Potential Method for Managing ISO / Shutter

K

kingtaj

New member
First, let me say that I’ve been scouring the internet for methods of controlling D90’s video mode, especially the ISO levels, for some time now. There are a few suggestions dispersed here and there, with Kholi’s method producing the best results.

I think I’ve found a new method at least worth exploring - it seems to be a pretty consistent way to estimate/control ISO level, though I’ve only played around with it for a few hours. Very interested to see what other users think.

The Video
To get right to it, I created a video of a dark scene, in which I methodically increase the ISO level, using a “gray screen” method. No lighting changes in the video, only the exposure - some combination of ISO and shutter speed. I’ll get into more detail later on why I think this method offers some control over ISO.

D90 ISO Control Test

In the video, no lighting changes and the aperture remains constant at f1.8 (using the Nikkor 50mm f1.8). As I step up the ISO, I attempt to keep the shutter speed to a minimum, and you can watch the difference as the video goes from Estimated ISO 200 to Estimated ISO 3200. It's not the best test in terms of scene lighting - when I get more time I might do another test with more interesting lighting.

The Lead-In
If you’ve never tried the Auto ISO feature, it basically works by automatically increasing / reducing the ISO based on the amount of light available. It allows you to specify the minimum shutter speed that is acceptable before increasing the ISO. So let’s say you set that to 1/30 - if the scene is too dark and the camera would like to drop below 1/30, instead it will increase the ISO automatically. The reverse holds true if the scene is overexposed.

Doesn’t this sound a lot like how the video mode seems to work? It automatically adjusts shutter and ISO depending on available light, and probably maintains some “bottom” shutter speed level.

The Technique
Essentially, use the Automatic ISO Sensitivity to make an educated guess about what ISO level you’re locking in. The idea is that when you have this turned on and you have made a good guess about the min. shutter speed the movie mode uses, you can get a good estimate of what ISO you’re at.

  1. In the menu, turn on Auto ISO Sensitivity. Set min. shutter speed to either 1/15 or 1/30 (more on this later).
  2. (EDIT) Set exposure compensation +/- to -0.3 or lower (i.e., -0.7).
  3. In Aperture Priority mode (other modes might work too?), set your desired aperture. Alternatively, use a manual aperture lens.
  4. Looking through the viewfinder or at the little screen on top, point the camera at the right amount of light to get your desired ISO. Obviously, point at brighter exposures to get a lower ISO. You can also use a laptop LCD with a dark gray background and adjust the brightness level to get a consistent ISO.
  5. (optional) Keep pointing camera at darker areas until it jumps to the next higher ISO, then back off slightly to get back to your desired ISO - this would hopefully keep the shutter speed low.
  6. Once pointed at the desired ISO, quickly push AE/L (Lock) and then immediately push Live View. You can almost push them simultaneously. (This step has some room for further experimentation)
  7. Now you should have a locked shutter and ISO. If your scene is too dark, then either add lighting or accept that you’ll have to use a higher ISO.
As far as the min. shutter speed in the Auto ISO Sensitivity menu, this really depends on what the movie mode is programmed to use as the minimum speed. Kholi mentioned speeds of 1/30 or 1/60 at the bottom range. For my test, I tried 1/15, but perhaps 1/30 would be more accurate.

This I think is where the community can help in determining what that bottom shutter speed really is. (It should be measurable from video right? (Given an object moving across the frame at a constant and known speed?) Knowing that bottom value might make it easier to mimic the movie mode ISO levels in Auto ISO Sensitivity mode.

One more consideration in trying to control shutter speed is that at any given ISO in auto sensitivity mode, there are a range of shutter speeds. Once the shutter speed gets too low, the camera boosts ISO. So if you slowly darken your exposure “gray screen” until just before the point the camera jumps to a higher ISO, you should be able to get the slowest shutter. Do the reverse to get a faster shutter speed.

Conclusion
This is a very presumptuous post - I don’t really know if the camera is doing what I hope it’s doing. I might be completely wrong about all this, so take it with a grain of noise, er salt. But when I’ve played around with it in low lighting, I did get nice clean images using this method. The best thing about this method is that you gain some feeling of control because you can see what numbers you “locked in” at even while you’re shooting video. Hopefully, this gives you more control over what the camera does. And it’s actually a very easy technique.

