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Focal length is the distance (measured in mm) between the surface of a lens and the focal point. Smaller focal lengths indicate wide-angle lenses, larger focal lengths indicate a telephoto lens.

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1answer
166 views

What is a 50mm focal length good for on an APS-C camera?

This is on a Sony NEX, so the 35-mm equivalent focal length is 75mm. What kind of photography is this focal length good for? I shoot low-light, landscapes / cityscapes, and the typical vacation ...
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1answer
88 views

Take a photo and print it to show approximate view of a human from a distance?

If I want to take a photo from about 600' away from my front door, and I want it to emulate what a person would see with unmagnified view, what mm would I set my camera lens length AND then what size ...
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2answers
275 views

Help me understand effective f-number

If I set a lens to, say, f/2 but my focus is set to its closest point, my effective f-number won't be f/2 any more but it will be higher by a factor that depends on focal length, image magnification ...
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1answer
388 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 ...
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2answers
273 views

Image size of the Sun / Moon from a telephoto lens

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 ...
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5answers
623 views

Keeping two subjects in focus (depth of field)

What is the best way to get two subjects in focus in a portrait (sometimes not at the same distance from the lens)? Obviously, this is a question of depth of field, but I am curious what some of the ...
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6answers
899 views

Why is focal length measured in millimeters?

Why is focal length measured in millimeters?
7
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1answer
236 views

Why do certain lenses increase angle of view upon close focus?

I recently picked up a superzoom lens, the Nikon 28-300mm. Although I got it primarily for its versatility, my intuition was that a lens that can do 300mm focal length at 50 cm, as indeed it can, ...
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4answers
911 views

How much does 1 mm get you in a wide-angle lens?

I'm looking at a Canon 17-40 mm wide angle lens, and I don't understand why anyone would buy it. EFS18-55mm II is the standard Canon 18-55 mm lens that DSLRs come with, and it seems almost as ...
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3answers
277 views

How can I take a picture at 50mm with a Finepix s8200?

I have this camera. How do I take a picture at 50mm with zoom lens? Does this camera support zoom lens at 50mm?
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4answers
769 views

What exactly is focal length when there is also flange focal distance?

If focal length is the measure between the rear element and the sensor then how can you have different flange focal distances? Is the focal length not literally the measure between the rear element ...
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1answer
124 views

What does “focal length multiplier” mean? [duplicate]

I have heard of something called a focal length multiplier, particularly in connection with the size of the image sensor in a camera. What I don't understand is what this is and why ans how it is ...
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2answers
70 views

Finding the point corresponding to a known height in an image

I have an image of a wall taken from a phone camera from a known height h from the ground. Assume that the camera was held perfectly parallel to the wall and that the bottom of the image is perfectly ...
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4answers
832 views

Is it the same if you take a picture by setting 50mm in a 18-55mm lens and by using a 50mm prime lens?

Is it the same if you take a picture setting 50mm with a 18-55mm lens and a 50mm f/1.8 prime lens? Assuming that ISO, aperture, and shutter speed are the same, will both the lens give same results? I ...
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2answers
4k 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 ...
8
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2answers
697 views

Do lenses with the same f-stop but different focal length gather the same amount of light? [duplicate]

I'm taking images of a light source in a scientific labratory, and I thought I had a good grasp on all these things, but now i'm second guessing myself after some results. The most important thing is ...
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2answers
128 views

Will old K-mount lenses have the same field of view on Pentax K01?

Will old K-mount lenses have the same field of view on Pentax K01? Or, will 50mm lens (made for 35mm film) function as a 75mm lens?
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2answers
287 views

Why is there no apparent relation between focal length and physical lens size?

Why is there no apparent relation between focal length and physical lens size? For example, the Nikkor 20mm lens has a physical length of 42.5mm! That's more than twice the focal length! And if you ...
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2answers
242 views

How much versatility does a 85 mm lens have?

Can it be effectively used for landscapes as I am not a portrait shooter? This may be first "prime" lens so I need to understand what it's usable for. How far of a "range" does it have as far as ...
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2answers
383 views

How does focal length chage perspective? [duplicate]

@MichaelClark answered a question I posted about zoom using focal length (emphasis added): You are correct that a focal length twice as long (2X zoom) as the original one will make objects appear ...
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2answers
1k views

How do I choose among the following lens of 55-250 IS, 70-300 IS and VS 75-300?

Sorry by this specific question, but I'm pretty crazy here looking for a difference. I've got to buy a lens tomorrow (I leave my country in 2 days) I could see the difference between 55-250 and ...
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3answers
272 views

Do crop sensors on SLRs changes the depth and flatness of the objects as well? (in comparison to same focal length on full frame sensors)

1- I know different focal lengths change the depth and flatness of an objects in the picture. For examples longer focal lengths make objects appear flatter so they will be appropriate for portraits. ...
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2answers
856 views

How to simulate different focal length and sensor size on an image?

I like to simulate different focal length and sensor size based on an image i have taken. I have a full frame body so I like to know how the picture would look like if I have taken with a cropped ...
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3answers
292 views

How do they come up with focal lengths for lenses?

There are a lots of lenses for each camera and I understand that each lens caters to a different use case but my question is on how they arrive at these numbers. For eg: there are prime lenses which ...
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5answers
2k views

Why do Canon EF and EF-S lenses exhibit the same crop factor?

I have a Canon 7D, which has a crop factor of 1.6x. When using a Canon EF-S lens I get the focal length stated on the lens, when using a Canon EF lens I get the focal length times 1.6 when used on ...
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1answer
6k views

How can I find a compact camera with an ultra-wide lens?

I'm looking to buy a compact camera, and having a very wide angle is important to me. I know that review sites often list the real focal length of the lens, but what I'm looking for is something that ...
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1answer
4k views

What is the focal length on your typical cell phone camera?

