Celestron RACI finderscope

The other day I was contacted by James in Philadelphia who has just got himself a Celestron AVX800. A fine scope on a fine mount.

But he’s having trouble with the 9x50 right angle correct image (RACI) finderscope. I had a look at the "straight through" one on our display model and yes, it’s fiddly.

When you set up the scope each night, you have to true up the finderscope so that it's parallel with the main scope. To do this, you use the adjustment screws at the back of the bracket.

This design is the "two screws" type - at 12 o'clock and 3 o'clock (see my side-by-side photo below). They work against a spring-loaded pin at 7:30 (which I've circled in the finst photo). Other finderscope designs use three screws spaced equally around the finderscope.

To adjust the spring-type finderscope, all you have to do is twiddle the screws at 12 and 3 o'clock. You don't have to back off one screw in order to advance another, which you have to do with the three-screw design. The spring is meant to do that for you, while holding the finderscope securely. 

However, James was concerned about situations where you have to adjust the scope a long way off centre.

This happens under a number of circumstances - most users will be familiar with this. My side-by-side photo here shows the finderscope adjusted as much as possible in two directions.

The problem is that if the finderscope has to be in the furthest top right position (right photo), the spring is fully extended and can't hold the finderscope securely. It can't actually fall out, but if the scope is at some angles, there is a risk that the finderscope will move within the bracket, defeating its purpose.

Here, I'd suggest some packing between the pin and the finderscope, such as a washer with a few layers of electrical tape to allow the pin a more positive contact.

This is just a quick and dirty solution. A better temporary solution would be to address why the finderscope is way off. Even better, the finderscope holder should be redesigned.