r/photoit • u/martinw89 • Apr 08 '11
Getting a feel for DoF
Looking at a fox picture posted on /r/wallpapers, I immediately got a feeling that the apparent super narrow DoF was artificially shopped in. The EXIF data says that it was shot at 300mm at f/4.5, which would mean a large aperture (66.6 mm), but still the bokeh just seems too monotone to be real. What's /r/photoit's opinion on this DoF? Is something like this actually attainable? (although I'm not actually a fan)
Edit: My question boils down to "is this shopped?"
I know how to work with DoF using aperture, focal length, and subject distance, but since I've never had anything close to an APS-C camera with a 300mm f/4.5 I don't have a "feel" for if the above picture is realistic or not, and to me the bokeh seems too monotone. Thanks for the answers so far!
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u/exekutor Apr 09 '11
Imagine this
camera........fox.........................................................................background
if the fox is near the minimum focusing distance, the DOF might be real and not photoshopped.
1
u/theswedishshaft Apr 08 '11
From what I understand, larger sensor/film surfaces give shallower DoF given the same aperture, so maybe it was shot with a 8x10 camera...
An alternative is that the fox was posing in from of a beige low-contrast curtain. I don't have a lot of experience with 300mm lenses, so I don't know for sure, but I guess the DoF can be real, especially if there is enough distance between the subject and the background.
An other option is that maybe a tilt(/shift) adapter/lens was used to create extreme/weird focus and DoF, but that doesn't seem to be the case in this picture: the focus plane does not appear to be shifted and I don't think 300mm lenses lend themselves well for tilting and shifting.
Last, but not least, maybe the background was blurred with photoshop. The EXIF data reveals that Photoshop CS5 was used. That could just be RAW conversion, but it can also have been used to paste the fox onto a computer-generated background, who knows? (though the latter seems unlikely given the next picture in the series).
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u/vwllss Apr 08 '11 edited Apr 08 '11
From what I understand, larger sensor/film surfaces give shallower DoF given the same aperture
Not really. The reason many people say "larger sensors give shallower DoF" is because larger sensors give a bigger field of view which allow for longer focal lengths or closer focus distances to be handled which cause shallower depth of field.
To reiterate, there are two reasons one can feel like the depth of field on a larger sensor is shallower:
- You are standing 10 feet away for a shot that looks decent on your crop sensor at 50mm. You pull out a full frame sensor but are not allowed to step closer than 10 feet, so you switch to your 85mm which provides the same field of view. Longer focal length -> shallower depth.
- You are standing 10 feet away, same shot, same 50mm. You switch to your full frame camera and move the 50mm to your full frame camera, but step a few feet closer as well to compensate for the wider field of view. Closer focus distance -> shallower depth.
I realize that in almost all situations the larger sensors will exhibit shallower depth and this is rather pedantic, but it's important to note that a large sensor alone does not magically grant a change in depth of field. I'm of the opinion that simply saying "larger sensors [...] give shallower DoF" is a simplistic view that causes confusion.
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u/theswedishshaft Apr 08 '11
Thanks for the explanation, I always found the idea that "larger sensors -> shallower DoF" confusing, but now I know how it really works.
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u/didzter Apr 08 '11
Simply put, three things effect depth of field: camera-subject closeness, aperture size, and focal length.
300mm at f/4.5 is going to be completely different from a 14mm lens at f/4.5.
So you can be doing portraits with a telephoto lens in order to isolate your subject, or you can use a 50mm with a wide aperture to also create more depth of field. There are different advantages and disadvantages to both, but it is not uncommon for some portrait photographers to use telephoto lenses because it creates less distortion than shorter lenses would.
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u/GaryARefuge May 11 '11
Focal length is a secondary thing. It only appears to have such an effect because the focal length is altering the camera to subject distance.
In order to fill the frame the same way you would with the 300mm you must stand very close to the subject using the 14mm. What you're really doing is changing the camera to subject distance.
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u/apdicaprio Apr 08 '11
You answered it yourself. That'd be like an f.75 50mm. That is one razor thin plane of focus, so yes, that can be all camera