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wavydavy

Best way to focus off axis with guider and image camera?

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Can anyone offer any advice or tips to reach focus using an off axis guider, with a guide camera attached and a CCD camera for imaging? I had a nightmare with a previous CCD camera (now returned) and want to try again with my new imaging CCD camera. I have spacer rings for both the cameras, but no fine adjuster for focusing properly.

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All I can suggest is that you get your main imaging camera focused using your scope's focuser, then, using the OAG focuser adjust the guide camera focus.

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Which OAG have you got ? I think TS or somebody makes an adjuster for OAG  guide cameras.

Dave

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Assuming for now that you have a refractor, do you have a focal reducer/flattener? If you do then the most important task is to get the spacing of the imaging camera correct so that the focal reducer works correctly. Once you have got the imaging camera spacing correct, focus on a distant daytime object and adjust the telescope's focus until a sharp image is captured. Next, adjust the pointing of the telescope until the same object is in the field of view of the guide camera and without touching the telescope's focus, move the guide camera up or down in its holder or add/remove spacers until it too is focused on the object.

That's it!

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It doesn't even need to be distant since you are just trying to match the two spacings the distance just needs to be the same. I can focus my scope on things in the same room which makes it very easy to test different setups.

Remember it doesn't have to be perfect either, slightly out of focus is fine for guiding.

Sent from my iPad using Tapatalk

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I'm using a Starlight Express OAG with two SX cameras, so a one manufacturer system.

As the other posters have already noted, firstly get the imaging camera to focus, then worry about the guide camera. If you have a one manufacturer solution it should all be fine, just adjust the guide camera to be parfocal, but if you have a mix and match system, you will need to play with distances, but once you have the guide camera parfocal with the imaging camera all your woes are over (well in a perfect world anyway.)

The degree you need the guide camera focused I find depends on your guiding software. I've tried PHD and Maxim, and PHD seems to guide just fine on defocussed stars.

Just my opinions as usual.

Huw

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As suggested, its much easier to set up an OAG during the day on a suitable (distant) object.

Set the imaging camera first and then "tune" the spacing of the guide camera to suit. If you find you can't get close enough to the optical axis then fit a spacer(s) between the imaging camera and the focuser. If you're using reducers/ flatteners/ coma correctors etc. this can lead to headaches....such is life.

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So I should use spacers on the guide camera, I didn't think that would adjust the focus on the guide camera, just move the focal plane??? Ie.... the same as moving the slider back and forth across the plain??? So adding spacers, adjusts the focus, but moving the slider doesn't....right????

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Yes, exactly that, moving the slider moves the point that the pickup prism sees,  you need to move the guide camera in relation to the pickup prism to adjust focus.

Does that make sense?

Huw

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