How to Photograph the Orion Nebula
This image was created with 24 individual exposures of 30 seconds each. I have a remote shutter release button that I plug into my camera, and it can simulate me holding the camera button down. I set my camera to take 30 second exposures at ISO 400, removed the lens, and then bolted the camera body to the back of an 8" Schmidt-Cassegrain telescope.
When you take long exposures of space through a telescope like this, the rotation of Earth about its axis will create star trails and blurred images. That's where the mount comes in! I have a Celestron CG-5 equatorial mount that I align to our planet's axis of rotation. Once it's set up, tiny motors in it make it rotate with the sky, eliminating the possibility of trailing stars. The alignment process takes me about a half hour because once once it's all fully aligned, you have to make slight adjustments and start over a few times. If people are interested in seeing how all of this is done, I might put up a video sometime in the near future showing how it's all done.
So here's a simple step by step for how to make your own image!
My materials (this is all mid-upper range stuff for an amateur I'd say):
Digital single lens reflex (DSLR) camera. I use a Nikon D5300. - $597
T-adapter. This goes onto the back of the telescope, one size shild fit all Schmidt-Cassegrain telescopes. - $24
T-ring for Nikon. This is what mates your camera to the t-adapter. Specific to camera manufacturer. - $10
Power supply. This powers the mount so it can track the rotation of Earth. - $57
Total price: $2288. You could definitely get by with a smaller telescope and a cheaper mount. You also don't need a $600 digital camera. Save your money and this is definitely an achievable purchase!
Throw everything into the back of your car.
Go to this page to find the darkest area you can find. Light pollution from cities and even the moon will make a HUGE difference when you're taking long exposures of space.
Go to this page to see if the sky will be clear. It's surprisingly accurate. Just plug in your own address or coordinates. The coordinates that I linked are from where I took my pictures last weekend.
Drive to your dark sky site!
Set up tripod, attach mount facing as close to north as you can. Secure everything tightly, and then bolt down the optical tube assembly on top.
Balance the OTA on your mount by loosening the mount locks and moving the scope to the side. Adjust the mount's counterweight and the position of the scope in the mount slide. If you want, you can attach the camera now to account for its weight.
Attach mount to power supply. If it's going to be cold, I suggest leaving the power supply in your car and running the cord out the door jam. Batteries don't like cold temperatures.
Turn on mount, enter your time and location, begin alignment process! I use an app on my phone called Stellarium [iOS] [Android] to help me with the alignment. The mount will spit out a star name, and it will slew to where it thinks it should be. Use the direction buttons to fine tune it. If you can't see it and you're not used to the finder scope, try de-focusing the telescope. A big ring of light will show you where any nearby bright sources of light are.
After you have done the 2-star align and have added 2-3 calibration stars, go into the alignment settings and do a polar align. Follow the instructions, and it will tell you to adjust the mount itself (NOT the direction buttons). This fixes for human error when initially setting up the mount.
Now that you've aligned your telescope, turn off the power and do it again! Now that you've aligned the telescope's axis of rotation with that of planet Earth, performing another 2-star align (with calibration stars!) will make things better. If I know I'll be doing longer exposures, I cycle power and re-align my 'scope twice. It used to take me 45 minutes or so, but I've gotten it down to about 20 minutes for a good telescope alignment.
Next, tell the mount to point at something interesting! In my case with this image, I was killing time taking pictures of the Andromeda Galaxy and the northern lights until the constellation of Orion rose.
Once you have your subject in the scope, you probably won't see anything too interesting. Most bright images of nebulae will only look like a faint smudge. When shooting a dark nebula like the Horsehead Nebula, you won't see anything at all.
Attach your T-adapter, your T-ring, and then your camera to the back of your telescope. I use a corded remote to do my exposures because I can set my camera to "bulb" (exposures for as long as you're holding the shutter release). The remote has a lock that holds the shutter button down.
If you used an eyepiece to align your scope, now you'll need to readjust your focus. Go to live view mode on your camera, and set the ISO to as high as it gets. Adjust the telescope's focus until stars are super sharp. If you'd like, you can invest in a cheap filter to throw on the objective end of the 'scope called a Bhatinov mask that will create light artifacts that will show you how focused you are.
Start exposing! Have your camera set to manual mode (important, you don't want your flash going off!). Since the camera isn't connected to a lens, it has no control over focus or aperture. You've got image sensor sensitivity and exposure time. For Orion I shoot 30 second exposures. I lock down the shutter release with my corded remote so that it can take 30 second exposures immediately one after another. Take anywhere from 20-100 images. My image is 24 30 second exposures, for a total of 12 minutes of exposure time. Nothing special.
Throw all of your images into a software like Deep Sky Stacker (Free) and watch it do its magic. It will use image processing algorithms to combine all of your images into one higher quality photo! You can also add dark frames (literally exposures with the lens cap on) to cancel out image sensor grain (noise).
Really, anyone can do this. I'm just a normal dude with a fun hobby!