CCD sampling

[Andyk93]

Hi, I have recently bought a WO star71 and I'm waiting patiently for it to arrive. While I'm waiting I'm thinking about what CCD to buy. Looking at the sample rates for a 350mm fl scope they seem to be very high. The lowest I can get is from a ZWO asi1600mm which gives 2.25"/pixel. Up to 3.2"/pixel on an atik 383l+. Surely people have come across this problem before? It's probably a non-issue with such a wide field but I just want to make sure before I make any stupid mistakes. Thanks

[Uranium235]

Try not to pay too much attention to the sampling rate with just one telescope. You are fine with 3.2"... in fact you are ok up to 4" and still get good stars.

If you want a higher sampling rate for individual objects or areas of interest, have another telescope on standby for when you need it. Thats why I have a range of focal lengths available - 135mm (Samyang), 350mm (Star71), 650mm (130pds), 1000mm (200pds).... choose the tool for the job (ie: I wouldnt go galaxy busting with a Star71, or try a galactic core mosaic with the 200pds).

Also, on a side note - smaller pixels may give you with one hand a better sampling rate, but with the other they take away dynamic range - and/or in the worst case, bits (for instance, the asi1600 is not 16bit).

There is nothing wrong at all with the 71/383 combo - the only time you will find it wanting is during galaxy season (same applied to the 80ED and 130pds). In fact, you want to be getting the biggest chip you can reasonably afford (8300) to make full use of the flat field the Star71 offers (sticking a small chip on a quintuplet astrograph is a bit of a waste IMO):

(16 panel mosaic, Star71, 383L+)

Im trying not to be biased but the 71/383 combo has served me (and others) quite well.

[Andyk93]

11 hours ago, Uranium235 said:

 

Thanks very much for the help. I do have a 200pds when I want to do anything smaller. That image is amazing, definitely made my mind up. I'm sure the 383L+ will be a massive step up from a dslr anyway

[swag72]

While I have a different scope than the WO71, I am working at 330mm and so slightly less than you. I have used 3 sensors on this scope - 2 Sony sensors (in the 460 and 490) and also the Kodak KAF8300 (in the 383) - My sampling rate is very much higher than is recommended at 3.38 arc seconds per pixel.

I am not seeing any detrimental effects at all and for me the wider field with the KAF8300 is FAR out weighed by any single advantages that people seem to think are around with the Sony chips. My advise is to talk to people who are using certain combos and look on the forum for people using combos that are similar (if not the same) - You'll soon get a feel if their sampling rate is problematic.

While theory is all very well and good, I'd rather see real life examples than anything else - Get hooked on theory at your peril..... it will prevent you doing a number of things  

[Davey-T]

Atik 383 in the for sale section.

I'm using Star 71 and QSI683

Dave

Single HA sub Star71 QSI683

 

 

[Uranium235]

4 hours ago, Andyk93 said:

Thanks very much for the help. I do have a 200pds when I want to do anything smaller. That image is amazing, definitely made my mind up. I'm sure the 383L+ will be a massive step up from a dslr anyway

The 200pds and 383 is also a good match (for speed and resolution - 1.1" p/p), it will also allow you to bin 2x2 - which Im sure is a feature not available with ZWO cameras (well, hardware binning anyway). But its a bit more of a fiddly setup (getting the spacing right etc..), but when you do get it right it really is the beans.

[Andyk93]

11 hours ago, swag72 said:

Thanks! I do like to check what other people are using but that's when I got confused that the theory wasn't adding up to the real life. The more I learn the more questions seem to open up

[ollypenrice]

We would all like to image with a chip which was as big as our optics' fully corrected circle and with a pixel size whch came close to the resolution of our optics, guiding and seeing. So, if any manufacturer is listening, I'd like a 40mm x 40mm chip with 4 micron pixels, please. Damn, it would be so nice to believe in fairies. 

Olly

[Thalestris24]

59 minutes ago, ollypenrice said:

We would all like to image with a chip which was as big as our optics' fully corrected circle and with a pixel size whch came close to the resolution of our optics, guiding and seeing. So, if any manufacturer is listening, I'd like a 40mm x 40mm chip with 4 micron pixels, please. Damn, it would be so nice to believe in fairies. 

Olly

You can probably get one, Olly - at a price!

Louise