Well winter is upon us. The north of the UK is seeing some pretty heavy snow fall and it’s due to spread south through the week. I regularly make trips to Norway and Iceland in the winter to shoot the Northern Lights (email me if you want to come) so I am used to shooting in the snow. It can be very difficult. Not only do you have to deal with the cold but also difficult exposure.
First off it’s vital to protect your equipment and investment from the cold weather. A good camera cover is essential, I use Kata covers on my cameras. If you don’t have a proper cover at the very least use a bin liner or other bag to wrap up your camera. If you have a sewing machine you could always use some fleece or waterproof material to make your own cover. If snow is actually falling, it will end up on your lens and probably melt. Most regular lens cloths just smear any water around the lens, leaving you with a blurred image. I find that the best cloth to use in wet conditions is a chamois (shammy) leather. Normally available in car accessory shops these are soft, absorbent leather cloths. Buy a large one, cut it into a couple of smaller pieces, then give it a good wash and you have a couple of excellent lens cloths that will work when wet and won’t damage your lens.
Exposing for snow is tricky. You want it to look bright, but you don’t want to overexpose. If your camera has zebras set them to 95 to 100%. This way you will get a zebra pattern on the snow as it starts to over expose. You also want your snow to look white, so do a manual white balance using clean snow as your white. Don’t however do this at dawn or near sunset as this will remove the orange light normally found at the ends of the day. In these cases it is best to use preset white set to around 5,600k. Don’t use cinegammas or hypergammas with bright snow scenes. They are OK for dull or overcast days, provided you do some grading in post, but on bright days because large areas of your snow scene will be up over 70 to 80% exposure you will end up with a very flat looking image as your snow will be in the compressed part of the exposure curve. You may want to consider using a little bit of negative black gamma to put a bit more contrast into the image.
If the sun is shining, yes I know this may not happen often in the UK, but if it is then the overall brightness of your scene may be very high. Remember to try to avoid stopping down your lens with the iris too far. With 1/3? sensor cameras you should aim to stay more open than f5.6, with 1/2? more than f8 and 2/3? more than f11. You may need to use the cameras built in ND filters or external ND filters to achieve this. Perhaps even a variable ND like the Genus ND Fader. You need to do this to avoid diffraction limiting, which softens the image if the iris is stopped down too much and is particulary noticeable with HD camcorders.
Finally at the end of your day of shooting remember that your camera will be cold. If you take it in to a warm environment (car, house, office) condensation will form both on the outside and on the inside. This moisture can damage the delicate electronics in a camcorder so leave the camera turned off until it has warmed up and ensure it is completely dry before packing it away. This is particularly important if you store your camera in any kind of waterproof case as moisture may remain trapped inside the case leading to long term damage. It is a good idea to keep sachets of silica gel in your camera case to absorb any such moisture. In the arctic and very cold environments the condensation may freeze covering the camera in ice and making it un-useable. In these extreme situations sometimes it is better to leave the camera in the cold rather than repeatedly warming it up and cooling it down.
Have fun, don’t get too cold, oh… and keep some chemical hand warmers handy to help stop the lens fogging and to keep your fingers from freezing.
Over the next few posts I’m going to look at why sensor size is important. In most situations larger camera sensors will out perform small sensors. Now that is an over simplified statement as there are many things that effect sensor performance, including continuing improvements in the technologies used, but if you take two current day sensors of similar resolution and one is larger than the other, the larger one will usually outperform the smaller one. Not only will the sensors themselves perform differently but other factors come in to play such as lens design and resolution, diffraction limiting and depth of field, I’ll look at those in subsequent posts, for today I’m just going to look at the actual sensor itself.
Pixel size is everything. If you have two sensors with 1920×1080 pixels and one is a 1/3? sensor and the other is a 1/2? sensor then the pixels themselves on the larger 1/2? sensor will be bigger. Bigger pixels will almost always perform better than smaller pixels. Why? Think of a pixel as a bucket that captures photons of light. If you relate that to a bucket that captures water, consider what happens if you put two buckets out in the rain. A large bucket with a large opening will capture more rain than a small bucket.
Bigger pixels capture more light each.
It’s the same with the pixels on a CMOS or CCD sensor, the larger the pixel, the more light it will capture, so the more sensitive it will be. Taking that analogy a step further if the buckets are both of the same depth the large bucket will be able to hold more water before it overflows. It’s the same with pixels, a big pixel can store more charge of electrons before it overflows (photons of light get converted into electrical charge within the pixel). This increases the dynamic range of the sensor as a large pixel will be able to hold a bigger charge before overflowing than a small pixel.
