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Webcam astronomy: simple but effective

Over the past 4 years, I have been steadily assembling equipment for the purpose of photographing deep sky objects (DSOs). These are dim, sometimes large, diffuse cloudy patches when viewed using binoculars or a small telescope. Starting with the Andromeda galaxy (see below), I used a simple, long tube telescope fitted to a tracking mount (that tracks the DSO as it moves across the night sky). This allows a camera to collect light over a long period of time (often up to several hours) showing features that would otherwise be far too dim to detect with the naked eye.

The Andromeda galaxy (M31) taken by collecting over 2 hours of photographic exposures.

The Andromeda galaxy (M31) taken by collecting over 2 hours of photographic exposures.

Although I personally find this type of astrophotography very rewarding, there are some major drawbacks. The first and most severe is how sensitive this type of photography is to unwanted light. Since photographing DSOs requires a really long exposure, any stray light from streetlights or the Moon simply washes out the object’s detail. The second is the sheer time it takes to collect the light to produce these types of photographs. The main issue is that as I take these long exposures (typically I take over 30 shots each lasting up to 5 minutes), any disturbance such as a gust of wind or nearby movement can cause the image to smear.

Mainly for these two reasons, I decided recently to branch into a different type of astrophotography – webcam astrophotography. Although I don’t have any pictures to show yet (I haven’t finished modifying the webcam yet, but watch this space!) I will briefly discuss the principles of this form of astrophotography and how it can be achieved with very limited equipment (and budget).

Put simply, webcam astrophotography involves taking a video of a bright night sky object (such as a planet or the Moon) and using the best frames of that video to produce a high quality image. There are several advantages to this approach. Firstly, since the object you are photographing will be bright, the exposures are short. This means that movement of the telescope will not cause image smear. In addition, the telescope mount does not have to track the night sky very accurately since each frame of the video is taken over a fraction of a second (normally 1/30s). Secondly, bright objects far outshine artificial light pollution, which makes this form of astrophotography very suitable for people living in towns and cities.

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Photo of a bird with strong chromatic aberration caused by improperly focused violet light.

So, with a webcam and a cheap telescope mount, some impressive   astrophotography can be achieved (see this link). However, I have neglected to mention anything about the telescope. When photographing bright objects overcoming chromatic aberration (CA) is a real problem. This optical aberration occurs when light being focused through a lens splits into its constituent colours and these colours focus at different points. The colour fringing effect caused by CA is shown on the right.

So, I decided t20160130_093248o use a telescope design known as a Maksutov-Cassegrain (modelled by my lovely fiancée Sarah) that avoids CA through an ingenious use of lenses and mirrors. There are three important advantages of using this telescope. (1) The light entering the telescope does not split into different colours (as mentioned). (2) Light is also neatly folded up so the actual telescope is conveniently small. Finally, although the telescope is short, it is capable of imaging at high magnification – an important feature if you wish to image small Moon craters or the great red spot on Jupiter.

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A excellent image of Jupiter taken using a Maksutov-Cassegrain telescope and a cheap webcam. Photo credit: Dion from the Astronomy Shed.

In hindsight, perhaps I should have started my astrophotography hobby with webcam imaging; I would have saved a lot of time and money and not developed an irrational hatred of streetlights or the Moon!

Post by: Daniel Elijah

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2 Responses to Webcam astronomy: simple but effective

  1. Xander Skyrien says:

    Curious to see how well this works. I suspect a typical Webcam would have very poor low-light capabilities and may introduce significant noise. I mean you’re bringing down the exposure time to 1/9000th of a 5-min shot. Hopefully I’m wrong!

  2. Instead of resorting to optics to deal with chromatic aberration, would it be adequate to use something like Photoshop? For example, take several shots, each with a slightly different focus, and in each one discard the out-of-focus part of the spectrum; then combine the images. Alternatively, place colored filters in the light path and re-focus for each before a snapshot. With bright objects the loss of light wouldn’t matter. In the final combined image the colors may be a bit off, but that shouldn’t matter much either. Actually, having separate images for different sections of the color spectrum could enable bringing out features of interest in the target.

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