In the pursue of sharpness

There comes a moment in the life of almost any photographer, when he is no longer satisfied with the sharpness of the pictures he makes. Everyone else finds your photos just great, but you see the unsharp edges, the blur here and there, the light washing around that twig, and you aren't happy. Welcome to the support place for that widespread illness of homo ludens photographicus, called Sharpitis!

Of course, you know as well as I do that sharpness is not the most important ingredient of a good photo. But still, it's just so nice to look at really sharp pictures! So, here you can read about my collected wisdom on getting the sharpest photos.

First of all, let's clear up a common mistake. Many people know that sharpness depends on many factors, and liken it to a chain, which is only as strong as its weakest link. Not so! Final sharpness of a photo will always, inevitable, be weaker than the weakest link in the chain! This is so because the final degree of unsharpness is a geometrical composition of all individual blur contributions. For the photographer it means that he has to care about all things that cause unsharpness, not only about the most important one! Only if one contribution is much more significant than all others, does it make sense to leave the others alone.

A photo can never be perfectly sharp. On the other hand, it can be "sharp enough": This happens when the final resolution of the photo is so much better than that the one the viewer with the best eyes can see, that even this privileged person cannot see any blurriness attributable to the photo. Of course, this depends a lot on the level of magnification used, and the distance from which the photo is seen. Age of the viewers also plays a big role! At the end of the story, there will always be someone able to see some blurriness, so it is worthwhile to strive for the very best sharpness possible!

The most important factors causing unsharpness are these:

Imprecise focusing

Don't say that you are free of this. Nobody can focus with perfect accuracy! While there is no excuse for sloppy focusing ruining a picture, even the best photographer can not always get the last bit of focusing perfection out of his equipment.
It helps to know that on many focusing screens the split-image does not agree perfectly with the matte screen! Often one or the other tool is more accurate, and this depends on how the camera was calibrated. It also helps to know that the split-image tool is a little bit sensitive to the exact angle from which you look at it. Try to center your eye before focusing. When you see one half of this tool going black, your eye is drastically off-axis! With longer lenses this becomes more critical, just as focusing them is more critical than for shorter ones.

It's a widespread myth that a photographer with myopic or astigmatic eye will necessarily misfocus. The focusing tools such as split-screen and matte screen are NOT sensitive to refraction errors in the eye! The only truth in this is that if you can't see the focusing screen sharply, then you can't correctly focus either! So, wear your prescription glasses if necessary, or use correction lenses on the viewfinder (not practical for astigmatic eyes!).

You say, you have automatic focusing, so you are free of this problem...? Unfortunately you are worse off! Autofocusing is often less precise than manual focusing. It has the advantage of speed, though, so it can produce sharper pictures than a photographer taking a snapshot in a hurry with manual focus might.

Wrong focusing

This is a very common and very pitiable reason for messing up a photo! Picture the following scene:  You want to take a candid shot of your girlfriend lying in a flower field. You know that it doesn't look good to have the main subject centered in the picture. But your split-image focusing tool is in the center! So, you center the finder on your girlfriend's eyes, focus to perfection on her using the split image, then turn the camera slightly away so that she is on one side in the field, and you press the shutter. And when the film comes back from the lab, you are terribly disappointed: Your girlfriend is out of focus, while the flowers behind her are sharp! And the worst thing is that she laughs about your misfortune!

Many hobby photographers do this mistake time and again, and fail to understand it. The reason for your unsharp girlfriend is that photographic lenses have a reasonably flat field, not a spherical one. Suppose you were 4m away from her. When you focused on her, you adjusted the lens to 4m. When you then aim to place her on one side of the picture, your lens will be focused for the plane that is perpendicular to the lens axis, and 4m away. That plane is considerably behind your subject!  If your girlfriend is at 30 degrees from the picture center, then the distance ratio is 0.86 (the cosine of the angle). So, your lens should have been focused to 3.46m, which is the distance along the lens axis to the plane which is perpendicular to the axis and passes through your girlfriend's face!

