Author Topic: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide  (Read 409523 times)

a1ex

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Re: ETTR (Exposure to the Right): - -History & Beginners Guide --
« Reply #25 on: June 07, 2013, 10:44:31 PM »
Look in image finetuning -> digital ISO. In raw video, it will only affect the preview, not the recorded image.

Marsu42

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Re: ETTR (Exposure to the Right): - -History & Beginners Guide --
« Reply #26 on: June 08, 2013, 12:02:36 PM »
You're trying to find flaws in my specific examples referencing all manner of different situations.

Not at all, I was just commenting that your theory "The shadows are where all the action is" is not a general truth, but you just ack'ed that yourself and maybe I misunderstood what you were trying to say.

But this matter is very important to me, because with my 60d I always struggle between underexposing iso800 (with the added benefit of preventing clipped specular highlights) or properly exposing something between iso1000 and iso1600. And my personal observation from the past seem to square with your observations as I understand them: higher iso gives noisier midtones but cleaner shadows, so unless I expect to raise the shadows in post I'm usually sticking with iso800. But I'm very open to suggestions :-)

Also this thread is important to tell two different uses of ettr from each other that might be confused:
1. properly expose for max. use of the available dynamic range, i.e. collecting *more* photons
2. collecting the *same* amount of photons but at different iso levels

Look at the data.

Interesting - where did you get that from?

a1ex

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Re: ETTR (Exposure to the Right): - -History & Beginners Guide --
« Reply #27 on: June 08, 2013, 01:06:44 PM »
Quote
2. collecting the *same* amount of photons but at different iso levels

Here it's all about the analog amplifier between the sensor and the ADC. If that amplifier is less noisy than digital gain (e.g. multiplying underexposed data by 2), you can start thinking to increase the ISO.

For digic 4, the analog amplification from ISO 1600 to 3200 is just as noisy as the digital one, so there's no point in going above ISO 1600.

Sure, by raising ISO you lose some dynamic range. You increase ISO by 1 stop => you lose 1 stop of DR from ADC saturation and you gain less than 1 stop of DR because of cleaner shadow noise. So, if you can increase shutter or aperture, do that first (because you don't lose DR by doing that, you just shift it).

But if you have more DR than your scene needs, you can throw away some of it, and increase ISO to get better results.

I recommend reading this: http://www.guillermoluijk.com/article/isos5dmkii/index.htm

Audionut

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Re: ETTR (Exposure to the Right): - -History & Beginners Guide --
« Reply #28 on: June 08, 2013, 02:29:56 PM »
Not at all, I was just commenting that your theory "The shadows are where all the action is" is not a general truth, but you just ack'ed that yourself and maybe I misunderstood what you were trying to say.

Shadows are where the biggest gains will be made, as they are closet to the camera noise floor.  I tried to emphasis this point, as there are a large number of users who appreciate clean shadows.  I guess it's sort of easy to keep your midtones clean, as they should be fine if you have a good exposure (not necessarily ETTR), and the highlights, unless you are severely underexposing them, they will almost always be clean, because they are at the right hand side of the histogram (where SNR is best).

So, to put it differently, any ol tom dick and harry can make clean highlights and midtones, getting your shadows clean is where the real challenge is.

I was honest when I stated that an understanding of exposure is needed to fully appreciate ETTR.  That's not directed at you personally, it's a general statement that I wanted to revisit.  In fact, I'd go as fare as to say, to fully appreciate ETTR, you also need a good understanding of your cameras sensor response (how it responds to light), and it's noise characteristics.


But this matter is very important to me, because with my 60d I always struggle between underexposing iso800 (with the added benefit of preventing clipped specular highlights) or properly exposing something between iso1000 and iso1600. And my personal observation from the past seem to square with your observations as I understand them: higher iso gives noisier midtones but cleaner shadows, so unless I expect to raise the shadows in post I'm usually sticking with iso800. But I'm very open to suggestions :-)


It's important to point out that highlights are the brightest parts of the scene.  Whether that is a candle or the sun.  Then from there, the midtones are around 18% of those highlights, and from there, the shadows extend down to pitch black.

