MetaGuide Collimation and Guiding

MetaGuide

by Frank Freestar8n

Collimate on the Airy pattern even in mediocre seeing

Better guiding with a mid-range mount using low latency video and novel centroiding

Don't just guide easily - guide well

Simple, accurate calibration with a single button

A very different way to guide with better results and tighter stars

Monitor your guiding on a different computer over your local network

Detailed guide plots updated every 0.5 seconds for better tuning

NEW! Version 5.1.3, July 2013 Many enhancements and improved performance!

New Support for FlexRX tool to correct for flexure when using a guidescope.

New Support for sensitive and small QHY5L-II guide/planetary camera

Also support for the ASI120 guide/planetary camera

SEEING measurement

FOCUS dialog

Better support for Pt. Grey cameras such as Flea


MetaGuide is a video-based tool for precise collimation using the in-focus diffraction pattern of a star. MetaGuide also autoguides and has several novel features that allow optimal guiding of mid-range mounts under typical seeing conditions. MetaGuide can provide insight into both the optics of your telescope, and the tracking behavior of your mount.

MetaGuide allows me to obtain sub-2" fwhm stars with a Celestron CGE and 11" SCT at 2800mm f.l. and 0.45" per pixel. The key is an accurate and low latency centroid that can be chased aggressively to overcome gearbox and bearing noise. This pushes autoguiding of a mid-range mount into a realm of performance that normally requires adaptive-optics.

MetaGuide is free, easy to use, works with any type of telescope, and most video cameras.

MetaGuide has many unique features, such as realtime measurement of flexure between two telescopes. This allows direct observation and measurement of flexure and mirror flop. MetaGuide also has a novel proactive guiding feature that locks onto specific high frequency gearbox or gear tooth terms that can be more of an issue than periodic error. MetaGuide also uses a novel form of "Lucky" centroiding to help determine a more accurate centroid that can be guided aggressively.

MetaGuide is highly quantitative, and provides live measurements of the radial profile of a star and its full-width at half-maximum for comparison to diffraction theory. It also measures drift, to aid polar alignment.

Although based on video guiding, MetaGuide can stack frames to create the effect of a long exposure that reaches faint guide stars. It also finds faint guide stars in the field and highlights them automatically. This avoids the user having to squint at the screen to find a guide star and then select it. When the guidestar is not faint, MG does not simply stack the exposures, but instead studies the centroid of each video frame and calculates the optimum centroid for the stack.

For the guiding component of MetaGuide, an ASCOM connection or other control of the mount must be provided (GPUSB, TOGA, AstroGene, LPT, and more).

What does MetaGuide do?

  • Allows a high power view of a star and its diffraction pattern even when seeing is not ideal
  • Shows a "coma dot" over the live star that guides collimation so the user just centers the dot over the star. This takes the guesswork out of collimation while keeping it interactive and realtime
  • Compares the observed diffraction pattern with theory, including secondary obstruction effects
  • Provides a simple "dump" of the raw and steady images of the star, along with a plot that shows how the stellar profile compares to theory, plus numeric values for the actual and theoretical FWHM's. This provides an objective and quantitative measure of a telescopes true performance, with less dependence on good seeing
  • Measures flexure/mirror flop using two telescopes, two web-cams, and two instances of MetaGuide that link to each other
  • Automatically re-centers the telescope during collimation so you can concentrate on the collimation adjustments and not have to re-center manually after each change
  • Acts as an autoguider with seeing effects partially removed from the error, so the "chasing of the seeing" is directly reduced
  • Locks onto a user-specified error frequency and corrects for it proactively, acting like a new level of periodic error correction that does not rely on indexing and can work at higher frequencies
  • Calculates centroid based on live view of stars using a very different algorithm than simple "center of gravity." To reach fainter stars, the frames may be stacked first for the effect of long exposures
  • Provides graphical output and logs of drift and periodic error in your mount, including the "noise" that can be hard to remove with PEC (Periodic Error Correction).

How does it work?

  • MetaGuide uses realtime image processing of the video stream to process each frame, find the star centroid, and output a realtime stacked version of the recent frames
  • Bad frames are automatically culled from the stack without user intervention
  • Normal autoguiding software assumes the guidestars are nice Gaussian shapes - but in fact they have broad and misshapen wings due to seeing. MG focuses on the central hot spot of the star in each video frame and guides on the centroids of these hot spots
  • MetaGuide is written in DirectShow/C++ for maximum performance since the amount of realtime computation is significant
  • The stacked view is magnified 4 times and aligned with sub-pixel resolution
  • This stacked view is also used as to determine guide corrections. Since this view has bad frames removed, the resulting error signal is a truer representation of the error due to the mount. This reduces the "chasing of the seeing."
  • The radial plot is calcluated based on the stacked image, allowing direct comparison to theory and calculation of FWHM

What are its requirements?

