Manual white balance

[Andrew McCabe]

So, I want to raise this frequently discussed and frustrating subject as a standalone thread.

This afternoon I spent some hours trying to get better colour coin photos through adjusting the white balance settings on my camera as I've been consistently advised on Forvm. So far I have failed; the results have been consistently worse than using auto settings. My camera has a range of automatic settings, and also has manual setting possibilities, which range from fully manual, automatic aperture setting with all others manual, automatic shutter speed with all others manual, automatic aperture / shutter with others manual, and fully automatic. In fully automatic it is not possible to adjust white balance. In all the manual settings, white balance can be adjusted to circumstances - shade, cloud, incadescent, flourescent, daylight, or custom where you set against a standard white. After trying a wide variety of settings, I focused on trying to get the auto aperture / shutter combined with custom white balance, checked against a white background, for settings. In perhaps dozens of shots with a range of settings, I got miserable results time and again. I suspect there is a golden answer in my camera settings, inside the vast multiplicity of options, most of which I literally don't understand (I don't understand the english words used for many camera setting options).

I then reverted back to automatic, chose the "tulip" indicating macro setting (all white balance adjustments are now disabled) and snapped some pics. Those against white background look like they were shot against a white background, the coin colours seem natural and true, and there was no evident colour cast - no blues or reds shading the images. The main problem was that the coin appeared impossibly dark. So I then chose the same setting (auto-macro) against a standard 17% grey card. Now it all looked perfect. This is of course what I've been shooting coins against for years with no special problems. I almost need to ask "what have I been doing right". If I get consistently good results in an automatic macro mode, and variably bad results with attempts to involve white-balance settings, shouldn't I just take the easy path?

Bear in mind I've never been an SLR photographer - I'm absolutely an amateur. But it seems to back up my process evolved over years - grey background, auto-macro settings, natural cloudy outdoor light. No headaches. It may be that there is a simple solution to achieving better results by messing about with balance settings (but without wrecking the auto functions that allow me to make good macro pics), but haven't found it despite following the camera's instructions (all the instructions are inside the camera in digital format). So, I'll revert to my tried and tested automatic settings which seem to produce great photos. Although I'll welcome any guidance to improve this process (beginners guide to really using manual white balance included...)

[maridvnvm]

I set my white balance with a photographic standard grey card, which is the normal method. This involves taking a photo of the grey card under my lighting and then using this image to the the manual white balance.

I haven't checked all the modes in which this can be used on my camera but I think I can use it in everything except the fully automatic program mode.

I have chosen an aperture priority mode of operation or fully manual with a fixed aperture for all my coin photos.

Regards,
Martin

[Heliodromus]

Andrew,
If you're using a stand of some sort (such that camera shake isn't an issue), then the best is to use fully manual settings with a small aperture (= large f-stop, say f 8.0 or more), and whatever exposure (manually chosen, but same for both sides of coin) is needed to get the picture bright enough. Use custom white balance (with these same aperture, exposure settings), using your grey card as the reference. You only want a single type of light source, either natural or artificial, so if you're using artificial light then best to close the curtains to block out sunlight.

The reasons for these settings are:

- fully manual ensure that both sides of the coins are shot with same settings to that lighting matches, and to allow picture brightness to be controlled
- small aperture gives larger depth of field to ensure coin is in focus (at macro range depth of field is very shallow, so the more help the better)
- use grey card as white balance reference since a "white" piece of paper/whatever may not really be white
- if you mix light sources, then there'll be a color gradient on your photos (e.g. warm by window/sunlight to cold by fluorescent light)

However, you'll almost certainly need the macro ("tulip") setting to get the camera to focus, so if that precludes using manual settings (seems odd - I've never heard of such a thing before), then you'll just have to continue using automatic settings (no problem if the results are OK).

If your only issue is white balance, you can always fix this up in software after the photo is taken, assuming the photo contains a white/grey area you can calibrate against. The free Picassa photo tweaking program has a simple white balance correct function where you just click on a white/grey point in the photo and it corrects automatically.

Ben

[Andrew McCabe]

Andrew,
If you're using a stand of some sort (such that camera shake isn't an issue), then the best is to use fully manual settings with a small aperture (= large f-stop, say f 8.0 or more), and whatever exposure (manually chosen, but same for both sides of coin) is needed to get the picture bright enough. Use custom white balance (with these same aperture, exposure settings), using your grey card as the reference. You only want a single type of light source, either natural or artificial, so if you're using artificial light then best to close the curtains to block out sunlight.

