Astrophotography with a smartphone camera? | Huawei P20 Pro versus Canon 70D

 

Can it be done? Chris Grimmer pits a high-end smartphone against a DSLR to find out which is best for astrophotography

 

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Chris Grimmer

Can you guess which is which? All images by Chris Grimmer

What is the Answer?

On the left is the Canon 70D and on the right, the latest smartphone camera. This is the same for the ones below.


I was recently asked a question in an interview with Wex: “Have smartphones turned everyone into a photographer?”

My answer was yes, and camera capability was a major consideration when I purchased my current phone. The question did get me thinking however – how might a smartphone hold up for astrophotography?

Modern smartphones come equipped with high-end cameras, all jumping on the megapixel bandwagon to try and outdo the competition. Most manufacturers have also caught on that some of us like to shoot in Manual mode, and will also offer the ability to save in Raw file format. This gives us astrophotographers a fighting chance – being able to set ISO and exposure length manually is a vital aspect of our craft. Some smartphones even have a “night mode” which stacks multiple exposures to brighten the final image.

So how might one of these smartphones stack up against a DSLR when it comes to astrophotography

 

The cameras

 

For this comparison, I will be using a Canon EOS 70D DSLR with a Samyang 14mm manual-focus lens: a mid-range crop sensor camera and relatively budget lens (this is a lens you will find in nearly all astrophotographers’ kit bags).

The smartphone is a Huawei P20 Pro, which was rated as one of the best smartphone cameras until recently. This camera comes with a 40-megapixel chip, manual mode and the ability to save in Raw. Like with most DSLRs, you can set exposure to a maximum of 30 seconds, ISO to 6400, and you have the ability to manually focus by means of a slider on the screen. This phone also has a “night mode”.

One word of advice – if your phone doesn’t allow manual settings by default, there are apps out there that can do this for most phones. Some will be free and some paid for, so make sure you read the reviews and do your research first.

Both cameras were attached to an inexpensive, stable tripod, with a ball head to allow the cameras to be moved and secured for the long exposures required.

The location for these shots was a relatively rural area with good dark skies overhead, although with a little light pollution around the horizons. All of my previous outings to my usual dark-sky sites had been thwarted by cloud – the common curse of being an astrophotographer in the UK.

 

Night mode

 

So first up I thought I would give “night mode” a try. I set the phone up in an adapter that enabled it to be mounted on a tripod – essential for long exposures. I set the smartphone to night mode, set ISO to 1600, and exposure to 24 seconds. I also tried 10 seconds and 32 seconds as well. As you can see below, it wasn’t a huge success. I’m not entirely sure what happened, but it seems the software couldn’t deal with the light pollution.

 

Chris Grimmer

 

 

Pro mode

 

After the disaster that was night mode, it was time to put the phone into Manual (“pro mode”), which would allow me to take control, and see what I could achieve. For this test I set the ISO to 1600, exposure to 24 seconds, and for the DSLR an aperture of f2.8. The Samyang lens is 14mm (so 22mm on my crop sensor) and the phone was at its widest, which is equivalent of 27mm on a full frame.

These images have been untouched and just converted to JPEG after downloading from the camera.

 

Chris Grimmer

 

As you can see there is not a huge difference in the DSLR to the phone image. There are however a few key differences and some real problematic areas in using a phone...

Focal length: When capturing the Milky Way, having a wide field of view makes life a lot easier. Both the above images were from the exact location, however in the phone shot I had to sacrifice any real foreground due to the longer focal length.

In addition, when shooting the night sky, we are limited in our exposure length if we want to maintain round stars. Due to the rotation of the earth, the stars are constantly moving, so if you run a long exposure, you end up with stretched stars, which is how you take a star-trail image. To combat this, we tend to use a wide lens, as this reduces the apparent effect and allows for longer exposures. Have a look at the “300 rule” to work out what exposure length you can get away with.

Aperture: In normal photography your aperture controls your depth of field, so a low F-number equals a shallow depth of field and a nice blur to the background. When it comes to night sky photography, depth of field is not as crucial, but the F-number still has a very big role to play. The lower the F-number, the more light a sensor can collect in a set time. As an example, a 20-second exposure at f/2.8 is equivalent to an 80-second exposure at f/5.6.

The Samyang lens I am using for this comparison has a manual aperture ring, so was set to f/2.8, which is as low as this lens goes. The smartphone has a fixed aperture, which in the case of the P20 Pro is f/1.6. (the phone itself allows you to edit the aperture, however this is not a ‘true’ aperture and uses focus stacking to apply or remove the background blur).

Focus: With normal DSLR lenses, you must focus manually when shooting under a completely dark sky. This is often done by using live view and zooming in on the screen on a bright star, adjusting the focus until you get a pinpoint star.

The issue with a smartphone is you have no manual focus ring; most don’t even allow manual focus at all. This is a major issue, as autofocus will not work when outside in a really dark location, which is what you need for astrophotography.

My smartphone has a manual focus function which gives you an onscreen slider that allows you to change the focus.

 

Chris Grimmer

 

This shows that focus can be adjusted between infinity and macro, however as with most lenses, this is not 100% accurate. The other issue on this phone is you can’t zoom in on live view, so trying to pick out a star to work with is nearly impossible. This means that you have to take an image, check the stars, adjust, and rerun until you have a good focus. As you can see in my original comparison, I still didn’t quite have focus spot-on.

Raw mode post-processing: Both DSLRs and smartphones offer the ability to shoot in JPEG format, however in doing so, you lose a lot of the hidden detail in the image. Generally for night photography, shooting in RAW is a must.

I loaded both images into Photoshop and ran my usual steps for post processing to try and clean them up and bring the Milky Way out. This is where the real differences stood out; there is just so much more that can be brought through from the DSLR image.

 

Chris Grimmer

 

 

In conclusion

 

If you have a smartphone that offers manual mode, then as you can see, you can obtain some nice shots. If you are looking for that beautiful Milky Way image however, make sure you take your DSLR.

Phone cameras have come a long way in recent years and are still progressing at a fast pace. So potentially this article is already out of date before I have finished writing it! As it stands at present, however, phones cannot truly match a DSLR for night photography.

The below photo is around 15 images stitched together, and shows the difference a good dark site can make, and what can be achieved with a relatively budget DSLR setup.

 

Chris Grimmer

 

About the Photographer

Chris Grimmer is an amateur astronomer, astrophotographer and photographer based in Norfolk. Follow him on Twitter and see more of his images on Flickr, Instagram and his website.

 

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