LX200 Imaging Primer
By Bill Worley

I should start this by telling you a little about my imaging experience.  I started imaging in 1999 with a Meade Starfinder 10 inch Dob!  I had a webcam hooked up to it and used it to image the moon and planets.  After playing around with that setup for a while I bought a Meade LX200 10" f/6.3 in 2000.   Again,  I used my webcam and bought a laptop to use with my new  scope.  Here is one of my first decent  Saturn images.  After that I decide I wanted more that a webcam could do.  So,  I bought a Pictor 208XT for $499 and a 3.3 focal reducer.  My first image from that imager was extremely pleasing to me at the time.  It was M82.  After several months of playing with the 208XT I bought a SBIG ST-237A in January 2002.  Shortly after that I bought a wedge.  The first image shot with the 237A and wedge was M42 and that got my blood pumping... :)  I used that setup until November of 2004.  The next imager, which is my current imager, was a SBIG ST-2000XM with the ST-237A guiding ccd in one unit.  To say on-board guiding is great would have been an understatement.  My last and final purchase was a SBIG AO7 unit in June of 2006.   Now to my primer.  This primer will hopefully give you some direction in your imaging and get you to level where you are satisfied with your images quicker.  Any comments are welcome!

The LX200 can be cranky at times for no apparent reason for those unfamilar with the LX200.  I've put the most important issues to solve at the top.  The first thing I strongly recommend is buy a wedge for your LX200.  Without a wedge you are limited to 15-45 seconds on your exposure length depending on your focal length.  Everything below assumes you are using a wedge.

POLAR ALIGNMENT - This is a very important aspect of imaging.  Get a good polar alignment using the drift method.  Once you've done it a few time it will become second nature.  Take notes the first few times out on what way make what adjustment.  I do not recommend using the iterative method if you want to image.  Use a recitle eyepiece at around 200x.  You will be able to see your polar mis-alignment alot easier at higher powers.  But,  don't crank it up to 400x as your probably be adjusting for seeing.  I ended up putting in a permanent pier because I was tired of 'wasting' time polar aligning.  But,  a good polar alignment can be done in 45 minutes using the drift method.  If you plan on guiding don't think guiding will solve a poor polar alignment because it won't.   One last thing...  do NOT use the bubble level on the wedge.  It is extremely inaccurate and will affect your polar alignment.

Dark Frames - will help you minimize the noise produced by your imager.  Subtracting dark frames from your images will improve your results alot.  If your camera doesn't have a shutter you will have to cover the end of the LX200.  My Meade Pictor 208XT
did not have a shutter but every camera I've own since has had a shutter.  A dark frame is basically a image with your shutter closed.  This produces a repeatable noise in the image from your ccd imager which can be cancelled out by subtracting it from each image you have taken.  Dark frames have to be take at the same temp as the light images.

FOCAL REDUCERS - In the beginning,  I'd recommend buying a focal reducer.  The shorter focal length will make a less that good polar alignment produce better result because the wider field of view  is more forgiving to errors.  With smaller ccd chips (700 x 700) you can use a 3.3 focal reducer.  If you have a ccd chip much bigger it will show sever vingetting and coma.  Vingetting can be fixed with flat field images but the coma can not be corrected.  There are also 6.3 focal reducers available which would be forgiving because you're shooting at a shorter focal length than at your full focal length.

PEC - or PPEC or SmartDrive.  Whatever you want to call it.  Training your PEC (periodic error correction) of your LX200 can reduce the spikes in errors of your RA gear to provide better images.  Every RA gear no matter how well made has inperfections.  PEC on a LX200 helps minimize those errors to (hopefully) a more manageable level.  It won't get rid of the errors  but will make the larger errors alot less.  This helps your auto-guider work less and provides better tracking.  PEC training can be done by either using a recitle eyepiece or a ccd imager.  Each tooth of a LX200 equates to 2.4 seconds.  A complete revolution of the RA gear takes 8 minutes.  If you use a imager an exposure of approximately 1.5 seconds should be enough to train the drive properly.  With an exposure less than that you will probably be following the seeing.

