Here’s the problem. You are getting older. Month-by-month, year-by-year, your eyes are aging. Just as joints and muscles become less flexible, so parts of your eyes harden and are less adaptable. You may find it more difficult to read small print at close distances.
The condition is called age-related long-sightedness, or presbyopia. It is not an illness or disease – just the result of having had lots of birthdays. People with perfect eyesight in their youth can expect to develop symptoms between the ages of 40 and 50.
Fortunately, for most photographers, the solution is simple. EOS digital cameras feature built-in dioptric correction. This is controlled by the little wheel to the top right of the eyepiece. Set this correctly and you will not need to keep your glasses on when using the camera.
But what’s wrong with wearing glasses? Do you really want the inconvenience of removing your glasses as you bring the camera up to you eye and then replacing them as you lower the camera?
Well Canon has thought of that too. The rubber surround on the viewfinder eyepiece means that you can press one of the spectacle lenses up against the camera to see the entire viewfinder frame without the risk of scratching the glass. But you still need to adjust the built-in dioptric correction to get a sharp viewfinder image while wearing glasses (it will be a different setting to the one without glasses).
The EOS digital camera built-in correction range is from –3 to +1 dioptres. This should be adequate for most photographers. However, if you can see the AF points getting sharper, but the dioptric correction wheel does not bring them into focus, you might need to extend the range. This can be done by adding a dioptric correction lens to the viewfinder eyepiece.
Dioptric correction can only help with presbyopia, myopia (short-sightedness) and hypermetropia (long-sightedness). It will not help with astigmatism or other eye conditions. Here, you need to see an optometrist. If you are prescribed spectacles, you might need to wear these while you use your camera. This is not a problem. Adjust the camera’s dioptric correction to see if this helps.
Dioptric correction lenses date back to the days of film cameras. Apart from the EOS 1, 1N and 1V, these cameras do not have built-in correction. Instead, Canon produces a range of adjustment lenses which slip over the viewfinder eyepiece. The lenses are available in different strengths, from –4 dioptres (for short-sightedness) to +3 (for long-sightedness).
There are three ranges of Canon dioptric adjustment lenses:
Adjustment Lens E
This fits most EOS digital cameras (the exceptions are listed below). It is available in ten strengths: –4, –3, –2, –0.5, 0, +0.5, +1, +1.5, +2 and +3 dioptres. It can be used with Rubber Frame Eb, which provides a soft rubber surround to prevent the scratching of spectacle lenses.
Adjustment Lens Eg
Designed for the EOS-1D Mark III, 1D Mark IV, IDs Mark III and 7D. This is available in 7 strengths: –4, –3, –2, 0, +1,+2 and +3 dioptres. Each lens comes complete with rubber frame and is ready to attach directly to the viewfinder eyepiece. Eg frames are fitted with release grips which must be pressed before the frame can be removed from the camera. This is an improvement on the Adjustment Lens E which slides on and off the viewfinder with no lock.
Adjustment Lens Ed
Designed for film cameras with the larger viewfinder needed for eye-control focus – EOS 3, 30, 33, 5, 50, 50E. Available in ten strengths: –4, –3, –2, –0.5, 0, +0.5, +1, +1.5, +2 +3 dioptres. Each lens comes complete with rubber frame and is ready to attach to the viewfinder eyepiece.
You will notice that there is no –1 dioptre lens in any of the ranges. This is because the designation is not the power of the dioptric lens itself, but the power when it is attached to the viewfinder.
A useful feature of the dioptre unit is that simple addition or subtraction is all that is needed when using two or more lenses together. So a +2 dioptre lens used with a +3 dioptre lenses gives a +5 dioptre power. A +3 dioptre lens used with a –1 dioptre lens gives a +2 dioptre power.
As there is a –1 correction built into the camera, every correction lens sold by Canon is actually +1 dioptre more powerful than its designation. A correction lens marked +2 is actually a +3 dioptre lens, for example (+3 dioptres becomes +2 dioptres when combined with the camera’s –1 dioptre lens).So a correction lens marked –1 dioptre would actually need to be 0 dioptre – a piece of blank glass with no optical power. This explains why the ranges include a 0 dioptre lens. It’s actually a +1 dioptre lens, which becomes 0 dioptre when combined with the built-in –1 dioptre lens. This is useful because it cancels the built-in correction lens.
The missing correction lens
All EOS viewfinders, for digital and film cameras, have a built-in correction of –1 dioptre. This is because many people either suffer from slight short-sightedness, or will do in the future. If you have good eyesight the –1 dioptre lens should not cause any problems. Your eyes will automatically adjust to take account of the built-in lens, and you should not even notice.
Do you need correction lenses?
Correction lenses are useful for film cameras, but the built-in correction of EOS digital cameras will be enough for most photographers. Only if you have severe long or short sight will you need extra correction.
Make sure you test the dioptric correction setting from time to time. If your eyesight is changing gradually, you might not realise the viewfinder is out-of-focus. Turning the dioptric correction wheel can make a big difference to the sharpness.
Setting the correction
What is the best way to set the dioptric correction? Start by removing the camera lens. Then aim the camera at a brightly lit sheet of white card or paper, or at a white wall. You should be able to see the AF points.
Rotate the dioptric adjustment wheel to the left or right until you see the sharpest view. Make sure you go past the sharpest view, and then back, so that you know that you have the best possible setting. The wheel has around 24 click-stop positions. This is more than enough accuracy. There is no index point and nothing to tell you the level of correction entered.
If you plan to wear your glasses when taking photographs, make sure you wear them when setting the dioptric correction.
Read the rest of this article in the January-March 2011 back issue of EOS magazine. Available as print and digital edition.
Try before you buy service from EOS magazine. Order several different strength corrections lenses and return the incorrect ones for a full refund.
Useful viewfinder accessory for low-angle work and landscape images. With dioptric correction and zoom level from 1x to 3.25x.
Canon dioptric lenses
Does the image in your EOS viewfinder seem less sharp than it used to be? Your eyesight might be changing. Fortunately, Canon has a simple solution to solve the problem.
Camera compatibility: All EOS cameras. Check details below for exact compatibility with different lenses.
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