Let me know what you think!
 
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Yeah the thing is, it's just a liveview. And what they wanted it to be doing is showing the user what's going on in front of the camera. For that purpose the LV gets all the options to set the brightness up, ignoring the manual values. The stupid result is, that if you take a picture, it's underexposed and worse. That's why not even amateurs are using LV under normal conditions, because it's bullshitting you. I only use it when holding the camera in difficult angles.

The problem is not the D-Movie funktion, which is just a capture feature poorly glued on the D90 afterwards. It's the crappy LiveView...
 
i rarely ever use liveview when taking pictures...but there is some method to your madness.....

but i think once you enter LV and even more video mode, all of your maual controls are overridden by videos own rules...i could be way off but........
 
OK-
So there's no easy way to know what shutter speed and what ISO the camera is on when it's left to it's own devices, so let's say I would like to shoot at an f5.6. What is the difference between setting the lens at an f5.6 then aiming the camera between dark and light until the auto exposure goes where I want it for this particular shot, locking it, shooting...OR- setting lens at an f11, pointing at bright spot, locking it, open lens up to f5.6, shoot? Don't they achieve same thing if it is the same exposure at the same f-stop?

To my eyes, after a few days with the camera, I see no difference between the two. I haven't done any scientific tests, but it seems either you have enough light to achieve a low ISO at a given aperture or you don't, right?
 
Apart from the right ISO, you'd want to set the right shutter too. At least in PAL countries with the 50Hz interwall for AC Powerlines, it's difficult to find the right spot for the best shutter, so you don't get the annoying scrolling lines.
 
yeehaanow said:
To my eyes, after a few days with the camera, I see no difference between the two.
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me neither. the camera doesn't know what your f-stop is so it can't tell the difference. adding exposure with the +/-, locking and then stopping down is said to have some effect though and while i'm not sure if i agree it seems more likely since the dial seems to have an effect on the shutter speed before changing iso.

/matt
 
When I point it at my laptop monitor I can see the shutter change, but it seems like it only changes between two speeds, maybe 1/30th and 1/60? Total guess.

One way to figure it out might be to use a turntable that has the strobe speed marks and see how it matches. ?
 
I would hope that you are right about the shutter speeds. Unless you are going for a special look the 24p capture would most commonly use a 1/48th shutter--so if our two choices are 1/30th and 1/60th then this would keep us in that ballpark. I was hoping that the camera wouldn't push us into very fast shutter speeds, eliminating motion blur and giving a very unfilmic look (though sometimes used as in the D-Day scenes in Saving Private Ryan).

Now if EV adjustment could consistently push us to the 1/30th or 1/60th setting we would be left with only one variable--ISO.

Doesn't someone out there have the ability to measure the shutter speeds???
 
Has anyone else tried playing around with this? I found that keeping exposure compensation negative also seems to help.

I am getting more consistent results with this method than Kholi's method, and it's much easier, and doesn't require a manual lens. Having said that, I may also be doing Kholi's method wrong. :P

Hoping others will give this a try and discuss their results. Thanks!
 
After banging my head on the wall for the past few weeks trying to understand this shutter/ISO thing, I've come to realize I can't make orange juice from apples. The D90 is what it is. So, apples it is!

The D90 is a fun camera but I wouldn't subject a client to all the time needed searching for a perfect exposure. My hope is that future DSLR's with video will have full manual controls and don't overheat.
 
hepabst said:
After banging my head on the wall for the past few weeks trying to understand this shutter/ISO thing, I've come to realize I can't make orange juice from apples. The D90 is what it is. So, apples it is!

The D90 is a fun camera but I wouldn't subject a client to all the time needed searching for a perfect exposure. My hope is that future DSLR's with video will have full manual controls and don't overheat.
Click to expand...

Badabing badabang! I couldn't agree more :)

The most practical things I could do with this camera to shoot video with is to eyeball the exposure then lock it and shoot through a VR lens or use a tripod. Every other combination results in footage that looks like home movies shot through a cell phone camera.
 
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The most annoying part of the equation is that even the Mark II shows you what it is deciding to shoot with, maybe you can't manually adjust it with the camera settings, but there are definitely workarounds when it shows you its settings. For us it's about as easy as being a blind sharpshooter.
 
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