HDI

[Notorious MCSE]

What did you all say about it before the server crashed and ate the thread?

Im going to have a crack at it tomorrow night.

Also: Ive seen a few photos of traffic (city scapes) etc where the car lights are just a smudge of light - if you follow me - how is that done, picture taken on a really slow exposure?

I am a photo tard, so forgive me.

[samhs]

This was taken with an exposure of 1.6 seconds, F8, 48mm Equiv (30mm lens on APS-C sensor). I'm quite pleased with how it turned out given I used a beanbag "pod" held as tight as I could against a lamp-post to get the image - no tripod due to strict wife ;o)

The key thing is the exposure time - the longer you can leave the lens open, the more you'll get streaks of light.


This is created from 5 seperate photos, each with a different exposure: -4ev, -2ev, 0ev, +2ev, +4ev. They are composited into a 32bit file in Photoshop using "Merge for HDR". This is then converted down into a 16bit file using photoshop; the process gives you a dialogue box which allows you to compress the extended definition range into one shot. Then I've applied some additional curves, duplication and multiply, a high-pass set to multiply and a levels adjustment. Looks a bit strange to me, but I think this was introduced at the 32bit --> 16bit conversion, and tbh I don't think the source material is worth any additional effort at this point.

This may have been easier with Photomatix which is what a lot of people use to create those bizarre photo/plastic fake looking images (a bit like I've acheived above, but more extreme).

-------

Both bits of info and examples bastardised from my previous threads:
Downtown San Fran
My first attempt at HDR

hth

Sam

[samhs]

By the way, I should mention that with HDR, it's essential that you vary the shutter speed, not the aperture - changing the F value will alter the depth of field, making for a bizarre combined photo of blur and non-blur. Alter the shutter speed only between shots and you'll ensure the same depth of field, and thus a better end combined result. Use of a tripod highly recommended for both HDR and light trails.

Sam

[Notorious MCSE]

Sam,

I feel that it is my lack of knowledge about my camera, and photography in general that is making this task a bit harder than it should be 

First, I need to download my cameras English instruction book 

Second, I need to understand aperture, and shutter speed. Both of these are selectable on my camera, except I dont understand either of them. I was just outside playing with my camera trying to get the good light streaks, for it is night time and I thought it would be a chance to play. I suck.

I have an option of 1" and something next to it that says F followed by a number, now 3.5.

I used different settings at opposite end of the scales it seems to take a few photos. Whats the best settings to get daylight streaky lights?

[slaughteredlamb]

Your Cut Out & Keep Guide To Correct Exposure

Exposure is controlled by three things, Aperture, Shutter Speed and ISO.

Aperture
Aperture is written as f/4, f/5.6, f/8 etc with the f standing for focal length. So f/4, for example, litterally means focal length divided by 4. But what does that mean? Aperture controls two things, it sets the size of the iris in the lens (much like the human eye) which therefore controls the amount of light passing through the lens i.e. a big iris lets in a lot of light whereas a small iris lets in less light. Confusingly the larger the number the smaller the iris (because you are dividing the focal length) therefore f/22 is very small but f/2.8 is very large. What Aperture also does is control depth of field. With a small aperture (f/22) the depth of field, i.e. the amount of the image that is in focus front to back, is very great but at f/2.8 the depth of field is very small. To put this into context you might use an aperture of f/5.6 for a portrait of someone so that the background is knocked out of focus whereas for a landscape shot where you want everything in the scene to be in focus you might choose an aperture of f/16 or smaller.

Shutter Speed
Aperture controls the amount of light that can pass through the lens, the shutter speed then controls how long that light is allowed to hit the sensor or film. Shutter speeds are written as a fraction of time e.g. 1/125th, 1/30th etc before going into seconds 1", 10" etc. The longer the shutter is open (the slower the shutter speed) the longer the light is able to hit the sensor. This is great if you are shooting in low light or with a very small aperture as light needs to hit the sensor for longer in order for an image to be recorded at the correct exposure. This is fine for static objects but for moving objects it's a problem as the slower the shutter speed the more chance there is that they subject will hvae moved before the shutter closes again resulting in blur. The same problem exists when you hand hold your camera except that it is not the subject that is moving and causing the blur but you. To avoid this you should always try to use a shutter speed greater than your focal length. In other words if you are shooting at 100mm you should use a shutter speed of at least 1/125th.

