Inter-image guiding

This new feature is designed for modern mounts, which are precise enough to keep tracking with sub-pixel precision through the single exposure, and irregularities only appear on the multiple-exposure time-span. Such irregularities are caused by many sources (polar misalignment, differences in refraction calculations, mount and telescope mechanical deformation etc.) and cannot be completely avoided. Inter-image guiding then performs slight mount position fixes between individual exposures of the main camera, which eliminates “traveling” of the observed objects through the detector area during observing session.

Because this guiding method uses main imaging camera, it does not use another guiding camera and naturally does not need neither OAG nor separate guiding telescope to feed the light into it. This also brings another consequences:

• The Guide using: Guiding camera/Telescope option is missing from inter-image guiding setup, as the inter-image guiding always use Telescope PulseGuide interface. If the particular telescope driver is not equipped with such interface, inter-image guiding cannot be used. Especially older mounts often rely on the “Autoguider port” only and thus require the opposite port, typically offered by the guider camera. But such mounts are often not capable to keep tracking for any reasonable long exposure without regular guiding, so this limitation is not that important.

• The Position detection: Brightest star/Plate solution is also missing as the guiding method is always Plate solution. This means stars are searched within the whole image and matched with the stars on the reference frame (reference frame is the first frame taken after the inter-image guiding is turned on). This method results into more reliable guiding compared to brightest star method, as the mutual offset between frames is calculated as an average of offsets of all detected and matched stars. Brightest star method also requires frame cropping around the chosen star, which is naturally not possible in the case of the main camera.

  Hint:

  It is necessary to detect at last 3 stars within the image to be able to use Plate match. If less stars can be detected, this method of guiding cannot be used.

  Remark:

  Searching for stars is crucial for proper function of the inter-image guiding. One algorithm as well as one set of parameters for star searching is used within all SIPS tools (there is a second set of star search parameters, intended for guiding camera, but this is not relevant in this case). It is recommended to use the Astrometry tool to check whether stars within the image can be properly detected and possibly to modify star searching parameters. This procedure as well as the searching parameters are thoroughly described in the SIPS User's Guide.

Inter-image guiding parameters are in the Guiding tab of the Imager Camera tool.

Similarly to regular guiding, also the inter-image guiding requires calibration. The only difference is the inter-image guiding calibration does not use predefined exposure time and read mode, but offers entering of exposure time for calibration only, as the normal imaging camera exposure time could be hundreds of seconds and the calibration would take very long time.

Also alarms for missing stars in the image and too long calibration pulse are present.

New features

Many smaller-scale enhancements and updates were added into SIPS v2.4.3.

Image zooming

Images could be easily zoomed simply using mouse wheel within SIPS. The “zoom slider” GUI tool for image zoom, also used for presetting of the zoom value when new image was opened or downloaded from the camera, was located in the Image Transform tool. This was not very intuitive, as the Image Transform tool offers operations, which alters the image bitmap itself and image zoom affects only how images are displayed. Also it was pretty difficult to find this zoom slider for new users, as the number of available tool windows is pretty high in SIPS.

This is why the new version of SIPS removed the zoom slider from the Image Transform tool and placed it directly into the tool bar. It is always visible and the zoom slider position also reflects mouse wheel rotation over any image.

Image pick-list

SIPS allows reusing of already opend/processed images beside opening new images from files on disk. The Image Pick List dialog box was extended with the ability to select and un-select all images as well as to select images based on the filter used.

Guider calibration

The Guiding Camera tool window parameters defining calibration pulse lengths are necessary only upon guider calibration. So these two parameters were moved to a modal dialog box, opened prior to calibration sequence. This somewhat reduced the complexity (and size) of the Guider Camera tool window itself.

FITS header updates

New SIPS version slightly modified the used FITS headers to comply with the latest FITS standards.

The DATE-OBS and TIME-OBS headers, each containing the date “yyyy-mm-dd” and time “hh:mm:ss” strings, representing the beginning of the exposure, were replaced with single DATE-OBS header containing both date and time in the form of “yyyy-mm-ddThh:mm:ss.sss” string. The TIME-OBS header was removed.

New FITS header JD was introduced instead of the removed TIME-OBS header. The JD contains the same time like DATE-OBS or DATE-BEG, but expressed as single double-precision floating point number expressing the Julian date of the exposure begin.

Photometry tool

While the Photometry tool is still marked “beta”, as it still does not contain astrometry based photometry, it was fixed to be usable for regular photometry measurements and light curve plotting/storing based on mutual match of images of the single observing night and manual marking of variable, comparison and possibly check stars.

Bug fixes

The new version fixed the problem with naming of files saved from the Series tab of the Imager Camera tool window. Because the Series tab defines only some exposure parameters (exposure time, filter and binning), other parameters are used as defined in the Exposure tab for individual exposure types. And while the Series tab allows taking of various exposure types (light, dark, ...), the parameters defined in the Exposure tab were not used according to exposure type defined in the series table, but according to exposure type currently selected in the Exposure tab.

Some updates were introduced into 64-bit version to fix possible structure and class sizes with respect to default packing in the 64-bit execution mode. This should increase the 64-bit SIPS version stability.

SIPS is a freeware and can be downloaded from the Download section of this web site.