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.

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Ghosting artefacts in narrow DOF photographs

Snapping with a Canon EOS 600D in narrow DOF situations (for example with low f-stop numbers at long focal lenght), I get ghosting artefacts on the parts of the photograph which are out of focus. ...
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69 views

What lenses have the most human eyelike images [duplicate]

I have heard wide lenses make your head inflated which isnt good for portraits like the telephoto which deinflates your head. So If I use 35mm prime on full frame. Does it mean I will get perfect ...
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What lens would I need to photograph a very distant cathedral dome?

I want to be able to photograph the dome of St Paul's cathedral from King Henry's Mound in Richmond Park. Would a telephoto or zoom lens be the best, what focal length/zoom would be the best for ...
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How do I calculate the difference in lens reach between a superzoom compact and a DSLR zoom lens?

I know it's a beginner question, but I spent the last 3 days reading this forum and other resources on the Internet and I reached a breaking point. So decided to ask the question after all, as I ...
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3answers
399 views

Do medium format lenses have a crop factor?

When having a 50mm lens made for a APS-C camera its often the case that the lens has a focal length of 50mm on fullframe. However this means that you are getting something like a 75mm due to the crop ...
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Question on f-number and exposure [duplicate]

Is there any mathematical proof to show that the exposure in a camera is independent of the focal length used, if the f-number (ratio of focal length to lens diameter) remains constant?
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Relationship between f-number and amount of light being let into the lens system [duplicate]

Why does smaller f-number imply greater aperture diameter and consequently, greater amount of light entering the lens of a camera? As evidenced from my study across a number of resources, an absolute ...
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95 views

What's the real focal length for 18-55mm in my APS-C camera? [duplicate]

I want to buy a new lens (canon ef 50mm f/1.8 stm) that I know that the real focal length in my camera is around 80mm, but my question is if this happens in the same way whit my actual lens (18-55mm). ...
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78 views

How do I estimate PPI from camera specifications? [closed]

I have an HDL-20D digital camera with 1000TVL horizontal resolution, S/N ratio 54dB and 2200k-pixel 2/3-inch 2x IT-CCD and these are the specifications: How do I calculate PPI from these details? ...
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54 views

How to calculate Sensor Pixel Pitch?

I need to compute the “Sensor Pixel Pitch (in mm/px)” for some calculation. I have the following data available from the manufacturer: Resolution: 1920x1200 Sensor Type: 2/3” CMOS Pixel size: 4.8 x ...
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2answers
169 views

Would adding an external lens allow one area outside the focal plane to be in focus?

I’m doing high speed scientific imaging. I have a camera mounted in a fixed location with a Micro Nikkor 105mm lens. It’s viewing a fixed subject that has a small mirror oriented 45 degrees underneath ...
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Can Tamron Tap-in Console solve focal length problems in metadata?

I recently found some issues on my Tamron 24-70mm f2.8 G2 (A032) lens for Canon. The first issue is about the focal length in the EXIF data. While the lens works well in autofocusing, I found the ...
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115 views

How did they do this beauty setup? What lights and focal length? Help me recreate this

From examination the lighting source appears to be 2 fluorescent panels and a light ring. How many lux/lumens/watts is he using? What's the focal length for the field of view is he using? (35mm ...
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60 views

Effect of increasing sensor size or focal length on resolution of target object

Suppose I have a camera of sensor size 8mmx8mm, optical class (2/3)" with a compatible lens of also (2/3)". The focal length of my lens is fixed (say 8mm), and the distance to my target object is also ...
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129 views

What lens do I need on a P&S camera for photographing faces?

I'm just someone who enjoys photography, but I'm not a photographer. I don't know a lot, so please try and keep things simple. I've been using a Fujifilm Finepix S9200, a bridge camera with a 24-...
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145 views

How do I calculate how high a camera needs to be to fit an object in the frame based on its field of view?

I'm doing a computer vision application related to snooker for my dissertation. In a section of my report, I’m talking about cameras and it would be good if I’m able to do the calculation stated above....
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Is 35mm on a cropped sensor good for fashion photography?

I am quite amateur with a camera but I want to become good in fashion photography. A top model has agreed for a photo-shoot for free and in return she wants me to make a portfolio. We are planning to ...
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82 views

Is there theoretical limit on the minimal focal length for a given sensor size?

There seems to be a limit, around 0.33, on the fastest possible aperture. Is there a theoretical limit on how wide a non-fisheye lens can be? That is, what is the minimal possible focal lens for a ...
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4answers
157 views

Does amount of background blur change with focal length given equal framing?

Let's assume I have two lenses, 50mm f/1.8 and 85mm f/1.8. I want to fill the frame with the photographed object. Now, if the object is 50cm wide, I need to take the photograph at a distance of 1.112 ...
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113 views

How to calculate the new focal length when usng a lens mount adapter

I'd like to know how to calculate the new focal length when using a lens adapter. Is there any formula? To be more specific: I need to attach my old lens (four third) to new micro four third system ...
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1answer
99 views

What focal length to use for full-body photography of a chubby person? [duplicate]

Recently I took pictures of someone that was slightly chubby. Close-ups using a 50mm lens went very well, but trying to get some distance in to get a full body shot were not really that satisfactory. ...
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3answers
109 views

Does field of view change for different lens model for the same focal length?

I am using two lenses - Tamron 75-250mm F/3.8-4.5 Model 104A and AF-P DX NIKKOR 70-300mm. When shot with lenses set to 250mm of focal length, the field of view for the Tamron lens is greater than the ...
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781 views

Would a 50mm lens on a Canon APS-C crop produce the exact same image as an 80mm lens on a full frame camera?

Scenario: I put a 80mm lens on a FF camera and take a picture I put a 50mm lens on a Canon APS-C crop camera (1.6x crop) and take a picture Going by the 1.6x crop, I understand the fields of view of ...
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188 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 ...
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146 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, ...
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130 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 ...
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950 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 ...
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691 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'...
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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 ...
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229 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 ...
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1answer
239 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 ...
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142 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 ...
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4answers
88 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 ...
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2answers
71 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 ...
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4answers
4k 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?
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127 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 ...
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3answers
881 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 ...
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2answers
209 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 ...
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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 ...
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4answers
350 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 ...
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4answers
431 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 ...
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2answers
609 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 ...
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1answer
52 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 ...
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199 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 ...
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2answers
567 views

Can a focal reducer be used with a teleconverter?

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 were to use a full-frame 50mm lens on a 2x teleconverter with a 0.71x focal reducer ...
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2answers
2k 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 ...
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3answers
163 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 ...
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2answers
625 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?
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1answer
473 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 ...
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2answers
245 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 ...