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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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3answers
375 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 ...
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3answers
207 views

What is the difference between shooting with different (but similar in quality) lenses at same focal length?

What are the theoretical and/or practical differences between shooting with different lenses at same focal length? For example, if we are shooting with a 24-70mm f/2.8 lens at 70mm focal length vs ...
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2answers
965 views

How far away can I be and still get a sharp subject with a 100mm lens?

If I have a 100mm lens, how far away can I shoot the subject? If I am shooting basketball, how far can I shoot the subject and still get a sharp picture?
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0answers
32 views

How to overlay the image scaling based on the user distance & focal length

I'm overlaying images on the cameraView and based on the user input of room width & height. The images are displaying proportionally to width & height ratio. but i need to overlay the images ...
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0answers
42 views

Which lens to use for landscapes? [closed]

I bought my Nikon D5200 camera with a 18-55mm f/3.5-5.6G lens as well as a Nikkor 70-300mm f/4-5.6 G lens. I was just wondering if you would be able to tell which lens to use in what situations. Like, ...
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1answer
372 views

Does the X-Pro 1's “Lens Focal Length Setting” do anything with automatic lenses?

In the X-Pro 1's custom menu, one of the options is Focal Length Setting. The manual says: FOCAL LENGTH SETTING (Defaults to 50mm) Enter lens focal length when using a lens that does not ...
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3answers
395 views

50mm vs 35mm cropped [duplicate]

For shooting portraits, why is 50mm preferable? For example with an APS-C sensor, why is it not ok to take photos with 35mm equivalent and simply crop them (to 50mm equivalent)? or take photos closer ...
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1answer
124 views

What focal length and quality of lens do I need to read 15cm high text at 500m away? [duplicate]

I have to photograph 15cm high printed text from 500 meters away. The text has to be human readable in the result. What kind of focal length do I need? Can i compromise, and get a camera with less ...
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2answers
369 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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3answers
113 views

Which lens/focal length offers the widest viewing angle without too noticable distorions/fish-eye-effect?

I am looking for a lens for my Sony Alpha 77 (APS-C), which gets me an as wide as possible viewing angle, but I also hate that fisheye effect one gets from using too low of a focal length. About where ...
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2answers
494 views

How do I convert focal length to maximum distance?

I would like to know whether there is any relation between focal length and distance. For example, what is the max distance I can shoot from a 55mm-300mm lens?
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1answer
533 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 ...
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1answer
99 views

How to calculate the new field of view from an existent one?

I have a photo having H x W (height x weight) pixels and I know, based on the EXIF, that it was shot at F1 focal length. How many pixels I must crop (or add) in order to see how it would be the photo ...
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2answers
283 views

Which is a better focal length for fashion models on the runway: 50mm or 35mm?

Which is a better focal length for fashion photography: 50mm or 35mm? I have Nikon D5100 and Nikon D7000 and I'm interested specifically for ramp walk.
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1answer
87 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
69 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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1answer
60 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 ...
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3answers
401 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? ...
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1answer
177 views

What's the practical difference in an image taken at focal length of 200mm vs 300mm? [duplicate]

I'm confused about the 200mm and the 300mm zoom ranges. I am looking for some examples of the same subject, in order to visualize the difference between 200mm and 300mm focal lengths. I want to ...
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1answer
212 views

Is this attempt to make lens measurements and focal lengths more intuitive correct?

I know next to nothing about cameras (other than how to push the shutter button). Up until a few days ago I thought of zoom as simply a multiple (e.g. my Canon S95 has 3 or 5X optical zoom) and had ...
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0answers
39 views

Which is better for portraits: 18-55mm or 75-300mm? [duplicate]

Would it be better to use a 18-55 or 75-300 for portraits? I inherited the Canon rebel xti kit and I'm new to photography. Eventually I will expand but for now just trying to get the settings down.
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0answers
67 views

How to get width and height of an image based on distance

I have an app to overlay the images on the camera overlay. But I need to set the width and height of the image based on the user distance. If the distance is, say 8 feet, how can I calculate the width ...
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1answer
56 views

How to obtain a subject's measurement from image [duplicate]

I am trying measure real object height from an image. I'm using the below formula real height = (object px height * pixel size * distance)/(focal length) my camera is Canon_EOS_550D, my values are ...
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1answer
49 views

Help to choose lens [duplicate]

I recent got 60d and EF-S 18-55mm Lens and i want to buy 1 more lens specially for product and fashion(portrait) photography... I decided EF50mm f/1.4 USM and EF85mm f/1.8 USM? Which one would be ...
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0answers
88 views

What is the basic relationship between aperture and focal length? [duplicate]

How does a photograph vary with a decrease or increase in aperture as well as focal length?
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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 ...
0
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0answers
82 views

How to calculate the zoom power (X factor) for a lens? [duplicate]

Possible Duplicate: How do I convert lens mm to optical zoom times? How can I obtain the "X factor" for a lens? I thought that to get the "X factor" I had to divide the largest focal ...
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1answer
102 views

Does manual focus carry over to a different aperture, lens or focal length?

This is in the manual focus mode. If I focus my lens so that a certain object is clear and crisp, and then do one of the following, will I have to focus again? Change the aperture Switch to a ...
-1
votes
3answers
153 views

At what distance from the lens will the image be in focus given a subject distance and focal length? [closed]

I've been trying to figure this one out for more than an hour now and I have no idea how to calculate this... You capture a picture of a tree which is standing 3m away from the camera. The focal ...
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votes
1answer
78 views

How does focal length determine lens quality? [duplicate]

What does an 18 - 50 mm lens mean? Are those numbers the first focal length and second focal length? How do you use this parameter to judge what kind of lens to buy? Does more equal better?
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3answers
193 views

Which is better: a smaller f-number lens or a bigger sensor size?

When choosing a camera, which of the following options would be the best in taking photo in low light situation and cropping photo situation? A smaller f-number lens with a bigger sensor size A ...
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1answer
1k views

What is the actual distance for taking a photograph with a 4.3-180mm Super Zoom camera lens vs. a 55-200mm DSLR lens? [closed]

What will be the true actual distance for both lens in terms of actual meters?