From: Milton Aupperle <milton@outcastsoft.com>

Date: January 21, 2009 3:16:46 PM MST

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Re: Stupid questions?

Hi Jess;

This has all been described and discussed before on the Astro IIDC list in past posts. I'll re-cap the hilights for you.

First thing to ask is "what do I intend to image"?

Doing bright field (moon, planets, sun, double stars) doesn't require a lot of additional hardware other than a camera, scope, a reasonably good mount (even goto alt azimuth) and maybe a barlow / televue lens to increase magnification. Going over 640x480 sizes for planetary is basically over kill and likely even for lunar you don't want to be much bigger than 1024 x 768.

For DSO's. your going to need a good to very good polar aligned mount, a guide camera, likely a GPUSB relay guider box, a focal reducer (0.63x or possibly smaller), a second guide scope mounted piggy back OR Off Axis Guider, probably an Light Pollution Filter, possibly (for Mono Cameras) 4 parfocal L R G B filters in a filter wheel, followed by patience and the desire to do lots of post processing and fiddling with things. You want as large as a camera as you can afford for DSO to give you a decent field of view and as big a pixel size as possible too.

The second thing to ask is "how much time do I want to devote to this" and do I want "instant gratification" or not?

With a color camera, your basically doing "point and shoot" imaging so it's "what you see is what you get". You don't have to shoot 3 (RGB) or 4 (LRGB) sets of movies using multiple filters, then process those movies, then import the L R G B frames in and fiddle with the alignment or rotation or scale to get them in place etc. etc. Although a color camera is easier, it does not have as good a resolving power as a mono camera does. But if your sky turbulence conditions are not great (mine suck, as I live right under the jets stream) , then you likely never or very rarely will get the full resolving power of a mono camera. Also color cameras are less sensitive (by 30 to 40%) than a monochrome camera is because of the built in bayer color filter array on the CCD.

With a Mono Camera, your going to need R G B filters in a Filter Wheel  to shoot color  images. Even for mono images of the moon, people use a red or green filter to help increase image sharpness. However you can get better resolution with a mono camera if you have good skies. Also if your planning on doing photometric type measurements of stellar objects or want to do narrow band imaging (i.e. UV filter to image venus's clouds), then a monochrome camera is a requirement.

The last one is the infrared filter for a color camera.

For lunar imaging it is essential and for planetary it largely is needed too (possibly not for Saturn or Uranus or Neptune). For DSO imaging, many of the manufacturer's built in IR filters cut off all infrared light above 650 nanometers, which means one of the main hydrogen alpha wavelengths that nebulas are visible at are completely lost (I think it's 680 nm). This makes those filter pretty much useless and you want an IR filter that gives you nearly 100% light up to at least 710 nm. So if you don't have it built in, then you'll need to by an Astonomical 1.25" IR/UV cut filter (like a Baadetr or Antares etc.) which exposes the important band widths and then attach it to the C-Mount 1.25"" nose piece.

Hope That helps..

Milton J. Aupperle

On 21-Jan-09, at 1:24 PM, Jesse Ohlsson wrote:

Thanks for all your answers.  That just about covers it.  All I really need to do is decide (how?) 

which if the TIS cameras to get.  640x480 to the 1280x960 41AF02.AS.  IR filtering or no?  

Why?  Color or monochrome?

I am thinking this may be a case of get the best I can afford to delay the day when I need to 

replace it.

Can anyone comment on camera selection?

Regards,

Jess