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

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Why do DPReview's charts show the G7X II as having an aperture around f/8?

I have a Canon G7X II camera, which has a 24-100mm f/1.8-2.8 lens. Why does DPReview's chart show it having an aperture of around f/8 at a focal length of 100mm?
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Will a focal reducer help me image deep sky objects using an 8" newtonian?

Will a 0.5x focal reducer help me if i am imaging deep sky objects using a 1200mm focal length optical tube(f/6), 32mm super view telephoto extension eyepiece and a nikon d5500 with a sensor size of ...
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Does using a lens adapter change focal length?

Does using a lens adapter change the field of view? I recently bought a Sony NEX-5, an extra Minolta MD 50mm 1.7/f lens and a MD to E-mount adapter and I was wondering, as the adapter increases the ...
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What is the relationship between field of view and focal length for fisheye?

What is the relationship between the focal length and field of view for an equal-area ("equisolid") projection fisheye lens? Alternatively, what is the relationship between the 180-degree image ...
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How far do I need to extend bellows to achieve particular minimum focal length [duplicate]

If I have a 200mm lens, and want to focus at, say, 450mm from the camera, two questions: can I (do I need to) use bellows to achieve this? is there a formula for how to work out how much extension I ...
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Why doesn't the background become blurred when I change the aperture on my Fujifilm S4000?

I am sorry if my question is too naive, but I am a complete beginner in photography, and I think I still need to understand well what aperture is. I have a Fujifilm S4000 camera, and I know I can't do ...
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3answers
209 views

Why are crop lenses indicated with focal lengths they don't have [duplicate]

If we will use crop lenses only on crop bodies, why do we all crop lenses for example "10mm" when they are actually "16mm" (with a crop factor of 1.6 in this case)? Edit: I am familiar with the ...
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107 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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53 views

Focus change after switch off camera?

I am using a zoom lens. The focal length is adjusted to 70 mm with manual focus. I then switch off the camera. Will the focus change after i re-turn on the camera? Noted that focal length and zoom ...
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4answers
137 views

What lens will let me take a photo of a bird high up in a tree?

What lens would work for a canon 6D to take up close photos of birds far away in the trees? My Canon 100mm-400mm lens just doesn't get that close.
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3answers
78 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 ...
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6answers
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Is there a difference between taking a far shot on a 50mm lens and a close shot on a 35mm lens?

I am looking for a prime lens to pick up, and I'm wondering if there is any difference between 35mm and 50mm in terms of the end product if I just stand back more with the 50mm. I use the Sony a6000 ...
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3answers
299 views

Which lens/focal length offers the widest viewing angle without too noticable distortion/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
1k views

Does a crop sensor affect closest focusing distance? Why does it not affect focal length in EXIF data?

Since I am considering to buy the Nikkor 105mm micro VR, I wondered if the cropped sensor does affect the closest focusing distance of 0.31m? Thinking about this, the following additional (and ...
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12answers
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What is crop factor and how does it relate to focal length?

I'm reading that a 50mm lens is recommended as a first prime lens for DSLR owners as it's supposed to give a 'natural' perspective, but when used on (most) DSLRs, the view is cropped, as if you were ...
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5answers
780 views

How can I explain focal length to someone who isn't into photography?

Context So my friends and family are curious about how far my lens can reach. I usually explain with focal length and show them a few pictures. Question Is there any easier way to explain what ...
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1answer
36 views

focal length 300mm on dx camera + 2X TC [duplicate]

I saw nikon Nikon AF 70-300mm f/4.0-5.6G which works on both DX and FX sensor camera. I have Nikon D3300 which have DX sensor. As lens works on FX sensor if we use this lense on DX camera what would ...
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224 views

Does an APS-C lens label itself with effective or true focal length? [duplicate]

I'm not sure if I've phrased this correctly, but I've just purchased two prime lenses: Nikkor 50mm f1.8/G (FX) Nikkor 35mm f1.8/G (DX) I know that the effective focal length of the 50mm FX lens ...
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5answers
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So my iPhone 6 camera lens is as wide as my full frame 35mm DSLR lens?

I am trying to understand what is the deal with "full-frame" and what difference it makes, so did a silly test: I sat at my bed and aligned the iPhone 6 camera with the door of the room and took a ...
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2answers
133 views

Shouldn't the diameter of the moon with a 600mm lens be double what it is with a 300mm lens?

I used a 300 mm lens and recently bought a 600 mm lens, thinking that the area in the frame with the 600 mm lens will be exactly half of the area covered by the 300 mm lens. Practically I am not ...
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35mm DX prime lense on dx crop sensor(nikon d3300) [duplicate]

I have Nikon D3300 DSLR. I'm confused with 35mm and 50mm prime lenses on FX and DX cameras. Somewhere I read that if a 35mm prime lens is used on a FX camera the focal length is equivalent to around ...
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How can a lens with a single focal length 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 ...
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What is a good focal length for street photography?

With a long lens you don´t disturb people but you are left "out of the scene", while with a short focal lens you are "inside the scene" but you may disturb people. What is a better alternative for ...
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What is the shape of the focal plane?

