How to select the sharpest aperture ?

Discussion in 'Nikon' started by orcama60, Feb 1, 2010.

  1. Hi guys, and thank you so much in advance for whatever help you can share with me. Sorry for the silly question, but I am confuse about this and I would like that somebody clear it up for me and plain explain the formula / technique or steps to follow to select the sharpest aperture. Maybe this is not relevant but I do have a D300 ( Nikon 16-85 mm and 70-300 mm VR ). I have made some investigation about this and there are some formulas to apply to select the sharpest aperture. Is there any simple way to find out which aperture is the sharpest without having to apply math to get the result ? I am not bad at math, I am just simply saying that there should be a quickest way to do this so if anybody would like to share that info with me, please do it and I will really appreciate it. Sorry again to ask this silly question but I am inclined to details and exact and clear information. I know that I have to focus on the farthest thing I want sharp and then on the closest thing I do want sharp but how do I calculate the distance for both to finally calculate the sharpest aperture ? Do you need to be in A mode or M ? How close to the closest thing you need to be to apply this ? Where do you need to focus ? 1/3 ahead or 1/2 ahead of the closest thing ? Sorry again to bother you with this question but I am not a pro but I am looking forward to be close to it some day. Can you help guys ?
    Thank you so much again for all of your help and please forgive me for this silly question !!
     
  2. What do you mean by sharpest? f/22 will have more of the picture in focus. So ignoring everything else, I suppose if this is what you care about you should always shoot at f/22.
    In reality, you shouldn't ignore everything else.
    You may WANT part of the photograph to be out of focus.
    You'll run into other issues w/ using lenses at f/22 (which will depend on the lens).
    And the big one...usually you don't have enough light to shoot at f/22 and still have a reasonable shutter speed.
    Or maybe this isn't what you meant at all...
     
  3. Maurice, photography is not all about mathematics and formulas. There is an artistic quality that is really fun to explore.
    I would recommend you go out and experiment. See what looks good to YOU.
    I don't think its really possible to apply a formula for what you are looking to achieve, as there are just way too many variables in composing each individual photograph.
    Got experiment and have fun.
     
  4. There is no "formula" for this. A rule-of-thumb is that pro-grade lenses, in particular long ones, are performing at their best 1 or 2 stops down from the maximum. For fast f/2-f/2.8 lenses that could mean f/2.8 or f/4 is in the peak region. For wide-angle zoom lenses you might have to go to f/8-f/11 to get peak sharpness. Test your lenses and you'll find this out for yourself, with your own gear.
    If you plan on shooting at f/22 all the time the above is moot because most of the available sharpness is wasted on getting a deeper depth-of.field, which might not even serve the photo the best. Learn how to use the aperture to get the final result you wish to have.
    The 1/3 in front, 2/3 i the back rule is one of the many myths floating around in photographers' circles. Just forget it. Focus on what's most important in the picture.
     
  5. If by the sharpest aperture, you mean to say the highest resolution, then for most lenses, it is most likely about 2-3 stops above the widest aperture.
    So, for a 50mm/1.4 lens, the peak tends to be around f/4 - f/8 and then, the resolution fades beyond that because of diffraction.
     
  6. Ok guys, thanks a lot for your help. Bjorn, I will apply what you told me and most of all, I will try not to be too technical. Mark you are right about being artistic.
     
  7. There's a great book that delves into this and I strongly recommend it. It is Understanding Aperture by Bryan Peterson.
     
  8. there is no formula. generally, the sharpest image in somewhere in the f5.6-f11.0 range. the actual sharpest fstop is also in that range. the only real way to find out is to let a lab test the lens.
    if you recall the old saying "f8.0 and be there". there was a very good reason why f8 was used. that is generally going to be very close the sharpest aperture. personally, i just use f8.0 and do not worry about it.
    also, there is the matter of difraction distorsion. this is what happens to light when it poasses through a small hole. it diffracts or distorts. for c sensor dslrs this means diffraction is beginning at any fstop beyond f11.0. yes you get a lot of dof at f16-22 but it is at the price of the diffraction. whether the dof is worth it is up to you. for me, i try not to shoot at any fstop beyond f11.0. higher fstop really are no t needed anyway if a dof table is used.
    http://www.dofmaster.com/dofjs.html
     
  9. Maurice, it's not a question of formulas, or the usual 2-stop above wide open thing, though it's likely right. It is a question of you becoming intimately familiar with your very own equipment and learning to do your own testing and analysis of images.
     
  10. If you're shooting digital and not paying for film, why not put the camera on a tripod, aim it at a complicated subject with some depth, lots of detail, and edges, and try all the apertures on a lens? Skip the math and see for yourself what your own equipment does, what aperture gives you the best sharpness, how much diffraction is actually visible, and how much it matters to you.
     
