Quote:
|
Originally Posted by avandonk
That is a very detailed beautiful image. What spectral width is your H alpha filter? I assume the smaller the spectral width is, the signal to noise improves.
How wide is the good field on the RCOS. I would really like to try my Hutech modified Canon 5D on this optic. Is this even possible hardware wise with your current setup.
Bert
|
Thanks Bert,
It’s a astrodon-schuler 9nm filter.
Bert your right, a narrowband filter will assist in providing better S/N under light pollution conditions *only* if your sub exposure length is sufficient to overcome the readout noise of your camera.
However, generally speaking S/N is mainly controlled by exposure times. The rule of thumb is that noise is the sqrt of signal. You can also reduce your noise by getting a camera with low readout noise, camera with higher QE, a dark site etc. Noise is a complex beast and comes from a large variety of sources.
So in short a 20 min exposure has double the signal of a 5 min exposure etc.
In other words a 16 hour exposure has 9.8 times more signal then a 10 min exposure.
The biggest noise challenge we face is overcoming readout noise. Otherwise you just end up stacking noise into your images. Very generally speaking for astro imaging you will need a 2-3min sub exposure to overcome readout noise with single shot or mono with RGB filters, with narrowband it gets a lot worse.
<o:p> </o:p>
In my case it takes me 45min to overcome readout noise when using a narrowband filter.
Hence the 1 hour sub exposures.
<o:p> </o:p>
The RCOS 12.5 will take about 6MP CCD before it really starts to show field curvature, I also have a field corrector which will take it well beyond a 35mm frame, I think the limit is about a 6cmx7cm medium format frame. The larger the RC mirror the larger the frame you can take, I know a 20” can take a full frame without any field corrector.
Your 5D would be a good match providing a FOV of 29.4 x 44.1 arc-mins at a pixel scale of around .5 arc-secs.
Fitting your camera wouldn’t be a problem I have a t-thread to 2.7" adaptor. I would most likely get a custom adaptor made up as the t-thread is a bit too small for the full frame CCD. Matter of fact I can take 2.7" thread, 2" nose piece, 1.25 nose piece and SCT thread.
Cheers,
Brad
Any offers?
<!--[if gte vml 1]><v:shapetype id="_x0000_t75" coordsize="21600,21600" o:spt="75" o:preferrelative="t" path="m@4@5l@4@11@9@11@9@5xe" filled="f" stroked="f"> <v:stroke joinstyle="miter"/> <v:formulas> <v:f eqn="if lineDrawn pixelLineWidth 0"/> <v:f eqn="sum @0 1 0"/> <v:f eqn="sum 0 0 @1"/> <v:f eqn="prod @2 1 2"/> <v:f eqn="prod @3 21600 pixelWidth"/> <v:f eqn="prod @3 21600 pixelHeight"/> <v:f eqn="sum @0 0 1"/> <v:f eqn="prod @6 1 2"/> <v:f eqn="prod @7 21600 pixelWidth"/> <v:f eqn="sum @8 21600 0"/> <v:f eqn="prod @7 21600 pixelHeight"/> <v:f eqn="sum @10 21600 0"/> </v:formulas> <v:path o:extrusionok="f" gradientshapeok="t" o:connecttype="rect"/> <o:lock v:ext="edit" aspectratio="t"/> </v:shapetype><v:shape id="_x0000_i1025" type="#_x0000_t75" alt="" style='width:12pt; height:12pt'> <v:imagedata src="file:///C:\DOCUME~1\BRADMO~1\LOCALS~1\Temp\ msohtml1\01\clip_image001.gif" o:href="http://www.iceinspace.com.au/forum/images/smilies/mad.gif"/> </v:shape><![endif]--><!--[endif]-->
<!--[if gte vml 1]><v:shape id="_x0000_i1026" type="#_x0000_t75" alt="" style='width:28.5pt;height:13.5pt'> <v:imagedata src="file:///C:\DOCUME~1\BRADMO~1\LOCALS~1\Temp\ msohtml1\01\clip_image002.gif" o:href="http://www.iceinspace.com.au/forum/images/smilies/shrugging.gif"/> </v:shape><![endif]--><!--[if !vml]-->
