Crop sensor effect on apertures

[Great Bustard]

That is, I think it's more useful to say that, for example, 200mm f/2 on 1.6x is equivalent to 320mm f/3.2 on FF

Of course this statement needs to come with the disclaimer that it applies to DOF equivalence only.

It is not " DOF equivalence only". See here for the details:

http://www.josephjamesphotography.com/equivalence/#equivalence

Otherwise, it immediately invites the 'f2=f2=f2' discussion - which is obvioulsy still not settled on this forum.

In fact, the issue is settled. Whether or not people understand it is another matter. More details on "f2=f2=f2":

http://www.josephjamesphotography.com/equivalence/#1

Sorry, I was planning to stay out of this but couldn't resist.

All players are welcome.

The equivalence essay is a very informative read but the discussion on the inverse square law and how 'the amount of light from the scene depends on how wide we frame' undermines the credibility of this huge effort.

That's discussed in detail here:

http://www.josephjamesphotography.com/equivalence/#fratio

Like I said, it's all "settled", but whether or not people understand what's going on is another matter entirely. They'd be well served by reading the links and asking questions if they still don't understand.

 

[x-vision]

Like I said, it's all "settled", but whether or not people understand what's going on is another matter entirely. They'd be well served by reading the links and asking questions if they still don't understand.

Here is a demonstration of how lenses of different focal lengths form an image.

Let me ask you this: do you think light intensity at the focus/image plane changes with focal length? How and why?



Source: http://www.digital-photography-school.com/photography-101-lenses-light-and-magnification

 

[Great Bustard]

Like I said, it's all "settled", but whether or not people understand what's going on is another matter entirely. They'd be well served by reading the links and asking questions if they still don't understand.

Here is a demonstration of how lenses of different focal lengths form an image.

Let me ask you this: do you think light intensity at the focus/image plane changes with focal length? How and why?



Source: http://www.digital-photography-school.com/photography-101-lenses-light-and-magnification

Like DOF, there are many qualifiers required to answer that question. As posed, it is not a simple "yes" or "no". Here's the link again:

http://www.josephjamesphotography.com/equivalence/#fratio

Which portion do you not understand or disagree with?

 

[Bogdan_M]

I’m only joking but the fact is as much as DOF is hard for many people to grasp, CoC, which is an integral part of DOF, is even more so.

And then you give us an example of how people still have trouble with it sometimes

Sure, You! ;-)

The good thing is the effect of CoC from sensor size and resolution is negligible for modern high MP sensors. We can pretty much consider it a constant compares to other variables such as output size, output resolution, viewing distance and visual acuity.

That is because we're not taking into consideration 100% crops, but the same output size, viewing distance and visual acuity. This has nothing to do with modern high MP sensors, this is how DOF is normalized.

No that's because the resolution of modern sensor is so high, its contribution to the CoC is minimal and can be ignored.

Nope, it's just a function of enlargement. Sensors of same size have same size of CoC. Look here:
http://www.dofmaster.com/digital_coc.html

On the other hand if we do include CoC in this discussion then what you said about cropping decrease DOF is actually wrong. DOF will increase because CoC is increased (you did get this part right) when we crop.

Nope, both decrease when we crop and view at the same enlargement. Peter didn't actually say what happens to the CoC.

No both increases. Less pixels gives larger CoC. Get it?

This actually makes DOF of full frame deeper instead of shallower.

This is true, and it contradicts the previous statement where you say that DOF will increase with cropping.

Wow! Increased DOF= deeper DOF. They are the same thing. What are you thinking?

I'm thinking you have a big problem with logics. Quote:

"DOF will increase because CoC is increased (you did get this part right) when we crop."
That's p, DOF is bigger for crop.
Next phrase:
"This actually makes DOF of full frame deeper instead of shallower"

Thats non p, DOF is bigger for FF. Pick one, both can't be true at the same time.

Again this effect is so small and can be ignored for current high resolution sensors. If you have any doubt of this just try imagine what happens when you crop the image down to 1 pixel. CoC will be the entire frame and you will get the deepest DOF not matter what.

Ha ha, no, you will get just one huge blurry pixel,

A pixel is a pixel. You can't have a blurry pixel.

DOF will be very, very small .

