I have spent a great deal of time with PEMPro
from its early beta stages to its current version (1.17). I can
honestly say that I have 100+ hours of testing and quantifying the
capabilities of PEMPro. Second possibly only to Ray Gralak who
developed the software.
During this time, I have learned many of the key issues that
determine how well PEMPro will improve the quality of your mounts
I have a circa 2000 AP900GTO with a GTOCP2 (REV D firmware). I have
tested PEMPro with a FSQ-106 and a STL-11000 at 3.5 arc seconds per
pixel, a Intes MK69 MakCass with a ST10XME at 1.50 arc seconds per
pixels, and more recently a Celestron 9.25 with a ST10XME at .88 arc
seconds per pixel. Through trial and error, I have been able to get
PEMPro to correct my mount as good as I think any mount can be
The results have been dramatically better guiding and better images.
This stuff really works!
I believe that many of my experiences can help those that have a
mount that has PEC playback firmware as part of its feature set and
are using to PEMPro to correct the mounts PE as best as possible.
First off, there are things that PEMPro can correct and those that
it cant. The quality of your mounts PEC recording and playback
firmware is an essential piece of the puzzle. If the mount does not
record PEC properly, or plays back PEC in a un-orthodox manner, this
is going to have adverse results in what PEMPro can accomplish.
CCDWare is in contact with certain mount firmware developers to
understand the methods in which they program and playback PEC.
Because PEMPro is such a revolutionary program, it really puts a
mounts firmware to the ultimate test as well as the developers who
create that firmware.
Currently we have had excellent success with the following mounts:
All Astro-Physics Mounts.
Paramount ME Mounts.
Many have had very good success with the following mounts:
Losmandy Mounts (Gemini and SkyWalker firmware) LX200 and LX200GPS
There are other mounts out there that we have had very good success
with and I would love for you to chime in and let me know about your
successes and/or failures with your mount. It would be a great help
to us all to see your results and understand how you got there.
The following is a summary of best practices that can have a large
impact of your success with PEMPro. I have put them in order of what
I believe to be the most important (or most mis-understood) factors
that determine your success. But understand, they all must be taken
into consideration in order to be successful with the product.
1. Setting your
In PEMPro's setup dialog, you must specify a guider rate. This rate
MUST match the guiding rate of your mount. The result of NOT having
the value in software match the value in your mount will result in a
drastic over-correction or under-correction of your PE.
This has caught me off guard many times. Let me give you an example.
I know that I have the guider rate set to .5X in PEMPro. But how do
I make sure it is set to .5X on my mount? In my case, I can set the
guider rate with the hand paddle of the AP900. I can also specify a
rate via the ASCOM driver. I can even set the rate with PulseGuide
made to remotely control AP mounts.
I have been in situations where the hand paddle was set to 1X guider
rate, then I loaded the ASCOM driver and it stated .5X guider rate,
and then I open up PulseGuide and can set the rate manually to .25X,
.5X or 1X. The changes I make with PulseGuide don't reflect in the
ASCOM driver, nor the hand paddle of the AP900 mount. I have found
myself baffled on what rate the mount is really set to. This has
been a problem that has bit me over and over.
So what to do, when in doubt, set everything to the same rate. So I
set my hand paddle to .5X, the ASCOM driver to .5x and turn on
PulseGuide and tell the mount to track at .5X. Now in my mind, there
is no doubt that the mount's guider rate is set properly.
I have found that with some mounts, the guider rate is not easy to
understand nor even locate. We must all be sure that the guider rate
on the mount equals the guider rate set in PEMPro. If you cant
achieve this, then PEMPro will disappoint.
your Image Scale
How many arc seconds per pixel does your imaging setup deliver? A
common problem I see users make is to calculate their image scale
using online calculators or using a simple formula based on pixel
size and aperture.
This is fine for getting a GENERAL idea of your image scale, but in
my experience working with 10 different OTAs, 4 SBIG cameras and a
pile of reducers, correctors and telecompressors, the calculated
image scale NEVER exactly matches the real world plate solve test.
Example, at the moment I have a C9.25 on my AP900. It has a DF-2
focuser, Optec Rotator, Celestron 6.3 reducer corrector, 50mm
extension tube connected to a SBIG ST10XME. If I just calculate my
image scale using the normal formulas, I get a calculated image
scale of .95 arc seconds per pixel. But I have a long image train
which adjusted the focal ratio of the SCT at the focal plane. In
addition, my extension tube from my reducer is 3mm to short for the
ideal distance from focal reducer to focal plan.
Using CCDSoft and TheSkys ImageLink tool, I find that with a simple
plate solve I have a .88 arc second image scale. That is almost a
10% difference than the calculated image-scale. That means PEMPro is
going to work 10% less efficiently as it could. In some peoples
case, I have seen image scale discrepancies or calculated vs. real
of more than 50%.
