Setting-up And Using a SAC Camera

 By Mark Estes, Digitec Optical

Introduction

The SAC imaging camera represents the easiest way to break into astrophotography. The cameras are easy to use but its more advanced capabilities will provide you with years of enjoyment. This article is not meant to replace the instructions that come with the camera but instead to give you an overview of the basic setup, testing and operation of the camera. This article covers the operations of all the SAC cameras including the SACIV, SAC7, SAC7b, and for the most part, the new SAC8. The SAC8 is a highly sensitive monochrome CCD camera and it's operation differs slightly. Refer to the SAC8 instructions for the differences but mainly the shutter control is adjusted on the screen in milliseconds, and the gain by a knob on the control box.

The SAC excels in high resolution imaging due to it's small pixel size. Its capability to record AVI movies will give you a high number of short exposure images in a very short period of time. This is a great benefit as it considerably reduces the demands on your mount and seeing conditions. A typical ten second AVI movie may contain over 150 images. You can easily weed out the bad frames using software described later in this article.

The AstroVideo program that comes with the camera is the only software needed to operate it. It comes with a 30 day free trial and must be registered. The registration is free, quick and easy. Instructions for registration can be found through the message box provided when you start AstroVideo, or by pulling down the HELP menu. A different registration code must be obtained for each computer that AstroVideo is loaded on.

Before jumping in, it is advisable to do some basic operational tests to check out your system and get you familiar with it's operation before getting under the stars with it.

Initial Camera Operational Test

The initial test should take place at your computer to see if it is operating properly. You can do this at your  desk without a telescope.

• First load the software as per the instructions included on the CD. This is important; DO NOT PLUG THE CAMERA INTO YOUR COMPUTER UNTIL AFTER THE DRIVERS ARE LOADED FROM THE CD. Doing so will cause Windows to load its own driver and the camera may not work properly.
• With the drivers and the AstroVideo program loaded, power down your machine, plug the camera into the USB port on your computer. For this test, the parallel cable need not be connected as it is used for long exposure shutter control.
• If you are using a SAC7b, plug the cigarette lighter adapter into a power supply of 12VDC capable of 3.5 amps.
• Start your computer. If you are using the XP operating system, you may see some warning messages just after your operating system loads. Disregard these messages.
• Start the AstroVideo program.
• Pull down the DRIVERS menu and select MICROSOFT WDM IMAGE.
• After a moment a viewing pane will open up on the lower left side of the screen. This is where the live video will take place. It is called the Input Window. It may be dark but that's okay.

• Pull down the VIDEO menu and select VIDEO SOURCE. A window will appear showing your camera controls. Your screen may differ slightly depending on the driver and version used.
• Grab the blue title bar of this window and drag the window to the right side of the screen so that you can see the Input Window.
• If the AUTO EXPOSURE checkbox is checked, uncheck it.
• Grab the GAIN SLIDER and move it to about half.
• Grab the SHUTTER SPEED slider and move it all the way to the right.

• Uncap the camera and point it near a light source. The preview pane should go white.
• Place your hand over the open end of the camera to block light from entering it. The preview pane should go black.
• If everything has worked up until now your camera is operating normally.

Getting Familiar with Camera and Software 

By far, the best way to get familiar with your camera is to test it outside during the daytime, or with your telescope pointing out the window. It is much easier to get familiar with the camera and software in this fashion instead of doing it in the dark. You can also interface the camera to a microscope if you have one. Basic digital microscopy is fun and is another area that many astrophotographers never consider.

Make sure that any sidereal or other tracking motors are turned off during this experiment.

• Start by placing a low power eyepiece into your telescope and lining up on a distant object. Focus it and place the object dead center in the field of view.
• Switch to a higher power eyepiece. A 6-9mm would be appropriate.
• Again focus the target and place it exactly in the center of the field of view.
• Remove the eyepiece and replace it with the camera.
• Start the AstroVideo program
• As before, load the driver and open the VIDEO SOURCE screen.
• Grab the blue title bar of this window and drag the window to the right side of the screen so that you can see the Input Window.
• If the AUTO EXPOSURE checkbox is checked, uncheck it.
• Grab the GAIN SLIDER and move it up to about 1/3^rd its travel
• Grab the SHUTTER SPEED slider and move it to the right until you can see some light in the preview pane. If you cant see any light, slide the gain and shutter controls all the way to the right.
• Your target will be out of focus because the camera will not reach focus at the same point as your eyepiece. On most telescopes you will need to run the focuser in. On SCTs and MAKs, usually you have to turn the focus control clockwise. Sometimes (especially in the dark) even though you may be on target, if your telescope is far enough out of focus you will not see any light in the preview pane.
• Adjust the focus. As you start to reach focus the object will appear in the preview pane. As you get closer to focus the object will get brighter and sometimes saturate the camera.  If, and once this happens, slide your gain control down to about 1/3^rd to ½ its travel. Continue to adjust your focus and shutter speed control until you see the object focused in the preview pane at the appropriate brightness.
• There are some camera/telescope combinations that may have trouble reaching focus. If you can’t reach focus, refer to the FOCUSING PROBLEMS section later in this article.
• Close the VIDEO SOURCE window.

You may now capture some images if you like. To capture an image, press the capture button located on the toolbar. The camera will pause for a moment and then your image will appear on the right viewing pane. If you have AUTO SAVE selected in the SETUP SCREEN then your image will be automatically saved to the specified directory. If not, you may pull down the FILE MENU and save your picture there.
After capturing an image you must click the preview button to resume live video.