All the electronics within a sensor generate electrical noise. In a sensor with big pixels which is capturing more photons of light per pixel than a smaller sensor, the ratio of light captured to electrical noise is better, so the noise is less visible in the final image, in addition the heat generated in a sensor will increase the amount of unwanted noise. A big sensor will dissipate any heat better than a small sensor, so once again the big sensor will normally have a further noise advantage.
So as you can see, in most cases a large sensor has several electronic advantages over a smaller one. In the next post I will look at some of the optical advantages.
UPDATE: You can download some frame grabs from the shoot-out by clicking here.
I just spent the day shooting the same scene with 6 different file based cameras. I am working with Visual Imapact to produce a series of DVD’s containing sample clips in their native format and file structure from a range of cameras. On the set today I had the following cameras: Sony PDW-700, Sony PMW-350, Sony EX3, Panasonic HPX3700, Panasonic HPX301 and a Panasonic HVX200. We also recorded the output from the PMW-350 on a NanoFlash and this footage will also be available within the DVD set. The idea is to provide people with a way to directly compare the image quality and workflow of all these cameras, in effect, side-by side.
In order to keep things fair each camera was set to it’s factory defaults. Now I know that with careful tweaking all the camera are capable of better pictures, but it was decided the fairest test was to present them in their default settings.
The scene used in the shoot comprised of a colorful Lego train on a small circle of track, some crumpled foil to give bright specular highlights, a chamois leather for natural texture along with a couple of rose blooms. A metal bodied torch and paint brush finished off the still life. In the background there is a sharpness chart and a color chart. All this was then placed on a chroma key green fabric covered table with a chroma key blue back drop.
The scene was shot at 3 different frame sizes in 1080P25, 1080i50 and where available 720P50 and SD. The scene was shot at 0db gain and also at +6db gain. It was exposed using a 50% grey card measured with a Hamlet Microflex scope to ensure matching exposures. A slate was used at the beginning of each shot to identify the camera, the frame rate, aperture and recording mode. The Panasonic P2 cameras were used in both AVC-I modes and DVCPROHD modes. All the 2/3? cameras used the same Canon HJ14x4.3 lens but I did in addition use the kit lens on the PMW-350 for comparison as well as an SD lens on the PDW-700. The HPX301 and EX3 used their standard lenses.
I’ll be spending the next couple of days checking the footage and compiling the DVD’s, but hope to have the full set of disks available for purchase very soon.
There is far too much emphasis on color charts and 100% one to one – set it up with a scope settings. Very often a 100% accurate one to one response won’t look right as the video gamut is smaller and lopsided than that of the human eye so a small amount of skewing of the color gamut can often help produce a picture that visually looks more natural. One of the very best ways to set up a camera is to use a high quality color photograph of a known scene. Shoot the photograph and look at the picture on a monitor and adjust until it looks right. This will give a more natural looking image than aligning with charts and scopes and is a technique that has been used since the very beginnings of color television. I have a scene that contains vibrant colored cars, green fields and trees, buildings and blue sky. I have a dozen large copies of this picture and use it whenever I am making camera adjustments to make sure my pictures still look natural. Of course scopes should still be used if you are making any extreme settings to ensure your images are still legal, but at the end of the day what you are after is an image that looks right too you (or the producer) and whoever else will view your material, not what looks right according to a chart and a scope.
If you set zebra 1 to 60 and then set zebra 2 to 90, then go back to zebra 1 you will find that the displayed value of zebra 1 will now be 90, however provided you don’t make any changes to zebra 1 if you go down to BOTH zebra 1 will work at 60 and zebra 2 at 90.
The thing is that going back to Zebra 1 (or zebra 2) and make any changes you select selects Zebra 1 (or 2) only, ie a single zebra and in doing so sets the level to the last level set. It’s only by going to BOTH that you enable both zebras together.
So to set two indendent zebras first set zebra 1 to your required level, then set zebra 2 to your required level, final scroll down to both and select. Now you zebras will be working at the independent levels you set, even though this may not appear to be the case in the menu.
It’s not the most logical way to lay out the menu as it does not show you both settings together at any point, hence the understandable confusion, but you will find that both zebras will work at the independent levels you set.
Camera setup, reviews, tutorials and information for pro camcorder users from Alister Chapman.