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Photography

Questions tagged [focal-length]

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.

409 questions
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3answers
140 views

A projection of a real-image is one fixed perspective, but looking through the lens with my eye, I see many perspectives. Why?

Assume that I have a camera obscura (with a large lens - something like a magnifying glass) setup projecting an image of some still life. I look at my projection on my projection plane and I see one ...
2
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2answers
113 views

Why can my eye focus on the real image of a convex lens at many distances from the lens, but a projection only works at a specific distance?

Say I have a single convex lens. I set it up like a camera obscura, shine a light on my object and project the image onto a projection plane. Given the focal length of my lens, the projection plane, ...
0
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2answers
92 views

How can the focal length for shake reduction be determined when the lens is mounted using a reverse lens adapter?

My camera (Sony A7RII) offers image stabilisation (SteadyShoot). I shoot macros using a 50mm and a 28mm Olympus lens reverse mounted with anadapter. What values should I enter in the menu to ...
4
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4answers
631 views

35mm for portraits

Ok everybody knows 35mm is not the most flattering focal length for a portrait and by portrait I mean somewhere from chest and above... and of course it gets worse as we get closer to the subject. So ...
1
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5answers
366 views

Why are lenses characterized by focal length and not the effective field of view?

In photography, it's the accepted norm to say that if you know the sensor size of your camera and the focal length of your lens, then you know the field of view of your system. However, in optics, it'...
2
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4answers
610 views

Dogs & Portraits: Should I buy the Canon 50mm f/1.4 or the Tamron 35mm f/1.8 for my APS-C DSLR?

I recently purchased a Canon EOS 77D (which offers an APS-C sensor) with a Canon 70-200mm f/4. Now, I am looking to purchase a prime lens. My research suggests a choice between the Canon 50mm f/1.4 ...
0
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2answers
207 views

How to take pixel-for-pixel aligned pictures with a DSLR and iPhone 7?

The Plan So I am trying to take two pictures, one with a DSLR and one with an iPhone 7. Why an iPhone 7? That's just what I own currently I want the photos to be aligned so that they are exactly the ...
1
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1answer
93 views

Pixel diameter of a given field of view calculation equisolid (equal-area) fisheye lens

I have a 180° equisolid (equal-area) fisheye lens with a focal length of 8 mm. I want to crop images to a circle defined by an angular field of view from the zenith angle of the lens (i.e. the middle ...
3
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2answers
96 views

What factors affect the detail and clarity of a photo taken by a digital camera?

By clarity, I mean to preserve as much detail as possible when zoomed in. For example, I take a photo of my cat 10 meters away, and I want to zoom in and able to see each single fur as clear as ...
1
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4answers
70 views

how many f stops should I allow for a given change in focal length - ISO and shutter speed remaining constant?

There are charts that show me what how many stops in shutter speed or ISO to allow when, for example, using an ND filter but given that a longer focal length reduces light available is there a chart ...
0
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2answers
58 views

Measure in photo formula help

Good Day I am trying to measure the width of an object in a photo as accurate as possible using the formula found in a previous question. Distance to object(mm)=f(mm) x real height(mm)x image ...
1
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4answers
1k views

How to find the focal length used by looking at image contents without examining metadata?

By looking at a photo, how can one tell what focal length was used without looking at the photo metadata?
1
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3answers
97 views

How is wide field-of-view possible using a tiny sensor?

From looking at the FOV tables on this page, I can see that FOV is greatly reduced as sensor size decreases. It seems that 1/2.3 sensors would produced fields-of-view that are tiny, even at the ...
3
votes
3answers
283 views

How can I see the equivalent focal length of the current zoom of my Nikon P900?

I have a P900 that I use for birding. It's great for carrying around and not so great when (as usual) the light is low. I'm considering using an alternate set-up, for example a D500 coupled with a ...
2
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2answers
111 views

How to test image quality with a camera that is focused to infinity?

I have to test a camera that is focused to infinity, but I cannot take an image of an object that is more then 1.5 meters away from the camera because I can't get it out of the room itself. (The room ...
22
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5answers
6k views

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

As your lens's focal length gets longer, fewer photons pass through the lens to hit the mirror/sensor. Why don't you see darkening when you look into the viewfinder and zoom in with a zoom lens, and ...
2
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4answers
237 views

Given aperture and focal length, what is the minimum distance for maximum resolution? [closed]

I'm going to describe a physics experiment involving imaging a proton beam using a CCD camera by reflecting it on a aluminium oxide surface, and we need some help about how close the camera should be ...
3
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4answers
363 views

What tiny lens to shorten the focus on a tiny camera?

