Guide Camera, how sensitive should it be?

[AstroGuy]

Hi all,

Anyone have any ideas how sensitive a camera should be for guiding?

[[1ponders]]

you can get away with a webcam. I used a ToUcam 840 and 900 successfully for ages. However the more sensitive, the more stars you have to select from. Probably of more use is the ability to have a longer exposure time. The ToUcams (unmodded) were limited to 1/25 sec. Being able to jump up to 1 or 2 secs is a big advantage.

Noise is also an issue at times, but using something like PhD give you the option of taking darks with can make a big difference, even with a toUcam

[wasyoungonce]

Well that depends...if you are off axis guiding then you would want someting quite sensitive like a loadstar (http://www.starlight-xpress.co.uk/Lodestar.htm).

If you are off axis guiding and imaging thru filters then guide camera sensitivity is even more important, maybe a cooled guide camera or loadstar..or maybe one of the new SBIG guiders (http://www.sbig.com/sbwhtmls/STi.htm) or a guide head inbuilt to your camera?

If you are guiding thru a guide scope..then the std Q guider/webcam etc will more than likely suffice for most.

Well...FWIW.

[AstroGuy]

Thanks for the reply people,

Any of you know what the lux rating of such cameras you mention are? The reason I ask is because I can pickup a .000001 lux on eBay for around 65 bucks Australian. The cameras you both mention are a little more than that.

I would like to save as much money as possible. I have thought about it carefully and if I did have to go with a good guiding system where price is no object, I'l go with Celestron's Nexguide for 299.00 US.

[[1ponders]]

Is that one on ebay digital (usb) or analog? Will the guiding software see it?

[AstroGuy]

You'll need a video USB/PCI capture card to webcam it for PHD etc... It has video and audio and 12vdc power. And of course a shoestring adapter to hook it up to a ST4 guide port. The camera is analog. You can also get a USB 4 port video capture dongle for about $8 delivered worldwide. It will only work on systems up to Windows XP/2000. Resolution of the camera is only 380 lines, but should be enough for guiding.
There are even cheaper ones but less lux .001. I think I'll get one anyway. Oh, and did I mention, they are colour.

[tlgerdes]

The problem with all that is "what software is going to recognise the camera to guide with":shrug:

Great to have a camera, but if no one recognises it, you will be guideing by hand.:screwy:

Dont re-invent the wheel....... unless you are happy to through away $100 if doesnt work.

[AstroGuy]

Say what?

Any guiding software that supports WDM multimedia interface will do it (and most do). There is a free one out there called guide dog for starters.
Are you sure we are talking about the same thing?

[AstroGuy]

Hello again,

I'm getting some mixed messages as to what kind of assistance I'm asking for.

All I need to know is what would be considered an acceptable lux rating for a camera to be used as a guidecam.

I've tested some software. Guide dog in particular, and it seems like it will do the trick. Primarily because it has the ability to control my Celestron 4se through the serial port. It will detect any camera you plug into a PC that will show up as a WDM device. I plan mounting a Canon 550D DSLR on the Celestron 4se and perform some Astrophotography. I'm also planning on getting a Skywatcher EQ6 Equatorial mount so I can get my Saxon 8" Mak up and running also. I would like to setup guiding on that eventually also.

But for now, all I need to know is what is an acceptable Lux sensitivity rating for a CCD camera so it can be used for guiding. Any help on this issue would be accepted gratefully.

Thank You.

[wasyoungonce]

No one can authoritatively tell you that and indeed this is a little more than what you started asking, so, if your confused, we are as well.

As for lux rating.....most web cams/video cameras use a Lux rating to rate their ability to see in low light where as dedicated CCDs use quantum efficiency (QE) rating. Lux is not a good guide on how well it will pick up dim stars.

Lux rating is good for daytime ratings of cameras but not so good for Astro ratings. If you increase the exposure time on your webcam you can see more feint objects, but the sensor noise may be unacceptable.

My older Philips SPC900NC web cam was rated as "<1 lux" and most people find it a reasonable guide camera and pretty good all round planetary camera.

But as for stating a camera can work in .0001 Lux..Hmmm that is pretty out there with 1000X magnification ratings of a 60mm dept store telescope. About the only thing I have seen and used that can work at .0001 Lux are Gen 3 light intensified photomultiplier night vision googles.

So be wary of some claims and look around to see what others are using.

Hope this helps.:D

[AstroGuy]

Hi WasYoungOnce,

Thanks for the tidbit. I am aware of the information you have expressed. These days though, CCD's are getting much more efficient at lowering noise. They are also being manufactured way cheaper than the old days, especially some stuff comming from China. I know, some people are iffy at stuff that comes from China, I have come across some dodgy stuff but by the same respect also some great products.

The purpose of this thread was mainly to get some form of concensus as to what others users of such equipment have found to be an acceptable sensitivity level for a guide cam. I'm aware that exposure factors help but this is not what I'm after. BTW, I thought the term "Lux" was just another way to rate light quanta in the detection process.

From what I have gathered so far, the Sony HAD sensors with around .001 Lux sensitivity and less are being used by a lot of guidecams. It just so happens the CCD I mention I plan to purchase has a Sony HAD CCD matrix.

Thanks for the input.