Expose Tab

For an introduction to this command please see CCD Focusing Tutorial,  CCD Imaging Tutorial – Basics, and CCD Imaging Tutorial – Advanced.

DSLR users may wish to review DSLR Focusing Tutorial,  DSLR Imaging Tutorial - Basics, and DSLR Imaging Tutorial - Advanced.

The Expose tab is used to control camera exposures. The functions of this dialog are only active if a camera has been activated using the Setup tab.

Exposure Presets

The most commonly-used control on the Expose tab is the Exposure Preset. Selecting a preset loads all of the settings for the Expose tab, including Autosave sequences. You can define your own presets to match your specific imaging needs, and switch rapidly between them. Typical uses for presets include settings for finding stars, finding deep-space objects, focusing, and Autosave sequences.

Exposure Presets are loaded simply by selecting from the drop list. If you change the settings manually, a * appears in front of the name of the preset, to indicate that you have modified the settings. The options for the preset menu are as follows:

Tip: the presets can be saved and loaded using File menu Configuration, so you can have different sets for different equipment configurations.

Note: if you define a preset for one camera model, and then disconnect and switch to another camera model, some of the preset settings may not be applicable. If this happens they will be reset to defaults. In some cases there is no sensible default, and you will not be able to take an exposure until you set the control. Note that this may apply to settings in the Autosave dialog.

Basic Exposure Controls

The most basic exposure control is the exposure time in Seconds. Depending on the camera model and drivers, you may be able to select exposures in the microsecond range, or be limited to tens of milliseconds. Please note that the Video DirectShow driver has special modes where the Seconds field determines the number of fields to sum (Frame Integration mode) or the length of video to record (AVI Capture mode).

Readout Mode allows you to select the readout mode for cameras that support this feature. The contents of the drop list depend on the camera model selected. Common options include Normal and Fast readout modes; typically the Fast mode is speedier but lower quality. In some cases the speed/quality tradeoff may be very useful during focusing. Other options include Color and RAW selectors (for one-shot color capable cameras), and special modes such as video capture, leaving images on a compact flash card, etc. Consult the Camera and Autoguider Setup section, or the manufacturer's instructions, for information on your specific equipment.

Speed is used for Digital SLR cameras, to select the ISO speed. This actually corresponds to a gain setting for the analog amplifier prior to the A/D converter. A typical setting for low-light use is 800; however you should experiment with your camera to determine the optimum setting.

Frame Type determines whether you are taking normal exposures or Light Frames, or a calibration frame such as Bias, Dark, or Flat. Please note that this control is not available if auto-darks are enabled (see Options menu below).

Filter Wheel selects the filter to use, if a filter wheel is configured (a "wheel" may also be a filter slider, LCD tunable filter, etc.). Focus is usually done using a Luminance filter or clear slot. If filters vary in thickness switching filters may change the focus. In this case you may want to set up automatic focus offsets; see Filter Wheel Setup for more information.

Subframe allows you to read out just a portion of the sensor frame. This has two main purposes: to speed up download during focusing, and to isolate a single target (e.g. a star) during focusing. You should note that some camera models, especially DSLR cameras, do not have built-in support for subframes and will not download faster (the subframe is extracted inside the MaxIm DL camera driver). For DSLR cameras use the Readout Mode selector to control download speed (see above).

The Subframe controls have an On check box, which is present to prevent accidental imaging with subframes, which could result in you unexpectedly shooting very tiny images. We strongly recommend that you only enable subframes in Presets that are intended for focusing.

The Mouse check box controls whether dragging the mouse on the image will automatically enter new subframe coordinates. This feature is extremely useful for quickly and easily selecting a focus target. If however you are inspecting the image, e.g. with the Graph Window or Information Window, you may want to turn this option off.

To the right of Mouse check box are two buttons. The first finds the brightest star in the image and automatically creates a subframe around it. The second resets the subframe to full size.

At the bottom of the Subframe box is a text field showing the numerical coordinates of the subframe. If you click on this box it will bring up the manual Subframe entry dialog. Simply enter the desired coordinates and click OK.

The X Binning and Y Binning controls allow you to simultaneously decrease camera resolution and increase sensitivity, by combining adjacent pixels into bigger "super-pixels". This is in many ways equivalent to decreasing the f/ratio of your optics. For some cameras you can independently set the binning on each axis; if not, only the X Binning control will be enabled. For convenience, you can set Y Binning to same, and adjust the binning for both axes with the single X Binning control.

The Camera 1 / Camera 2 selector allows you to choose which camera operates as the main camera, and which operates as the autoguider. When you change this control, the selection on the Guide Tab automatically switches to the opposite setting.

The Expose Tab can be configured to take Single images, Continuous images, or Autosave sequences. Single causes one exposure to be taken every time Start is clicked. Continuous causes exposures to go on indefinitely until Stop is clicked or the exposure selector is changed. Autosave sequences are explained in detail in a following section.

Advanced Settings

The Options menu brings up a pop-up menu with a number of groups. The first group controls auto-calibration.