Imaging System Analysis

The Imaging System Analysis page defines a quantifiable and systematic procedure to collect the data necessary to analyze your digital imaging system with the goal of producing “quality” images with minimal tracking error.

Background

Since the Paramount’s began shipping in 1996, many users, from expert to novice, have concluded that their Paramount mount 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.”

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.
• Tube flexure that is prevalent in all earth-based imaging systems, and particularly in larger truss mounted OTAs that produces a repeatable and quantifiable “non-sidereal tracking rate” (and other errors).
• Poorly mounted cameras, focusers, filter wheels, rotators, and/or autoguiders that may introduce random pointing and tracking errors.
• OTAs mounted using a dovetail mounting that non-uniformly flex depending on the mechanical orientation.
• Optical aberrations with the OTA, including poor collimation, pinched optics, etc., that can produce elongated stars.

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 “Train PEC“
• 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 unable to provide free consulting to all 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.

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 Periodic Error Correction

Step 4 Details

Step 5: Collect a Series of Short, Back to Back Photos

Step 5 Details

Step 6: Collect Unguided Images of Various Lengths

Step 6 Details

Step 1 Details: Sharing 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 camera/focuser/filter wheel/rotator/AO mounting.

Please share the following information.

1. Take five 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.

If you have hired 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: Sharing 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 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, imaging camera, and accessory configuration. That is, do not change anything equipment-wise during the analysis.

1. The make and model of the optical tube assembly used to acquire images. If you own multiple OTAs, please use one, and only one OTA during this analysis.
2. The make and model of the camera used to acquire images. If you own multiple 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.).
4. Upload your data to a cloud-based file sharing service (Dropbox, Google Drive, Microsoft OneDrive, etc.) and include the URL of these files in a post to the support forum.

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. Upload your TPoint Settings file to a file sharing service (Dropbox, Google Drive, Microsoft OneDrive, etc.) and post the URL of the files in a post to the support forum.

TPoint Settings Overview

The TPoint settings (specifically, a file with the extension .tptx that is generated by TheSky Professional Edition and saved to the TPoint folder in TheSky’s Settings folder.

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

Step 4: Details for Collecting Tracking Log Data With and Without Periodic Error Correction

The purpose of this step is to quantify the mount’s periodic error before and after periodic error correction (PEC) is applied. All mounts that use worm gears have periodic error, and, with periodic error correction disabled, this error produces elongated stars on in photos.  The mount’s peak-to-peak periodic can be approximated by measuring the angular size of a star’s elongation.

If your imaging system is producing elongated stars, you can determine if the elongated stars are due only to periodic error, or periodic error plus other sources of tracking factor (such as tube flexure).

1. From TheSkyX, click Help > Check for Updates, and install the latest release if necessary.
2. Turn the Apply PEC checkbox off, then collect 10-15 minutes of tracking log data.
3. Turn the Apply PEC checkbox on, then collect 10-15 minutes of tracking data.
4. If you have hired Software Bisque to help you analyze your system, post the two tracking logs to the support forum.  Please use the “Train PEC” button on the Bisque TCS Window, PEC tab, Compute PEC Curve subtab.  In the alternative, manually collect PEC data.  Carefully review “Collecting and Using Periodic Error Tracking Data” and in the Paramount User Guide for step-by-step procedure to do this task. To ensure the tracking log data is formatted correctly, please use the Camera Add On to create the log. 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 support staff member has instructed you to do so.

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

Look at the resulting photos to determine the quality of stars on the images. Stars in the photo should be round, and should not move significantly between successive photos. Otherwise, the stability/rigidity of the system comes into question or there may be a bad guider cable, or the wrong tracking rate is being applied.

1. Collect a series of images when there are no external changes to the telescope’s position.  Specifically there can be no periodic error corrections applied, no ProTrack corrections and no autoguider/DirectGuide corrections).
2. Using TheSky, slew the telescope near Dec 0 degrees and near the meridian (within five degrees or so).  A reference line at declination 0 degrees can be displayed on the Sky Chart by clicking Tools > Database Manager > expand Sky Databases (SDBs) > expand Optional Databases and turn on the Celestial Equator checkbox.
3. Use 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 recommended). Strive to acquire the first 10 second exposure shortly after the slew help evaluate the system’s settling behavior.
4. Use a file sharing service (Dropbox, Google Share, OneDrive, etc.) to post them and share the URL on the Software Bisque Support Forums.

Do not proceed to Step 6 until a Software Bisque support staff member has instructed you to do so.

Step 6: Collect Unguided 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:

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 above can be repeated with, for example, the Apply PEC checkbox turned on (or ProTrack enabled, or while autoguiding).  The resulting photo must be better than the photo with the Apply PEC checkbox turned off (or ProTrack disabled, 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.

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