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Author Topic: Canon may be expensive but...  (Read 19544 times)

dave

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Re: Canon may be expensive but...
« Reply #90 on: February 02, 2013, 06:22:27 PM »
Five pages back I was embarrassed for starting this thread, now I'm mortified. :(

I'd try and contribute but I honestly don't follow most of it.

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Re: Canon may be expensive but...
« Reply #90 on: February 02, 2013, 06:22:27 PM »

neuroanatomist

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Re: Canon may be expensive but...
« Reply #91 on: February 02, 2013, 06:41:41 PM »
no Im saying by exposure after 400 iso you have create a head room by 2 stops compare to 100iso
what is so difficult to understand Neuro! = exposure after 400 iso = halving the hitting lights twice compare to 100iso


Hypothetical example: I shoot jpg. I am taking a picture of a forest scene. I am in Av mode, and I set f/8 to obtain the desired DoF, and I chose ISO 400 to get a 1/100 s shutter speed at metered exposure to avoid camera shake, because I foolishly left my tripod at home. Please note, I couldn't care less about what exposure settings would be at ISO 100, 50, or 3200, that's tangential and irrelevant - I choose f/8 and ISO 400 for the reasons I stated.  I take a shot, look at the review image, and see blinking highlight alerts where I want detail of the sun-dappled forest floor. I've read that HTP can preserve my highlights.

If that scenario is confusing, I'll summarize - with HTP off, I set the camera in Av mode, f/8, ISO 400, and the metered exposure gave a 1/100 s shutter speed.

Answer these questions about what happens when I set HTP to Enable:

1) Does my selected aperture of f/8 change?
2) Does the camera-selected shutter speed of 1/100 s change?
3) Does the amount of light hitting the sensor change?

Please, no hand-waving, no 'please read my earlier posts', no repeating what you've posted before, no referring to what may happen at some other ISO setting that I didn't select and don't care about - just answer those three, simple questions with a yes or a no.

 Answer : yes

Sorry, Mikael - it was a pass/fail test, and you have failed.  The answer to all three of those questions is "no".  In Av mode, f/8, ISO 400, enabling HTP does not change aperture or shutter speed, and therefore the amount of light hitting the sensor does not change. If anyone believes there a chance Mikael is right, feel free to set Av, f/8, ISO 400 then enable HTP and see if shutter speed or aperture change as a result.

Back in the other thread, I had come to the conclusion that this was semantics and your inappropriate extrapolation of what happens in the special case of ISO 100 in an autoexposure mode to a general explanation of how HTP works.

But...the fact that you answered "yes" to the above questions clearly demonstrates that you do not understand how HTP really works.  Despite repeated attempts by several people, including TheSuede, to provide an explanation which you could understand, you fail to grasp some details of the concept.  At this point, the only logical conclusion is that you are simply incapable of understanding the mechanism of HTP.  Not due to language, semantics, etc. - just a fundamental inability to comprehend this concept.  You are wrong, you don't get it, and apparently you never will, much less admit that you're wrong and/or incapable of understanding the concepts.

To paraphrase an earlier statement of yours, it's impossible to discuss this with someone who does not understand the basics - and that someone is you, Mikael.  For my part, this discussion is done.  Any further statements or questions from you on this matter will be ignored.
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LetTheRightLensIn

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Re: Canon may be expensive but...
« Reply #92 on: February 02, 2013, 07:18:31 PM »
Their 800mm lens isn't $18000.


http://www.thedigitalpicture.com/News/News-Post.aspx?News=4073


And that is why Canon is discontinuing the current one for a Mark II soon....

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Re: Canon may be expensive but...
« Reply #93 on: February 02, 2013, 07:57:01 PM »
By all means, people should read that thread and observe Mikael 'Half The Photons' Residal's staunch defense of his explanation that the general mechanism of HTP is that the camera reduces by half the amount of light hitting the sensor, his consistent refusal to admit that his 'explanation' applies only at ISO 100, his avoidance of specific questions from several posters to describe how HTP works at any other ISO setting than 100, etc.  Note how here in this thread, he reposts TheSuede's correct description of how HTP works, which matches what others in the thread were saying, but not his own flawed and incorrect explanation.