What can you do without using math in the field? Simple: Compose the picture first, and focus after that, while keeping the camera in the exact position at which you will shoot. That means, on most cameras you need to use the matte screen instead of the split-image tool. The reward for the slightly bigger effort will be a sharp girlfriend!

The more expensive autofocus cameras may be able to take care of this problem, as long as they provide some way to decide correctly where you want the focus to be. The cheaper autofocus cameras simply can't take this kind of photo correctly using autofocus, since they measure focus only in the center. If you have such an autofocus camera, switch off the autofocus and focus manually. With a point-and-shoot camera that does not allow manual focusing at all, the only hope is to look for an object that is at the correct distance, focus there, and then compose. That object needs to be closer than your subject is. And you will need some math, or at least some guesstimation!

Camera shake

Almost every photographer knows that old rule of thumb: When shooting free-handedly, use a shutter speed that is one second divided by focal length, or faster. But this rule will by no means guarantee pictures free of motion blur! It is just a good rule to have a reasonable chance that motion blur will not be the main contribution to overall unsharpness.

A lot depends on how steady a hand you have. If you can stand very still, with slightly spread legs, hold the camera with both hands, press your elbows against your body, hold your breath and time the triggering between two heart beats, then you should be able to go to considerably longer speeds with no detectable motion blur! I have used 1/15 with a 50mm lens with good results - but there is no guarantee! It's impossible to know if the picture will be usable. For safe, reliable motion-free pictures you may need to go as high as five times the rule of thumb, that is, using a 50mm lens at 1/250! Photographers suffering from Parkinson's disease need to go even higher, and strong wind may require very high shutter speeds too! It depends a lot on what degree of motion blur you can accept. No picture will be totally free of it; the issue is to reduce motion blur to an insignificant level. This level may vary a lot, according to conditions, and to quality expectations!

A tripod is a good tool to combat camera shake. A sand bag (often called bean bag) is even better, since it won't resonate as the tripod does. Mirror lock-up is a marvelous tool, but a fully mass-compensated mirror mechanism is even better! It comes as a corollary that point-and-shoot cameras can be a lot better than reflex cameras regarding shake! After all, they have no heavy mirror slapping around. And flash photos are almost always free of visible motion blur, because the flash duration is very short.

Subject motion

Many people can't hold still. The same is true with animals. But even grass and flowers will move with the slightest breeze! If you want to stop this motion on your picture, you need to do some math. Choose how much blur is acceptable to you. Considering the distance and focal width, calculate to what transverse distance the acceptable blur translates. Estimate how fast the things move. The transverse distance divided by subject speed gives the shutter time. Of course, you must be working inside a given system of units for this to work out, like distance in meters, shutter speed in seconds, subject speed in meters per second.

If a subject moves linearly at a relatively constant speed, like a car, racing horse, airplane, runner, etc., then the best way to make a photo is not to freeze the subject's motion, but to swing the camera along with the subject. In this case, background blur will be given by the above calculation. The lowest shutter speed you can use while still getting your subject sharp is given by the accuracy of the camera motion. Typically this would be 10 to 20 times slower than when not moving the camera! If you can move the camera rather accurately, a good rule of thumb is to apply the same minimal speed as you would for a static subject with that lens!

Depth of field limitations

A lens will deliver its best sharpness only at one very specific distance - the one at which it is focused. Any objects at different distances will be blurry. You can close the aperture to reduce this blurriness of out-of-focus objects, but however much you stop your lens down, still the sharpness will be best at the distance the lens is focused at. The depth of field markings on many lenses are just a guide that tells you over which distance range the sharpness is acceptable under a given set of conditions, for each aperture setting. It does not mean that the image will be sharp over that range! Still, a smaller aperture will always produce a larger depth of field.

