Slop lost motion is very difficult to predict so it does not model well. Performed correctly, the conversion between "mean" and "apparent" coordinates introduces no errors worth consideration. If these coordinate transforms are the only corrections applied, then the telescope pointing accuracy will be limited by atmospheric refraction.
The correction for atmospheric refraction is a function of zenith distance and atmospheric density pressure, temperature and humidity. The correction amounts to about 30 arc minutes at the horizon at sea level conditions.
An approximation of the atmospheric density can be made by correcting for altitude only. This will lead to an error in the refraction correction of about 1 to 2 arc seconds at a zenith distance of 70 degrees. Polar misalignment errors can be minimized for pointing or for tracking, but not both. Normally the telescope is polar aligned on the refracted pole to minimize field rotation during tracking. The resulting altitude misalignment introduces pointing errors primarily in Declination as a function of hour angle.
These errors can approach 1 arc minute in amplitude. Optical and mechanical non-perpendicularity errors introduce large pointing errors in Right Ascension and may exceed 2 arc minutes in amplitude. With a generalized and nonspecific site pointing model, a corrected telescope will have an RMS root mean square or a form of average pointing error in the 3 arc minute range.
The RMS error can be reduced considerably with site and telescope specific pointing model coefficients. Many professional observatories quote a pointing error in the few arc second range. However, these values may be the best they have achieved and not necessarily what they achieve on a routine basis. Even the "best" telescopes will need some form of guiding or correcting the telescope tracking using optical feedback from a star.
If the telescope tracks perfectly, tracking corrections will still be needed to correct for small refraction effects seeing for example. Guiding may be performed with a reticle eyepiece or using some type of electronic detector. In any case, the guider optical system will have a finite field of view. The guider is used to acquire and center the object and then to provide tracking corrections. The pointing accuracy should be sufficient to place the object within the field of view of the guider system open loop without optical feedback.
Small telescopes tend to have a relatively large field of view while large telescopes have a very small field of view so the pointing needs to be better for large telescopes. This level of pointing is considered "Good". The guider system will often have a field of view of several arc minutes so the pointing needs to be a fraction of an arc minute.
For moderate size telescopes 0. The DFM Engineering data sheets provide very conservative pointing accuracy with typical values of 30 arc seconds RMS or better stated. The following table shows actual values for a few of the DFM telescopes installed or serviced lately. The pointing model used by DFM is a geometric model. Typically, the DFM telescopes have little to no flexure to correct which demonstrates the high stiffness and symmetry of the structure. The following 4 graphs show the various pointing errors for the Dickinson College DFM inch telescope.
Notice the largest error is less than 30 arc seconds and this error occurs at a zenith distance of 80 degrees where the refraction model is not very good. MaxPoint is designed to solve this problem through mount modelling. When you first set up MaxPoint, it creates a model of your telescope mount, including any polar axis misalignment, offsets, and mechanical flexure. Once this is done, MaxPoint automatically corrects your telescope position to ensure it is always on-target. With MaxPoint, even very low-cost GOTO mounts can routinely achieve a pointing accuracy of arc-minutes over the whole sky!
The telescope model is easily generated using one of two methods. The first is to manually make a series of observations. Simply double-click on a reference star on the sky map. If you have MaxIm DL, this process can be completely automated. MaxPoint slews the telescope to a series of points across the sky, takes images using MaxIm DL, and then automatically calculates the pointing offset using the included PinPoint LE measuring engine.
Just sit back and watch! Once a model has been defined, MaxPoint lets you see exactly what the errors in your telescope mount are, including a direct measurement of your polar alignment error.
MaxPoint includes a complete ASCOM-Compliant scripting interface, so you can quickly and easily integrate it with your own programs or scripts. Quickly see where the telescope is pointed green square. Click on a calibration star to automatically point the telescope. The image at left shows the measured residual pointing errors for an inexpensive GOTO mount. Despite large pointing errors across the sky, after MaxPoint correction the RMS error is less than one arc-minute.
Please note that all software sales are final. No refunds are given on software products. A free demo period with full technical support is available to determine suitability of the software prior to sale. Also, any application that connects to one of APCC's virtual ports will get the benefit of the pointing model. To perform a quick polar alignment, you can perform a small point model and apply the offsets shown when hovering over one of the two polar alignment terms.
Mach 1. Mach 2. Azimuth Knob divisions. Altitude Knob divisions. Because of flexure, polar misalignment, refraction, and other effects, the apparent tracking rate of stars and deep sky objects in the sky is not exactly equal to the sidereal rate. The reason is that the magnitude of these pointing errors change slightly as the position of the telescope changes. This causes the target to drift in the telescope's view over time. Tracking rate correction is very important if you want to:.
The tracking rate model uses the pointing model to calculate the necessary adjustments to the tracking rate to keep a target centered. The adjustments are made to both the Right Ascension and Declination tracking rates once every second.
0コメント