- To guide or not to guide???  When you first start imaging I'd recommend not guiding.  Only because that is one more piece in the puzzle that can go wrong.  Start with getting good images with a 3.3 focal reducer then move to longer focal ratios which are less forgive that don't hide the LX200 error as easily because of the pixel scale of your image.  After you've started getting decent images with a focal reducer buy an auto-guider and give it a try.  I highly recommend SBIG's ST series of imagers with a guiding ccd intergraded into the ccd camera.   With the intergrated guide ccd chip you don't have to worry about a guidescope.  You can also guide with a seperate imager through a ccd imager and a guidescope piggybacked ontop of your LX200.  I did not like that setup.  Too many issues with flexure, etc.  I also only run my guiding aggressiveness at 3 or 4.

BALANCE - Once you start guiding with your LX200.  You'll soon realize how very important a good balance is especially in DEC.  If your balance is off in your LX200,  your DEC correction in one direction will be almost non-existant if not entirely non-existant.  If you have trouble calibrating your guider your balance is probably off some.  To get good performance in guiding make sure the LX200 is balanced!  Setting your backlash on your LX200 up will help tremendously in your dec corrections will guiding.  Experiment with the backlash setting to see what setting your LX200 works best at.

- Collimation is yet another important aspect in getting the most out your scope.  A scope that is out of collimation will produce less than stellar results.  Here is an image of NGC891 with my scope out of collimation.  Notice how the stars are in focus on the right but look strange on the left?  That's the collimation of my LX200 being out.   I usually use a recitle eyepiece to help me know where the center of my field of view  is which is important in collimating a SCT.  I get a decent collimation with the eyepiece on BOTH sides of focus then attach my imager.  Using my imager I use the focus mode and take a 1 to 5 second exposure of a slight out of focus star.  Then I adjust my collimation to make the out of focus star pefectly circular the whole way across my imager's field of view.  Make sure you adjust collimation on both sides of focus.  Pay attention to the four corners of your focusing images

Flat Field Images
- are basically correcting for any vingetting (unevenness in light) over the field of view  and any dust on your imager or scope that may show up in your images of your LX200.  Typically, there is a brightness towards the middle that gets dimmer as you move away from the center of the scope.  A flat field is obtained by taking a short image of a bright uniformly lit light source.  I made a lightbox for less than $20 that I put on the end of my scope.  The effort is well worth it.

AO7 - Adaptive Optics 7 has been a god send for those owning a LX200 and wishing to do any higher resolution imaging.  It has been a welcome addition to anyone into imaging no matter what the quality of their mount is.  AO7 is one of the reasons I highly recommend the SBIG ST series of imagers.  The SBIG AO7 unit corrects by using tilt/tip mirrors that are able to do 10 milliseconds corrections for any mount errors.  The rate of corrections is alot faster than any mount could ever do.  Bar None!  I've done more than 8 corrections per second using my AO7 in the short time I have used it.

Software - Most of us find that we prefer different software for post processing of our images. I prefer CCDSoft for dark and flat field subtraction, alignment, and combining frames.  for combining of my LRGB and DDP (if I use it) I prefer AstroArt.  Adobe Photoshop is used for finally adjustments.  Your taste may be different.

Exposure Length - When I was imaging in alt/az mode I shot anywhere for 15 to 30 seconds at f/3.2 or f/2.  When I bought my wedge my exposures were usually 45-60 seconds.  Since I started guiding I prefer to shoot 5 minute exposures.  5 minutes is a good balance for minimizing noise but not losing too much if something goes wrong during the exposure.  Sky pollution can affect how long you can expose a image before it gets light gradients or just over saturates the image.  In your area, 3 minute exposures might be the maximum.  Experiment to see what is best in your area.  I have seen decent images from 30 second subs.  I've seen some horrible 5 minute exposures.  Don't get too wrapped up in going to a longer exposure before you're ready.

Some final thoughts on imaging using a Meade LX200...  I'd highly recommend viewing Richard Bennion's Image Acquisition Best Practices Video if you have a broadband internet connection.  It is excellent and gives alot of insight into understanding the 'smaller' issues that can really affect resolution of your images such as collimation and focus.

Here's a couple of links to my imaging progress over the years.  If someone would have given me more direction the learning curve would have been alot shorter.  Hopefully,  you find direction in this primer. 

First Pictor 208XT Image - M82.
First SBIG ST-237A Image - M42.
Last SBIG ST-237A Image - M27.
One of my First SBIG ST-2000XM Images - Horsehead Nebula (B33).
Latest Image from my SBIG ST-2000XM Imager - NGC6820/3.

Please E-Mail me with any comments, corrections or suggestions are welcome.