70D vs D7100 ISO Comparison at 100%

[AlanF]

Here is a nice experimental approach to what HTP actually does. There is a lot of rubbish on the internet, but these results are very clear.

http://www.galileosolutions.co.uk/blog/highlight-tone-priority-with-canon-cameras-review/

 

[Jim O]

M mode, 1/100 s, f/8, ISO 400, change HTP from disabled to enabled, what happens to the number of photons? Nothing. No difference. Av mode, f/5.6, ISO 200, change HTP from disabled to enabled, what happens to the number of photons? Nothing. No difference.

This is basic physics, assuming of course the situation external to the camera is controlled. Anyone who does not understand this can easily learn it. Admitting one is wrong is another story evidently.

Again, assuming controlled lighting from outside the camera, the number of photons hitting the sensor can only be changed by exposure settings - the f-stop and the amount of time the shutter is open. No artificial computer driven setting in the camera's software can magically create photons or destroy them. That is contrary to the laws of physics.

Hi, How does changing the Exposure increase or decrease the amount of photons hitting the sensor?
It does make sense(brighter/darker image), but i'm just wondering what actually happens.

Without intending to be rude I'll have to answer that you'd need to understand what a photon is, or at least what it is theorized to be. Around 100 or so years ago Albert Einstein realized that the wave theory of electromagnetic energy could not explain all observed phenomena with respect to light. So he proposed a particle theory. A photon a quantum particle of light. All photons of the same wavelength contain the same amount of light energy. There are no "bright photons" or "weak photons" at the same wavelength. Exposure is determined by how many photons hit the sensor and the sensor's sensitivity to them (ISO).

The sensor (or film) may act a little differently during prolonged exposures, but for the numbers that neuro gave, this rule holds true.

So if you open the aperture, thus doubling its size, twice the number of photons pass per unit of time. If you halve the exposure time, half the number of photons pass per unit of time. That's why we know that an image made at f/2.0 and 1/500th will have the same exposure as an image made under the same light and ISO at f/2.8 and 1/250th. The second image will have the half the number of photons per unit of time, but will have twice the amount of time. Changing sensor settings like ISO will not change the number of photons reaching the sensor, it only changes the sensor's sensitivity to each photon. Same thing with film.

 

[Apop]

M mode, 1/100 s, f/8, ISO 400, change HTP from disabled to enabled, what happens to the number of photons? Nothing. No difference. Av mode, f/5.6, ISO 200, change HTP from disabled to enabled, what happens to the number of photons? Nothing. No difference.

This is basic physics, assuming of course the situation external to the camera is controlled. Anyone who does not understand this can easily learn it. Admitting one is wrong is another story evidently.

Again, assuming controlled lighting from outside the camera, the number of photons hitting the sensor can only be changed by exposure settings - the f-stop and the amount of time the shutter is open. No artificial computer driven setting in the camera's software can magically create photons or destroy them. That is contrary to the laws of physics.

Hi, How does changing the Exposure increase or decrease the amount of photons hitting the sensor?
It does make sense(brighter/darker image), but i'm just wondering what actually happens.

According to theoretical physics photons flow, and so aperture physically restricts the amount that can pass, and shutter speed restricts the amount in time.

But from what I understand, it is theoretical physics, the emphasis being on theoretical.

Oke, i Must have misunderstood , I thought he meant 3 things ( not 2)

I misinterpreted it for exposure compensation , the part of aperture and shutter speed was clear.

But i still wonder what exposure compensation actually does, is it an electronic signal boost?

 

[jrista]

M mode, 1/100 s, f/8, ISO 400, change HTP from disabled to enabled, what happens to the number of photons? Nothing. No difference. Av mode, f/5.6, ISO 200, change HTP from disabled to enabled, what happens to the number of photons? Nothing. No difference.

This is basic physics, assuming of course the situation external to the camera is controlled. Anyone who does not understand this can easily learn it. Admitting one is wrong is another story evidently.

