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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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79 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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5answers
887 views

Does crop factor still apply to a vintage film SLR lens?

My friend has a Tamron 24mm lens on his Nikon D5000 and he says that because of its age and the fact it is manual focus, it is still actually a 24mm on his crop sensored camera. Is this right? If so, ...
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4answers
998 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
1k 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
162 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
354 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
316 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
4k 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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2answers
1k 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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5answers
803 views

What are the different focal lengths of macro lenses and their advantages?

I am interested in macro-photography. I see there are macro telephoto (zoom?) lenses (e.g. 200mm), or smaller macro lenses (e.g. 40mm) ... What are the different types of macro lenses and their ...
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3answers
346 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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11answers
9k 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 ...
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1answer
7k 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
648 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 ...
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2answers
381 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
348 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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1answer
798 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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3answers
620 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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3answers
11k views

What does “the telephoto end” and “the wide angle end” of a zoom lens mean?

In the Canon Rebel T3i Manual, page 59, it's mentioned that "If you have a zoom lens, use the telephoto end to fill the frame with the subject from the waist up." Same note on page 61 and another one ...
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4answers
324 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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4answers
4k views

How to test actual focal length?

From Matt Grum's comment to my previous question, I learned that manufacturers may casually "round" actual focal length of a lens to some nice number that gets printed on the box and stored into EXIF. ...
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2answers
186 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 ...
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3answers
600 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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3answers
3k views

50mm lens=75mm on DX camera? [duplicate]

I'm looking for a 50mm lens for my nikon d3100 and I just came across an AF-S 50mm f/1.8G lens and it says in the description that if it's used on a DX camera, the angle of view is going to be 75mm. I ...
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1answer
245 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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1answer
2k views

Why does a 50mm lens appear to give a human perspective, rather than a normal lens?

I grew accustomed to the notion that what one sees through a normal lens equates (or is close to) what can be seen with the naked eye (although that is not the "pure" definition of a normal lens, ...
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5answers
7k views

What focal length gives a “normal” field-of-view on APS-C cameras?

I wish to purchase a "standard angle-of-view" prime lens for my Canon Rebel, which has an APS-C sized sensor. Various articles note that the popular "nifty 50mm" lenses are a little too much of a ...
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2answers
986 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 ...
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2answers
1k 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 ...
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1answer
312 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
538 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
1k 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
467 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
719 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
2k views

When I use FX lenses on a DX camera, does the focal length or minimum aperture change?

If I put a Nikkor 35mm f/2 FX lens on a DX camera, is it still 35mm f/2, or has the effective focal length or minimum aperture changed, because it is being used on a smaller format than what it was ...
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2answers
234 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 ...
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2answers
2k 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 ...
8
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3answers
998 views

How can a 24-70mm and a 10-22mm both be “wide angle” lenses?

I've been looking at a 10-22mm lens for my Canon T2i. I've also come across some other "wide angle" lenses, like the Sigma 24-70mm F2.8. I don't understand how a wide angle lens can have such high ...
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3answers
214 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 ...
15
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5answers
4k views

Can I use my APS-C kit lens as a reference for choosing between 50mm or 35mm prime lenses?

I'm looking at getting a second lens in addition to my Nikon D7000's kit lens. I want to know if it's possible to use my 18m-105mm kit lens to get an idea of the focal length for a 35mm lens vs. a 50 ...
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2answers
1k 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 ...
4
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1answer
6k views

How do I find a camera's focal length in pixels?

I am working on camera pose estimation. For this, I need the focal length of my smartphone camera in pixels. (My phone is HTC Wildfire S, with Android 2.3).
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1answer
162 views

Where exactly would the focal length of a lens in the ray diagram fall?

If a lens is specified as (EF 50mm f/1.8), where exactly is the 50mm distance if I were to show it in a ray diagram? Considering that a lens is made up of multiple elements, I could not find a ...
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2answers
965 views

What are the technical camera specs for the HTC Wildfire S?

I am trying to do some CGI manipulations on pictures I've taken. In order to fake reality with some 3D object inserted in the picture, I need some information to configure my virtual camera so it can ...
3
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1answer
266 views

EOS M focal length conversion to cropped frame and full frame camera

I am thinking about EOS M .. it looks appealing to me ... especially for Hiking .. the thing i want to know is if I use my 18-55mm Canon lens (that normally come with 550D, 600D series) on EOS M with ...
30
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3answers
4k views

What does it really mean that telephoto lenses “flatten” scenes?

This is another perspective distortion question. I understand that perspective distortion is primarily a function of capture and viewing distance, but I am still working on fully understanding the ...
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1answer
103 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 ...
3
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2answers
6k views

What is the conversion between focal length and times zoom? [duplicate]

Possible Duplicate: How do I convert lens mm to optical zoom times? What is the conversion between focal length in mm (e.g. 50mm) and x zoom (e.g. 20x) commonly used in compact cameras? Is ...
3
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1answer
1k views

Taking pictures with fixed/full focus camera

I have got a fixed focus, 5 MP camera with 3.3mm focal length (not sure what it means) on my phone. I want to know what's the best way to take pictures with since it's missing auto-focus feature. Is ...
5
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1answer
2k views

Should my flash zoom match my lens focal length or its 35mm equivalent?

I have a camera with an APS-C sized sensor. Should my flash zoom match my lens's actual focal length or its 35mm equivalent? I am hoping that someone can shed some scientific light to this matter.