The Orion Constellation
is one of the most prominent and easily identified constellations in the night sky. My goal was to make a close-up photograph of the Orion constellation that can stand out. In order to stand out, you often have to take a different approach from the usual. To do this on purpose, you need to know what the “usual” is. If you are not familiar with exposing for astrophotography, I recommend you do an online search. There are numerous blog articles and tutorials that explain in detail how to expose for the stars. In the following, I have summed up the basics.
Basics of Astrophotography
- use a wide angle lens
- use the 500 rule to work out the longest possible shutter speed
- shoot wide open, i.e. lowest f-number for your lens
- high iso (up to 10000)
- focus well
- use a remote shutter release
- use a sturdy tripod
- don’t forget to use compositional techniques
- BE SAFE
Different Exposure Approach – Focal Length & Shutter Speed
Instead of a wide angle, I used a 50mm prime lens. This allowed me to frame mostly for the Orion constellation, and end up with a close-up shot. To assure that the final photo depicts the stars as sharp “points” (instead of fuzzy and streaky lines), you cannot exceed a specific shutter speed. To estimate the maximum shutter speed, you divide 500 from the focal length of the lens you are using. The reference for this rule is full frame (35mm). In my case, it was: 500/50=10. This means that I can use shutter speeds up to 10s and will get “point-like” stars. If your sensor is not full frame, find out the conversion factor and multiply the focal length with that factor.
Unlike Canon and Nikon D-SLR cameras, Pentax cameras have in-camera image stabilisation (as opposed to in-lens stabilisation). The Pentax approach has many advantages, one of them resulting in the so-called “astro-tracer” function. Basically, in combination with GPS and orientation of the camera, the image sensor in the camera will move in three axes in a manner to counter-act the movement of our planet in relation to the photo being taken. In other words, I can use shutter speeds 2-4 stops longer than the 500 rule. The shutter speed I used was 60 s.
When you view photos on a small screen, image ISO noise is often not apparent. It is a different story when the photo is viewed on a big screen or the large print is observed. I used ISO1600 for this shot to minimise image noise, and to produce a photo which resembles what I could see with the unaided eye. I am not a fan of high ISO astroshots that result in photos which are completely different from what you can observe with your eyes. These photos have, arguably, a “wow” effect. In this case, my goal was to get a close-up of Orion and make this constellation stand out in the photo. Keeping the same exposure and increasing the ISO would have resulted in a brighter image. However, the distinction of the brightness of the Orion constellation in comparison to other, much more distant stars, would have reduced significantly.
In terms of aperture, I could have shot wide open at f1.4. I decided to use f4. This is for two reasons:
- the sweet spot for sharpness is never at the aperture extremes (at f1.4 (wide open), the photo would have been considerably less sharp)
- when the aperture is wide open, objects that emit/reflect light appear soft and disk-like
I was after a very sharp and defined result. I used f4 (8 times less light than f1.4) which at a long shutter speed like 60s results in “star-bursts”. The best way to understand the difference is to take a photo of the sun (ideally around sunrise and sunset times) with a wide open aperture and the typical f16 or higher. Wide open gives a disk-like sun without a sun-burst (rays or “beams” radiating out from a central disk), while f16 and above gives the typical sunbeams. Look at Betelgeuse or Rigel in my Orion photo and note the starbeams. By the way, the amount of rays (or “beams”) is a measure for lens quality. The more blades the diaphragm of the lens has, the more rays you can see.
Noise Reduction & Raw
Whilst sorting out exposure and composition, I turn these in-camera functions off. However, for the final shot I turn them on and set them to their highest setting.
- high iso noise reduction
- long shutter speed noise reduction
When I have these function turned on, the camera takes at least twice as long to make a photo. In this case, it took 60 seconds for the exposure, then about 60 seconds to shoot against dark and finding reference noise level for this exposure. I like to do as much in-camera to optimise a photo and do as little as possible in post-production using a software on a computer to convert the raw image into a jpeg or tiff image. I also recommend to shoot always in raw when making astrophotography.
Here is another take on Orion. This time I purposefully made an out of focus image. I like the result and accentuated the colours and “burned” the shadows. Making a photo like this is technically easier than one where the focus is spot on. So how do you focus for the stars?
- you can focus during daylight for something that is in the horizon, put the camera in manual focus and tape the focus ring (only do this if you really know what you are doing)
- when you shoot a lot with a lens, you know where the ideal focus for “infinity” is
- alternatively, set camera in manual focus
- turn the focus ring to the end, where the “infinity” sign is
- set an exposure of 2s, iso40000 and the aperture you want to use (the idea being that you can view the result quickly)
- make a photo, enlarge on the display and look at the bright stars
- gradually and in tiny increments move the focus ring until you go from unsharp to very sharp and to unsharp again
Now It’s Your Turn
I hope this article will help you to obtain better astro-photos. At the end of the day, you need to know the basics about exposure and focussing correctly, and then you can start shaking things up and do things a bit differently to get different results. Most importantly, the more you get out there, the more you shoot, the better results you will get. Stay safe, know your equipment and surroundings and best wishes, Ben