Now, let me clarify (or...divulge) a few things. I know cell phone cameras are generally wide angle, which makes sense because hey, people wanna go out to dinner, or a show, or at the park with their ...
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3answers
443 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 ...
3
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2answers
308 views

How can lenses with different focal lengths have the same angle of view?

I always assumed that there was a fixed relation between focal length and angle of view. But compare the technical data for the following lenses, all from the same manufacturer: Canon EF-S 15-85mm ...
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1answer
574 views

Relationship between camera sensor size and lens focal length [duplicate]

I am choosing a camera and lens. I want to buy a Canon EOS 650D, as this camera seems to be a good point of entry into the world of SLR. My question is in the following: The EOS 650D has a cropped ...
3
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1answer
306 views

How do I properly understand what f-stop is? [duplicate]

I don't quite understand why most lenses seem to have approximately the same diameter aperture regardless of focal length. F-stop is, by definition, a ratio of focal length to diameter, so a 20mm ...
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3answers
403 views

Does lens metadata from crop-sensor cameras factor in the crop?

I use a Canon 60D, which is a crop-sensor DSLR. Does the metadata found in Lightroom or Bridge report the actual focal length or the crop-sensor equivalent? For example, if the metadata says the ...
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4answers
302 views

At what focal range does it make sense to have Image Stabilization turned on when using a Tripod?

I was always under the impression that one should turn off the Image stabilization when using a tripod but when I see lenses with long focal length (300mm, 600mm etc...) comes with IS on them. ...
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2answers
180 views

What happened to multi-focal lenses?

Apparently multi-focal lenses such as the Tri-Elmar 16-18-21mm went out of fashion but I was wondering if the reasons for that were technical or commercial. Are multi-focal harder to build compared ...
2
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3answers
424 views

Are there specific use-cases in mind that make the 70-200 F2.8 worth its weight/size?

I've been looking to upgrade my Mark iii's kit lens, and am comparing lens strategies. The 70-200mm canon F2.8 seems like an enduring and very popular lens. After holding one, i am left wondering why? ...
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1answer
198 views

What factor determines the largest usable sensor size with a certain lens?

Reading this excellent answer about field of view, focal length and sensor size a new question came to mind. From the drawn diagrams it is clearly visible that for the same focal length an increase ...
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5answers
21k views

What lens focal length most closely resembles the human eye perspective?

For example, if I have a lens that is 16mm-50mm, which focal length would be the closest to the human eye view? (I don't have a camera yet, so I'm just curious). Would 50mm be more zoomed in than ...
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2answers
9k views

How do people shoot very large moon views?

I see pictures of the moon that looks like it is very close to the earth; I am wondering whether they are real or is there a trick to show the moon that big? Here is an example: ...
3
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3answers
418 views

Is lens focal length specified considering the effect of barrel distortion on field of view?

Given a Nikon 14mm f/2.8D ED AF Ultra Wide-Angle Nikkor Lens on a full-frame sensor, in theory the field of view is HFOV: 104° x VFOV: 81°. However this lens exhibits noticeable barrel distortion ...
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2answers
719 views

Is there a difference between using a telephoto or wide-angle lens for portraits? [duplicate]

Possible Duplicate: Which focal-length lens is usually used for portrait photography, and why? Assuming a similar aperture, what difference would you see using a 50mm, 85mm, or telephoto ...
1
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3answers
710 views

Will a short focal length cut it for indoor event photography? (Context: It's Crowded, Dark, Has Mixed Lighting, and Requires Walking Around.)

Short version: What primes are good walk-around lenses for an indoor, dark, crowded environment where you'll be taking pictures of individuals or small groups ad-hoc, walking around and stopping in ...
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2answers
894 views

What is the benefit of a dedicated wide angle zoom vs a superzoom?

I am considering buying a Sigma 10-20 mm F3.5 wide angle lens for my canon 550D, but not sure what the benefit would be compared to using the wide angle end of my existing Sigma F3.5-6.3 18-250 mm ...
3
votes
1answer
249 views

Why 5-50x focal length for autofocus micro-adjustment?

When we do an AutoFocus Micro Adjustment session, the general opinion is to set the focusing target at 25 x focal length (or somewhere in the range of 5-50 x focal length). Why is so? What happens if ...
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3answers
389 views

Is it possible to calculate focal length if you know the aperture?

I need focal length (for my IA homework), but I didn't know that in real world I would only get the aperture. Ok, my camera is an Olympus X-21, and manual says: -----Olympus lens: 6.3 to 18.9 mm, ...
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3answers
716 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 ...
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3answers
388 views

How to get focal length from a camera specification which gives a value like “4.5-22.5”?

I am using a Sony W520 camera. The specifications mention Focal Length (f= mm) 4.5-22.5. What number should I take? The lower value or the higher? And if not both of them, then how to calculate actual ...
6
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3answers
549 views

Must I allow for crop factor in the viewfinder when shooting with a Nikon DX format camera?

Will a Nikon D5100 (dx format) viewfinder show me what the captured image will be, or do I need to allow for "crop" factor? Will that depend on/alter with using a DX lens or an FX lens? I don't have ...
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2answers
226 views

What does different focal length offer me?

I have a beginner photographer and I have spent a lot of time learning the basics (exposures, lenses, focal lengths, crop factor etc). It's all good except I'm not so sure when I need to buy lenses of ...
14
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11answers
6k views

Will a 50mm f/1.8 work for general outdoor photography?

I want to know if it's advisable to use 50mm lens for general outdoor photography. I'm torn between 35mm and 50mm primes, and have read all the pros and cons. I understand that 50mm could be tight in ...
2
votes
2answers
1k 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 ...