phd2 min-mo or no no!

[gonzostar]

Hi

Between gusts of wind yesterday i managed to get some guiding done.

I ran the guiding assistant it told me to take min mo down to 0.1 and 0.15 in RA and Dec. Did so and the graph was all over the place! Re adjusted min mo to 0.90 the graph was so aggressive and was peaking around 2-4" e

RA and Dec agression set at 90 is that to high? and exposure time at 3secs

Have other people had this situation and what have you done about this?

Gave up after more gust of wind

 

Cheers Dean

[Andyk93]

My min.mo is usually around 0.10, when I started guiding I did what you did and put aggression up really high thinking it would correct better. I've now got a lot better results by doing 4 second exposures and the aggression is usually 10 Dec, 20-40 on RA. I only guide in one direction for Dec also.

[gonzostar]

 

I do dec in one direction also. So high aggression makes guiding worse? and keep minmo down

Thanks

Dean

[Andyk93]

Give it a go, that's what I found. Too high aggression on my neq6 was making the RA snap backwards and forwards instead of gently correcting it

[gonzostar]

Will do Weekend looking good for clear night, touch wood!  

[frugal]

Min-mo is Minimum Movement; the smallest amount that your guidestar can be off centre before PHD will try to make an adjustment. So making it smaller should lead to more smaller movements. The default is 0.1

Agresssion is the percentage of the guide error that you want to correct in a single guide pulse. If you set it to 100, it will try to undo all of the guiding error in a single step. So if part of the error was from seeing, you are going to overshoot and have to correct back again. It seems that setting agression too high is a major cause of yo-yo guide corrections.

There are a couple of excellent videos on YouTube covering PHD set up and what the effect of all of the settings are: 

 

[gonzostar]

cheers for this will look at the clip  later  

[iapa]

15 hours ago, Andyk93 said:

Give it a go, that's what I found. Too high aggression on my neq6 was making the RA snap backwards and forwards instead of gently correcting it

My understanding is simalr to that of @frugal : that the 'aggression' setting is basically a % of the amount of movement that PHD2 has determined is needed to correct errors.

So, if you are guiding in one direction only for DEC you would have aggression set fairly high.

RA needs to be gentler to stop over shooting.

4s- 6s exposures seem to be the area to be aiming for - this will help over come seeing, you don't want to be changing everytime a wee heat bubble passes overhead.

I often use AUTO to start, then when using the guiding assistant, not the value there and use that .

 

[gonzostar]

Ok so this is where i am going wrong, For some reason i was going opposite to what you are saying. I i do tend to aim for 3-4 sec exposures and did set my min-mo high say at 0.8 -1.0!

So do you tend to follow advice from guiding assistant?  

[gonzostar]

thankyou everyone for you assistance Last night for the first hour and half guiding "seemed" really good. error no more then 3" small aggreesion and min-mo seemed to be doing the trick. I guess proof will be in the processing. I was doing the star clusters in Auriga. 

Then of course decided to go to Leo triplet and guiding went slightly array, but anyway Promising start!  

[JemC]

1 hour ago, gonzostar said:

Then of course decided to go to Leo triplet and guiding went slightly array, but anyway Promising start!

When you went from Auriga to Leo Triplet did you re-calibrate PHD, Sure i have read somewhere that you should re-calibrate when moving to a different part of the sky, maybe that's why it went slightly array,

[gonzostar]

Quite possibly as i was attempting to the impossible, and beat the clouds!