Tag Archives: viewfinder

How We Judge Exposure Looking At an Image And The Importance Of ViewFinder Contrast.

This came out of a discussion about viewfinder brightness where the compliant was that the viewfinder on the FX9 was too bright when compared side by side with another monitor. It got me into really thinking about how we judge exposure when purely looking at a monitor or viewfinder image.

To start with I think it’s important to thing understand a couple of things:

1: Our perception of how bright a light source is depends on the ambient light levels. A candle in a dark room looks really bright, but outside on a sunny day it is not perceived as being so bright. But of course we all know that the light being emitted by that candle is exactly the same in both situations.

2: Between the middle grey of a grey card and the white of a white card there are about 2.5 stops. Faces and skin tones fall roughly half way between middle grey and white. Taking that a step further between what most people will perceive as black, something like a black card, black shirt and a white card there are around 5 to 6 stops and faces will always be roughly 3/4 of the way up that brightness range at somewhere around about 4 stops above black . It doesn’t matter whether that’s outside on a dazzlingly bright day in the desert in the middle East or on a dull overcast winters day in the UK, those relative levels never change.

Now think about this:

If you look at a picture on a screen and the face is significantly brighter than middle grey and much closer to white than middle grey what will you think? To most it will almost certainly appear over exposed because we know that in the real world a face sits roughly 3/4 of the way up the relative brightness range and roughly half way between middle gray and white.

What about if the face is much darker than white and close to middle grey? Then it will generally look under exposed as relative to black, white and middle grey the face is too dark.

The key point here is that we make these exposure judgments based on where faces and other similar things are relative to black and white. We don’t know the actual intensity of the white, but we do know how bright a face should be relative to white and black.

This is why it’s possible to make an accurate exposure assessment using a 100 Nit monitor or a 1000 Nit daylight viewable monitor. Provided the contrast range of the monitor is correct and black looks black, middle grey is in the middle and white looks white then skin tones will be 3/4 of the way up from black and 1/4 down from white when the image is correctly exposed.

But here’s the rub: If you put the 100 Nit monitor next to the 1000 Nit monitor and look at both at the same time, the two will look very, very different. Indoors in a dim room the 1000 Nit monitor will be dazzlingly bright, meanwhile outside on a sunny day the 100 Nit monitor will be barely viewable. So which is right?

The answer is they both are. Indoors, with controlled light levels or when covered with a hood or loupe then the 100 Nit monitor might be preferable. In a grading suite with controlled lighting you would normally use a monitor with white at 100 nits. But outside on a sunny day with no shade or hood the 1000 Nit monitor might be preferable because the 100 nit monitor will be too dim to be of any use.

Think of this another way: Take both monitors into a dark room and take a photo of each monitor with your phone.  The phone’s camera will adjust it’s exposure so both will look the same and the end result will be two photos where the screens will look the same. Our eyes have iris’s just like a cameras and do exactly the same thing, adjust so that the brightness is with the range our eyes can deal with. So the actual brightness is only of concern relative to the ambient light levels.

This presents a challenge to designers of viewfinders that can be used both with or without a loupe or shade such as the LCD viewfinder on the FX9 that which be used both with the loupe/magnifier and without it. How bright should you make it? Not so bright it’s dazzling when using the loupe but bright enough to be useful on a sunny day without the loupe.

The actual brightness isn’t critical (beyond whether it’s bright enough to be seen or not) provided the perceived contrast is right.

When setting up a monitor or viewfinder it’s the adjustment of the black level and black pedestal which alters the contrast of the image (the control of which is confusingly called the brightness control). This “brightness” control is the critical one because if the brightness adjustment raises the blacks by too much then you make the shadows and mids brighter relative to white and less contrasty, so you will tend to expose lower in an attempt to have good contrast and a normal looking mid range. Exposing brighter makes the mids look excessively bright relative to where white is and the black screen surround is.

If the brightness is set too low it pulls the blacks and mids down then you will tend to over expose in an attempt to see details and textures in the shadows and to make the mids normal.

It’s all about the monitor or viewfinders contrast and where everything stits between the darkest and brightest parts pf the image. The peak brightness (equally confusingly set by the contrast control) is largely irrelevant because our perception of how bright this is depends entirely on the ambient light level, just don’t over drive the display.

