# Tagged Questions

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

61 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 ...
131 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 ...
95 views

### How do I correctly convert from aperture diameter into f-stops?

I'd like to know whether it's possible to convert the radius of the focal point into f-stops properly. The following equation illustrates that the diameter is dependent on the f-stop: aperture ...
19 views

### ImageMagick Distort Perspective around a rectangle, without affecting aspect ratio

I have an imperfectly aligned/distorted photograph against a repeating rectangular pattern background, where one can easily identify what should be straight lines, both horizontally and vertically. I'...
104 views

### How can I automatically get a (approximate) Lux value from overexposed and underexposed pictures?

As you will soon understand, I am not a photographer. For research in a completely different field, I am interested in estimating, even with a large approximation, the brightness of the environment in ...
270 views

### How do I get the right size image for a specific small photo frame?

I have a picture frame that is 2 1/2 x 3 1/2 inches. I would like to know what kind of dimensions, in pixels, I should use with my Nikon D3300 to make a photo for the frame?
103 views

### Difference between focal point and distance away from object? [duplicate]

I have a macro lens for the camera on my phone. I want to calculate the magnification of the lens because the one i purchased does not state it. I've found this guide which states the mathematical ...
157 views

### Can I increase 35mm-equivalent focal length with both the crop factor and an extender?

I have a Canon EOS 7D Mark II (1.6x crop factor), and I have a Canon EF 100-400 IS USM. Working with just 400mm for the purposes of this question, my understanding is that my 35mm-equivalent focal ...
140 views

### White balance math for white, black, and grey color cards

This question got me very close to my answer, but I'm looking for more precision: What is the math behind white-balance, and how to choose it? I have an image with white, grey, and black color cards ...
95 views

### Why I am getting different values for depth of field from calculators vs in-camera DoF preview?

When using depth of field and hyperfocal calculators, I get very different result versus the in-camera DoF preview of my Fujifilm X-M1. For example: With DOFMaster (or any other online calculator), ...
50 views

### When calculating subject size, how do I adjust for zoom with an aerial camera at known altitude? [duplicate]

I am currently doing a project on aerial camera-video surveillance. The camera is mounted on a drone, and I need to count the number of heads in an image. The head size varies with the altitude of the ...
141 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)?
86 views

### When to use the LV formula?

EV = log2(f^2/T) LV = EV + log2(ISO/100) Question is to those that this is already clear. It is not a math question, it is a photography question about using Light Value. My puzzlement is "what ...
79 views

### How do I interpret flashlight specs for light painting at a distance?

Context So I've seen light painting shots and I'd like to try it out sometime. I'm more interested in painting say parts of the landscape so they stand out during a long exposure. Question Is there ...
50 views

### Proper method to measure the magnification of a reversed lens [duplicate]

I have a 50mm prime lens and a 18-55mm standard lens at my disposal. How do I measure the magnification of a reversed lens when used with a reverse mount. What are the factors that come into play to ...
431 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 ...
102 views

### Why does my camera give a very different reading from my lightmeter?

I'm new to digital photography. I start shooting in aperture priority mode, unless some situation require some shutter speed attention. Both ISO and SS is calculated by camera. I am looking at some ...
248 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 ...
198 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 ...
279 views

### How do you calculate the focal multiplier of a non-full frame camera?

I'm currently using a Sony RX100 Mark 3 camera and want to buy a Canon 6D + 24-105 F4 L lens from an online retailer, which is not in my country. (before continuing I'd like to state that there are ...
239 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 ...
41 views

### DoF app: should I round the image format/width up or down?

The DoF app I have calls for the sensor width to be set. The specs for my Sony α33 say the image format is 23.4 x 15.6mm. Do I dial-in the 23.4 or the closest to it? If I must go slightly over/...
60 views

### Choosing lens for a studio to record classes [duplicate]

I'm building a home studio to record Math classes: I have a blackboard (1,90m width by 1,20m height) and the distance from the camera to the blackboard would be around 1,80m (on a tripod, 1,70m from ...
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 ...
122 views

### Can I calculate my phone's sensor size from f-stop, focal length, max aperture, or other metadata? [duplicate]

Could I work out sensor size of my phone from these info: F-stop= f/2.6 , focal length = 3mm, max aperture = 2.8 and others info like: resolution unit, exposure time?
59 views

### Mathematical relation between aperture and DOF [duplicate]

I know that aperture and DOF are inversely proportional. But, can anybody explain to me the Physics/Optics behind that? What's the mathematical relation that relates aperture with DOF?
78 views

### How do I calculate the total exposure value of two light sources?

Assume that I'm taking the photo of a lamp in an outdoor cloudy day. The lamp itself has the luminance corresponding to 17EV. The environment has the illuminance corresponding to 14EV. What will be ...
248 views

### How can I tell what focal length a zoom lens was set to for a photo of the moon?

It appears that neither the Sony 55-210 mm f/4.5-6.3 nor the Canon EF-S 55–250mm f/4–5.6 reports the actual focal length to the camera: both cameras' metadata show the lens but report the focal length ...
51 views

### Should addition of RGB values be used when adding lens flare to an image?

From the physical theory of lens flare, it is the image of the light source after many times of light reflection between the optical lens surfaces. So it would sound reasonable to add lens flare ...
77 views

### How can I determine the distance to a subject in a old photo with little other information?

My question is similar to this one, but I don't know how accurate the formula will work with old photos. If I assume that the runners would be 1m80 (5'11"), would it possible to estimate how far ...
90 views

### How do I measure the distance from an object to fit it in the screen? [duplicate]

I'm curious if there is any math formula for this. Let's take a close-up of a human face for instance, given the human face is about 20cm/8 inches, how do I choose the right focal length and from ...
105 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 ...
656 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 ...
144 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 ...
98 views

### How can I calculate settings for manual flash to reduce trial and error? [duplicate]

I have two Yongnuo 560-III flashes that I have been using for a while, In order to get good results I am having to do a lot of trial and error. Adjusting power, zoom, moving them around etc. Is there ...
279 views

### How do I find the focal length that will fit a poster in the frame from across the room?

If suppose I want to take a photograph of a poster on the wall of the room, so I can't back away any farther than 5.0m to take the shot(max dist of the room). The poster is 0.80m wide and 1.2m tall, ...
202 views

### Does the crop factor affect the field of view (FOV)? [duplicate]

I'm working on smartphone cameras. I want calculate Field Of View of different smartphone cameras using the formula : FOV = 2 arctan(SensorSize/2f) where: f is the focal length sensor size is the ...
353 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 ...
242 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 ...
324 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 ...
682 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 ...
207 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 ...
3k 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 ...
2k views

### Do I use the crop factor in calculating aperture size and area?

How do I calculate the aperture size and area, considering an 35mm equivalent focal length value and non-equivalent aperture f-number (in terms of exposure, no multiplication of the crop factor of the ...
1k 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?
135 views

### Invariants in subject size and depth of field? [duplicate]

I was curious if I could cheat my way around having to focus stack an object by using different lenses. Playing with the Depth of Field calculator I noticed something interesting: No matter what ...
173 views

### Where can I find tables of common shutter speed and aperture values? [duplicate]

I'm working on image processing software (mind that I'm a programmer and when talking about photography, I'm "tabula almost rasa"). In this software, I'm using a RAW decoder that returns a data ...
144 views

### calculate the 1/x format of shutter speed from given floating point value

How to calculate the x in 1/x format when all i got is decimal floating point representation of the shutter speed ( for example 0.0101316 and possibly other data in exif )?