Bob's Knobs - corrector plate was loose so its time to collimate - again

[g__day (Matthew)]

I did some sugery on my mounts to improve DEC backlash again - which I think I achieved nicely - but was surprised to see some donuts in my imaging.

I checked all the gear was firmly mated (turns out the Canon DSLR -> 2" Bintel adapter (held on by only one bolt screwing into angled metal isn't the best design in the world). Next I thought I may as well I clean the optics on my SCT's (C9.25) front corrector plate. In the process of doing this I discover the front mirror assembly turns easily! This didn't sound right I thought! On examination there are no locking bolts holding this thing in place - it appears to simply screw in clockwise to hold firmly to the front corrector.

So I tightened this manually by hand until its firm again and thought next clear night I re-comimate again. Last time I did this with CCD Inspector - on a trial licence (too bad that's expired - may try it on another networked PC thought!) I love this software - but I use it maybe once a year and at $180 US its a bit pricey to justify if its a once a year - 1 hour effort.

But to the point of this post (sorry the background happenings distracted me). I purchased Bob's Knobs from Bintel just after I nailed collimination last year - and never got around to installing them. If I have to re-collimate I figure its a good time to swap the old bolts out for Bob's ones. Three questions folks:

1. Are they really that easy to instal (I just remove and replace the original bolts - one at a time)

2. The 1" long Knobs come with a 1cm white spacer (I presume these are always used just to space knobs out from the front corrector plate far enough to make adjustments easy)?

3. CCD Inspector is the best collimination software to use - there is no free ware equivalent I should consider?

Many thanks all for your thoughts!

Matt

[Dennis]

Hi Matt

To ease my collimation work, when I fitted Bob’s Knobs to my C9.25 I had it clamped on my work bench, targeting a centred object over 100m away in the day time.

As I removed each knob and replaced it with a Bob’s Knob, one at a time, I simply kept on re-centring the target (using the secondary collimation screws) before fitting all 3 knobs in turn and this procedure almost eliminated the need to do a star test. Just a small tweak was required later that night.

Cheers

Dennis

[sheeny (Al)]

G'Day Matt,

I did as Dennis did, except I had my scope mounted on the mount tripod, and pointing slightly downwards and focussed on the tray of a truck a hundred or so yards away. Pointing it downwards (or level at least just helps to minimise any problems with the secondary wanting to "fall away" as you change screws.

Al.

[g__day (Matthew)]

Thanks guys - got it done and reasonably collimated - have to try CCD Inspector on another PC I reckon to get the collimation as good as it used to be.

Now this weekend I can tune the mount again to improve DEC guiding. I moved the worm closer to the shaft - now the motor is a bit too far from the worm gear - should be easy to adjust - so I'm obivously doing something wrong.

Meanwhile I was puzzled by how poorly the mount was calibrating its RA guiding (on Tuc 47) tonight. I was using PHD - and whern I pressed calibrate in 60 RA pulses the Guide star moved about 12 pixels (say 20 arc seconds). Normally it takes 13 pulses to move the requsite 25 pixels (I was inside the house doing this remotely). I tried PHD Guide Test program - and everything was fine. So I cursing until I remembered that Tuc 47 was just about on top of the SCP so you'd need alot of RA movement to make it detectable - a real doh moment for me!

I did one more DEC motor placement adjustment - I think its slightly better now - so now hopefully finish all the remaining tune up activities this weekend and be back to serious imaging again soon!

Many thanks all,

Matt