QHY & OAG compatability

[astronobob (Bob)]

Hi all,

As some may know, I'm venturing into purchasing a dedicated CCD one shot color. My flavour of this month is QHY's : )
So, would like to kindly ask if any who are using a QHY ccd's and whether you have addapted an OAG with it, and/or whether it is possible to do so ?
As I would like to go OAGuiding with QHY on a Newtonian, being the Skywatcher 10" F4.7 which only has approx 50mm focus travel.
Also, I need to fit the Baada MPCC with it, so, I may need to add extension between OAG & guide camera, (Orion Starshooter) which shouldnt be much of a problem ?
So, fitting an OAG, which brand/type would be most feasible/practical in the above set up ?
Thanx very much for any assistance, input, advice etc

[Peter.M]

I have a qhy9 and a mpcc and I use a ssag. I am using the ts OAG9. you should have tonnes of room to fit one if you are shooting using a OSC camera because you dont need to fit the filter wheel in too.

[Lee]

I use a TSOAG9 too, just this week.... working well, about 12-13mm thick after you account for the adaptor to screw it to the MPCC.
Without a filter wheel, you should be able to use a pair of T-thread extensions to locate the OAG at a nice distance from the CCD so focus is simplified without extensions on the OAG stalk....

[astronobob (Bob)]

Originally Posted by Peter.M

I have a qhy9 and a mpcc and I use a ssag. I am using the ts OAG9. you should have tonnes of room to fit one if you are shooting using a OSC camera because you dont need to fit the filter wheel in too.

Thanx Peter, What doas the 'ts' stand for & what is meant by OSC, something Single Color ? ? ? Thanx Peter

Originally Posted by Lee

I use a TSOAG9 too, just this week.... working well, about 12-13mm thick after you account for the adaptor to screw it to the MPCC.
Without a filter wheel, you should be able to use a pair of T-thread extensions to locate the OAG at a nice distance from the CCD so focus is simplified without extensions on the OAG stalk....

Thanx Lee, so, a couple of T thread extension to keep things snug & straight, sound like a nice application.
Do you have a link for where to get these Lee ?
Thanx again

[Peter.M]

Originally Posted by astronobob

Thanx Peter, What doas the 'ts' stand for & what is meant by OSC, something Single Color ? ? ? Thanx Peter

Sorry TS is the brand, and OSC is one shot colour.

The TS oag is available here. You may be able to use another OAG because you dont have the filter wheel to deal with but this was just about my only option.

http://www.teleskop-express.de/shop/...ial-Offer.html

[Tandum (Robin)]

Bob,
You need to know distance to sensor for your OSC camera, the distance to sensor of your guide camera, the thickness of the OAG and the backfocus for your corrector. Then on paper, draw it up. The distance from the prism on OAG needs to be the same to the sensors on both the OSC and the guider plus you need the correct spacing from the OAG to the corrector.

[astronobob (Bob)]

Originally Posted by Peter.M

Sorry TS is the brand, and OSC is one shot colour.

The TS oag is available here. You may be able to use another OAG because you dont have the filter wheel to deal with but this was just about my only option.

http://www.teleskop-express.de/shop/...ial-Offer.html

Thanx Peter A nice looking slim unit actually. Ill have to research further on adaption Re; no filter wheel Cheers.

Originally Posted by Tandum

Bob,
You need to know distance to sensor for your OSC camera, the distance to sensor of your guide camera, the thickness of the OAG and the backfocus for your corrector. Then on paper, draw it up. The distance from the prism on OAG needs to be the same to the sensors on both the OSC and the guider plus you need the correct spacing from the OAG to the corrector.

Thanx for explaining this Robin, yep, get onto the drawing board I havent done detailed draws since calculating/measurin proportion for placement of 2dary flats to newt scopes when making my own mirrors 20yrs back Im sure drawing this to scale will be most benificial
Cheers , ,

[Tandum (Robin)]

err, I don't think you need hi end drawings, You just need to include thread distances etc in you calculations. ie how wide is a threaded connection.

[naskies (Dave)]

Hi Bob,

I've done some quick back focus calculations for you (see the diagram). Probably best if you check them yourself!

