Jump to content

GH2 - How best to control Exposure for a beginner?


techstyled
 Share

Recommended Posts

I just got my GH2 yesterday and I've applied the 44 Vanilla hack, enabled High ISO, set camera to recommended settings on the GH2 Hack Vault page, purchased and read Andrew's EOSHD Shooter's Guide.

I've setup my Creative Movie Mode settings as per recommended in the Shooter's guide. In the guide, in the beginner's boot camp section, he details that Exposure should be set to Manual which leaves 3 ways to control Exposure; Shutter Speed (which should usually be at 1/50 or 1/60 anyway), Aperture, and ISO.

First of all, from a _complete_ beginner's standpoint, I have to say the guide (though GH2 specific), never mentions HOW to change any of these. I learned by basically pushing everything (I know, RTFM), the Shutter Speed and the Aperture are both set by the "Thumb Wheel" (which, to be explicit, is the wheel most available to your thumb) and you toggle between the two by depressing the Thumb Wheel. The ISO is o/c accessible via the ISO button (the UP button on the D-Pad).

I think it's weird that the recommendation in the book and repeated almost everywhere is to set the Shutter Speed according to the 180 rule but then in the guide Andrew says that "for beginners the shutter speed is the main way to control the exposure".

I would think the main way to control the exposure would be the Aperture and the ISO because when it comes to Shutter Speed, "ideally it should be kept at 1/50 or 1/60".

I understand that both Aperture and ISO have other ways they impact the video other than exposure and, according to the guide, "1st priority of the aperture setting is to control [b]depth of field[/b]". So, that leaves us with ISO which can also impact noise.

However, it would seem to me that [b]the main way to control exposure would be ISO[/b]. Playing around with ISO, I'm starting to think that ISO 160 is only going to work well outdoors and I seem to consistently have to set ISO up to 640 minimum for indoor shooting.

Now, granted that's with my 14-42 which has a minimum aperture of 3.5 so with a "faster"? lens, ISO 160 might be fine for most indoors.

I started out with a particular question in mind but I think now I'm just down to, am I right about all this???
Link to comment
Share on other sites

Four additions:

• on a sunny day, you need help to control the exposure. To maintain 1/50-60 shutter and to avoid too narrow apertures you must use an ND-filter. This could be an "ND2" (a hundredth of light gets through), "ND4" (one tenthousandth of light gets through) or an "ND8" (the hundredmillionth of light gets through). These numbers look exaggerated, but these are indeed the dynamics between the coin in the shadow of the car tire to the details in the white clouds surrounding the summer sun at noon. You often get these three filters as a set. There also are "VariNDs". These are two polfilters, and if you rotate one you get a stepless darkening of the image. Convenient, but with some side effects. If you decide for a VariND, buy a bigger one and use step-up-rings to adapt it to your lenses or otherwise you'll get vignetting [i]sooner[/i]. To complete the filter review, there are "ND Grades", typically used to bring the brighter part of the image (the sky!) down to moderate values. Because the horizon may not always be in the middle of your image -  :-X - you should use a mattebox then (or a [url=http://www.ebay.com/sch/i.html?_nkw=cokin+p+series&_sacat=0&_odkw=ND-filter&_osacat=0&_from=R40][u]cokin[/u][/url] filter holder, not so impressive-looking, but with the same effect). EDIT: You will need NDs rather sooner than later, buy them now. The ND Grades will be used for serious landscape photography, you might wait with the purchase.

• with ISO higher than 1600 you may see a bright stripe in the lower third of the image (sometimes visible in EVF/display, sometimes only too late). Then you better half the shutter speed to 1/25-30 (or rather double the exposure time, because strictly speaking there is no shutter anymore). Avoid fast camera moves and too fast moving objects then.

• you forgot to mention the control of light and shadow with lights and shadows. Position yourself so that your motif is in an appropriate light. If you stage the scene and you have the manpower, then use a [url=http://www.ebay.com/itm/43-5-in-1-Light-Mulit-Collapsible-disc-Reflector-110cm-New-/140731698805?pt=LH_DefaultDomain_0&hash=item20c4434e75#ht_5311wt_1165][u]reflector[/u][/url] to redirect light or to cast a shadow. A useful thing is a little LED-headlight ([url=http://frankglencairn.wordpress.com/2011/01/02/the-cheap-video-led-light-shootout/][u]here[/u][/url] a review of some of them). It doesn't have to be on the shoe mount on top of your camera, it can also be on a tiny lamp stand. Never use it in the way people use a flash, to nuke any mood off the image. See it as an electric reflector that helps to softly brighten some parts. Use the [i]dimmer[/i] for a subtle change.
EDIT: Lighting of course is an important subject for "DSLR filmmakers" (title of this site). Very interesting. You can approach it very directly, in the so called WYSIWYG-fashion. Thanks to EVF and display you see what you get. I find the term "painting with light" useful. Use every and any light source to the effect you desire. You can simplify the many rules from the books to two different concepts. The first is, you see the light conditions that already exist and you just correct minor things. With the second you create a mood from scratch, either by mimicking a natural light or by exaggerating everything to force an expressive impact. It's up to you.

