This article is one in a series of articles aimed at photographers starting out in photography. For an article on how to use exposure compensation, you might want to take a look at that article once you have read this one.
The Lens Cap and Its Function and Effect With Different Kinds Of Cameras
The purpose of the lens cap is to protect the front glass element of the lens. It may protect the lens from scuffing caused by careless handling, or in extreme cases from the scouring effect of sand in a sandstorm.
If you use an SLR (a single lens reflex) camera then you don’t have to worry that you forgot to remove the lens cap when you take pictures.
An SLR looks like this, or rather this is a picture of an SLR with the lens removed.
A Single Lens Reflex Camera
The reason you don’t have to worry about whether you remembered to take off the lens cap is because the light comes in through the lens, gets bent upwards vertically by a mirror and then horizontally (again by a mirror) and out through the viewfinder at the back of the camera. So if you can’t see anything, the lens cap is still on (or you are in a pitch-black room).
In case that is not clear, here is a little diagram showing the light coming from the model, traveling through the lens, getting bent upwards by the first mirror, getting bent again by the second mirror, and entering the eye of the photographer:
Light Enters an SLR Through The Lens
You put your eye up to the viewfinder and if you can’t see anything it is because the lens cap is still on. If the lens cap is on you will see this:
Black - Everything Is Black
If the lens cap is off, you might see this:
I Can See A Cat
That’s an SLR. Now For Something About Rangefinders
Rangefinders work differently. The light comes in through the lens, but the photographer doesn’t see the scene through the lens. Instead, he sees through a little window in the body of the camera near the lens.
Rangefinder cameras look like this:
A Rangefinder Camera
The main disadvantage of an SLR over a rangefinder is that an SLR has to have a hump at the top to accommodate the mirror arrangement. And one of the mirrors has to swing out of the way at the moment the shot is taken.
That is because at that moment the light has to reach the film (or the digital sensor), and it can’t do that if there is a mirror in the way.
That means there is another disadvantage to SLRs, and that is that exactly at the moment the shot is taken, the photographer cannot see the scene. It blacks out for a moment when the mirror swings out of the way.
That is why SLR are called reflex cameras. It is because the mirror swings out of the way and then swings back again.
Now looking at things the other way around, the main disadvantage of rangefinders over SLRs is precisely that the light does not come in through the lens.
That means that the photographer does not see exactly what the lens sees. The lens lets in the light a little bit to the side of what the photographer sees.
You might think the difference is very small. After all, the viewfinder the photographer sees through with a rangefinder is very close to the lens. But it is not so, and it is very easy to prove this to yourself – like this:
Hold one finger up at arm’s length. Hold a finger from your other hand up, but near your eye. Now line the two fingers up so one is hidden behind the other.
Now just move your head an inch to the left or right. See? Now you can see a bit to one side of the finger further from you. But because the frame of the film in the camera is only so big, it will have lost a bit of what can be seen to the other side of the finger.
This is called parallax. What it means is that you might think you are taking a photograph of something, but in fact you might chop off a bit of the scene on one side and get in a bit more than you intended on the other side.
This problem is worse when you are taking a photograph of someone and you chop part of their face off. It might not matter so much if you are taking a photograph out in nature. A tree here or there might not be so important.
The next disadvantage of rangefinders is that they are hard to focus with long lenses.
Long lenses means long focal length lenses. They magnify and home in on things more than short focal length lenses do.
In the photo of the SLR above, the lens has been removed from the camera body. This ability to switch lenses and put long lenses on SLRs and still focus very well with them is one of the reasons that SLRs have won the day and why there are comparatively few rangefinders on the market.
Digital
Nothing has changed with digital cameras. Digital SLRs (dSLRs) and digital rangefinders have exactly the same advantages and disadvantages that SLR and rangefinder film cameras had.
You are probably wondering how those cameras that show the image on an LCD at the rear of the camera fit into this scenario. Look out for the follow-article about these kinds of cameras.