The depth of field limitation is a basic fact which cannot be eliminated. So, a good photographer includes it in the composition. Very good photos can be made by intentionally letting the background blur while having the subject sharp. It helps if the subject is rather flat! A very useful feature that unfortunately is lacking on many cameras is depth of field preview. It's simply a lever that closes down the diaphragm to the set value (it is fully open during focusing in most reflex cameras), so that you can see on the matte screen how your picture will really look. I would not consider buying a reflex camera without this feature!

Lens aberrations

Countless people blame the bad quality of their lenses for their unsharp photos. In most cases the main reasons for unsharpness are other than lens quality, but still it is true that not all lenses are born equal, and that even the best lenses suffer from aberrations. These are most noticeable at wide aperture settings, and with the vast majority of lenses they are more noticeable in the periphery than in the image center.

To stay clear of excessive sharpness penalty from aberration, it's a good idea to use the smallest aperture you can - but read the next section before doing that!


What would happen if you had a perfect lens, one that is absolutely free from aberrations? And if you could focus it to perfection? You would expect it to produce a perfectly sharp image, right?


To produce that perfect image, the perfect lens would also need to have infinite aperture! Now try and buy a 50mm f/0 lens! Tell me if you find one! :-)

The problem is that the very fact that the lens diameter is not infinite causes image degradation. Light rays bend slightly at the borders of the lens, or the diaphragm, and this causes blur. This is a physical phenomenon called diffraction, and no lens manufacturer in the world can avoid it, unless he employs Harry Potter.

Diffraction gets worse as the aperture gets smaller. So, use the widest aperture you can - but read the previous section before doing that! :-)

With most 35mm photographic lenses, diffraction starts becoming noticeable at f/11 or so, dominates at f/16, and is terrible at f/22. Even smaller apertures are useless for 35mm work. Since diffraction depends on the angle spanned by the lens, wide angle lenses suffer more than tele lenses at a given aperture setting. You may get away shooting at f/16 with a 200mm lens, but with a 15mm you should avoid f/16 and even f/11!

Larger formats than 35mm tolerate smaller apertures, simply because a larger amount of diffraction blur is acceptable on the larger frame! Likewise, smaller formats are more affected, which is why typical digital cameras with their very small CCDs (compared to 35mm film) have lenses that stop down only to f/11 or so.

Camera misalignment

A photo camera cannot focus directly on the film, which has to be kept dark until exposure. So, reflex cameras focus somewhere else: A matte screen, or an autofocus sensor. It is fundamentally important that the distance from the lens to these focusing surfaces be exactly the same as the distance to the film!

In all cameras I have ever seen, this distance is adjustable. In reflex cameras, either the mirror or (more commonly) the focusing screen has set screws that allow adjustment. As a camera ages, and the mirror hinges wear out, this adjustment must be corrected, or the camera will give badly focused pictures, however careful the photographer is! An especially bad case is when the mechanism wears in such a way that the mirror position becomes unpredictable. Such a camera must either be repaired or replaced.

Non-reflex cameras can be even more tricky, since they often don't even focus through the main lens! But just as with the reflex camera, proper alignment keeps things in check.

Film flatness problems

Film is thin, flexible stuff. It may bulge out of the perfectly flat plane. The result is that the film will not be where it is supposed to be, specially near the image center, and the image will be unsharp. Some high-end cameras have vacuum systems to suck the film against the pressure plate. Most cameras do without this. Given that the picture area of 35mm film is small, and the borders are wide, it should be possible to achieve excellent film flatness without such vacuum methods. With large formats it's a different matter!

Film resolution

Even if your lens could produce a perfectly sharp image, the photo would not be so sharp! The film isn't able to record infinite sharpness. This has to do a little with graininess of the light-sensitive material and the color dyes, but graininess is by no means the same as unsharpness! Another important contribution to film unsharpness is simply the thickness of the light sensitive layers. The lens is focusing at one specific distance, but the film emulsion covers a range of distances that can be quite noticeable!  So the film records a slightly misfocused image anyway.

