Jonathan's blog

A friend of mine is a researcher in the field of chemical physics. This week, he invited me to his lab to take a photograph of his 5 megawatt laser, which strikes a copper target and makes a plume of plasma that lasts for just a few fleeting nanoseconds. Normally, I like taking photos of landscapes or architecture, but there’s no way a geek like me can resist the invitation to play with a frickin’ laser.

Naturally such a powerful laser is potentially rather dangerous, so I was under strict instructions not to touch anything, lest I get my hand zapped off or something. Laser safety goggles were the order of the day. As they say, “do not stare into beam with remaining eye.”

Laser sign

The laser table is large and complex. The laser itself is on the far side of the table, behind the computer screen. The beam then bounces around various mirrors and lenses in the section of the table on the left, which has black safety screens to catch any stray reflections. I am told that if any dust gets on the mirrors, it will absorb enough laser energy to become hot enough to damage the mirror.

The beam then enters the metal tube at the front of the table, and finally zaps the copper target in the square metal box in the near-left corner. The box contains a near-vacuum, with a pressure of just 3 ten-billionths of normal atmospheric pressure. The box has an observation window, and if you look carefully you can see my black camera over the hole, peering through the window.

The white box in the very foreground is a specialised laser detector, fitted out with all sorts of gizmos, including the computer on the trolley.

Laser table

Finally, the image we’ve been waiting for. This picture shows the inside of the box. The green laser beam enters the picture from the right, but you can’t see it because there is no mist or smoke for it to reflect from. The centre of the bright flash is where the beam strikes the copper, and you can see a bit of green in there. The plume of plasma then spreads back along the beam, heading right. It isn’t also going left – what you can see there is a reflection of the plume on the shiny copper surface. Not sure what else I can say about this. I’m no expert!

Laser plume

I love photography, and I have an interest in astrophysics and astronomy. It only makes sense to combine them, and have fun with astrophotography. But which equipment is best for the beginner without breaking the bank? Let’s explore the options.

Some interesting photographs can be captured using a wide-angle lens to view the whole sky, but here I am specifically talking about long, telescope-like lenses. There are three solutions that I have at my disposal:

• Meade 60AZ 700mm f/11 telescope, with T-mount adapter for 35mm SLR or DSLR
• Tamron 70-300mm f/4-5.6 telephoto lens, native mount on DSLR with 2× teleconverter to make it a 600mm f/11
• Tokina 400mm f/5.6 telephoto lens, native mount on 35mm SLR with adpater for DSLR and 2× teleconverter to make it a 800mm f/11

So the “zoomiest” lens is the Tokina but that isn’t the only factor. Which lens is sharpest? What about chromatic aberration? What about other things affecting practical use for astrophotography?

First let me say a few words about each lens (and offer my apologies for the quality of the photos of the lenses – as you can see, my DSLR is in each picture so I was using my phone).

Meade 60AZ

The Meade 60AZ is an inexpensive 700mm telescope. The front element is 60mm in diameter, making it an f/11.7. There’s no variable aperture. It has the usual 1.25″ eyepiece fitting, so it’s easy to get hold of an adapter to turn this into a T-mount fitting. Once you’ve got T-mount, well, Bob’s your uncle, and you can adapt T-mount to anything else – including 35mm and digital SLR cameras, such as my AE-1P, EOS 450D and EOS 300. I bought mine from a car boot sale for £15, and then paid about £20 for the adapter to mount the camera.

Meade 60AZ on Canon 450D

It has an optically simple design with few elements, so chromatic, comatic and spherical aberrations may not be so well corrected for. This isn’t important for viewing by eye with an eyepiece, but aberrations show up more significantly in photographs that can be studied. Technically it is not a telephoto lens, since it does not have a telephoto group, and is correctly known as a long-focus lens.

Being a telescope, it comes with its own tripod which is a little flimsy, but easily capable of taking the weight of a camera.