By attempting to retain specular highlight detail, you are increasing the dynamic range requirements of the camera by a spectacular ;) amount.
Cameras have a limited ability to capture bright whites and dark blacks (dynamic range).  If you are attempting to shot a scene with a dynamic range in excess of that of your camera, no amount of ETTR is going to help.

I can blabber on with fancy graphs and fancy dB readings all day long, but the best way to understand your camera, and the benefits of ETTR is to go and try it.

Find a scene with a limited dynamic range to test, as this will highlight the benefits of ETTR.  From there you will have a better understanding on how ETTR and dynamic range interact.

A bare wall very slightly out of focus is a good test.  Noise is more prominent where detail is less.
Noise can actually increase the perceived detail when viewed at sufficient viewing distances.  Anyway, that's a different topic :)

Shot @ ISO 800 @ 0EV on the Canon meter.  Then increase ISO to 1600 and reduce shutter speed until you start to overexpose the image.  I also recommend using RawDigger to determine true overexposure in the shot.  Or thanks to the absolutely marvelous advancements with ML, use the Raw histogram in LV for quicker results.

Take a look at both images.  The ISO 800 shot we'll call underexposed (even at 0EV on the Canon meter), and the ISO 1600 shot we'll call ETTR.  Which one has the least noise?  Cameras generally have around 3EV of highlight headroom (detail capturing ability above 0EV), so take a shot @ ISO 400 @ 0EV on the camera also.  Compare it to the ISO 1600 shot.  Which has less noise?  ;)


It all boils down to how much dynamic range the scene contains, and where 18% (middle grey) (or 12% or 13%, take your pick) of the overall luminance level of the shot is.  With a large dynamic range scene, 0EV on the Canon meter is going to be accurate, because it's got lots of detail (data) to determine precisely where the correct (18%) exposure is. 

On scenes with limited dynamic range, there often might not be enough detail (data)/(information) for the camera to determine where a correct exposure is.  And it will tend to underexpose, or, more precisely, not push the exposure to the right hand side of the histogram where the sensor is performing at it's best.  In this case, ETTR will net you a much better (cleaner, and more accurate color rendition) shot of the scene.

As a1ex points out, best case is using shutter and/or aperture to push the exposure to the right.  You're increasing the photon capturing ability of the sensor, without all the side effects that come from increasing that sensitivity via analog gain (ISO).
But if you take a look at the sample images I posted on page 1 of this thread, I show where ISO can be increased, and results in less overall noise in the photo.  Noise increases constantly with analog sensor gain (lower ISO's), but, noise decreases exponentially with increased luminance (in the shadows at least, the roll off is less at higher luminance levels).

Interesting - where did you get that from?

DxOMark.

The link a1ex gave above makes for good reading.

Note:  There's some words in there with links to meaning.  This isn't directed sorely at you, but is included for the benefit of other readers, particular those without English as their first language.

AnotherDave

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Re: ETTR (Exposure to the Right): - -History & Beginners Guide --
« Reply #29 on: June 08, 2013, 03:33:47 PM »
a1ex pointed out in another thread that you can use image finetuning to display the "correct" exposure on the display in liveview without affecting the raw recording.

I tried shooting an h.264 this way, and the .mov file was tuned correctly... without noise!

So it seems this can be applied to h.264 recording as long as you're tuning the image correctly in camera.

a1ex

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Re: ETTR (Exposure to the Right): - -History & Beginners Guide --
« Reply #30 on: June 08, 2013, 03:37:17 PM »
Right, the digital ISO from image finetuning is effectively exposure compensation applied "in post" (after the raw data has been captured). But since it's applied before H.264 compression, it can help a lot.

I've pointed this out one year ago I think, but it got buried in the google groups :P

A little scratchpad (feel free to polish it, fix mistakes and turn it into a nice article): http://magiclantern.wikia.com/wiki/ISO . That one represents my opinion from one year ago, so take it with a grain of salt.

duncanidaho25

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #31 on: July 10, 2013, 02:57:52 AM »
I'm sorry to ask for more of an explanation after such in depth descriptions, but I'm still left with questions.

With auto ETTR on, it is controlling ISO and shutter, meaning if I try to change either it automatically replaces it where it thinks it should be.  So, is the only adjust to make the % of highlight to ignore? 

Is the idea to get the White # inside the histogram to balance out to 0? 