We don’t look at a VF and think – “Ah that face is 100 nits”.  We think – “that face is 3/4 of the way up between black and white” because that’s exactly how we see faces in all kinds of light conditions – relative levels – not specific brightness.

So far I have been discussing SDR (standard dynamic range) viewfinders. Thankfully I have yet to see an HDR viewfinder because an HDR viewfinder could actually make judging exposure more difficult as “white” such as a white card isn’t very bright in the world of HDR and an HDR viewfinder would have a far greater contrast range than just the 5 or 6 stops of an SDR finder. The viewfinders peak brightness could well be 10 times or more brighter than the white of a white card. So that complicates things as first you need to judge and asses where white is within a very big brightness range. But I guess I’ll cross that bridge when it comes along.

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Pxw-fx9 Viewfinder Mounting

After playing with a number of FX9’s I have noticed that the way you arrange the viewfinder rods can alter whether the viewfinder sits level or may tilt just a tiny bit. Based on experimentation with several cameras I believe the orientation of the rods and clamps shown in the pictures here works best to ensure the VF stays level.

DSC_0623-1024x576 Pxw-fx9 Viewfinder Mounting
I believe this is the best orientation for the FX9s viewfinder support bars.
DSC_0621-1024x576 Pxw-fx9 Viewfinder Mounting
Another view of the FX9 support bars.
DSC_0619-1024x576 Pxw-fx9 Viewfinder Mounting
Arranging the FX9 support bars this way seems to minimize any VF tilt.

PXW-FS5 Screen Protector updated images.

Here are some updated pictures of the screen protector for the FS5 that I sell via Shapeways. It’s not an exciting product, it’s just a clip on plastic cover that protects the LCD panel from damage when you are not using the camera. I travel a lot with my camera and the unprotected LCD screen is very vulnerable and could easily get scratched or worse still smashed. Arriving for a shoot and finding the FS5’s LCD screen smashed would be a disaster!

If you want one for yourself you can order them through my Shapeways store: https://www.shapeways.com/shops/alisterchapman

AJC05188 PXW-FS5 Screen Protector updated images.
PXW-FS5 screen protector front view.

AJC05190 PXW-FS5 Screen Protector updated images.
PXW-FS5 screen protection cover clipped on to the LCD screen.

AJC05192 PXW-FS5 Screen Protector updated images.
PXW-FS5 clip on screen saver attached to the LCD.

When is a viewfinder a viewfinder and when is it just a small monitor?

It’s interesting to see how the term viewfinder is now used for small monitors rather than monocular viewfinders or shrouded dedicated viewfinders. Unless the a monitor screen is properly shielded from external light then you can only guess at the contrast and brightness of the images feeding it in anything other than a dim/dark room.

This is one of the key reasons why for decades viewfinders have been in fully shrouded hoods, snoots or loupes. As one of the key roles of a viewfinder is to show how your recordings will look for exposure assessment, if it doesn’t have a full shroud then in my opinion it isn’t a viewfinder, it is simply a monitor and exactly what your images will look like is anyones guess depending on the ambient light conditions. Furthermore even a young person with perfect can’t focus properly at less than 6″/150mm and that distance increases with age or in low ambient light. So most people will need a loupe or magnifying lens to be able to make full use of a small HD LCD for critical focus. In order to be able to see the sharpness of an image you need contrast, so an unshaded LCD screen on a sunny day will be next to useless for focus – perhaps this is why I see so many out of focus exterior shots on TV these days?

To be truly useful a viewfinder needs to be viewed in a controlled and dark environment. That’s why for decades it has been normal to use a monocular viewfinder. The eyepiece creates a tightly controlled, nice and dark,  viewing environment. This isn’t always convenient. I will often flip up or remove the eyepiece for certain types of shot. But – if you don’t have the option to fully shade the viewfinder – how do you work with it on a sunny day? On a camera like the FS5 I often find myself using the small, enclosed viewfinder on the back of the camera when the sun is bright. These tiny built in viewfinders are not ideal, but I’d rather have that than a totally washed out LCD or trying to shoot with a jacket over my head as my only option.

So next time you are looking at upgrading the monitor or viewfinder on your camera do try out a good 3rd party monocular viewfinder such as the Zacuto Gratical or Zacuto Eye. Perhaps consider a Small HD monitor with the  Side Finder option. Or an add-on monocular for the existing LCD panel. Without that all important shading and magnification it isn’t really a viewfinder, it’s just a small LCD monitor and in anything other than a very dim environment it’s always going to be tough to judge focus and exposure.

