Quote:
Originally Posted by coldlegs
Greg
You learn something every day on this website! Didn't know there was a thing called “Gradient Exterminator”. Did some investigation and it brought me to my old problem...how do I get a full copy of Photoshop with out pretending to be a student or paying more than a good RC costs. Damn that software's expensive. I'm just going to have to get used to trying to use freeware like gimp etc because I'm way to stingy to pay a small fortune for photoshop! Back to the problem at hand.
I've looked at the 8300 and although it's around the right price range, it's a reasonably heavy beast at 2lbs. I would be worried if I had that on the end of a barlow and a comma corrector and a filter wheel. Still people do it so it must work.
My thoughts at the moment are to but a QHY8PRO colour (about $2.3K) and a 10”F5 black diamond newtonian (about $550) with a baader coma corrector kit (about $350). That leaves me with roughly $800 that can be used to buy OIII/H-alpha/CLS filters or maybe some 2” powermate barlows. I would probably go 12”F4/F5 but the weight including guider etc would be getting up to the top end for an EQ6PRO. The 10” should give me at least two and a half times more photons than my 6” and I'm familiar with the F ratio. I looked at the RC's from Andrews but an affordable 8” wont give me much of a gain and a 10” is amazingly heavy and out of my range for the moment. A light bucket newt and a good colour camera will probably perk up my interest for a year or two.
Stephen
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That sounds like a well thought out setup.
You can sometimes pick up a 2nd hand copy of Photoshop on Astromart. I got a copy of CS4 that way. It cost $200 as I recall.
New that is more like $1200 or something.
As far as 8300 versus QHY8. My first astro camera was a Nikon D70. It used a 6.3mp Sony chip which I believe is the same CCD chip in the QHY8. It was quite a good chip although in the Nikon it gave bad amp glow ( a purple glow area that worsened with longer exposure). That was the Nikon not the chip. I assume the QHY8 does not suffer from amp glow. Amp Glow is caused by the amplifier circuit that was heating up the chip in one part of the chip. Canon CMOS chips have the amplifier built into each pixel. They also shield the chip from other circuits. The Nikon had circuitry behind the chip touching the back of the chip. Not smart.
The ST body I thought was quite light. What does a QHY8 weigh? It must be very light. Sure weight factors in as you don't want flexure. But at F5 with no barlow if the focuser is half decent you should be ok.
It comes down really to mono CCD imaging versus one shot colour. Unless of course you get the 8300C which is the one shot colour SBIG.
One shot colour is fun. I did it for a while with an SBIG STL11000XCM. Its nice to see the download coming off the camera in colour.
It has advantages and disadvantages:
Advantages:
easier processing
every image counts whereas in mono you need LRGB (4 images) or at least RGB to make an image. So you often miss out in an imaging session if cloud comes in and interrupts and you only got LRG or something.
its cooled so its a step up from DSLR and cleaner electronics plus its CCD versus CMOS.
Disadvantages:
less sensitive
less flexible - not really ideal for narrowband imaging as only 1 in 4 pixel is really picking up anything ie Ha can still be done but slower. O111 and S11 are probably mostly impractical. If light pollution is an issue then you miss out on the ability to do narrowband as an option.
less resolution - mono is 4 times the resolution as every pixel registers part of the image rather than the pixels grouped in 4s to create the colour (called the Bayer matrix which is the layer of micolenses that are coloured and laid over the mono chip).
less noise and especially less colour noise ("smarties" in the background - lots of little red green or blue dots very often).
less noise and more response in the dimmer areas - nebulas often have dim areas of dust. One shot colour is weakest in the dim areas where the noise can get very bad. Mono also does this but nowhere near as bad.
So you have in the end one shot colour gives ease but comes at a cost of not as good quality images and less resolution with more noise.
Not to say of course you can't do a good one shot colour image. Of course you can and there are lots to prove that. But you may need to image for longer to make up for the lack of sensitivity (one shot colour chips are usually around 25-33% QE (QE is a measure of efficiency of a chip converting light to electrons) compared to around 55-60% QE in the mono so about twice as sensitive. It is a bit complicated to do a straight comparison like that as there are other minor factors so in the end it may be closer to 50% more sensitive.
Of course one shot is lighter (no filter wheel), cheaper - no filter wheel and no filters and easier. Mono may require more software.
So it can be a budget decision or it can be an make imaging easier decision. But like everything else in life - to get better results usually requires more effort.
Greg.
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