Lens / Aperture sharpness, I can't tell the difference!

[TheStupidForeigner]

Ok this is driving me mad.... I have read, watched and heard over and over how certain lenses are sharper than others, certain apertures are sharper, and generally how important the lens is to getting a super sharp photo....

So I bought a 50mm 1.8 prime, the sharpest lens in my tiny budget, but I REALLY can not tell any difference... Then I learnt how aperture also affects sharpness, so I took 10 shots of some magazine print at different apertures, cropped them in and flipped through.. I think there is a very slight difference from wide open to the rest but im not even 100% sure about that... The rest were all completely the same, despite slight exposure differences.

My only idea now is that maybe it is because my camera body (Canon d1100) sucks so no matter what lens I use it wont really make a difference.... But is that really the case? Or is this whole sharpness thing just over rated? Or am I just doing something completely wrong?

 

[Braineack]

look at the corners of the frames.

 

[TheStupidForeigner]

Hmmm.... Never thought of that, was always checking dead center because that's where the focus was, will need to do the whole test again making sure the focus is on the corner then.

 

[soufiej]

Your camera is fine, your ability to see still needs improvement. That's really just a process you go through, not a character flaw.

The same lens on a different camera can be better or not so better. You can pretty much be assured any testing facility for a lens will not be testing that lens with an older camera or a lower price range camera. If you haven't checked to see that your camera has the latest software/firmware updates, do that first. Then don't rely on the lens/camera system only. To test a lens on your own, make sure you've eliminated all of the other variables which could affect the image quality. That generally starts with using a tripod to assure there is no camera shake or other movement being introduced by the shooter. A tripod also assures you can have the same image from corner to corner of the image for your comparisons.

Auto focus is pretty good nowdays but it may not be your best choice in some situations. Manual focus in available on your lens and you should learn how to make the most of the feature. One lens may do auto focus better at landscape distances and less so at close in focus points. In general, I've found the 50 mm lens to be a bit better when given a manual focus tweak at close in focus points but perfectly fine when shooting distant subjects. But the new STM kit lens that came with my SL1 can focus at a closer minimum distance than the older design of the 50 mm. Read up on your specific lens and know its strengths and weaknesses. If you're trying to critique a lens, it generally helps to know how to critique a lens. However, realize the folks who criticize equipment for a living have a slightly different viewpoint than the average weekend photographer. Like the folks reviewing wine will have a different experience with this vintage from this producer than you and I will if we simply have wine with our dinner at a mid-priced restaurant. Don't know about you but I'm not so picky in that instance that I care whether it's a 2009 or a 2010.

Your 50 mm is great for some things and not always the choice for others. If you learn when to use the lens, you'll know why it is good and bad for certain situations. More importantly, if you know why your kit lens is not the best choice for some situations, you'll understand why the 50 mm is the better choice for those situations. But, if you're expecting a lens to make your photos better overall, then you are going to be disappointed. The lens is only a tool for you to learn how best to control.

When it comes to aperture, that's a fairly complex subject IMO. When doing macro or close in photography, f-2.8 is very different than when you are shooting a landscape. Focal length and focal distance both affect the depth of field you will have with a similar aperture. Therefore, if you were to set up a line of soup cans and photograph them from three feet away you would notice the effects of aperture at that focal distance. If you were to set up a line of trash cans and photograph them from forty feet away, you would notice a different effect of the same aperture. (An adjustable dof app may make your studies a bit easier here; A Flexible Depth of Field Calculator Put such an app on your smart phone to have with you in the field.) Student photographers often stop their lens down to, say, f-16 for a landscape when that is seldom the best aperture for any lens and doing so introduces other problems with available light vs shutter speed vs ISO. Reading up a bit on hyper-focal distance might further explain what's happening with your lens when you alter aperture.

A single focal length lens though is going to be superior overall to a kit zoom when you know the time to use either. But just owning the lens isn't going to make you a better photographer. You should learn your lens just as you are learning your camera. Together they form the system you will use to create better photos.

Finally, how are you viewing your images? If your processing system doesn't provide the ability to get the most from your camera's data, then it's very difficult to make useful judgements regarding what the camera is capable of achieving. If you are not yet able to use your processing software to get a higher quality result, you may be putting the cart before the horse when judging your lens. RAW files will look one way and Jpegs will look another. Know what you're looking at on your monitor before you judge the lens.

Don't assume everything about photography comes down to sharpness; Lens Sharpness

 

[fjrabon]

Yes, most modern lenses are sharp past the point of your eye being able to notice in the dead center of the frame at most "normal" apertures.

Also people #onhere are overly obsessive about sharpness.

 

[Derrel]

I think soufiej has a good thought, that your ability to see might need some improvement. There was a time when I could not understand when people said things like,"There's too much green in the skin tones," or, "This shot's sky is too cyan." Everything is a process.

