Problems with Sharpness

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  One of my camera club's competitions produced a judge who (rightfully) made some comments about the perceived sharpness of many entries. Rather than arrange a workshop or lecture about the problem I thought it would be of more use to produce an information sheet that would be available to all. It took some digging around to come up with all these possibilities and I keep adding to the list from time to time. This is more or less an expanded copy of a printed information sheet I produced, later it will grow to be more user-friendly and sport some photos to illustrate the problems.

 There are a number of reasons for loss of sharpness and some detective work with a magnifier may need to be done. Use the 4" x 6" prints or the 35mm slides or B/W negatives and a decent magnifier of some sort in the range of 4x to 8x for prints,  maybe 8x to 12x for 35mm negatives and slides. Buying a purpose- made loupe from a camera store probably is the most convenient way to go. The prices range from maybe $10 to many hundreds but a good usable one may be found for around $50. A good quality general purpose magnifier from an optical shop is an excellent and cheaper alternative. Make sure you take a slide or print or two along to test them on. If you have an enlarger then you have all you need to examine negatives and with a projector you can examine slides. After a few samples it becomes fairly easy to see what the problem is, often without the magnifier.
 


 Now for some possibilities and causes.
Fuzzy more or less all over
really bad lens
mediocre lens at maximum aperture
camera shake
grainy fast film
underexposure
out of focus
dirt and filth on lens and/or filter
really bad printing
problem inside camera with pressure plate
SLR mirror alignment problem
SLR focussing screen problem

 
Fuzzy corners and edges but sharp in centre
really bad lens
mediocre lens at maximum aperture
bad printing

 
Fuzzy in unexpected places
out of focus
camera shake
depth of field problem
subject movement
SLR mirror alignment problem
SLR focussing screen problem
film kinks
automatic camera oddities

Really bad lens. A bad lens can cause a number of problems but where sharpness is concerned you will find that inferior lenses may be able to give good results but only at an aperture of maybe f/8 to f/16. Maybe the lens contrast is low which makes the eyes think it is less sharp.
If using your camera in auto or shutter priority mode and depending on film speed and the light, your camera may have selected an aperture at which the whole frame is slightly fuzzy (due to lens characteristics) despite correct focussing. This effect may not be readily discernable on a 4"x 6" print but will become noticeable if enlarged to 8"x 10" or more. Get used to evaluating prints in full sunlight, that way the eyes give the best performance.
A bad lens may have problems like loss of contrast, bad colour rendition, flare, colour fringing, small maximum apertures and lack of close focussing. Cheap zooms are the usual culprit. Good zooms can be built but they are more expensive, usually of more limited zoom range and only approach the quality of a good fixed lens.
The first solution is always to buy the "standard" fixed lens for your camera, you will find more use for it than you will think. It can also be the comparison lens for quality (when evaluating another lens to buy) and it doesn't have to break the bank. An example - the Nikon 50mm f/1.8 lens performs better than the 50mm f/1.4 which is a lot dearer and either lens performs better than any zoom at the same aperture, plus giving the advantage of the larger aperture when needed. At a camera club outing or a local friendly store, try to borrow a better lens for a few shots and see if your photos improve.
If using a compact auto everything camera, then there is not a lot to do except maybe make sure you use quality ISO 400 film. You lose a bit in grain size but more than make up in the way the auto mechanism chooses better apertures and speeds than it would if using ISO 100 film. If you still get bad pictures taken in good sunlight, then ask about the problem at your club or photo store or on the Internet through one of the Photo Forums (found on my Links page).