  • MetaGuide requires only a video camera and Windows 7, Vista, XP or 2000 computer (not Win98, ME, NT, Mac, or Linux) with recent DirectX installed to perform the core diffraction analysis of a star. MetaGuide and its install package are compatible with Win7/64
  • Most video cameras are supported - of any size - along with analog video cameras (NTSC/PAL) with a simple video2usb converter. The user can specify any resolution the camera supports. The main requirement is that the camera have a DirectShow video driver
  • Modified web-cams are not supported; MetaGuide relies on streaming video to correct for seeing
  • For the guiding features of MetaGuide, a connection to the mount is needed. The mount must be either equatorial or on a wedge, and for ASCOM it must support PulseGuide
  • A view of the diffraction pattern requires high power and a stable mount, so a Barlow and good tracking may be needed. The guiding and collimation aspects of MetaGuide will work with any f/ratio

Recent News

  • See examples of the new FlexRX tool for longer exposures when guidescope guiding
  • Nice Edge HD gallery by Andre Paquette with images guided by MetaGuide. Be sure to click and navigate to the All Sizes button to see them full sized, up to 4kx4k
  • MetaGuide observed the Airy pattern in a ground based 20" CDK telescope, with a measured live FWHM of 0.45". This required a focal length of 25,000 mm
  • MetaGuide is linked by the Lucky Seeing group for its use of "Lucky Guiding"
  • MetaGuide revealed a novel "dispersion wedge" shape to stars even at fairly high altitude that differs markedly from the Airy pattern

Actual comparison of Airy patterns from several telescopes of different apertures, all shown at the same arc-second scale. Note that the small refractor and Maksutov have well-shaped diffraction patterns that make the stars look good, but the angular size of the stars is much larger than the telescopes with greater aperture. This is a direct recording of the likely reason that refractors appear to out-peform larger aperture SCT's.


Download and Documentation

NEW! July 2013 version 5.1 (available now)

  • Support for FlexRX
  • Support for the new QHY5L-II guide camera and its st4 port
  • Support for ASI120 cameras and st4 port (support for st4 port guiding coming later)
  • Better support for Pt. Grey cameras such as Flea
  • Many performance enhancements and bug fixes
  • New SEEING measurement turns your telescope into a seeing monitor
  • New FOCUS dialog with novel audio feedback
  • More accurate centroiding
  • More sensitive collimation, for low coma designs such as Edge, CDK, RC, etc.
  • Many performance enhancements and bug fixes
  • Support for AstroGene and TOGA autoguide controllers with hardware timing

DISCLAIMER:This software is supplied as-is and without any guarantees or warranty. The author is not responsible for any damage or losses of any kind caused by the use or misuse of the software. The author is under no obligation to provide support, service, or corrections

MetaGuide 5.1.3 Installation, with extensive documentation and fixes for clean install on Windows (About 10MB)

Unzip the install file and run MetaGuideInstall_5_1_3.exe. You will be asked to install a Microsoft software patch. This is a needed step for many XP installations, but may not be needed for your computer. A pdf of documentation and a text file of updates will be installed in the MetaGuide directory. You can access the help using the menu of F1 from within MetaGuide.

Latest MetaGuide Beta version For people who want to test and experiment with the latest version. Unzip this file into the MetaGuide directory and overwrite any files that are there. Then go to a command line and type: regsvr32 GuideFilter.ax

MetaGuide 5.1 documentation alone, in pdf format, for perusal without doing the install. Detailed instructions and many examples, including a comparison of an SCT with a Maksutov. This manual is included with the installation.

MetaGuide 5.1 documentation in html format

Support

For support, please send feedback and questions to the AstroGeeks Yahoo group.

Contact (spam encoded address): freestar8n *at_t& yahoo _d_ot_t+ co*m

Guiding

Low latency guiding with video. Quick and accurate corrections for mid-range mounts.

Achieve tighter and rounder stars than with long guide exposures and standard centroid algorithms.

Let MG find and select faint guidestars as they come into view so you don't have to squint at the screen.

Collimation

Collimate using a star with the telescope aimed at the correct angle to the sky. Just center the coma dot on the star while the mount re-centers it. In better seeing you can use high power and collimate on the in-focus diffraction pattern.

Take an annotated and scaled image of your collimated star to show how well your star diffraction pattern matches theory.

Seeing measurement

Measure size of the star spot as it moves around over each 2-second interval, with live plots. Can be used as a dedicated seeing monitor with a telescope, or just to check seeing conditions

Drift alignment

Measure the dec. drift of the mount quickly so you can make rapid polar alignment adjustments to null out the drift.

Periodic error logging

Log periodic error in detailed formats for analysis in other tools. These measurements are taken every 0.5s with an accurate centroid, allowing high resolution studies of your mount behavior including gearbox and other noise. This may be the most important type of error for good guiding compared to the slower and more easily corrected terms.

GuideView mode

GuideView mode lets you watch the live guide corrections in video mode so you can see the small, fast motions of your mount that are the key to getting tight stars.