  11. this is an easy one. for both your current lenses, max. sharpness will be at...wait for it...2-3 clicks from wide open at each focal length. since you have two variable aperture zooms, that means if wide open is f/4 or 4.5, max sharpness will be f/ 7.1-8. at 5.6 max sharpness will be at f/8-11. now, each lens has different characteristics/quirks at different focal lengths. so you might get sharp center and borders at, say, 135mm and f/8 with softer corners. stopping down to f/11 might increase corner performance but you might lose some sharpness in the center.you want to know your lenses inside and out, up and down at every focal length and aperture combo so you can dial in the right settings. photozone has detailed MTF charts which can help give you an idea of how lenses perform in lab settings and which aperture/focal length combo has highest resolution, but some of these findings may not be completely applicable to field situations. other than that, what bjorn said.
     
  12. Many of my favorite photos are taken at the "wrong aperture"... Have fun and be creative.
    That said, I also like to test my lenses (not on a brick wall or newspaper, but on some "scene" either inside or out) and shoot at all the different apertures (at various focal lengths) from a tripod to get to know the lens. Sometimes the wider apertures will have noticeable vignetting (I sometimes like that), sometimes a lens starts to suffer from diffraction at f11, some at smaller apertures. My 55mm micro seems to suffer a lot less from vignetting than others. I don't know why, but I do know the characteristics of the lens and shoot accordingly. This is how I discovered that almost any lens at f8 and f11, shot correctly, was as good as any other lens at f8 or f11, be they pro or amateur.
    Also, the guidelines mentioned above are, in my experience, spot on. A better "pro lens" is best 1 or 2 stops down, a "non-pro" lens (like yours) 2 - 3. On DX almost all lenses are limited by diffraction (google it if you need to know more) to f8 or f11.
     
  13. Most decent primes are at their best 2 stops down from wide open and stay that way right up until diffraction kicks in. Some zooms and less well performing lenses require stopping down further (especially to get sharp corners) so do some testing with mirror lockup and a tripod. No maths required ;)
     
  14. Ok guys thanks for the input. Very useful advises and I will apply them from now on but, for a f/2.8 lens, the sharpest aperture will be f/5.6 - f/8 ( 2 above the widest right ? ), how about if I have to select f/2.8 for a low light picture ? How will balance that out to make the picture the sharpest possible ? For this shallow depth, probably only the center ( 1 inch ) will be sharp, how about the rest ? I do have the book of Brian Peterson ( Understanding Exposure ) but in that book, he does mentions also that the "Who Cares" apertures are precisely f/8 - f/11 and encourage to use the large and short apertures to be more creative. I also understand that being creative does not necessarily means to have a very sharp picture. I am clear about the concept to be 2 - 3 stops above the widest to get the sharptest picture but how do you make your pictures sharp when using large apertures ? For example, if I use f/4, the subject will be sharp in relation to the background, but how to make the foreground, the sharpest possible when selecting large apertures ? Does the focal length affects that ? If so, what should be the proper distance to the subject to get the best result ?
     
  15. You can use this tool in dpReview to see for yourself how the center resolution starts to drop beyond f/6.3. Just push the slider of the aperture and you will see how the MTF behaves.
    http://www.dpreview.com/lensreviews/nikon_50_1p4g_n15/page4.asp
     
  16. You can look at the lens reviews on Photozone - one of their charts shows the resolution of lenses at various apertures.
     
  17. how about if I have to select f/2.8 for a low light picture ? How will balance that out to make the picture the sharpest possible ? For this shallow depth, probably only the center ( 1 inch ) will be sharp, how about the rest ?​
    f2.8 on aps-c really isn't such a problem people sometimes make it to be. Camera / subject distance matters too, take test shots and get comfortable with your gear.
    I shoot at f1.4-2 on aps-c and 35mm and f2.8 on 6x6 all the time. Things can get very shallow indeed so make sure you focus on something important. Rest? Compose your image so that it doesn't matter. After that forget 100% crops and take a look how the image looks at the size you're actually going to use it, be it print or screen. Does it look sharp enough? Great.
    Take basic Canon 50/1.4 for example. When you look at Photozone tests you'll see that its performance, especially in corners on 35mm, is rather poor wide open. Yet there are tons of photos taken with that lens at f1.4-2 that look sharp as anything. Interesting.
    In low light decreased sharpness from large aperture is usually the last concern. Other variables tend to rob most test chart peak performance way before that (subject motion / camera shake / high ISO / muddy light). Luckily I find that superb lens sharpness is rather over rated when it comes to low light stuff and that human eye is a master of fooling itself with perceived sharpness. If an interesting subject is in focus and looks sharp compared to the rest of the scene then everything's fine, even though the subject may be actually wayy softer than the lens is capable of. Same goes for striking contrast. Light, contrast and composition come before lens sharpness.
    Light and color. If you shoot in dull light your images won't look very sharp even though you stopped down to optimum aperture etc. Take a shot in bright light and try to get good contrast (including how different colors match/mismatch) between the subject and background, use fill flash if needed, and you can do fine even with a kit lens.
     