Again, assuming controlled lighting from outside the camera, the number of photons hitting the sensor can only be changed by exposure settings - the f-stop and the amount of time the shutter is open. No artificial computer driven setting in the camera's software can magically create photons or destroy them. That is contrary to the laws of physics.

Hi, How does changing the Exposure increase or decrease the amount of photons hitting the sensor?
It does make sense(brighter/darker image), but i'm just wondering what actually happens.

According to theoretical physics photons flow, and so aperture physically restricts the amount that can pass, and shutter speed restricts the amount in time.

But from what I understand, it is theoretical physics, the emphasis being on theoretical.

Oke, i Must have misunderstood , I thought he meant 3 things ( not 2)

I misinterpreted it for exposure compensation , the part of aperture and shutter speed was clear.

But i still wonder what exposure compensation actually does, is it an electronic signal boost?

Exposure Compensation is usually only available in modes that are not fully manual. Av, Tv, even M with Auto ISO, you often have EC. Simply put, EC changes one of the "automatic" variables to achieve your chosen "exposure".

In Av or Tv, EC usually adjusts the factor not controlled by your dial. If you EC in Av, that will usually change shutter speed, unless shutter cannot be changed...in which case, if ISO is auto, EC will change ISO. Same goes for Tv, except that EC will change aperture when it can. Exposure Compensation is not something mystical or magical, or having to do with electronics. It is simply changes one of the settings you are already intimately familiar with.

 

[Apop]

M mode, 1/100 s, f/8, ISO 400, change HTP from disabled to enabled, what happens to the number of photons? Nothing. No difference. Av mode, f/5.6, ISO 200, change HTP from disabled to enabled, what happens to the number of photons? Nothing. No difference.

This is basic physics, assuming of course the situation external to the camera is controlled. Anyone who does not understand this can easily learn it. Admitting one is wrong is another story evidently.

Again, assuming controlled lighting from outside the camera, the number of photons hitting the sensor can only be changed by exposure settings - the f-stop and the amount of time the shutter is open. No artificial computer driven setting in the camera's software can magically create photons or destroy them. That is contrary to the laws of physics.

Hi, How does changing the Exposure increase or decrease the amount of photons hitting the sensor?
It does make sense(brighter/darker image), but i'm just wondering what actually happens.

According to theoretical physics photons flow, and so aperture physically restricts the amount that can pass, and shutter speed restricts the amount in time.

But from what I understand, it is theoretical physics, the emphasis being on theoretical.

Oke, i Must have misunderstood , I thought he meant 3 things ( not 2)

I misinterpreted it for exposure compensation , the part of aperture and shutter speed was clear.

But i still wonder what exposure compensation actually does, is it an electronic signal boost?

Exposure Compensation is usually only available in modes that are not fully manual. Av, Tv, even M with Auto ISO, you often have EC. Simply put, EC changes one of the "automatic" variables to achieve your chosen "exposure".

In Av or Tv, EC usually adjusts the factor not controlled by your dial. If you EC in Av, that will usually change shutter speed, unless shutter cannot be changed...in which case, if ISO is auto, EC will change ISO. Same goes for Tv, except that EC will change aperture when it can. Exposure Compensation is not something mystical or magical, or having to do with electronics. It is simply changes one of the settings you are already intimately familiar with.

Thanks a lot for the explanation(!) and useful information.

 

[jrista]

M mode, 1/100 s, f/8, ISO 400, change HTP from disabled to enabled, what happens to the number of photons? Nothing. No difference. Av mode, f/5.6, ISO 200, change HTP from disabled to enabled, what happens to the number of photons? Nothing. No difference.

This is basic physics, assuming of course the situation external to the camera is controlled. Anyone who does not understand this can easily learn it. Admitting one is wrong is another story evidently.

Again, assuming controlled lighting from outside the camera, the number of photons hitting the sensor can only be changed by exposure settings - the f-stop and the amount of time the shutter is open. No artificial computer driven setting in the camera's software can magically create photons or destroy them. That is contrary to the laws of physics.

