Dodgy diagonal?

[Ags]

I was playing with a reducer lens and some spacers and as I added spacers the the focal point would move inward significantly. I noticed something strange - as the focus moved in, the edge of the wall I was looking at moved sidewards. This was not Mak focus shift as I hadn't touched the focus knob yet. Also my Castor mount was locked tight and definitely wasn't moving. But by changing the optical length between the field stop and diagonal I was seeing a different part of the field!

The only thing I can think of to explain this is the mirror diagonal is not sitting square and it is reflecting the light up to the diagonal at a slight angle to one side. That of course means that the telescope's optical plane is not level with the optical plane of the eyepiece.

If the diagonal is to blame it is not much of a surprise - I am still using the cheap diagonal the Skymax 102 ships with. Always planning to buy a better one, always finding something else to spend the money on... 😀

[mikeDnight]

I'm not sure I'm understanding the problem, but what I will say is that I've seen many scopes let down by inadequate low quality diagonals. I've never set them free among the astro community, but rather promptly executed them. If I'd have had my witts about me, I should have posted their remains back to the manufacturer's,  namely Meade with their 1.25" mirrors, Celestron 1.25" prisms & Vixen flip mirrors.