Celestron Off-Axis Guider for Long-Exposure Astrophotography

I use this on a C11 EdgeHD, with a full frame imaging camera. The prism for the guiding camera, relative to competitors, is very large and so it is much easier to find a guide star. It comes with a nice collection of adapters to the scope side and camera side (though it should come with a wider 3.28" scope side adapter, that Celestron now sells separately). It is also easy to rotate the camera (guide and imaging) separately, or collectively, by loosening a couple screws. On the downside -- adjusting the prism position (how far down into the frame) is rather tedious. Not hard, just tedious. Fortunately you should have to do it only once. The other downside - partly because of all the other features -- is that it adds quite a bit of backfocus, which may be an issue on some SCT's especially if you want separate focus, filter wheels, etc. But overall, well built and does what it should.

besides those irrelevant ratings categories on amazon I like it very much, it's a substantial piece of equipment. double edged sword there - that means it's also heavy. with a lot of digging I found out it's 18 ounces. just over a pound - that information is not very freely advertised but if you're buying this in the first place you'll already know that the weight of the item is very important. It does have a lot of bells and whistles included for increasing your focusing distance and adapters for various threads, plus a top focus ring for your guider cam which is a very helpful inclusion vs trying to just set the cam in and out trying to match focus. I personally find the prism up to the guide a bit dim, but I guess that's to be expected from a diagonal. All in all I found it to be pretty solid, I had another off axis from a brand I can't mention that was pretty flimsy and difficult to focus and this was definitely a step up.

I like this product a lot. I didn't at first, but I purchased it for use in a Celestron SCT, since installing a guide scope on the side of the scope tended make the vertical balance in dec difficult (read: impossible) to achieve without adding additional weights to the scope to balance it. The Celestron OAG makes vertical balance in dec easy to achieve, because it keeps most of the weight of imaging and guiding cameras along close to the radial axis of the optical tube. The weight of a 9.25" SCT optical tube alone is about 20 lbs, which is within 2 or 3 lbs of the (actual) load limit of the Celestron AVX mount. I don't recommend AVX + 9.25" SCT, because if it is at all breezy, or one wants to add something like a filter wheel, one runs a significant risk of getting a bunch of astropix with unstackable content (elongated stars, with long periods of backlash recovery and jiggly star streams in several shots). I'm just saying that the OAG was the only way I was able to use the AVX + 9.25" SCT combo. I finally ended up getting a more robust CGX mount, which is 10 times the price of the OAG, but also I am now happy to have the OAG available, since it simplifies the weight and cable management of the mount. The hardest part of dealing with the OAG is when you first set it up, because you have to bring your imaging and guiding cameras to focus together. This can take a while as you work your way through the various adapters and combinations provided. Once this is done, though, it is possible to treat the whole conglomeration of OAG, imager, and guider as a single attachment for your telescope (just lock the focus of the guider with a set screw before disassembling), which is always at or near focus once it is attached. Saves a lot of time in the field. If you have more than one combination of telescope, imager, and guider that you want to use the OAG for, you either must go through the headache of parallel focusing the components, or, if you are wealthy (enough), I suppose you could get a dedicated OAG for each combination. Be careful when adjusting the height of the pick-off prism that relays some light to the guide camera. The prism can drop off, and getting it back on is a HUGE headache (Celestron allowed me to RMA mine when the prism dropped off, even though it was entirely my fault that this had happened; for this, they have earned a rating of totally awesome for life; they didn't have to honor the warranty, but they did). It turns out that the prism height was optimal to begin with, so that was a totally unnecessary adventure. One feature that this OAG has, which you won't find in most, is the ability to rotate the imager (and, separately, guide camera) very easily. Other things I like is the fact that it keeps the imager close to the guide camera. I use a ZWO camera that has a built-in USB hub, so I can attach the guide camera and filter wheel with two six-inch USB2 cables that run from the ZWO hub, which keeps everything neat and tidy, and easy to balance. All in all, this is a great solution for SCT deep-sky astrophotography. In retrospect, I believe the reason I didn't like the OAG when I first got it is that it required me to change a lot of preconceptions I had about the relationship and positioning of equipment on the mount. The fact that Celestron replaced the OAG that I myself had damaged brings my rating to 5 stars.

