Sharpness: Difference between revisions
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# '''Diffraction limits''' is a physical limitation that gets worse with smaller [[apertures]]. Basically the problem is that light falling on your pixel will have an airy disc shape and will ''spill over'' and contribute to neighboring pixels. This gets worse as you the [[aperture]] gets smaller. | # '''Diffraction limits''' is a physical limitation that gets worse with smaller [[apertures]]. Basically the problem is that light falling on your pixel will have an airy disc shape and will ''spill over'' and contribute to neighboring pixels. This gets worse as you the [[aperture]] gets smaller. | ||
# '''Lenses''', they are not perfect and they will create various non-idealities that will contribute to ''blur'' your images. Usually the goal is to limit these problems to the edges and corners of the frame. [[Zooms]] that cover a wide [[focal distance]] range have to optimize many different parameters ([[cost]]/[[weight]]) and can have issues at various [[focal lengths]]. | # '''Lenses''', they are not perfect and they will create various non-idealities that will contribute to ''blur'' your images. Usually the goal is to limit these problems to the edges and corners of the frame. [[Zooms]] that cover a wide [[focal distance]] range have to optimize many different parameters ([[cost]]/[[weight]]) and can have issues at various [[focal lengths]]. | ||
The picture in this section is taken with a [[Nikon 105]] on a [[Nikon D850]]. This is not a particularly ''sharp'' (or good) picture, but highlights a lot of issues that will haunt you. The lower half of the picture contains a roof part that is too close, and is therefore slightly out of [[focus]]. The air (in London) was not particularly clear, the building in the distance started to disappear in the haze, and there are plenty of chimneys that expel hot air and vapour which ''blurs'' parts of the image. There is a tiny cut out 160x100 pixels on the left side of the image, which shows actually how ''sharp'' the lens is. So anything that is ''blurred'' here is not really due to the lens. | |||
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<div class="panel-heading">'''Two main distortion types'''</div> | <div class="panel-heading">'''Two main distortion types'''</div> | ||
<div class="panel-body"> | <div class="panel-body"> | ||
[[File: | [[File:sharp_london.jpg|class=img-responsive]] | ||
[[File: | [[File:sharp_london_zoom.jpg|class=img-responsive]] | ||
</div> | </div> | ||
</div><!-- End of pan --> | </div><!-- End of pan --> | ||
</div><!-- end of col 1--> | </div><!-- end of col 1--> | ||
</div><!-- End of row 1--> | </div><!-- End of row 1--> | ||
---- | |||
===You need to look really close to see these issues=== | |||
== | <div class="flex-row row"> | ||
<div class="col-xs-6 col-md-6 col-lg-6"> | |||
Here I have an example to illustrate what is happening, it is a head on shot using [[Nikon 70-300]] of a house in Zurich, in decent light using a [[Nikon D850]] with 45 [[Megapixels]] resolution. The image on this www site has been scaled down to 1280x853, and it should look quite OK when you are viewing it on a computer. Below there are two sets of [[crops]] of 640x400 pixels, this is about 0.5% of the image. | |||
You can see that the center of the image is better defined while the sides/corners have gone ''soft''. This is actually the issue of this lens at this [[focal length]] <kbd>70mm</kbd> and [[aperture]] <kbd>f/5.6</kbd>, and it takes a lot of effort to highlight this issue. In practice you will be bothered by such things only if you zoom like crazy on all our pictures, or you end up making pictures of large flat surfaces (i.e. maps on walls). | |||
</div> | |||
<div class="col-xs-6 col-md-6 col-lg-6"> | |||
[[File:sharp_house_annotated.jpg|class=img-responsive]] | |||
</div> | |||
</div> | |||
<div class="flex-row row"> | <div class="flex-row row"> | ||
<div class="col-xs-6 col-md-6 col-lg-6"> | <div class="col-xs-6 col-md-6 col-lg-6"> | ||
<div class="panel panel-success"> | <div class="panel panel-success"> | ||
<div class="panel-heading">''' | <div class="panel-heading">'''Crops from the middle'''</div> | ||
<div class="panel-body"> | <div class="panel-body"> | ||
[[File: | <Center> | ||
