# Tag Info

Accepted

### Why doesn't the picture become darker the more you zoom in?

The answer to this question revolves around explaining how zoom lenses function because you are correct in your observation: As you zoom to higher and higher magnifications the image dims unless ...
• 39.4k
Accepted

### Do convex lenses make parallel light rays of different wavelength converge to different points?

Do convex lenses make parallel light rays of different wavelength converge to different points? Yes. The separation of different wavelengths of light is called dispersion. Different wavelengths of ...
• 33.1k

### Are lenses marked with the true focal length?

Oh, it is worse than that. Many lenses designed for still photography exhibit focus breathing, where the angle of view varies over the range of distances the lens can focus. Normally this isn't an ...
• 4,026

### 50mm mirror lens. Does one exist?

The mirror lens design resolves two key optical problems: All lenses suffer from chromatic aberration. This is color fringing due to the failure of the lens to refract (bend inward) all colors of ...
• 39.4k

### Do convex lenses make parallel light rays of different wavelength converge to different points?

Light from a far distance object, like a star, arrive at the lens, as parallel rays. As they transverse the lens, they are forced to change their direction. They bend inward, we call this refraction ...
• 39.4k

### Why is the background bigger and blurrier in one of these images?

The easiest way to think of this is with an image. When you use a wider lens, you have to be closer to your subject, which emphasizes the distance between the subject and background by making the ...
• 500

### How does crop factor affect perspective?

When I started photography, this one took me ages to figure out, because people tend to explain it with a lot of math, or in a way that makes sense once you already grasp the principle but not before. ...
• 23.4k

### Are lenses marked with the true focal length?

Published focal length is rounded in some degree, normally to nearest 5 or 10, or in some short cases, to the nearest 1. More precision would not be realistic, because the marked focal length is only ...
• 12.9k
Accepted

### Is this "tack sharp with blurred background" look done with Photoshop?

No photoshop necessary for that background. That's simply what happens when shooting a telephoto lens, f/2.8 or larger, and having the subject closer to the camera and much further from the background....
• 20.5k

### Would a 50mm lens on a Canon APS-C crop produce the exact same image as an 80mm lens on a full frame camera?

Would these two photos be identical (i.e. depth of field, perspective etc.)? Depth of field: not exactly, but very similar if you also multiply the f-number used by the same crop factor. If you use f/...
• 176k
Accepted

### Is a lense with an aperture larger than f/8 useful with an EOS 80 D?

So I have a EOS 80D and supposedly it has a max aperture of f/8. That's incorrect. The aperture is in the lens, not the body. All Canon EF and EF-S lenses, including the one that came with your ...
• 31.7k

### What focal length do I need to get the same field of view as an iPhone SE?

According to this the iPhone SE has an 29mm-equivalent lens, so on a Fuji with a 23.6x15.6 sensor (Fuji XT-3)(crop factor 1.53) you need a 29/1.53=19mm lens for the same field of view.
• 21.6k
Accepted

### focal length and sensor width of a phone

The Redmi 6A uses the Sony Exmor IMX486 sensor, which is a 1/2.9" format sensor. Note that "1/2.9 inch" is merely a name, not its diagonal dimension (see: Why is a 1" sensor ...
• 33.1k

### Longer Zoom Lens

The rule is learn to get closer. Really the best wildlife shots are made by people who have learned to get closer to wildlife ( a tricky skill ) and to wait ( find a spot you think they'll come near ...
Accepted

### does focal length change across an image?

There's really no such thing as a 'theoretically perfect' rectilinear lens with a perfectly flat field of focus and no geometric distortion. Even a lens that perfectly matches its blueprint would not ...
• 176k

### Is focal length measured relative to the sensor or the lens?

Focal length is the distance from the conversion point to the image plane. The image plane could be film, or a digital sensor. For the purpose of understanding focal length, think of the lens as ...
• 17.4k

### How to estimate pixels per degree for an image from a camera phone using EXIF data?

I assume this is a still frame from a video, because 16:9 is a common video ratio. In order to maintain constant frame size, "digital zooming" needs to be reinterpolated. Thus, yes, you need to ...
• 33.1k
Accepted

### Why would I need a portrait lens if I have a telephoto zoom lens covering the same focal length?

There is no such thing as a portrait lens. Just some are known to produce more appealing portraits. It can be used to shoot any other thing where the focal-length desired is the same. Note that I didn'...
• 103k
Accepted

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

Your intuition is right. To validate it, we can dig into basic high-school geometry. Although a camera lens is actually a complex lens made from many elements, conceptually and mathematically for ...
• 143k
Accepted

### What does a pair of numbers in parentheses mean as a focal length value in metadata?

Values in Exif metadata can be stored as various data types, including ASCII text strings, "short" or "long" integers, or "rationals". A short integer is stored in two bytes; a long integer takes four ...
• 143k

### How do I calculate the difference in lens reach between a superzoom compact and a DSLR zoom lens?

Assuming that the quoted 1365mm focal length is in 35mm full frame equivalent terms (because otherwise, it would be huge), then the actual focal length of the lens assembly is around 1365 / 5.6 ~= ...
• 5,158

### How can I get more magnification when shooting wading birds?

Shooting from the same point of view will always result in the same image (in terms of magnification) with every 300mm lens you can get (zoom or prime doesnt matter). To achieve a higher magnification ...
• 1,633
Accepted

### Can I use a 127.5mm focal length on a crop camera to see what the view would be like using an 85mm full frame lens?

No. You should set your zoom to 85mm to see what an 85mm lens looks like on your camera. The focal length of a lens is a physical property that does not change no matter what size sensor you put ...
• 52.6k
Accepted

### Why do images sometimes look "softer" at higher focal lengths (like 300-500mm)?

Several focal-length-related factors can influence sharpness: It is usually harder to manufacture long focal lens, so at constant cost, expect a 50 mm to be sharp, a 200 mm to be not-so-sharp, and >...
• 1,673

### At what distance will I start seeing atmospheric effects?

Atmospheric effects aren't caused by using a particular focal length. They are caused by how much air is between the camera and the subject, by the uniformity or lack of uniformity of the temperature ...
• 176k

### APS-C crop factor 1.5x or 1.53x

Nikon 1.5X APS-C sensors in their current lineup are actually 1.52-1.53X depending on the exact measurements of the various different sensors in different models. Some older, discontinued models in ...
• 176k
Accepted

### What is so special about the 18mm focal length in kit lenses?

It's mostly because the standard zoom kit lens for film cameras would start at 28mm. This is the widest you can typically go before hitting the more expensive exotic glass. The APS-C field-of-view ...
• 52.6k
Accepted

### Why is the background bigger and blurrier in one of these images?

In the case of the second shot (20mm focal length), the camera was positioned closer to the lamp, thus making it appear bigger than the background. As the camera moves further away from the subject, ...
• 881

### Can I convert binocular zoom to equivalent lens focal length?

Binocular zoom and lens focal length just aren't equivalent and can't be converted in any meaningful way. A camera lens is an image-forming system. It has a focal length. Binoculars and telescopes (...
• 143k