Doug Kerr
Well-known member
Most of my photographic images are "delivered" for electronic viewing, as components of blog posts, on forums (such as this one), or embedded in e-mail messages.
I thought it would be interesting to see how we might do "depth of field planning" in that context.
The various parameters I will assume match my common practice. Others may want to follow the template using parameters that fit their practice. Your mileage may vary.
I will assume that the shot will be taken by my new (not yet in hand) Canon PowerShot G16, but we can imagine the use oif a G15, for which the pertinent parameters are identical.
Its sensor size is 7.44 x 5.58 mm. Its sensel layout is 4000 x 3000. I assume I will take the maximum resolution output, so the pixel dimensions are also 4000 x 3000. The pixel pitch is thus 0.0186 mm (1.86 µm).
The images I use for electronic viewing are almost always cropped, so for this exercise I will assume a 75% x 75% crop, a cropped image of 3000 x 2250 pixels.
My practice is to deliver the images for electronic viewing with a maximum pixel dimensions of 800 px, so in this case the image would be resized to 800 x 600 px.
I will start by considering the use of the human-acuity basis for determining the COCDL for use in depth of field calculation. That is because my concern is with blurring as it might be perceived by the viewer (in a certain assumed viewing situation), not as it might affect preservation of the camera's basic sensor resolution. (The latter approach would be absurd, since that resolution is diluted to 26.7% of its original value by the downsizing.)
I will assume presentation of the 800 x 600 px image on a display with a width of 1680 px and a physical width of 17" (my ViewSonic VX2035WM). Thus the image, on-screen, will have physical dimensions of very nearly 8.00 " x 6.00 ". The on-screen pixel pitch is essentially 0.01".
I will assume viewing at a distance of 24"". (In my personal case, that is enforced by how I have my glasses made.)
We will use as our COCDL the "half-cycle" resolution of a human eye with 20/20 vision, namely 1/60 degree (one arc minute). At a distance of 24", that angle subtends a distance of 0.007". That is better resolution than the display supports, so we will shift gears. We will use a COCDL that corresponds to one pixel pitch on the display, 0.01" on the display.
Now we can do the depth of field calculations. We will assume the following shot parameters:
How about that!
Guys, you can pre-order your G16 at B&H right now!
Best regards,
Doug
I thought it would be interesting to see how we might do "depth of field planning" in that context.
The various parameters I will assume match my common practice. Others may want to follow the template using parameters that fit their practice. Your mileage may vary.
I will assume that the shot will be taken by my new (not yet in hand) Canon PowerShot G16, but we can imagine the use oif a G15, for which the pertinent parameters are identical.
Its sensor size is 7.44 x 5.58 mm. Its sensel layout is 4000 x 3000. I assume I will take the maximum resolution output, so the pixel dimensions are also 4000 x 3000. The pixel pitch is thus 0.0186 mm (1.86 µm).
The images I use for electronic viewing are almost always cropped, so for this exercise I will assume a 75% x 75% crop, a cropped image of 3000 x 2250 pixels.
My practice is to deliver the images for electronic viewing with a maximum pixel dimensions of 800 px, so in this case the image would be resized to 800 x 600 px.
I will start by considering the use of the human-acuity basis for determining the COCDL for use in depth of field calculation. That is because my concern is with blurring as it might be perceived by the viewer (in a certain assumed viewing situation), not as it might affect preservation of the camera's basic sensor resolution. (The latter approach would be absurd, since that resolution is diluted to 26.7% of its original value by the downsizing.)
I will assume presentation of the 800 x 600 px image on a display with a width of 1680 px and a physical width of 17" (my ViewSonic VX2035WM). Thus the image, on-screen, will have physical dimensions of very nearly 8.00 " x 6.00 ". The on-screen pixel pitch is essentially 0.01".
I will assume viewing at a distance of 24"". (In my personal case, that is enforced by how I have my glasses made.)
We will use as our COCDL the "half-cycle" resolution of a human eye with 20/20 vision, namely 1/60 degree (one arc minute). At a distance of 24", that angle subtends a distance of 0.007". That is better resolution than the display supports, so we will shift gears. We will use a COCDL that corresponds to one pixel pitch on the display, 0.01" on the display.
So in fact we will proceed on the basis of preserving the system resolution - as it exists for the delivered image! Preservers of system resolution, rejoice! Kerr has given up his damned visual acuity premise!
Now. blowing this back to the sensor, we find that COCDL will correspond to 3.75 sensor pixels. That is very nearly 0.007 mm.Now we can do the depth of field calculations. We will assume the following shot parameters:
Focal length: the geometric mean of the camera's minimum and maximum focal lengths (6.1 - 30.5 mm): 13.6 mm. (For reference, the full-frame 35-mm equivalent is 63 mm.)
Focus distance: 10 m
Aperture: f/2.8
COCDL: 0.007 mm (per the above rationale)
Based on these parameters, we calculate the depth of field. We find that the limits of the field are:Focus distance: 10 m
Aperture: f/2.8
COCDL: 0.007 mm (per the above rationale)
Near: 5.86 m
Far: Infinity
So in fact in this case, we could better our position by focusing at the hyperfocal distance, 9.45 m. Then, the limits of the field will be:Far: Infinity
Near: 4.73 m
Far: Infinity.
Far: Infinity.
How about that!
Guys, you can pre-order your G16 at B&H right now!
Best regards,
Doug