Testing your lens sharpness with just a few photos
Posted: 12 Feb 2021 23:02
Thank you to Rob for letting me post here. These are usually written for one person who asks me something. Then I try to edit it to be useful to you who are reading this now. Some people ask me questions about my posts via messenger. If you have a question, you can ask it here as others may have the same question. If you want to contact me direct, my name is Eloha Peoples (and yes that is an opinion about social media if you spell my first name backwards) on messenger (facebook).
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Testing you lens sharpness with just a few photos
There seems to be a large interest in sharpness or lenses. I personally think sometimes this is overrated. We often pay for sharpness that is not seen in the final photo we create. Especially if it is for post on a photo site or social media. Still, it is useful to know how sharp your lenses is and when it is sharpest. It is also good to understand how your autofocus will work. I am attaching 3 photos. These were not lenses test, but rather photos I took so show what the sharpness looks like.
I mentioned before looking at the jpeg size to determine which shot is sharpest before editing. That is still the fastest way to know which of your shots is sharpest.
In Photoshop, to see the sharpness of your lens, just open the RAW file. Do not do anything in in ACR or Lightroom. Then go to Filter > Stylize > Find Edges. The darker areas will be the sharpest. When I want to learn how my lens works, I do this on a fodo ball field taking a photo of the grass from 3 yards, 10 yards and depending on the lens, 50 or 100 yards. This tells me how the lens performs at different focal lengths. If using auto focus (and most of us do this all the time), I take 3 shots. One shot I focus on infinity and then once it is focused, I focus and shoot. The second one I focus as close as I can, then focus at the chosen distance. Then I focus, release the shutter and refocus. If you do this will your lens, you will find that all 3 shots are focused at a different distance. At slower apertures, the subject will be in the sharp area, but what is in focus in front of or behind it will be very difference. With fast apertures, you may find that the subject is not the focus point. This is common. PDAF goes to a set distance based on what is sees initially. That has always needed fine tuned (which the better cameras allow you to do) for each lens camera position. CDAF goes back and forth until it finds focus. In order to save time, it does this until it is good enough, not until it is the maximum best. The direction the lens is moving affects where this is. Back button auto focus is usually more accurate on the Olympus cameras I have used. However is seems slower. Some shots, you cannot half hold and then focus. You have to shoot when it happens. Continuous auto focus also has its own quirks. The only way to know is to do this test on your lens to see how it functions. Knowing your lens allows you to get sharper photos (if that is your goal which many times it is not for me).
If you can rent or use a friend's lens, this is also the fastest way I know to compare 2 lenses at the distances and apertures you will be using. The other thing this is a great help with is sharpness and dof. You can see the dof and also how closing the lens more may lower sharpness. It also tests if you have good lens. If one side is sharp and the other side not for example, return the lens and get a better copy. Lens have curvature. The grass pattern will show this curvature. If you are wanting to shot something that is relatively flat (a group shot for example or a building) this will tell you where to set your focus point. If you focus in the center, the curvature will mean near the edges are softer. If you know the midpoint of the curvature is 1/3 off center (as an example), then you set the focus point there and sharpness will be the same across the frame. At least to the limit of the lens as few lenses will have maximum sharpness at the very edge (which giving breathing room to your subject takes care of. The other thing this can do is help you cull photos or know how to process or crop. A photo with sharpness over a wide area of the frame may benefit from different processing than a photo a photo with a limited sharp subject.
Now for some examples: The one of the robin shows what front focus looks like. You can see the grass in front of the robin is darker than the the grass around the robin. This is because I was focused on something close and then used autofocus. I know this lens needs focused twice if I am going from close to a more distant subject. The second shot was focused properly. The EM1s are fast enough I just know to take 2 shots to get the best focus with this lens. In something like this that may be cropped quite a bit, this is handy to do before trying to edit. In this case I saw the crop would not work and culled the photo. 40-150 150@5.6
In the cemetery shot you can see focus is right on the tombstones. You need to look at the grass where there is a lot of detail. You can see the darkness is pretty even in front and back of the subject. This is what a good shot looks like. Except! Look at the left side. It is not as dark as the right side. Is is obviously softer. I know the lens is good and this is not the lens. In this case it was "flare". Not flare that shows up as a spot on the photo. But light hitting the surface of the lens can lower contrast of an image making it appear less sharp. In this case I was riding with my camera on as my wife drove. I just stopped and did some quick shots. I did not put on the lens hood. I was not shooting into the sun and it did not appear to me (at the time) to be required. I know better and should have used the lens hood. It did improve with an adjustment brush in Lightroom. This is a case of where doing this quickly can determine how to process a photo. 12-60 60@5.6
The bridge across creek was shot @6.7 for greater dof and sharpness. While you can see some limits to supposedly great dof with a wide angle at a optimum aperture, it also shows the obvious fact that you need detail (grass is commonly available) and the other objects without fine detail show nothing about the lens.
Summary:
Many lens tests you read our done at one distance with a flat subject. This has little to do with how sharp your lens will be the way you use it. There are variances in individual lens and I only know of one place that tests many samples to get an average This still does not tell you how you how sharp your lens will be for the photos you take. I would suggest that if you do this for your lens when you get it, from then on you will know how to get the best from it for the photos you take. Also you will know how to get the best from auto focus for your lens and camera. Since my memory is not as good as yours, I have a small piece of tape with the optimum aperture and any autofocus notes taped in my bag for each lens. Some may have a close and infinity aperture as they can vary. If you use a lens for one thing, then of course you only need to test it at those distances.