I'm trying to set up a tiny camera for a tiny science experiment. The camera is an OmniVision OVM6211: It's pretty much a 3mm cube, containing the image sensor and all the lenses. It has a 90º FOV ...
3
votes
2answers
325 views

Does changing the focal length change the depth of field for the same magnification?

When taking pictures with lenses with the same f-stop and different focal lengths, and magnifying the same subject to the same size (by changing the distance), how does the depth of field vary? I am ...
2
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1answer
50 views

Retrofitting of an old image documentation system with a new camera

I am trying to retrofit an old laboratory gel documentation system (Kodak 2000r) with a new camera (the original is dead). I connected to system lens a Basler acA1300-200um but the image I got is from ...
1
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1answer
192 views

42.8mm on Nikon COOLPIX P7700 > 55mm on Canon EOS 77D? [duplicate]

I have a Nikon COOLPIX P7700 and because it has been losing function due to wear and tear after 6 years, and I wanted a better zoom range for wildlife, I decided to get a Canon 77D DSLR so I could get ...
1
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2answers
456 views

Can you use a focal reducer with a teleconverter?

I don't believe it would be possible to do it but, is it? If I was to use say a full frame 50mm lens on a 2x teleconverter with a 0.71x focal reducer on APS-C would it work? Would you also get the ...
2
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2answers
949 views

How do I obtain sharp images on full body portraits?

I currently have a 50mm 1.8 and 85mm 1.8 and would want to know if the bokeh or sharpness would be any different at all. Many seem to say that the 85mm woud work best, but wouldn’t I have to bump up ...
6
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3answers
131 views

How does sensor size affect minimum front element size for a given f-stop and focal length?

Does the sensor size affect the needed size of the front element given a focal length and f-stop? My intuition tells me that a bigger image circle would require a bigger front element to maintain the ...
6
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2answers
583 views

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

Looking at this Wikipedia article, a huge portion of kit lenses start with 18mm For example: 18-55 18-70 18-135 18-200 Why?
5
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1answer
385 views

Is this “tack sharp with blurred background” look done with Photoshop?

I’m relatively new to photography and although I feel like each photographer has their own style when capturing an image it seems that sometimes I just don’t have the right equipment. The pictures ...
3
votes
2answers
134 views

Which lens focal length to match binoculars' magnification: An alternative approach

The question of how lens focal length and binocular magnification appears to have been asked over 3.86 quinzillion times. Regardless, it's still hard to get an answer the layman can understand. I'd ...
3
votes
5answers
832 views

How is focal length facial distortion different on an APS-C sensor compared to a full frame? [duplicate]

From my understanding (and research) focal length affects how a face will end up looking on a photograph. Here's an example of focal length distortion on a full-frame sensor: My question is: will a ...
5
votes
3answers
206 views

Why would lens be much longer than its focal length?

I accidentally saw Nikon 17-35mm f/2.8 lens and noted that it is rather large for its focal length. Here's the first review of this lens search offered - looks like it's 107 millimeters long. Given ...
3
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2answers
192 views

Focal length measurement and definition in DSLR cameras [duplicate]

So i am a bit confused when it comes to focal length in DSLR cameras. According to multiple sources online i found and as per NIKON "It is a calculation of an optical distance from the point where ...
2
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2answers
159 views

At which focal lengths is it ‘safe’ to have the sun in frame?

I've seen both beautiful wide angle pictures that include the sun as well as camera damage from pointing long lenses at the sun. At which focal lengths is it safe to have the sun in frame? assuming ...
0
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2answers
130 views

Best focal length for Micro 4/3 camera for a shoot of gardens and garden features?

I am mainly a web developer but now have become also a sort of a semi-pro photographer as well - shooting only portraits on my micro 4/3 system with only one lens - a beautiful Leica 25mm. I have a ...
5
votes
3answers
1k views

APS-C crop factor 1.5x or 1.53x

I'm having issues wrapping my head around how to get crop factor based on 35mm. I understand what crop factor is but my math is confusing me. For example, everyone knows that aps-c is a 1.5x crop ...
6
votes
6answers
687 views

How does crop factor affect perspective?