Mediocre lens at maximum aperture. This situation is really the same as the above section but maybe is not so apparent until the lens is at its most open aperture. You could try using the lens at a smaller aperture but the real solution in both cases is to use better lenses. "Professional" (=expensive) zooms or good fixed focal length lenses are the answer. With just a 28mm, a 50mm and a 100mm made by the camera manufacturer you will be happy for a long time, plus you have the better maximum apertures to work with.
My little collection is at present 20mm, 35mm, 50mm, 55mm macro, 85mm,105mm macro, 180mm and a 28-105mm and a 75-300mm zoom. I know I'm a bit critical of zooms, but there really are good ones available (there are also bad ones around, so do be careful). It's cheaper (and lighter) to buy fixed lenses than it is to buy zooms of similar quality to cover the same focal lengths.
A handy zoom though can make all the difference of getting a picture and missing it, while I would still be fooling about in my camera bag finding and fitting that other lens. That's why I like landscape and still life!

Camera shake. This is probably the most common cause for unsharp pictures. I've heard that Kodak estimate that 90% of shots they process will show some degree of camera shake. Shake can be caused by the photographer due to natural body movement that is present at all times or by a jerky shutter button depression. Another cause is being buffeted by wind (or earthquake if in L.A.).
The most difficult cause to eliminate is shake caused by the camera itself. A simple viewfinder camera with a leaf shutter has the least and lightest parts in it that move when a photo is taken thereby contributing little shake. An SLR camera has a mirror that has to crash up out of the way before the shutter fires. Then the diaphragm clatters down to its operating diameter. If the camera has a focal plane shutter then there is another cause of shake as the shutter has mass and in moving causes a slight reaction to the camera body. This reaction, combined with the quite substantial aftershocks of the mirror slapping up can cause problems. The noisier and clunkier the sound of mirror and shutter, the more likelihood of shake. A heavy camera body helps dampen it. My semi-joking suggestion at one club meeting to Araldite a brick to the camera would help a lot to steady it. Go to a camera store and compare the noise and vibration in a second-hand old pre-electronics single lens reflex, then compare that to the latest Minolta/Canon/ Nikon/Pentax expensive models. Great improvements have been made in dampening camera induced shake. More expensive cameras usually used to have a mirror lock or mirror pre-release that allows the mirror shock to die away before the shutter is fired. Most modern SLRs do not have mirror lock up as the mirrors are now  motor driven and the acceleration and deceleration of the mirror can be controlled nicely to avoid most shake. The shutter and diaphragm are not so much of a problem as their mass is a lot less than that of the mirror.
To help reduce shake the good book says to use the reciprocal of focal length as the slowest shutter speed when forced to use slow speeds. Example 50mm, don't go slower than 1/50sec  (=1/60 nearest setting) and for 300mm then 1/300 (=1/250 nearest or better 1/500). Camera shake can be seen with the magnifier or even the naked eye and is usually an equal general smearing of the whole image in all areas close or distant. Combine shake with out-of-focus areas and the cause of un-sharpness may be hard to detect. The longer the focal length of the lens, the more apparent the shake. The closer the subject the more apparent the shake.
 The nit picking department has found that shake is a lot more prevalent than first believed and examination under the microscope shows that the average person will exhibit shake in the case of the 50mm lens at 1/60 and even 1/125, so 1/250 is really recommended for the 50mm lens for critical work. This means if you are concerned about a picture and may want to enlarge it to poster size or enter it in a competition, then use a heavy tripod and remote or delayed release on the camera and mirror lock if available. For general work though don't be so fussy, just be aware of what shutter speed you're using and be careful releasing the shutter and if possible brace yourself against a wall or tree. Even a monopod helps a lot, or a camera bean bag sat on a convenient post or rock.
With automatic cameras with no shutter speed readout you are not always aware of what the shutter speed will be, so make sure when you press the shutter (steadily not jerkily) that you keep holding the camera steady for a little longer. Most cameras do have some means of warning you of possible shake, be aware of what the indication will be by reading your camera manual. This advice is generally not needed for good daylight but for low light situations. It is easy to take a shot, move the camera then hear it go "click" as it completes the shutter timing. Nice smeared photo. Been there, done that.

