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04-05-2017, 10:07 PM   #16
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QuoteOriginally posted by GUB Quote
I wonder if we will see a generation of cameras that leave the Iso to the raw developing and have an autocorrected JPG for playback . It would still need an indicator somewhere to let you know how underexposed you are but no Iso control in raw. How simple could photography get!! Set your shutter and aperture simply for the reasons above and off you go!!
So according to the DPReview preview of the new Hasselblad, the X1D-50c does exactly that for ISOs above 1600. Which seems to give them more dynamic range for ISOs above 1600 than other comparable cameras. (Warning: the 645z is mentioned in this comparison.)

Hasselblad X1D-50c First Impressions Review: Digital Photography Review

04-06-2017, 12:52 AM   #17
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QuoteOriginally posted by leekil Quote
So according to the DPReview preview of the new Hasselblad, the X1D-50c does exactly that for ISOs above 1600.
That part of the review is fairly well-written, and may I say, with the sensor size difference, that choice looks somewhat consistent with ISO800 indicated above for the K-1 :-)
(Not really that simple, but I'll skip the theoretical analysis as it doesn't add value over the empirical finding and contains several unknowns.)
04-09-2017, 01:37 AM - 2 Likes   #18
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Thanks for the input everyone. I have had a good week thinking about things. Here is a sum up.

Prerequisites :

Working in Raw -
Working in lighting that requires higher Iso for correct exposure
Working with a camera that is at least reasonably iso invariant.
Editing skills

Potential gains :

Exposure tolerance in constantly changing lighting conditions.
Major gains in controlling highlights.
Improvement in Dynamic Range

What you won't gain:

An improvement in noise levels. This is not about that.

How I will approach it:

The idea of Underexposing 2 to 3 stops rather than right down to base iso makes a lot of sense if only to get a rough idea of what you have taken in the LCD rather than a toally black screen.

Using TAV with exposure compensation makes a lot of sense and is quick to get in and out of.

Final note;
The idea of utilizing Iso-invariance does not conflict with the principle of ETTR. But it does identify what should have been an obvious point about ETTR (and one I hadn't thought of!) . And that is that the Iso is irrelevant to maximizing the number of photons hitting the sensor which is the driving force behind ETTR. Only Aperture and shutter speed can do that.
So take your Aperture and shutter speeds to their brightest appropriate levels and underexpose by Iso alone.

How does all that sound
Thanks people.
04-09-2017, 05:36 PM - 2 Likes   #19
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Great summary, GUB!

To a first approximation, ISO invariance means that the sensor has very low read noise. For such sensors, the noise level in the final image is the same whether the signal is electronically amplified before analog-to-digital conversion (by setting a higher ISO) or after read-out (by boosting exposure in PP).

With ISO-invariance, there's no advantage to boosting ISO to get a "proper" exposure (and some disadvantage if it causes clipping of highlights). But, by the same token, there's no advantage to leaving it at base ISO either. If boosting ISO clips no highlights, the "proper" ISO can make review of the image in the field easier. Yet the later is hard to do in many situations.

ETTR is fine in principle but it can be hard to do correctly. There's many kinds of scenes that have very small numbers of highlight pixels (night sky, cities at night, reflective objects with catchlights, forest canopies with dappled sky, sunlight on water droplets, etc.) where the histogram doesn't clearly show the brightest pixels. It's too easy to push the mass of the histogram to the right and clip all the tiny highlight regions (looking for blinkies while chimping can catch the problem but it's still too easy to go too far right).

04-09-2017, 07:52 PM   #20
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QuoteOriginally posted by photoptimist Quote
Great summary, GUB!

To a first approximation, ISO invariance means that the sensor has very low read noise. For such sensors, the noise level in the final image is the same whether the signal is electronically amplified before analog-to-digital conversion (by setting a higher ISO) or after read-out (by boosting exposure in PP).

