6
votes
Accepted
If focal length does not affect DOF, why doesn't a 25mm lens at an f-stop of 4 give me the same DOF as a 100mm on an f-stop of 16?
Because magnification (focal length and subject distance) affects the Depth of Field more than aperture does (approx twice as much generally).
Start with 50mm @ f/8 focused at 10 ft. If you halve the ...
- 14.8k
5
votes
Convert Zoom % to Focal length
20mm is the wide view. A 2x zoom lens would zoom to 40mm. A 3x zoom lens would zoom to 60mm. A 10x zoom lens would zoom to 200mm. And a 60x zoom lens would zoom to 1200mm. That's basic multiplication ...
- 11.7k
5
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If focal length does not affect DOF, why doesn't a 25mm lens at an f-stop of 4 give me the same DOF as a 100mm on an f-stop of 16?
Focal length totally affects DOF. That's one of the reasons that older video camera footage and current-day cell phone video doesn't look "filmic". The sensor is tiny, so a short focal ...
- 151
4
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If focal length does not affect DOF, why doesn't a 25mm lens at an f-stop of 4 give me the same DOF as a 100mm on an f-stop of 16?
In short: there are two reasons your expectations don't hold true:
In order for crop 'equivalence' to hold true, everything must scale with crop factor, including subject distance and subject size. ...
- 32.3k
4
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If focal length does not affect DOF, why doesn't a 25mm lens at an f-stop of 4 give me the same DOF as a 100mm on an f-stop of 16?
Circle of confusion is an absolute value. Circle of confusion can be drawn on the image itself. If you were to scale the image from 25mm lenses to match the image from 100mm you will find out that ...
- 4,780
4
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Why is aperture expressed as a function of focal length and not in absolute size?
The brightness of the image is proportional to the amount of light admitted by the lens. We are interested in quantifying image brightness because we will use this value to determine what settings are ...
- 38.7k
3
votes
Accepted
Convert Zoom % to Focal length
The Panasonic FZ70 has a focal length of 3.58-215mm (20 - 1200mm in 35mm equiv.)
This is right from the Panasonic website for your camera.
LUMIX® Digital Camera DMC-FZ7
The actual “500 Rule” formula ...
- 12.2k
3
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What is the definition of focal length for a camera lens?
You are not missing anything, you are exactly correct!
The confusion comes about from terminology and an omission of rigor that would be distracting for most purposes. When the articles you mentioned, ...
- 2,231
2
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What is the definition of focal length for a camera lens?
Focal length is a fixed property (i.e., constant) of a lens element, lens group, prime lens, or for a given zoom setting of a zoom lens. It has nothing to do, directly, with where the lens is located ...
- 32.3k
2
votes
What is the definition of focal length for a camera lens?
Focal length is measured from the point where parallel rays from the source begin to converge to a focused point on the image plane. This point is the optical center (H' in the diagrams).
For the rays ...
- 14.8k
2
votes
Why is the commonly utilized aperture for moon photography much higher than that provided by DoF formula?
Short answer:
When you are shooting the Moon, you need to set your focus to infinity, so DoF also tend to infinity. This suggestion has nothing to do with the DoF but other properties of an optical ...
- 141
2
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Accepted
What focal length is best for photography of rugs?
You already have a camera and a lens. Try them.
But the real answer depends on the relation between the size of the object you are photographing and the available space you have to move further back ...
- 24k
2
votes
Accepted
DOF formula vs the simplified DOF formula
The simplified formula makes two assumptions; that subject distance is greater than the focal length, and that the subject distance is less than the hyperfocal distance. And that is true when the DOF ...
- 14.8k
2
votes
Accepted
Is this diagram I've drawn in regards to Depth of field correct?
So I am thinking, if this graph I have made is incorrect, since the distances between \$i-i_2\$ and \$i_1-i\$ should be the same, as depth of focus is symmetrical.
(Emphasis mine) Your assumption ...
- 32.3k
2
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Is this diagram I've drawn in regards to Depth of field correct?
i1-i and i2-i should not be the same. What makes them symmetrical w/in the depth of focus is that their resulting blur radiuses are the same size at the image plane... i.e. o1 and o2 record equally ...
- 14.8k
1
vote
120mm with 35cm minimum focus distance for Macro?
Magnification (how does size of image compare with real life size) M = lens to image distance divided by lens to object distance. All values in millimeters M = 120 / 350 = 0.3. This tells us that the ...
- 38.7k
1
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Why do telephoto lenses have long focal length?
Put simply, every time you bend light it reduces the potential IQ; every lens element, aperture restriction, etc... there are definite negatives to making a lens more complicated than necessary; ...
- 14.8k
1
vote
Why do telephoto lenses have long focal length?
Law of physics
In the image above, assume that the "object" is sufficiently far way from the camera so that the distance between the sensor plane where the "Image" is projected ...
- 20.6k
1
vote
Why do telephoto lenses have long focal length?
Let's put it the other way round:
If you were to construct a lens for a desired focal length, under which circumstances would you use a telephoto lens construction?
To make it concrete, let's talk ...
- 1,229
1
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Why do telephoto lenses have long focal length?
Let us say we want a focal length of 10mm.
In order to be "shorter than its focal length", our lens design needs to be shorter than 10mm and still be large enough to illuminate our sensor. ...
- 716
1
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Why is aperture expressed as a function of focal length and not in absolute size?
What is important for determining exposure is the amount of light per unit area on the sensor. For a given object and aperture absolute size, a larger focal length lens will produce a larger image ...
- 111
1
vote
Why is aperture expressed as a function of focal length and not in absolute size?
My explanation in simpler terms.
Because it is actually a relationship, not an absolute size.
Any division is a relationship between the top number and the bottom one.
When defining the aperture we ...
- 24k
1
vote
Image metadata contains Focal length and calibrated focal length but the values are different
The focal length is 8.8mm. Often this value is expressed in terms of the equivalent focal length lens that delivers the same angle of view when mounted on a 35mm full frame camera format 24mm height ...
- 38.7k
1
vote
Accepted
Focal length reducer on FF camera (24mm F2)
TL;DR: Use the 24mm lens directly. Forget about the focal length reducer.
(If the lens is compatible with your body, and if such a focal reducer exists - which I don't know. If they are incompatible, ...
- 1,229
1
vote
Accepted
Determining the size of a pixel at a given distance
If you know the focal length, find out the field of view from https://www.nikonians.org/reviews/fov-tables then it's just trigonometry:
pixel size = tan ( horiz.fov /2 ) * distance / image width in ...
- 1,329
1
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Determining the size of a pixel at a given distance
How accurate do you expect/need to be?
IMHO between the inaccuracy of the focal length (especially since you are not focused to infinity) and your lens correction, the GIGO principle says that you ...
- 20.6k
1
vote
How to calculate the optimal distance to photograph details for mobile phone lenses?
The ideal distance to record the most resolution/details of the subject at the focal plane will be the minimum focus distance... because the details are presented as large as possible to the lens.
At ...
- 14.8k
1
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Why is the commonly utilized aperture for moon photography much higher than that provided by DoF formula?
Practically speaking the sharpness of moon photos is not limited by depth of field as your calculation shows, but by „seeing“. Seeing is caused by the inherent movement of the earth’s atmosphere, same ...
- 453
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Why is the commonly utilized aperture for moon photography much higher than that provided by DoF formula?
Quite simply, photographing the moon from earth will never be subject to depth of field issues, at all.
Using your numbers, the required depth of field of the moon is 38,1630 ± 870 km (38,1630 km ± 0....
- 32.3k
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