* OAG to QHY9C:
1. Front of OAG to prism centre: 6.7 mm (listed under Technical details)
2. Prism to OAG camera mount: 4.5 mm
3. (A T2 spacer / extension tube might be needed between the OAG and QHY9C here.): 0 mm
4. Camera mount to main sensor: 29 mm (see here and here)
--> OAG to sensor distance: 40.2 mm

* OAG to SSAG:
1. Front of OAG to prism centre: 6.7 mm
2. Prism to OAG T2 mount: 26 - 38 mm (it's adjustable)
3. Orion SSAG mount to sensor: 12.5 mm (see here - the SSAG is same mechanically as the QHY5)
--> OAG to SSAG distance: 45.2 - 57.2 mm

Okay, so we have two problems to solve now by adding one or two spacers (extension tubes) into the image train:

1. The MPCC-sensor distance for both light paths (SSAG and QHY9C) needs to be 55 mm so that your coma corrector works properly.

2. The two light paths need to be the same length so that both cameras are in focus simultaneously.

Since the OAG path is "within range" of 55 mm, the easiest option is just to add 14.8 mm worth of spacers between the OAG and QHY9C. For example, this 15 mm extension tube might work.

However, the down side of this is that the OAG pick off mirror is way out to the edge of the field - guide stars will probably be dimmer and more likely to have optical aberrations.

A better approach is to add one extension tube between the OAG and QHY9C (e.g. a 10 mm extension tube), and another between the MPCC and OAG (e.g. a 5 mm extension tube). In theory, this gets you very close to 55 mm between the MPCC and QHY9C sensor, with a bit of room to focus the SSAG too.

Other combinations are possible too - e.g. 3 x 3 mm = 9 mm in front of the OAG, and 2 x 3 mm = 6 mm in front of the QHY9C will let you move the OAG prism even closer to middle. I'm not sure what the ideal distance off-axis is for your prism - but at f/4.7 I'd imagine you wouldn't want it too close.

I hope this helps! (I'm most probably off by a couple of mm here and there for thread connections etc...)

[astronobob (Bob)]

Originally Posted by Tandum

err, I don't think you need hi end drawings, You just need to include thread distances etc in you calculations. ie how wide is a threaded connection.

Thanx Robin

Originally Posted by naskies

Hi Bob,

I've done some quick back focus calculations for you (see the diagram). Probably best if you check them yourself!

* OAG to QHY9C:
1. Front of OAG to prism centre: 6.7 mm (listed under Technical details)
2. Prism to OAG camera mount: 4.5 mm
3. (A T2 spacer / extension tube might be needed between the OAG and QHY9C here.): 0 mm
4. Camera mount to main sensor: 29 mm (see here and here)
--> OAG to sensor distance: 40.2 mm

* OAG to SSAG:
1. Front of OAG to prism centre: 6.7 mm
2. Prism to OAG T2 mount: 26 - 38 mm (it's adjustable)
3. Orion SSAG mount to sensor: 12.5 mm (see here - the SSAG is same mechanically as the QHY5)
--> OAG to SSAG distance: 45.2 - 57.2 mm

Okay, so we have two problems to solve now by adding one or two spacers (extension tubes) into the image train:

1. The MPCC-sensor distance for both light paths (SSAG and QHY9C) needs to be 55 mm so that your coma corrector works properly.

2. The two light paths need to be the same length so that both cameras are in focus simultaneously.

Since the OAG path is "within range" of 55 mm, the easiest option is just to add 14.8 mm worth of spacers between the OAG and QHY9C. For example, this 15 mm extension tube might work.

However, the down side of this is that the OAG pick off mirror is way out to the edge of the field - guide stars will probably be dimmer and more likely to have optical aberrations.

A better approach is to add one extension tube between the OAG and QHY9C (e.g. a 10 mm extension tube), and another between the MPCC and OAG (e.g. a 5 mm extension tube). In theory, this gets you very close to 55 mm between the MPCC and QHY9C sensor, with a bit of room to focus the SSAG too.

Other combinations are possible too - e.g. 3 x 3 mm = 9 mm in front of the OAG, and 2 x 3 mm = 6 mm in front of the QHY9C will let you move the OAG prism even closer to middle. I'm not sure what the ideal distance off-axis is for your prism - but at f/4.7 I'd imagine you wouldn't want it too close.

I hope this helps! (I'm most probably off by a couple of mm here and there for thread connections etc...)

Hi there David, much appreciate your time/effort here, has help a lot & has given me plenty to go on & prolly need get my mind into 'focus' at a better hour for this lot or maybe stay with seperate Guidescope, not because of the addaptors/spacers etc, just to insure a good selection of guide stars. With this 10" and at times with possible barlows, Id like the opertunity to get close at some galaxies & know that some are difficult as is with finding stars to guide on, so, weighing up lots of odds at the moment mate ! truly appreciate your reply
All the best ! !