How long does it take for PHD to calibrate for you?
Hi Guys.
I'm delving into the world of guiding (Joy).
I've set it up before and got it working using PHD/Eqmod a microsoft web cam taped to my 32mm eye piecethough my 8" newt, dont laugh.... hey, I said dont laugh it worked just fine.
Last night i thought I'd try and tape the web cam to the finder scope, (hey I said dont laugh) and see if I could get it to guide.
After much futsing around with the calibration in the brain I settled on about 8500, default is 750 he he he. It would calibrate but man it would take about 15 minutes. The more I increased the calibration the longer it would take. I assume this is because the magnification is smaller and therefore the movement is smaller.
So my question is how long does it take you to calibrate phd on a star?
thanks
Last edited by White Rabbit; 20-03-2009 at 01:44 PM.
Reason: The title made no sense.
As Doug mentioned unless it, the scope is pointed pretty close to the SCP, it can take a little longer, but usually about a minute or even less.
15 minutes is just to long.
It will also depend on the exposure time. On bright stars I sometimes use .5 second, and when this is going I can be done in way less than the minute my two colleagues suggest.
Depends on the step size - I beleve a smaller step size, with longer exposures would give you the best guiding. However I often use 2.5 - 3 second exposures with 300 msec steps - which might take a few minutes (less than 5). The longest I ever tried was 5 sec exposures on 150 mssc steps - no guide easily found in the frame around the Helix nebulae - wasn't much of a success.
Remember, what PHD is doing is taking a picture, moving the mount, taking a picture, moving the mount, etc. Each motion is "calibration step size" long. So, you're moving the mount at guide speed for 8.5 seconds each time.
I'm going to suggest something here that I've suggested to a number of users. PHD isn't actually moving your mount and you're not actually calibrating. Drift and/or PE are faking a calibration (PHD doesn't know if it moved the star or if something else did -- it's smart, not psychic). Use the Manual Guide dialog to make sure your signals are really getting through to the mount (I can hear my motors change pitch for example). On my 250 mm f/l guide scope I run a second or two for the cal step size and that's probably as long as you should ever need to go on it.
I normally get PHD do calibration in 14-15 steps in each direction.
This means that if i am calibrating near the pole i just set the calibration steps longer (eg 1700ms instead of 750ms).
You dont want PHD to go for 35 steps because i found out that it will not guide better or worse than with say 15 steps.
The way to make the guiding better is to set the sliders on the RA/DEC so the graph line doesnt oscillate up and down.
This is all with a DSI pro on a 600mm f/l guide scope.
So it all depends on f/l and guide camera and position in the sky.
As soon as you have to use more than 2 seconds there must be something wrong.
Remember, what PHD is doing is taking a picture, moving the mount, taking a picture, moving the mount, etc. Each motion is "calibration step size" long. So, you're moving the mount at guide speed for 8.5 seconds each time.
I'm going to suggest something here that I've suggested to a number of users. PHD isn't actually moving your mount and you're not actually calibrating. Drift and/or PE are faking a calibration (PHD doesn't know if it moved the star or if something else did -- it's smart, not psychic). Use the Manual Guide dialog to make sure your signals are really getting through to the mount (I can hear my motors change pitch for example). On my 250 mm f/l guide scope I run a second or two for the cal step size and that's probably as long as you should ever need to go on it.
Craig
PS - I'm the author of PHD.
well there you go -and all this time i thought it was done with smoke and mirrors . Thanks Craig for the detailed explaination . I have found it not to take no longer than a minute or so, then it was off happily guiding away.
I fixed my problem, allthough not all my guiding problems. I can calibrate in about 25 steps now, but guiding is still off. If the weather ever clears up I'll be able to refine what I'm doing....I hope.
Here is what I did for anyone else that suffers the problem.
In EQmod, hit the display window until the "Pulse Guide Monitor" is displayed. If you increase the pulse width PHD calibrates much faster. Although I'm sure If I'm just moving a fundimental problem with my set up around.
I normally get PHD do calibration in 14-15 steps in each direction.
This means that if i am calibrating near the pole i just set the calibration steps longer (eg 1700ms instead of 750ms).
You dont want PHD to go for 35 steps because i found out that it will not guide better or worse than with say 15 steps.
The way to make the guiding better is to set the sliders on the RA/DEC so the graph line doesnt oscillate up and down.
This is all with a DSI pro on a 600mm f/l guide scope.
So it all depends on f/l and guide camera and position in the sky.
As soon as you have to use more than 2 seconds there must be something wrong.
All
On the subject, my calibrations do take about forty steps.
This dosent bother me too much but now I have a problem that every time it goes to guiding I get the flashing red signal saying Low SNR. It want even guide for more than a couple of seconds. Star seems bright enough and calibration even though a little long ,there's no problem.What am I doing wrong?
Thanks if anyone can give me help Kepp
In all honesty I can only think that your Polar alignment is out or you've got a dicky mount.
On the other hand how long have you set the PHD exposures.
Calibration now for me usually takes about 20-25 steps
I've only ever had a couple of problems using PHD and they have resulted from either picking the wrong type of star to guide on, leaving the mount unattended or my polar alignment was out
Thanks
Is polar alignment important, My mount is "roughly" polar aligned and my mount is working fine. It was guiding ok for a while, this problem has just started. Cannot guide at all. Keep getting Low SNR
Hi Geoff.
Pictures say more than words
First pic is where to press the button to get to the RA and DEC fine adjustments, these settings have to be set back to 100% everytime you do a new calibration, or else the pulse guiding makes the calibration steps the percentage you have the sliders on.
Second pic is the sliders you have to move to smooth the guiding out.
Experimentation is to be done here.
Third pic is what you get when you press the settings button.
Always put the pulseguide sliders on 0.90 here when calibrating or else calibrating will take very long as with the RA and DEC sliders not on 100%.
All
On the subject, my calibrations do take about forty steps.
This dosent bother me too much but now I have a problem that every time it goes to guiding I get the flashing red signal saying Low SNR. It want even guide for more than a couple of seconds. Star seems bright enough and calibration even though a little long ,there's no problem.What am I doing wrong?
Thanks if anyone can give me help Kepp
Kepp,
Can you take a screencap or do a File, Save and dump the raw sensor data to a file? Remember -- too bright is as bad as too dim. Big fat guide stars are poor choices (as they've likely saturated the CCD)
. Thanks Craig for the detailed explaination
. I have found it not to take no longer than a minute or so, then it was off happily guiding away. 