Hi, How does changing the Exposure increase or decrease the amount of photons hitting the sensor?
It does make sense(brighter/darker image), but i'm just wondering what actually happens.

Photons move from their source over time. They also disperse from their source over time, covering a larger area. We could get into some complicated math, using solid angles, light intensity measurements like cd/m^2, etc. But none of that is really necessary to actually understand the answer to your question.

Lets say you have a 60watt light bulb. That bulb produces light. That means it produces a continuous flow of photons, emitted from the bulb's entire surface area, every moment. If you take a photograph of the bulb with a DSLR camera, there are two things that will affect the "exposure" of the image: aperture and shutter speed. Why these two? Why is ISO not a factor?

If we think of the distance between the bulb and our camera's aperture as a water pipeline, we can come up with an analogy for aperture. For a given quantity of water, a large pipeline can move a large volume of water at a low pressure, and a small pipeline can move a smaller volume of water at a higher pressure. Volume and pressure are both important here, but for now, I'll only cover volume. A large aperture is like a large pipeline...it allows a lot of light to flow through in a given amount of time. Similarly, a small aperture is like a small pipeline, it allows a lesser amount of light to flow through in a given amount of time. Aperture changes the total volume of light passing through the lens.

Shutter speed is a very simple concept. It is simply the time factor for exposure. Since light from the bulb "flows" over time...since a certain amount of photons are emitted in any given unit time, changing shutter speed affects how many photons actually reach the sensor. Shutter changes exposure time at the sensor plane.

Let's say that an exposure of 1/500s f/4 of our light bulb produces a reasonable exposure...the bulb is not blown, but it is very bright. We can do one of two things to reduce the exposure by a factor of two, such that we can start to see some detail in our bulb. Since aperture affects the volume of light passing through the lens, we can reduce the aperture by "one stop" to reduce the volume of light by a factor of two. That gives us 1/500s f/5.6. Similarly, we could double the shutter speed, again a "one stop" change, to reduce the amount of light reaching the sensor by a factor of two. That gives us 1/1000s f/4.

I mentioned that ISO does not actually affect exposure. From a literal standpoint, ISO is not an exposure factor. It is technically a post-exposure factor. From a logical standpoint, ISO as far as the average photographer is concerned, is an "exposure" factor. ISO simply takes the actual exposure on the sensor, and amplifies it. ISO 100 is base ISO for the vast majority of cameras. Increasing ISO from base always has the effect of making an exposure brighter. Changing ISO, however, does not affect the amount of light!! It uses electronic signal amplification and digital boost to simulate a brighter exposure, hence the reason noise increases as you increase ISO.



Finally, I compared aperture to a water pipeline. There was a specific reason for this, and it has to do with diffraction. A more realistic analogy would actually have been to compare a lens to a water pipe with a variable exit opening...which is basically the same thing as an aperture. If you force water through a large pipe, lets say a pipe with a 1-foot diameter, at a fixed pressure, it will exit the other end and spread out a little bit. If you double the pressure in the pipe, the amount the water will spread out as it exits the pipe will increase. Double the pressure again, and water will start to spray out at almost a 180 degree angle to the direction of the pipe. Pressure can be changed by adding a cap to the end of the pipe with differing hole sizes...or apertures. We could call the uncapped pipe f/1, so to double the pressure, we add a cap that produces an f/1.4 hole (8.6" diameter), and to double again we add a cap that produces an f/2 hole (6" diameter). Water moving through the pipe is technically a longitudinal wave, and therefor it experiences diffraction when it encounters the cap.

Light also behaves as a wave, so when it passes through a lens and encounters the diaphragm, it must spread out. Reducing aperture therefor must increase the diffraction of light, as it bends more around the edges of the aperture opening by an increasing degree as aperture diameter approaches the wavelength of light. (Similarly, in the case of a telescope, rather than light bending around the edges of the diaphragm blades, it bends around the secondary mirror support in the center.)

 

[Loswr]

I have explain what is actually does several times in this thread

Yes, and every time you've explained it incorrectly.