Tamron 70-300mm

The Tamron 70-300mm is an inexpensive autofocus SLR zoom lens, offering a maximum aperture at 300mm of f/5.6. It mounts natively to the Canon EF mount, for use with 35mm and digital SLR cameras, including my EOS 450D and EOS 300. The 13 elements are coated to reduce flare and correct for various aberrations. My sample was bundled with my 450D at Jessops, but it costs around £100 new at the time of writing. I bought a Kenko Teleplus teleconverter for £30, second hand.

Tamron 70-300mm on Canon 450D

Autofocus is practically useless for astrophotography since there isn’t enough available light. On this lens, the focus ring is quite sensitive, undamped, and hard to use accurately. This will count against it in practical use.

Using a 2× teleconverter will double the effective focal length to almost match the Meade telescope, at the cost of a couple of stops of light and some sharpness – but still faster than the telescope.

This lens does not come with a tripod mounting collar but should be used with one, since the fully-extended lens with teleconverter is quite heavy, and unstable when the tripod attaches to the camera.

Tokina 400mm

The Tokina 400mm is a fixed focal length prime lens, with a maximum aperture of f/5.6. With a 2× teleconverter this gives me the longest effective focal length at 800mm while still being faster than the Meade telescope. It’s a manual focus lens with a large and well-damped focus ring which actually makes it easier to use than its contemporary rival, the Tamron. I paid £50 for this lens, second hand, and the Super Paragon teleconverter was about a fiver, I think.

Tokina 400mm on Canon 450D

It mounts natively to Canon FD-mount manual focus cameras like my AE-1P, but will work with Canon EF-mount EOS cameras with an adapter, which I wrote about recently. This adapter has the effect of making the lens a bit zoomier. I haven’t exactly measured the amount, but it could make this 800mm lens produce an image like a 900mm. We shall see.

This lens also does not come with a tripod mounting collar but should be used with one for best effect, because it is long, metal and heavy. They sure don’t make lenses like they used to.

Sample images

This article is about astrophotography really, but taking test photos of the moon or other celestial objects means carrying equipment to a dark place. I’m not sure I can be bothered to carry these three heavy lenses and two tripods and other accessories out at night, so for now you’ll have to make do with these images of the chimney at Frenchay Hospital, which is about one mile away. This is a city, so the atmosphere is quite hazy.

These pictures were taken with a Canon EOS 450D. The main images are exactly as they came out of the camera – no editing. The second images are cropped around the top of the chimney to show fine detail.

Meade 60AZ

Meade 60AZ

It’s immediately obvious that the image from the Meade telescope suffers from very poor contrast and colour saturation. This is perhaps obvious given its inexpensive and crudely coated elements. It might be possible to improve the contrast by using filters and shooting in black & white, since colour isn’t always important in astrophotography.

In its defence, the sharpness is good and I’m frankly shocked at how small the chromatic aberration is, given that this is a cheap 2-element lens.

Tamron 70-300mm

Tamron 70-300mm

The Tamron 70-300mm, a modern multi-coated lens, has no such problems with colour and contrast. The colours are vibrant and bold. However, it suffers badly from chromatic aberration. We might expect this from a cheap zoom lens – the effect will be less prominent with a fixed focal length prime lens.

As before, it might be possible to reduce the effect of chromatic aberration by using a coloured filter and shooting in black & white.

Tokina 400mm

Tokina 400mm

It’s immediately obvious that the Tokina 400mm is the zoomiest lens, with its teleconverter and FD-EF converter to mount it on the 450D. The colours and contrast are good, especially for a lens manufactured in the 1970-1980s.

The effect of chromatic aberration is also extremely small, presumably because it is a fixed focal length prime lens. I think the overall image quality is best out of the three lenses tested here.

Summary

The Tokina 400mm definitely seems to be the most useful for astrophotography and lunar photography. It has the longest effective focal length, the best sharpness, the best chromatic aberration and reasonably good contrast. Its manual focus ring is easy to use

Don’t forget that these images aren’t the best that each lens can produce – they are the lowest common denominator of what each lens can do. With careful processing, the images could be sharpened and have their contrast boosted. For some subjects, it might be appropriate to stack the images. For certain images, coloured or other filters could be used to work around the effect of chromatic aberration and atmospheric haze.