Doesn't it sort of halve the collected photons though, depending upon how you go about talking about it? If you set ISO400 HTP it uses ISO200 but exposes as if you were using ISO400 so you are shooting ISO200 but as if you were ISO400 so the camera metering does toss away a stop of light compared to what it does when you shoot ISO200 as 200 instead of 200 as ISO400 HTP. So, using the proposed tone curve, it shifts the middle gray and everything else down a full stop so you have 1 stop more room for highlights.

If you compare ISO400 to ISO400 HTP they expose the same way and collect same # of photons but the one without HTP applies one stop more gain than the other and assumes a more typical tone curve will be applied and doesn't shift all of that down 1 stop. But looking at it from the true RAW level ISO400 HTP actual corresponds to ISO200 not ISO400....

It depends how you go about talking about it in detail. I don't know if talk about photon collection is really is the best way. I didn't read that other thread of much of this yet so I don't know went on.

I think it is simplest just to say that:

1. HTP isn't anything special and isn't a real new mode and it is nothing more than software and metering games.

2. You can do the exact same thing (for RAW shots) by using ISO stop lower in regular mode than what you set in HTP mode and then setting EC -1 to all your shots (or for M mode decide simply use the ISO you want in either case and then for the times you want the 'HTP' shots you decide to set shutter speed one stop faster so as to save one stop more highlights)*.

3. All HTP is is metering at the labelled stop but applying the gain of one stop less and, in cam (or default in RAW converters), applying a special tone curve that shifts most of the data down one stop and applies different tail and especially top end curves.



*And then you shift things around with the RAW settings to give it a curve a mid-tone point that works (using some built-in profiles you may run into the twisted profiles issue and if you are not skilled at moving sliders and setting TRCs and such it might be a bit trickier with some software to work it out as well than having the software give you automatic starting point under the hood though perhaps, although since most standard starting points and exposures are not fully ETTR you might not actually hit all that must problems at all and might even hit less).



Quote
That's all you had to say, Mikael.  Why did you feel in necessary instead to lead off by insulting my knowledge and intelligence?

I'm just guessing, but maybe he was just snapping after all the grief dumped on him in some other threads and stuck in fight fire with fire mode after all of that? Jrista and plenty others certainly insulted him by the bucket load (myself too in some of those threads  ;D  :'( :'( :'(). Some people who were rather incorrect about a lot of things had been dumping all sorts of insults over a few members for a long time, maybe he just got sick of it and now just snaps back at the slightest hint of anything? Maybe not the best way to go about it, but you can understand a bit where it comes from (plus it is interesting that none of those bashing him now ever got on the cases of everyone who started insulting him and others way back when and they were all fine with it all in that case, why, probably because the ones insulting and bashing in those cases tended to rarely ever treat Canon as anything less than a god.).


« Last Edit: February 02, 2013, 08:00:31 PM by LetTheRightLensIn »

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Re: Canon may be expensive but...
« Reply #94 on: February 02, 2013, 08:09:51 PM »

Of course, headroom is needed to preserve the highlights. We agreed on the 'what' - your error concerned the 'how'.  My point was that HTP achieves the additional headroom by exposing at a one-stop lower ISO than is actually selected, not by reducing the exposure so that 'half the photons' hit the sensor as you repeatedly stated.

Isn't is basically just semantics?

And from a RAW RAW perspective what is using an ISO as if it were one ISO stop higher but exposing that ISO by one less stop? From that perspective it is collecting half the photons. If we try to do what HTP does ourselves without using it, which we can do because it is not a special mode, then what do we do? We keep using the same ISO we were just using and then make the shutter speed 1 stop quicker = the whole less photos collected scenario. What really is going is a simply a collecting less photons thing.

If you look at from the perspective of does ISO400 HTP collect any less photons (going by autometering) than ISO400, then no it doesn't it is just applying less gain, but then if it is applying less gain it is NOT really ISO400 any more is it so you might say the early way of looking at it is the more natural way?

Both perspectives can be said to be correct but I actually think Mike's seems a bit more the natural way to think about it although I suppose one can argue back and forth about what one considers natural.

