C925 finder screw thread size -and how to balance ?

[powerlord]

Hi chaps,

can someone tell me with certainty what the thread sizes of the screws around the rear cell of the C925 are ? Not the flat ones which hold the cell, the equally rubbishy philips round head ones that can be used for mounting finderscopes, etc ? there are 3 sets of 2 around the rear tube opposite the mount.

The internet tells me they are 8/32 - which is mince as I measure the thread diameter of one of the screws I removed at 0.14in which is not 8/32 (0.25). Its clearly some sort of prehistoric non metric hell, but not sure what ?

Balance wise, my C8 was bad enough, what with all the weight at the back cell, then you add reducer, lots of back focus and a camera off the end ..trying to get it clamped on my EQ6 was bad enough - and yet they all seem to come with vixen or lomany bars only the length of the scope.. do folk mount finders on the front of OTA to aid balance ? or it is matter of raking around looking for a lomandy bar longer that the tube, but with correct holes and/or drilling my own.

the shear number of different threads and stupid hole configurations in all this stuff is just as irritating now as it was 9 months ago when I started this hobby, I can tell you that... sigh

 

[powerlord]

ah.. 8/32 is an 8-32... a no.8 32... of course.. sigh. so.. think I've ordered right screws.

losmandy wise..will have to see how it all balances

[PeterCPC]

I have one of these on my C9.25 https://www.firstlightoptics.com/adm-losmandy-type-d-series/adm-losmandy-dovetail-for-optical-tubes.html

I have two finders at the rear but have no trouble balancing on the mount.

[powerlord]

thanks Peter. is it not right up against the end of the bar to get balance when attached to your mount ?

And while I've got a fellow C925 owner with some of the same kit - can I ask you what back focus you are using ?

afaik with no reducer, its supposed to be 139mm right ? And with the celestron 6.3 reducer, 105mm ?

So, with reducer, for example, that means in addition to the M42 spacers that come with the ASI533 for example (7.5 to sensor+10+21+16.5) = 55. I need to add another 50mm of M42 tube...which seems to be the size of the celestron t-adapter-sc.

So I do:

reducer + celestron t-adapter-sc +10+21+16.5 + asi533 =105mm back focus?

And for using with no reducer, I need to find another 34mm ?

celestron t-adapter-sc (+34mm??) +10+21+16.5 + asi533 = 139mm back focus ?

[PeterCPC]

I don't use (so far) my 533 with the C9.25. I only use the C9.25 for planetary imaging so either my 224 or 385 and I also use a flip mirror so the camera is about 200mm from the scope if you include the clicklock that I have attached to the scope. I have a 9x50 finder at the back as well as an RDF and, when mounted and balanced, I have about 45mm of the losmandy dovetail behind the mount plate (Losmandy on AVX). I don't use a reducer. Hope that helps.

[JeremyS]

Bit difficult to see, but here is my C9.25 on my AZEQ6. Balance point is certainly well down the dovetail but certainly not at the end