Processing effects

A standard processing will neither add nor subtract much sharpness. But it is possible to do sharpness-enhancing processing. This usually consists in certain agitation patterns of the developer that make contrasted edges stand out compared to even surfaces. The effect is very similar to sharpness enhancement in digital images. It does not imrpove the image resolution, but only makes the images look sharper, at the cost of increased graininess. By the way, grain often makes a picture look sharper than it would look without grain, since it adds detail, even if this detail is totally artificial and "untrue"! Of course, real picture resolution is certainly not improved by grain!

I wonder how much sharpness can be lost by diffusion of silver halide or dyes inside the gelatin. Not much information seems to be available on this.

Copying or projecting losses

At this point you have you negative or slide. To enjoy it, you need to enlarge you negative onto paper, or project your slide against a screen. Both processes involve many sharpness losses of the same kind that happen when making the negative: Imprecise or incorrect enlarger or projector lens focusing, projector vibration, enlarger or projector lens aberration, diffraction, screen or paper resolution limits... But at least the subjects won't move now!

After all these chilling news,  I would invite you to do a simple exercise: Take some of your latest pictures, look at them, and repeat with me:

Given all the above, my pictures are incredibly sharp!!!

A good question is how much sharpness can be achieved, and how to achieve it. The simple answer is that a good lens, properly used on high quality material, may be able to resolve up to 100 lp/mm, meaning that objects sized 5 microns on the film will still be visible! Some people claim even slightly better values. On the other hand, most color photography work falls far short of this, and for much work such a resolution exceeds the real need.

In several occasions I have run lens tests, both for my own lenses, and for other people's ones. The process I use is this:

Two USAF resolution test charts are taped to a wall and photographed with the lenses under test at various aperture settings. The camera is mounted on a stiff tripod and all precautions are taken to minimize shake. The film used is fine grain black-and-white (Kodak T-Max 100). Under a microscope, the smallest discernible line image is identified and its size on the film is computed, for both test charts, on each image. The pictures are taken in such a way that one test chart is at the center, and the other at a specific distance from the center. Then curves can be drawn for each lens over its aperture range.

Below is a graph of my latest test, involving all reflex lenses I currently use (April 2002). The continuous lines represent data at image center, while the broken lines are data at 12mm radius. The criterion used to determine limiting resolution was "the smallest line pairs at which the lines could still have been counted by eye, in at least one orientation". This is not very scientific, and it tends to give slightly optimistic values, so take my data with a grain of salt. But at least, the graph should give an idea and be a reasonable comparison of my lenses!

The lenses tested here are the following, in order of focal length:

- Tokina 17mm f/3.5, Pentax-K mount
- Cosina 28mm f/2.8, Pentax-K mount
- Pentax SMC-M 50mm f/2, Pentax-K mount.
- Pentax SMC-A 135mm f/2.8, Pentax-KA mount
- Vivitar zoom, 75-205mm with macro, constant f/3.8, Pentax-K mount
- Russian (I don't know how to spell the brand) 1000mm f/10 Maksutov catadioptric, Pentax-K adapter
- Kalimar 2x teleconverter, Pentax-K mount

The theoretical diffraction limit at image center was added to the graph, as a handy reference of performance vs. possibilities. The graph contains actual measured values, which include any measuring error, tripod shake effects, focusing errors, and so on.

As you can see, each lens starts from a certain resolution at full aperture, and when stopping down it improves, reaches a peak, and then again reduces quality because of diffraction. At first I was surprised by the two sharpness peaks exhibited by some lenses, and the drop in between. I asked an optical engineer about this, and he explained that such curves are perfectly normal: The higher peak is the "natural" one, and the other peak at larger aperture is where the designers aimed when calculating corrections for the aberrations! According to the optical engineer, this target aperture for best correction is often about 70%, which would be one stop down from fully open.