What’s wrong with my viewfinder, my old camera had a much better viewfinder!

This is something that keeps popping up all over the place and it’s not just one camera that attracts this comment. Many do, from the FS5 to the FS7 to the F55, plus cameras from other manufacturers too.
One common factor is that very often this relates to the newer super35mm cameras. Cameras designed to give a more rounded, film like look, often cameras with 4K or higher resolution sensors.
I think many people perceive there is an issue with their viewfinder because they come to these new high resolution, more rounded and film like cameras  from traditional television centric camcorders that use detail correction, coring and aperture correction to boost the image sharpness.
SD and even HD television broadcasting relies heavily on image sharpening so that viewers perceive a crisp, sharp image at any viewing distance and with any screen size (although on really big screens this can really ruin the image).
This works by enhancing and boosting the contrast around edges. This is standard practice on all normal HD and SD broadcast cameras. Especially camera that use a 3 chip design with a prism as the prism will often reduce the images edge contrast.
As most people will prefer a very slightly sharpened HD image or a heavily sharpened SD image over an unsharpened one, it’s sharpened by default. This means that the images those cameras produce will tend to look sharp even on screens that have a lower resolution than that of the camera because the edges remain high contrast even when the viewing resolution is reduced and as a result look sharp.
Most current manufacturer supplied LCD EVF’s run at 1/4″ HD with 940 x 560 pixels (each pixel made up of an RGB 3 dot matrix). In addition many of the 3rd party VF’s such as the very popular Alphatron are the same because they all use the same mass produced, relatively low cost panels – panels that are also used for mobile phones and many other devices. 
 
The problem then is that when you move to a camera that doesn’t add any image sharpening, if you view the cameras image on a lower resolution screen the image looks soft because — it is. There is no detail correction to compensate. Incidentally this is why often these same cameras can look a bit soft in HD and very soft in SD compared to other traditional or detail corrected cameras. But, that slightly softer, less processed look helps contribute to their more film like look. This softness and lack of sharpening/processing is particularly noticeable if you use the focus mag function as you are then looking at an enlarged but completely un-sharpened image.
 
It could be argued that the viewfinder should sharpen the image to compensate. Some of the more expensive viewfinders can do this using their own sharpening processes. But the image that you are then seeing is not the picture that is being recorded and this isn’t always ideal. If it is over done then it can make the entire image look sharp even when it isn’t fully in focus. Really you want to be looking at exactly the image that the camera is recording so that you can spot any potential problems. But that then makes focussing tricky.
 
There are a few 3rd party viewfinders such as the Gratical that have higher resolutions. The Gratical and Eye have screens that are 1280×1024, but in normal use you only use 1280×720 for the image area. This certainly helps, but even the 1:1 pixel zoom on these can look soft and blurry as you loose the viewfinders peaking function when you crop in.
 
Sony’s Venice and the F55/F5 can use Sony’s new DVF-EL200 OLED viewfinder. This costs around £4.5K ($6K) and has a 1920×1080 screen. It’s a beautiful image, but even this needs a fairly good dose of peaking to artificially sharpen the image to be able to see that last critical bit of focus. Again when you zoom in the image looks soft and a bit blurry (even on a Venice) as the camera itself is not adding any sharpening. The peaking function on the DVF-EL200 is quite sophisticated as it only enhances the highest frequency parts of the image, so only sharp edges and fine details are boosted.
 
Go back to the days of black and white tube viewfinders and these used tons of peaking to make them useable. Traditional SD and HD cameras add sharpening to their pictures, but most of our modern large sensor 4K camera do not and as a result often the viewfinder images appear soft compared to what we used to see on older cameras or still see today on cameras that do sharpen the pictures.
 
All of this makes it hard to nail your focus, especially if shooting 4K. Even with a DVF-EL200 on a Venice I struggle at times and rely heavily on image mag (which is still difficult) or better still a much larger monitor with a good sun shade and if necessary some reading glasses to allow you to focus on it up close.

So before you get too critical of your viewfinders performance do also consider all of the above. Try to see how another similar viewfinder looks on your camera (for example an Alphatron on an FS7). Perhaps try a higher resolution viewfinder such as a Gratical, but don’t expect miracles from a small, relatively low resolution screen on a modern digital cinema camera. This really is one of those areas where you can’t beat a big, high resolution screen.