Grainy fast film. This problem is easy to spot because eyeball examination of any plain area such as sky or bare ground will show the graininess. This graininess softens the edges of any detail and makes it look less sharp. The answer is to use better film. Cheap odd brands of film made with outdated technology will exhibit bad grain structure. My current favourites are Fuji Superia 100, 200 and 400 and Fuji portrait NPS 160 and NPH 400 speeds for print films. In fact, stick to latest versions of Kodak or Fuji and you will be very happy. The comments off the Internet indicate that Kodak and Fuji are probably ahead of everyone else by a few years of technology. Don't be afraid though to try other brands, they just may have the colour and contrast results you are looking for.

Underexposure. Some films, particularly Kodak 400 print film (in 1999), get very grainy when underexposed. This has the same effect as the previous paragraph. Usually the graininess will be worst in the shadowy areas (less exposure to light) of the print. The fix is to use a better film or try and overexpose to get the grain size down a bit. Print film can usually handle up to about 2 stops overexposure very easily. Slide film has to be spot on.

Dirt and filth on lens and/or filter. This one is a bit unlikely as the dirt would have to be piled on pretty thickly. I have seen cameras with filters on the front that were totally covered in dust. If you take a photo pointing towards the sun, the light shining on the dust would make the image have a lot of flare thereby losing contrast and possibly sharpness. Shading the front would help a bit, but cleaning off the muck would be the best idea.
Maybe you were at the zoo and a giraffe licked your lens and you forgot to clean it  (the lens, that is). Keep lenses clean using a squeezy puffer and micro fibre cloth (available at any reasonable camera store). Giraffe licks may require lens tissues and lens cleaning fluid to improve the situation. Don't use your handkerchief or the front of your shirt like I saw a knowledgeable(?) camera shop assistant do.

Problem inside camera with pressure plate. A fairly improbable event but is worth checking for next time the camera is empty. Easy to check when the camera is open, the plate on the back cover should be clean and smooth and flex lightly on its mountings to hold the film flat when closed. As I said, very unlikely and it would be a repair shop job to fix. Also make sure the rails on the camera body that guide the film are clean.

SLR mirror alignment problem. It could be that the mirror is not seated or returning properly or positioned properly, so when you achieve apparently correct focus through the viewfinder the optical path length is different to what it should be so that what's in focus on the screen will not be in focus on the film. This can be found by critically examining the negative/slide and see if the point of correct focus is always in front or behind where you focussed using the viewfinder. A repair shop job to fix.

SLR focussing screen not seated correctly. In some models the screen can be replaced, maybe it's not seated properly giving a similar effect to the mirror problem above. Try reseating the screen or get a repair shop to look at it.

Bad printing. If using a commercial printer, complain loudly and/or go elsewhere in future but be really sure it's their fault before you go off the rails. Just get a test reprint done somewhere else to see how it turns out.  If doing your own printing, then the enlarger focus was bad or you decided to use a really bad enlarger lens at maximum aperture, or maybe you should get a better magnifier or microscope for checking enlarger focus. Certain types of enlarger lamp have been known to cause problems with print sharpness.

Out of focus. Some tele lenses, like my Sigma 75-300 APO zoom will manually focus "past" infinity (to allow for dimension changes in high temperature situations). This has the effect of making the whole picture unsharp at maximum aperture when manually focussing not very carefully. Another circumstance is where you may have taken a grab shot thinking the camera was in autofocus mode when it was in manual focus mode and left at the wrong distance for what you needed. Another variation on that is having the camera in the mode where the shutter will fire regardless of the focus condition, maybe best to change it to the mode where the shutter won't fire until the focus is correct. Possibly try again, or if the shot is gone forever, then too bad, be more careful another time.
Focus problems show up differently to shake problems, as the sharpness (focus error) changes with distance. Dots tend to become bigger circles with mis-focus, with camera shake the dots are usually smeared in one direction. A little examination will show what areas are in focus (if any) and what are out by what degree. From the relative distances of the objects and their sharpness or lack of it you can see whether you focussed too close or too far. If like in our camera club "fences" competition you had the main area of the fence in focus but a nearer post and a further post were unsharp, then you have a depth of field problem.
Another problem could be that the autofocus mechanism failed. A lot of things can disturb and fool autofocus. Fog, mist, shiny surfaces, windows and clouds being the most likely culprits. Certain patterns on the object you're focussing on can fool certain types of mechanism. Photographing boats at a marina is a good example where things can go wrong, all the vertical lines of masts and stays can confuse the circuitry into focussing at the wrong distance. Sometimes it just decides not to work for any apparent reason. If a shot is really important, take your time and switch to manual focus to guarantee the results. When taking a scenic photo with an all auto compact, get in the habit of using Infinity Lock (sometimes called Landscape Mode) if available. That will at least stop the auto focus mechanism vainly trying to focus on a cloud or mist or passing bird or all those masts and wires.

