Off-axis guider instead of guidescope?

[EzyStyles (Eric)]

Hi Guys,

I'm doing abit of research on guiding and was wondering if an off-axis guider can be used instead of a guidescope therefore eliminating the purchase of one?

I have an off-axis guider lying around somewhere not doing much.

cheers guys.

[xelasnave]

Eric if you have one why dont you try it??? I believe finding a guide star will be more difficult (why I am not sure maybe the "range" maybe they dont get as much light and you need bright stars). If it works you eliminate any flex problems sometimes present with a guide scope.
alex

[Dennis]

In the good old days of 35mm film photography, I started using an off axis guider for manual guiding and they do require some getting used to, compared to the relative ease of finding a guide star in a separate guide scope.

As Alex rightly points out, locating a suitable guide star can be more difficult, as with the off axis guider, you generally do not have the luxury of the wide field of view, and independent pointing (within reason) of a separate guide scope.

So, you are limited to finding a guide star within the physical geometry of the off axis guider movements, and I understand this varies significantly from model to model. Some allow a 360 degree of freedom to rotate the guide star viewing port, others limit it to less than 180 degrees.

Cheers

Dennis

[EzyStyles (Eric)]

Thanks for the reply guys. The off-axis guider came with my scope as i have never used it before. Im not sure if i can even reach focus in my 8" newt with it. Suppose to come with 2 eyepieces but instead i requested the off-axis guider rather than the 2 plossls from the seller. what i really want to do is autoguiding instead of manually on the EQ6 with 2 DSI cams both connected to the off-axis guider. not 100% sure if this setup will work or not.

cheers guys.

[Dennis]

I think that off axis guiders are more suited to 'scopes with more back focus than the traditional Newtonians. I have read that some people fit their Newts with a low profile focuser, or even modify the location of the secondary and/or primary mirror, to provide sufficient (increased) back focus for an OAG.

Good luck

Dennis

[Lester]

Eric as others have said, give it a go. But on some DSOs you may not even find a bright enough guide star.

[[1ponders] (Paul)]

As Dennis has said Eric, getting focus will likely be a problem without either a much lower profile focuser or shifting the mirror forward. Tornado33 uses one but he had his custom built.

I tried using an oag with my sct for autoguiding and gave up in frustration. I found it too difficult to find a guidestar most of the time, that I could use with the ToUcam. It might be different with the DSI with the longer exposure time.

Having said all that, there are a lot of great imagers out there who use an oag, I just don't know how they do it to themselves.

[astroboy]

Just another issue is you will have guide stars with lots of coma because you are looking at the edge of the field before your coma corrector if you have one this can make guiding or auto guiding difficult and the stars even fainter.
The only setup I found to solve this is the Lumicon offaxis ( which is only 25mm thick plus thier coma corrector that fits at the front.
I have these if interested would make a good setup for DSLR as well.
Main advantages are wieght and flexture

Zane

[Merlin66 (Ken)]

I agree with you. The Lumicon OAG is great. I just upgraded mine to fit the MX7c Starlight CCD.