This is something I just realised I don't entirely know the answer to, so I'm going to ask it here as I think it's interesting. In most non-scientific writing on depth of field, diagrams generally ...
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7answers
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How do I convert lens focal length (mm) to x-times optical zoom?

What is the rule to convert the 'mm' notation to the 'optical zoom' notation? I searched a bit and found this one: optical zoom = maximum focal length / minimum focal length For example a 18-55mm ...
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Why do Full Frame lenses and crop body lenses exhibit the same crop factor when used on a crop body camera?

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
256 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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What is a normal lens?

I've heard people call 50mm lenses "normal lenses". For a lens to be considered normal, does it have to be exactly 50mm or is there some leeway? Does the normal focal length depend on crop factor of ...
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Does my crop sensor camera actually turn my lenses into a longer focal length?

So, I mount a 200mm lens on my Canon 450D. It effectively becomes a 320mm lens. Is this the equivalent of 320mm on a full frame camera? That is, from what I've figured out I get an equivalent field of ...
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How to achieve full-frame look/view on a crop-sensor - without changing the lens?

I have a Canon 600D, which is crop-sensor camera. If you're shooting with a Canon EF 50mm, it'll be (50x1.6) = 80mm on a normal full-frame body right? I'm also a street-photography-kinda guy, which I ...
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1answer
879 views

Below which focal length are lenses considered to be wide angle?

Focal length is the only factor that decides whether a lens is described as being normal or wide angle. Below which focal length are lenses considered to be wide angle? Is this focal length the same ...
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380 views

What is the sweet spot of the Canon's 18-55mm IS STM lens?

I'm plannning to photograph negative film like this. And I would like to know what would be the sweet spot of my lens to achieve best sharpness possible, what f stop and at what mm I should be ...
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Does 4.0-72mm on the lens when equivalent focal length is 24-432mm mean crop factor of 6×?

The Samsung WB250F has 4.0mm-72.0mm printed on its lens, and its 35mm equivalent focal length range is 24mm-432mm. Does that mean it has a 6x crop factor?
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Circular polarizer works great at shorter focal lengths, but significantly degrades the image at longer lengths. Why?

I bought a cheap CP recently to play around with, and noticed an interesting phenomenon: Using it with my 24mm lens on full-frame, images turn out tack-sharp - there is hardly any difference in ...
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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.
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Is an EF 50mm f/1.4 the same as 50mm with an EF-S lens on a Canon 550D?

I have a Canon 550D with the standard 18-55mm kit lens. The 550D has a 1.6× crop factor. My question is very simple but whenever I've asked before (Yahoo Answers) I always got overly-complicated ...
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3answers
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How do zoom lenses restrict their widest aperture at the telephoto end?

Does the aperture ring lock the apertures beyond, say 5.6 at length lens's telephoto end? Does the lens introduce an obstacle to the aperture ring so the lens can't be opened anymore beyond the ...
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1answer
237 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 ...
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1answer
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What prevents a f/1.8, 24 mm - 70 mm or similar range zoom lens from being made? [duplicate]

I see that it is common to have professional grade lenses such as 24-70mm lenses made at f/2.8. After using a 50mm/1.8, I was wondering what would prevent a more versatile zoom lens to be made that ...
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5answers
470 views

What focal length is used in photos that both model is zoomed in and the background is open

It is easier to explain my question just by a sample photo from Lyndsey Adler: See the models are so big in the photo and still that big RV is also in the image. What focal length do I need for a ...
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4answers
483 views

How is actual focal length greater than focal range of lens?

This image (not shot by me) is shot using 70-300mm f/4.5-5.6 lens, but the EXIF shows the focal length to be 302 mm. How is it possible to be shot at a focal length (302 mm) greater than the ...
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2answers
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Where is the image sensor located in a camera with a fixed-focus lens?

I am working on some research on the Kinect for XBOX One. I am looking into the depth measurements of the device. I have read that the depth values are calculated from the devices focal plane. So i ...
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6answers
425 views

What do the mm numbers on lenses mean?

I'm confused about lenses and numbers. Why are some lenses ex. 50mm-300mm Different sizes? Some lenses with the same mm numbers are huge and some are small... What's the difference? Also the prices ...
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3answers
5k views

Is the formula for object image size given focal length, etc. independent of sensor size?

I am trying to figure out how big an object of, say, 50cm height at 100m distance and 600mm focal length would appear on a camera's sensor. The ubiquitous formula object size in image = focal length ...
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6answers
156 views

What is the shortest focal length before a black ring appears?

I know it depends on brand to brand and model to model, but in general terms, what is the shortest focal length I can have before the black zone (A) starts to form, or it is barely noticeable? (B) ...
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4answers
714 views

Why do two zoom lenses set to 200mm on the same camera produce different fields of view?

I've been testing out a Nikon 18-200mm F3.5-5.6 against a Nikon 55-300mm F4.5-5.6 I took two pictures of a door knob from an equal distance of about 3 meters away with the same Nikon d7100 DX camera ...
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5answers
3k 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) ...
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Which focal length lens generally has the sharpest lens? 24, 35, 50 or 85?

Context I realize that the above four focal lengths lend to having a different perspective that make them all unique. It might be possible to use one as the other but that isn't always true with the ...