Early Astrophotography

© martyn pearce
Comets

In 1996 I took some photos of comet Hyukatake and in 1997, of comet Hale Bopp. Looking at what I wrote on back of those photos I can see that I used a Canon SLR with a 50mm f1.4 lens at exposures of 20 seconds / ISO 100 film. The few bright stars that were captured at the same time were nice little points of light.

I also tried photographing the constellations on their own and found out that as soon as the exposure time was increased to capture the fainter stars, they ceased to be dots and became streaks. Using a wide-angle lens to capture a wider section of sky was more successful as the stars were too small to see that they were really little streaks, but when using a longer lens the smaller maximum apertures meant that the exposure had to be longer and that increased the streaking unacceptably. I knew that something that could track the movement of the stars was needed if I wanted to photograph the night sky properly but I just never got round to doing anything about it. More later.


 

Eclipse of the Sun

On August 11th 1999 at around noon, there was to be an eclipse of the Sun that would be a partial eclipse for most of the UK and totally eclipse at the extreme tip of Cornwall. I didn't think about trying to photograph it from home and I had no chance of going to Cornwall. Then at the last minute, on the day of the eclipse, I was offered a seat on a plane specially chartered to fly along the coast of Cornwall and into the path of the umbral shadow.

I only had a few hours to get to Bristol Airport and so I had to act fast. All I had was a Canon F1n SLR loaded with Agfa CT100 slide film and a set of Canon FD prime lenses in my bag. I grabbed it and left for the airport. As I flew south I thought about the best way to attempt it. I decided that my 200mm f2.8 would give me the best chance. I fitted the lens and stopped it down to f32. I added a polarising filter, hoping that it would reduce the glare a little. I decided to set the shutter speed at the maximum of 1/2000 sec and work down, taking as many shots as I could. I guessed that the heat from the sun might damage the film or the focusing screen but I was prepared to take that chance. The screens on an F1n were changeable and so it was easy to replace one.

It became obvious that I was going to need to point the lens high into the sky to see the sun through the small window of the Dash-7 aircraft. I removed the AE prism finder so that I could simply look down at the focusing screen rather than trying to look up through the viewfinder. As totality approached I watched the sun through my eclipse glasses. At the moment of totality I raised the lens, centred on the sun, adjusted the focus and started to shoot. It was only a second before the sun started to appear again and within a few more seconds the screen was flooded with light. I lowered the camera and watched through my eclipse glasses again. The focusing screen was warm but there seemed to be no damage. All I could do then was to send my film for processing and hope.

When my slide film was returned, I found that I had taken nine shots but only one was any good. I have no idea at what shutter speed it was taken though. Just something less than 1/2000 sec. The film had also been slightly buckled by the heat of the sun.

© martyn pearce
1999 eclipse just after totality. Canon F1n with 200mm f2.8 lens and a bit of luck.

 

D-I-Y Solar Filter

© martyn pearce
D-I-Y Solar Filter

 

On the 20th March 2015 there was to be a partial eclipse of the Sun with at least an 80% coverage of the sun everywhere in the UK. I decided to prepare for this one. Glass solar filters suitable for photographing the sun are available but are expensive if you are only going to need one now and then, so I decided to make my own.

I bought a sheet of solar safety film and sandwiched a piece of it between two rings of strong cardboard so that it was reasonably crinkle-free. I taped the ring to a cardboard tube that I made that was just large enough to slip over the hood of a Nikon 300mm f4 lens.

IMPORTANT: Looking directly at the sun especially through a lens will damage an eye irreparably so the right kind of foil must be used. I used Baader AstroSolar Safety Film.

 

© martyn pearce
Cloudy 2015 partial eclipse, nearly over. Nikon D300 with 300mm lens.

 

On the day of the eclipse there was a total cloud cover but I set up my camera with D-I-Y filter on a tripod anyway and waited. I watched until well past the point of maximum eclipse, but the cloud never lifted so I gave up.

Shortly after, I went to walk into the town but as I left the house I glanced up and unexpectedly saw the sun through the thinning clouds.

I rushed back into the house, grabbed my camera and removed the D-I-Y filter; there was no danger of me getting an eye-full of sun now. I managed to take a few hand-held shots before the cloud cover thickened again. The eclipse was nearly over but locally, most people didn't even get to see that much.

This photo was only slightly cropped.

 

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Later Astrophotography

My early attempts at photographing the night sky were in 1996-1997 when I took photos of comet Hyukatake and Hale Bopp. In 2021 I decide that it was time to do some more. This is a picture taken of the Milky Way from my garden in West Dorset. I used a sturdy tripod and a camera fitted with a wide-angle lens. It was a long exposure so the stars are very slightly elongated but as they are very small it hardly shows. Fujifilm X-T3 with 10-24mm f4 lens at 10mm. ISO 800, 30 seconds exposure. No post processing except to increase the brightness and contrast. However, although I mention elsewhere on this website that I prefer to keep post processing to a minimum, photographing distant stars, nebulae and galaxies does require more than a minimal amount of post processing in order to get the best out of what are very feint objects.

© martyn pearce
The Milky Way.


© martyn pearce
Meade ETC125 with a Fuji X-T3 attached to the photo port

This is a Meade ETC 125 astronomical telescope that I acquired from my brother who is buying something more up-to-date. It has a Maksutov-Cassegrain optical design using mirrors and a 125mm-diameter front lens. It can automatically track across the sky to counteract the rotation of the Earth to keep an object in view. The object is viewed through an eyepiece on the top of the telescope achieving from 48 times to 279 times magnification depending on the eyepiece chosen.

