Lenses and Pinholes: What Does "In Focus" Mean? - Comments

In Summary,Stevendaryl submitted a new PF Insights post about lenses and pinholes. Lenses and pinholes are important for camera technology because they allow for better focus and less blurry pictures. Pinholes are better than holes because they don't produce rainbows.
  • #1
stevendaryl
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stevendaryl submitted a new PF Insights post

Lenses and Pinholes: What Does "In Focus" Mean?
lensfocus.png


Continue reading the Original PF Insights Post.
 
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  • #3
For an introductory article, I think it would be good to include a small paragraph why we need the pinhole in the first place.
 
  • #4
I like what you've done with figure 2. It shows that if you take 2 different rays from the same point, then they essentially help form two separate images of the same object at slightly different locations which may overlap each other. Taken to the extreme, this means that without a lens, there are an "infinite" number of overlapping images that wind up being a blurry mess. The smaller the aperture, the tighter the grouping of the images and the less blurred the overall image is.
 
  • #5
"It seems like a superior way to do cameras, because there is no need for focusing."

Reference https://www.physicsforums.com/insights/lenses-pinholes-focus-mean/

As a matter of fact, extreme depth of focus is not always an advantage. Limiting the depth of the sharp field is an important aspect of many photos for artistic reasons and also for emphasising and isolating detail. Binoculars can often allow you to see a bird behind a bush because the bird can be in sharp focus and the bush can be a blur. Also, of course, diffraction rears its ugly head with small apertures. If you want to image two closely adjacent stars, you will be needing a telescope objective of many (even hundreds of) cm diameter. It's horses for courses, as ever.
 
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  • #6
sophiecentaur said:
It's horses for courses, as ever.

I'm... not sure I know what that means, lol.
 
  • #8
After reading this , I understood what is exactly meant by " in focus".

Thank you, thanks a lot for posting this insight post.
 
  • #9
Why do you need a lens over the hole? The simple answer is: to make sure that the image is in focus.

Even pinhole cameras can give good focus. The reason we use lense is lense can gather much more light thus giving bright sharper picture unlike a tiny hole.
 
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  • #10
Frenemy90210 said:
Even pinhole cameras can give good focus.
Good(ish) :smile:. The image will have no more detail than the diameter of the pinhole. That is probably not as good as a 20MPx camera sensor can record. But, projected on a big screen, the perceived sharpness can be good. (Darkened room needed, of course)
 
  • #11
sophiecentaur said:
Good(ish) :smile:. The image will have no more detail than the diameter of the pinhole. That is probably not as good as a 20MPx camera sensor can record. But, projected on a big screen, the perceived sharpness can be good. (Darkened room needed, of course)
Different colors within the image refract at different angles at the lens boundary. Thus different colors will have a different focal lengths for a glass lense. A pinhole does not have this problem. Pinholes never give rainbows unlike a powerful lense.
 
  • #12
Frenemy90210 said:
A pinhole does not have this problem.
True. It masks the problem with problems of its own; the image from a pinhole is blurred for a start. It is a really trivial matter to make a lens with an aperture of, say f22 which will produce a sharper image than the equivalent pinhole and in which the Chromatic Aberration is hardly detectable. So in what respect would a pinhole be 'better'? In this game of Top Trumps, the only parameter for which the pinhole scores higher is on Production Cost.
The problem with a pinhole is basically that it doesn't let in enough light. Taking the Sun as the brightest subject for for observation, a pinhole camera is inadequate, even for that, if you want any serious resolution for sunspots etc.
Frenemy90210 said:
a powerful lense.
How "powerful" are you suggesting and how would a pinhole achieve the same result.
 

Related to Lenses and Pinholes: What Does "In Focus" Mean? - Comments

1. What is the purpose of a lens in a camera?

A lens in a camera is used to focus light onto the image sensor or film, creating a clear and sharp image. It also helps to control the amount of light that enters the camera.

2. How does a lens affect the focus of an image?

A lens can change the focus of an image by bending and refracting light. When the lens is adjusted, the distance between the lens and the image sensor changes, allowing for objects at different distances to come into focus.

3. What does it mean for an image to be "in focus"?

An image is considered to be in focus when the light from a specific point on the object being photographed is focused onto a single point on the image sensor or film. This results in a clear and sharp image.

4. Can a pinhole camera produce images that are in focus?

Yes, a pinhole camera can produce images that are in focus. The small opening of the pinhole acts as a lens, creating a focused image on the film or image sensor. However, the image may not be as sharp as with a traditional lens due to the lack of precision in the pinhole's size and shape.

5. How can I tell if my camera is in focus?

Modern cameras typically have autofocus systems that automatically adjust the focus for you. However, if you are using a manual focus camera, you can tell if your camera is in focus by using the viewfinder or LCD screen to check the sharpness of the image. You can also use the camera's built-in focus assist features, such as focus peaking or magnification, to ensure the image is in focus.

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