A bit about Cameras for CG Artists

We use the term 'Photorealism' a lot in CG world. Why Photorealism in particualar instead of just realism?

I think it's because things we see on our screen, we captured with cameras. Whether with SLR or Film Cameras or your phone.

So it's not like we see the world directly with our eyes. Images from any sort of camera are processed and filtered a lot. So it's definitley different than seeing something directly with your eyes.

If you see some images on your screen, that means someone must took that picture (or movie) with a camera.

So, if we make images 100% computer generated and want to make it look real, it should look like it's captured by camera. That's why 'Photorealism' is important in CG

You see cameras in pretty much every software you use and these cameras are simulating real-world cameras. It has all the options you might or might not know well.

Focal length, Shutter Speed, Aperture, ISO, F-Stop, Filters, Lenses, Exposure...

You've seen these parameters in Maya or Max or Nuke or whatever software you use.

I've seen many people using only 'Auto' mode on their 1200$ SLR and that makes me sad.

Are you rendering your images without changing anything on your camera attribute? Like using Auto mode? Let's not.

You can manipulate CG cameras in the same way you do with your actual cameras.

And it becomes more important when creating photorealistic images.

Focal Length

This means distance between lens and sensor.

Usually measured by mm (millimeters)

All you need to know is this.

When it get's smaller numbers, you get wider angles on your frame and more distortions.

When it get's higher numbers you get narrow angles and more focused shot.

Since we can't change our sensor's location (it's inside of cameras) Focal length is determined by lens you choose.

You maybe saw some numbers like this. 28mm - 50 mm, 75mm, 120mm on your lens or attribute in softwares

between 35 mm - 50 mm are usually okay with everything. Shooting people, cars, buildings, just random daily pictures are in these range. You see nothing exetreme. Just normal pictures.

But when it gets under 30mm or even 20mm, angles become more wider. It's good for landscapese or when you want to something look big and wide.

If you buy 75mm - 250mm lens, it means you can zoom in a lot. Narrow angles. In CG, you just put numbers. you don't buy 499$ lens becuase we're poor CG artists.

Choosing Focal Length wisely is critical for your shot.

For example, showing cityscapes as your establishing shot with 300mm lens is not a good idea in general.

Shutter Speed

When you click the shutter button on your camera, shutter speed means how long you're going to open your shutter.

This is related to overall brightness of your image and motion blur.

The longer you open your shutter the brighter image you get.

1 / 800 sec shutter speed is much faster action from open to close the shutter than 1 / 8 shutter speed

and 1 / 125 is twice brighter than 1 / 250 picture.

So general rule is,

When you have a lot of light (or in bright situation like day time) you can get faster shutter speed like 1/500, 1/1000, or even 1/2000 and it will make crisp & sharp image even though when you shake your hand little bit when pressing the shutter button.

When you're in dark or not much of light (usually inside or night time) you need slower shutter speed to get enought brightness of your shot. So when you use slow shutter speed like 1/8, 1/4 or even 1 sec or 2 seconds, more chance to get shaky image (if you moved camera holding hand even just little bit) or motion blurred image if object were moving. This is why party pictures are shaky.

In CG, same principles. If you have no idea what numbers to put in your shutter speed, try to use actual camera in simialr situation and put that number in as your starting point.

Aperture

Aperture is a gate that light goes through inside of camera when you shooting. So you can control how much light goes into your camera.

Aperture looks like this.

You can open it wide or narrow it down.

Wider Aperture gets more lights and makes your picture brighter.

Narrower Aperture gets less lights and makes your picture darker.

We call these F-stops.

Smaller F number means wider the aperture is.

F 2.8 is more open aperture than F 8

Wider Aperture (smaller numbers) makes more Depth of Field

Narrower Aperture (Larger numbers) makes less Depth of Filed.

Same for both actual cameras and CG cameras.

There are few stops in F number. It goes F 2.8 - F 4 - F 5.6 - F 8 - F 11 - F 16 - F 22

It gets x2 more lights as you go one step smaller numbers.

So pictures with F 4 is twice brighter than F 5.6 image.

There are more F stops in some lenses. (like F 1.4)

Usually in real world, smaller number F-stop lenses are good lenses. It means you can get more lights without having slower shutter speed or higher ISO. It means more controls you can get and more clean images.

2 Major things determind overall exposure of your image. Shutter Speed, Aperture.

These 2 things are related.

If you want to use higher shutter speed (means less light comming in) you probably consider using wide open aperture unless it's very bright situation.

If you use F 2.8 to get some good Depth of Filed effect in sunny day time, you may need to consider using slower shutter speed.

Sounds Fun right?

ISO

ISO is sensitivity of sensor (or film in traditional)

What does it mean sensitivity on sensors? It means if the sensor gets more sensitive to light, you need less light to get right exposure of your image.

If you're in very dark room and need to take a photo without using flash, you need to use very sensitive sensors. Higher number ISO. So camera can capture very little amount of lights. and you can have good shutter speed and pick F number you like.

But it has a downside.

As you go up higher (gets more sensitive) you introdue more noise in your image.

You've may noticed a lot of photos taken at night are very noisy. This is because if you set Auto mode on your camera and use it at night, camera automatically sets ISO very high like 3200 or 6400 to get more light (or to be sensitive to light). And if you shoot photos during the day, camera sets ISO something like 50 or 100

That's real world cameras. But in CG, there is no such things like ISO noise. Noise in your render is caused by renger engine. You can use whatver ISO number you want. It's very useful when you locked shutter speed and aperture you like and don't want to change. but your image is too bright or dark.

Keep in mind you don't use crazy numbers in ISO. When it get's too sensitive, adjusting your lights gets more harder.

There are crazy amount of information on internet and this might be dummer version of expaining these but hope it's helpful to someone.