# Questions tagged [calculations]

Photographic math — equations, formulas, algorithms related to making or processing images.

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7answers
185k views

### Is there a general formula for image size vs. print size?

What size images do I need for common print sizes, such as wallet size, 8x10, and 16x20? Is there a general formula? How could that size change if, for example, a 16x20 was printed on canvas rather ...
5answers
144k views

### How do I calculate the distance of an object in a photo?

If I took a picture of a windmill on the horizon — given that I know the sensor size and the focal length of the lens and other factors to do with the shot — could I calculate how far away an object ...
9answers
6k views

### Can a smaller sensor's “crop factor” be used to calculate the exact increase in depth of field?

If APS-C and similar crop-sensor digital cameras have a focal length multiplying effect such that a 50mm lens has an apparent focal length closer to the field of view of an 80mm on a full frame camera,...
6answers
35k views

### Is there a formula to calculate DOF?

I am pretty clear about that DOF depends on: Focal length Aperture Distance from subject Sensor size and more (as pointed in the comment). But what is the question here is: Is there any formula that ...
3answers
3k views

### How to determine camera location from an existing photograph?

I have old photos of a town and landscape around it. I'd like to take these photos again, from the same locations. In some cases I am struggling with finding the original location of the camera. I ...
3answers
4k views

### What is the formula for percent of frame filled at a specific distance and focal length?

I am thinking about buying a new lens specifically to take photos of distant targets (birds, bears, etc). I currently own the Canon 70-300 IS USM, which is a nice lens, but I find that if I want to ...
2answers
28k views

### How to calculate the FOV in degrees from focal length or distance?

How does one to calculate the field of view (or angle of view) in degrees from the following details: sensor size (for example, 1") distance to target (for example, 7 feet) focal length (for example,...
1answer
8k views

### How to calculate the optimal pinhole size?

As far as I've understood, optimal diameter for pinhole size is calculated by formula where d - the optimal diameter for pinhole c - constant f - focal length (distance between pinhole and ...
4answers
30k views

### What is the relationship between size of object with distance?

How does the size/length of an object vary with distance? Is it a logarithmic relationship? exponential? linear? I plotted a curve of the size/length of an object for different distances from the ...
1answer
14k views

### How do I calculate the ground footprint of an aerial camera?

I have a very simple math problem, but I cannot seem to figure it out. I need to calculate what portion of the ground will be visible when viewed from a UAV mounted camera. I believe I have it solved ...
8answers
3k views

### If viewers don't respond to the rule of thirds, why do some photographers still emphasize it?

Previous posts (1, 2) explain the concept of the Rule of Thirds and the Golden Ratio. Some previous answers state that the Rule of Thirds is the Golden Ratio, but that is not true. The two are ...
5answers
1k views

### Why doesn't the focus distance at which my lens has magnification 1 match the formula?

From the Magnification Wikipedia page, I have the following equality: M = di/do = f/(do – f) = (di – f)/f with M the magnification, f the focal length, do the distance from the subject to the lens,...
3answers
1k views

### Why do depth of field calculators show *more* DOF for larger formats with the same lens parameters?

I thought I had a pretty good seat of the pants understand of DOF. But I've been playing with DOF calculators and it's giving me results that don't line up with my practical experience, so I'm ...
3answers
2k views

### How much distance should one move so that a shot that can be framed at xx mm be framed at yy mm?

Is there a website / app that will tell you approximately how much distance a person should move so that they are able to frame the same shot at different focal lengths? Say for example, I'm using ...
3answers
4k views

### Can we measure size of an object using EXIF data from a photo?

A lot of people have asked if we can measure the distance of an object in photo. But I was wondering if we can measure the size of an object in photo. Of course assuming we know everything from sensor ...
5answers
3k views

### How do I calculate the “effective focal length” of a cropped photo?

Suppose I’ve taken a photo and then cropped it. If the crop is extreme enough then I might want to go back and take the same photo with a more telephoto lens so that I can take full advantage of my ...
5answers
1k views