Again I'm pretty sure you have no idea what large or small DOF means.Yeah

Right, and Joe Mama and Dave trying to educate you are as ignorant as me. How about the other, more plausible explanation that you might be wrong this time?

Let's see what the DOF calculator has to say:

FF, 35mm f 1.4, distance 10 feet, DOF 2.11 feet
Canon APS-C, 35mm f 1.4, distance 10 feet, DOF 1.33
Wait, they probably have no idea what DOF is, right?

What I, and many others, said about sensor formats only affect FOV and not DOF, unless when you try to make FOV the same, is true. Just can't believe this is that hard to understand.

I looked at some of your posts. You are totally ignorant on this subject but didn't want to understand and just want to argue. If you want to ask questions politely I might try to help you but I'm not going to go down your level if you just want to argue. Bye.

That's new, somebody who doesn't have a clue about something and uses at personam attacks to hide their ignorance... I was polite and tried to be nice in my reply to you. You, otoh , are arrogant and insist in your mistake. I have nothing to ask you on this subject, you need to redo your homework. This is a good start:
http://www.dofmaster.com/dofjs.html

There is FOV difference but no DOF difference. DOF will be different ONLY if you try to make FOV the same by: 1) change distance or 2) change focal length. This has been repeated by so many people so many times I really don't know why there are still people who can't get it.

When you crop, and display/print the same size, the apparent softness increases (so called COC - a term that I hate). This decreases the DOF.

I really don't know why there are still people who can't get it.

Here is an example (taken from Bob Atkins DOF but any other DOF calculator will give you the same):

FF, FL=50mm, distance to object = 2m, f/2. DOF = 0.19m
crop, FL=50mm, distance to object = 2m, f/2. DOF = 0.12m

--
Kind regards,

Bogdan

--
Kind regards,

Bogdan

 

[x-vision]

Which portion do you not understand or disagree with?

The whole explanation about how a wide lens collects more light from a scene than a long lens is incorrect (said politely ).

Assume that you have a 50mm and 85mm lenses - both on FF - and you are framing a perfectly uniform white wall from the same distance using f2.8 for both.

Do you think exposure would be different on the two cameras? After all, the 50mm camera is framing wider - so it gets more energy from the scene, right?

As you step back with the 85mm lens, do you think exposure will start decreasing?

 

[Great Bustard]

Which portion do you not understand or disagree with?

The whole explanation about how a wide lens collects more light from a scene than a long lens is incorrect.

The explanation, as given in the link, is correct:

http://www.josephjamesphotography.com/equivalence/#fratio

but, the statement, in and of itself, that "a wide lens collects more light from a scene than a long lens" is not answerable without giving additional qualifiers, which the link gives.

Assume that you have a 50mm and 85mm lenses - both on FF - and you are framing a perfectly uniform white wall from the same distance using f2.8 for both.

Do you think exposure would be different on the two cameras? After all, the 50mm camera is framing wider - so it gets more energy from the scene, right?

The exposure (density of the light) is the same in both cases. The 50mm collects light from more of the scene, but the 85mm lens has a larger aperture diameter (85mm / 2.8 = 30.4mm, 50mm / 2.8 = 17.9mm), and the two effects exactly cancel each other out, resulting in the same exposure.

Again, all explained in the link.

As you step back with the 85mm lens, do you think exposure will start decreasing?

As you step back, you collect light from more of the scene, which, once again, is exactly cancelled out by the fact that less of the light from the scene is reaching the aperture, due to the ISL (inverse square law).

Please take care in what you call incorrect, especially when it appears that you haven't read the explanation that was given.

 

[x-vision]

As you step back, you collect light from more of the scene, which, once again, is exactly cancelled out by the fact that less of the light from the scene is reaching the aperture, due to the ISL (inverse square law).

So, if you step back, you collect more light from the scene, right? Let me ask this then:
Does light intensity stay the same as you step back?
Because if it does, more light + same intensity = higher exposure, no?

OTOH, if light intensity decreases as you step back, wouldn't this imply that the scene gets darker and darker as you move further away (and keep framing wider).

