Making a DIY right angled viewfinder for a star tracker polar scope

Newly arrived to my blog? Want to know more about me before you dive into my posts? Why not visit the home page first and start your exploration from there: 

https://undersouthwestskies.blogspot.com/2025/01/welcome-to-my-new-astronomyastrophotogr.html

And welcome. Welcome to 'UnderSouthWest Skies'. Thanks for stopping by. I hope you find the experience worthwhile. This blog post has been written from my own 'beginner perspective' after doing lots of reading on the topic below.  In getting my head around it all, I may have got odd bits slightly wrong; but, like you, I am on a leaning journey, so please forgive any unintentional errors.  Meanwhile, clear skies to you. Take care and thanks for visiting   Steve aka PlymouthAstroBoy 

Finally, I have got around to making a right angled polar scope viewfinder. The cost of them is around £80 mark with postage, here in the UK. I had an old pentax DSLR right angled view finder and I was sure I could 'adapt' it. Now there is an issue in that this old one mirror flips everything horizontally....but more of that little quirk later in the post. 

I've wanted one of these right angled viewers for quite some time. I find it increasingly difficult to bend down and look up through the central polar scope of my skywatcher star adventurer tracker (same for my Ioptron sky tracker as well).  There isn't an astrophotographer alive who uses a star tracker who doesn't understand this issue. Here at a latitude of 50N - the tilt of the tracker is such that when the polar scope is inserted, you are on your knees with your back arched to look up through it. If you can do that! When I'm on my knees below it, my eye is around 14" away from the viewfinder - rendering it useless! If I try to get underneath it and closer, I invariably end up knocking the tripod and then struggling to get back off my knees - very frustrating! 

When doing DSO astrophotography and using my ASIair mini - then there is no problem if I am slightly out in the initial polar alignment as the ASIair helps me correct it quickly. But when doing milky way astrophotography - then a right angled viewing gizmo is going to be very helpful indeed. 

So what stuff did I use?

• an old pentax right angled DSLR viewer
• electrical tape
• an old polar scope cover piece I had knocking about
• some very tiny phillips screws 

(I should at this point just explain for those not in the know, that a polar scope is essential to getting good alignment with the stars so that the camera tracks their movement above and trailing stars is avoided. This involves aligning the tracker with the north star Polaris. The bigger the lens you use, the more accurate you have to be in your alignment processes - otherwise you will have horrible trailing and photos that cannot be stacked together in any available software.)

I removed the metal silver viewfinder frame off my ebay purchase by undoing the four tiny screws and then took the protective cover lid off the polar scope. Using the silver viewfinder slot as a template I then marked out drill holes and also a central large hole to be cut out.

Ten minutes judicious use of my multi-tool with drill and then sander bits and hey presto - the protective lid had been cut out. It was then just a matter of screwing the lid back onto the DSLR viewfinder and then doing a few trial fits. 

It proved to be a little loose but a thin strip of duct tape on half of the lid lip - turned it to a fairly snug push-on fit. 

Does it work?  OF COURSE IT DOES! 😁

I have genuinely surprised myself - no more wet knees, cricked neck or wrecked back muscles. 

And it works on the star adventurer too.

So what about the flipping issue? 

Ok, how best to describe this? For some reason, the right angled viewer mirror flips the view of the polar scope reticules. So, 3 o'clock is at the 9 o'clock position and obviously, 9 o'clock switches over to the 3 o'clock position.

What does this mean in reality? Well when positioning Polaris on the correct place in the inner circle of the reticule using a polar alignment app to help determine its position - if Polaris is shown at the 5 o'clock position on the app, on my reticule, when using the polar scope, it will have to be placed at the 7 o'clock position instead.  It takes a minute or two to get your head around it - think mirror flip of the reticule along the vertical axis. 

It may sound confusing but in reality is quick and simple to work out; as long as I remember!! 

I spent around £2 in all instead of £80 so I am happy and I have reused/recycled something to boot. 

With plastic 3D printers etc - I am sure there is a free template for making the bit which fixes a viewfinder to the polar scope on the tracker. 

I found this Sky at night article which gives a better overview on how to do it than I have above 

https://www.skyatnightmagazine.com/advice/build-a-right-angled-polarscope-adaptor