Off axis guider

[martin_h]

Where in the imaging train is the best position? close to the imaging chip, far away, does it matter where it is?

[wavydavy]

Id say it was best around the imaging area and not in the centre, if possible, as you would be cutting the light down (bit like a central obstruction on a  newt).......

[wavydavy]

I use an off axis guider on my 10" newt...............and its a pain to get focus on both cameras.............let me know how you get on!

[Davey-T]

I've got the Atik EFW2 and Atik OAG and the OAG bolts straight onto the filter wheel.

Dave

[martin_h]

So closer to the chip than not.

[swag72]

I guess it all depends on roughly where your spacing will take you Martin. This will be your dictate for sure I would think otherwise you'll not get focus. Normally I would think that the OAG would go straight after the filter wheel so that you have the minimal amount of space between the OAG and sensor.

[r3i]

I always thought that the OAG should go in front of the filter wheel so that the guide camera got unfettered access to the light from a guide star.

[swag72]

I always thought that the OAG should go in front of the filter wheel so that the guide camera got unfettered access to the light from a guide star.

 Sorry didn't explain myself well - I think of it as going behind the filter wheel on the side of the telescope - Opposite to the sensor. Definitely to catch the light before any filters get in the way.

Infront or behind ....... That's the least of our wording worries

[Singlin]

I have a 9mm oag and when placed immediately after my EFW2 the distance from the ccd chip to center of oag prism is shorter than the minimum focus distance I can get with my guide camera to the oag prism.I have yet to fit an oag to my Quattro 10" and have not found a solution.

Excuse me for my grammer I am tired and can't be bothered to try and correct it.

Regards,

Simon

[sloz1664]

Hi Martin,

Are you looking at attaching this to your Z71. If so, you will struggle getting an OAG in the imaging train if you are using a filter wheel.

I couldn't achieve it with the Atik 460ex, TS OAG and Truetek filter wheel combo on my Z71.

cheers

Steve

[martin_h]

Hi Martin,

Are you looking at attaching this to your Z71. If so, you will struggle getting an OAG in the imaging train if you are using a filter wheel.

I couldn't achieve it with the Atik 460ex, TS OAG and Truetek filter wheel combo on my Z71.

cheers

Steve

Not the Z71, I know that wont work. I'm thinking of the new Star 71 with a OSC camera, so plenty of back focus space............. So if the OAG is set about 10mm infront of the chip everything should be ok......perhaps!

[Zakalwe]

The design of the OAG (how much movement is in the prism), the guiding camera (distance from nosepiece to sensor surface) and the imaging camera (distance from nosepiece to sensor surface) will pretty much dictate where the OAG will end up. The guide and imaging camera have to both be in focus. You will have a little bit of flexibility by moving the pick-off prism up and down, but you won't want it intruding too far into the light cone or you will get vignetting.

In addition, a further complication will come from using a focal reducer or field-flattener, as these will dictate the distance to the imaging sensor. You are intending to use a OSC camera, so that will help as you won't face the challenge of squeezing a filterwheel in there as well.

On my setup (TS Photoline Focal reducer, slim Skywatcher OAG, SX filterwheel, QHY5L-II guide camera and Atik 428) I had to do a lot of bodging to get it all to fit. I had to remove the front off the QHY (easy as it just screws off) and had to sand the shoulder off the SX filterwheel adapters. I also needed a straight TS T-thread adapter (male-to-male without any shoulder) to get the Atik as close to the FW as possible.