With ISO-invariance, there's no advantage to boosting ISO to get a "proper" exposure (and some disadvantage if it causes clipping of highlights). But, by the same token, there's no advantage to leaving it at base ISO either. If boosting ISO clips no highlights, the "proper" ISO can make review of the image in the field easier. Yet the later is hard to do in many situations.

ETTR is fine in principle but it can be hard to do correctly. There's many kinds of scenes that have very small numbers of highlight pixels (night sky, cities at night, reflective objects with catchlights, forest canopies with dappled sky, sunlight on water droplets, etc.) where the histogram doesn't clearly show the brightest pixels. It's too easy to push the mass of the histogram to the right and clip all the tiny highlight regions (looking for blinkies while chimping can catch the problem but it's still too easy to go too far right).
Yes I have never been a big fan of ETTR. My instinct has been to always underexpose a bit to protect those highlights. This stuff has vindicated that stance but only if I underexpose via the Iso.
Doing bokeh shots have driven me to under expose. Nothing ruins a bokeh shot more than a fried out blob!!
05-26-2017, 01:46 AM - 2 Likes   #21
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So I have had a bit of playing around with the camera with an awareness of using iso invariance as a possible tool. Come up with a couple of examples where underexposing stopped my highlight being unexpectedly clipped.
In the fern I underexposed about 2 stops - f5.6 1/8 sec Iso 200. I think you will agree that I couldn't afford to give the sensor more light than that. (f5.6 1/8 sec) And also notice how the brightest area of highlit hairs is already bight enough. I think this is a great example of utilizing Iso invariance.
And with the gas station there was a 3 stop difference in the shots. Here it is a moot point what actually is the correct exposure for the subject - it is almost inevitable that something will be burned out. But that 3 stops gave me a heck of a lot more control of the details. This is a 3shot panorama with the 40mm xs.
Spot the detail and colours difference in the 100% crop shot.
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05-26-2017, 05:32 AM   #22
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QuoteOriginally posted by GUB Quote
So I have had a bit of playing around with the camera with an awareness of using iso invariance as a possible tool. Come up with a couple of examples where underexposing stopped my highlight being unexpectedly clipped.
In the fern I underexposed about 2 stops - f5.6 1/8 sec Iso 200. I think you will agree that I couldn't afford to give the sensor more light than that. (f5.6 1/8 sec) And also notice how the brightest area of highlit hairs is already bight enough. I think this is a great example of utilizing Iso invariance.
And with the gas station there was a 3 stop difference in the shots. Here it is a moot point what actually is the correct exposure for the subject - it is almost inevitable that something will be burned out. But that 3 stops gave me a heck of a lot more control of the details. This is a 3shot panorama with the 40mm xs.
Spot the detail and colours difference in the 100% crop shot.
That's possibly the most convincing argument I've seen for shooting this way. I need to rethink my workflow, at least in certain situations.

05-26-2017, 09:06 AM - 1 Like   #23
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Excellent work, GUB!

It clearly shows there's two philosophies for exposure: 1) getting a "nice" SOOC image (which often blows some highlights in order to bring the bulk of the image up into pleasing middle grays); 2) capturing the greatest range of raw signal values for post-processing.

What I wish Pentax would do is add some exposure meter interpretation modes. The 86,000 pixel metering sensor in the K-1 should be able to measure the light levels of highlights as small as 20x20 pixels. I could envision a "area highlight" mode that uses the brightest reading of the 86,000 to set the exposure and a "spot highlight" mode that assumes whatever the spot meter is pointed at is a highlight that should be kept just under the clipping point. And if Pentax wants to get fancy, they could offer ETTR and ETTL modes or have both dials do something when you hold down the meter-mode button (maybe the front dial picks the pattern-mode and the back dial picks the highlight/18% gray/ETTR/ETTL meter data interpretation mode).

