Diffraction Limit Discussion Continuation

Started 6 months ago | Discussions thread
Mike Davis
Contributing MemberPosts: 690
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Re: Diffraction Limit Discussion Continuation
In reply to Steen Bay, 6 months ago

You're making an excellent point, Steen.

Steen Bay wrote:

Mike Davis wrote:

Yes, enlargement factor and desired print resolution are the only variables affecting the selection of a CoC diameter for DoF calculations (assuming you have considered viewing distance when specifying your desired print resolution). And they are the only variables affecting the f-Number at which diffraction will begin to inhibit a desired resolution.

What about the resolution of the sensor/system? Think it's necessary to take the max potential resolution in account too if we want to know at which point the resolution will be visibly affected. Both when calculating DoF and 'diffraction limit' at 100% view (equivalent to a large print). Guess that app. 2x pixel size/pitch is 'appropriate' in both cases.

I ended an earlier post with an invitation to keep reading...

With both CoC (defocus) and f-Number "limit" (diffraction) calculations relying on user-specification of a "desired print resolution," further reading is available here: http://www.dpreview.com/forums/post/40100820

Quoting myself from that post:

Before you can select a "desired" final image resolution, you have to be realistic when selecting an enlargement factor.

For example, the Nikon D300's 15.7 x 23.7mm sensor captures 4288 x 2848 pixels (12.21 MP) at a moderate pixel density of 181 pixels/mm.

Taking into account the loss of resolution caused by the RGBG Bayer algorithm and AA filter, typically a 30% loss relative to actual pixel count, if you "desire" to record subject detail in the final image at a resolution of 5 lp/mm, you'll be limited by pixel count to the following print dimensions:

Max. 5 lp/mm Width: 4288 pixels / 360 dpi = 11.91 inches
Max. 5 lp/mm Height: 2848 pixels / 360 dpi = 7.91 inches

Assuming you plan to make 7.91 x 11.91-inch prints (where the Pixel Count will support a desired print resolution of 5 lp/mm), your enlargement factor (without cropping) would be 11.91 inches / 23.7mm = 302.54 mm / 23.7mm = 12.8x

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