Watch your viewfinder in bright sunshine (viewfinders with magnifiers or loupes).

Just a reminder to anyone using a viewfinder fitted with an eyepiece, magnifier or loupe not to leave it pointing up at the sun. Every year I see dozens of examples of burnt  and damaged LCD screens and OLED displays caused by sunlight entering the viewfinder eyepiece and getting focussed onto the screen and burning or melting it.

It can only take a few seconds for the damage to occur and it’s normally irreversible. Even walking from shot to shot with the camera viewfinder pointed towards the sky can be enough to do damage if the sun is out.

So be careful, cover or cap the viewfinder when you are not using it. Tilt it down when carrying the camera between locations or shots. Don’t turn to chat to someone else on set and leave the VF pointing at the sun. If you are shooting outside on a bright sunny day consider using a comfort shade such as an umbrella or large flag above your shooting position to keep both you and the camera out of the sun.

Damage to the viewfinder can appear as a smudge or dark patch on the screen that does not wipe off. If the cameras was left for a long period it may appear as a dark line across the image. You can also sometimes melt the surround to the LCD or OLED screen.

As well as the viewfinder don’t point your camera directly into the sun. Even an ND filter may not protect the sensor from damage as most regular ND filters allow the infra red wavelengths that do much of the damage straight through.  Shutter speed makes no difference to the amount of light hitting the sensor in a video camera, so even at a high shutter speed damage to the cameras sensor or internal ND’s can occur. So be careful when shooting into the sun. Use an IR ND filter and avoid shooting with the aperture wide open, especially with static shots such as time-lapse.

 

Calibrating your viewfinder or LCD.

smpte-arib-bars-sample Calibrating your viewfinder or LCD.One of the most important things to do before you shoot anything is to make sure that any monitors, viewfinders or LCD panels are accurately calibrated. The majority of modern HD cameras have built in colour bars and these are ideal for checking your monitor. On most Sony cameras you have SMPTE ARIB colour bars like the ones in the image here. Note that I have raised the black level in the image so that you can see some of the key features more clearly. If your using a LCD or OLED monitor connected via HDSDI or HDMI then the main adjustments you will have are for Contrast, Brightness and Saturation.

First set up the monitor or viewfinder so that the 100% white square is shown as peak white on the monitor. This is done by increasing the contrast control until the white box stops getting brighter on the screen. Once it reaches maximum brightness, back the contrast level down until you can just perceive the tiniest of brightness changes on the screen.

Once this is set you now use the pluge bars to set up the black level. The pluge bars are the narrow near black bars that I’ve marked as -2% +2% and +4% in the picture they are each separated by black. The -2% bar is blacker than black so we should not be able to see this. Using the brightness control adjust the screen so that you can’t see the -2% bar but can just see the +2% bar. The 4% bar should also be visible separated from the 2% bar by black.

Color is harder to set accurately. Looking at the bars, the main upper bars are 75% bars so these are fully saturated, but only at 75% luma. The 4 coloured boxes, 2 on each side, two thirds of the way down the pattern are 100% fully saturated boxes. Using the outer 100% boxes increase the saturation or colour level until the color vibrance of the outer boxes stops increasing, then back the level down again until you just perceive the color decreasing. I find this easiest to see with the blue box.

Now you should have good, well saturated looking bars on you monitor or LCD and provided it is of reasonable quality it should be calibrated adequately well for judging exposure.

I find that on an EX or F3 the LCD panel ends up with the contrast at zero, colour at zero and brightness at about +28 on most cameras.

Alphatron EVF uses iPhone Retina Display Panel.

I am hoping to get time to play with the soon to be released Alphatron EVF at NAB. This new EVF boasts a range of pro features and a much higher resolution screen than currently available in the other low cost EVF’s on the market. To get good resolution TV-Logic scoured the world looking for a good, small LCD panel. Anyone with an iPhone 4 or 4s will know how good that display is and that’s the panel thats going in the new viewfinder. The panels resolution is 960×640, but the viewfinder will only use 960×540 pixels so you get easy 2:1 image scaling for 1920×1080 video. There is more information on the benefits of this simple 2:1 scaling on the Alphatron web site.

