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Image capture

 

I use SharpCap for lunar imaging. SharpCap works well with the ASI120MM, the camera I currently use.

 

Below is a description of the capture process I follow.

The Sharpcap interface

 

Sharpcap has a very simple interface. Once the imaging camera is plugged in and SharpCap is running, this is the opening screen. I have highlighted in red rectangles the main functions.

 

  1. "file" (1), allows  to create a folder in which future AVIs may be save. If no folder is created, SharpCap saves AVIs on the desktop, which can become crowded very quickly, if dozens of AVIs are shot during the imaging session.

  2. "cameras" (2) allows to select the camera you wish to use.

  3. "reticule" (3) provides a very visible red reticule. very useful for centering objects.

  4. The appropriate codec is selected via the "compression" button. MONO8 is the codec used with the ASI120MM.

  5. The camera's framerate can be adjusted with the "framerate" function. I always set it to 'maximum', as advised by ZWO, the manufacturer of the ASI120.

  6. A range of resolutions are available through the "resolution" button. The ASI120MM's full resolution is 1280x960. This resolution may slow down some computers during capture. If it does, change the resolution to the next one down (1280x720). I have noticed that I never reach the optimal framerate as advertised by ZWO. It has to do with how powerfull my computer is as well as my camera-computer connection (USB 2.0).

  7. The "exposure" slider allows you to adjust the exposure, that is to say the quantity of light reaching the camera chip. Exposure adjustment depends on several factors such as the brightness of the zone to be imaged and the "gain" setting. Consequently, the exposure often need to be adjusted.

  8. "Gain on a CCD camera represents the conversion factor from electrons (e-) into digital counts, or Analog-Digital Units (ADUs)'*. The "gain" function allows to vary light sensitivity. The more gain, the more sensitivity, but the more noisy (or grainy) the AVI will be. "gain" and "exposure" may be ajusted in relation to each other. Don't hesitate to increase the gain when capturing large numbers of frames, as a large stack will compensate for high levels of gain. I often have gain set up at 30+ when I capture 1500 frames or more.

  9. "Gamma" is set at 50 as recommended by ZWO. "Brightness" (which isn't highlighted in the ohoto)  is set at 10.

 

* Source: http://www.qsimaging.com/blog/understanding-gain-on-a-ccd-camera/

Once you have selected the area to image and have adjusted the exposure, gain and gamma, you are ready to capture.

 

  1. The Start capure function brings up the caputure window.

  2. This window allows you to either set a number of frames to capture (e.g. 30000) or set a time limit (e.g. 120 seconds).

  3. Click Start to begin the capture.

  1. A progress bar in the bottom right end corner of the screen tells you how many frames have been capture during the operation. Once the capture is over, a new window pops up to tell you that the capture is complete (your computer may also produce a "ding" sound).

 

At the end of the session, your AVIs have been save in the designated folder on your computer. You may close SharpCap and move to the next step: "stacking".

 

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