I started off by sticking a ruler onto a poster onto which I glued pages from a magazine. The purpose of this was to provide the Kodak DX6490 digital camera something to focus on. I was going to determine what the closest and farthest distances were where the camera's autofocus would still work, (resulting in a green indicator in the LCD).
I wanted to measure the range of distances where I could get sharply focused images, and also determine what subject height would fill the vertical frame in the photo. When you know your camera, it makes it easier to decide how far to stand from a subject to get a specific subject height in the photo.
I put the DX6490 on its highest megapixel value, which is 4MP resulting in images of
2304 x 1728 pixels.
Accoring to the user manual the camera has the following focal distances for the 2 different modes:
Normal:
------
Wide angle : Focus Range S = 60 cm - Infinity
Telephoto : Focus Range S = 2 m - Infinity
Macro:
-----
Wide angle : Focus Range S = 12 cm - 70 cm
Telephoto : Focus Range S = 1.2 m - 2.1 m
Where
Wide angle = 38 mm (35mm equivalent focal length)
Telephoto = 380 mm
This means that by switching the camera first in Macro mode and then in Normal mode, you would be able to focus on subjects anything from 12 cm up to Infinity.
You can then display the range as follows:
Range:
12cm-----70cm (Macro,wide angle)
60cm-------------------------> Inf (Normal,wide angle)
1.2m-----2.1m (Macro,telephoto)
2m--------> Inf (Normal,telephoto)
The problem is that you cannot easily determine the opposite: In order to render a subject with a specific height a certain size on the photo, what the zoom/focal length must be.
In my measurments I would start off with the Wide Angle setting of 38mm of the DX6490 and then increase it to about 1/3, 1/5, 2/3 and 3/3 the distance to the Telephoto setting of 380 mm. Unfortunately the DX6490 does not show you the 35mm effective focal length in the LCD. Im sure that I am not alone in wishing they had put it in.
At each of these focal lengths I would then determine for the Normal and Macro setting what the approximate closest and farthest distances are where the Auto Focus would focus on the subject, which was in this case the poster.
I would make a not of all the pictures I take and also use the EXIF info to match up the image with the distance I measured to the front of the camera's lens. From the image I could then determine the real world vertical distance/height of the 1728 pixel photo.
Here follows my measurements:
At 1728 pixels vertical image size we get:
Normal:
------
Wide Angle:
f = 38 mm effective/6.32 mm
Closest distance: (which camera can focus)
d = 23.6 cm (from front of camera)
h = 180 mm (96 pixels/cm)
Farthest distance:
d = Infinite
1/3 from Wide Angle (approx):
f = 139 mm eff
Closest distance:
d = 44 cm
h = 102 mm (169 pixels/cm)
Farthest distance:
d = Infinite
2/3 from Wide Angle(approx):
f = 268 mm eff
Closest distance:
d = 103 cm
h = 118 mm (146 pixels/cm)
Farthest distance:
d = Infinite
Telephoto:
f = 380 mm effective
Closest distance:
d = 121 cm
h = 112 mm (154 pixels/cm)
Farthest distance:
d = Infinite
Macro:
------
Wide Angle:
f = 38 mm effective/6.32 mm
Closest distance: (which camera can focus)
d = 4.5 cm
h = 51 mm (339 pixels/cm)
Not Farthest distance:
d = 151cm
h = 1047 mm (17 pixels/cm)
Farthest distance: ??