Mikael, why do you think that typing your explanation for how HTP works in bold will make it correct? You're still wrong. Even if you use ALL CAPS AND A LARGER FONT, you'll still be wrong.

Ok to be fair, you're not totally wrong. You are correct, in an analogous way to a broken/stopped analog clock that is correct twice per day.

You have (repeatedly) asserted that HTP reduces by half the number of photons reaching the sensor. In some cases, you specifically state that shutter speed/time value is changed. In other cases, you mention f/stop might change, too. That is true under the following conditions:

• Turning on HTP with the camera set to ISO 100 and Av changes the shutter speed to reduce by half the number of photons reaching the sensor
• Turning on HTP with the camera set to ISO 100 and Tv mode changes the aperture to reduce by half the number of photons reaching the sensor
• Turning on HTP with the camera set to ISO 100 and P mode changes the shutter speed or aperture (usually the former) to reduce by half the number of photons reaching the sensor

It does that because ISO 100 is not available as a selection when HTP is enabled, so if ISO 100 is selected when HTP is enabled, the camera changes it to ISO 200. If you happen to be in an autoexposure mode, the camera then changes another parameter (aperture or shutter speed) to maintain the metered exposure. Setting HTP at ISO 100 is an oxymoron - if you enable HTP, your camera isn't set to ISO 100 anymore.

In M mode, enabling HTP changes neither aperture nor shutter speed, and the number of photons reaching the sensor is unchanged. So, in M mode, your explanation of what HTP does is wrong. At ISO 200 or higher, enabling HTP changes neither aperture nor shutter speed and the number of photons reaching the sensor is unchanged, and again your explanation of how HTP works is wrong.

Therefore, as a general explanation of how HTP works, your statement that it works by halving the number of photons reaching the sensor is WRONG.

I know you understand the goal of HTP. Guess what? So do I (despite your repetitive and annoying suggestions to the contrary). I also fully grasp how HTP works. Maybe you partially (or even fully) grasp how it works, but no one would know that, because you can't explain it properly.

Maybe you should try reading Emil Martinec's explanation of HTP, he does a much better job:

[quote author=Emil Martinec]Instead of using the ISO gain set by the user, the camera uses a lower ISO (but exposes with the indicated aperture and shutter speed), effectively underexposing the image; this provides more highlight headroom. In post-processing, the image data can be brought back up while preserving the highlights with a modified tone curve in higher exposure zones. The place where image quality suffers is in shadows at lower ISO, precisely as the above quantitative model predicts.[/quote]
Does he mention a reduction in the number of photons? No. He states that the exposure is "with the indicated aperture and shutter speed," and if that's the case, how exactly is the number of photons being reduced, as you have repeatedly stated is occurring?

Maybe you think that an analog clock with the hands stopped gives the right time, because it just happens to do so twice per day. But the reality is that such an analog clock is broken, just like your explanation of HTP.

 

[Marsu42]

I think people here can read by them self what kind of escape you are trying to do

As one of the people here it is beyond me why you are so insistent to make this into an unfriendly flamewar, and neuro in this case repeats what has been figured out on CR by multiple people some time ago because what htp does is certainly not self-explanatory.

I'm going to strip you naked

Congratulations, my ignore list now contains one name, and that's yours.

 

[jrista]

So please explain what happens if you set your cameras at M and base iso 100 HTP and if the exposure time or f-stop is not changed? (have I understand you correctly) And why there are a choice of HTP in other modes as AV etc

He already did explain, but maybe a preschool level explanation is necessary here.

If you enable HTP, you cannot use ISO 100. Not in any auto mode. Not in any semi-auto mode. Not in manual mode. The lowest user-selectable ISO is 200. Plain and simple.

 

[jrista]

Neuro wrote:
Therefore, as a general explanation of how HTP works, your statement that it works by halving the number of photons reaching the sensor is WRONG.

same here, I have time after time explained that at base iso you must create a head room
in every iso step you are halving the photons/infalling lights to the sensor

Sorry Neuro-you still not get it

Neuro does get it, it is you who does not. The camera does not change aperture or shutter. You, the user, do. By restricting the lowest possible ISO setting to ISO 200, you effectively shift the USER into a mode of actively selecting a higher shutter or a narrower aperture to compensate for the METERED exposure, which is a stop higher when HTP is enabled.