In the past, I experimented with a catadioptic mirror lens but the results were not great. In theory, mirror lenses should be well suited to astrophotography, so perhaps I had a bad sample. I also wrote some thoughts on other types of long-focus lenses for general use, and some of it might be relevant to astrophotography.

That’s enough discussion of lenses. I’m now waiting for a clear summer’s night when I can go for a short drive out of the city and hopefully capture some great images of the moon, and maybe other things in the sky. I should probably read up on astronomy so I know what to point the camera at!

I wrote a while back about software to generate star trails from a series of images of the sky. They are pretty and a fun and interesting form of art, but I wanted to have a go at taking photos of the night sky as it actually appears: still, and without trails.

It’s pretty hard to achieve good photos with a consumer DSLR. You have to keep the shutter speed faster than 4-5 seconds, otherwise you start to see motion blur creeping in. This means you have to turn up the ISO sensitivity of your sensor, which in turn leads to noise. As soon as you start to examine these photos closely, the noise is so distracting and it ruins the picture.

There are some ways to alleviate this – buying a faster lens, or a lower noise, higher sensitivity sensor – but these will cost you money. Lots of money.

I’ve been playing with the concept of stacking – where you take multiple images and later combine them to remove the noise. “Adding” the photos is the easy bit, but the stars will have moved slightly in between each photo, so they will need to be aligned by rotation and translation.

Some crazy people have attempted to do this by hand in Photoshop, but I’m far too impatient for that. There are some apps for Windows (both commercial and free) that will automatically align and stack photos. However, I wasn’t able to get any of them to work reliably under Wine on Linux, so I set about finding a native Linux stacking app.

The best I found was ale, which is command-line only but very easy to use. Both Fedora and Ubuntu package ale by default. To use it with default settings, it’s just a case of doing this:

ale image1.jpg image2.jpg image3.jpg image4.jpg output.jpg

This picture of The Plough was taken using a Canon 450D with 50mm f/1.8 lens. I took 12 exposures at ISO1600, 1″, f/5.0 and stacked them with ale. On my PC, a Core 2 Quad 8200 with 8GB RAM, it took about 53 minutes to stack 12 photos.

The stars are very small so you will probably need to click to see the larger version. You’ll notice that the background is very dark as ale has removed sensor noise, cosmic ray strikes and light pollution (I’m shooting in a city).

The Plough

I’ve been practising traditional silver-based black & white photography for a couple of years but today it occurred to me that I don’t really know what is going on with the various chemicals. It’s just a process of remembering which bottle is which. I had a vague idea of what was going on, but I decided to look it up – and summarise it here.

Exposing

The light-sensitive film (or paper) contains crystals of silver halide, which is light sensitive. At this point, the film is opaque grey. When light hits the film, the silver halide crystal splits into a silver ion and a bromine atom.

Ag⁺Br^- (crystal) + hν (radiation) → Ag⁺ + Br + e^-

Then, the silver ion recombines with the free electron to give an atom of metallic silver.

Ag⁺ + e^- → Ag⁰

After exposure, there is an image on the film made from a tiny quantity of metallic silver. This is known as the latent image. It would be invisible to the eye and the film is still dull and opaque. For an individual grain of the silver halide emulsion to count as “exposed”, at least two photons must have interacted with it, to form small silver crystals consisting of two or more silver atoms.

Development

The purpose of developer is to amplify the latent image. The chemical composition of developer varies and is complicated so I won’t go into it here – other than to say that it promotes silver crystal growth where the small silver crystals already exist.

After development, the latent image has been converted to an actual image, made of metallic silver crystals. It appears black, although the film itself is still opaque.

Stopping

Even after taking the film out of the developing solution, it continues to develop (your hands are still wet after taking them out of the sink, right?) so a stop bath is used to halt development. Developing requires an alkaline environment to work, so stop bath is simply a weak acid – usually acetic acid.

The stop bath causes no other changes to the film.

Fixing

Although we have now developed the film and ended up with a black image in metallic silver, the areas of the film that were not exposed to light are still opaque, and still sensitive to light. Bathing the film in fixer dissolves the unexposed silver halide, leaving a near-transparent film backing that is not sensitive to light. At this stage, you can take the film out of the developing tank and look at it in daylight.

