Finderguider/PHD - an improvement

[adamsp123]

I have been using a 50mm finderscope for guiding for a fair while now, one problem I have encountered on a number of occasions is an oscillation in the star guidebox in PHD which translates to elongated stars in the image.

After reading a CN thread I increased the "minimum motion (pixels)" from 0.15 to 0.4 based on a post that one chap said that after calculations this parameter should be increased so as not to "chase the seeing".

I have done so and it has made a real difference for the good.

Thought I would let you know

Pete

[samtheeagle]

Cheers for the tip Pete I'm a finder guider user so that's useful info, though tbh I've not noticed elongated stars to this point.

They do a fantastic job for something so small and basic, and are great value for money. I keep getting tempted by a "better" guiding setup, but when it comes down to it the 50mm finder is doing the business, so why change it?

[Psychobilly]

Good tip

Dimmer stars and longer exposures also helps to stop chasing the seeing...

Peter...

[beamish]

Cheers Pete,

another finderguider !!

[dark knight]

Cheers from me too...

[adamsp123]

You are all welcome!

Sam, I keep getting tempted myself but a load more weight isn't for the best and if it ain't bust why fix it.

Over last night I had no oscillations although the guiding plots were more spikey but the results were better, very happy bunny, I hope it lasts.

[samtheeagle]

Guiding when it works is a dream isn't it?

What I really want to do is get the finder piggy backed onto the imaging scope, so that I can plonk in another finder for actually finding things I've got a load of bits of aluminium that I'm trying to make some guide rings from, but it turns out that I'm not much of a metal worker! Two rings and six collimation screws looks so simple, but thus far I've not got particulary straight cuts.

[adamsp123]

Sam, I added an extra synta shoe to both my Newt and SNT, camera and guider are inboard towards the mount which significantly reduces the amount of CW needed, and the finder finder! sits out the way. On my 120ED I simply swap the finder for the guider using the same shoe.

BTW I drilled and tapped a standard synta finder bracket - get rid of the rubber ring 6 screws, 3 front and back job done, can do a pic if you want.

[dark knight]

I put a flat metal bar between the main scopes mounting rings and then mounted the finder guider on that, saved drilling holes in the main OTA...

[samtheeagle]

That's what I was thinking of doing Carl

[dark knight]

It works well Sam and keeps it out of the normal finders field of view...

[Glider]

Thank's for the tip, I'll give it a go. I added an extra shoe for the finderguider to my Newt by drilling it and then bolting it to the rear tube ring.

[daneel]

Could you post a picture Carl?

[dark knight]

Daneel, I'll try to post one later tonight or tomorrow

[MartinB]

For those who are interested in learning more about the benefits of setting minimum and maximum allowable moves the CCD ware site has a nice calculator.

AutoGuider Calculator V4.00

[adamsp123]

Martin,

maybe I have this all wrong but looking at the calculated figures it seems to suggest for a finder guider the minimum motion in PHD should be REDUCED compared to a 80mm F5 scope not increased????