Question about guide camera

[kookoo_gr]

i am thinking of changing my qhy-5 to a starlight xpress costar since it is cheaper than the lodestar. my question is, if anyone has it, how much sensitive is it with the use of an oag from the qhy, since i see they have the same cmos sensor

[riklaunim]

You will get the same sensor-performance. The only change may be in drivers/electronics (available gain levels etc.).

What's your problem that makes you change the guide cam?

[kookoo_gr]

at my latest imaging runs i had a really difficult time finding a suitable guide star with my oag and after increasing the time to 2.5 secs i was able to find a dim star and phd at half the times couldn't get a proper lock at my fov

[riklaunim]

On long focal lengths OAGs may have problems with the amount of stars they see. Micron CMOS based guide cameras will be rather to noisy for multi second exposures. So you either need a low noise guider like Atik Titan (and around 5-10 sec exposures), or using the QHY5 and trying to frame a good guide star within the OAG FOV (or trying external guider).

[nytecam]

SX homepage shows comparative shots of the same starfield via Lodestar and Costar with reference to relative sensitivity of the cams

[ollypenrice]

Are you confident that your OAG prism is as fully inserted into the light path as it can be without creating shadows which flats won't remove? It does make a big difference to the availability of viable guide stars. For me guiding with an OAG is a necessary evil with the large telescope but I don't use them where our separate guidescope will do the job.

Olly