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Guide scope f/#


NickRose2006
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Currently I'm using my LX SPC900nc on an old Celestron refractor that has a 700mm FL and is f/11. Would the focal ratio be the reason why I can't pick up fainter stars for guiding? Would a faster scope be better for the SPC900nc? I'm currently looking at the Orion Mini 50mm guide scope.

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400 mm & f5... something like an ST80... will give you loads of stars without needing a very sensitive guidecam... I use a 500mm f8 Telephoto lens with a Meade DSI IIc as my guidescope on the obs setup but an ST80 with the Synguider...

These days guiding software guides to sub pixel levels so the need for longer FL guidescopes is diminished if your imaging at reasonable FL's...

Peter...

Edited by Psychobilly
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  • 2 weeks later...

A few days ago I recieved my Celestron 9x50 finder scope and tonight just finished the mod. I didn't have time to test it the proper way, but I put the camera/finder on the ground pointing up to the sky. Tried sharpcap first and had gain at full and exposure at 1sec and picked up many stars but when I went to PHD it did not pick up any stars. I tried changing the gain and exposure slider but nothing. The camera Im using is a LX SPC900.

Tomorrow or Sunday I'll test it the proper way on the main scope and mount.*

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A few days ago I recieved my Celestron 9x50 finder scope and tonight just finished the mod. I didn't have time to test it the proper way, but I put the camera/finder on the ground pointing up to the sky. Tried sharpcap first and had gain at full and exposure at 1sec and picked up many stars but when I went to PHD it did not pick up any stars. I tried changing the gain and exposure slider but nothing. The camera Im using is a LX SPC900.

Tomorrow or Sunday I'll test it the proper way on the main scope and mount.*

Well, speaking as someone who has absolutely no experience of this at all, it seems to me that the problem has to be in the PHD settings - you know the camera is working. Is the program 'seeing' the camera? That seems to me to be the most obvious answer - and something that can be tested away from the scope. But then, based on my 'experience', I could be talking complete rubbish.

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Is the program 'seeing' the camera? That seems to me to be the most obvious answer - and something that can be tested away from the scope. But then, based on my 'experience', I could be talking complete rubbish.

PHD does see the camera. I have used the camera on another scope before with PHD and it does pick up the very bright stars like Vega.

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I have attached a MS LifeCam Cinema to my 9x50 finder scope but the FOV is very small it seems to me. It's difficult to find a star. I haven't had a chance to try it with PHD as yet. I'm beginning to think an ST80 might be worth buying rather than faffing about too much. They aren't all that expensive :)

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A finderguider is about 200mm at f/4, so gives a nice wide field and a bright image. I use a QHY5 guide cam rather than a modded webcam, but have no trouble finding guidestars. It seems to work very well indeed.

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Yes, I've decided to take that route as well. When funds permit I shall be buying a QHY5 to attach to my 9x50 finder scope - I already have the adapter. It should be a big improvement over any webcam being more sensitive and having a much bigger sensor.

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Yes I used the SPC900/880 1.25" adapter. What I did was put two layers of the gorilla tape on the adapter and then put that into a PVC reducer bushing SP which I also put two layers of gorilla tape on. One side note, you might have slight trouble putting the adapter into the bushing so you might need to use a hammer to fully set it into place in the bushing.

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