When ETTR is on, and the image is still underexposed, I'm assuming it's because I have a blown out window in the frame (for example).  Is this correct?  If so what is the correct procedure to compensate? 

I'm currently uploading some video I shot with ETTR to show you where I'm at.  I'll add it as soon as its uploaded. 

Thanks for the help. 
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Audionut

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #32 on: July 10, 2013, 03:35:59 AM »
With auto ETTR on, it is controlling ISO and shutter, meaning if I try to change either it automatically replaces it where it thinks it should be.

AutoETTR adjusts shutter/ISO only.  Aperture is left for the user to control.
Depending on settings (AutoETTR), if you adjust shutter/ISO, AutoETTR will adjust the shutter/ISO again.

So, is the only adjust to make the % of highlight to ignore?

Also the exposure target.  IIRC, this determines how close to full saturation to ETTR.
And clipping mode.  You can clip the green channel for instance and recover the lost detail from that channel in post processing.

Is the idea to get the White # inside the histogram to balance out to 0?

Digital cameras have a maximum pixel saturation.  After pixel saturation (blowout/clipping), detail is lost.
ETTR is about pushing the exposure as bright as possible without saturating the pixels.

When ETTR is on, and the image is still underexposed, I'm assuming it's because I have a blown out window in the frame (for example).  Is this correct?  If so what is the correct procedure to compensate? 

Correct.  You can adjust highlight ignore to try and compensate for specular highlights (or other detail you don't mind being blown), otherwise you are left to manually adjusting the exposure as needed.
Raw based zebras will show the areas of overexposure (pixel saturation).  Use these to determine if wanted detail is being blown.
With your blown out window frame for example, AutoETTR is trying to maintain all detail (subject to it's settings), but since the window frame retaining detail is resulting in underexposure of your scene, you could use raw zebras to keep increasing exposure as desired while monitoring wanted detail to ensure it's not being blown out.

duncanidaho25

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #33 on: July 10, 2013, 04:48:24 AM »
Here's me trying to figure out ETTR.  https://vimeo.com/69923344

I processed using:

RAW2CDNG
Resolve - with Hunter's LUT (https://vimeo.com/67970827)
exported as QT 4:4:4
I then played around with the colorgrading (colorista, fast color corrector) I probably would have been better off just to leave it as is though.
then exported h.264
I noticed some heavy aliasing (on the medicine bottles) that vimeo introduced.  (I think I exported with the wrong settings for vimeo).

*Side note, watch out that in 3X crop mode that you shoot in the middle of your frame.  As you can see I was too far left on a few shots.

Anyway, as you can see I'm struggling getting the correct exposure.  I'll try again after your response.  (Thanks by the way).
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ronl

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #34 on: July 18, 2013, 03:55:52 AM »
I have yet to install ML onto my camera but interested in both Auto-ETTR and raw histograms.

Is there any way to have Auto-ETTR and Raw histogram features when shooting still images without using live-view?  I typically shoot using AI Servo mode tracking subjects where using live view is not an option.

Ideally, the raw histogram would replace the jpg histogram when reviewing images and the Auto-ETTR hint would be visible in the viewfinder when shooting in Manual Exposure mode telling you how many EV you are off.

Audionut

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #35 on: July 18, 2013, 07:31:11 AM »
In photo mode, Raw based histograms/zebras/spotmeter only work in quick review (the image shown immediately after a shot).
If you press the play button to view images, these will not have raw based histograms/zebras/spotmeter.

Each line in the raw histogram represents 1EV.  You can also enable ETTR hint which will give you a numerical value of how far EV is from maximum.

AutoETTR works in photo mode just fine.  Here you adjust trigger mode in AutoETTR settings.  Always ON will adjust the camera settings after taking a reference pic, and will continue to adjust settings as needed for all shots.  Auto Snap will take consecutive shots until the best settings are found.  Press SET allows you to press the SET button to engage liveview and find the best settings.  The same also applies for HalfS DblClick, obviously this will happen with a double press of the shutter rather then the SET button.

No Magic Lantern information is available through the viewfinder.

If you need visual confirmation through the viewfinder of the best ETTR settings, your only choice is the Canon exposure meter at the bottom.  Put the camera in manual mode with SPOT metering.  Find a plain wall.  Adjust settings so that the Canon exposure meter is showing +2EV.  Take a shot and inspect the photo with a raw utility such as RawDigger, or the raw based data from Magic Lantern.