As a user, if I would normally use 1/100s f/4 to photograph a scene at ISO 100, when I enable HTP, in manual mode, I must compensate for the fact that my ISO settings are now one stop brighter. That means I will select 1/200s f/4 or 1/100s f/5.6 instead. The camera will then "preserve" my highlights by using an ISO setting one stop lower (technically speaking, the camera didn't preserve anything...I did by manually reducing exposure by a stop). If ISO 200 was selected, then the camera will use IS0 100. If ISO 400 was selected, then the camera will use ISO 200. Etc.

The camera does not change aperture or shutter in HTP...the user does! HTP, and similarly ADL for Nikon, is a user conditioning setting. It does not actually change the exposure (which is solely controlled by aperture and shutter speed). It changes the users behavior by forcing the user to change exposure, then compensates by using a different ISO (which changes a post-exposure adjustment, but not the exposure itself.)

It couldn't work any other way...ISO is the sole "side effect free" setting (noise isn't a side effect in this context). If the camera changed the shutter speed or the aperture, it could potentially change things other than exposure...such as depth of field, motion blurring, etc. that the photographer EXPLICITLY CHOSE to use.

 

[jrista]

So please explain what happens if you set your cameras at M and base iso 100 HTP and if the exposure time or f-stop is not changed? (have I understand you correctly) And why there are a choice of HTP in other modes as AV etc

He already did explain, but maybe a preschool level explanation is necessary here.

If you enable HTP, you cannot use ISO 100. Not in any auto mode. Not in any semi-auto mode. Not in manual mode. The lowest user-selectable ISO is 200. Plain and simple.

Thanks then this subject is clear/ finished investigated -or what do you think?

any comments Neuro?

this forum could become an institution of knowledge if some people could learn to listen to other, and not be so damn confident in their own ability

You are going to get yourself banned with the attitude, man... ???

You seem to have the assumption that everyone else on this forum is dumber than you, and that everyone should always listen to everything you say without questioning any of the discrepancies that constantly stream out of your posts. Why not take your own advice, eh?

 

[Sporgon]

Is there a psychiatrist in the house ?






With a LOT of time to spare

 

[jrista]

So please explain what happens if you set your cameras at M and base iso 100 HTP and if the exposure time or f-stop is not changed? (have I understand you correctly) And why there are a choice of HTP in other modes as AV etc

He already did explain, but maybe a preschool level explanation is necessary here.

If you enable HTP, you cannot use ISO 100. Not in any auto mode. Not in any semi-auto mode. Not in manual mode. The lowest user-selectable ISO is 200. Plain and simple.

Thanks then this subject is clear/ finished investigated -or what do you think?

any comments Neuro?

this forum could become an institution of knowledge if some people could learn to listen to other, and not be so damn confident in their own ability

You are going to get yourself banned with the attitude, man... ???

You seem to have the assumption that everyone else on this forum is dumber than you, and that everyone should always listen to everything you say without questioning any of the discrepancies that constantly stream out of your posts. Why not take your own advice, eh?

not at all, if you read what Im writing so can we all have a benefit of greater knowledge

Wow...not much from you surprises me, but the arrogance in that line is rather surprising...did you not understand what I just wrote? Eh, it doesn't even matter anyway... ???

I have reported Neuro twice now, or does he have a free ticket to make him funny over other persons posts?

You can report us all you want. The only one here who is being directly and actively degrading of other members is you. Neuro, and now myself, are addressing a technical misunderstanding you seem to have regarding HTP. The debate is regarding verifiable facts, and the fact that we engage in that debate with you is not a commentary on your person (i.e. we are not calling you an idiot), it is a commentary on your words (i.e. we are saying your facts are wrong).