ISO
Aperture controls the amount of light passing through the lens, shutter speed controls the amount of time that light is able to hit the sensor and ISO controls how sensitive the sensor is to that light. The higher the number the more sensitive the sensor is to light. The way this works is that the electrical current passing through the sensor is amplified. The amplification makes the sensor more sensitive but it also generates noise.

So what does this all mean?

The one governing thing between shutter speed, aperture and ISO is that the difference between any one value e.g. ISO 100 - 200, Shutter speed 1/60th - 1/125th, Aperture f/2.8 - f/4 is one stop of light.

Therefore lets say in Aperture priority your camera tells you to use the following for a correctly exposed image:
ISO 100 f/4 @ 1/125th

You could switch to Manual and use any of the following settings and still end up with a correctly exposed image

ISO 200 f/5.6 @ 1/125th
ISO 200 f/4 @ 1/250th
ISO 100 f/2.8@ 1/250th
ISO 100 f/5.6 @ 1/60th

In the first one I've made the sensor more sensitive to light so I've kept the shutter speed the same but used a smaller aperture
In the second I've made the sensor more sensitive to light kept the aperture the same but sped the shutter speed to compensate for the extra sensitivity of the sensor
In the 3rd I've kept the ISO the same but used a larger aperture which means that I need to use a faster shutter speed to control the increased amount of light entering the lens
In the 4th I've used the same ISO, but used a smaller aperture which means I need a slower shutter speed in order to let the smaller amount of light hit the sensor for longer.


As hopefully you can see there is no such thing as one correct exposure. Instead you should use the exposure that gives you the effect you want. Therefore if you want shallow depth of field (background out of focus) you should use a large aperture but then counter balance that with a fast shutter speed and/or increase the sensor sensitivity. If you want lots of depth of field than you should use a small aperture but counter balance that with a long shutter speed and/or a high ISO.

So what do you need for light trails?

Light trails are caused by the subject moving whilst the shutter is open so this means that you need to use slow shutter speeds. How slow will depend on how bright the light is, how fast the object is moving and how long you want the light trails to be. The thing to remember is that the longer the shutter is open the more light is going to hit the sensor so you want to set the lowest ISO you can, typically 100 as this means that the camera is the least sensitive it can be to light. Whether you now set aperture or shutter speed will depend on whether you need to have a shallow depth of field or not. If you do then you are going to have to set a large aperture which will force you to use a faster shutter speed which is the opposite of what you want. Setting a small aperture will let you use a longer shutter speed and the smaller the shutter aperture the longer a shutter speed you can use. But what if even at the smallest aperture your shutter speed is still too fast for light trails (more than likely during the day) or what if you want a shallow depth of field but your shutter speed is too fast? In situations like this using a slow shutter speed will just result in an over exposed or completely white photo. You can't make the sensor any less sensitive to light, you can't use a slower shutter speed and you can't use a smaller aperture so what do you do? You use a Neutral Density Filter (ND). An ND filter is a grey piece of glass that you put in front of your lens that reduces the brightness of the light entering the lens thus allowing you to use larger apertures and /or slower shutter speeds. ND filters come in different strengths from reducing the amount of light by 1,2,or 3 stops. You can also stack ND filters together to reduce the amount of light even further. If you want light trails in daylight this is pretty much your only option.

It should also be pointed out that you can also buy Graduated Neutral Density filters (GND) which are grey at the top and graduate out to clear glass at the bottom. The purpose of these filters is to even out the exposure between the sky and the land so as to avoid white sky's when shooting landscapes for example. The reason for this is simply, the sky is a lot brighter than the land and digital only has a small amount of latitude (the amount of difference it can cope with between highlights and lowlights) and usually anything beyond 2 stop difference between sky and land is too much for it to cope with and you'll just get white sky or black land. A GND will dull the sky bringing the sky exposure within the range of the land allowing you to get a more even exposure and retain detail in both land and sky.