The reasons for these settings are:

- fully manual ensure that both sides of the coins are shot with same settings to that lighting matches, and to allow picture brightness to be controlled
- small aperture gives larger depth of field to ensure coin is in focus (at macro range depth of field is very shallow, so the more help the better)
- use grey card as white balance reference since a "white" piece of paper/whatever may not really be white
- if you mix light sources, then there'll be a color gradient on your photos (e.g. warm by window/sunlight to cold by fluorescent light)

However, you'll almost certainly need the macro ("tulip") setting to get the camera to focus, so if that precludes using manual settings (seems odd - I've never heard of such a thing before), then you'll just have to continue using automatic settings (no problem if the results are OK).

If your only issue is white balance, you can always fix this up in software after the photo is taken, assuming the photo contains a white/grey area you can calibrate against. The free Picassa photo tweaking program has a simple white balance correct function where you just click on a white/grey point in the photo and it corrects automatically.

Ben

Thanks Ben (and Martin), that's very helpful. I know enough to know that I would have no idea how to follow your suggestions - whilst I recognise the words, I don't really know what f-stops, aperture or exposure really mean (other than the plain english meaning of aperture as in the size of lens opening, or exposure as in the length of time it opens). As it happens I don't have a problem (including with white balance), with photos shot with my Sony Nex camera (whether using 55mm lens or 35mm macro lens) but as it is often quoted as a solution to various problems presented here, I was just investigating if a better understanding of it, or some trial and error, might help me take better pics. Hence I spent some time trialing and erroring. I can confirm that in the auto tulip mode, all the manual settings are disabled. I can also now reconfirm that I'm not competent to mess with manual anything. I'll try stick to auto-photography and manual numismatics.

[maridvnvm]

Andrew,
Please excuse me if I am telling you stuff you already know but I thought that this might be useful for an audience that doesn't know somw of the fundamentals about photography.

The aperture size is quite important when used in macro photography. The smaller the aperture size (the higher the f-stop) then the greater the depth of field. This is the extend of the depth that is in focus.

I saw a great example that can be used to illustrate this in the "Get me some relief" thread and I have attached this image below. I hope that the member (Dominicus) doesn't mind. There is nothing wrong with the image but it does serve as a great illustration.

This coin was photographed with the coin tilted back rather than square on to try and show off the relief. The focal point on the coin can be seen as the centre of the area of the coin that is in focus. I have added a small white dot (roughly in the centre of the image) at the place that I think is the focal point as assessed by the camera. As you scan towards the top of the coin you can see that the coin become more blurred because it is "out of focus" and the same wwhen you scan from the centre towards the bottom of the coin. The area that you can see that is acceptably in focus is called the depth of field.

The illustrated coin was photographed with a shutter speed of 1/100th of a second at F2.8.

The extent of this depth of field is a function of the aperture. The larger the aperture (smaller f-stop) then the smaller the depth of field i.e. the less area of this image that would be within acceptable focus and thus a smaller aperture allows you to increase this depth of field. The problem with this is that the smaller the aperture the more time is needed to get the correct amount of light into the camero for a correct exposure and thus the shutter speed gets larger with a smaller aperture. The shutter speed for any given aperture is a function of the amount of light and determined by the meter reading.

This now leads us to another potenital problem. As we make the aperture smaller to increase the depth of field and the shutter speed has increased i.e. the shutter is open for longer then we need the camera to be stable to maintain a sharp image. Any shutter speed slower than 1/90th of a second is open to introducing camera shake and even at these speeds it can impact on an image. With a macro image of a coin where we are trying to bring out as much detail in focus as possible any shake in the camera is liable to introduce blur. The image may well be in focus but because the lean is moving around the image blurs. As a result of this we need to use something such as a tripod or stand to keep the camera stable. Even having the camera on a tripod doesn't eliminate vibration however as the act of pressing the button on the camera can cause the camera and tripod to brirate which can introduce blur. The solution to this is to use some form of remote shutter release or time delay release for the camera to avoid any chance of vibration.

I apologise for the lengthy email but once I started it just seemed to go on and on.... (sums me up!)

Regards,
Martin