I just replied regarding HTP. Read my answer, see if you understand what Neuro, and pretty much anyone else who understands the feature and has commented on the topic of HTP or ADL, is trying to say. There is no ISO 100 in HTP, because it is ISO...not shutter or aperture...that the camera changes. The user's selected exposure remains the same, how that exposure is treated by the electronics or post-processing software is what changes.

 

[ajfotofilmagem]

Why hijack the topic? Those people who need to write hundreds of words to prove that they are always right, I do not deserve to lose my time.

 

[jrista]

no explain, and keep it short, i have some problem to read your posts, 5% information and the rest a lot of words
so please explain
do you mean that this forum could not be better with all people like Pi and Hulls knowledge as two example ?
That neuro has not been understanding or misunderstood
or what?
scratch my back?

I'll happily admit Pi often knows exactly what he is talking about. I think he sometimes comes from an unconventional angle, but he has frequently backed up his claims with very solid information (such as the excellent Equivalence article he linked to in a recent thread.) Key point there...he backed up his claims. Once I read the information he provides, his angle becomes clear, and his perspective on the subject usually makes sense. Sometimes that is necessary.

You are, seemingly, trying to compare yourself to Pi, with the claim that you have superior knowledge than any Canon user on these forums. That is an arrogant claim, and one which, given the lackluster and frequently incorrect content of so many of your posts, has no backing. Maybe sometimes you do know what your talking about, and there may simply be a language barrier/cultural gap that is preventing people from understanding you...but you rarely back up your claims. When you do sort of try to provide references or evidence, it is usually contrived or incomplete, or linked reference material actually backs up what other members are saying and not what you are saying...and people can't help but question why.

So, once again...why not try to take your own advice? Why not listen to what other members here have to say, instead of just blindly assuming you always have superior knowledge and that no one else here could possibly know what they are talking about? I don't think there are very many members here who truly want to get involved in a conversation, let alone a debate, with you...it is a taxing endeavor that always leads nowhere. You eventually become highly antagonistic, aggressive, arrogant, and insulting. No one wants to listen to you insult them all the time, Mikael. No one wants to be on the receiving end of endless antagonism (and there is no question you are the supreme antagonist in the ongoing story of Canon Rumors. )

It is also human nature to retaliate, especially if someone thinks they have the upper hand...and when you say something that comes across as factually incorrect, well, that gives your opponents the upper hand...

 

[Apop]

no explain Jrista , and keep it short, i have some problem to read your posts, 5% information and the rest a lot of words
so please explain
do you mean that this forum could not be better with all people like Pi and Hulls knowledge as two example ?
I know David from dpreview since years back
That neuro has not been understanding or misunderstood
or what?
sorry but you two are used that people are not question you.
what good does that lead to?
a little self-criticism would be good, especially if you're wrong

Neuro and Jrista strike me as the people who like to share their knowledge, but also read others opinions which might influence their beliefs/point on certain topics.

I like the way they constructively explain things, in a ''slightly'' less aggressive way than yourself.
It seems like you feel the need to attack anyone that disagrees with your pov, how can that ever lead to a serious discussion?

The reason that people won't question them as much as you, Is that they actually explain things or support it with facts/research. The way they approach people (and ignorance) is also working for them .

I asked a rather stupid question about exposure/exposure compensation, instead of getting flamed at that I am a dumb idiot that doesn't understand how a camera works and that the one accusing me of being so has been doing it for 30 years and has great knowledge, they just fed my ignorance with information ...(actual useful information).

That you don't like a lot of words seems to support my feeling you have a rather short fuse.
And the 5% you do read is most likely what you had filtered out and interpreted as an insult.

This forum would be better if there weren't as many flaming people around like yourself,
If anyone is to get a ban ( I doubt it), it's more likely you than Neuro .
( that can be based on the fact alone that the admins eyes disagrees with dxo mark results, so i don't expect him to be in your corner lol)

 

[jrista]

End of discussion for me in this thread

an apology can I probably not expect from a man who has committed jokes at my expense, and where he has shown great ignorance.

