Wednesday, August 31, 2011

Focusing your DSLR even while wearing glasses

Nikon D200 with vertical gripAccording to the Vision Council of America, about 75% of US adults use some sort of vision correction. About 64% wear glasses, and about 11% wear contact lenses exclusively, or part time with glasses the remainder of the time.

It seems safe to assume that the same percentages apply to photographers in general, including travel photographers, and those on vacation.

Unfortunately, many photographers who wear glasses seem to have difficulty focusing their DSLRs and composing their images due to their inability to see the image fully in their camera's viewfinder, “edge to edge.”

Fortunately, for most photographers who wear glasses, there are both equipment solutions and techniques to help with focusing and image composition.

We need to start with the photographer's glasses. Prescription lens glasses are either single-focus or multiple-focus. Multiple-focus lenses can be bifocals, trifocals, and progressive lenses. Of these, the most difficult to use while photographing are trifocals and progressive lenses.

When looking through the viewfinder, a photographer's vision must be the same, “consistently,” so that corrected, every time you look through the viewfinder, the focus screen and viewfinder display will be in sharp focus.

Since multiple-focus glasses, have small areas of discrete focus on the lenses, it is essential that photographers look through the same area of the lens each time they look into the camera's viewfinder, so that they will have the “consistency of vision” necessary to produce sharp, well composed images.

With a “consistency of vision” the DSLR's “diopter adjustment” can be properly configured to allow each photographer to see the focus screen with its AF (auto focus) and grid markings, and viewfinder display in sharp focus.

Looking through the viewfinder, you adjust the “diopter adjustment” via its control until the viewfinder display, focus screen's focus points, and AF area brackets (if any) are in sharp focus. Once that's complete, an image on the focus screen will display the image's focus accurately.

According to your vision, the camera's built-in “diopter adjustment” may be inadequate. If it is, many camera manufacturers, such as Nikon, sell “correction eyepieces” which attach to the viewfinder. They are available in both “+” and “-” corrections. Coupled with the “diopter adjustment,” and your glasses, most vision correction can be accommodated.

Many photographers who wear glasses add an eye-cup, with or without magnification, on their viewfinder to enhance looking through it. If the viewfinder eyepiece is hard plastic instead of rubber, and doesn't have some sort of rubber bumper, an eye-cup is an especially good idea, as it will prevent your glasses from being scratched.

Even taking into account the above, getting your images in sharp focus and getting solid composition is not a slam dunk. Understanding your camera's features which can assist manual focus, and understanding how auto focus works, is critical to good focus.

Auto focus, in DSLRs, generally works passively, not by emitting a signal to determine distance, using contrast detection or phase detection. Both these methods rely on contrast for achieving accurate auto focus.

For stationary subjects, for example, (I'll discuss focusing on moving subjects another time.) if you can, focus on an area of your subject by selecting a focus point which corresponds to a sharp edge or pronounced texture. If you're using a single focus point, make sure it's one which is a cross-type sensor which uses two-dimensional contrast detection, as it gives higher focus accuracy.

This may mean that you need to first focus, and lock it in, recompose your image, then make the photo. Frankly, it's often the case that you can't expect to achieve sharp focus by composing your image and immediately pressing your shutter release.
Note: There are a number of reasons you may not achieve a sharp focus quickly enough; low contrast subject, slow focusing lens, previous focus setting far from new setting. To eliminate that problem, prefocus your camera/lens before making your photo.
Most DSLRs have a “focus indicator” in their viewfinder displays, which can be of enormous assistance when you are manually focusing, especially for those who wear glasses, and whose vision is corrected.

I recommend the use of the “focus indicator,” even for those with excellent eyesight to at least confirm your focus is in the right range when focusing manually.

Also, if you're having trouble getting your focus dead-on at times, you can increase your depth of field to give yourself extra latitude in focusing, to allow your focus to be off a bit.