Cineroid HDSDI EVF Review.

cineroid-evf1-300x200 Cineroid HDSDI EVF Review.
Cineroid EVF-4MSS

I needed an external viewfinder for my F3 rig. I could have got either a Zacuto or Cineroid HDMI viewfinder, but I felt that HDSDI would be more useful. As the HDSDI  Zacuto is not available just yet, I picked up one of the new metal bodied Cineroid HDSDI EVF’s (EVF-4MSS).

The viewfinder has the same 800 x 480 pixel 3.2″ screen as the HDMI version but in a robust metal body. There are threaded 1/4″ mounting holes on the top and bottom of the viewfinder. It is supplied with a generic battery compatible with Sony’s L series batteries and a tiny little charger.

cineroid-evf3-300x195 Cineroid HDSDI EVF Review.
Rear of the Cineroid EVF-4MSS

So what’s it like. Well for a start it’s very solidly made. The body and the slide on part of the eyepiece is made from metal (some kind of hard anodised aluminium I think). The diopter adjuster is made out of plastic. On the rear of the body mine was fitted with an adapter for a Sony L series battery which has a short flying lead going to a high quality lemo connector for power. The battery adapter can be removed by unscrewing two small screws if you intend to power the finder from an external supply. The supply can be anywhere from 6 to 17 volts. There is also a pair of BNC’s for the  loop through HDSDI in and out connections.

cineroid-evf4-300x200 Cineroid HDSDI EVF Review.
Cineroid EVF with eyepiece flipped up and menus activated.

The eyepiece on the EVF flips up like most pro viewfinders, this allows you to see the screen directly, as an alternative you can slide the entire eyepiece assembly off completely, which turns the EVF into a tiny monitor. I have a slight issue with the slide off function as there is some light leakage along the top edge of the screen as a result. On a bright sunny day this is distracting as you can see it inside the finder. It’s easily solved with a small strip of electrical tape over the tiny gap, but you shouldn’t really need to do this. All Cineroid need to do is add a small lip to the top of the slide off assembly to fix this.

On powering up and using the finder for the first time I was pleasantly pleased. The screen is bright and clear and there is only the smallest amount of lag. When I showed the EVF to some of the visitors to the Sony booth at IBC there were many comments that this version has less lag than the HDMI version. My guess is that the HDMI processing in the camera plus the HDMI processing in the EVF adds up to a fair bit of a delay. This would appear to be much reduced with the HDSDI version.

f3-viewfinder-bracket-150x150 Cineroid HDSDI EVF Review.
Cineroid EVF on PMW-F3

Some people have complained that they can see the pixel structure of the screen in both the Cineroid and Zacuto EVF’s. I could just about make out the pixels, the screen appearing to have a slight texture, but in operation this has not caused me any issues. This EVF is a vast improvement over the EVF fitted to the back of the F3. Using either the Cineroid’s Peaking or 1:1 pixel mapping I can focus very accurately. Higher resolution would be nicer, but it is adequate as is. You have to consider that even the Sony HDVF20A that costs £3,000 only has around 600 lines of resolution. As well as peaking there are a number of other useful tools including the usual zebras. Some of the more unusual functions include a coloured clipping indicator and various false colour modes. I have to say that I have not been through all the different modes and functions yet. I’ve just been using it with peaking and zebras. You can have a full range of safe area overlays and there is the ability to work with anamorphic camera outputs, flip or mirror the picture. The peaking is adjustable and can be either white or red, I prefer red. A couple of different colours would be nice for when your shooting scenes that already have a lot of red in them. When you have it enabled (single button press) the up and down arrow buttons on the side of the EVF will adjust the peaking sensitivity up and down, so no need to go into the menu system.

Overall I am pleased with my Cineroid viewfinder. It does the job that I purchased it for and the price was quite reasonable (£799 + VAT). It’s compact and well constructed and looks like it will survive the inevitable knocks and bumps of everyday use.

PS. I was reminded by respected DoP Jody Eldred that the LCD panel in these (and many other) viewfinders is easily damaged if the sun starts shining into the eyepiece. The eyepiece acts as a magnifier and will focus the sun onto the LCD and burn it. The large size of the loupe on the Cineroid means that it doesn’t even need to be pointed directly at the sun for this to happen. So, when not in use, point the eyepiece down towards the ground, if your mount won’t allow you to do that easily, flip open the eyepiece. This is good practice with all monocular viewfinders. I’ve seen many scorched LCD’s and melted plastic interiors over the years.