Now for the detail about what all of the settings do both in real life and within the realms of Forza, and ways to make the most of them. All of the values quoted are purely approximations; as always you will need to fine tune them depending on the shot and the situation, so go by your judgement of what looks best rather than sticking to the numbers below -
they are just a guide.
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Shutter speed____________________________________________________________
As the name states, this defines the amount of time the shutter for the camera is open. In real life, shutter speeds are primarily used to change the exposure of an image, but in Forza the main alterations are the blur of objects when the car is at a fast speed. When using it in Forza, it is best to keep it at 0 for static shots, even if the car is already stationary, as the focus will be more defined. The only exception to this that I can think of is when you try extremely small depth-of-fields in your shots, like the one below (however shutter speed only has minor effects here, so isn't important for such shots).

When taking motion shots (where the car is moving) I would recommend either using values around 10-20 or 50-80, depending on the shot. If the background is very detailed and you cannot use much aperture, then using 50-80 shutter speed will hopefully smudge out the background enough for it to not detract attention from the focal point. However, if you want to catch the spokes of the wheels (instead of turning them into a circle full of blurred lines with no discernible wheel spokes) then a slower shutter speed is better.
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Focus____________________________________________________________
If I'm honest, I find that focus makes only a negligible difference to most shots. In real life focus is extremely important, and when something is out of focus all detail will become blurred. In Forza, as long as you remember to press X to focus on the point you want to, the focus setting won't have much effect in the majority of circumstances. Again though, one main exception are shots like the example above, with high aperture creating either bokeh in the background or giving an extremely small depth of field. In these situations setting the focus to 0 will increase the effect. It can also be used creatively when making abstract photos, however I'm not very experienced with these types of shots.
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Aperture____________________________________________________________
Aperture is one of the settings that has a large impact on a shot. In real life it has several uses as it changes the depth of field but also changes the amount of light falling on the camera sensor/film, allowing either faster or slower shutter speeds depending on how it is changed. In Forza it changes the depth of field and is what gives the best bokeh.

The photo above uses a small amount of aperture, and as a result a larger range of objects are in focus, from the close up writing in the foreground to the car and pit wall in the background.

This shot however, uses more aperture, and as a result the background is blurred out, and even the close foreground tarmac is softer and not in focus.
The shot at the top uses extreme aperture to give an incredibly small depth of field.
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Exposure____________________________________________________________
In real life, the only way to change exposure without changing any of the other settings is to change the ISO. In the days of film cameras, the ISO rating was given to the film and tells you how quickly the chemicals on it react to produce an image. Lower ISO numbers (i.e. 100) take longer to expose (so you'd need a longer shutter speed or more aperture) while higher ISO numbers (i.e. 2600+) expose quickly, allowing much shorter shutter speeds. The only downside to higher ISOs is that it increases noise (random pixels that aren't exposed correctly). Forza doesn't have this issue, as the exposure setting would appear to effect the lighting just like a longer shutter speed would in real life, without increasing the shutter speed. The game usually underexposes images as 60 is usually OK to use on some tracks, and around 55 on most others.
Some good comparisons of different exposure settings are these shots of an Audi RS3 and a Subaru Impreza. A few other settings were tweaked in the Audi RS3 shots, but the overall main change is the exposure.
Lower exposure:


Medium exposure:


High exposure:


As you can see, the exposure has a large effect on the mood of the photos, but all of them look good in their own way.
A good tip to get higher exposures without blowing out the shot is to find locations where the car is in shade - popular locations include parking under the bridge on the Benchmark high speed oval (and other bridges/tunnels), under pit building overhangs, on corners shaded by trees etc. Higher exposures are a lot easier to make natural and realistic looking, and if you include a bright area in the background you can often white-out the backdrop without burning out spots on the car.
"Burnt out" spots are areas of the photo where the exposure is so high the area becomes a white glow. They are often easy to spot, however small burnt out areas on chrome trim, windows and other highly reflective surfaces can sometimes go unnoticed and ruin a shot. If you're using a high exposure or feel that the image is near the borderline of being overexposed it is almost always worth checking over the image quickly. To help, if you memorise the exposure setting you're on, you can then move the slider up to over-expose the image and see where burnt out areas appear first. Then set it back down to what you originally had and check that those areas are fine. If they are, you'll know that the rest of the image won't be burnt out. Also there is a difference between a white area and a burnt out area - white highlights are often a great way to pick out detailing on your subject, however if the white area is glowing or looks too brightly white in the context, it is probably burnt out. When shooting into the sun, a burnt out look can make for a powerful effect if done correctly, so don't shy away from them all the time.
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Contrast____________________________________________________________
Contrast is often changed post-shoot, using editing software. Luckily FM4 allows you to change the contrast while composing the shot. I typically use a contrast around 52, although this varies greatly with most shots. High contrast can produce great artistic shots like this one of the Pike's Peak Suzuki SX4:

Unlike most of the other settings, there is little point on using very low values for contrast. In the twenties and below the image usually will look horribly washed out and loose much definition - I rarely go down even to the high 30s. Going to the 40s works, especially when taking old-fashioned style photos as it mimics the results photographers got with the methods used years ago. Combined with sepia and getting the exposure right can produce great old looking shots. There are a few exceptions to this but they tend to be extreme artistic photos.
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Colour____________________________________________________________
Colour is an important aspect of photography, and in Forza this is no different. The thing with colour is that it's quite a balance, and will change with each shot depending on the mood. You don't want to use too much colour or the shot will look oversaturated and unrealistic, but then again too little can leave it looking washed out and bland. The colour balance in FM4 is pretty well balanced, and usually to get the vibrancy you need you only need to go up to the 60's or low 70's on the slider. In some close ups, high contrast/vignette or artistic shots you may need to use high (even up to 100) colour, and in others you may need to use 0 (to get B&W). One trick you can achieve is turning the colour up too high, then increasing the Sepia bit by bit until the colours look almost normal, as this can add a warmth to the colours of the shot or make them less bright. This can be seen in the shot below of a Nissan 350Z:

In the above shot, the colours are too vibrant and distracting, whereas with higher colour and sepia, the colours become less dominating:

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Brightness____________________________________________________________
Brightness is applied in-game in pretty much the same way as it is in real life using photo processing software (such as Photoshop) on a jpeg image, although a little more image data is retained in the FM4 photomode. As the setting name suggests, the brightness of the image is altered.
Increasing the brightness value can give a photo a washed out look, which is undesirable; whilst reducing it too much causes it to look too dark, and the white areas to turn a dirty grey colour. Often for realism in reasonably well-lit environments, values near to the default of 50 are best. Here is an example of a shot ruined by an overly high brightness:

And here is an image with much better brightness setting, resulting in a more aesthetically pleasing contrast:

Increasing the brightness is usually accompanied by an increase in contrast to counter the washed out look.
For old fashioned style photos, lowering the brightness until the image is slightly washed out can help add to the style, and is best combined with sepia, washed out colours and slightly lower aperture than usual, and possibly even a mild amount of the first or second vignette options (obviously though, this effect only works well with older cars or scenarios).
In low light situations such as in dark shadows, a higher brightness (70+) will sometimes work with a slightly higher exposure and a very high contrast.
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Sepia____________________________________________________________
Black and white photos may fade with age, and you'll probably have noticed that with the sepia setting at 100 the shot looks like an aged photograph. The effect of the sepia slider then is pretty obvious; with 0 colour the slider increases the saturation of the brown-ish hue of the black areas in the image, and with colour still left in, they become slightly muddy and the whiter areas become slightly cream-coloured. Sepia is best used when the photo you are taking is of an old fashioned scene in black and white, as it gives a good old-fashioned feel to the image. Also, low colour and low sepia can give the effect of an old, faded colour photograph which again works best with scenes depicting classic cars.
Modern cars can look great in sepia as well so don't be afraid to try it, however naturally the old-fashioned feel will clash with the modern lines of the car.
Sepia can also be very useful for toning down colours that are too strong - see the Colour section (scroll up 2 sections) in this post for more information.
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Vignette____________________________________________________________
There are three vignette styles in Forza 4, and each can be used to give dramatic styles to your photo. The first vignette style is very useful for retro/old-fashioned style photos, as it mimics the vignetting that often occurred with old camera equipment. The darkening of the corners is caused by the circular lens producing a circular image which isn't large enough for the rectangular sensor or film to be completely exposed - this effect can be exaggerated when a lot of filters are applied in real life. Too much vignette in FM4 looks awful and cheesy the vast majority of the time, so I wouldn't encourage you to go much higher than the 30s and not to add it unnecessarily.
The second vignette style - darkened sides of the image - can be useful for low-light shots to help remove distracting bright areas from the backdrop of your photo, however too much of it can also darken the edges of the car in subject, which gives the appearance of uneven lighting and isn't desirable.
The third vignette option is perhaps the most interesting of the three, but also the most difficult to use well. Use too much, and you'll be left with an overexposed line in the middle of the image and murky lighting on the rest of it. But in small amounts it can be perfect to compensate for an overexposed sky.
Vignette is particularly useful for black and white photography as the effects can often be much harder to see to the untrained eye. For example, this photo of the MINE'S R34 Skyline uses the third vignette style but has blended it into another line in the background so it isn't as obvious:

And this shot of an Aston Martin DBS uses a fence in the background to disguise the vignette line:

Just like all the rules in photography, this one is made to be broken. If you plan your background and car's position in relation to the light source, you can get photos like these:


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Lastly, here are the default settings I use as a starting point for most of my photos:
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- Shutter speed: This will vary greatly for each individual photo
- Focus: 100 (or 0 for high aperture shots)
- Aperture: 63
- Exposure: 60
- Contrast: 52
- Colour: 51
- Brightness: 50
- Sepia: 0
- Vignette: 0
Don't use these for everything or treat them like they'll guarantee good looking shots though - I don't use them as they are for my photos, but use this as a starting point and make adjustments to each one accordingly. Also this doesn't suit some locations or styles of photo, so again you'll need to make your own judgements and change most (if not all) of them.
Edited by user Monday, September 8, 2014 2:23:58 PM(UTC)
| Reason: Not specified