Is there overexposure?  There should not be.  In which case, adjust settings so that the Canon meter shows +2.3EV, take another test shot.  Continue until you find the Canon meter reading which starts to result in overexposure.  This should be around +3 to +3.5EV.

If +3EV is the maximum Canon meter reading that results in no overexposure of your shot, you have found how to manually ETTR with the Canon meter.

Stick in spot meter mode and use your spot meter to judge exposure.  Taking a landscape, spot meter off a bright cloud at +3EV.  Done!
Doing a wedding and want to ensure the white dress is the maximum luminance and retains detail.  Spot meter it at +2.6EV (leave a little headroom).  Done!
Want to nail a correct exposure of a pale skinned person, spot meter them at +1EV.  Highlights will fall where they fall, shadows also.  But the skin will be correct ;)

duncanidaho25

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #36 on: July 22, 2013, 01:42:14 AM »
Here is my ETTR test:

I probably should have tested without the motion.  It wasn't very smooth, and even warp stabilizer didn't salvage it.

I did 5 shots.  I used the AUTO ETTR settings for shots 1 & 3, the others I did not use the settings suggested ( I used the 2 times half shutter mode).

Can someone help me understand how to read and use the E # and RGB #s. 

I did grade these.  I guess I should have left them alone for a more accurate test.  Again, Thanks for your help!


**also, how do you use vimeo video embedding correctly in this forum?


SETTINGS for the 5 shots:

Shot 1:
ISO: 800
Shutter: 48
fstop: 2.8
ETTR= 1.4 R-1 G-4 B-2
Shot2:
ISO: 100
fstop: 2.8
shutter: 48
ETTR=4.1 RGB = _ _ _(all blank)
Shot 3
ISO 800
Shutter: 48
fstop 2.8
ETTR= 1 RGB=264
Shot 4
ISO: 1600
fstop: 5.6
shutter: 48
ETTR=2.0 RGB=121
Shot 5
ISO 100
fstop 1.4
shutter: 48
ETTR= 2.7 RGB= _1_
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Audionut

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #37 on: July 22, 2013, 03:19:34 AM »
**also, how do you use vimeo video embedding correctly in this forum?

You need to remove the s from https and embed the link in the vimeo tags.  I've edited your post.  Click the modify button on your post and check how I've done it.

What exactly is it that you're trying to test?  I understand your using ETTR, but how?  What do you want it to accomplish?

Where are you getting these ETTR and RGB numbers from?

duncanidaho25

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #38 on: July 22, 2013, 03:56:38 AM »
I'm just trying to understand how to use the Auto ETTR module.  I'm only trying to accomplish good exposure and get the wide dynamic range I should get with shooting raw. 

I got the numbers from the RAW histogram in Magic Lantern.
Inside there is a Red#, Green#, Blue# and a "White E#"

Thanks for the embed tip.  I've got it now.
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Audionut

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #39 on: July 22, 2013, 05:03:51 AM »
I got the numbers from the RAW histogram in Magic Lantern.
Inside there is a Red#, Green#, Blue# and a "White E#"

The RGB numbers represent the percentage of overexposure in each channel.  So for instance, Green 4 is reporting 4% of the pixels in the green channel have become white (overexposed).

The White E represents the amount of EV until overexposure.  Or the amount of -EV for no overexposure.


I'm just trying to understand how to use the Auto ETTR module.  I'm only trying to accomplish good exposure and get the wide dynamic range I should get with shooting raw. 

AutoETTR is only helping with the white (brightest) point of your exposure.  If you have a scene with a low dynamic range (difference between brightest part of the exposure, and darkest part), AutoETTR will be extremely useful as it will push the exposure to the right, and the camera will capture the scene with the highest Signal to Noise Ratio and best color rendition.

On scenes with large dynamic range, things get a little more complicated.  Do you want a bright light to remain exposed (not pushed to white), which will underexpose the rest of your scene, or do you want to ensure the correct exposure for one part of your scene (skin tones for example), which will result in other parts of the scene becoming overexposed.