Some comments are in order. For example, note that the 50mm from about f/11 onwards tracks the theoretical limit quite closely. I would think that most of the difference between the limit and the actual curve is attributable to the losses in the film. The very high peak of the 50mm at 12mm center distance at f/8 is probably a measuring error, caused by fringe interference, or maybe at that aperture the focus changes, so that given the field curvature the image is better focused in the periphery than the center! I did not retouch focus between individual shots, and stopping down a lens can indeed change its focus a slight bit!

The very high resolution of the 17mm at center at f/8 seems to be true, given the rest of the curve. Unfortunately it looses a lot in the periphery, but this is to be expected from a lens as wide as this!

The 135mm lens stops down to a position marked f/32. But from the curve it is obvious that the true aperture at this setting cannot be smaller than f/26 or so, or it would have to be a Harry Potter lens to exceed the theoretical diffraction limit! The two curves taken with teleconverter also exceed the limit at small apertures. I suspect that this converter is not a full 2x, which would explain the effect.

Since the 1000mm has no aperture adjustment, it was plotted as a circle around the only data point, instead of a curve.

The test photos were made at distances of less than 1 meter for the 17mm lens, ranging to about 8 meters for the 135mm and longer lenses. But most long lenses will deliver best sharpness at infinity, or close to infinity setting! This may explain at least in part the generally lower performance of the longer lenses in my test.  Maybe a test at the longest practical distance would place the longer lenses a bit higher!

This graph can give good advice at how to use the lenses. It's clear that the 17mm should be used at f/8 whenever practical, the 135mm at f/11, and when the latter is combined with the teleconverter it should be set at f/8, giving a true f/16. The 28mm and 50mm lenses provide good performance over the range of  f/4 to f/11, giving more room for creativity than the other lenses. Unfortunately the graph also shows that the 1000mm lens is unsuitable for serious photography because of its very low resolution, and that the same is true, to a lesser extent, for the zoom/teleconverter combination.

The graph gives a good starting point for the optimal use of my lenses, but there is a lot more to making sharp photos! For example, the test almost eliminates shake and depth of field issues, which in most practical work are very important.

Keep in mind that this graph only shows limiting resolution of the lenses. Much more important for photo quality is the contrast delivered at about 10 lp/mm!  I have measured this too, but the results can only be used as relative data, since I have no way to calibrate them. I used my film scanner to measure the ratio between the density of the centers of black and white lines at the 10 lp/mm groups, and graphed this data. There were very strong fringe interference phenomena, which, added to my scanner's nonlinearities, made some curves shoot far out of the graph and even bend backwards! I plotted them just as measured, limiting the graph to the interesting zone. You should visually smooth the peaky curves to get usable ones!

It's interesting to see that once the measurement quirks are discounted, this graph tells pretty much the same as the sharpness test! This makes me think that in practice one can use a contrast measurement just as well as a limiting resolution measurement, to determine lens quality. But there are some differences. The most notable one is that at fully open diaphragm, the contrast drops more than the resolution. Another is that contrast is often better in the periphery than at image center, while sharpness is better near the center. The most notable exception to this is the Tokina 17mm, which shows extremely high contrast in the center, and only average in the periphery.

How much sharpness is needed?

This depends on what you will do with your photos. If you want to make photos of your kids for the family album, and not enlarge them to more than 10x15cm, then you don't need much sharpness. 3 lp/mm may be all you can discern when looking from 25cm distance, which is a normal reading distance. That would be 12.5 lp/mm on a 35mm negative! As long as the negative is clearly better than this, it will not compromise the quality of that rather small print. Looking at my graph, you can see that any lens except the Maksutov is up to the task, only that when using the teleconverter the widest apertures should be avoided.

