From oag to guidescope

[iapa]

7 hours ago, SimM said:

A 10mm thin OAG is just the OAG throat with an adjustable prism and possibly a focuser. That's good, because you can add t- adapters et.c each side to get the required setup and BF.

I'm finding it hard to get a decent spec. on any of the available (and not to specialist/expensive) OAGs.

They don't seem to do a good job at detailing the available movement of the prisms and what the BF behind the prism is.

By only concentrating on the total BF for a camera e.g. when using a DSLR, they neglect to say important details about the range of adjustments on the OAG for the prism.

Since the BF is common to both cameras, it needs more information about the prism adjustments to allow selection and operation of the OAG.

As an example, if you don't know the range of prism height adjustment available, then you can't be sure that the prism can be moved into and out of the way of the main sensor, especially when the available depth of the guide camera has to be considered before adding extension tubes between the OAG and the camera, which will effect how much the prism interferes with the main sensor.

Simon

 

There a couple of utoob video covering the ZWO OAG, and he goes into the whole theory and numbers.

I think it was these two.

 

 

 

[wimvb]

As long as you use zwo products, it should be a smooth ride. Zwo have included all adapters and spacers you need with their cameras, oag and filter wheels. But if you deviate from their path (dslr, other astrocam), you’re very much on your own. That being said, zwo also have published a chart with  all possible variations, on their web site.

[nfotis]

On 02/06/2020 at 21:38, Freddie said:

I can’t imagine why everyone would suggest a guide scope would be better than an OAG on a Newt.

 

On a Mak?

(just curious, as I expect to receive a used Skymax 127 with an OAG ring)

 

N.F.

 

[Grierson]

On 03/06/2020 at 16:47, SimM said:

...............  Off-topic, sorry. I'm looking to use an OAG with an EdgeHD 800 and a 0.7x Reducer - but finding an OAG that will work is proving difficult   .........

With apologies to Robin could I ask SimM what you decided on. I have the same ‘scope and reducer and the same dilemma! 

[SimM]

7 hours ago, Grierson said:

With apologies to Robin could I ask SimM what you decided on. I have the same ‘scope and reducer and the same dilemma! 

Just received QHYOAG-M and some M54/M48 adapters. Thickness of the OAG is 2(1.5 + 3)+10= 19mm. An 8x8 prism + 7.5mm clear aperture.

EdgeHD 800 0.7x Reducer has 26mm image circle with 35mm objective (In comparison, Celestron OAG had minimum prism centre height ~17mm).

I want the prism centre height to be 12mm - 14mm above the central axis with minimal OAG spacing after the prism (think F/7 cone of light to the main sensor).

I have to do setup in daylight with M48 extension tubes and test operation with clear skies later. Guide camera is QHY5III-178M with 2x2 camera binning.

Simon

Edited June 23, 2020 by SimM

[Grierson]

Yes, thank you for the response Simon. I did look at the QHYOAG-M and the more I read the more difficult it is to come to a conclusion. Received wisdom on CN seems to suggest that the larger the prism size the better. Exactly how correct that is must be open for debate however. The QHY OAG prism is I believe 8mm, the ZWO 8.8mm and the Celestron c. 12mm.  

[Robindonne]

17 hours ago, Grierson said:

With apologies to Robin

No please ask all.  I highjack threads all the time.  Its far more better to have multi brand/item threads regarding the same issue.  😅

[SimM]

1 hour ago, Grierson said:

Yes, thank you for the response Simon. I did look at the QHYOAG-M and the more I read the more difficult it is to come to a conclusion. Received wisdom on CN seems to suggest that the larger the prism size the better. Exactly how correct that is must be open for debate however. The QHY OAG prism is I believe 8mm, the ZWO 8.8mm and the Celestron c. 12mm.  

Hi John

I would agree with you that it's difficult to reach a conclusion. QHY OAG has an 8mm prism (small/medium and large OAG have same prism), ZWO has a prism/mirror also 8mm (but has only a limiting 5mm aperture) and Celestron has a 12.5mm prism with a limiting lower prism height. ZWO also uses a dovetail like Celestron but it's not 360 degrees - some users get flexure as a result depending upon the weight of the camera used.

Bigger is always better? Probably true with many mounts and also for prisms. However, there is a point reached where the prism interferes with the main image - do you want the prism to be closer to on-axis but also provide a reasonable "view" for the camera? For 174 the sensor is too big for QHY or ZWO OAGs - better for 178 or 290.I have a 178 as a guide camera 5x7mm sensor. 17mm height of the COAG is just too close to the diameter of the back of the 800 0.7x reducer, so limited view and poor image quality. For the EdgeHD 800, the image circle from the Reducer is 26mm - so being at 34mm diameter is a big "ask" and can get closer with a smaller prism.

I also wanted to use my Baader ClickLock for visual/AP switching and to keep one BF behind the prism e.g. one setup across all scopes (no refocusing of the GC). 

Simon

[Robindonne]

What would really help in the future is a section on this forum where all can post his or hers setup, gear, assembly etc.  And their satisfaction rating when using that equipment.  Just like astrobin registers the setup used with the showed image, it would be great to have a forumsection like this.  
Search for scope brand/model, oag and cam and see how much of us use this combo and how its rated.   I think it’ll work because who doesnt want to showcase their arsenal?😉.  Or just Search for a scope type and see what others use to complete their ap setup for example.  How much the combo is used and rated.  Etc.  Maybe for the future.  Im sure that a lot of satisfied hobbyist, without facing issues, don’t show up as often as the ones that have questions/issues. And therefore a lot of good info will be missed in info-asking-topics.  
There are so immense much accessoires available that wont work when used with another accessory.  

like an advice/gallery/review section 

oag A wont work with cam B or scope C🙄.   On the other hand its fun to find out yourself.   

 

maybe forget about it.🙄.  Interaction and Discussions are more fun in the end
 

 

Edited June 23, 2020 by Robindonne