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Imaging System Analysis

   

Imaging System Analysis

 
 

The purpose of this web page is to define a quantifiable and systematic procedure to collect data necessary to analyze your CCD imaging system with the goal of producing "quality" images with minimal tracking error.

Background

Since the Paramount ME began shipping in early 2002, many users, from expert to novice, have came to the conclusion that their Paramount is “not able to track accurately” or "the sidereal tracking rate is wrong" or the mount is "not able to point accurately" or "the periodic error of the mount is above specification".

To date, after careful, objective, scientific, systematic analysis of their entire imaging system, every undamaged Paramount that Software Bisque has analyzed met or exceeded specification with regard to tracking and pointing performance.

With respect to the Paramount, Software Bisque has found that the imaging system components that produce poor tracking or poor pointing are generally caused by one or more of the following (but not necessarily limited to):

  • Inadequate, unstable or improperly mounted piers
  • Piers with sympathetic frequencies that produce vibration from an external source
  • Optical tube assemblies that have mirror flop
  • Excessive tube flexure from optical tube assemblies that create a measurable "non-sidereal tracking rate" (and other errors)
  • Poorly mounted CCD cameras that introduce random pointing and tracking errors
  • OTAs mounted using a dovetail mounting that flex

One such experienced non-technical astronomer was considering returning his Paramount because his imaging system was producing "elongated stars." After following the procedures below (and with some guidance from Software Bisque), he was able produce quality images that not only exceeded his personal expectations, but enabled him to capture an APOD

What Tools to Use?

There is a great deal of confusion and misinformation among amateurs about how to analyze your imaging system's tracking to produce a “quality” image (specifically, symmetrical stars).

The tools that can be used to analyze your imaging system's tracking and pointing include: 

  • TPoint Telescope Modeling and Analysis Software for Windows (to quantify and optimize polar alignment and improve all sky pointing)
  • ProTrack (modeled tracking using a TPoint model)
  • Periodic Error Correction (PEC) and PrecisionPEC
  • Autoguiders
  • AO-7 devices.

 

Where to Start?

If you are having difficulty getting "acceptable tracking or pointing performance", and need a procedure that will help objectively analyze your imaging system, here's the place to start...

Imaging system diagnosis is a time consuming, and can be a painstaking process. Unfortunately, Software Bisque does not have the manpower to provide free consulting to mount owners.

Our hope is that, by using the systematic procedure below, you'll be able to quantify, identify and isolate the problems so that you can use your imaging system to produce tracking and pointing performance that meets or exceeds the Paramount published specifications.

If you have hired Software Bisque to help you analyze your system, please send the information requested below.  Otherwise, you can follow the steps below to help diagnose potential sources of tracking error in your imaging system.

 


 

Step 1: Acquire Digital Photographs of your Imaging System

Step 1 Details 


Step 2: Quantify your Imaging System Configuration

Step 2 Details 


Step 3: Send your TPoint Model

Step 3 Details


Step 4: Collect Tracking Log Data With and Without PEC

Step 4 Details 


Step 5: Collect a Series of Short, Back to Back, CCD Images

Step 5 Details


Step 6: Collect Unguided CCD Images of Various Lengths

Step 6 Details

 

Step 1: Details for Sending Software Bisque Digital Photographs of your Imaging System

The purpose of this step is to analyze the physical setup of your imaging system. You must scrutinize every mechanical component and mounting interface to ensure there is no "slop" or "play" that might cause pointing and/or tracking errors. This includes the earth to pier, pier to mount, mount to OTA, OTA mirror mounting, OTA to CCD Camera/Focuser/Filter wheel mounting.

If you have hired Software Bisque to help you analyze your system, please send this information.

Take five digital photographs the imaging system.

    1. Two “wide field” views showing the pier, mount and optical tube assembly from two different angles.
    2. A photograph of the pier-to-earth interface.
    3. A photograph of the camera to optical tube assembly interface.
    4. A photograph of the Versa-Plate to OTA interface.
  1. Create a "zip" file named ISAPhotographs.zip that contains each photograph, and email the zip file to support at bisque.com. The subject of the email must read "ISA Step 1 <Your Last Name Here>". Where <Your Last Name Here> should be replaced by your surname. For example, John Smith's subject would be "ISA Step 1 Smith".