The viewing eyepiece for the telescope is mounted on the top but there is also a photo-port at the back where a camera body can be fitted directly. The magnification achieved is not as high as the eyepiece can achieve but using a full-frame 35mm camera, the telescope becomes a 2300mm f18 lens (about a 46x magnification). When using an APS-C camera the telescope can become the equivalent of a 3,450mm f18 lens (about 70x magnification).

The tracking mechanism of this telescope is fine for viewing by eye but it is not smooth enough for taking long exposures with a camera. However, photographing the moon is not a problem as a fast shutter speed is used.

© martyn pearce
The moon

 

This is a photo taken through the photo-port of the above-mentioned telescope using a Nikon D750. Notice that the moon fits nicely in the frame. This gave me an idea. I had read that it was possible to take a photograph of the International Space station when it passes in front of the moon now and then. So I decided to give it a try. See below.

Photographing a Lunar transit of the ISS

The exact time that the ISS will make a solar or lunar transit can be found on the website transit-finder.com. Knowing the exact location that you are photographing from is essential to get an accurate timing. The website can auto-detect this or you can use your known latitude and longitude. For maximum accuracy I use the readings from my hand-held GPS. As the transits are timed to hundredths of a second and can take less than a second I also use the GPS unit to time the shooting.

My best attempt so far was in my back garden on a cool September night in 2021 at 00:47 minutes and 57.07 seconds past midnight. The transit was to last for 0.97 of a second. I used a Fujifilm X-T3 (mirrorless camera) switched to its vibrationless electronic shutter. With this camera fitted, the Mead ETC125 telescope becomes the equivalent of a 3,450mm f18 lens. This made the moon slightly larger than the vertical field of view of the lens.

With a lunar transit, when the sky is dark and the sun is not too far below the horizon, it will illuminate the ISS so you can watch it approaching and start shooting just as it gets to the moon. But for this transit, at a quarter to one in the morning, the ISS was in the shadow of the Earth so the approach was not visible. The only way to be sure to record the transit was to start shooting just before the time stated. I started shooting at 00:47 and 56 seconds and shot for five seconds. This gave me about 50 shots, 10 of which had the ISS in them.

The images were taken with the X-T3 set at ISO-1600, 1/2000 sec, 10 fps.

To view the transit: click the arrow on the right of the picture.

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Photographing Solar transits of the ISS

I have also photographed several solar transits, but as yet I have been unable to get anything better than a fuzzy butterfly shaped blob crossing the face of the sun.

To be able to view the sun, a telescope must be fitted with a solar safety filter to block out most of the light. This is to protect the eyes (and the camera). This filter causes the sun to appear much dimmer so it requires a bit of ISO/shutter-speed balancing to get a reasonable image at a high shutter speed.

After several attempts at different ISO and shutter speed settings, my best results were when shooting a 0.59 second transit with a Fuji X-Pro2 at 1/4000 sec, ISO 12800. The high ISO that I used, in order to get a fast shutter speed, might have contributed to the fuzziness as well as possible mechanical shutter vibration. Also I used a small extension tube on the camera to increase the magnification. That may have contributed too. The dark areas at the centre of the sun are sunspots.

To view the transit: click the arrow on the right of the picture.

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© martyn pearce

Photographing the night sky without a telescope

I now use a Sky-Watcher tracker when I want to photograph the night sky using a camera and lens. It allows longer exposures to be made without getting streaky stars and planets.

The tracker is attached to a sturdy tripod. The tracker has a motorised rotating plate to which a ball-and-socket head for holding the camera is attached. Once the axis of the tracker body has been accurately pointed at the celestial north pole, which is a point in the sky near Polaris, the axis of the battery powered rotating plate becomes parallel to the axis of the Earth. The plate turns in the opposite direction to the rotation of the Earth, allowing the camera to be aimed at any area of the sky, which, as far as the camera is concerned, will then appear to remain stationary.

This picture shows a Fujifilm X-E3 fitted to a Nikon 300mm f4 lens using a Fuji to Nikon adaptor. This is equivalent to a 450mm f4 lens. This sort of focal length is fine for photographing small areas of sky and relatively large objects such as nebulae and nearby galaxies.

Below is the first photo that I took using this set-up. It is of the Andromeda Galaxy, M31, our nearest neighbouring galaxy, which is about 2.5 million light years away. It was a 90 seconds exposure taken at ISO 1000. The small galaxy above and behind Andromeda is M110. This image has not been cropped so it shows the actual field of view of the lens.

© martyn pearce
The Andromeda Galaxy. Single 90 seconds exposure.

October 2022

To take really good photographs of the night sky it is preferable to take multiple images and manipulate them using a process called stacking, which uses software to produce one final image. The idea is that taking tens or even hundreds of short duration images will produce a higher quality image than one very long exposure and will not cause the over-exposure that a long duration image would have produced. A tracker is needed to keep the camera pointed at the object being photographed.

Below is my first attempt at using stacking software on multiple images taken using the tracker. I took ten 60-seconds exposures at ISO 1600 of the Pinwheel Galaxy, M101, and put them through some stacking software to produce this single image. The galaxy is quite small in the frame but I didn't enlarge it as I wanted to show you the actual field of view of the 300mm (450mm equivalent) lens. Ten exposures isn't really enough to get a brilliant image but it's a start. M101 is 25 million light years away.

© martyn pearce
The Pinwheel Galaxy. 10 x 60-second exposures, stacked.

 

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