Celestron Deluxe Off-axis guider for SCTs and long focal length telescopes


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The Celestron off-axis guider #OAG93648 is designed for use with SCTs, EdgeHDs, and long focal length telescopes that require the most accurate guiding possible. 
Our Product #: OAG93648
Celestron Product #: 93648

Product Description

The Celestron off-axis guider #OAG93648 is an essential accessory for astroimaging with DSLRs or a CCD camera/separate CCD guider combination. It is particularly useful with long focal length telescopes that require the most accurate guiding possible. The #OAG93648 has a 48mm clear aperture that supports full frame cameras without vignetting.

Using an off-axis guider eliminates the possibility of differential flexure (and its resulting star trails in your images) that can arise when using a separate photoguide telescope. 

The Celestron off-axis guider #OAG93648 mounts securely onto the rear cell or focuser of your telescope. The guider has a small prism off to one side of the guider body that intercepts a portion of the telescope's light cone (outside the field of view of the main imaging camera) to locate a guide star. Any movement of the guide star in the guider will be the exact same movement seen by the imaging camera mounted at the rear of the guider body. Guiding this way corrects for tracking errors, as well as any opto-mechanical errors or flexure in a separate photoguide scope. The result is better astroimages with pinpoint round stars.

Off-axis guiders have been around for a long time, but typically pose three main challenges:

The first challenge is that finding a guide star at the far edges of the telescope's focal plane can be difficult, considering the small field of view and sometimes less-than-ideal illumination. Celestron addresses this challenge by providing a large 12.5mm multicoated prism with aluminized backing for maximum reflectivity and illumination to the autoguider. The prism can be adjusted to move in and out of the telescope's light path, depending on the size of the chip in the imaging camera. This results in brighter guide stars, with the help of the large prism to fully illuminate the autoguider sensor. In addition, the guider body can be rotated to find a guide star. 

The second challenge is that getting both imaging camera and autoguider to reach focus with one another is time consuming and sometimes requires experimentation. Celestron helps here by using a high-quality, fixed-orientation Helical focuser with 8mm of focuser travel. This provides extremely smooth and accurate focus of the autoguider without changing (or twisting) the autoguider camera orientation.

The third challenge is that additional spacers and adapters are usually required for your particular camera, telescope, and autoguider, which adds to cost and complexity. Celestron helps here by including all the spacers and adapters needed for most common imaging configurations, including DSLR cameras, Nightscape CCD cameras, and other popular astroimaging cameras. The following adapters are included: for telescope connection you get M42 T-thread, M48, and SCT/EdgeHD adapters; for CCD guider to autoguider connection you get M42 T-thread, and standard 1.25" adapters; and for camera connection you get M42 T-thread and M48 adapters and T-thread spacers.

Some telescopes, primarily Newtonian reflectors and some refractors, will not have enough focuser in-travel accomodate the Celestron Off-Axis Guider. To help in configuring the Celestron off-axis guider #OAAG93648 to the available back focus of your particular telescope the following dimensions are the actual amount of back focus used by each of the adapters: 

OAG body: 29mm
SCT adapter: 25.3mm
Male M42 and M48 camera adapters: 12.5mm
Female M42 and M49 telescope adapters: 4.5mm
Short T-thread spacer ring: 6mm
Meadium T-thread spacer ring: 11.55mm
Long T-thread spacer ring: 24.25mm
Medium M48 spacer ring: 11.55mm

Tech Details

Weight 18 ounces
Warranty 2 years


Review by:
I use this OAG with my Celestron Edge HD 9.25; and it works like a charm. I replaced the stock adapter with the Celestron Large Adapter for OAG; this combination gives my zero vingetting with my full-frame DSLR. The challenge with any OAG is getting proper back focus. The spacers that come with the OAG were insufficient for my particular setup, so I had to purchase an M48 extension tube kit, which came with a variety of spacers (5, 8, 10, 20 and 30mm); that gave me plenty of options to achieve proper back focus. (Posted on 7/23/2019)
Review by:
This is a good solid off axis guider (AOG) for beginning and middle work. Is a bit bulky so you need to watch your back focus. I have an SCT, and it is recommended that you use and OAG for guiding. My first OAG was kind of flimsy and always got the feeling that it would slip and move through the night. Since I got this OAG I can say that if can detect a star, I can guide... unless clouds move in.

Alvaro (Posted on 12/16/2018)
Review by:
Pros: I purchased this for the large pick-off prism to give me a better chance of finding guide stars in my light-polluted location - it certainly hasn't let me down in this regard. I also like the helical focuser is very smooth and provides good fine control of guide star focus (or slight de-focus, if you prefer). I also like how easy it is to rotate the entire assembly (both on the 'scope side and the camera side). A well thought-out design and comes with plenty of adapters and spacers.

Cons: it is quite large, so definitely check your back focus calculations. Additionally, on my 6SE, the width of the OAG assembly means I have to add some form of spacing between the telescope and the OAG so that it will clear my Feather Touch focuser. Thankfully, I usually image with a reducer/corrector in place, which adds just enough space for the OAG to clear the focuser. (Posted on 10/18/2018)
Review by:
The Celestron OAG makes a solid connection between the scope and the camera. The smooth helical focuser for the guide camera allows for sharp pinpoint guide stars and the adjustable pick off prism allows for flexibility for your imaging train setup. With a variety of adapters of varying sizes included, this OAG provides flexibility for swapping between DSLR and CCD cameras. (Posted on 10/11/2018)
Review by:
The quality is very good and solid on this off axismguider. It comes with a wide selection of adapters which is nice for various cameras. The focuser is nice and smooth. (Posted on 10/7/2018)
Review by:
Well put together and fairly straight forward set up. Comes with numerous adapter rings to change the back focus distance to whatever your rig requires. I'm very satisfied with it and use it with both a CCD and DSLR setup. (Posted on 10/6/2018)
Review by:
This unit is one of the best ways for precision guiding of your scope. No need for a heavy refractor hanging off the side of your setup, causing ballance problems and unknown flexing of a guide camera.
The fine adjustment for the focus of the off axis camera makes it simple to tune your system to your main imager camera. The adjustable pick-off prism adds additional flexibility to a great piece of equipment. Celestron includes a nice set of adapters to make it easy to mount most cameras. With the addition of a simple adapter or two, it is easy to switch from camera to eyepiece without removing most of the OAG assembly. Overall a easy to use, accurate guiding addition to your scope. (Posted on 10/6/2018)
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