 

[TCampbell]

I'm wondering what it is that you're trying to shoot that makes you so concerned about "sharpness".

Backing up a bit... there's no such thing as "sharpness" in a lens. Ultimately there's a large combination of factors... resolution, acutance, contrast, distortion, chromatic aberration, etc. and you combine all this to decide how "good" your image looks. Some issues, such as chromatic aberration, can actually be corrected fairly well in post processing.

Here's an article that might be informative on the subject: LensRentals.com - Have You Seen My Acutance

And then there are other issues such as diffraction which are impacted by the aperture size. This particular issue has nothing to do with lens quality. The physics of diffraction assume "perfect" optics and yet the effect will happen anyway. Due to the wave nature of light, a single point on a subject does not technically focus to a single "point" on your image. It focuses to something called an "Airy Disk" (named for the astronomer George Airy who first discovered it). The Airy Disk will be physically larger if the aperture you use is tiny. This means you could have the world's most flawless lens, shoot a subject at f/32, and be disappointed when you inspect it for detail as you discovered that it's not all that "sharp".

Most lenses tend to do their best work somewhere in the f/5.6 to f/8 range. If you want optimal "sharpness" and you don't need to care about depth of field, pick one of those "middle" f-stops like f/8 and you'll probably do fairly well.

Some lenses and some types of lenses are better simply as a generalization. Macro lenses (true macro lenses -- not zoom lenses that happen to have a macro range) tend to have extremely good ability to resolve fine detail. It's sort of the whole point of that type of lens. So I could take a photo with the EF 50mm f/1.8 that you have, and then take another photo with the EF-S 60mm f/2.8 Macro and you'd probably notice that the macro lens was able to resolve much finer detail.

But is it really better to resolve finer detail? For portrait work, there can be a point where the detail is just a little too fine. It's sort of like the transition from regular NTSC video to 1080HD caused viewers to notice tiny little flaws in the complexion of the actors skin. Sometimes you just don't want to reveal that much detail. My post processing software actually has a "skin smoothing" brush -- specifically so that when the skin detail is just a little too good you can reduce the detail and make the skin look healthier and younger.

There can be other issues at play... you (or your camera's auto-focus system) may actually be missing focus. Imagine if I laid out a sheet of newsprint on your dining table and we stuck a push-pin in the center. We then focus (or try our best to focus) on print right at the location of the pin... but the camera is taking a photo of that newsprint from the side -- looking downward at an angle (not directly flat to the paper as if the camera were suspended from the ceiling). If we then inspected that newsprint in our image, would the text located at the pin position really be the point with the best focus? Would the best focus be a few millimeters closer or perhaps a few millimeters farther? To do such a test we'd need a tripod because we can't trust a human not to sway by so much as a single millimeter when attempting to hand-hold a camera for a shot (and THIS can be a reason why your images aren't as "sharp" as you want.) But even if we know the camera didn't move (we used a tripod), there's the possibility that the focus system misses the focus by a tiny amount (it's usually not by much.)

If you allow the camera to auto-select it's focus point then it will pick the point with the closest focus distance. In other words, if one focus point is on your subject's eye... but another is on their nose... it's going to focus on the nose because the nose is closer. This is one reason why it's important to know how your equipment was designed to work... because knowing this, you can switch off the automatic AF selection and force the AF system to use the point you select.

 

[soufiej]

Most lenses tend to do their best work somewhere in the f/5.6 to f/8 range. If you want optimal "sharpness" and you don't need to care about depth of field, pick one of those "middle" f-stops like f/8 and you'll probably do fairly well.

IMO it's fair to say that most lenses today are "best" at their middle ranges. However, the middle range will depend on where the lens begins. The 50 mm Canon lens will begin at f-1.8 while your kit zoom lens may begin at f-3.5. That would make the 50 mm "better" in low light conditions given the same shutter speed and ISO. The wide open aperture's ability to produce a shallow dof is mostly considered a benefit over the slower kit len's limitations. Given the idea most lenses will be "better' when used in the middle range of their aperture range, the lower value of f-1.8 as a starting point will provide more working room for the 50 mm before problems begin to show up. It is, in that sense, a more "usable" lens, which would, for a lot of people, make it a "better" lens.

But you really need to know where each lens has its strengths and not just assume one is better than another based on one value. As I wrote in another post today, knowing the difference between a paring knife and a boning knife means you'll know when to make the best of either and not make an utter mess of what you're using the knife for.

Photographers have become accustomed to the idea of "zoom", which will allow them to frame a subject without much thought other than zoom. Take your 50 mm out and stand in one spot. Think about how you would go about taking photos from that one spot with a single focal length lens. The time required to see the potential of a photo and to actually get to where you can take a good shot is far different when you have one fixed focal length. If you're currently the type who simply snaps photo after photo without much thought to framing beyond using the zoom feature and making the subject more than just another snapshot, sticking to the single focal length lens for, say, a week is likely to change how you think about what you shoot.