Depth of field problem. As described above, the image is sharp at one spot but gets fuzzy closer to the camera or further away from the sharp spot. In that case you should have used a smaller aperture (use aperture priority or manual mode or an automatic mode probably called "landscape" or has a pictogram of mountains) and employed the depth of field preview or the depth of field scale or tables for your lens or maybe used a different focal length that will give the desired depth of field for the same aperture.
If in doubt and the shot is important to you, take a few pictures at different apertures. Film is cheap, life is short. When you get down to the small apertures, the shutter speeds may get a bit long, so maybe it's time to set up the tripod.
One trap is to believe the information on hyperfocal distance focussing to get infinity "in focus" (see Depth of Field Revisited by Harold M Merklinger). Careful examination of an enlarged print taken using the depth of field scales on the lens will show problems at the far limits. For  90% of the time all will be well but that favourite shot that you want made into a poster will just not be right. In general for scenic shots with any lens in any film format (where you want the distance in focus and a good depth of field towards you) focus on infinity and use an effective aperture of 3mm to 5mm (use depth of field preview button and look in the front of the lens at the aperture, or do some quick maths).

Subject movement. This is usually obvious because something moved when the shot was taken. The situation probably was that you were using a slow shutter speed and the wind moved the trees or the person started to move their arm or the car was moving past too fast.  As a result some parts of the picture will be sharp and some parts not sharp. Sometimes the effect is only just noticeable, which is disturbing to the brain because you can't quite see what the fault is.
If photographing from a moving train or car then the whole scene will be smeared by a low shutter speed, sort of like a grand camera shake. The solution is to use faster shutter speed and/or a faster film. Most compacts should use ISO 400 to get reliable results. Package SLRs with their 35-80 or 28-80 zooms should use  400 film to achieve a sensible range of shutter speeds. If using professional zooms or fixed lenses with f/2.8 or wider apertures then 100 or slower film is able to be used.

Film Kinks. Another finding on the Internet has been that a very critical examination of pictures/slides sometimes reveals a narrow, slightly out of focus vertical area. This is caused by the kink of the film as it comes out of the cartridge if the camera has sat for a few hours or more without a picture being taken. The picture taken on the neg already in place will be fine, it's the next one taken that may show the fault. The lesson seems to be that you have to realise that this fault may happen and either use the film all in one session, or sacrifice the second picture. This assumes auto film wind, with manual wind it depends on if you wind on or not to the next frame after the current shot. Kodachrome is the worst film for this fault, others are only slightly affected, if at all.

Automatic camera oddities. Most automatic compact cameras in low light conditions will fire the flash and use slow shutter speeds of maybe up to as slow as 4 seconds depending on type. This means shake is inevitable. With some cameras you have to select a mode with slow shutter speed and optional flash. The trap is that in low light the flash will fire and give good exposure to things in the foreground but it will also use the slow shutter speed and things in the background won't be reached by the flash  but will have the benefit of the long exposure, hence a chance of movement in the background figures. The foreground will be well exposed by the flash and will look sharper.
Careful examination of the foreground will reveal the underlying smear caused by shake with a similar obvious amount in the background. I have seen many examples of this problem some glaringly obvious, some a bit more subtle.



 Be aware that you may have more than one of these problems combined in the one picture. This will make it harder to decide what is wrong. Investigative work on other pictures taken with the same lens may have to be done.


© 2000 Guy Parsons     
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