If you have entered a consulting contract with Software Bisque to analyze your system, please send this information, do not proceed to Step 2 until a Software Bisque engineer has instructed you to do so.

 


Step 2: Details for Sending Software Bisque your Imaging System Configuration

The purpose of this step is to determine the image scale of your imaging system. Image scale is the metric that you can use to quantify tracking errors on your CCD images. Once the the magnitude of the tracking error is quantified (by measuring the "width" of the elongated stars), then the "rate" of tracking error can be computed and compared to the sidereal tracking rate. This will help determine where the tracking error is coming from. 

For the purposes of this analysis, please use a single optic, CCD imaging camera, and accessory configuration. That is, do not change anything equipment-wise during the analysis.

If you have entered a consulting contract with Software Bisque to analyze your system, please compile the follow information and email it to support at bisque dot com. The subject of the email must read "ISA Step 2 <Your Last Name Here>". Where <Your Last Name Here> should be replaced by your surname. For example, John Smith's subject would be "ISA Step 2 Smith"

  1. The make and model of the optical tube assembly used to acquire CCD images. If you own multiple OTAs, please use one, and only one OTA during this analysis.

  2. The make and model of the CCD camera used to acquire CCD images. If you own multiple CCD cameras, please use one, and only one camera during this analysis.

  3. A detailed description of all auxiliary devices being used on the system (specifically, the make and model of any/all motorized focusers, filter wheels, AO-7 devices, focal reducers, field flatteners, Barlow lens, field rotators, etc.).

Do not proceed to Step 3 until a Software Bisque engineer has instructed you to do so.  

Step 3:  Details for Sending Software Bisque your TPoint model

TPoint pointing data reveals problems or errors with the imaging system, and is very important to this analysis.

  1. If you have entered a consulting contract with Software Bisque to analyze your system, please email Software Bisque your TPoint Document (with 100 data points, minimum), either as a file with the extension ".TPT", or a Sky Document (.SKY) file that includes a TPoint model, and email this file to support at bisque.com. The subject of the email must read "ISA Step 3 <Your Last Name Here>". Where <Your Last Name Here> should be replaced by your surname. For example, Jim Smith's subject would be "ISA Step 3 Smith".

TPoint Document Overview

The TPoint document (that is, a file with the extension ..tpt generated by TPoint for Windows, or tptx from the TPoint Add On) includes the pointing or "mapping" data, as well as the terms you've added to the TPoint model.  If you've inserted a TPoint model into TheSky, then the Sky Document (that is, a file with the extension .SKY that is generated by TheSky) contains the TPoint model, as well as your current TheSky settings.

Do not proceed to Step 4 until a Software Bisque engineer has instructed you to do so.


Step 4: Details for Collecting Tracking Log Data With and Without PEC

The purpose of this step is to quantify your mount's periodic error before and after Periodic Error Correction (PEC) is applied. Mounts that use worm gears all have periodic error, and, with periodic error correction disabled, this error will produce elongated stars on your CCD images.

If your imaging system is producing elongated stars, you can determine if the elongated stars are due only to PE, or PE and some other factor (such as tube flexure).

  1. Install the latest versions of TheSky and CCDSoft or the Camera Add On (from www.bisque.com/download).

  2. Collect 10 minutes of tracking data with PEC off.

  3. Collect 10 minutes of tracking data with PEC on.

  4. If you have hired Software Bisque to help you analyze your system: email the two tracking data logs . Please see the Collect Periodic Error Data topic in the Paramount manual for step-by-step procedure to do this task. Please do not send tracking data acquired using any software other than CCDSoft or the Camera Add On. The subject of the email must read "ISA Step 4 <Your Last Name Here>". Where <Your Last Name Here> should be replaced by your surname. For example, Jim Smith's subject would be "ISA Step 4 Smith".

 

If you have hired Software Bisque to help you analyze your system, do not proceed to Step 5 until a Software Bisque engineer has instructed you to do so. 