To take the framing of a uniform white wall as an example again - as you step away from the wall:

• you should either be getting higher exposure, since you are framing wider (and more light + same intensity = higher exposure), or
• you should be getting the same exposure, in which case the wall must be getting darker (more light + less intensity = same exposure)

If you think the latter is correct, how do you explain we are able to see objects in the distance. After all, as we move away from objects they become darker, no?

Or is it possible that object do not get darker with distance - and you are maybe simply wrong about how light is collected as you frame a scene differently with different focal lengths.

 

[dsjtecserv]

As you step back, you collect light from more of the scene, which, once again, is exactly cancelled out by the fact that less of the light from the scene is reaching the aperture, due to the ISL (inverse square law).

So, if you step back, you collect more light from the scene, right? Let me ask this then:
Does light intensity stay the same as you step back?
Because if it does, more light + same intensity = higher exposure, no?

OTOH, if light intensity decreases as you step back, wouldn't this imply that the scene gets darker and darker as you move further away (and keep framing wider).

To take the framing of a uniform white wall as an example again - as you step away from the wall:

• you should either be getting higher exposure, since you are framing wider (and more light + same intensity = higher exposure), or
• you should be getting the same exposure, in which case the wall must be getting darker (more light + less intensity = same exposure)

If you think the latter is correct, how do you explain we are able to see objects in the distance. After all, as we move away from objects they become darker, no?

Or is it possible that object do not get darker with distance - and you are maybe simply wrong about how light is collected as you frame a scene differently with different focal lengths.

I can't possibly explain it as well as the otis tarda , but you do need to recognize the difference between light intensity and the total amount of light gathered over the full sensor area, or transmitted by the lens. Those are two different things, and his analysis hinges on those differences. Go back and study those aspects of his equivalency discussion.

Dave
--
http://www.pbase.com/dsjtecserv

 

[Peter 13]

As you step back, you collect light from more of the scene, which, once again, is exactly cancelled out by the fact that less of the light from the scene is reaching the aperture, due to the ISL (inverse square law).

So, if you step back, you collect more light from the scene, right?

[you collect light from more of the scene] not the same as [you collect more light from the scene]

 

[x-vision]

I can't possibly explain it as well as the otis tarda , but you do need to recognize the difference between light intensity and the total amount of light gathered over the full sensor area, or transmitted by the lens. Those are two different things, and his analysis hinges on those differences. Go back and study those aspects of his equivalency discussion.

Thank you for the recommendation. Quick question for you: do you actually know what gerenerates electrons in a sensor - amount of light or intensity.

Thank you for your recommendation. Quick question - I was wondering if you know the answer:

Do you know what generates electrons in a sensor - the amount of light or its intensity.

 

[Kellen]

...you've stumbled upon a very contentious issue

Here's an article that I read recently which addresses your question better than I can http://www.clarkvision.com/imagedetail/does.pixel.size.matter/

 

[mattr]

As you step back, you collect light from more of the scene, which, once again, is exactly cancelled out by the fact that less of the light from the scene is reaching the aperture, due to the ISL (inverse square law).

So, if you step back, you collect more light from the scene, right?

This is surreal and funny! Did you actually read what you are responding to?

 

[mattr]

CoC is affected by sensor resolution among many other factors including lens’ resolution, output size, output resolution, viewing distance and visual acuity. The effect of sensor/film resolution can be significant with low-resolution sensor/film (e.g. a

CoC is a well defined, albeit a little complicated, quantity. Anyone who does not TRULY understand the concept will not be able to understands DOF well. I’m sorry but I’m really tired of having to argue with people who have some faint idea but not really understand what it is and where it came from. There are many good articles about the subject. Make sure you thoroughly read though and understand them if you are interested. Google is your friend.

I looked at a few posts in this thread. The ones with the most confused concepts are yours.

 

[dsjtecserv]

I can't possibly explain it as well as the otis tarda , but you do need to recognize the difference between light intensity and the total amount of light gathered over the full sensor area, or transmitted by the lens. Those are two different things, and his analysis hinges on those differences. Go back and study those aspects of his equivalency discussion.

Thank you for the recommendation. Quick question for you: do you actually know what gerenerates electrons in a sensor - amount of light or intensity.

Thank you for your recommendation. Quick question - I was wondering if you know the answer:

Do you know what generates electrons in a sensor - the amount of light or its intensity.