Calculators only get you in the ballpark. In order to get your exact
image scale, use
with TheSky or use Maxim's plate solve capability with PinPoint LE
to find your EXACT image scale.
Knowing your exact image scale will help you with many other
programs as well. For instance, you cant measure your FWHM of your
stars in your image unless you know your exact FITS scale. You cant
use software automation software like CCDAutoPilot and perform
meridian flips without knowing your image scale. If you use T-point
or any other pointing corrector, you need to know your image scale.
Bottom line, the wrong image scale will not provide you with an
accurate arc second measurement with PEMPro.
What Image Scale is Best to use?
I am going to start out this section with something that I think we
all learned early on with CCD Imaging and focusing. You cant focus
at a 2x2 bin and then image at 1x1 binning. You can, although, focus
at 1x1 binning and image at 2x2 binning. If you are going to image
at 2x2 binning only, then you can focus at 2x2 binning. The rule is
you must focus at the highest binning mode you plan on using.
I have found that PEMPro follows the same rule. Think of it as
focusing the periodic error of your mount. If you only image at a
3.5 arc seconds per pixel for wide field work, then you can use that
image scale to program your mount with PEMPro. But don't expect to
throw on your 12 inch Meade at .55 arc second per pixel on your
mount and still expect the same level of performance.
Use the smallest image scale you will use with your mount to program
your mount. The better then sampling rate (i.e. smaller the image
scale) the better PEMPro can analyze and correct your mount.
Remember, ideal sampling is the seeing in your local area divided by
3.3. If your local seeing conditions averages 2.0 arc seconds, then
you should aim for a image scale of ~.60 arc seconds per pixel.
Anything more than that wont achieve much better performance.
Now, if you only image at 1.75 arc seconds per pixel, then use that
to program your mount. I have programmed my mount with PEMPro at 3.5
arc seconds per pixel and it worked great with my wide field set-up.
But when I measured my PE with a C9.25 SCT, I found the error to be
to large for that image scale. So I re-programmed my mount with the
C9.25 and decreased my PE error by 4X! Now the next time I do wide
field imaging, my mount will be 'super-tuned' for the job, and
that's just what we want.
4. How Many Worm
Cycles should I Collect?
Think of each worm cycle as a sub-exposure from your CCD Camera. The
more you take and average, the better your signal to noise and the
better the quality of the image.
PEMPro works the same way. Each worm cycle you collect is an 'image'
of the gear. The more you take, the better you can increase your
signal to noise. Think of signal as mechanical error and noise as
seeing induced errors. We want a clear picture of the mechanical
error and minimize seeing artifacts. If you take 2 worm cycles, you
are not going to get a very clear picture. If you take 5-10 'images'
of the gear, you are going to get a great picture. PEMPro uses very
sophisticated averaging algorithms to separate signal from noise.
The better the image of your mechanical error, the better PEMPro can
When you analyze how well PEMPro corrected your mount by collecting
data with PEC turned on, do at least 2 runs to make sure you have a
fairly flat line.
After I Program, My PE is Worse!
I know, it happens to me too. Why? Camera orientation. What side of
the meridian you are on. Does your cameras X axis = RA and Y = DEC
or does X = DEC and Y = RA? Which way is up???
Here is my advice regarding orientating your camera for best results
with PEMPro. We want X = RA and Y = DEC.
With the above orientations, we now know that X IS RA and Y IS DEC.
Now, start collecting data, use that RA + button. Hold it down for a
while until you see the graph start moving up or down. If it moves
up we are all set. Restart collecting data. If the graph moves
down, check the REV checkbox, push the RA + button again, and make
sure that the graph moves up. Mission accomplished. Restart
Now here is a TIP that I would like to share with my fellow PEMPro
users. Sometimes I do everything above, collect data, and program my
mount. I then re-collect data with PEC on and find that my error is
twice as bad as before.
Simple fix. Go back to the Acquire data tab, click the REV checkbox
and re-program your mount.
I am not sure why this happens to me sometimes, but it does. If you
see this behavior, follow my steps to correct the problem.
Also remember, you acquire, analyze and program your mount all in
one session with PEMPro. PEMPro keeps track of where your worm gear
by using its own clock. If you close PEMPro or move your mount, you
will have to start all over.
* Note, if you have a new AP mount with a GTOCP3 mount, this is not
the case. You can upload and download curves whenever you want. I
need to get one of these soon!
There are a lot more advanced topics to discuss regarding PEMPro,
but I wanted to share these experiences with everyone who owns or
evaluates the software to make sure you get the best results
My belief is, if you can get your mounts PE under 1.5 arc seconds,
you are beating the seeing, time to start imaging. If you can go
from +/- 30 arc seconds to +/- 5 arc seconds, you are getting 6X the
performance of your mount. An improvement that any imager will
BTW - This evening, I was able to reduce my PE from +/- 10.5 arc
seconds to +/-0.9 arc seconds at .88 arc seconds per pixel image
Richard A. Bennion