HTH

[Notorious MCSE]

Mr. Lamb,

I believe you really do need to change your job if you have the desk time to write such replies to my tardy photography questions.

Tomorrow, all going well, I am going to have a fiddle with my camera and ill post the results.

Cheers Mr. Lamb, with what you've said, my cameras instruction book and a bottle of beer I should be able to get a few decent results. Hopefully.

What would you recommend for day light light streaks, i.e. early mornin'

[slaughteredlamb]

In daylight, even early morning without any ND filters it's going to be tricky unless you are talking about REALLY early morning where it's still basically night i.e. the sun hasn't yet come above the horizon.

Assuming you are talking a more sociable hour than chuck your camera in Aperture Priority at ISO 100 and select an aperture of f/22. This sets your camera to the least sensitive setting of your sensor and is the smallest aperture you typically can set meaning you will get the least amount of light through the lens as possible. The camera will then choose a shutter speed that will result in a correct exposure. However if this is too fast than there really is nothing else you can do other than buy some ND filters. If you are lucky and the shutter speed is too long than just choose a slightly larger (smaller number) aperture and you'll see the shutter speeds get faster.

EDIT: If you find that by setting an aperture of f/22 the shutter speed is only slightly too fast you could try using exposure compensation. By adding say -2 stops of exposure compensation you'll keep the aperture at f/22 but the camera will use an even slower shutter speed. Typically exposure compensation is only used on scenes that will fool a cameras internal light meter like photographing in the snow or anything brilliant white but it might also help you a bit with light trails

HTH

[Notorious MCSE]

SL,

Although what you said hasnt fully sunk in yet, I did have a play around tonight and is starting to become clearer, as are my cameras many functions, in short, cheers yuo fag!

[slaughteredlamb]

Just knowing that I have helped has given me a warm tingly feeling in my stomach. Scratch that, it was just wind. 

The best way to understand how your camera works is to just keep using it and try the different settings. In time it'll become clear. Either that or you'll sling it against a wall.

[Notorious MCSE]

One quick one.

ISO: Higher the ISO number, (i.e. ISO1600) then their will be more light in the photo?, ISO100 very low?

Today I was in the woods taking pictures of mountain bikers (not gay) but the pictures came out grainy, in such a situation, what would you pros do?

[samhs]

The ISO (previously has also been known by the name ASA) setting refers to the responsiveness of the film to light. Essentially, the larger the grains of silver halide, the more responsive it is to light, so the more likely you are to get a meaningful image in lower light. The downside is that you end up being able to see the individual grains, hence you get a "grainy" image. In film, you get a range of different options from ISO50 or even ISO25, right up to ISO1600. ISO50 (a "slow" film), for example, has a very fine grain that will allow very smooth images with no visible noise, but the downside is that you need very good light to be able to record an image (or a slow shutter speed). The ISO1600 ("fast") film will give you a photo when you're standing in a dark forest taking gay mountain bike porn shots, but will give a gritty, noisy result - it's a trade off.

Worse still, in digital noise tends to manifest itself as random pixels of bright inappropriate colour -  much less aesthetically pleasing than the random shaped grain of fast films. What can you do about it? Get a camera that deals with low light better. Or change the style of your photos to allow you to use a slower setting - e.g. pan shots would work well, or perhaps flash fired shots to freeze the action. Modern DSLR cameras deal really quite well with fast ISO settings, so I've never really had this as a major problem, but there is one other thing you can do - use software to remove the noise by taking a photo with the lens cap on, or against a pure white background for reference. Never had to do this, and don't know any more about it other than that it is possible.

hth

Sam

[Mr Anderson]

Photoshop has built in noise reduction filters that can help a fair bit, and Noise Ninja gets very good reviews if PS can't do a good enough job for you.

[slaughteredlamb]

If noise really is an issue than really you need to look at using software to remove it. Photoshops built in filter isn't really up to much and has already been mentioned Noise Ninja is very, very, very good. I personally use Neat Image http://www.neatimage.com/ because that's what I used when I was a PC user and Neat Image was the first anti noise filter that supported Intel Mac's which is why I stuck with it. Personally I really like Neat Image and have never felt the need to look to anything else anyway.