Finder Guider connection conundrum

[Brent]

I'd appreciate some help if possible, please.

My guiding quality seems to be a little too variable and I'm starting to think flexure could be the issue.

More often than not I'm getting eggy stars. I still have some testing to do with regard to sub length but as I get the same eggy stars at 3,4,and 5 mins, I suspect they'll be the same at 10 mins.

My fiinder guider is connected to the main scope via the standard finder shoe as in the first picture below, and I know that this connection (and the spring adjuster) can be a major cause of flexure.

To that end, I've been searching (and searching!) for 50mm tube rings (rather than guide rings) to connect it to a dovetail instead. Sadly, this size of tube ring seems to be unobtainable.

So my only option appears to be keep it as is, or use the finder rings I do have (pic below). They also connect via the shoe, but they don't have the spring adjuster (although the thumbscrews are nylon tipped )

My question is - in theory, which would I be best off using? (Practical testing doesn't look like it will be possible for at least a week or so)

[IanL]

The three point rings would almost certainly be better than the one you are using. If you still suspect flexure, try removing the nylon tips or replacing with all-metal screws. I try to use metal screws for anything like this and put a piece of thin fibre washer between the screw and the paint to protect it. (You can get fibre washers in the plumbing section of any DIY shop).

[Brent]

Thanks Ian, that's pretty much what I thought. I'll have a go at getting the nylon off because there will still be enough length on the screws to hold the finder.

I used your advice I found last week on calculating the relative pixel size of imager and guider and I'm at 4.48x so that's not good, but I haven't got any way of getting a barlow in the guider train so it'll have to do.

I did also think about putting the finder shoe on a dovetail anyway - if nothing else it will aid balance I think.

Thanks for the Imaging Toolbox as well, I had a play last week and find it much better than 12dstring.

[IanL]

Thanks Ian, that's pretty much what I thought. I'll have a go at getting the nylon off because there will still be enough length on the screws to hold the finder.

I used your advice I found last week on calculating the relative pixel size of imager and guider and I'm at 4.48x so that's not good, but I haven't got any way of getting a barlow in the guider train so it'll have to do.

I did also think about putting the finder shoe on a dovetail anyway - if nothing else it will aid balance I think.

Thanks for the Imaging Toolbox as well, I had a play last week and find it much better than 12dstring.

Well bear in mind that 4x is just a rule of thumb, you should be okay at 4.48x but it just makes life harder if you go too far above it when starting out. Glad you like the toolbox.