On the other hand, if you want to project slides to a size of 1.5 x 1 meter, and have the audience sitting at 1.5 meter distance, which would be typical in a home slide show, the situation is different: People will be able to discern about 0.5 lp/mm on the screen, which translates to 21 lp/mm on film. Your slide needs to be clearly better than that, so that the final quality depends more on the projector. 40 lp/mm is a good value to aim at. This rules out teleconverter use almost completely, and leaves some lenses quite hard pressed. Keep in mind that 40 lp/mm comes close to the limit of many color films! The much higher values stated by film manufacturers (typically 120 to 160 lp/mm) are valid at very high subject contrast and very low resulting contrast on the film, which is not usable in practice.

A similar case as the slide is a negative that will be enlarged to a large print, if this print will be viewed from close distance. And when you want to crop a negative and enlarge only a part of it (for example for panoramic prints), even the best possible resolution may be too poor!

On the other hand, an image intended to be displayed on a computer screen has the lowest sharpness requirements of all. For example, all photos in my galleries ar scanned at 500 pixels vertical resolution (horizontal resolution varies according to the selected format). Most of them show an entire 35mm frame. 500 pixels can resolve roughly 160 line pairs, which on the original slides (horizontally oriented) would be less than 7 lp/mm! If the original slide resolves at least 15 lp/mm or so, the scan will be almost indistinguishable from that of a top quality slide!

Most people set their screens at 1024x768 pixels, or at most at 1280x1024. That would be the equivalent of roughly 10 to 12 lp/mm on 35mm film, so that an original having a resolution of 25 lp/mm is good enough to let the computer screen be the main limiting factor in image quality! That's also why so many people are happy with their 1  to 4 megapixel digital cameras - after all, a 1024x768 screen has less than  0.8 megapixels! Even considering that a pixel of a digital camera usually records only one color, a 3 to 4 megapixel camera can fill a 1024x768 screen just as well as an excellent scan of the best 35mm original!

So, people who only intend to make digital images for today's computer monitors can forget this entire page. But those who still like to make real photographs, and strive for high quality, need to consider points like the ones presented here!

Practical advice for sharpest photos

Avoid consumer grade zoom lenses and teleconverters, if possible. The zoom tested here is a relatively expensive one, compared to the most common zooms sold today, and is still worse than modest prime lenses. Most zooms tested on other occasions gave significantly lower quality than prime lenses. Especially, avoid super-zooms spanning a range of 1:5 or greater! Try to buy decent lenses, but don't overpay! In a brand comparison of different lenses, the famous and expensive ones were not drastically better than the reasonably priced middle class! On the other hand, some of the cheapest lenses really were quite bad. Try to steer a middle course to get the best performance/price ratio. Interestingly, a few rather expensive lenses also are quite bad, while many really inexpensive lenses are surprisingly good! If you can, make some test pictures with a lens before you buy it, specially if it is an expensive one!

For any given lens, try to use it near its optimum aperture whenever practical. This optimum aperture is somewhere between two stops down from fully open, to about f/16. The optimum is more towards the open side of this range when the lens is of high quality and/or of short focal length, and more on the f/16 side when the lens is of low quality and long focal length.

Depart from this optimum aperture setting as required in each case. Some reasons to choose a smaller aperture are:

- you need more depth of field;
- there is too much light (a bad reason! Better use less sensitive film!);
- you want to blur motion (waterfall photos) (this is really a "too much light" situation!);
- you want to be able to focus carelessly and still get decent sharpness (a very bad reason!).

Among the reasons to use a wider aperture are:

- you want less depth of field, to make a subject stand out from the background;
- you don't have enough light (better use a tripod and go for a good aperture setting!);
- the combination of wider aperture and faster shutter may give better sharpness due to less shake;
- you need to freeze subject motion through fast shutter speed;
- using flash at a large distance (a stronger flash would be better!).