If you have COLOR IMAGES selected in the SETUP SCREEN, three files will be saved to disk. The will be one for red, another for green and another for blue. These images can be later combined into a full color image during processing. If you have COLOR IMAGES unselected, only one file will be saved. All files (automatically) saved will be in 32 bit FITS format. FITS is the standard for all astro-imaging applications. If you save the image using the FILE MENU, then you may save it in BMP or JPG format.

Your First Nighttime Shoot

When you go outside at night with the camera for the first time, follow the same instructions that you used for the daytime test. The only difference is that while you have your high power (6-10mm) eyepiece in, use that opportunity to assess your telescope's tracking. If the target constantly drifts from your field of view you will have a difficult time using the camera. Make sure that you are polar aligned properly and that your tracking motor is engaged.

Start with a bright target, a planet or the moon. I usually recommend the moon as it is a bright target, easy to find and you can get some stunning lunar pictures even with your first attempt. Shoot along the terminator between day and night on the moon. The light will be at an acceptable level there and targets are easy to focus. Use a moon filter if necessary on the front of the camera. You will get most of your best images shooting along the terminator.

Once you have successfully taken your first lunar pictures, try placing a 2x barlow in front of the camera (if viewing conditions permit) and refocusing.. This will double your f ratio (and magnification). You usually wont need to use any type of light reduction filter but targets may look a little out of focus and are more difficult to center. You may wish to lower the speed of your mounts panning controls so the target wont speed off the screen at the touch of the button. On the up side, using a barlow will widen the “critical focus” area.

Once you have your first shoot under your belt, you may wish to use some of the advanced features of the camera, long exposure and movie captures. Consult the manual for this as it is beyond the scope of this article.

Plato and The Apline Pass

The Appenines

The Straight Wall

Focusing Problems

Focusing problems are normal and can happen with any camera. For the SAC, this can sometimes happen with a Newtonian telescope/ SAC7b combination. In these cases the focuser will be racked in completely and still not achieve focus. If this happens to you, do whatever is necessary to get the camera closer to the telescope. On some focusers, the actual eyepiece barrel can be unscrewed from the focuser revealing a 42mm T thread that will screw directly into the front of the SAC if you remove it's nosepiece. The Konus 1793 8in reflector has such a setup. If you are really stuck on this issue, contact Bill at SAC Imaging and he will modify your camera by elevating the CCD chip slightly. service@sac-imaging.com  In the meantime, you can use a barlow or eyepiece projection setup to achieve focus. Sometimes even the use of a color filter screwed into the nosepiece may do the trick.

If you have trouble reaching focus with a refractor, follow these instructions.

• If your focuser is racked all the way in and still cant achieve focus, remove the 90 deg. diagonal (if you are using one) and insert the camera directly into the telescope.
• If your focuser is racked all the way out and still cant achieve focus, try using a 90 deg. Diagonal between the camera and telescope.

Sometime you may have difficulty if you space the camera too far from the telescope using diagonals, prisms, off axis guiders, flip mirrors and the like. I've noticed this on refractors and some Maksutov telescopes. Try not to use diagonal mirrors if possible.

I haven’t run into a situation yet where an SCT would not achieve focus in any configuration.

Equipment Configuration, Image Processing and Information Resources

Telescope Mount
Almost any type of telescope mount can be used if you image the brighter targets, however the proper operation of your telescope mount is critical to your success. Try to adjust as much backlash as possible out of the gear train. When you setup, level the mount and get a good polar alignment. If you don't, you will be spending all of your time on the panning buttons chasing declination drift when you should be focused on the software and capturing images. This is especially important if you are running the camera at higher powers.
For long exposure astrophotography you should use a good Equatorial mount, possibly with autoguiding. An Equatorial mount, or a fork mount on a wedge is best as it will also reduce the field rotation to nearly nothing.

Optics
Clean all of your optics before any imaging session, especially optical surfaces that are close to the camera like barlows, filters, focal reducers and diagonals. Even a small speck of dust will create huge "dust motes" in your images that are very difficult to remove (if at all) in processing. Use an air bulb and a fine optical brush. I have a special set of filters, barlows, etc that I use ONLY for imaging. They only make it outside if I am imaging and I keep them in pristine condition. Nothing is more irritating to me than having dust moted images.

Image Processing
Image processing is an art form in itself. Research this deeply. The two most important points are dark frame subtraction (image calibration) and image stacking. These are common and simple techniques used to reduce noise and enhance the quality of your images.

There is plenty of free information on the Internet as well as many good books that you can purchase. The best book that I have found is Ron Wodaski’s “The New CCD Astronomy”. Although not focused specifically on the SAC cameras, it covers the entire spectrum of equipment, software and image processing techniques. Even after years in this hobby I still use it, although the pages are falling out of it.

When you are ready to move up to a really nice image processing program, there are a few good titles out there. AstroArt, MaximDL and Adobe Photoshop are my weapons of choice. In my opinion, AstroArt is the most cost effective and contains many advanced processing and filtering features. There are also many free plug-ins available to allow AstroArt to control a variety of CCD cameras.

Registax is another good program, and is a free download on the Internet. The combination of the small pixel size of the SAC camera with a decent size telescope can make extremely high resolution planetary and Lunar images possible. If you shoot AVI movies with your SAC, Registax will split the movie into its individual frames, allow you to uncheck all the bad ones, and with the press of a button will automatically align, stack and process the movie into a single BMP file. There is no easier way to process planetary and lunar images than this. AstroVideo also has this capability but to a lesser degree.

Before I close I want to send a special THANK YOU to Bill Snyder and the team at SAC Imaging for providing us with this fine camera.

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