### Is rotation an intrinsic lossy operation (for angles not multiple of 90 degrees)?

mattdm's statement "that blur is largely reversible if you do the exact same thing in reverse" raised the question in my mind. The rotation is a geometric transformation of the image that consist of a ...
2answers
1k views

### What is the power output from two speedlites combined?

When you have two speedlites in a softbox firing at the same time, let's say at 1/64 power, what is the total power output?
1answer
1k views

### How do I calculate the coordinates for secondary colors on a CIE chromacity diagram?

Imagine a typical device gamut on CIE xy diagram: x and y coordinates for primary colors (red, green and blue) is defined and known, how to calculate secondary colors (cyan, magenta and yellow)?
1answer
2k views

### How can I calculate the change an extension tube makes to the maximum magnification of a lens? [duplicate]

Possible Duplicate: How can I calculate what the effect of an extension tube will be? My understanding is that extension tubes increase the magnification of lenses by reducing their minimum ...
2answers
17k views

### How can I calculate focal length from a photograph?

I posted this question over on Stack Overflow, but someone suggested this site might be of more help to me. I'm doing a college project where I'm trying to calculate the focal length of a camera ...
1answer
18k views

### How do I find a camera's focal length in pixels?

I am working on camera pose estimation. For this, I need the focal length of my smartphone camera in pixels. (My phone is HTC Wildfire S, with Android 2.3).
3answers
179 views

### How to scale between two white balance settings for perceptually equal increments?

If I have two white balance settings (say, one for direct noon sunlight, and one for full shade) and I want to create a series of interpolated settings that span between the two, what would be the ...
1answer
198 views

### How does blur radius change with distance from the point of focus at macro distances?

In a macro situation, is there a known function that maps the blur radius as a function of the physical distance from the plane of focus? I'd expect this function to give near zero (in pixels) at ...
1answer
5k views

### Calculate angle/field of view from 2D image

I want to calculate the angle of view (or field of view) from a photograph, without knowing anything about the camera (or lens). Please have a look at this example: It is assumed the angle between ...
6answers
1k views

### Why don't cameras provide you with DOF information?

The viewfinder is usually not 100% accurate in representing the final image you will get and I've lost a few shots while using a too narrow DOF. I would imagine that cameras, knowing the focal length, ...
5answers
3k views

### Is it exactly true that doubling the focal length makes everything look twice as big?

I had come to the conclusion that if one lens has twice the focal length of another, that means it makes everything look twice as big. Conversely, if a lens has half the focal length, you see twice as ...
2answers
4k views

### What is the image size of the Sun / Moon in the frame with a given focal length?

I'm interested in taking a picture of the Sun / Moon using a telephoto lens. For example like this. It would be very helpful for me to know what the approximate image size of the sun / moon would ...
2answers
6k views

### How can I get the image/sensor dimensions in mm to get Circle of Confusion from EXIF?

I need to get calculate some formulas based on Circle of Confusion and/or image dimensions (diagonal) in millimeters based on EXIF data only. IOW, I cannot say "this photo was shot with Canon 5D3 ...
2answers
3k views

### How do I calculate the number of stops between two shutter speeds?

What is the math equation to calculate the difference between two different shutter speeds in stops?
3answers
907 views

### Why isn't my computation of the actual size of an object in a photograph matching the expected value?

Let's say I have a full frame camera (Sony A7) with a 50 mm lens (Canon FDn 50mm f/1.4) mounted on it. At a given object (a plane) distance I should be able to compute the size of the image in real ...
2answers
4k views

### How do I calculate equivalent focal length from field of view?

I'm working with zone sieve and zone plate photography. Zone sieve/plate is similar to pinhole photography but it can give a softer, dreamier, look. This is a zone sieve photo I've taken: Zone sieve/...
1answer
268 views

### Effect to reduce width of photo without cropping or stretching

I saw a documentary a few years ago (about 5) demonstrating a photographic manipulation formula, which can reduce the width of an image, without stretching, or cropping. It would do this by ...
4answers
2k views

### Is there a formula for calculating exposure when enlarging prints?

I'm curious if there is a formula to determine my exposure in the dark room. Suppose my print comes out perfectly with the following: 8 seconds f/11 height of 8 +3 contrast filter Is there a ...
1answer
459 views