The amount of light, measured in photons, that is collected by an individual sensor location over a period of time is a function of the intensity. The total amount of light collected by a sensor is a function of its area. And again, I'll yield to GB, who explains it better.

Dave
--
http://www.pbase.com/dsjtecserv

 

[x-vision]

As you step back, you collect light from more of the scene, which, once again, is exactly cancelled out by the fact that less of the light from the scene is reaching the aperture, due to the ISL (inverse square law).

So, if you step back, you collect more light from the scene, right?

[you collect light from more of the scene] not the same as [you collect more light from the scene]

This is different. In a non-uniform scene, the amount of light depends on your subject.

For example, if you frame a black crow in the sky with a telephoto lens, you are likely going to capture less light because your frame will be filled with the black crow.

If you use a wide lens, however, the black crow will be a small black spot in the wide bright sky.

But consider framing a sunset at the beach. You will certainly get more light if you zoom at the sun with a telephoto vs framing the entire horizon with an ultra wide.

For a uniform scene, the amount has nothing to do with the field of view and the framing.

You are getting neither more, nor less light, for example, as you change the framing of a uniformly lit white wall.

 

[x-vision]

The amount of light, measured in photons, that is collected by an individual sensor location over a period of time is a function of the intensity. The total amount of light collected by a sensor is a function of its area. And again, I'll yield to GB, who explains it better.

Let's not confuse light intensity with amount of light.

Let me give you a simple example:

You are in room with a single window. Is it easier to read a book closer to the window or in the opposite corner of the room? Also, do you think more light enters the room through the window as you are closer to the window?

During photo-electric conversion, the intensity of light determines how many electrons will be created.

 

[carlk]

It can be simple, intuitive but wrong or it can be right but hard for some to understand. I'm sorry if it is too hard for you to understand. I know there are different technical capabilities among the audience. I will stop reply unless you tell me what technical levle you are on.

CoC is affected by sensor resolution among many other factors including lens’ resolution, output size, output resolution, viewing distance and visual acuity. The effect of sensor/film resolution can be significant with low-resolution sensor/film (e.g. a

CoC is a well defined, albeit a little complicated, quantity. Anyone who does not TRULY understand the concept will not be able to understands DOF well. I’m sorry but I’m really tired of having to argue with people who have some faint idea but not really understand what it is and where it came from. There are many good articles about the subject. Make sure you thoroughly read though and understand them if you are interested. Google is your friend.

I looked at a few posts in this thread. The ones with the most confused concepts are yours.

 

[x-vision]

As you step back, you collect light from more of the scene, which, once again, is exactly cancelled out by the fact that less of the light from the scene is reaching the aperture, due to the ISL (inverse square law).

So, if you step back, you collect more light from the scene, right?

This is surreal and funny! Did you actually read what you are responding to?

Right. I guess I misread this.
Still, the incorrect assumption is that as you frame wider, you get more light.

Consider the example with zooming at sun with a telephoto vs using an ultra -wide to frame the horizon. Does the wide lens get more light?

 

[mattr]

As you step back, you collect light from more of the scene, which, once again, is exactly cancelled out by the fact that less of the light from the scene is reaching the aperture, due to the ISL (inverse square law).

So, if you step back, you collect more light from the scene, right?

This is surreal and funny! Did you actually read what you are responding to?

Right. I guess I misread this.

OK

Still, the incorrect assumption is that as you frame wider, you get more light.

No, GB also replied to this one. When you frame wider in front of a white wall, you collect light from a larger area. However, the exposure stays the same at the same f-stop because the physical aperture of the wider lens is smaller.

Consider the example with zooming at sun with a telephoto vs using an ultra -wide to frame the horizon. Does the wide lens get more light?

Are you talking about the direct light from the sun?

 

[graphikal]

The general consensus has been you, with all the misleading statements and ignorant opinions you have posted, should be the one who stop posting but then again you own the keyboard.

No, that's not the consensus; a "consensus" of just you is just you, the same old opinonated carlk who regularly exposes his ignorance as well as his bad manners.

Really, you would be due more civillity if you gave it out more often. When you rush in to "educate" others, exposing your ignorance, you both pathetic and offensive.

BTW, I guess this proves that you didn't hide my posts as you claimed, eh?