Thursday, July 03, 2014

Shutter actuation count

Although the modern DSLR contains a mass of electronics (and more computing power than the average university had when I was an undergraduate!), it is still in many respects a mechanical device. The mechanisms that flip the mirror out of the way and move curtains across the sensor to make an exposure are very similar to those from film SLRs going back to the 1960s. Inevitably, these mechanical devices eventually wear out and fail. The shutter mechanism in particular is quite complex and delicate and must operate at high speeds to make fast exposures. Camera manufacturers test the reliability of their shutter units and rate then for some expected number of actuations before failure. Canon does not publicise this information and it is not quoted in the specifications of cameras on their web-site but, since about 2009, photo-journalists have been ale to get hold of the figures - presumably direct from Canon. For example, the table about 2/3 way down this 2012 review of the Canon 1DX. To summarise this table, consumer models like the 400D are rated at 50,000; models aimed at enthusiasts like the 60D and 70D are rated 100,000 and professional models are rated several times higher, with the 1D X having the highest rating of 400,000.

Your camera keeps count automatically and internally of the number of times you click the shutter. Some manufacturers (e.g. Nikon) include this shutter actuation count in the EXIF information embedded in each photo, but this is not the case with Canon. In fact it is not easy to discover the actuation count for Canon DSLRs! If you Google "Shutter actuation count" you will find plenty of web-sites that claim to be able to give you this information.

Most are based on reading the EXIF data from a photo taken using the camera. Typically they invite you to take a picture (a small, low quality JPEG will do fine) and upload it. A number of these specifically list a whole load of Canon DSLRs amongst those covered (e.g. this one -which lists "Canon EOS 60D"). If you try it, you will find that they tell you that the info is not available. So why include these Canon models amongst those they claim to support?

Another tranche of sites will tell you about a Windows utility called EosInfo. The idea is that you download and install this program (there is a download link about half way down the page), connect your camera to the computer via the USB lead, turn it on and then run EOSInfo. It should connect to the camera via USB and report the info you want. It claims to work on "Canon DIGIC III/IV DSLRs *except* the 1D* series". However, it has not been updated since 2009 and camera models and firmware move on. With my Canon EOS 60D (firmware version 1.1.1), although it is based on DIGIC IV, on connecting the camera and running EOSInfo, the program falls over with a exception error during the connection attempt.

I have found two methods that DO work on my camera:
  1. Astro Photography Tool (APT). From the download page, download the demo version and install it. Connect your camera to the computer via the USB lead, turn it on and then run APT. It shows a black screen with dim-red text (presumably designed to protect the astronomer's night-sight). The shutter actuation count is shown in the bottom-left corner of the screen.
  2. Magic Lantern. This is a firmware add-on for certain Canon DSLRs. If your camera is supported download it and follow the instructions to install it on your camera. Once installed, it has a Debug menu which shows the shutter actuation count - amongst other data. (I have been experimenting with Magic Lantern for many other reasons and will post about it in due course).
Should I be concerned about my shutter actuation count? I am inclined to look at it rather like the mileometer reading on my car. It gives me a rough idea about when I should expect to need a major service and I would take it into account when buying second-hand. It gives some indication whether it has been heavily used by a commercial driver or kept in the garage by one careful owner! And I would expect the price asked to reflect this. After all, the shutter mechanism can be replaced. It would be a major repair and would probably be expensive - but considerably less that a new camera. However, I have had my 60D since Dec 2010 and the actuation count is roughly 28,000 (in 3.5 years). At that rate of usage, I would expect it to take 12.5 years - that is another 9 years - to get to 100K actuations. Well before then, I think I am likely to want a new camera for many other reasons!

Tuesday, May 27, 2014

Dragonfles at Woodwalton

I spent a couple of afternoons at Woodwalton Fen last week photographing dragonflies - especially Libellula fulva (Scarce Chaser). I think there must have been a big emergence recently. When I went on Wednesday there were quite a loy of immature males about which either had not yet developed their blue pruinosity or only had it partially developed. This one has the blue colouring only partially developed down his mid line, with the yellow base colour of the abdomen still showing through down the sides. I think they look rather attractive at this stage.

Male Libellula fulva with partially developed blue pruinosity
Since it has been rather warm and sunny, there was a tremendous amount of activity with males chasing each other around and mating pairs also being quite numerous. Male dragonflies (like most insects) produce a packet of sperm called a "spermatophore" which is passed to the female during copulation. She then stores it internally and uses sperm from it to fertilise her eggs before they are laid. The male's genitalia open near the end of the abdomen, but he has "secondary genitalia" located near the base of his abdomen. A spermatophore is loaded into the secondary genitalia before he goes looking for a mate. He will try and grasp any female he encounters. If she is not receptive she will try and evade him and fly off. Otherwise, he grasps her using "anal appendages" at the end of his abdomen which lock into grooves in her pronotum - just behind her neck. These are complex structures with grooves and teeth in both sexes which act like a lock and key, so they will only connect up properly if they are the same species. Male dragonflies are not very discriminating and will try and grapple anything vaguely female-dragonfly like - including other males and individuals of other species! Once they are connected up, the female curls the tip of her abdomen round and inserts it into his secondary genitalia and the spermatophore can be passed across.

Pair of Libellula fulva in cop.
This takes some time in L. fulva and they remain coupled up like this for 15 minutes or more. They usually settle on a reed stem or something similar, but if disturbed they will fly around still coupled up. (I assume only the male uses his wings when they fly in this position).

You can tell a male who has mated because the female's front legs, grasping the males abdomen during copulation, leave a "mating scar" - a dark patch where the blue pruinosity has been scuffed up.

Mature male L. fulva showing "mating scars"
The other species that are common at Woodwalton at the moment are L. quadrimaculata (Four-spotted Chaser) and Brachytron pratense (Hairy Dragonfly). I saw females of both of these ovipositing, so I suspect they emerged a bit earlier and are a bit further on in their season.

L. quadrimaculata male


These shots were taken using a 60D with a Canon 70-200 f2.8L lens at the 200mm end of the zoom range and at an aperture of f8. The closest focussing distance of this lens is 1.2m at which it gives a reproduction ratio of 1:5 (one fifth life size - 0.21x according to Canon's specs). These shots were taken a bit closer than that using an extension tube on the lens. All were taken using a tripod at a shutter speed around 1/160 - 1/200s.