Hi Roland,

If you want to reduce periodic error just for the fun of it,
then by all
means do so. Just do it and see what your results are.

I've experimented with various levels of periodic error in my

(not only did I reduce PE but I made it artificially higher for

loading an appropriate PE curve). Using a 5-second autoguider cycle

turning on PEM reduced FWHM by 0.15 arc-seconds when going from 3.0

PE to 0.5 arc-sec . The stars looked just as round in each case,

FWHM of the stars with PEC on were tighter.

Also, for those autoguiding through a narrowband filter with an

good PEC is critical. It will allow you to increase the autoguider

time to get a guide star through the narrowband filter.

-Ray

OK, this may be why I see the large jumps when guiding. I'll turn it on and
see if they
still happen.

The manual says that the error curve from the factory testing procedures is
already
loaded into the the servo system. Is this active upon arrival, or not?

No, it is in memory, just as if you had placed your own curve into the memory
(PEM = Periodic Error Memory). Use the keypad to turn it on or off. You can
also use PEMPro to turn it on. In the keypad, PEM is located under Tools in the
Main Memory. Just follow the instructions on the PEM screen.

If you want to reduce periodic error just for the fun of it,
then by all
means do so. Just do it and see what your results are.

Another question: should i run a 'PEM' routine before the above? I have not
yet done so.

Not necessary unless you want to do unguided imaging. PEM is for periodic
error compensation. That means during any unguided imaging, you can drastically
reduce the priodic error (which is a very slow moving error that crops up after
tracking for a fairly long time period within the 6.4 minute worm cycle). The
error is small to begin with, between 3 and 5 arc seconds, so there is no use
trying to chase your guiding problems with yet another issue - an issue that
really does not affect guiding one iota.

for those autoguiding through a narrowband filter with an SBIG camera,
good PEC is critical. It will allow you to increase the autoguider exposure
time to get a guide star through the narrowband filter.

I have to ask, because NOT getting rid of the periodic error is contrary to
everything
I've ever heard. So, why would I not want to drastically reduce the error?

How long could you go, unguided, with the Mach1 mount...under 800mm
FL.?

In a message dated 12/10/2007 1:59:26 PM Central Standard Time,
alanv12952@... writes:

Thank you for the guidance. I will attempt to view the ST-4

next
opportunity.

Another question: should i run a 'PEM' routine before the above?

yet done so.

Alan

Not necessary unless you want to do unguided imaging. PEM is for

error compensation. That means during any unguided imaging, you can

reduce the priodic error (which is a very slow moving error that

tracking for a fairly long time period within the 6.4 minute worm

error is small to begin with, between 3 and 5 arc seconds, so there

trying to chase your guiding problems with yet another issue - an

really does not affect guiding one iota.

Rolando



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[Non-text portions of this message have been removed]

In a message dated 12/9/2007 1:09:22 PM Central Standard Time,
alanv12952@... writes:

All attempts to guide failed until I did the calibration at 0.5

guiding at
0.25.

You MUST calibrate at 1x, otherwise you may not get good cal

the ST4 guider, you are working basically blind, so it won't be easy

figure out what is going on. You might want to place an eyepiece

telescope while the ST4 is guiding, so you can see what is really

instead of relying on the numbers on the guider screen. Otherwise

forever groping in the dark, not knowing cause and effect.

Calibration at 1x is needed to get the proper amount of movement on

chip. Just make sure that the cal time is long enough to get 50 or

movement, but not too long to run the star off the chip. You can

the guide speed to 1x, .5x or .25x if you wish to slow down the

however .25x is almost never needed unless you have settings that

screwy.

While the ST4 is calibrating, LOOK through your eyepiece so you can
understand what is happening. Again, if you don't do this at least

setup, then you will be forever wondering what is happening. If you

eyepiece, and things don't look right, then at least you can explain

what you are seeing. Right now you can only say that something is

right, so that leaves all of us to guess. Take the guesswork out of the
equation and LOOK! (that advise is for anyone who has any guiding

equipment, no matter what equipment you are using).

Roland Christen




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You MUST calibrate at 1x, otherwise you may not get good cal numbers. With
the ST4 guider, you are working basically blind, so it won't be easy for you to
figure out what is going on. You might want to place an eyepiece into your
telescope while the ST4 is guiding, so you can see what is really happening,
instead of relying on the numbers on the guider screen. Otherwise you will be
forever groping in the dark, not knowing cause and effect.

Calibration at 1x is needed to get the proper amount of movement on the guide
chip. Just make sure that the cal time is long enough to get 50 or so pixel
movement, but not too long to run the star off the chip. You can then adjust
the guide speed to 1x, .5x or .25x if you wish to slow down the movement,
however .25x is almost never needed unless you have settings that are somehow
screwy.

While the ST4 is calibrating, LOOK through your eyepiece so you can
understand what is happening. Again, if you don't do this at least once with your
setup, then you will be forever wondering what is happening. If you do use an
eyepiece, and things don't look right, then at least you can explain to all of us
what you are seeing. Right now you can only say that something is not working
right, so that leaves all of us to guess. Take the guesswork out of the
equation and LOOK! (that advise is for anyone who has any guiding issues with their
equipment, no matter what equipment you are using).