Step 5: Details for Collecting a Series of Short, Back to Back, CCD Images

The purpose of this step is to acquire images in an optimal part of the sky to measure tracking accuracy with no tracking, no guiding, and no periodic error correction enabled. Analyze the resulting images to determine the quality of stars on the images and blink compare them. These images should have nice, round stars and they should not move significantly from photo to photo. Otherwise, the stability/rigidity of the system comes into question or there may be a bad guider cable, or the wrong tracking rate is enabled.

  1. Collect a series of CCD images without any tracking corrections.

  2. Using TheSky, slew the telescope near declination 0 degrees, near the meridian (within 5 degrees or so).

  3. Use CCDSoft or the Camera Add On to acquire a series of 15, 10 second images in succession (1 x 1 binning on the larger detector if the camera has two detectors).  Do not perform any image processing on any images (dark frame removal is okay). Strive to have the first 10 second exposure shortly after the slew help evaluate system settling time.

  4. If you own a large format camera, the images may be large and difficult to send via the internet. So, either email to support at bisque dot com, place on web site and provide a URL, or burn to a CD-ROM and mail the unprocessed, 16-bit FITS files to Software Bisque. The subject of the email, or any other written correspondence must read "ISA Step 5 <Your Last Name Here>". Where <Your Last Name Here> should be replaced by your surname. For example, Jim Smith's subject would be "ISA Step 5 Smith".

If you have hired Software Bisque to help you analyze your system, do not proceed to Step 6 until a Software Bisque engineer has instructed you to do so.

 


Step 6: Collect Unguided CCD Images of Various Lengths

The purpose of this step is to acquire images in an optimal part of the sky to access tracking accuracy over various exposure lengths, but no guiding, and no periodic error correction enabled. Analyze the resulting images to determine how the mount tracks without any corrections.

Paramount worm periods are listed in the Paramount User Guide. Compare the elongation of stars for each set of data to determine the magnitude of tracking errors.

Using the same setup parameters as in Step 5:

  1. Acquire 1, one-minute "raw" image. Specifically, unguided, un-pec corrected, no TPoint, no ProTrack, no AO-7 guiding, no guider cable plugged in, no joystick plugged in, 1x1 binned image using the larger detector if the camera has two detectors.
  2. Acquire 1, 2.5 minute "raw" image. Specifically, unguided, un-pec corrected, no TPoint, no ProTrack, no AO-7 guiding, no guider cable plugged in, no joystick plugged in, 1x1 binned image.
  3. Acquire 1, five-minute "raw" image. Specifically, unguided, un-pec corrected, no TPoint, no ProTrack, no AO-7 guiding, no guider cable plugged in, no joystick plugged in, 1x1 binned image.

If you have hired Software Bisque to help you analyze your system:

If you own a large format camera, the images may be large and difficult to send via the email.

FITS Image Distribution Options

  • Email the images to support at bisque.com.
  • Place the images on a web server, and then email Software Bisque the URL to download them.
  • Burn them to CD or DVD media and mail them to Software Bisque.

Notes:

  • The images must be unprocessed, 16-bit, grayscale FITS files.
  • The subject of the email, or any other written correspondence must read "ISA Step 6 <Your Last Name Here>". Where <Your Last Name Here> should be replaced by your surname. For example, Jim Smith's subject would be "ISA Step 6 Smith".

The above data should be sufficient to characterize the tracking of your mount and help isolate most any kind of tracking issue.  Some experience is required to know if there are egregious issues with the raw data, significant enough that cannot be corrected by Software Bisque technologies.  If the raw data is reasonable, Steps 5 and 6 can be repeated with say PEC on (or Protrack On or while Autoguiding) and the resulting photo will (must) be better then the photo with PEC off (or Protrack off or not Autoguiding).  By comparing the raw data collected to the same data collected with a particular technology turned on, its possible to isolate where a tracking error is being introduced.

If you have entered a consulting contract with Software Bisque to analyze your system, once Steps 1 through 6 have been successfully accomplished, Software Bisque can begin its analysis of your imaging system.

Software Bisque, at its discretion, may need to obtain additional information as required.

 

 


   

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