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Re: Canon may be expensive but...
« Reply #95 on: February 02, 2013, 08:10:58 PM »
I felt cheated on learning that Canon publishes hypothetical MFT charts and does not actually test a sample lens.

Would you feel any less cheated if your shh copy didn't come close to their best of 50 that they used for the real test though?  ;) ;D

Although it would make f/2.8 vs f/8 performance clearer (since diffraction would be hurting f/8 performance real world) and some designs as I believe Leica once insinuated referring to Canon may be easy enough to make perform in a simulator with every lens carved and placed perfectly and yet an utter bear to produce on a real world manufacturing line where for some tricky designs 99.9% of lenses coming out may have nothing to do with the calculated charts at all. It might make them tune more for real world reasonably consistently produceable designs more??? But they probably do what they do anyway.
« Last Edit: February 02, 2013, 08:14:59 PM by LetTheRightLensIn »

LetTheRightLensIn

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Re: Canon may be expensive but...
« Reply #96 on: February 02, 2013, 08:26:25 PM »
My problem with you [Michael] arose at the time of the "Half The Photons" discussion where, from your [Michael's] posts I got the impression that changing the ISO would somehow change the photons hitting the sensor. I'm sure you knew fully well that changing the ISO does not change the number of photons hitting the sensor then why the charade? What's the point of your expertise if you ultimately end up confusing people - Well you may very well say I'm a noob but there are a number of noobs on CR who log on only to look for some help?

Because is not just changing the camera back to ISO200. It keeps metering at ISO400 while changing the camera gain to ISO200. And if you meter at ISO400 you are getting less exposure than you would metering at ISO200 which the camera is actually working at. If anything, I think looking at it from his point of view seems less misleading. Effectively it is just an automatic and hidden EC -1 to the shutter speed, that is how you'd replicate it yourself in RAW without using the mode, with an automatic tone curve (applied in cam, and suggested to the RAW converter) making the JPGS and histograms look like EC0 with more highlights instead of a flat EC -1 across the board. How do you replicate ISO400 HTP in say Av mode for RAWs? You shoot ISO200 Av mode with EC -1.

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Re: Canon may be expensive but...
« Reply #96 on: February 02, 2013, 08:26:25 PM »

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Re: Canon may be expensive but...
« Reply #97 on: February 02, 2013, 08:32:20 PM »
This does not automatically happen in M or B! Do you not agree? I agree that your statement would be true for P, Av, Tv and the Green Rectangle... Your statement is a generalization. However, it cant be true for all the settings on my 5D3.

But if you shoot a RAW at ISO400 HTP mode at say 1/60th and f/2.8 and looked at the linear RAW file histogram it would look like an ISO200 HTP-off 1/125th and f/2.8 taken image and not an ISO200 HTP-off 1/60th and f/2.8 image.

Or more aptly, if you look at the blinky suggested metering line shown to you in M or B mode it would act just as you say it will for P, Av,Tv,etc.

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Re: Canon may be expensive but...
« Reply #98 on: February 02, 2013, 08:44:41 PM »
no Im saying by exposure after 400 iso you have create a head room by 2 stops compare to 100iso
what is so difficult to understand Neuro! = exposure after 400 iso = halving the hitting lights twice compare to 100iso


Hypothetical example: I shoot jpg. I am taking a picture of a forest scene. I am in Av mode, and I set f/8 to obtain the desired DoF, and I chose ISO 400 to get a 1/100 s shutter speed at metered exposure to avoid camera shake, because I foolishly left my tripod at home. Please note, I couldn't care less about what exposure settings would be at ISO 100, 50, or 3200, that's tangential and irrelevant - I choose f/8 and ISO 400 for the reasons I stated.  I take a shot, look at the review image, and see blinking highlight alerts where I want detail of the sun-dappled forest floor. I've read that HTP can preserve my highlights.

If that scenario is confusing, I'll summarize - with HTP off, I set the camera in Av mode, f/8, ISO 400, and the metered exposure gave a 1/100 s shutter speed.

Answer these questions about what happens when I set HTP to Enable:

1) Does my selected aperture of f/8 change?
2) Does the camera-selected shutter speed of 1/100 s change?
3) Does the amount of light hitting the sensor change?

