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This is part 4 of a series of notes on using light in photography – Exposure.

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  • Ian Beckerton
    replied
    Exposure!

    Exposure is really one of the most important aspects of creating an image that will do justice to your product. Does anyone need more information on this subject?

    I..

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  • Ian Beckerton
    replied
    Sorry Ifor,

    Typical PC problem or was it the glass of wine that helped it?

    I..

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  • Ian Beckerton
    replied
    Mmmm

    I should have a signature here!

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  • Ian Beckerton
    replied
    Very Strange!!

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  • Chris W
    replied
    Hi Ian,

    Love your images, especially the wine glass shot, that must have been hard to do.

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  • Ian Beckerton
    replied
    Double Ooops

    Sorted now , I think.

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  • Ian Beckerton
    replied
    Ooops

    Try this one.

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  • Ifor-Jones
    replied
    Don't seem to be able to view your photos. Not sure if it is just me, or whether there is a problem.

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  • Ian Beckerton
    replied
    Images

    As promised, here are a few of my images,

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  • Ian Beckerton
    replied
    Flash Arry!

    Hi Chris,

    I am pleased that you understand where I am coming from, Using the camera in manual mode is essential if you want to get the best image possible using indifferent lighting conditions. But don’t you use flash?

    With flash, especially with studio heads you have to be in the manual mode, as you can’t control them from the camera unless you spend a lot of money. You don’t need to spend lets of money to get excellent results, you demonstrate this already. And as I said a little earlier the front page image on your site is as good as they get and way above anything I have seen on the forum so far.

    I..x

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  • Chris W
    replied
    Exposure

    Thanks for all the information you put Ian, it must have taken you ages to write. I have certainly noticed how important exposure is when it comes to translucent beads. If I don't get the exposure right the beads look washed out in parts. Once the information is lost your image seems to break down.
    I usualy take three shots with different camera settings to be sure I get the right exposure. I do use manual settings which I find gives me better results.

    Leave a comment:


  • Ian Beckerton
    replied
    Lenses - may be!

    I think I will visit camera lenses next. I did think about digital processing but that is just too boring even for me!

    Is there anyone out there that has a specific question or a problem they don't know how to resolve?

    I..
    Last edited by Ian Beckerton; 28-03-2008, 09:16 PM. Reason: Additional Topics

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  • This is part 4 of a series of notes on using light in photography – Exposure.

    This is part 4 of a series of notes on using light in photography – Exposure.

    Exposure is a difficult subject to write about because of the amount of subjectivity involved. It would be wrong to say that the only correct exposure is the one that shows all the tonal range of the image. It is in fact an impossibility to do this as the image sensor or film will only respond accurately over a specific range of frequency’s which make up the visible spectrum of light. An artist would argue that light is basically totally subjective, you can do what you like with it as a creative tool. A scientist would argue that light was objective and would be tools for research, both are right of course. In our case we, I think want to be somewhere in the middle of these arguments. We want to use light to accurately portray an object but at the same time we want to be creative with the light to get the best image possible.

    The exposure system in a camera will only give you an average value (In general terms) for exposure over the image frame. Some manufacturers systems are better at doing this than others and some exposure systems can be made to work selectively (spot metering, ect,ect) but in general you will only get the average value for exposure for that particular image frame.

    This presents quite a few problems to Jo Snapper especially if this principle is not understood. All cameras exposure systems are based on the same principle, which is that the light being reflected off an object will have an average value of 18% reflectivity. This 18% is derived from the eyes response to the tonal (or shades) range of all the colours displayed.

    Unfortunately, cameras are not intuitive; all they see are areas of light and dark and so will only work out the average exposure based on these areas. This means that if the image frame has lots of white in it the camera will work out that the image will be too bright and so will reduce the exposure to correspond to the 18% reflectance that is its preset average value. This is why that when you shoot anything that has lots of white or bright areas in it or surrounding it they will appear to be grey or under exposed.

    The same applies to dark areas or black but this then will be the other way round. The exposure system thinks that the area is under exposed and so will instruct the camera to add more exposure to reach what it thinks is this 18% reflectance value.

    In practice what means is that whites look grey and blacks and shadows are impenetrable and every thing else is either ‘burnt out’ or the colours are muddy looking. So we need a fix to get round this problem. Fortunately all you need is at hand! Yes, the palm of your hand has a reflectance of about 22% which isn’t that far away from the value you need to have for a good exposure and it doesn’t matter what your ethnicity is either as all palms are very similar in reflectance. You could if you so wished go out and buy a set of grey cards from your local photo dealer, they aren’t expensive. A grey card is just a piece of cardboard that has a specific reflective value and the one that is used is 18% grey.

    I use a grey card to calibrate my exposure meters or if I want to have a very accurate exposure for a particularly sensitive item. The principle is the same in either case; you take an exposure reading off the palm of your hand or off the face of the grey card just in front of the object you want to photograph and in the same path as the camera is pointing. In your case you would use the cameras exposure system. So lets say for example that the reading that the camera has taken is 1/60 of a second at an aperture of F8 (I will go through this relationship in another note). Most cameras will display these values either through the view finder or on the rear viewing panel. At this point it might be advantages to have the cameras instruction manual to hand as I want you to transfer this information to the manual settings on the camera. Once the camera is in manual mode all the settings are locked out from being changed by the automation system, so the only way they can be changed is when you do it.

    Now, if you are using daylight or even if you are using a daylight lamp you will probably need to use a tripod to hold the camera steady if you want really sharp and in focus images. I have noticed other threads that mention this fact so I have no need to cover this subject. Fortunately in manual mode the camera will still focus automatically so you shouldn’t have to worry about that.

    Now that you have the camera pointing at the thing you want to photograph and the exposure settings set take a photograph. Look at the photograph and think to yourself is this what I want from the image. If the answer is no then you can adjust one of the parameters either the speed or the Aperture (F value) to give you the best image possible. In practice, you would for rostrum (Still Life) work adjust the speed as this is not critical unless you are trying to capture motion. Adjusting the aperture (F value) will change the depth of field (that’s the area that is in focus) so you may wish to increase this area by increasing the F number to say F 11. In doing this you will have to decrease the value of the speed setting by one stop to 1/30 second as the exposure ratio is fixed to maintain the same image quality. To get the adjustment needed you only need to change one of the values

    All this is not as horrendous as you might think and you will soon get the hang of it and in reality its just the same as operating a dimmer control on your lights in the house, adjusting one of the values up or down will make the image lighter or darker. It’s ok to do this as you have already set up the basic light dark ratio in the initial measurement all you are doing is optimising the image to suit what you want from it.

    They may be other issues here that will need clarification but all you need to do is ask if you want more information.

    I..
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