Guide scope or OAG

[darknight]

I dunno, thinking of going to an OAG, seems a simpler way to image with even less weight, not that its a prob on an eq6 with an ed80, but what are your thoughts? do you prefer a guide scope say an st80, or an oag that's lighter

[PeterCPC]

If you are imaging with an ED80 you want a guidescope not an OAG. OAGs are normally for much larger aperture scopes. I use a 50mm guidescope with mine.

Peter

[darknight]

ok, why is that peter? I thought the oag would work as the ed80 having a wider field would still have enough stars to guide from, but I'm open to insights

[swag72]

An OAG will absolutely work with a short foal length scope - I use one with 330mm....... But I guess the point is more that you don't NEED to use one, and in my opinion you'll see little benefit, when compared to a long focal length scope, of using one.

 

[darknight]

 thank you Sara, just a bit did heartened got a st80 that's not right(bought 2nd hand), weirdly works fine visually, but when a ccd is added it blurs all the stars, so I think the lenses are out just a bit, could sit there for eternity adjusting them lol.

maybe better getting a new st80 from flo

[swag72]

5 minutes ago, darknight said:

 thank you Sara, just a bit did heartened got a st80 that's not right(bought 2nd hand), weirdly works fine visually, but when a ccd is added it blurs all the stars, so I think the lenses are out just a bit......

Could it be that the focus is out plain and simple? It  *may* be that the spacing for the focus is wrong and you need some thing extra to get focus with a CCD? Hopefully someone will be along soon that uses an ST80 and can confirm...... 

[xanthic]

I've tried this. You need an extension tube, I'm pretty sure over I needed 50 mm with my QHY5-II.

 

Edit - I use an Altair Astro 60 mm guide scope. Much better in my opinion. Lighter, less chance of flexure, better optics.

[darknight]

oh yea, I use an extension tube, its just pretty weird problem.

when I first got the scope, it was terrible, took it apart and the lenses were the wrong way round, contacted the guy and he assured me he done nothing so whatever.

I corrected the lenses and visually it works just fine, even see the moons on Jupiter.

as soon as a ccd goes on, it will not focus, back and forth past focus point so I know I have enough back focus, the stars are just a white blurry lump, even Jupiter.

so the only thing I can think is the lenses are slightly out, may need a small twist one way or another, not enough for a visual scope, but the extra power of a ccd brings it out

[DaveS]

I took the lenses out of the cheapo 2x barlow that comes with the ST80, that enabled me to reach focus with a QHY5-II, but I did have to use the short extender that came with it.

[darknight]

yea same here  its an altair gpcam2, so about the same needed back focus of 50mm

[ollypenrice]

I also used 'dead' Barlow bodies to extend the ST80s which guide both our imaging rigs.

Like Sara I think you could guide with an OAG but they are a bit of a faff to set up and are not, I believe, necessary for guiding refractors. They come into their own at long FLs and with reflectors whose mirrors can shift. If they do the OAG 'sees' the shift and corrects it.

You don't need sharp stars for guiding. Craig Stark of PHD fame suggests deliberately soft guider focus because you don't guide on a guide star, strictly speaking, you guide on its calculated centroid. This calculation works better, it seems, on a soft focus. Who am I to argue? I haven't touched the focus on our ST80 guide scopes, quite literally, for years.

Olly

[darknight]

thank you, maybe I will give it another try tonight before launching it into next week!

should be clear tonight fingers crossed

[ollypenrice]

2 hours ago, darknight said:

thank you, maybe I will give it another try tonight before launching it into next week!

should be clear tonight fingers crossed

Rather a lot of moon though! Beddie-boes for me...

Olly