PEMPro FAQ
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 PE.

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 programmed.

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 mounts.

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 Guider Rate

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.

2. Knowing 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 ImageLink 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.

3. 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 correct it.

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.

5. 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.

Fork Mount:

 

GEM Mount:


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 collecting data.

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 possible.

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 accept.

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 scale.

rb

Richard A. Bennion
CCDWare Publishing
http://www.ccdware.com

Ewell Observatory
http://www.ewellobservatory.com