Why would you expect an apology from someone you have been insulting for much longer than he's been making jokes at your expense? As I said...it is human nature to retaliate. Maybe if you apologized to him for all the insults and derogatory comments you've made about him, he might apologize to you for the jokes.

As for me, you regularly bring my name up in threads I have never participated in, just to include me in an insult of one kind or another. I have no interest in hiding my dislike of you, Mikael, but I'll apologize for any insults I may have levied at you in the past. That does not change the fact that I think you are continually, and pointlessly, antagonistic here on CR forums, and that we would probably be much better off without you around at all...but here is my apology nevertheless. I'm sorry if I've ever insulted you.

 

[ME]

I have explain what is actually does several times in this thread

Yes, and every time you've explained it incorrectly.

Mikael, why do you think that typing your explanation for how HTP works in bold will make it correct? You're still wrong. Even if you use ALL CAPS AND A LARGER FONT, you'll still be wrong.

Ok to be fair, you're not totally wrong. You are correct, in an analogous way to a broken/stopped analog clock that is correct twice per day.

You have (repeatedly) asserted that HTP reduces by half the number of photons reaching the sensor. In some cases, you specifically state that shutter speed/time value is changed. In other cases, you mention f/stop might change, too. That is true under the following conditions:

• Turning on HTP with the camera set to ISO 100 and Av changes the shutter speed to reduce by half the number of photons reaching the sensor
• Turning on HTP with the camera set to ISO 100 and Tv mode changes the aperture to reduce by half the number of photons reaching the sensor
• Turning on HTP with the camera set to ISO 100 and P mode changes the shutter speed or aperture (usually the former) to reduce by half the number of photons reaching the sensor

It does that because ISO 100 is not available as a selection when HTP is enabled, so if ISO 100 is selected when HTP is enabled, the camera changes it to ISO 200. If you happen to be in an autoexposure mode, the camera then changes another parameter (aperture or shutter speed) to maintain the metered exposure. Setting HTP at ISO 100 is an oxymoron - if you enable HTP, your camera isn't set to ISO 100 anymore.

In M mode, enabling HTP changes neither aperture nor shutter speed, and the number of photons reaching the sensor is unchanged. So, in M mode, your explanation of what HTP does is wrong. At ISO 200 or higher, enabling HTP changes neither aperture nor shutter speed and the number of photons reaching the sensor is unchanged, and again your explanation of how HTP works is wrong.

Therefore, as a general explanation of how HTP works, your statement that it works by halving the number of photons reaching the sensor is WRONG.

I know you understand the goal of HTP. Guess what? So do I (despite your repetitive and annoying suggestions to the contrary). I also fully grasp how HTP works. Maybe you partially (or even fully) grasp how it works, but no one would know that, because you can't explain it properly.

Maybe you should try reading Emil Martinec's explanation of HTP, he does a much better job:

[quote author=Emil Martinec]Instead of using the ISO gain set by the user, the camera uses a lower ISO (but exposes with the indicated aperture and shutter speed), effectively underexposing the image; this provides more highlight headroom. In post-processing, the image data can be brought back up while preserving the highlights with a modified tone curve in higher exposure zones. The place where image quality suffers is in shadows at lower ISO, precisely as the above quantitative model predicts.

Does he mention a reduction in the number of photons? No. He states that the exposure is "with the indicated aperture and shutter speed," and if that's the case, how exactly is the number of photons being reduced, as you have repeatedly stated is occurring?

Maybe you think that an analog clock with the hands stopped gives the right time, because it just happens to do so twice per day. But the reality is that such an analog clock is broken, just like your explanation of HTP.
[/quote]

Thanks for your explanation of HTP Neuro. Another poster gave what seems to be much confusing garbage as an explanation.

 

[Factor7]

Hope you're happy, MichaelTheMaven..!
;D

 

[Pi]

Light also behaves as a wave, so when it passes through a lens and encounters the diaphragm, it must spread out. For a given light illumination in the scene, you have a fixed incoming "light pressure". Reducing aperture therefor must increase the diffraction of light.

OMG!