This was the second Celestron OAG I ordered. The first one came with the prism fallen out, and rattling around inside the package, all chipped up! The second one came and the prism was intact, but it was glued in crooked. The one thumb screw that holds the guide camera was bent, and when the camera was installed, it binds on the inside of the focuser tube because of mis-alignment. I sent this one back and got a third one. The third one seems OK so far, but I haven't had a chance to test it on a clear night yet. SHAME on you Celestron! For $300 I would expect better quality control.

This is the best option for guiding your long focal length SCT. The pick-off mirror is larger than most of the competition, making it easier to find acceptable guide stars. The OAG comes with numerous adapters to fit standard scope/camera configurations, but not the Large OAG Adapter, for 9.25 and above EdgeHD OTA's, to maximize imaging circle. I recommend that you install and sort out your back focus and spacers during the day, focusing on a distant object, then fine tune in the dark using the appropriate focus tools in imaging and guiding applications.

My guider also had a broken set-screw; I contacted Celestron and they offered to replace it immediately, however the way I will be using my guider will be by screwing it on directly, and not using the nose-piece. The set screw is only for the nose-piece. So ultimately no problem there. I have the NexStar 8SE and this guider is absolutely perfect for this scope. It comes with a great selection of adapters and is surprisingly easy to use with this scope. I also have the 80ED, a lovely refractor. You can use this OAG with this scope (and a Canon T3i on the other end) ***but you cannot use the very necessary field flattener!*** because the guider it just a little too thick. I am considering one of the very thin OAGs for my 80ED but the reviews on them are horrible. Overall this is a very well made (other than one set screw apparently) product that is very easily adaptable to a great many astrophotography solutions - but not all of them.

This OAG is very sturdy. It did require alot of getting used to. Initially, the helical focuser was not properly attached to the brass gears, but this was easily resolved by taking the focuser off and attaching it properly. It comes with several adapters to allow you to connect different back plates. It screws directly onto the visual back of the telescope or focal reducer. I did have to adjust the prism ever so slightly to get great focus with my guide camera, but was very pleased once everything was setup correctly.

Works great with different cameras. Use with a mini cam like a 174 mini. Very well made. I would recommend this product.

I bought this to replace the ZWO OAG I had thought I could use with my Celeston EdgeHD 8" scope. The ZWO has too small a mirror for the focal length of the scope and thus I struggled to find suitable stars to guide on. The Celestron version is much more suited and has a few other features that make it easier to use, too.

I bit pricey, but comparing to other options this is by far a good bang for your buck! Very good quality components and the prism is larger than competitors! I’d recommend!

Fantastische OAG van Celestron. Voorzichtig met het prisma.

Lo uso con un celestron C8 con reductor y a foco directo. Con la cámara ASI 120mm es muy difícil encontrar una estrella guía a foco directo, ya que esta cámara no es muy luminosa y a f/10 pocas o ninguna estrella se consiguen ver. Cambié la cámara por una ASI 174 mm, mucho más luminosa (Ganancia de 0-400) y con un chip de mayor tamaño, lo que permite ampliar el campo. Con esta nueva cámara no tengo ningún problema para encontrar estrellas a f/7 y a veces se complica a f/10 en alguna Galaxia. Casi todo lo hago por comodidad a f/7 y luego hago un recorte de la zona de interés. Para enfocar recomiendo empezar con estrellas muy lumosas (Sirio, Arturo, Antares, etc) o bien de día con un objeto lejano. La posibilidad de mover el espejo del OAG permita ampliar el campo y obtener más estrellas. Yo lo tengo en el límite en el que empieza a tapar el sensor de la cámara y me funciona perfectamente con la ASI 174 mm, eso si, siempre hago un recorte aunque sea mínimo. Hay que ajustarlo al gusto de cada uno, pues con algunas galaxias no hay problema pero para cielo profundo es mejor que el prima no tape el sensor. lo uso en un Celestron C8 y en un refractor de 540 mm.

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