• You have the luxus to be able to judge exposure not only by your photographically unexperienced eyes (no offence intended) but by the histogram also. With video, the world sooner ends at the right side, representing the highlights. Filming in lowlight is much easier than in the bright sunlight, because you have less contrasts. You have to test this for yourself: In highkey-situations underexpose deliberately at least one stop, so that no clipping (if the lights fall from the right edge of the histogram into digital Nirvana) occurs. This will get you shots that look terribly underexposed indeed. But don't worry, everything is fine. What needs to be done now varies in description depending on the software you use. Determine which part of the image is >black< (the darkest part, if there is no fog) and which is >white<, perhaps you have an "Auto-Balance"-button. The image will still look too dark. Instead of applying a [i]brightness[/i]-filter (which would affect the whole image, making it foggy), you [i]grade[/i]. You rise the midtones only (and afterwards you correct the highlights and depths again). Whether you do this with [i]curves[/i] or with a [i]3-way-colour-corrector[/i] (one of the three ways meaning midtones) or whatever, depends on your software (it is important to find out, if your software is able to render in 32bit, please check). Rule of thumb: If something looks overexposed, nothing can help. The lower midtones however, let a lot of detail drown in the tar (not only in underexposed clips). If you draw them into the middle, you save the day.
Link to comment
Share on other sites

Awesome, awesome information. And surprisingly, I understood at least half of it.  ;D  I'm kidding, I think I at least understand most of the concepts here. You did a good job of anticipating the depth of explanation I'd need. Hopefully that's because I did a good job explaining where I was at with my limited knowledge.

The bit about you'd rather underexpose than overexpose makes sense and is a good point. I've never graded video (or photos) before but I think I have the right software. I have Adobe's Production Premium Suite 5.5 and Edius Neo3 (which I'm more familiar with).

I'm a programmer and this is a hobby so I've never yet tried to understand histograms and such. The good thing is that right now, the weak spot is what I'm using behind the camera (me) and I can work on improving that.  :)
Link to comment
Share on other sites

You got Premiere? There you are. There is a very good tutorial for a very fast method, approprietly named the
[i]fast colour correction[/i] - filter under the effects tab.
[url=http://www.youtube.com/watch?v=rrJaNHi1c08#ws]Adobe Premiere Fast Color Correction Tutorial[/url]
EDIT: I have to correct this video in one respect: The x-axis doesn't represent time, it traces the spreading of the pixels in their actual position in the image. Also, I wonder why the midtone-values are only corrected indirectly by shoving the white- and black-triangles. Though this is a good starting point, at the end you clearly see too many details swallowed by darkness: Below 30 there is more, very likely the dresses don't need to blend into the background ...

You see in the list of effects a column of icons "32" and "YUV". This one [i]has[/i] a 32-bit icon. This means, though your pixels are described in 256 tonal steps, every change you make now is calculated not only with integer numbers (256 = 0-255, 8-bit), but with fractions. Only at the very last moment, when the video is rendered to it's final master, the numbers are rounded again to fit into the 8-bit model. But beware: If you only use [u]one[/u] filter without "32" [u]everything[/u] will be 8-bit and look really awful (the "steps" become visible).

Once you understand the principle, it is best not to rely only on the fast colour corrector. There are mightier tools, [i]Colorista[/i] for example. And you have one in After Effects. If you save your Premiere project, you can import the "prproj" in AAE and use the >effects >synthetic aperture >Color Finesse. Google for tutorials.
Link to comment
Share on other sites

Axel said so much that I learned from here that I'll only reinforce one point - get ND filters as soon as possible. They make [i]the[/i] difference shooting outdoors. I was choking a bit to drop the coin on a variable ND (I bought the Fader) rather than several separate filters I could stack. I am so glad I spent on the variable. The tune-ability for exposure control is very helpful.

Grab a 77mm or whatever size of your largest lens diameter and inexpensive step-up rings to fit your other lenses.
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...