Toning

So far, we have ended up with either a film or a print which has an image made from metallic silver. If there’s one thing we know about silver, it’s that it tarnishes. Depending on the storage conditions, silver prints may degrade with time. Toning the image serves two purposes: it improves the longevity of the image, and it can produce the colourful sepia effects.

Various toners exist, but they all work in the same way. They react with the silver to produce silver salts, such as silver sulphide which is more stable then pure silver. It is also slightly brown in colour, hence the sepia tone.

References

• http://www.cheresources.com/photochem.shtml
• http://en.wikipedia.org/wiki/Photographic_developer
• http://en.wikipedia.org/wiki/Photographic_print_toning

Everyone knows that Coke is bad for their teeth. It’s sugary and acidic.

The acidity is at least partially caused by carbon dioxide (CO₂) dissolved in the water, to make carbonic acid. We also know that if you pour a Coke and leave it, it fizzes away as the CO₂ comes out of solution and returns to its gaseous state. Does this mean that Coke becomes less acidic if you pour it and leave it for ten minutes before drinking?

Well, perhaps.

It’s also worth remembering that small changes in temperature can cause large changes in the rate of chemical reactions. If we assume our can of Coke was in the fridge at perhaps 3°C, then it will warm up in the time we leave it to fizz away. So even if it’s less acidic, the weaker, warmer acid might be able to react with our teeth faster than the stronger, cooler acid.

I am not a chemist but I want to find the answer to this thought experiment.

After a little research, it seems that dissolved CO₂ (carbonic acid) is only one contributor towards the overall acidity. The most significant acid is phosphoric acid. As the CO₂ comes out of solution and escapes as gas, the acidity only decreases slightly. On the other hand, when the coke warms up from 3°C to maybe 10°C as it approaches room temperature, the action of the acid will be massively accelerated.

So based on this mini experiment, Coke is worse for your teeth when it goes flat and gets warm. This, of course, neglects the action of the sugar on your teeth and all the other things  we haven’t considered, so don’t blame me if you lose your teeth from drinking gallons of ice-cold Coke

Outdated medical technology isn’t normally the kind of thing I’d be interested in, or would write about – but I was given some old glass autoradiographic stripping plates. I didn’t know what they were at the time – I assumed they were normal photographic plates, but I’ve done a little light reading.

Autoradiography

The gist of autoradiography is that you:

• inject a creature with a radioactive chemical
• allow the radioactive blood to be pumped around its body
• kill it
• cut it into thin slices
• stick the slices onto an autoradiographic plate
• leave the radioactive slices stuck on the plate for days or weeks while the image forms – in effect a contact print but the “illumination” is provided by the sample itself, rather than an external light source
• develop the plate in the same way as normal photographic prints

I found the following account in the Journal of Anatomy, 1978:

The investigation was carried out on 10 days old rats. Of the 11 animals used one served as a control and the rest were each injected intraperitoneally with a single dose of tritiated thymidine (2 μCi/100 g of body weight). The rats were killed by decapitation either 2, 12 or 48 hours after injection. The knee specimens were collected, fixed in absolute alcohol for 48 hours and then washed in distilled water. Cryostat sections 7-8 μm thick were cut and mounted on glass slides coated with a thin layer of gelatin. The sections were then stored in an oven at 37 °C.

J. Anat. (1978), 126, 3, pp. 547-554

The article continues to describe how the plates are developed and treated afterwards, which seems fairly typical of any printing done in a darkroom.

This is all good and well, but I have no intention of force-feeding a rodent some Red Bull and then cutting its head off. I’ve hardly been able to find any data about these particular plates – marked as Kodak AR.10. However, both the leaflet with the plates and the previously referenced article mention using a dark red safelight, which implies that the plates are indeed sensitive to visible light as well as X-rays and γ-rays.

Sensitivity to visible light sounds much more useful to me.

Making my own contact prints

As I had a box of 12 I thought it might be fun to try making some prints. And as they were free (saved from the bin!) there’d be nothing lost even if they’d expired or if I ruined them. The plates are 4¾ × 6½ inches, which is a nice size for a novelty glass print (I think).

