Frequently Asked Questions

MetaGuide relies on the benefits of video for accurate, low latency guiding. Some cameras do not have a DirectShow video driver and they simply will not work with MG. Examples are the SX Lodestar and CCD cameras with no video mode. Most cmos cameras of all types (planetary and deep sky) will work, but qhy cameras require special handling. Color cameras will also work, but there is a loss of sensitivity with the Bayer matrix. Canon DSLR's should work in video mode with the EOS webcam utility installed.

USB, Firewire, and Ethernet video cameras should all work, as long as they have DirectShow drivers.

Many cameras will require a special download of the DirectShow driver as an option - so look for a DirectShow or WDM driver download option.

MetaGuide requires a DirectShow driver, whereas SharpCap can connect either with the camera's native driver or DirectShow - if it is installed. If SharpCap does not show a DirectShow option for your camera it means you need to install it.

Unfortunately QHY dropped their direct support for DirectShow, but you can connect to them in "broadcast" mode. Make sure you install the WDM Broadcast driver as part of their driver installation. Then connect to the camera in SharpCap and enable broadcast mode. You should then be able to connect to the camera via the broadcast driver from MetaGuide. See the MetaGuide documentation for more details.

Enter the camera and telescope data for the system MetaGuide is looking through. If guiding with a small guidescope enter data for the guidescope and camera. If collimating with the main camera on a large telescope, enter the large telescope.

That's the idea. The goal of MetaGuide is to use Lucky Imaging methods to create an aligned and stacked view of the star that is smaller than the typical seeing over a 1-2 second timespan. This "Aligned" FWHM is labeled as AFWHM and it shows what MG can do given the current seeing - with video and novel centroiding. So it is expected to be smaller than "seeing."

MetaGuide includes a calculation of seeing every 2 seconds - and that should approximate the current "seeing" conditions. But note that it assumes the telescope is well focused and has large enough aperture not to be limited by diffraction. In general it is hard to make a reliable "seeing" measurement - but the value provided by MG should at least give a ballpark value, and let you tell the trend from one night to another. If you use OAG, the guidestar "seeing" value will be heavily affected by the off-axis appearance of the star - so again it should not be taken literally.

MetaGuide focuses on novel centroiding methods to reduce the impact of seeing, and low latency for prompt corrections to the mount. This allows your mount to act as if you are using adaptive optics with 1 second corrections - without the added complexity of AO.

Autoguiding performance is always limited by how well it is tuned, and in order to tune you need good feedback on changes to things like aggressiveness. MG is unique in providing accurate guide error plots that update every 0.5 seconds - so you have a "live" view and prompt feedback on changes.

MG is also unique in providing a "GuideView" that shows a live video view of the guidestar as it jiggles around the target pixel location.

"Chasing the seeing" is a myth that is preventing people from getting good autoguding results. One of the worst things for any feedback system is latency, and a long guide exposure means there will be latency between the centroid measurement and the correction. Instead, if you measure the star quickly and immediately correct the guide error, you get *improved* guiding, and the only thing you chase is errors in the mount - which is a *good* thing.

Guide logs are only an indication of what the autoguide system *thinks* it is doing. If the centroid isn't very accurate on a sub-pixel basis, the actual motion of the star on the image plane may be much larger than the recorded motion of the centroid. This is particularly true with a well focused guidestar in a short focal length guidescope. And, of course, flexure may make the problem even worse - with perfect guide logs that contrast with oblong, sausage looking stars in the image.

MetaGuide always tells you the fwhm, in arc-seconds, of your guidestar. If the fwhm with a short guidescope is 25", it will be very hard to autoguide at the scale of 2" fwhm in your images. Instead, I recommend very small and round and well sampled guidestars that are 1-2" fwhm.

Any error in the shape of the guidestar will translate to errors in the centroid, and centroid errors lead to errors in the image. I would try to keep the guidestars small and round for best centroiding. In order to make prompt corrections for the mount, the guide exposures need to be short and the guidestars will be somewhat distorted by seeing. MG uses novel centroiding to guide on the hot spot of each video guide image and reduce this effect.

Distorted guidestars also means the light is spread out and you will lose the ability to guide on faint stars that would otherwise be fine.

The two ways to validate results from MetaGuide are in the match of the Airy pattern to theory, and the smallness of stars in long exposure images with mid-range equipment. The Airy pattern can be revealed even in mediocre seeing, and shows a good match to diffraction theory. This indicates the novel centroiding works for collimation.

MetaGuide has demonstrated low 1" fwhm's in 10-15m exposures with mid-range mounts that have relatively high PE, and cost much less than high-end mounts with expensive bearings. I commonly see high end equipment produce stars in the 3.5-4.5" range - and I think the autoguiding software and technique are factors in explaining the difference.