Please, no hand-waving, no 'please read my earlier posts', no repeating what you've posted before, no referring to what may happen at some other ISO setting that I didn't select and don't care about - just answer those three, simple questions with a yes or a no.

1,2,3,
no, no, no

BUT you forget that when you hit the HTP button you are no longer at ISO400 any more but you are at ISO200 only the camera is still metering at as if it were at ISO400. You are not getting to the point of what HTP really is, it is NOT some magic hardware where a new set of photosensors are enabled to capture extra highlights or something, it isn't a 'real' mode, if you want to replicate the mode yourself you can even with a camera that has no HTP button. If you want HTPISO400 and were shooting scenes at say EC0 then you just use ISO200, lock your aperture and then EC -1 or roll up the shutter speed yourself, if in M mode say, 1 stop.

What the camera is actually really doing is just exposing 1 stop less, collecting less photons for any given auto-metering or placement of suggested metering mark.

I can see where your way of looking at it comes from too, but I think it kinda is a less natural perspective.

It doesn't really matter what the camera labels and calls things but what matters in the end is what the sensor is doing, what the shutter speed is, what you get in the RAW file. I think it makes more sense to look at it from if I want to do HTP myself what do I need to do? To get the exact same result I shoot at my selected ISO, keep my selected aperture and then I raise the shutter speed 1 stop faster.


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Re: Canon may be expensive but...
« Reply #99 on: February 02, 2013, 08:56:56 PM »
This does not automatically happen in M or B! Do you not agree? I agree that your statement would be true for P, Av, Tv and the Green Rectangle... Your statement is a generalization. However, it cant be true for all the settings on my 5D3.

But if you shoot a RAW at ISO400 HTP mode at say 1/60th and f/2.8 and looked at the linear RAW file histogram it would look like an ISO200 HTP-off 1/125th and f/2.8 taken image and not an ISO200 HTP-off 1/60th and f/2.8 image.

Or more aptly, if you look at the blinky suggested metering line shown to you in M or B mode it would act just as you say it will for P, Av,Tv,etc.
I think you need to read that part again. That was not about HTP. That was before HTP sucked up this thread too... :)

neuroanatomist

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Re: Canon may be expensive but...
« Reply #100 on: February 02, 2013, 09:06:40 PM »
@ LetTheRightLensIn - Changing the ISO has no direct effect on the amount of light that hits the sensor.  At ISO 400, enabling HTP does not result in a change in the amount of light hitting the sensor, no difference in the number of photons. Period. What the camera does is apply one stop less gain to the signal generated from those collected photons, then applies a tone curve to the jpg data to boost everything but the highlights back up that one stop. 

Suggesting that at ISO 400, HTP reduces the light hitting the sensor is not just misleading, it's plain wrong.  Neither aperture nor shutter speed are changed - and that's a damn good thing because aperture should be selected to give the desired DoF and shutter speed selected to control motion in the image as desired, and the camera shouldn't be changing those parameters if I don't want it to.  I disagree with your statement, "...if I want to do HTP myself what do I need to do? To get the exact same result I shoot at my selected ISO, keep my selected aperture and then I raise the shutter speed 1 stop faster."  What if you wanted motion blur of a fountain, but to preserve the highlights in the scene - would you sacrifice the motion blur you wanted, or stop down and change your DoF or lose sharpness to diffraction?  I would do what the camera does with HTP - underexpose by lowering ISO as many stops as needed, and if that took me to ISO 100, it would be time for an ND filter.

HTP has limitations, foremost being it's limited to one stop of 'highlight recovery'.  But if you understand the technical principles behind it, you can overcome those limitations to some extent, while still capturing the desired image in terms of DoF and motion control.

Like Mikael, you are confusing the actual collection of light by the photon wells of the sensor with what happens to the electronic information into which the energy of those photons is subsequently converted, and with the processing applied to the digitized form of that information even later in the image acquisition process. Those are discrete steps with their own characteristics, and if one is going to discuss the technical details of the image data generation, one should correctly describe and apply those details.  You can think of it as a semantic issue if you like, but there was no semantic confusion about providing an incorrect answer to simple yes/no questions - questions which you answered correctly but Mikael did not.

