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# Questions tagged [focus-distance]

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### What units are used for zoom and focus distance for the varifocal Dahua camera? [closed]

I've been working with an industrial Dahua camera and since I do not have a full model of how the camera works (and because I'm a complete newbie to cameras in general), a few elements are still ...
7k views

### Can you tell from a blurry photo if focus was too close or too far?

If you focus on a focal plane that is sufficiently in front of your subject, or past it (relative to depth of field), the subject will appear blurry. Is there some way of telling purely from the ...
82 views

### Why does some lenses have red focus points on their focus rings? [duplicate]

A typical lens have white focus indicators on their lenses [5m 50m and infinity] but some have red points for 85m and farther and some lenses have a red curve instead of numbers. What are these red ...
154 views

### How to accurately determine the size of a nearby object (~15cm) using the autofocus focus distance?

The problem I'm trying to determine the size of an object using the focus distance determined by the autofocus of a smartphone camera (Galaxy Note 8). But I don't seem to be able to get an accurate ...
1k views

### Why doesn't the focus distance at which my lens has magnification 1 match the formula?

From the Magnification Wikipedia page, I have the following equality: M = di/do = f/(do – f) = (di – f)/f with M the magnification, f the focal length, do the distance from the subject to the lens,...
206 views

### Sharp focus photography with APS-C [closed]

So, it happens that I am really passionate about the sharp focus photography, where some points on the picture looks sharper than the usual, just like the example I've attached. My question is: how ...
48 views

### Angles and distances for photogarametry

I want to photoshoot rocks which are about 20cm by 20cm by 20cm and make a 3D model of it. I am yet to find the software to create the 3D model but might use VisualSFM. Question is what angles, ...
360 views

### What is the depth of field if the the focus distance is set to infinity?

If the camera format is 35mm, the focal length of the lens is 35mm, the aperture is f/4, the subject distance is 25ft, and the hyperfocal distance is 39'7", then what would be the range of focus when ...
477 views

### Does focusing at infinity mean the sensor is at F?

According to thin lens optics, an object focused at infinity should correspond to the sensor position exactly at F, which is the focal length of the lens. It also means that the image of every point ...
4k views

### Since it's not “focal length”, what is the term for the distance at which things are in focus?

I was under the impression that the “focal length” of a lens is the distance at which stuff appears in-focus. (E.g., perhaps I set the camera so that objects 3 meters away appear sharp, ...
468 views

### Do the out of focus elements in this photo look normal?

I just shot this picture with my Canon T5i (75-300mm) lens. I zoomed from a distance to take this picture. As you can see, the focused area looks normal, but the grass that is out of focus looks ...
563 views

### Is it possible to make your own focus distance scale?

I'm using a Nikkor 18-105mm kit lens and it doesn't have a distance scale on its focus ring, is it possible to create your own distance scale by knowing the 0 and the infinity focusing points on the ...
63 views

### Focal length of the sony DSC-H20 [closed]

I am working in finding the distance of the objects in a video taken using a Sony Camera model DSC-H20 and suppose that any lens or zoom distortions were applied. In order to know the position I need ...
1k views

### 50mm and 100mm macro lenses difference at the minimum focus distance?

So I bought a Kiron 105mm f2.8 1:1 lens recently to be used with my Sony a6000. I know that the difference between a 50mm macro and a 100mm macro is how close you can get to your subject, that is with ...
640 views

### Is the distance scale on a lens linear?

I have Nikon lenses with distance scales on them so I can set the lenses to the hyperfocal distance when I need. Say now the focal length is 28mm and the aperture is f/16. The corresponding ...
5k views

### How do extension tubes affect focusing distance?

How do extension tubes affect focusing distance? More specifically, what I mean to ask is : why does the maximum focusing distance become shortened when an extension tube is attached? - Why does the ...
6k views

### Why can't my DSLR with kit lens focus on objects close to the lens?

I have a Nikon D5200 with the 18-105 kit lens. I cannot focus the objects which are 15-20 cm away from the lens. Can anyone tell me how to manipulate the settings so that i can focus those objects? ...
163 views

### Tricking compact's camera autofocus

I'm trying to get some bokeh using a compact (almost premium) camera, a Nikon Coolpix p300 (although the question is general). Since the camera hasn't got a manual focus option, I'm trying to use the ...
221 views

### What lens is needed to change the minimal focus distance length of my camera?

Here is my problem, I Have a scientific camera, a Sony Block FCB-EH6500, which has an automatic focus. The minimum focus distance is 1 cm when completely zoomed out and 120 cm when fully zoomed in. I'...
5k views

### Why is the focus distance for a mirror image further than the surface of the mirror itself?

When I take photographs of a subject reflected by a surface (water, mirror, glass) I notice that the focussing distance is not the distance from my camera to the surface, but mostly it is close to ...
2k views

### When a camera auto-focuses, is the current focus distance reported from the lens to the camera?

The question says it all -- does the camera "know" how far the subject is from the lens, i.e. what is the current exact focus distance set at the lens?