Frequently Asked Questions

Q1 I would like to look around the Club before I decide to join. How can I do this?

You can come along to one of our Club Nights. These are a mix of informal evening talks, social events and photo walks that anyone is welcome to attend. Check the Club Calendar for upcoming Club Night events.

Q2 What's the difference between a mirror lens and an ordinary telephoto lens?

With an ordinary telephoto, the glass elements inside are arranged in a straight line and the light travels straight through the lens from the front to the back. With a mirror lens, the light enters through the front element, is bounced off a concave mirror in the back of the lens, is then reflected back from another mirror behind the front element and finally exits through a small hole in the centre of that first mirror at the back. So why would you choose one over the other? The answer here is a question of price over usability. As described above, the mirror lens is shorter than it's equivalent ordinary lens! A mirror lens does tend to be cheaper for the same focal length. The down side is to do with the operating window; a mirror lens will typically have a narrower depth of field than its comparable ordinary lens. In other words around 2 stops less than a comparable lens; simply it will need more ambient or artificial light than a normal lens.

Q3 What is the difference between prime, wide angle and telephoto lenses?

A prime lens has a fixed focal length. A 35mm prime lens shows you the kind of view and perspective that you are used to seeing with your eyes on a crop sensor camera. A 50mm prime lens shows you the kind of view and perspective that you are used to seeing with your eyes on a full frame camera. Wide angle lenses (can be had as telephoto or prime lenses) open up the field of view, bringing more of the top, bottom and sides of your subject into the picture. Telephoto lenses are rather like telescopes. They increase the magnification and bring far subjects closer. The longer the lens, the higher the number in its focal length and the greater the magnification. The wider the lens, the lower the number in the focal length and the more the scene is opened out for you. As a rule of thumb prime lenses are usually considered to be sharper, telephoto lenses mean that you do not need to keep changing your lens.

Q4 If the aperture controls the amount of light overall and the shutter controls the amount of time the light is coming through the lens, surely they both control the exposure of the sensor to the light. Why does a camera need shutter and aperture?

For different types of picture. If you are shooting fast action and want to freeze it, you use a fast shutter speed, coupled with a wide aperture (f8 or less). On the other hand, in some pictures depth of field is important. This is something that can be controlled with the aperture. So for landscapes you would use, say, a small aperture (f11 or greater) for a great depth of field and couple that with a slower shutter speed. In the end, as you so rightly say, the same amount of light reaches the sensor, but it has been controlled in different ways for different subjects and different effects.

Q5 I have an autofocus camera with auto focus lenses and thought that meant every picture I took would be in focus. What am I doing wrong?

Assuming that you have a correctly matched lens to camera and that the mechanics and electronics are functioning correctly, there are two further things to consider. Are you shooting at the correct shutter speed and Depth of Field (DOF). The rule of thumb for the shutter speed is to have a shutter speed equal to one over the focal length of the lens; eg 500mm lens = minimum shutter speed 1/500s. The depth of field question is more complex. Basically f2.8 is a very shallow depth of field. F22 is a large depth of field. So the rule of thumb here is the smaller the f number, the more of the image either side of the point of focus will be out of focus.

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