[[File:sharp_roof.jpg|class=img-responsive]] | |||
[[File:sharp_window.jpg|class=img-responsive]] | |||
</center> | |||
</div> | </div> | ||
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<div class="col-xs-6 col-md-6 col-lg-6"> | <div class="col-xs-6 col-md-6 col-lg-6"> | ||
<div class="panel panel-danger"> | <div class="panel panel-danger"> | ||
<div class="panel-heading">''' | <div class="panel-heading">'''Crops from the side'''</div> | ||
<div class="panel-body"> | <div class="panel-body"> | ||
[[File: | <center> | ||
[[File:notsharp_roof.jpg|class=img-responsive]] | |||
[[File:notsharp_window.jpg|class=img-responsive]] | |||
</center> | |||
</div> | </div> | ||
</div><!-- End of pan --> | </div><!-- End of pan --> | ||
Revision as of 17:59, 11 January 2021
It is almost never the lens at fault
When you have a blurry or fuzzy picture, it is so easy to blame the lens. After all many reviews compare the sharpness of lenses all the time. Speaking from experience, it is very rarely the lens at fault.
There are a couple of reasons why your image is blurred (opposite of sharp) in order of importance:
- Movement, either you or the object moved during exposure. This creates a blur. You can decrease the exposure time, hold the camera (or the object) still or use a tripod
- Out of focus, not all of your picture is in depth of field due to the aperture and the focus you have. Note that fast lenses may have very small depth of field making it very difficult to keep everything in focus.
- Environment, the light is an important contributor to the sharpness, both direct and indirect (well lit scenes can be exposed faster). Similarly the clarity of the air between the lens and the object will contribute as well. This is especially true for landscape shots using long lenses.
- Diffraction limits is a physical limitation that gets worse with smaller apertures. Basically the problem is that light falling on your pixel will have an airy disc shape and will spill over and contribute to neighboring pixels. This gets worse as you the aperture gets smaller.
- Lenses, they are not perfect and they will create various non-idealities that will contribute to blur your images. Usually the goal is to limit these problems to the edges and corners of the frame. Zooms that cover a wide focal distance range have to optimize many different parameters (cost/weight) and can have issues at various focal lengths.
The picture in this section is taken with a Nikon 105 on a Nikon D850. This is not a particularly sharp (or good) picture, but highlights a lot of issues that will haunt you. The lower half of the picture contains a roof part that is too close, and is therefore slightly out of focus. The air (in London) was not particularly clear, the building in the distance started to disappear in the haze, and there are plenty of chimneys that expel hot air and vapour which blurs parts of the image. There is a tiny cut out 160x100 pixels on the left side of the image, which shows actually how sharp the lens is. So anything that is blurred here is not really due to the lens.
You need to look really close to see these issues
Here I have an example to illustrate what is happening, it is a head on shot using Nikon 70-300 of a house in Zurich, in decent light using a Nikon D850 with 45 Megapixels resolution. The image on this www site has been scaled down to 1280x853, and it should look quite OK when you are viewing it on a computer. Below there are two sets of crops of 640x400 pixels, this is about 0.5% of the image.
You can see that the center of the image is better defined while the sides/corners have gone soft. This is actually the issue of this lens at this focal length 70mm and aperture f/5.6, and it takes a lot of effort to highlight this issue. In practice you will be bothered by such things only if you zoom like crazy on all our pictures, or you end up making pictures of large flat surfaces (i.e. maps on walls).
These pages are for Amateur Photographers and not really for seasoned photographers and professionals. I have no affiliation or commercial interest with any brand/make. I write from my own experience. I ended up using mainly Nikon, so I am more familiar with this brand than others. See price for notes on pricing as well as photography related links.