Avoid camera shake as much as possible. When hand-holding the camera, hold it with both hands, press the elbows against the body, lean against some support, don't breathe while taking the picture, time the shutter release between two heartbeats. Don't drink strong coffee before taking photos, if you are sensitive to coffeine. At any shutter speed that is not really high for the lens used, try to support the camera with a bean bag, press it against a wall/tree, or use a tripod. Do carry a small but sturdy table tripod among your basic outfit! It's very light and very useful! Such a tripod can be pressed against a wall too! If the camera is firmly supported, such as on a tripod, use a cable release, or better than that, either a wireless remote control or the self-timer. This will avoid shake introduced by touching the camera. Specially with reflex cameras, avoid shutter speeds in the neighborhood of 1/8 second even when using a tripod, since at such speeds the mirror shake is most noticeable! Either faster or slower speeds are better than 1/8 second!

Do not use filters when it isn't necessary. Many people have UV blocking filters or 1A color filters permanently on their lenses. This degrades image quality. The degradation comes not so much from optical imprecisions of the filters, which according to my tests are insignificant for a UV filter and produce less than 10% sharpness degradation for a polarizer. They come mainly from light loss, which, all other parameters being equal, forces the shutter speed to be slower and thus motion blur to increase. Most filters are uncoated, and thus loose 8% of the light by reflection alone! A typical decent quality UV filter will absorb perhaps another 4% of the light, making for a total loss of 12%, so that you will have 12% more motion blur when shooting at a given aperture. Polarizers typically loose two thirds of the light, so that shutter time will be three times slower and motion blur will be three times worse!

I don't mean to say that you should never use filters. Some filters, especially the polarizer, can often be extremely useful, offsetting the image degradation they introduce. The point is to avoid using them when they are not needed! Most modern films are not really UV sensitive, and the chance of any UV radiation to pass through the several different types of glass in a photo lens is slim indeed. So, UV filters are simply not needed! A 1A color correction filter may make sense when shooting slides that should look like sun-lit while in fact the scene is shadowed and lit by blue sky... but when shooting negatives, anyway the lab making the prints will destroy the subtle pink tone introduced by that filter! And the reason most people bring up to defend their use of UV or 1A filters, which is protecting the lens from scratches, makes sense only when photographing a sand storm. I have been shooting without such a lens protection for many years, I have cleaned my lenses countless times using a simple rag, and they are still in good shape.

Now think of how much flare an uncoated filter fully exposed at the very front of your lens can cause, compared to how little flare the multicoated lens elements back inside the tube can cause. My contrast tests made with the 50mm lens at f/2 (which is really an overly benign way to test!) show a 10 percent contrast loss for the UV filter, and a 20% loss for the polarizer!  This should make you remove that UV filter now! If you absolutely want to stick something in front of your lens, get one of those collapsible rubber shades! It is cheaper than a filter, looks bigger if that's important to you, and can actually increase the quality of your pictures! Just be careful to avoid vignetting.

Check your camera periodically for focus accuracy, and especially check it if you have any suspicions that it may not be optimally adjusted!

When having subjects at different distances, choose an aperture that will give enough depth of field, and set the focus for an intermediate distance that is properly weighted for the relative importance of the subjects. Usually it's better to have more sharpness on the closer subjects, and often it's better take the decision and show just one subject sharply, intentionally blurring the other through a wide aperture setting!

Use good quality film. If using negatives, exert great care in selecting the lab that will do the enlargements. Don't be afraid to change lab if the quality is not good! If using slides, get a good projector and a grainless screen! It's absurd to buy a 500 dollar lens for the camera, use it at f/8 for best sharpness, and then project the slides through the wide-open 20 dollar lens of a low grade projector onto a coarse-grained pearl screen! And please, place the projector at screen center height, not on a low table!!!

And the most important recommendation for sharp pictures: Do focus accurately and correctly!!!  Check focus just before shooting, because some lenses tend to move on their own! Trust the matte screen more than the split-image, and for off-center girlfriends, NEVER use the split image!

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