My Equipment
I live in a highly urban area with a Bortle value of around 8 or 9. I finally ditched the mostly reliable Meade LX 200 classic that I have had since 1996. It was a real workhorse in its time, but as equipment technology advanced, it became harder and harder to integrate into the latest gear setup. Not only that, but the gear mechanism for tracking was starting to develop a large tracking error that was becoming harder and harder to compensate for with autoguiding software. Parts are no longer readily available. Since the LX 200 was both a telescope and mount, I had to replace both.
The Telescope and Guide Scope
Since my primary interest was astrophotography, I had to limit my choices to telescopes that have larger flat fields. All telescopes can reach focus obviously, but most have curved lenses or mirrors that reach focus in only a small central area. With larger image sensors, this will result in star shapes looking out of focus (also called coma) in the periphery. Some telescopes can compensate with corrective lenses resulting in a larger area of focus, also called flat field. These telescopes are called astrographs and are often quite expensive. I also wanted a telescope with a mid range focal length. The larger the focal length, the smaller the field-of-view, and vice versa. I wanted to be able to image some larger nebula, so I didn’t want too short a focal length. I settled on a William Optics Fluorostar 120. This telescope has a focal length of 780 mm. The downside is it won’t be ideal for imaging small galaxies without magnification (this can be accomplished with a Barlow lens). I did have to purchase a separate field flattener, the PFLAT 68III. This would result in a flat field of 43 mm, which corresponds to the size of a full field camera sensor.
I opted to use a separate guide scope since it is a bit easier to set up than an off-axis guider. It is arguable that using off-axis guiding may be a bit more precise, but today’s guide scopes and mounting hardware eliminate many of the disadvantages of using a separate guide scope. I chose one of the most popular guide scopes, the M-G50III also from William Optics.
The Guide Camera
I am using the ZWO ASI174mm Mini Monochrome camera.This nifty little camera has a 2.3 megapixel CMOS sensor with 5.86-micron pixels measuring 11.3mm x 7.1mm, resulting in a a 1936×1216 resolution. It is an outstanding guide camera with a monochrome sensor, so without filters it cannot do color imaging, but for guiding you don’t need color. And the sensor is sensitive enough to detect multiple guide stars in the field of view when paired with a relatively short focal length. It can even serve as a planetary imaging camera with a longer focal length telescope. You simply cannot go wrong with this camera.
The Mount
There are many options when deciding on a quality mount. The most important factor for me was a mount made by a reputable company that was easy to set up and could track the sky with good precision. It also needed to be able to respond to precise correction commands from the guiding software. The price range for quality mounts can range from $1,000 up to $10,000 or more. The higher end mounts have additional technology that allows for near perfect tracking without corrections. I chose something in the middle of the price range, the iOptron CEM 70. This mount comes with an aid to polar alignment, which is essential to maximize the tracking accuracy of the mount.
The Camera
Choosing a camera can be difficult with the many options available. The choices basically come down to whether you want to do color imaging or grayscale imaging. Color imaging can be done with dedicated astrophotography cameras or digital color cameras that are modified for astrophotography. Dedicated astrophotography cameras can be monochrome or color. The monochrome cameras can be used for color imaging, but they require a number of color filters to merge into a color image. This technique can result in very high quality images, but requires exposures with each filter, resulting in much longer time to take each filtered image and assemble them into a color image with software. The advantage of dedicated astrophotography cameras, either color or monochrome, is that they can cool the sensor, resulting in much lower “noise” generated by the electronics.
Color cameras, whether they be dedicated astrophotography cameras or modified digital cameras, simplify the process of obtaining color images. But they suffer from overall lower effective resolution, since each pixel is covered with a tiny red, green or blue filter in the from of a matrix. Each quadrant of pixels is combined by the camera to create a color pixel.
I settled on a modified digital camera made by Canon specifically for astrophotography, The.model is the EOS Ra, which has a 30.3 megapixel sensor with a resolution of 6720 x 4480 pixels and a full frame size of 36mm x 24mm (43mm diagonal).
The Software
I use:
- PHD2 for autoguiding (free Windows or Mac)
- Nighttime Imaging ‘N’ Astronomy (N.I.N.A.) for image planning and acquisition (free Windows only)
- Pixinsight for image processing (paid Windows, Mac, Linux)
Light Pollution Filter
In my location, light pollutions is a real problem. Most dimmer deep sky objects are washed out by the wavelengths of the typical street light. There are a number of really effective options that are very good at filtering out light pollution. The way these filters work is by only allowing certain light wavelengths to pass through the filter. Depending on the filter, the wavelengths that are allowed to pass correspond to typical colors produced by astronomical objects. Artificial light source wavelengths are not allowed to pass, effectively filtering them out. Longer exposures are usually required to collect enough light, but the resulting image will show more detail. Currently I am using the Optolong L-eNhance filter for this purpose.
Focuser
A very important component of an automated setup is a mechanical focuser that can respond to commands from software to achieve a perfect focus. I use N.I.N.A. software to control my ZWO EAF focuser. There are several electric focusers to choose from, but the ZWO focuser was well matched to my equipment. What is even more impressive is that N.I.N.A. can even be programmed to refocus depending on certain parameters. This is important since focus changes during the course of the night with dropping temperatures.
Conclusion
This setup requires a pretty sizable investment, but there are many examples of equipment that can achieve really good results for less. The point is that with the right equipment and software combination, an evening of imaging can be mostly automated. I typically will chose an object based on the time of year. And then I will use N.I.N.A. to frame the object artistically, move the telescope to center the object perfectly, and then take a series of dozens or hundreds of images, along with calibration images. Amazingly this can be done with only a little input at my laptop. I can then go inside to watch TV or do something else. Periodically, I will check the progress to make sure nothing has gone wrong (and there is a lot that can go wrong). After all, technology is not perfect.