At the outset, everyone deserves respect, appreciation of cultural and linguistic differences, patience, and the benefit of the doubt. If, over time, someone consistently displays rude and insulting behavior (to the self-admitted point of being placed under strict regulations by the mods), makes no significant effort to contribute in anything but a negative manner, is repetitious and combative, and offers neither apology nor any redeeming characteristics, that person deserves to lose the respect of the community...as Mikael has certainly lost mine.
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LetTheRightLensIn

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Re: Canon may be expensive but...
« Reply #101 on: February 02, 2013, 10:18:32 PM »
My problem with you [Michael] arose at the time of the "Half The Photons" discussion where, from your [Michael's] posts I got the impression that changing the ISO would somehow change the photons hitting the sensor. I'm sure you knew fully well that changing the ISO does not change the number of photons hitting the sensor then why the charade? What's the point of your expertise if you ultimately end up confusing people - Well you may very well say I'm a noob but there are a number of noobs on CR who log on only to look for some help?

Because is not just changing the camera back to ISO200. It keeps metering at ISO400 while changing the camera gain to ISO200. And if you meter at ISO400 you are getting less exposure than you would metering at ISO200 which the camera is actually working at. If anything, I think looking at it from his point of view seems less misleading. Effectively it is just an automatic and hidden EC -1 to the shutter speed, that is how you'd replicate it yourself in RAW without using the mode, with an automatic tone curve (applied in cam, and suggested to the RAW converter) making the JPGS and histograms look like EC0 with more highlights instead of a flat EC -1 across the board. How do you replicate ISO400 HTP in say Av mode for RAWs? You shoot ISO200 Av mode with EC -1.

Jisses, how many times has I said exposure/metering after a ISO NR
setting iso 1600 from 400 does not mean skit more than you are exposing  2 stops shorter/ less and raising the iso gain

I have to confess that I don't have a clue what you are trying to say here.

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Re: Canon may be expensive but...
« Reply #102 on: February 02, 2013, 10:19:27 PM »
no Im saying by exposure after 400 iso you have create a head room by 2 stops compare to 100iso
what is so difficult to understand Neuro! = exposure after 400 iso = halving the hitting lights twice compare to 100iso


Hypothetical example: I shoot jpg. I am taking a picture of a forest scene. I am in Av mode, and I set f/8 to obtain the desired DoF, and I chose ISO 400 to get a 1/100 s shutter speed at metered exposure to avoid camera shake, because I foolishly left my tripod at home. Please note, I couldn't care less about what exposure settings would be at ISO 100, 50, or 3200, that's tangential and irrelevant - I choose f/8 and ISO 400 for the reasons I stated.  I take a shot, look at the review image, and see blinking highlight alerts where I want detail of the sun-dappled forest floor. I've read that HTP can preserve my highlights.

If that scenario is confusing, I'll summarize - with HTP off, I set the camera in Av mode, f/8, ISO 400, and the metered exposure gave a 1/100 s shutter speed.

Answer these questions about what happens when I set HTP to Enable:

1) Does my selected aperture of f/8 change?
2) Does the camera-selected shutter speed of 1/100 s change?
3) Does the amount of light hitting the sensor change?

Please, no hand-waving, no 'please read my earlier posts', no repeating what you've posted before, no referring to what may happen at some other ISO setting that I didn't select and don't care about - just answer those three, simple questions with a yes or a no.

1,2,3,
no, no, no

BUT you forget that when you hit the HTP button you are no longer at ISO400 any more but you are at ISO200 only the camera is still metering at as if it were at ISO400. You are not getting to the point of what HTP really is, it is NOT some magic hardware where a new set of photosensors are enabled to capture extra highlights or something, it isn't a 'real' mode, if you want to replicate the mode yourself you can even with a camera that has no HTP button. If you want HTPISO400 and were shooting scenes at say EC0 then you just use ISO200, lock your aperture and then EC -1 or roll up the shutter speed yourself, if in M mode say, 1 stop.

What the camera is actually really doing is just exposing 1 stop less, collecting less photons for any given auto-metering or placement of suggested metering mark.