I started off trying to make a simple contact print, by placing a heart-shaped pad of post-it notes on the plate and exposing under the 60W bathroom light for one minute. I then developed in Ilford ID11 for five minutes, diluted 1:1 with water. I washed the plate in stop bath for one minute and fixed in Ilford Rapid Fixer for two minutes.

The plates certainly hadn’t expired, as the area exposed to the light was black, and the area under the post-it pad was clear. However, the outline of the pad was extremely blurred to the point where it wasn’t possible to tell what it was. I think this was worsened as I had accidentally had the plate upside-down, with the emulsion on the opposite side of the glass to the pad.

I tried again, this time with the emulsion face up. The result was hardly any better. I was disappointed, since if I couldn’t make a simple contact print of a white heart on a black background, the chances of doing anything else successfully were slim at best.

Building an enlarger

My original plan, if the simple contact prints had been successful, was to make some more contact prints of some 6×9 cm 120-format negatives on the plates. They would certainly look unusual. Having failed at any sort of contact print, I wondered if it would be possible to project an image onto the plate.

I don’t have an enlarger or a project, but I do have some very crude cameras that I thought might work in reverse. Using a 1929 Voigtländer Bessa folding camera, a porridge box and a light bulb, I managed to project a 120-format negative onto my wall in a dark room. As you can see, I’ve placed a book on top of the box to keep it still, and propped up the nose of the camera with a smaller box. You can also see the silver shutter release cable. Finally, I draped a black T-shirt over the entire arrangement, allowing just the nose of the camera to protrude, because it was leaking light quite awfully.

My homemade enlarger

The image of the 120 negative was reasonably sharp, but at the camera’s closest focusing distance of four feet, the image stood some 18 inches tall. For too large for a 6″ plate. After a bit of tinkering with some card and I managed to make a holder for a strip of 35mm negatives. When projected, these produced images that were still somewhat larger than the plates, but I thought it would be OK to “crop” them and represent only the central area of the negative on the plate.

Making the image

Given that one minute under a normal bathroom light had produced roughly the right exposure, I reasoned four minutes using a 40W bulb in my enlarger (significantly dimmer) would probably be OK.

After exposure, I processed the plate the same way I had done before. But this time, success! Here’s my finished plate – a picture of my brother riding his bike. (You can see the original image on my photo blog).

My finished plate

Given that the grain is kind of awful, I would guess that the exposure time was too short and the development time was too long. I still have plenty of plates remaining, so I will try more like this after I’ve selected some more of my negatives from the archives. I will probably try exposing for ten minutes and developing for three.

I don’t know about you, but I think this retro-looking plate is incredibly cool. Anyone can do anything with a DSLR and Photoshop, but I think it’s more fun to play with expired X-ray plates and cameras from before my grandparents were born

I spotted this article on the web earlier today, which discusses a possible cure for peanut allergies. But one particular section jumped out at me:

The largest ever trial to find a treatment for potentially fatal peanut allergies is to give sufferers tiny amounts daily to build up tolerance.

Twenty out of 23 sufferers in an earlier study became able to eat more than 30 peanuts safely.

Umm… what happened to the three people who were not able to eat the peanuts safely…?

Some years ago, my dad bought me a book about electronics, computers and robots from a jumble sale for 10p. It was published in 1984 and probably about 15 years out of date when I received it.

Today I came across it on my bookshelf back at my parents’ house, and there’s a double-page spread in it called Television and Video in the Year 2000. It has a picture of how a house might look in the millennium year.

Of course, speaking today with a decade’s hindsight, the house looks like something from Thunderbirds, but some of its predictions have indeed come true. Let me reproduce it for you here.

When you are grown up and your children are going to school, this book may not exist. In fact, schools as you know them may not exist either, and libraries with books may be museums. All this will happen because of television and video. Television was invented during the 1920s by John Logie Baird.