### Lens f-number and speed on adapted lenses

A lens has a focal length, and its entrance pupil has a diameter. The ratio of these is an f-number. The size of the entrance pupil is limited by the size of the front element, and we describe lenses ...
3answers
392 views

### How to estimate the minimum magnification to capture features of a certain size?

What is the correct way to estimate the minimum magnification (maximum subject distance) at which features of a certain size are resolved? My thinking is that given a system capable of resolving a ...
3answers
2k views

### More megapixels to compensate for small zoom (Or: How good is Sony's Smart Zoom?)

Short version of my question: How can I compare cameras with different optical zooms and different megapixels (more megapixels can allow cropping for a fake zoom effect) in order to tell which camera ...
2answers
772 views

### How to calculate object size dependent on distance?

I shot some images for use in a blog post. With the closeups, I ran into the problem of too low depth of field. Because I only need them for the web, I think that the easiest way to solve it would be ...
2answers
611 views

### Can I use my camera to measure lens light transmission?

I want to compare and quantify the light transmission of various lenses (with some custom modifiers). So I have a target setup with constant illumination, and a camera body for them ready to shoot ...
3answers
13k views

### Calculate object size when I have physical pixel size

How do I calculate the object size when I have focal length = 25mm distance to object = 700mm CCDs pixel size = 4,4µm ? My camera is this one. Appreciated! Edit: Could this work: real height = (...
1answer
2k views

### How do I calculate the maximum aperture at each focal length on a 35-200mm lens

I am looking for the linear maximum aperture of a 35-200mm 3.5/4.5 Nikon manual focus lens. I already know the max & min of the 35 & 200mm it's the 50, 70,105, & 135 that I am interested ...
1answer
170 views

### Why is the field of view of my lens narrower than my calculations show it should be?

The field of view of the Panasonic GH4 Micro Four Thirds camera with a 12mm lens is 84°. At a height of 120m, pointing straight down, I should be able to see 216m1 of ground across the diagonal of ...
1answer
506 views

### Why isn't the size of an object in macro image exactly proportional to the ratio of the focal length and distance in front of that?

Using a Canon 550D with a EF 100mm f/2.8 Macro USM lens, I can make a 1:1 macro photo at shortest film plane to subject distance of 310 mm, thus getting 22 mm of a scale on the APS-C sensor, which is ...
2answers
5k views

### How to automatically measure subject dimensions (width/height/distance) without physically measuring?

What methods are used for automatically measuring the dimensions (width/height/distance/etc.) of a subject without having to get in there with a measuring tape? I am just starting to get into ...
1answer
1k views

### How can I calculate the effect of a supplementary close-up lens (a.k.a macro filter)?

If I have a +1, +2, +4, or +10 close-up lens which attaches to the front of my regular lens, how can I calculate its effect on close focusing distance, figure out how much magnification I can get from ...
1answer
466 views

### How to understand the definition of dynamic range?

I have the following formula: DR=(1.4L_Sat G_i)/N_D where DR is the dynamic range; L_sat is the luminance at the “margin level”，70.1% of the maximum recordable （saturation）luminance（yes，L_sat is ...
1answer
559 views

### Calculating exposure when using ND Filter during/after the sunset or sunrise

It is very simple to calculate the exposure time when using ND Filters when the light is constant. Long exposures captured during changing lighting conditions make it much more difficult to calculate ...
1answer
1k views

### How to calculate the correct focal length needed for a subject of a given size and distance?

I need to purchase my first ever lens. So far I've only used lenses that were built into a camera. This specific lens is for the BlackMagic Deign Pocket Cinema Camera (a video only camera, but one ...
4answers
6k views

### How to calculate the size of the image circle at infinity focus?

How can I determine the diameter of the image circle (i.e. the diagonal size of CCD required to fully utilise a telescope's optics) at near-infinity focus? I have looked around online and found this ...
3answers
2k views

### Which SS/F-stop table is the correct one?

While reading a book that was recognized as a good one by many readers, I found the following table: This means that any of these settings would each result in the same amount of light hitting the ...