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Meade Pictor XT-Series CCD Autoguider/Imagers
 Section 16: Imaging Tips
IMPORTANT NOTICE! Never use a telescope or spotting scope to look at the Sun! Observing the Sun, even for the shortest fraction of a second, will cause irreversible damage to your eye as well as physical damage to the telescope or spotting scope itself.
Following are a few tips that may help you take better images. Some of this is subjective, and you will undoubtedly develop your own methods as you gain experience.
  • Bright objects such as M82 require shorter exposure times than fainter objects. However, the sky background (or light pollution, full Moon, etc.)needs to be balanced with the length of exposure.

  • For planetary photography, use higher power. Use a 2x Barlow lens with the Pictor. Exposure times for Jupiter will usually be under 3 seconds. For imaging the Moon, a neutral density or dark blue filter will be needed to reduce the brightness.

  • If you use a large telescope, you may wish to stop down the instrument by placing a cardboard cover, with a small hole off-centered 4-5 inches, over the end of your telescope.

  • Don't be too quick to discard raw images; images that look terrible when raw may clean up nicely.

  • Always keep an imaging log.

  • Take new sets of calibration frames if the temperature changes significantly.(or change the set you are using or the scaling if you are reusing calibration frames).

  • Remember: calibration, consistency, cooling, and patience are the keys to good imaging.

  • CCD chips are very sensitive to red and infrared light. When doing calibrations especially, it is a good idea to use the CCD Vision feature of PictorView XT.

  • You can use a black filter in the color filter wheel (216XT and up)to take a dark frame without being at the telescope to cover it.

A Word on Calibration Frames:

Flat Fields:

Take a set of flat fields in early twilight or on evenly overcast days, using short exposures. Do not wait until night or deep twilight, as stars can spoil the flat field. Plastic supply stores sell opal plastic which diffuses light and is opaque. If you place two thickness of this plastic over the end of the telescope, you can take flat fields during the day. Also, flat fields can be taken at night with the plastic and a boxed in light source. You can re-use the same set of flat fields over and over if you remember to keep the Pictor in the same orientation in the eyepiece holder as it was when you took the flat fields. (You can make small marks on the Pictor and telescope to verify this).

Dark Frames:

Because the camera's temperature can be accurately set and maintained, dark frames can be taken at various temperatures and used over and over. You can save a range of popular temperatures and exposure times until you have all the ones you are likely to use. An easy way to name these files is by exposure time, then temperature, e.g. a one minute exposure at 3 degrees(C) would be saved as 1m3d_drk.xxx, where xxx is any supported file format.

You can also use scaleable dark frames called thermal frames.

If you use thermal frames, you will only need to make one or two, and remember to enter the scaling information in the scaling window when you subtract a dark frame. See the Image Menu section for more information.

Note that some astronomers do take new dark frames and even flat fields with each image. Again, it is largely a matter of personal preference. However, if you wish to reuse dark frames with images of different exposure times, you must turn the dark frame into a thermal frame by subtracting the bias information.

Bias Frames:

A bias frame is a zero time exposure. This calibration frame is generally taken to turn a dark frame into a thermal frame. By subtracting the bias information, you can re-use and scale the thermal frame even if the exposure times of the thermal frame and the image are different.

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