Studying by Television

Let’s visit a home of the future, say in the year 2000, and see what everyone is doing. Alice is 12 years old. She is not wasting time watching television; she is at school. That’s her teacher on the screen. She manages to see Alice once a week to check her written work, but not for long. By teaching on television she could have a thousand pupils in her class at once, but she doesn’t have more than a hundred. Alice likes to ‘go to school’ in the living-room where there is a row of flat screens against the wall. She wears headphones to listen to the teacher.

Alice’s brother, Peter, likes to work by himself in his bedroom with a smaller, personal screen. He is 20 years old and, although he lives in Britain, he’s studying with the Massachusetts Institute of Technology in the United States. His microcomputer and screen are linked by telephone to the local library. They are sending Peter a new article written in America. They received it overnight from the United States during the cheaper-rate computer time.

Work and Leisure

Dad has worked at home for the last five years, ever since his supermarket became fully automated. As supply manager for the supermarket, he checks the stock on the shelves every Monday morning visually through the closed-circuit television cameras. On his home screen he can also study the computer totals produced by the automatic check-out tills.

Mum is watching a live television programme. Her favourite daytime programme is the 24-hour European news station which the family receive through their satellite dish receiver on the roof.

Grandad Jones is the only member of the family who uses the video disc. At the moment he’s looking at a dahlia catalogue, and the video disc gives the best picture available on any system.

Granny Jones can hardly walk and spends her time watching the goings-on out in the street through the local closed-circuit camera system. The council originally set up the system to help stop burglaries.

I’ve also photographed the image from the book – apologies for the quality. I might even get round to scanning it one day. Click for a larger version.

A house of the future

So how accurate were the predictions?

Lots of  the things mentioned in the picture are easily possible with today’s technology. But few people do them because they are inconvenient or expensive, or simply a bad idea.

It would be easy to set up a videoconferencing system to allow pupils like Alice to have school lessons at home – but nobody would do it because it misses out on an awful lot of face-to-face contact. Peter’s use of technology to get hold of documents is more realistic.

Likewise the father working from home – it’s possible to install cameras around Tesco and have the stock manager working from home, but it’s useless and expensive.

As for the mother watching 24-hour live news and the grandad watching what’s essentially a DVD – spot on. But how bored must the granny be to sit there watching CCTV in her own street?

It seems to me the biggest omission of this futuristic house is the use of computers and the Internet – although lots of the video systems in use seem to do computer-like tasks. Each person in the house is using specialist equipment for each task, and each piece of equipment has its own source of external connectivity.

The beauty of modern computers is that they can do a wide variety of tasks, and that the Internet can be used to carry any sort of data, whether it’s a text document or a video stream.

The most saddening thing about that house is that nobody is talking to anyone else, and nobody has any reason to go outside. I hope that doesn’t come true!

Ever wondered how much it’s costing you to leave your computer on overnight? Or the hallway light?

I used to go with “One watt for one year is one pound” but clearly with the way energy prices are climbing, this isn’t true any more.

So I knocked together a simple script that can calculate how much it’s costing you to run your stuff. You can use it in the frame below, or in its own frame at this link.

For anyone who also reads my photo blog, you might have seen that I went out around sunset last night to see if there were any interesting photos to be taken.

Before I left the house, I checked the official time of sunset on the BBC Weather website, and found it to be 9:04pm. I wasn’t really sure how “sunset” is defined, so I left the house early to cover myself.

My observations on the evening didn’t really help me deduce what is meant by “sunset” as it’s hard to tell when the sun goes below the horizon when there’s a gorge, some cliffs and a tall forest in the vicinity. I also wasn’t sure if it was the time that the leading edge, trailing edge, or midpoint of the sun touched the horizon. So I looked it up on Wikipedia.

In astronomy the time of sunset is defined as the moment the trailing edge of the sun’s disk disappears below the horizon in the west. Due to refraction of light in the atmosphere, the ray path of the setting sun is highly distorted near the horizon making the apparent astronomical sunset occur when the sun’s disk is already about one diameter below the horizon. Sunset should not be confused with dusk, which is the moment at which darkness falls, when the sun is about eighteen degrees below the horizon. The period between the astronomical sunset and dusk is called twilight.

So now you know. The official time is not only defined in a vague way (what’s the horizon?) but also hard to measure.