Many who wear glasses can't see the image in the viewfinder edge to edge, which makes composing each image accurately, a little more difficult. This occurs because when you wear glasses, your eye is not right at the viewfinder eyepiece, but instead back a bit, behind your glasses' lens.

You can compensate for this by literally looking around your viewfinder, by moving your eye behind your glasses up and down and side to side to see the edges, while keeping your glasses steady to maintain your “consistency of vision.”


James said...

Ned, this article is a DSLR saver. I was ready to chuck it. I didn't know Nikon sold corrective eyepieces. I've just ordered one after reading your article and speaking to my eye doctor to get the right one. She knew about the eyepieces. but didn't know I had a DSLR.

Thanks very much.


Julie said...

Wonderful article Ned. I wear progressives. I tried the techniques you mentioned when out shooting this morning and I finally am able to get consistent focusing.


Harvey said...

Great article. I didn't understand how to adjust the diopter, but now my viewfinder is sharp as a tack.


Agitater said...

Do left eye shooters have a bigger problem with glasses/viewfinders than right eye shooters? I'm a right eye shooter. Personally, wearing glasses for the past 17 years, I've never once mashed my glasses against a viewfinder cup or eyepiece. Most often, I simply look above my glasses and can get my eye almost fully in contact with the diopter-adjusted viewfinder for a full view. If the stock diopter doesn't work for your vision, get at replacement from Nikon or your Nikon authorized dealer.

For best results, wear your glasses on a retainer loop and just drop them before a shot. You'll get your left or right shooting eye fully engaged with the viewfinder and you won't ever mash the glasses into your face and you won't ever accidently mark up or scratch your glasses. Works for me.

Ned S. Levi said...

That's a very interesting question you posed Howard. I'm a left eye shooter myself.

I don't know why we left eye shooters would have more trouble than photogs using their right eye. Of the people who have written to me about their problems with glasses, and mentioned which eye they use, it's generally split down the middle.

From what I can see, the characteristic which defines who's having the most trouble wearing glasses and using a DSLR, is the type of glasses they're wearing. Those with progressive lenses are having the most difficulty.

When I wear glasses, I wear progressives, and they are a pain to use while shooting. Fortunately, I rarely wear glasses until the end of the day (night). I wear contacts while shooting.

I think your ideas are great for those who can shoot without wearing their glasses. The idea of the retainer loop is great.

Unfortunately, for many, they need to wear glasses to shoot due to their particular eye problem(s). For example, those who have more than a minor degree of astigmatism find the the diopter adjustment, even coupled with the corrective eye pieces available from the camera manufacturers insufficient for their needs, and must wear their glasses when shooting.

According to a study published in Archives of Ophthalmology, nearly 3 in 10 children (28.4%) between the ages of 5 and 17 have astigmatism. A Brazilian study found that 34% of the students in the city studied were astigmatic. The most recent study of adults I've found showed that nearly 1 in 3 (32.4%) of those over the age of 30 had an astigmatism of greater or lessor degree.

A number of studies in North America have found that the prevalence of astigmatism increases with age.

So, for those who can follow your example, and drop their glasses before a shot, I would suggest it's a great idea. For those like me, who can't, we'll have to rely on technique, unless we can and do eschew our glasses for contact lenses, or refractive surgery.

Prasanna said...

Thank you for this article. I adjusted the diopter and I'm able to see the images in the viewfinder clearly without glasses.

Ned S. Levi said...

Thank you Prasanna. I'm happy you were able to make the adjustment which will help you improve and enjoy your photography more.

Networx said...

A great article that will really help me get the most out of my Lumix FZ300 Bridge camera. I've avoided using the viewfinder because I wear progressive lenses and have been too impatient with the results so far to bother. That big LCD screen on the camera is also pretty tempting for someone who's moving up from being an iPhone photographer for the most part. I will try some experiments with your methods and see if I can't get better results. It's a great camera and takes good shots out of the box but I know it can do so much more. Learning how to use it properly has been a challenge but your article really helps. Thanks.

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