Astronomy with a cellphone — equipment

Basics to get started with

19-Jan-21 Mars and Uranus conjunction. Crop from photo taken with Pixel 3a with 60mm Sirui lens, unprocessed. Reference star is 19 Arietis. One of a series of pictures over a few nights to show the motion of the two planets relative to each other and the reference star.

For those that are interested to try out things for themselves, as well as to save cluttering up subsequent articles with details, this article covers the basic equipment being used.

First and foremost is a cell phone that has both good low light sensitivity and ability to take long exposures. By long we mean in the 30 second to several minute range. In the case of the Pixel phones the Google photo app takes care of exposure and ISO settings as part of the software’s astrophotography mode.

Ideally the phone’s software includes an astrophotography processing capability so that you don’t need to try and process the images outside of the cellphone.

This series of posts is based on using a cellphone that checks all 3 boxes: The Google Pixel 3a. The Pixel 4a or Pixel 5 can also be used. Most references indicate that the 4a and 5 have the same image sensor as the 3a, though the 4a and 5 have software that can provide a 4 minute exposure time versus the 1 minute time of the 3a. For the Pixel 4a and 5, astrophotography mode is with their regular camera lens; support for the ultra-wide lens was removed by Google.

Late model Apple and Samsung phones are reported to check two of the boxes (imaging sensor that functions in low light and capable of long exposures) but lack the in-camera software. Using separate software introduces the potential for additional complexity to get a usable image.

On the upside, image processing software used on a PC offers the ability to produce much better results than what Google’s in-phone processing can achieve.

Cell phone holder and tripod. Add a cell phone and you’re ready to do astronomy.

It’s all about keeping it simple:

• Phone (Pixel 3a for these posts)
• Phone holder with standard 1/4" mounting thread for use with tripod
• Tripod

If you already own these things then there’s no equipment investment needed.

If not, a Pixel 3a can be purchased used in the US for around $100. Phone holders are in the $10 — $20 range; stability is important, so spending extra for a metal one is probably worth it. Since the camera is aimed and then a long exposure taken, fancy tripod heads for smooth motion (like what you might want for shooting video) aren’t needed. If you can’t find a tripod at a yard sale, $30 will find you something good enough on the internet.

Creating pictures like on astrophotography sites can take a dozen+ hours of exposure time using equipment costing over $10,000, fifty times our target budget. As mentioned in the first post the goal is to use a simple setup to aid in explaining astronomy topics; the details here are for those that would like to experiment on their own.

In the next post: An under $100 upgrade to the basic setup can vastly expand your capabilities for both astrophotography and regular photos from your phone.