I can see where your way of looking at it comes from too, but I think it kinda is a less natural perspective.

It doesn't really matter what the camera labels and calls things but what matters in the end is what the sensor is doing, what the shutter speed is, what you get in the RAW file. I think it makes more sense to look at it from if I want to do HTP myself what do I need to do? To get the exact same result I shoot at my selected ISO, keep my selected aperture and then I raise the shutter speed 1 stop faster.

I have newer said any different, you gays are mixed up with something we call head-room, a 400 iso HTP motive are exposed after 400iso with the less gain. TO CREATE A HEAD ROOM  and  400iso  in its self means 2 stops head room from 100iso = halving the signal twice from base iso.

By you guys are you referring to me too or just the others here???

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Re: Canon may be expensive but...
« Reply #102 on: February 02, 2013, 10:19:27 PM »

LetTheRightLensIn

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Re: Canon may be expensive but...
« Reply #103 on: February 03, 2013, 03:34:43 AM »
@ LetTheRightLensIn - Changing the ISO has no direct effect on the amount of light that hits the sensor.  At ISO 400, enabling HTP does not result in a change in the amount of light hitting the sensor, no difference in the number of photons. Period. What the camera does is apply one stop less gain to the signal generated from those collected photons, then applies a tone curve to the jpg data to boost everything but the highlights back up that one stop.


this may be a mess since i typed this out quickly with no thought but:

Yes hitting the HTP button doesn't change the total light now hitting the sensor, but HTP mode both secretly changes the gain 1 stop less AND the metering normally used for that gain by to meter 1 stop down from normal.

If you want some HTP thing then you have some sort of scene with extra amounts of highlight stuff say a full stop more than typical so you have some gain that manages to let you maintain a high enough shutter speed to stop motion or to handhold. You then go one gain down and that gain is now getting shot letting in 1 stop less light than you'd normally let in for that gain for a scene that had less highlights.

Or you can go tripod and then you do ISO100 and just raise shutter more and more or you add on more and more ND filters and you are saving highlights by exposing the scene to less and less light.

ISO400 HTP EC0 is no longer ISO400 EC0 it is ISO200 EC0 metered to expose (or suggested to be so in M mode meter readings provided) 1 stop less than the camera normally would do at ISO200 EC0, i.e. it is effectively as if you were to shoot ISO200 EC -1.

You are not gaining a stop of highlights at a given gain and keeping the same light coming in, that can't be done of course.

Yeah it is at the face of it just applying 1 stop less gain but normally when you apply 1 stop less gain you'd also let in 1 stop more light too and in this case you are not so you are basically letting in 1 stop less light than you'd normally do for the gain. ISO400 HTP the camera isn't doing ISO400 at all it is doing ISO200 and it decides to do it at EC -1 metering instead of EC 0 metering and because of the latter part you might look at it that is letting in a stop less light. In an M mode scenario where you end up needing in some case to fix both aperture and shutter exactly it might be weird to think of it in terms of letting less light in since in this scenario you always want to let the same light in, but it is still metering in way that is compatible with thinking about it that way. And your scenario below where it adjusts many stops to match your light sounds more like AutoISO button than HTP button to me.


Anyway, you can only save 1 stop more highlights than the prior shot by either now letting 1 stop less light come in at the current gain (set EC -1) or by keeping same light coming in and lowering the gain 1 stop (by either dialing gain down 1 stop and then setting EC -1 or swapping on HTP because that is HTP). HTP lowers the gain one stop BUT to keep the same light coming in it must be set to meter 1 stop less than normal at the new gain that HTP selected under the hood (or simply fail to report the new actual gain being applied). So HTP is metering to let a given gain get 1 stop less light than it would normally be metered for.

So in the sense that it meters 1 stop darker than it normally would for the gain that it is actually using you might say it is letting in one stop less light than normal. If not it would no different than shooting 1 stop lower with normal metering. When you go to replicate it yourself, that is what you'd do set ISO 1 stop lower than what you had it in with HTP and then set EC -1.

If you set your camera to ISO100 EC -1 and then shoot all day in P,Av,Tv you'll get RAWs that can be made to give same results as ones from ISO200 HTP EC0. In M mode you could get files that can be made to deliver the same results using either ISO100 EC -1 as ISO200 HTP EC0 and meterings suggest to you to use would be the same in either case.

