Setting up

After receiving my Askar M54 OAG, I went about installing it into my imaging train, which includes an Askar 130PHQ telescope and ZWO ASI 2600MC camera. OAGs have a reputation for being tricky to set up, but the good news is that the Askar M54 OAG has a few tricks up its sleeve to make things easier.

First up is a good-sized prism (10mm x 10mm) with which to pinch some of the telescope’s light and divert it to the guidecamera.

In order to work, it needs to be rotated to the correct angle. Basically, the top of the prism should be parallel to your main camera sensor’s long edge, but not blocking it. This photo shows what I mean:

The Askar M54 OAG comes with a whole load of adapters so that it will not only fit pretty much any telescope system, but can also be rotated so you can get the right angle. This was a reason I opted for the Askar OAG and not the ZWO equivalent; that one doesn’t come with all these adapters. And, wouldn’t you know, I did need some of the kit that Askar bundled with theirs. It’s really annoying when you need to buy extra adapters, and I appreciate Askar’s approach here: just throw loads of useful things in the box.

So after all that I had the Askar OAG and guidescope attached, as shown below. (Note that after taking this photo I realised that the guidescope needs to be inserted further into the OAG to gain focus. After doing that it doesn’t stuck out as much).

I then took a test photo and realised that the prism was protruding too far down, and so casting a shadow onto the main camera sensor. This is what that looks like in reality; the big dark shadow at the top is the prism’s shadow:

Askar have anticipated this. The prism is on a kind of metal stalk, and the OAG comes with an Allen key that can be used to loosen a screw that holds this stalk in place. It’s then a simple procedure to adjust its height. After a few trial-and-error attempts, I had it perfectly positioned.

Next comes focussing. The first step here is to ensure that your main imaging camera is in focus. Then, you need to physically move the guidecam higher and lower until it too is in focus. The Askar M54 OAG comes with a helical focusser that allows for precision fine-tuning of the focus, and this makes things easier. The general advice is to do as much of this as you can during daytime, by pointing your telescope at something on the horizon, like a distant house chimney. Then you’re in the ball-park, and can do your fine tuning at night under the stars.

And that’s about it for set-up. Some good news: once that’s all done, you basically lock things down and never think about them again.