wanted


Hi Milton,



On Dec 11, 2006, at 4:19 PM, Milton Aupperle wrote:

Hi Dale;


On 11-Dec-06, at 1:46 PM, Dale J Martin wrote:

An Imaging Source AF or BF series Mono camera would do the trick as  

it allows up to 30 second exposures and should give you more light  

gathering capability. The main issue with the Unibrains mono or  

color are that they are really noisy, especially at high gains.


This is the problem I'm having with the Unibrain camera, I'm having  

it having to turn the gain up and Astro IIDC is having problems  

locking onto a star and not noise.


Try adjusting both the Brightness and the Black Point setting too. I find that adjusting them both can improve the S/N ratio, especially in conjunction with the CCD Overdrive option. It's tricky but you can improve the S/N ratio to isolate out a star.


I have been playing Brightness and Black point, but as you say it is tricky, and a bit of a pain since you can't adjust those on the fly.




As far as sensitivity goes, their is a 50% difference in  

sensitivity between the DSI CCD (EXHAD and larger pixel sizes) ,  

however that can be compensated for by using 2x2 or 4x4 binning in  

Astro IIDC.


Would binning help with the Unibrain camera as well? I haven't tried  

that!


Yes it would.


The 2x2 binning improves light gathering by 400% and with 4x4 Binning by 1600%, especially if the star is slightly defocussed which spreads it's light over more pixels. However be careful with using high gains, as it amplifies all the pixels and those get picked up by the binning too.


What also helps remove noise (including stuck pixels and fixed pattern edge noise) is doing a Dark Frame Subtraction. So basically get the gains up to where you can see the target star visually, cover the scope and have it do an average of 10 dark frames. Then have a look at the target star again and maybe increase the gains a bit more to improve the S/N further. The main thing to remember with guiding is to knock back the background noise so that Astro IIDc can lock onto faint stars.


Now a days I normally uses 4x4 mono binning with any camera initially just for achieving initial focus (even badly defocussed stars show up with 133 ms exposures with 4x4 binning). And when hunting for dim targets, I'll set it at 133 ms to 1 second exposures  and with the MAK 127 aperture mm scope, I could pick up 8th to 10th mag stars easily even in light polluted Calgary.




I will try binning tomorrow night along with the Dark Subtraction, this might save me from buying a new camera! It is overcast here tonight.......


Thanks,


Dale