d = 8.3 m
h = 5.6 m (3 pixels/cm)
1/3 from Wide Angle(approx):
f = 139 mm eff
Closest distance:
d = 38 cm
h = 89 mm (194 pixels/cm)
Not Farthest distance:
d = 155 cm
h = 306 mm (57 pixels/cm)
1/2 from Wide Angle(approx):
f = 209 mm eff
Closest distance:
d = 65 cm
h = 99 mm (175 pixels/cm)
Not Farthest distance:
d = 155 cm
h = 216 mm (80 pixels/cm)
2/3 from Wide Angle(approx):
f = 268 mm eff
Closest distance:
d = 78 cm
h = 91 mm (190 pixels/cm)
Not Farthest distance:
d = 167 cm
h = 177 mm (98 pixels/cm)
Telephoto:
f = 380 mm effective
Closest distance:
d = 79 cm
h = 78 mm (222 pixels/cm)
Not Farthest distance:
d = 167 cm
h = 148 mm (117 pixels/cm)
Farthest distance:
d = 175 cm
h = 109 mm (159 pixels/cm)
Here follows a summary of the above info:
----------------------------------------
where d=distance to subject from front of lens
Normal:
------
f = 38 mm eff
Closest distance: d = 23.6 cm (96 pixels/cm) 18 cm subject
Farthest distance:d = Infinite (<0 pixels/cm)
f = 139 mm eff
Closest distance: d = 44 cm (169 pixels/cm) 10.2 cm subject
Farthest distance:d = Infinite (<0 pixels/cm)
f = 268 mm eff
Closest distance: d = 103 cm (146 pixels/cm) 11.8 cm subject
Farthest distance:d = Infinite (<0 pixels/cm)
f = 380 mm eff
Closest distance: d = 121 cm (154 pixels/cm) 11.2 cm subject
Farthest distance:d = Infinite (<0 pixels/cm)
Macro:
------
f = 38 mm eff
Closest distance: d = 4.5 cm (339 pixels/cm) 5.1 cm subject
Not Farthest : d = 151 cm (17 pixels/cm) 104.7cm subject
Farthest : d = 8.3 m (3 pixels/cm) 560 cm subject
f = 139 mm eff
Closest distance: d = 38 cm (194 pixels/cm) 8.9 cm subject
Not Farthest : d = 155 cm (57 pixels/cm) 30.6 cm subject
f = 209 mm eff
Closest distance: d = 65 cm (175 pixels/cm) 9.9 cm subject
Not Farthest : d = 155 cm (80 pixels/cm) 21.6 cm subject
f = 268 mm eff
Closest distance: d = 78 cm (190 pixels/cm) 9.1 cm subject
Not Farthest : d = 167 cm (98 pixels/cm) 17.7 cm subject
f = 380 mm eff
Closest distance: d = 79 cm (222 pixels/cm) 7.8 cm subject
Not Farthest : d = 167 cm (117 pixels/cm) 14.8 cm subject
Farthest distance:d = 175 cm (159 pixels/cm) 10.9 cm subject
Reverse info:
s = Subject size to fill height of photo
d = distance from front of lens
f = focal length (effective)
s d f Macro
--- --- --- -----
5.1cm 4.5cm 38 mm yes wide
7.8cm 79cm 380mm yes tele
8.9cm 38cm 139mm yes 1/3
9.1cm 78cm 268mm yes 2/3
9.9cm 65cm 209mm yes 1/2
10.2cm 44cm 139mm no 1/3
10.9cm 175cm 380mm yes tele
11.2cm 121cm 380mm no tele
11.8cm 103cm 268mm no 2/3
14.8cm 167cm 380mm yes tele
17.7cm 167cm 268mm yes 2/3
18 cm 23.6cm 38mm no wide
21.6cm 155cm 209mm yes 1/2
30.6cm 155cm 139mm yes 1/3
104.7cm 151cm 38mm yes wide
560 cm 8.3m 38mm yes wide
It is supposed to be governed by the formula:
(but this approximation does not hold for multiple lens elements)
f = v * d / h
where v is the vertical size of the image on the CCD
h is the vertical field of view in the subject plane
d is the distance from the (thin lens approximation) lens element
f is the (thin lens aproximation) 35mm effctive focal length
I have been able to figure out that the DX6490 has the following:
Focal Length Multiplier = FLM = 380/63.2 = 38/6.32 = 6.01266...
and
FLM = 43.3mm (diagonal) / sensor diag = 6.01266
where 43.3 mm is the size of 35mm film
This means that the DX6490 must have a
Sensor diag = 7.201471 mm
this means that:
x^2 + y^2 = 7.201471^2
with an aspect ratio of: 4/3
x = (4/3)y
Solving the equations gives:
y = 4.32088 mm
x = 5.761177 mm
for the sensor.
This will result in a physical resoltion for the CCD sensor of:
x res = 2304/5.761177 = 400 pixels/mm
y res = 1728/4.32088 = 400 pixels/mm
The Kodak DX6490 therefore has a CCD image resolution of 400 pixels per millimeter or
400 x 400 = 160 000 pixels per square millimeter.
I have also determined that if the 2.2 inch LCD (which is actually 2.165 inch) has 153000 pixels, then 153000/(4/3) = y^2
y=338 pixels
x=451 pixels
451 x 338 pixels
I hope this helps someone out there. Please give me some comments.
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