I have a question about crop factor and how it affects the perspective. Suppose you have one Super 35 camera and one APS-C camera. As far as I understand, to photograph the same image on the APS-C ...
1
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1answer
416 views

What is the typical FOV / focal length for house interior shots?

I don't do interior shots, but I do see a lot of them these days because I am house hunting. If you look at high end houses on Redfin.com, you can see typical examples done by professional ...
2
votes
1answer
434 views

Will 50mm f1.4 and 85mm f1.8 lenses produce the same bokeh, given the same framing?

I have recently upgraded from a DX Body (Nikon D3300) to a FX body (Nikon D750) and also I have Sigma 70-200mm f2.8 & Sigma 150-600mm Sport lenses. While I was using the DX body, I had a Nikon ...
2
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4answers
2k views

Finding focal length from image size and FOV

I have bumped into this statement in an Engineering journal. The statement is mentioned on right side example. A 640x480 image with a horizontal FOV of 47 degrees gives focal length f = 740 pixels. ...
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3answers
157 views

If a camera has two lenses, where is the focal plane? In the sensor or in the second lens?

For example, this exercises asks where is the focal plane. Is in the sensor or in the second lens?
1
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1answer
327 views

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

I have a EOS 80D and supposedly it has a max aperture of f/8. Does this mean that my camera can't take advantage of lenses with larger aperture? E.G. This one for example: Canon EF-S 24mm Camera ...
0
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2answers
980 views

Crop Factor in real world, Sigma 150-600mm C on Canon 1300D [duplicate]

After I bought Sigma 150-600mm f5-6.3 Contemporary DG OS HSM Lens I ran some tests. This test was to see the difference in focal length compared to a crop sensor lens vs this full frame lens on a same ...
1
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3answers
59 views

Query on focal length of Canon SX520HS [duplicate]

I was checking specification of Canon SX520HS and this is what i found regarding focal length: Focal Length 4.3 – 180.6 mm (35 mm equivalent: 24 – 1008 mm) Now to get 35mm equivalent focal length,...
2
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1answer
206 views

How to enlarge an object by x-times with an optical zoom

My camera employs a 30x optical zoom, with focal length ('f' from here on out): f = 4.3 mm to 129 mm. If I am at 1x and I see an object as 100 pixels, to enlarge it to 150 pixels, can I set the zoom ...
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1answer
333 views

Focal length, sensor size and field of view in digital photography

For a robotics project, I've been testing two cameras 1)ELP USBFHD04H, sensor AR0330, 1/3 inch 2)ELP USBFHD06H, sensor Sony IMX322, 1/2.9 inch Besides, I've been testing different lenses, all of ...
12
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3answers
2k views

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

I'm starting to study cameras and lenses. By reading explanations and watching videos on convex lenses, I learnt that they make parallel light rays converge to a single point called the focal point. ...
5
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1answer
836 views

50mm mirror lens. Does one exist?

I like the bokeh and limitations of mirror lenses. I however, also love my 50mm 1.4. Does a 50mm mirror lense exist? I searched but could not find one. If not 50mm what is the closest to 50mm one can ...
6
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1answer
181 views

Determining the size of the smallest resolvable detail for a given camera

My generic question: Given camera specifications, e.g: sensor resolution, sensor image area, pixel size (area), optical size, focal length (ratio), fov (horizontal and/or vertical) and ...
4
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1answer
795 views

Decrease the focal length of lens

Reading about tele extenders for lens and how they change the focal length/field of view I came up with the idea if there is something/some way to shorten the focal length of the lens. And the ...
-1
votes
6answers
615 views

How to get a clear image of a distant subject?

i have to shoot a subject which is 300 meters far and i need the image as clear as a portrait i took by a 18-55mm lense. Which lense i can use?
0
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1answer
509 views

FX & DX Lenses on DX Body [duplicate]

If I use a 50mm prime FX lens on a FX camera, I will get 50mm. If I use a 50mm prime FX lens on a DX camera, I'll get 75mm (assuming 1.5x crop factor). Now, if I use a 50mm prime DX lens on a DX ...
0
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2answers
136 views

Confused about different optical zoom on different lens [duplicate]

I'm looking at 3 different lens mainly for distance shots but with a bit of Macro occasionally. Tamron AF 70-300mm F/4-5.6 Nikon AF-S DX NIKKOR 55-300mm f/4.5-5.6G Sigma 70-300mm f4-5.6 The bit ...

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