  18. maurice, with large apertures, you're not going to get sharp corners with most lenses. hopefully a 2.8 or faster lens will be sharp in the center wide open, tack sharp in the center and borders at f/4, and about the same but with better corners at 5.6.
    in low-light, forget about corner performance; usually that doesn't matter as long as your main subject is illuminated and sharp. if you need detail, like a low-light landscape, use a tripod, a narrow aperture and a long exposure time.
    if i'm using my wideangle at dusk or in the evening for a landscape pic, i set up my tripod, close down the aperture to f/8 or 11, dial in the lowest ISO value, and take an exposure of, say, anywhere from 1/30 to 6 seconds.
    if i'm shooting nightlife in a club with my 2.8 zoom and no flash, i'll do the opposite: set aperture to 2.8, dial in the fastest shutter i can get away with, then bump the ISO accordingly (or set it on Auto with a max of 1600). of course sometimes, i might actually want a lower shutter to induce motion blur to give the effect of action or movement, rather than a static "freeze". the trick is to select a focal point like a face, which ideally remains fairly sharp while arms and legs move.
    the other thing with fast lenses capable of shallow DoF is the "illusion" of sharpness. having a defocused background and a nicely focused main subject gives the illusion that the subject is sharper than it actually is, because the degree of sharpness is then relative to the entire frame. so a portrait at 2.8 might actually appear to stand out (or "pop") more than one shot at 5.6 due to selectively controlling the depth of field, though the 5.6 pic should show more detail. this is called DoF isolation. of course, you'd want to use a narrower aperture if you want more of the scene in focus.
     
  19. Thanks Eric, very useful tips that I will apply from now on. I really appreciate this and thank you guys again for taking the time to help me out.
     
  20. Just go out on a sunny day, put the camera on a tripod and live view on and look at how the image changes when going from aperture to aperture. The optimum aperture depends on the lens and on the subject. Familiarize with how your lenses perform at different apertures.
     
  21. Line pairs?
    Lenses used to come with a spec sheet for each lens by the manufacture. This spec sheet would have a curve showing line pair results for each aperture in use at a specific wave length. Is this what you are interested in?
    You have to control all other conditions, at least you know what to expect from the lens you bought.
    You may be able to find this on line.
     
  22. Go to the museum or art galleries and look at some of the work by the masters.
    Some of the best images ever made are out of focus.
    Sharpness is over-rated
     
  23. You didn't specify if you are talking sharpest depth of field or sharpest resolving power. The answer to the first one is pretty much self-explanatory. The answer to the second one is dependant on the lens but a good rule of thumb is 2 to 3 stops down from the maximum aperture.
    Jon Kobeck , Feb 02, 2010; 09:02 p.m.
    Go to the museum or art galleries and look at some of the work by the masters.
    Some of the best images ever made are out of focus.
    Sharpness is over-rated​
    You can never have TOO MUCH SHARPNESS. If the image is too sharp for your tastes, you can always take the sharpness down a notch in Photoshop or whatever editing program you use. It's always better to have it and not need it all than not have it and wish you did.
     
  24. Thanks Scott for clarifying to Jon Kobeck. This is the same principle of having a picture overexposed or underexposed. It is better to have it underexposed than overexposed because it is easier to fix it. Better have sharpness rather than not. I do agree and thank you for understanding Scott.
     
  25. This is an interesting thread.
    Regarding lens sharpness there is the theoretical and the actual. Theoretically a lens is sharpest at its wide open aperture, but practically, for the lenses we are talking about, it doesn't work that way. Sharpness is also a factor of sensor density with digital. i.e. the more dense a sensor is the smaller the "circle of confusion" and the more critical things like focus, motion blur and lens quality becomes.
    In fact at any aperture the focal plane is thin, stopping down the lens increases the apparent depth of field but again that is dependent on the density of the sensor. Here is an interesting link that illustrates this: http://www.tawbaware.com/maxlyons/calc.htm Note that if you reduce the circle of confusion the focal plane or "in focus" segment gets smaller. I find the DOF indicator on the lens to be inaccurate with the D3x and I suppose those lines would work with film but not with all digital cameras.
    Generally 2-3 stops down from wide open will yield the sharpest image but it's not totally reliable to use that rule of thumb. The best way to tell is to make some simple tests yourself with your lenses.
    You can check out some of the popular lens testing web sites too. They will give some indication of optimal aperture for a specific lens on a specific camera but this is only an indication and you may find your own results to be different. Check out these links: http://photozone.de/Reviews/overview - http://www.slrgear.com/reviews/index.php
    Happy shooting !
     

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