How To: Astrophotography

There are several considerations when deciding to pursue the hobby of astrophotography. Budget should be the first thing you think about. This hobby can be quite expensive if you want the most sophisticated equipment available. But you really don’t need to break the bank when making important choices. The learning curve is steep, although automation is making it much easier to get good results. And why would you spend a lot of money on a hobby that you ultimately don’t like or might give up on. I am not trying to scare you away from astrophotography, quite the opposite. But I want you to make reasonable choices as far as budget goes, while still allowing you to achieve very satisfying results. Once you have a budget in mind, then you need to allocate those funds into the various essential equipment items that you will purchase. The following equipment considerations are general concepts. You can find more specific information in other posts and pages.


Camera Choice

When it comes to photography in general, one of the most important choices is the camera itself. The choices for which camera to purchase are vast. With modern equipment, the options basically come down to whether you want to take color photographs or black and white (or grayscale). With either one, you can choose either a digital camera that is not specific to astrophotography or a digital camera that is designed with astrophotography in mind. There are some very affordable DSLR or mirrorless digital cameras that allow you to take very satisfactory images that are in color. You will often see these cameras called OSC cameras, or one-shot-color cameras. One thing to keep in mind is that digital sensors in general produce noise that can impact the overall quality of the image. Newer sensors, like CCD’s and particularly CMOS sensors, produce less noise and can achieve good results at ambient temperature. But to really minimize the noise, cameras designed specifically for astrophotography have cooling mechanisms that cool down the sensor, which in turn considerably reduces the noise that the electronics create. These cameras also come in two varieties, either monochrome or OSC versions. Just because a camera is monochrome doesn’t mean you are limited to just grayscale images. With the use of color filters, you can combine the images to obtain a color image. If you choose an OSC astrophotography camera you will lose a bit of resolution since the color is achieved internally by red, green or blue filters placed in front of each pixel. The final image is obtained by combining each color pixel to create an overall color image.


Telescope Choice

The next choice is the lens or telescope. With this choice, focal length is one of the most important things to consider. Focal length and field of view are directly related. Shorter focal length translates into a larger field of view. Planets and galaxies are generally very small objects, even when viewed with a telescope. For this reason, if you want to take beautiful images of the planets or galaxies, you will require a longer focal length, since long focal lengths result in smaller field-of-view and thus more magnification. Nebulae can be very small or very large. For the larger objects, a shorter focal length will give you a large enough field of view to encompass the entire object. For very large nebula, mosaic tools will allow several sections of different parts of the object to be stitched together to make one all-encompassing image.


Mount Choice

One often overlooked piece of equipment (or at least given lower priority) is the mount. I would argue that the mount if perhaps the most important choice. Obviously, the earth rotates during the course of the night. Even with exposures as short as 30 seconds, the image will move slightly, resulting in elongated stars. This is why a mount with tracking ability is absolutely essential for taking astrophotos. Even with bright objects such as planets, the high magnification required makes it hard to keep the image in the field of view without a tracking mount, even with very short exposures. Tracking mounts make taking long images possible, but all but the most expensive mounts have minor tracking errors that will require corrections during longer exposers. This leads us to autoguiding, which automates the process of making the small corrections that are necessary while taking longer exposures.


Autoguiding

Autoguiding refers to the automated process of making tiny adjustments to the telescope position to keep the image precisely in the same spot. Even a few pixels deviation can make the stars look elongated, spoiling the image. In general, autoguiding is done with a camera (either the primary camera or a second camera that serves only to monitor stars’ positions) that monitors a guide star or stars. The guide camera is controlled by software that monitors for slight deviations in the object’s position. If any movement of the guide star is detected, the software issues commands to “nudge” the telescope back to its original position. The good news is that one of the most widely used guiding software is freeware. It is called PHD2. Amusingly the PHD stands for “push here dummy”.


Why You Should Take the Plunge

If you are just starting out, these choices seem to be confusing and maybe even intimidating. I am sure that many people will do basic research and just decide that it is just too compIicated or expensive. Some will suffer from “analysis paralysis” and will do nothing. As technology advances, much of the complexities of this hobby can be overcome. When I started in this field, automatic autoguiding was in its infancy and digital cameras were just beginning to supplant film cameras. Over the years I have seen equipment advances that have taken me from hours of frustration with occasional breakthrough “nice” images, to a set-up that requires about 30 minutes (or less) of setup time in the evening. And basically, with the push of a button, I can have my equipment automatically point to an object, center it, auto-focus the camera (a topic to be discussed elsewhere), and take a series of guided images, while I watch TV or a movie or do something else. And when the images are processed the next day, some very satisfying and even amazing images are created, even from my light-polluted back yard. Please come back and visit my site often for more detailed articles and recommendations.

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