Relation between dust and aperture setting

Started 9 months ago | Questions thread
jfriend00
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Re: Relation between dust and aperture setting
In reply to SushiEater, 9 months ago

SushiEater wrote:

jfriend00 wrote:

SushiEater wrote:

jfriend00 wrote:

When you shoot at a small aperture, the small aperture is excluding the light rays that come from the outer parts of the lens. As such you end up with only light rays that are of very similar angle through the lens. This means that the light rays hitting a given pixel on the sensor are generally all arriving in at approximately the same angle. This means that a dust particle that's on the glass above the sensor is going to cast a much stronger shadow on that particular pixel and thus it's effect will be quite noticeable.

If you shoot at a large aperture, the entire lens are is used to collect light and light arrives at a given pixel from many different angles. Because the light arrives from many different angles, the dust particle doesn't cast a very pronounced shadow on the pixels and thus you don't notice it as much.

Not even close. Regardless of aperture used the entire lens collects the light. At large aperture light hitting the sensor is straight (er) and at small aperture light is at the angle scattered more thus you get diffraction. It works exactly the same as your eyes. The more you squint the more you see in focus (DOF) but squinting does not prevent seeing less. No matter what your entire pupil collects light you see. The brighter the light the more pupil contracts.

Sorry, dude but you just don't appear to understand here. Why do you think large aperture lenses have much bigger optics.

First of all don't call me dude. It is not polite.

Second of all large aperture lenses have much bigger optics because small lenses don't collect as much light as larger lenses. For the same reason the last element of the lens has to be larger too.

It's because the EXTRA light for the larger aperture comes from collectig more light with the larger lens. When you then take a large aperture lens and use a small aperture with it, you are restricting light so that only light from a narrower set of angles (through the central part of the lens) is actually used, the other light rays are blocked by the aperture.

Again, not even close. Regardless of the aperture the front element collects all of the light.

I am not talking about quantity of the light, I am talking about just light. Of course, if you close aperture less light coming in but all of the view coming in anyway. This light just being angled otherwise you would see nothing more than the aperture opening on the sensor.

Do this (this is an old trick), glue a small mailing stamp on the front element. Take a picture. See if the stamp is in the picture. I have a lens with lots of dust behind the front element. Never seen it in the pictures.

And squinting does not make less light going in to your eye because you are not covering the pupil.

If you squint your iris does not get larger, indication of the less light. Only your pupil collect light not he whole eye. Stand in front of the mirror and see for yourself.

The soft box makes light to go around the object and it doesn't have to be large but the larger it is the more light goes around. And it is not the only reason. Bouncing light can eliminate shadows too by simply throwing light on the shadows.

You are so wrong here. Light travels in straight lines.

But it also bends and goes around.

Take two objects. The disk and the ball of the same diameter.

Shine the light on the ball. If you are correct light should produce the same shadow as the disk.

Nope!!!! Light will go around the ball and produce smaller shadow.

It NEVER goes "around" an object (except for diffraction which is not what we're talking about here). The softbox works because the light comes from many different sources at many different angles, thus the light can't for a sharp shadow boundary.

Of course it does. Light is a stream just like liquids and air. That is how air dynamics of the car works.

Take a ball and light up the candle behind it. Now blow strong stream of air on the ball and candle will go out.

Or do this, position the object 1 foot from the wall and shine the light on it. you should see harsh shadow. Now move the object another foot away and shadow gets smaller. Same light, same object. Why? Because light bends around the object and lightens the shadow.

And if you don't believe me just Google.

Ignoring diffraction effects and extraordinary things that might happen in space with large bodies like planets, neither of which I think we're talking about here, light in a constant medium (like air) travels in a straight line. As long as you insist otherwise, it is not worth discussing further with you.

If you want to share a reference on the ball and disk that shows light bends and it's not purely a diffraction effect, then folks could take a look.

Oh, by the way why do YOU think that a small aperture makes dust particles more visible if it's not for the reasons I've outlined.

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