Last edited by photoptimist; 05-27-2017 at 05:01 PM.
05-27-2017, 09:50 AM - 1 Like   #24
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QuoteOriginally posted by starbase218 Quote
If camera manufacturers or application companies were to automatically balance the exposure for playback it would make things a lot easier.
The K1 does it in Green Mode (Auto Scene analysis).

---------- Post added 27-05-17 at 18:59 ----------

QuoteOriginally posted by photoptimist Quote
What I wish Pentax would do is add some exposure meter interpretation modes
Looks like the green mode does it.
05-30-2017, 12:32 AM   #25
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Underexposing and utilising Iso in-variance isn't abandoning the base principle of ETTR.
Best practise still is to put as much light on your sensor as possible given your aperture and shutter speed limitations.
It is only the practise of increasing your Iso to achieve ETTR that is obsolete with an Iso invariant sensor.
Canons on the whole are not Iso invariant so that might explain why they are more into ETTR.
I suspect a lot of pentax users have , like myself, discovered that there was more to gain from underexposing and avoiding clipped highlights by trial and error without understanding the concept of utilising Iso invariance.
The key is to only do it with Iso.
11-08-2017, 06:20 PM   #26
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QuoteOriginally posted by GUB Quote
Thanks for the input everyone. I have had a good week thinking about things. Here is a sum up.

Prerequisites :

Working in Raw -
Working in lighting that requires higher Iso for correct exposure
Working with a camera that is at least reasonably iso invariant.
Editing skills

Potential gains :

Exposure tolerance in constantly changing lighting conditions.
Major gains in controlling highlights.
Improvement in Dynamic Range

What you won't gain:

An improvement in noise levels. This is not about that.

How I will approach it:

The idea of Underexposing 2 to 3 stops rather than right down to base iso makes a lot of sense if only to get a rough idea of what you have taken in the LCD rather than a toally black screen.

Using TAV with exposure compensation makes a lot of sense and is quick to get in and out of.

Final note;
The idea of utilizing Iso-invariance does not conflict with the principle of ETTR. But it does identify what should have been an obvious point about ETTR (and one I hadn't thought of!) . And that is that the Iso is irrelevant to maximizing the number of photons hitting the sensor which is the driving force behind ETTR. Only Aperture and shutter speed can do that.
So take your Aperture and shutter speeds to their brightest appropriate levels and underexpose by Iso alone.

How does all that sound
Thanks people.
Thanks for putting me onto this GUB, you pointed me here from here remember?

I have a few events coming up (a Wedding in December and this weekend another 'Science at the Local', I'm keen to try and carve out myself a mode that is suitable to these kind of event, indoors, low light and no flash use. I will also need to think about the use of MF to be quiet (church), perhaps ES mode and Live View things the whole time (perhaps monopod as well...)

If I understand correctly an easy way to use this method would be to simply be in TAv mode, adjust the shutter and aperture to how the user sees fit (I have snapped very animated speakers requiring upwards of 1/200th!, and others where 1/50th is fine), press the +/- EV compensation button and dial it back to say -2.3 or so, and then just snap away. Chimping will reveal darker images than normal, but PP should fix all that. I can see by giving the -2.3 in the EV comp the ISO drops accordingly and that's what we're after. Lower ISO images that are darker but when lifting exposure during post processing all good.
Talking of post processing, I shall check out the aforementioned Fast Raw Viewer (as I currently use Fast Stone) for means of gaining a quick insight into any RAW worth keeping during the culling process, is there any other preferred method of bringing the exposure up during PP? I use LR predominately, just adjust the Exposure slider bar?

Cheers,

Bruce
11-08-2017, 09:10 PM   #27
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QuoteOriginally posted by BruceBanner Quote
Thanks for putting me onto this GUB, you pointed me here from here remember?

I have a few events coming up (a Wedding in December and this weekend another 'Science at the Local', I'm keen to try and carve out myself a mode that is suitable to these kind of event, indoors, low light and no flash use. I will also need to think about the use of MF to be quiet (church), perhaps ES mode and Live View things the whole time (perhaps monopod as well...)

