OAG fails to find a star, Change to a Mini Guiderscope

[carlosgib]

 Hi Group, my  telescope is a Tak CCA 250 Cassegrain reflector, FL 1250. My Dome shutter window space is limited and putting large guider scope on top of the main scope will be obscured when the scope change declination position, I have had always worked with guidescope and never had an issue with the Tak106 refractor. 

 Currently my OAG has a lodestar 2 and is finding it difficult to find a star (to say the least) so I thought  of changing back to the guiderscope but  to a small version:  mini guider scope with a small pixel camera.  Now the rule of thumb say that the guider scope FL should at least 1/3  to the telescope thus I was looking at the  QHY5-III 178 Mono and QHY MiniGuideScope Kit believe that the miniscope is 130mm.

 

Any suggestion will be appreciated, either with the combination above or changing the current lodestar. Thanks

 

Carlos

[Davey-T]

It can be tricky finding OAG guide stars especially when aiming out of the Galaxy imaging small DSOs, I have the same problem and have to resort to rotating the guide camera and moving the target off centre hunting for a suitable guide star.

Dave

[Xplode]

I'm having a scope being installed in Spain at the moment with 1841mm FL with an off axis guider, to get a larger sensor the ASI174mm was chosen for the task, if it works ok i will know for sure in a few days
The scope is a f5 just like yours.
I will let you know how it works out.

[Kaliska]

Maybe look at the ASI290mm fantastic sensitive guide camera.

I had the same problem (but was with the Lodestar 1) with my F5.8 setup. So I bought the ASI and the difference was like chalk and cheese.

Now, I don't even think about it, I always have at least 10 stars to guide from.

Edited June 24, 2019 by Kaliska

[carlosgib]

Thanks Ole, please keep me inform, I am interested with the result.  And Dave thanks as well, moving the object center would work and it wouldn't be that big issue with SGP  'Framing & Mosaic Wizard' tool, thanks for the advice.

Carlos

 

[ollypenrice]

Is the OAG turret pushed as far into the light cone as possible without shadowing the chip? It should be pushed in close to the longest side of the chip (to go deeper) and be at right angles to it. Sorry if this is obvious and you've thought of it.

Olly

[Xplode]

I had a chance to test the ASI174mm Mini tonight, at 3s exposures there weren't a lot of stars in the FOV, in the area around M13 i got 2!
With just 2 stars on the large large ASI174mm sensor there would be a big chance of 0 stars on a smaller sensor since they are 1/4 the area or even smaller.
I will test more tonight and increase exposures and gain to see if i can catch more stars.

I saw no hot pixels at the settings that were used, but they might appear at higher gain.