AutoETTR doesn't know what you want.  All it's doing is ensuring that nothing gets overexposed (within the limits of its settings).  You need to make a conscious decision on what to do with your exposure.

On scenes with large dynamic range, use the Zebras.  Zebras will show what areas are being overexposed, and what areas are being underexposed and pushed into the noise floor of the camera.  This will allow you to make the best decision on what to do with the exposure.

duncanidaho25

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #40 on: July 22, 2013, 05:14:49 PM »
This is a big help.  Thank you.
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ronl

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #41 on: July 24, 2013, 09:54:15 PM »
Thanks for the info Audionut!!  Do you know how long the camera takes after each shot to process the Raw histogram?  Would enabling raw histograms be practical when shooting an event where you are shooting many consecutive frames using AI servo mode?  I noticed that in a different thread, you have asked for the priority of the raw histogram to be lowered to allow the camera to be responsive more quickly.

I would guess that Auto-ETTR might not be practical as it may do several shots back to back and then evaluate what exposure is ideal in that situation.

Audionut

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #42 on: July 25, 2013, 02:49:11 AM »
Thanks for the info Audionut!!  Do you know how long the camera takes after each shot to process the Raw histogram?  Would enabling raw histograms be practical when shooting an event where you are shooting many consecutive frames using AI servo mode?  I noticed that in a different thread, you have asked for the priority of the raw histogram to be lowered to allow the camera to be responsive more quickly.

To be fair, it was only a very narrow period (of time) where shooting became unresponsive.  a1ex has recently fixed it.  Raw histogram no longer effects shooting response.

I would guess that Auto-ETTR might not be practical as it may do several shots back to back and then evaluate what exposure is ideal in that situation.

It will only take consecutive shots when the trigger mode is set to Auto Snap. 
It may need several shots to settle on accurate settings.
Like everything, it has it's uses, but is not the be all and end all of correct exposure  ;)

ouuzi

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #43 on: August 02, 2013, 03:37:15 PM »
Audionut,so if i have the camera on tripod for landscape photography,I just have to choose press SET and that will calculate the exposure?Correct?

ShootingStars

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #44 on: August 06, 2013, 08:24:15 AM »
Been using ETTR for a few days... do not use for portraits if your background is bright like the sky/sunny... ETTR will try to expose for sky/highlights and your portrait will be recoverable but the result is horrible.

Audionut

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #45 on: August 06, 2013, 10:31:55 AM »
@ouuzi

You can trigger the ETTR calculation as you see fit.  The end result will be the same.

@ShootingStars

That's been explained in this thread already.  AutoETTR only considers the white point!

feureau

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #46 on: August 06, 2013, 09:11:12 PM »
I read the thread, but can't seem to find a confirmation of this. It seems the ETTR module works only by changing the ISO and shutter speed, is that correct? Or is there a way to make it set the aperture (and ISO)?

Thanks

Audionut

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #47 on: August 07, 2013, 03:29:48 AM »
It does not adjust aperture at all.

AutoETTR will use lowest ISO as priority, and then adjust shutter speed as required.  You can set the slowest shutter speed used in the AutoETTR menu.

If you need to force a slow shutter speed, you can either increase aperture manually, or control exposure entirely yourself.

tankvps

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #48 on: August 18, 2013, 01:46:47 PM »
Thanks for the detailed steps.
I have a question about the Trigger mode.
What's the meanings of  Always ON Auto Snap, Press SET, HalfS DblClick?

For "press set", I understand it. When press set button, the camera will change to liveview automacticly. And measure how to adjust the iso or shutter, then return to the normal mode, let you to take pictures.

For "auto snap", it seems that when you finish one picture taken, ML will calcurate this picture to get the params, and then trigger another shoot automacticly(Am I right?).

For always on and halfs dblclick, I'm getting confused.

Halfs dblclick, does it means that I point the camera to the subject, and click the shutter button half twice. Then ML will calcurate the params, wait for seconds, I can click the shutter button fully to take the picture?

Thanks and sorry for these questions

Audionut

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Re: (Auto) ETTR (Exposure to the Right): -- History & Beginners Guide
« Reply #49 on: August 18, 2013, 02:18:17 PM »
That's correct tankvps.

And always on means that it continually calculates the exposure based on the previous shot.