If I understand correctly an easy way to use this method would be to simply be in TAv mode, adjust the shutter and aperture to how the user sees fit (I have snapped very animated speakers requiring upwards of 1/200th!, and others where 1/50th is fine), press the +/- EV compensation button and dial it back to say -2.3 or so, and then just snap away. Chimping will reveal darker images than normal, but PP should fix all that. I can see by giving the -2.3 in the EV comp the ISO drops accordingly and that's what we're after. Lower ISO images that are darker but when lifting exposure during post processing all good.
Talking of post processing, I shall check out the aforementioned Fast Raw Viewer (as I currently use Fast Stone) for means of gaining a quick insight into any RAW worth keeping during the culling process, is there any other preferred method of bringing the exposure up during PP? I use LR predominately, just adjust the Exposure slider bar?

Cheers,

Bruce
Wouldn't it be great if you could bracket iso in M mode. Take a dual of say Iso 1600 and 100.
Oh if you are thinking of shifting raw developers check out Rawtherapee. I use it the other day for some -3EV shots and it auto corrected them to near enough to correct exp.
11-08-2017, 09:39 PM   #28
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QuoteOriginally posted by GUB Quote
Wouldn't it be great if you could bracket iso in M mode. Take a dual of say Iso 1600 and 100.
Oh if you are thinking of shifting raw developers check out Rawtherapee. I use it the other day for some -3EV shots and it auto corrected them to near enough to correct exp.
Yeh I use RT already for sorting out motion correction in Pixel-shifted images, haven't used it beyond that. LR doesn't have an auto exposure correctness really does it?

And oh, does what I typed make sense, is my set up approach ok?
11-09-2017, 02:59 AM - 1 Like   #29
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Yeah I think it makes sense - thing is I am pretty well always M mode. One thing with my K1 in M mode and using liveview the brightness of the screen doesn't change with settings change so seeing and focusing the subject isn't an issue.
I use an LCD viewfinder and when chimping I can see enough of a -3EV to know whether I have a good one.
If you are going Manual focus and liveview then a Lcd viewfinder is a real bonus. Aftermarket LCD Viewfinder for K1 - PentaxForums.com
I have a friend who does a bit of opera photography with her FF nikon. She grasps the potential of utilising iso invariance but she struggles to find the confidence to actually commit to it and these crazy almost black images. I think she is using the TaV -3 sort of approach.
But think about it - if you have the aperture as open as you dare and the shutter as slow as you dare , then so long as the resulting image is actually underexposed how does Iso or the final EV matter- that is the whole point of utilising Iso invariance. Sure if the image ends up -5EV then there is no chimping but that is not the end of the world.
11-09-2017, 04:59 AM   #30
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Interesting thread GUB, thanks. You have obviously put a lot of thought and work on this. Just a couple of thoughts that may be of general interest:

1. The raw editor you use is also important as some such as Adobe (ACR and LR) use a Base Line exposure compensation which may be either negative or positive and can be close to 2/3 of a stop. Couple to this the actual raw conversion factors (Process Versions) where exposure and contrast applied prior to display (Sliders will still appear zeroed) per camera and you may find that what appears to be a correct exposure is already less than optimal potentially up to -2.0 EV.
The values may be different per manufacturer and even per camera model.

2. ETTR was mentioned a few times in this thread. IMO worth revisiting the principles of ETTR at least from my understanding as expounded by Thomas Knoll (early 2000's):

a. ETTR only applies at base ISO
b. ETTR is only really useful when the scene dynamic range will fit comfortably within the sensors DR range

Although I believe that these statements still valid a lot has changed in digital acquisition in the years since this published. Camera Dynamic range has probably doubled, sensors improved, ADC advanced etc.
So perhaps ETTR not quite as important as it used to be?
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