SPC900 question

[nmoushon]

In regards strictly for guiding purposes why is the SPC900 so good? Is it just that it has 90 fps where most other web cams have 30fps or is there something else that makes this one stand out over all the others? Since getting my hands on one of these is quite hard atm I'm trying to find a good alternative to it. I know that there are dedicated CCD guide cameras out there but I can see spending $300 on just that. Then another $100-200 on a cheap guide scope. So if someone could fill me in on the details I appreciate it. Thanks.

[Bizibilder]

You won't get 90fps from an SPC900! Maybe 10fps (without image compression) if you are lucky. The SPC900 is favoured for its (comparatively) sensitive chip, but mainly for the ease with which you can control it - especially the gain control and the ability to do long exposure modifications.

As a guide camera it does work - for a while I used an SPC900 and 50mm finder to guide, using PHD software and EQMOD to control my mount. The only downside was that I soon realised that a cheap webcam is really not that sensitive, often it was difficult to find a bright enough guide star without having to aim the finder well away from the target.

I now use a QHY5 / Finder guider and it works perfectly.

[nmoushon]

Well i guess the 60-90 fps I read on a website is full of bs then. Thanks for point that out. So the fps doesn't really matter then when it comes to guiding just how sensitive the chip is? If so how do I tell how sensitive a chip is? Is it the type? CCD vs CMOS? or something else?

[JamesF]

Plus of course that you could get an SPC900 modified for guiding and it would cost about 10% of what a "proper" guide cam cost. I don't believe there really are any good alternatives in the same kind of price bracket now. Probably the cheapest way you can do it is with something such as the QHY5 and a finder-guider as Roger suggests, though I suspect that it's not an awful lot cheaper than using an ST80 unless you make your own finder or happen to get hold of a suitable scope very cheaply.

James

[JamesF]

CCD as in the past tended to be more sensitive than CMOS, though CMOS is catching up. For any given sensor chip you should be able to find the sensitivity rated in "Lux". The smaller the number the better. Off the top of my head ISTR the SPC900 sensor is < 1 Lux, whereas many webcams are around 5 Lux and some are even as high as 10 Lux.

Regarding frame rate, the SPC900 has to compress the image at anything over 5fps at 640x480 because USB 1 just doesn't have enough bandwidth for more. It won't do any more than 30fps to the best of my knowledge.

James

[nmoushon]

Is the SCP900 or something similar only good if I use it on a separate modded finder scope or does it still work well with an OAG?

[nmoushon]

So new question....could I use the orion star shoot camera for a guide cam? Or is that still not sensitive enough?

[JamesF]

Really not sure about using it as a guide cam. It may well not be possible to use with an OAG. I believe that it's better to have as sensitive a camera as possible for use with an OAG.

James

[nmoushon]

So if I go the OAG route then I'm the QHY5 is pretty much the minimum then? And if I go with modded finderscope or ST80 the SPC900 is the minimum?

[JamesF]

That's probably a sensible approach unless someone steps forward and says "I've tried this and it works fine". Of course, you could be that person

James

[nmoushon]

Ok thanks for the help James. I'm still going to look through the web and see what I can find. Do you know of a way I could test some webcams for their sensitivity without destroying them? (So I can return them and test another ) As most of them don't give very good spec details as most people don't care/know what they mean anyways.

[JamesF]

With the webcams I think the only way to do it is to try to find out what sensor they use and then look up the manufacturers specifications for that sensor. It's rare to see it shown by the webcam vendor because as long as it's sensitive enough for normal webcam use then they probably don't care.

James

[astromerlin]

Shhhsss, There's a Philips PVC840k on the bay, 2 days to go. Ideal for planetary possible guider and can be modded for long exposure if your electronically minded.