# Can I get this kind of DOF out of the 35mm 1.8 DX???

Started 6 months ago | Discussion thread
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 Re: Here is what you need to know In reply to slimandy, 6 months ago

Your statements are both correct (expect for the "narrower FOV"), as well as the calculation above. The confusing part starts with the fact, that all the books and magazines start to explain "background blur" with the term "Depth of Field", which is confusing matters. Depth of field actually describes the area in which the subject can be considered to be sharp. This is different from the "strength in background blur" or "blurriness" you will see in the picture, when viewing out of focus background. In your example above you will have the same framing with the 35mm lens at 3.5 feet vs. the 85mm at 8.5 feet. And yes, the DoF is the same. However the "strength of background blur" is 85/35=2.4 times larger for the 85mm lens or the background will "look 2.4 times more blurry" (e.g. blur discs will appear 2.4 times larger in diameter). If you are interested in this subject, please have a look at my article here at dpreview:

http://www.dpreview.com/articles/6091822765/background-blur-and-its-relationship-to-sensor-size

Cheers

Carsten

Take a shot of an object close to the camera with a wide lens then frame it the same with a long lens. The long lens captures much less of the BG but still fills the same size frame, thus the amount of blur is greater. This is pretty much what your calculation says, so it is down to the narrow FOV.

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www.andrewsandersphotography.co.uk

Yes, that's exactly what the article descibes (well actually the article is focused on the impact of different sensor size). Apologies for the FOV confusion. I was confusing it with the framing size in the focus plain (which is given in brackets in the exif data along with the angle). But of course you are right, FOV is is related to the angle and a longer lens has a narrower FOV when framing the same subject.

... the whole subject usually seems to steer up some very active debate (not just in this thread) and I personally think this is probably because of the confusion around the difference of DOF and background blur, or?

Carsten

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