# the 45mm doesn't provide shallow enough DoF... [image + shooting notes]

Started 6 months ago | Discussions thread
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 Re: the 45mm doesn't provide shallow enough DoF... [image + shooting notes] In reply to ryan2007, 6 months ago

ryan2007 wrote:

Bob Meyer wrote:

ryan2007 wrote:

Three things effect depth of field. Focal length, aperture and camera to subject distance.

Focal length doesn't affect DOF except as it affects camera to subject distance. Take two shots from the same positions, one with a 100mm f2.8, the other with a 50mm f/1.4, then crop and enlarge the second image to the same size as the first. DOF will be identical.

Nope,

What do you do if your 40 feet from the subject. You have a 50 1.4 and a 100 2.8 which is still too short and you can't crop the image to "fake it" or whatever. You need the lens to do the work.

If you need to fill the frame by cropping is not good unless you want to loose that "pixel" information.

I can take a 300 mm 5.6 lens to your 50 1.4 and not have to crop anything at the working distance.

A telephoto lens inherently has shallow depth of field and a wide angle lens has greater depth of field no matter the f-stop. The aperture enhances that effect.

Take a the equivalent 300 mm lens at 5.6 and the other at 2.8 from the same 20 foot distance. That 2.8 lens has shallower DOF and will blur the background more so.

This is photo 101 stuff.

Just to throw some real-world numbers into the discussion, from the EXIF data:

• Focus distance: 2.655 m/8.71 ft
• Angle of view: 22.2 degrees and 1.04 m/3.41 ft (but I also cropped the image slightly). [Interesting question: does Olympus EXIF calculate the linear measure as a diagonal based on the focus distance and the AoV for the lens?]
• DOFMaster.com says DoF near limit = 2.57 m/8.42 ft; far limit = 2.75 m/9.02 ft; total = 0.18 m/0.60 ft
• My notes: at about 5" (= 0.13 m/0.42 ft) from the eye to the ear front-to-back, this DoF calculation seems about right, with the back portion of the ear just starting to show some blurriness at 100%.

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