Astro Photography on a budget

INTRO

First, I am not Astro Photography expert and, in this article, I talk about my own experiences and pass on the little bit of knowledge I have.
People often ask me how I take photos of the night sky. But when I start to explain and tell the equipment I use, people quickly loose interest due to the cost involved.
Photographing the night sky is not difficult and yes, you can even take photos with your mobile phone. But in this article, I focus on the use of digital cameras.
In this article I want to explain that you can do Astro photography with little investment.
But, yes sorry there is a but, I will make a few assumptions from the outset.

  1. You have an interest in photography.

  2. You already have a digital camera that:

    • will need to be held very steady to prevent it wobbling and the image blurring (e.g. using a tripod).

    • can take exposures of at least 15 – 30 seconds to collect more light.

Let’s get started

The ability to take nice photos of the night sky has become a lot easier in the last few years as digital cameras have improved a lot.
They are much more sensitive than film and pick up faint objects very quickly. Photos taken with a digital camera can also be manipulated afterwards, or added together, using image processing software to bring out a lot more detail. The biggest change, I found, was the ISO settings.
These days ISO settings of can easily be set to above 10000. And this is ideal for a bit of night sky photography as it means the shutter times can be a lot shorter.

A higher ISO mean your images will be a bit more grainy, but it is a great and easy start. ISO is a legacy term from the days of photographic film and refers to the sensitivity to light.
Also a higher ISO means more sensitive to light.
This increase of sensitivity is achieved by increasing the grains of light sensitive material on the film. The downside is that your photos will look grainier.

For digital photography, ISO refers to the sensitivity—the signal gain—of the camera's sensor. As you increase the ISO on your digital camera, you increase the gain of the sensor. This is great as it increases the light sensitivity, but the downside is that you introduce more noise. You can associate the increase in noise with the bigger grains of photo sensitive material on film.

The bigger problem with long exposure photography of the night sky and that is the small issue of our planet earth rotating. The rotation can cause stars not being stars but streaks when taking long exposure photos. The longer the camera shutter is left open, the longer the streaks will appear. Easiest solution would be to stop the earth from rotating while we take photos, but I have not yet found a phone app that does this,

What options do we have to prevent these star trails/streaks?

I will try to answer this using the next few chapters as there are different solutions based on your equipment. But the assumption will be that you use a tripod and a remote shutter. The remote shutter is important as it allows you take photos without touching the camera and therefor cause any vibrations on the camera.

Do nothing and leave the streaks

This is an option and can give some really great results. What you do is setup your camera on your tripod and point the camera to the Pole Star (see below in the Guiding Tripod/Mount chapter on how to find the Pole Star (Polaris). Then take many long exposure, wide field photos (exposure time of 30-60 seconds).

Make sure you take many. Then you can use a piece of software named StarTrails (https://www.startrails.de) to combine all the photos in to one photo with the result looking something like this ->







Rule of 500

If you do not want star trails, this is the easiest solution. You can do this by dividing 500 by the focal length of the lens of your camera. This will give you the maximum number of seconds for your exposure before you start to see star trails. 

500/(lens focal length) = max seconds of exposure.

e.g. 57mm focal length will give you a max exposure of approx. 8sec. And 300mm focal length will only give you a maximum 2 sec. exposure.

Using this solution, means the higher your ISO the more you will see in the image.

Guiding Tripod/Mount

A camera on a tripod will allow you to take photos without you shaking the camera. This is especially important when you take longer exposure photos.

If you then want to go beyond the rule of 500 and want to take photos with exposures of 30 sec and beyond you will need something added to your tripod. You will need to invest in a simple mount which you can fit on your tripod. An example of such a mount is the popular SkyWatcher Star Adventurer (http://skywatcher.com/product/star-adventurer).
This is a portable Equatorial Mount, which when setup properly, counters the rotation of our little planet and means you can take longer exposures (at any focal length). The challenge with these mounts is that you need to align it with the Pole Star (Polaris) and this might be a challenge if you are not that familiar with the night sky. The easiest way to find Polaris is using the big dipper (ursa major) as per the picture on the right.

Then use the manual that comes with the mount to complete the setup.

For Faringdon, Oxfordshire the latitude of Polaris is 51°39'23.18"N


Focussing

Yes, we do need to discuss focusing as this can be a challenge when you are taking photos at night and the autofocusing does not work. Focusing might require preparation during the day if autofocusing at night does not work on your camera.

To do this is all depended on your camera. I will explain here how I did it with my Canon DSLR.

During the day I would connect the lens(es), I was planning to use at night for my photography and set the camera to autofocus. I would let the camera with lens focus on a distant object. When focused, switch the camera to manual focus and if you use a lens with anti-vibration, also switch this off. Then use a bit of Sellotape or any other tape to fix the focusing on the lens.

Why switching off the anti-vibration on the lens you ask. If anti-vibration is left switched on the lens, it can cause slight wobbles with your camera securely mounted on the tripod.

When done, make sure you do not change the focusing on the lens and leave your camera in manual focus. Very important to leave you camera and lens in MANUAL focus as you do not want your camera to try to autofocus during the night.

What is next

Now that you have yourself all setup and you are ready to take some photos. Take lots of the very same images, one after the other.
These can be added together (stacked) during image processing.

Many photos mean many photons (light particles) and means more details of what ever you are imaging (photographing).

Processing the Photos taken

Now that you have finished and are back home with a nice warm drink, what is next. You have these many photos of the object you where photographing but how do you process all your photos.

Your next step is to combine all the data (photos) you have into a single image.

The combining of the photos is called stacking. You stack all the photos on top of each other which will provide more details and your final photo. To do this you will need the help of some software.

Some of the software for this is free and for others you pay.

If you are already a keen photographer, you might have Adobe Photoshop (one of the newer versions) and comes with the ability to stack photos.

But if you do not have Photoshop, I do not suggest you purchase it as it is not cheap as it will be a monthly subscription. But there are 2 alternatives I would suggest:

1. Affinity Photo - https://affinity.serif.com/en-gb/photo/ (approx. £47.99 at time of writing)

2. Deep Sky Stacker - http://deepskystacker.free.fr/english/index.html - Free

Regardless of the processing software you use, you will need to know what to do. Personally I am not familiar with any of these 3 as I use a fairly expensive piece of software named PixInsight. But I would suggest to have a look around YouTube as people will have created video tutorials on how to process data (e.g. stacking) or you can buy yourself a little book to assist you with process.

If you want to buy a book, I will strongly recommend the material of a good friend of mine Dave Eagle. Yes, I know, this is a plug for his material. But it is very good, easy to follow and not expensive. You can find his books here: https://www.star-gazing.co.uk/WebPage/shop/

After you have stacked all your photos into a single photo, you can start to process your photo. This is like what you do with your normal photography, increase saturation, sharpen, contrast etc.

This is where you let your artistic interpretation loose on your photo. Yes, most of the amazing deep sky photos you see are not the real colours.

Many photos you find on the web (even mine), like the ones from the Hubble telescope are all processed and are heavily depended on the artistic interpretation of the person who processed (developed) the photo.