PHD woes

[adamsp123]

For some reason my PHD will not calibrate in DEC, does the RA fine then does the north DEC movement but when it tries to go South the guide star "runs away" very quickly in roughly the same direction it was heading when the north calibration was running. (The RA calibrates very quickly but in DEC moving north it takes lots of steps approx 50!)

I went back to the older version of PHD but no change, I have tried changing the calibration steps, my starbook autoguide settings, but no joy.

Any ideas very welcome.

Pete

[greenkat]

I'm probably totaly wrong, but possible declination axis sliping ? or a bit unbalanced ?

Just an idea but hope you sort it , good luck

[adamsp123]

I'm probably totaly wrong, but possible declination axis sliping ? or a bit unbalanced ?

Just an idea but hope you sort it , good luck

Cheers greenkat,

You may well be right about the balance, this morning I set everything up on the mount, F/4 Newt, camera, finderguider etc in place.

RA balance was spot on, DEC Tube balance with the counterweight down, the tube horizontal was vitually spot on, just a slight ajustment needed (a bit mirror heavy but only a smidging).

I then swung the whole thing over so counterweight bar was horizontal and the tube vertical but when I slackened off the DEC clamp the tube immediately moved with the camera and finderguider trying to move towards the ground with quite a force until it reaches balance at about 30 degrees fron vertical, then after a moment I realised as the finder and camera are quite close to each other at the top of the tube, the combined C of G needs to be on the same axis a the counterweight (ie inline with the CW bar) to stop this mass acting against the DEC axis! and it is DEC calibration where my problem lies.

So twisting the Newt in its rings I now have the whole lot nicely balanced in all directions and waiting for next clear night to test.

Pete

This may explain why my gotos have been not so good lately!

[MikeP]

Advice offered to me recently (for an EQ6 anyway) is to have both axes slightly unbalanced. The RA being such that whatever is on the east side of the mount is slightly heavier - this means if you flip across the meridian, you'll need to "re-unbalance" slightly. For Dec it does not matter which way you are out of balance.

For balancing a side by side - not sure if that is what you have - see Balancing a side-by-side setup

Mike

[adamsp123]

Cheers Mike

I wasn't using a side by side, although I will be setting one up for widefield refractor imaging so thanks for the link, with my Newt I just replace the finder with my FinderGuider.

I know about the east heavy and I am sure the DEC is not exactly balanced but the way I had the Newt rotated in the tube rings ( for my convenience ) meant I had a major imbalance when the tube was near vertical, as it was last night for my target, now I have rotated the camera/guidecam mass C of G in line with the Counter weight the CW takes care of that load and the tube is now stable.

Having given it more thought that would explain the PHD DEC cal behaving the way it did, struggling to get any movement N but when moving S it lost control.

Pete

[MikeP]

Ah, the penny has dropped - I see where the imbalance was now. Good luck next time.

Mike

[adamsp123]

Ah, the penny has dropped - I see where the imbalance was now. Good luck next time.

Mike

Cheers, I blooming hope it fixes it I was getting "near to tears" last night with frustration

[roundycat]

don't ever aim for perfect or near perfect balance in Dec. especially when imaging near the zenith. The whole mass will wobble about in the Dec backlash and will never calibrate or guide reliably. Make sure you calibrate near the meridian/equator as the movements in RA and Dec should be more equal.

Dennis

[adamsp123]

Hopefully I will not incur the wrath of the Autoguider god but I have my guiding working, careful balancing and bit of judicious mis-balance (cheers roundycat) and a couple of tweaks to PHD I am getting nice 5 min subs.......note to self - must write PHD settings down including the ones on my starbook!

Oh my I have cursed it haven't I? best go and check!!!!