Lens coverage

I often get friends asking me what type of lens to buy after they have bought a new shiny digital SLR. A lot of them have switched over from an old analogue model to a new digital body.

A friend asked me last week to recommend a lens for her. She found that the wideangle lens which came bundled with her EOS 550d wasn't wide enough.

"Would you recommend that I get myself a 24mm?" she asked

I knew then that she had probably previously owned an analogue SLR.

"A 24 mm lens on your camera would be equivalent to a 38mm on your old SLR" I told her.

"How is that?" she asked.

Well to cut a long story short. I explained to her about the coverage provided by the APS-c sensor in her camera compared to the sensor in my camera (an EOS 5d)

"Your camera's sensor magnifies the centre part of the picture by 1.6, where as mine uses all of the picture."

I showed her this little chart that I put together. The pictures were taken one after the other using the same lenses my EOS 5d and my new 7d. The figures in brackets refer to the magnification factor from the 7d, so for example, the 300mm on a 7d body is "equivalent" to a 480mm lens on my 5d.

This simple chart explains more than reading about it on the 'net.

She is now looking for a 16mm Sigma lens which will be equivalent to a 25mm wideangle.

When I bought my first digital EOS (a 20d), the widest lens in my arsenal was a 24mm. For someone doing architecture, this was useless, giving the coverage equal to a 38mm. I forked out for a 20mm but this was also too limiting, being equal to a 32mm. So I sold that lens and bought the very lovely Canon EF 17 - 40L. I also bought a full frame body to be able to use it effectively as the widest setting was only like using a 27mm!

This means that my lens collection now goes from a 16mm to a 300mm, but when I use both bodies, taking into account, the magnification factor, the focal length of the longest lens is increased to 480mm

Well. It's now nearly the weekend. Time to charge up your batteries and take some photos. As usual I welcome your comments and emails.

Have yourselves a great weekend.

Sensor cleaning. My method.

The sensor on your digital SLR is a very delicate object and can very easily be scratched.

It is however a dust magnet and these artefacts will, after repeated use and changing of lenses, show up on your images.

The major manufacturers normally recommend sending the body in for a clean from time to time.

I have however, been cleaning my sensor myself for a long time,  without resorting to buying products like the Arctic Butterfly and their ilk.

Here’s what I do. Please note. This is not for the faint-hearted or for those of you with unsteady hands.

I use compressed air in a can. It must have the long drinking straw like extension on it.First make sure that your camera has a well charged battery or is running on mains electricity. This is because holding the mirror in your camera in a raised position puts a drain on the battery. My cameras tell me if there is enough charge to carry out the task.

Hold the camera securely and with the lens throat facing down. This is because I want the dust to fall out and not be redistributed inside.

Then I remove the lens and activate the “sensor cleaning” setting. The mirror flips up and the sensor is exposed.

Taking my canned air in one hand I first blow out a second or two of gas. I do this because the first attempt always blows out liquid and this can damage the sensor.

When I can’t see any more liquid coming out, I slowly move the “straw” inside the lens throat whilst keeping a steady pressure (gently) on the air can trigger.

This next bit is important. The can must then be kept steady. Don’t move it around or shake it because this can cause the expulsion of liquid gas. Instead, move the camera body around whilst facing down. Sounds difficult whilst reading this but is actually in practice, quite easy.

Move only the camera and not the air can

When finished, remove the straw from the lens throat and deactivate your camera’s mirror up mode (I do this on my EOS 5 by powering off the camera).

That’s it. One clean sensor. I must say however, that this method is only good for light dust and hairs. It won’t (always) get rid of anything physically stuck to the sensor. For the times when I have something that won’t budge with my air can method, I use a Sensorklear device from Lenspen which I bought from 7dayshop. This is recommended for 50 uses and cost me less than a tenner.

Here’s one pic of my sensor before the air can method.

... and here’s the image taken afterwards.

Well that’s it for now. Please feel free to email me or leave a comment. I really do value your opinions.

Till next time.