**************************************
Testing you lens sharpness with just a few photos
There seems to be a large interest in sharpness or lenses. I personally think sometimes this is overrated. We often pay for sharpness that is not seen in the final photo we create. Especially if it is for post on a photo site or social media. Still, it is useful to know how sharp your lenses is and when it is sharpest. It is also good to understand how your autofocus will work. I am attaching 3 photos. These were not lenses test, but rather photos I took so show what the sharpness looks like.
I mentioned before looking at the jpeg size to determine which shot is sharpest before editing. That is still the fastest way to know which of your shots is sharpest.
In Photoshop, to see the sharpness of your lens, just open the RAW file. Do not do anything in in ACR or Lightroom. Then go to Filter > Stylize > Find Edges. The darker areas will be the sharpest. When I want to learn how my lens works, I do this on a fodo ball field taking a photo of the grass from 3 yards, 10 yards and depending on the lens, 50 or 100 yards. This tells me how the lens performs at different focal lengths. If using auto focus (and most of us do this all the time), I take 3 shots. One shot I focus on infinity and then once it is focused, I focus and shoot. The second one I focus as close as I can, then focus at the chosen distance. Then I focus, release the shutter and refocus. If you do this will your lens, you will find that all 3 shots are focused at a different distance. At slower apertures, the subject will be in the sharp area, but what is in focus in front of or behind it will be very difference. With fast apertures, you may find that the subject is not the focus point. This is common. PDAF goes to a set distance based on what is sees initially. That has always needed fine tuned (which the better cameras allow you to do) for each lens camera position. CDAF goes back and forth until it finds focus. In order to save time, it does this until it is good enough, not until it is the maximum best. The direction the lens is moving affects where this is. Back button auto focus is usually more accurate on the Olympus cameras I have used. However is seems slower. Some shots, you cannot half hold and then focus. You have to shoot when it happens. Continuous auto focus also has its own quirks. The only way to know is to do this test on your lens to see how it functions. Knowing your lens allows you to get sharper photos (if that is your goal which many times it is not for me).
If you can rent or use a friend's lens, this is also the fastest way I know to compare 2 lenses at the distances and apertures you will be using. The other thing this is a great help with is sharpness and dof. You can see the dof and also how closing the lens more may lower sharpness. It also tests if you have good lens. If one side is sharp and the other side not for example, return the lens and get a better copy. Lens have curvature. The grass pattern will show this curvature. If you are wanting to shot something that is relatively flat (a group shot for example or a building) this will tell you where to set your focus point. If you focus in the center, the curvature will mean near the edges are softer. If you know the midpoint of the curvature is 1/3 off center (as an example), then you set the focus point there and sharpness will be the same across the frame. At least to the limit of the lens as few lenses will have maximum sharpness at the very edge (which giving breathing room to your subject takes care of. The other thing this can do is help you cull photos or know how to process or crop. A photo with sharpness over a wide area of the frame may benefit from different processing than a photo a photo with a limited sharp subject.
Now for some examples: The one of the robin shows what front focus looks like. You can see the grass in front of the robin is darker than the the grass around the robin. This is because I was focused on something close and then used autofocus. I know this lens needs focused twice if I am going from close to a more distant subject. The second shot was focused properly. The EM1s are fast enough I just know to take 2 shots to get the best focus with this lens. In something like this that may be cropped quite a bit, this is handy to do before trying to edit. In this case I saw the crop would not work and culled the photo. 40-150 150@5.6
In the cemetery shot you can see focus is right on the tombstones. You need to look at the grass where there is a lot of detail. You can see the darkness is pretty even in front and back of the subject. This is what a good shot looks like. Except! Look at the left side. It is not as dark as the right side. Is is obviously softer. I know the lens is good and this is not the lens. In this case it was "flare". Not flare that shows up as a spot on the photo. But light hitting the surface of the lens can lower contrast of an image making it appear less sharp. In this case I was riding with my camera on as my wife drove. I just stopped and did some quick shots. I did not put on the lens hood. I was not shooting into the sun and it did not appear to me (at the time) to be required. I know better and should have used the lens hood. It did improve with an adjustment brush in Lightroom. This is a case of where doing this quickly can determine how to process a photo. 12-60 60@5.6
The bridge across creek was shot @6.7 for greater dof and sharpness. While you can see some limits to supposedly great dof with a wide angle at a optimum aperture, it also shows the obvious fact that you need detail (grass is commonly available) and the other objects without fine detail show nothing about the lens.
Summary:
Many lens tests you read our done at one distance with a flat subject. This has little to do with how sharp your lens will be the way you use it. There are variances in individual lens and I only know of one place that tests many samples to get an average This still does not tell you how you how sharp your lens will be for the photos you take. I would suggest that if you do this for your lens when you get it, from then on you will know how to get the best from it for the photos you take. Also you will know how to get the best from auto focus for your lens and camera. Since my memory is not as good as yours, I have a small piece of tape with the optimum aperture and any autofocus notes taped in my bag for each lens. Some may have a close and infinity aperture as they can vary. If you use a lens for one thing, then of course you only need to test it at those distances.
Glad you find value in what I write.