It might make more sense to think of ISO200HTP not as any sort of ISO200 at all but as ISO100 and as an ISO100 that gets exposed to 1 stop less light than typical.

You could think of it as exposed to the same light and then has 1 stop less gain applied which it is but since the basis for that decision was based on the meter thinking it had been getting 1 stop more gain....

So you shoot your fountain at f/4.5, 1/15th, ISO200HTP or you shoot it at f/4.5, 1/15th, ISO100 HTP-off and get the same thing, same shutter, same aperture,same SNR,same DR,RAW files are store a touch differently but are basically 1:1.


Quote
Suggesting that at ISO 400, HTP reduces the light hitting the sensor is not just misleading, it's plain wrong.

Yes, swapping ISO400 to ISO400HTP doesn't change the light hitting the sensor. Hit the button and the total light hitting the sensor stays the same.

But saving a stop of highlights for a given amount of sensor gain does mean 1 stop less total light hitting the sensor.

Under the hood, HTP it is doing 1 stop less gain and then setting the metering to expose 1 stop less than normal for that gain. If you have an ISO400 HTP shot and then want to do that on a camera without HTP you would set ISO200 and EC -1. If you shot at ISO400 and EC 0 and wanted to save a stop more of highlights while shooting at ISO 400 what would you do but EC -1 and let 1 stop less total light hit the sensor.

Although it is probably simplest to not talk about getting less photons.


Quote
What if you wanted motion blur of a fountain, but to preserve the highlights in the scene - would you sacrifice the motion blur you wanted, or stop down and change your DoF or lose sharpness to diffraction?  I would do what the camera does with HTP - underexpose by lowering ISO as many stops as needed, and if that took me to ISO 100, it would be time for an ND filter.

HTP doesn't lower as many stops as needed. AutoISO does.
HTP just shoots one stop lower and then meters that ISO one stop under.

In this particular scenario of M mode, we are not talking about an at any given gain scenario any more. You just set the gain to balance how much shadows detail you want vs highlights saved. Once you get it ballpark you can then +/- 1 it to save more or less highlights. (although you might want finer tuning than whole stops and might want to tweak aperture or shutter 1/3 of a stop unless you MUST have it left as is exactly).

In the ap AND shutter MUST be exactly locked sub-case of M mode scenario deciding to lower gain a stop might be a bit odd to think of in terms of shooting a given ISO with 1 stop less light coming in since you are in a we decided to keep that fixed scenario, granted so yeah a bit weird. It is still true though that if ISO200 HTP is what ended up working for the particular scenario then so would ISO100 instead and if you cared what the meter told you, then setting that EC -1 same as always though.

Quote
I disagree with your statement, "...if I want to do HTP myself what do I need to do? To get the exact same result I shoot at my selected ISO, keep my selected aperture and then I raise the shutter speed 1 stop faster."

It is probably best to just say that shooting HTP at a given gain an EC 0 is 1:1 in RAW to shooting without HTP but at 1 stop less gain and metering set to EC -1. That is normally what I say. Of course in the latter case the histogram and image review may be a bit tougher to judge at first.

At high ISO where they disallow HTP is would actually make sense to always have it on since the digital gain just lops off the top stop each ISO you go up.

« Last Edit: February 03, 2013, 03:54:48 AM by LetTheRightLensIn »

neuroanatomist

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Re: Canon may be expensive but...
« Reply #104 on: February 03, 2013, 06:34:12 AM »
Yes hitting the HTP button doesn't change the total light now hitting the sensor

Thank you, you can stop there.  I fully understand how HTP works 'under the hood', and how to emulate or 'improve' on it when shooting RAW, as do you - I don't think we need to explain it to each other.  My point was that someone who states the opposite of the quoted statement above (repeatedly) is wrong, and does not understand the general mechanism of HTP.  Incorrect statements like that can confuse people who are trying to understand the concept, and which is unfortunate and should be corrected.
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Re: Canon may be expensive but...
« Reply #104 on: February 03, 2013, 06:34:12 AM »