# Tagged Questions

59 views

### Is there an “optimal” background distance when striving for a minimally distracting background?

Let's assume a thin lens and an object O in focus at a distance of dO from the lens. Further, let's assume there's a large out-of-focus background object B at a distance of dB. Now, we know ...
293 views

### 35mm vs 40mm: Does it matter?

I want to buy the lens Voigtlander Nokton 40mm F1.4, \$449 Voigtlander Nokton 35mm F1.4, \$629 I am asking, why the slightly difference in focal length, the price difference in so much as \$180? ...
405 views

### Why image at 400mm is LARGER THAN DOUBLE of image at 200mm? (according to lens formula)

Like most of us, I thought it was yes. Until I really look into the Lens Equation: (1/subject distance) + (1/image distance) = (1/focal length) ...
310 views

### Size of the entrance pupil vs size of the aperture

I understand that the entrance pupil is the image of the aperture as seen from the front of the lens. However, is the size of the entrance pupil the same as the size of the effective aperture? In ...
416 views

### What does it mean that a lens is x millimeters?

Every lens has different focal length in terms of millimeter so if I have a 100mm lens, what does that refer to? Does it mean the length of the lens itself is going to be 4 inches long, or does this ...
697 views

### Why does calculated distance of an object in an image vary when zooming?

I would like to calculate the distance of an object from my camera, so i used the formula given in this question and I got a very good answer, but I've found that when I zoom and take the picture and ...
2k views

### What is the reference point that the focal length of a lens is calculated from?

I understand the idea of a focal length for a single lens, i e the distance from the lens to the point at which parallel rays of light converge. However, in the case of a photographic lens with ...
1k views

### Do bigger focal lengths capture more light?

I never understood what the f really stands for in the f-stop values, like f/1.8. Wikipedia explains it in various articles, but I still find it very confusing. What I understand, though, is that it ...
1k views

### Is it normal for focal length to change while focusing?

When I change the focus distance on my Pentax 55-300mm lens, the focal length appears to change. More specifically, the lens appears to zoom in as I focus towards the minimum focusing distance. This ...
2k views

### Why is depth of field affected by focal length?

As the focal length decreases, the depth of field increases as well. Why is this? I'm not so much interested in a physics lesson as I am interested in a simple, down-to-earth explanation.
5k views

### Is the difference between a good 50mm vs 85mm lens just your distance from the subject?

I was wondering: is the difference between a 50mm f/1.8 lens and a 85mm f/1.8 lens just your distance from the subject? Let's assume that distortion is minimal; both lenses are of high quality. Does ...
2k views

### How can a prime lens focus on more than one plane?

By definition, a prime lens is a fixed lens system with a fixed focal length. Then, simple physics tells us that it should be able to focus only on one plane (at a fixed distance) in front of it. But ...