PHD Guiding drift

[Aster]

Lee,

Have you read the Advanced Settings and played around with the RA Aggressiveness Setting.???

Just a thought

[Lee]

Originally Posted by Aster

Lee,

Have you read the Advanced Settings and played around with the RA Aggressiveness Setting.???

Just a thought

No - all settings are default so far.... will have a play soon though....

[g__day (Matthew)]

Ah, I adjust min movement before a guide pulse is sent, and RA aggressiveness down - yo yoing is my main enemy.

With that said I re-balanced the scope - two 5kg weights were a cm too far down I reckon - now even a 10 minute unguided shot at 2300mm focal lenght looks far better - given across is 30 arc minutes - I'd say under 20 arc seconds of drift in RA - huge yah!

My choice of autoguide camera - a DSI on a 1500mm focal length MAK is probably now limiting me. Have a look at a guided 10 minute versus unguided 10 minute at 5 second PHD adjust intervals on a real faint star. Only a botched levels and curves applied here - look for stair trails.

Surprising the unguided one is on the left! I'd say re-balancing the shot so far has created terrific results for me! Now if I could juist autoguide better

[Garyh]

I have been giving it some thought also to try to work out if its a balance or a flexure problem between the 2 OTA`s.?
My thoughts are setup guidescope with camera and PHD and have a illuminated reciprocal eyepiece in the other scope at high power with a star centred. Make sure you are well east or west of the meridian. Let PHD do its thing..Does the star stay centred in the other scope? Give the scope a very slight tap every now and then. does PHD pull it back to where it was or does its position change slightly every time in the same direction or is there drift in the same direction?
Now change the eyepiece and the camera around and try the same things again? does the star drift or move the same way or is it now moving the opposite way?
My thoughts are if the movement is reversed then there`s some sort of differential flexure betwen the 2 scopes but if it still keeps moving the same way it maybe some misbalance in the setup?
I`m not sure if this is right? someone correct me if my idea is mislead!
I will give this a go myself if this cloud goes away anytime soon!
cheers Gary

[bird (Anthony Wesley)]

Something I see with my own scope is that the primary tilts a bit in its cell as the scope moves across the sky, due to the very "soft" mounting system I use. This means that it slowly points away from my guide scope even though the two are firmly bolted together.

So this or some form of tube flex might be the answer :-) It has to be something that causes the two scopes to drift apart in relation to each other, no doubt the guide scope is still doing it's job and keeping the guide star where it ought to be.

You can check this, watch your collimation carefully and see if it changes as the scopes drift apart. If you started off in perfect collimation, then recollimating should bring the two scopes back into alignment again.

cheers, Bird

[Aster]

Gary

Had the same idea, but couldn't try it out as my shoestring guide system won't be ready until January next year.

On the other hand, looking at tech-guru test photos who needs automatic guiding

[Aster]

This has nothing to do with PHD Drift but might be interesting to some to overcome imbalance of side by side scopes.

Many years ago when I first started in astronomy and photography I had a 8" newt sitting on a very cheap japanese mount. Touch it and the object you were looking at just about moved out of the FOV. Couldn't put a guidescope on top of the newt as the whole lot would have collapsed. Also couldn't afford to buy or make anything else.

After a lot of reading, going to the library, and a lot of thinking, grey matter still worked in them days, I came up with what I thought was a brilliant idea. Why not put the guidescope where the counterweights are. No extra weight to destabilise the mount and no extra counterweights.

Found a nice piece of aluminium U channel, made a couple of adjustable tube rings ,mounted the lot on the end of the dec shaft and the problem was solved. Used that type of setup for a couple of years doing deep space photography guiding manually with excellent results.

Was going to do the same thing if I would have used the 304mm tube assembly on top of the EQ6 mount to save weight.

[Garyh]

Hi Alex,
Now thats a idea I havn`t seen in a long time!
In my very oldest book on Astrophotography they used to attach there wideangle plate cameras in a similar fashion on the end of the dec shaft.
good idea!

[Lee]

A problem with that is the guide scope wouldn't clear the observatory walls for low objects.....