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Going digital?

by Charles Hood

Reproduced from in focus 78 (Sping 2004)


How many times have you arrived home after a great diving trip, had your films processed and had that horrible sinking feeling when you discover all of your images are incorrectly exposed? I have lost count of the times it used to happen to me. Even if you did get the exposure spot on, what about the framing? What about the focus? What about the exact amount of balanced light you desired? Unlike topside photography underwater we can't use Polaroid. We have to guesstimate, bracket and shoot heaps of frames just to get one good one. However, now this is all history - the digital age has arrived. I can honestly say that in my opinion the launch of the digital SLR is the most revolutionary change in photography since the invention of film itself. Imagine shooting an image. Within a fraction of a second that image appears on a screen in front of you and you can see exactly what you took. Any corrections, adjustments or fine tweaks can be made and you shoot again. And again, and again until you get the image absolutely perfect, All this is done in situ underwater on location. Alternatively, just suppose you only managed to get one shot of a fast moving subject. The exposure is say two stops out. Simply download the image on to a Mac or PC and correct the exposure electronically. Furthermore you get over 100 images per dive. This is a no-brainer. It doesn't take a rocket scientist to work out this is an inf initely superior way of getting images than any previous modus operandi.

So what's it all about?

Very simply a CCO (charge-coupled device) replaces film. For the user the camera is virtually identical in appearance and feel to a film SLR camera. When you take a shot the mirror Iifts and Iight is picked up by the CCD and stored as a computer file onto a chip. The camera then displays this image on a small screen at the back of the camera. When the storage chip, a common one is a Compact Flash Card, is full, you simply download all the images onto a computer and start again. A 1Gb card can store approximately 100 RAW f iles. All the images can now be viewed on a monitor and prepared for use or archived. No processing. No scanning. No spotting. No repairing of scratches. No manual filing.

Do you need to be a computer wizard?

Well no - but an appreciation of computers is useful. Lets look at some of the terminology. The CCD picks up the light as a series of dots. These dots are called pixels. CCDs are
usually described in pixel capacity, typically in millions of pixels. Take the Nikon D100 for instance. The CCD can pick up 3000 pixels along the longest side and it can do this for 2000 rows. So the total number of pixels captured is 2000 x 3000 = 6,000,000 or 6 mega pixels. What do these pixels mean? Take an Apple Mac, which usually displays pixels on the screen at 72 ppi (pixels per inch). So our image could fill a screen measuring 3000/72 = 41.67 inches by 2000/72 = 27.78 inches or a 50 inch monitor (monitors are measured by the diagonal). When this 6 mega pixel image is transferred into an imaging application such as Photoshop the terminology changes and we say it has 6 million dots not pixels. This is because printers represent a pixel as a dot. A magazine usually prints at 300 dpi so this would give us an image of 10 x 6.67 inches or nearly a f ulI page. A PC usually displays at 96 ppi so the maths will be slightly different. You may think a PC is thus better but the reason why the majority of graphic designers and publishers use Mac is that designers get a better feel of the weight of their fonts when laying out a page at 72ppi.

What about the file type?

Essentially there are 3 types. RAW, this is in eff ect propriety machine code and is what the CC[D recorded. RAW f iles require special software to view the image. TIFF, this is a virtually uncompressed image and is a standard so all computers will be able to view them. JPEG is a compressed f ile, the image requires less memory to be stored so more images can be put onto the Compact Flash Card. JPEG images are also a standard.

Which do you use?

To get a high quality initial image it is advisable to shoot in RAW or TIFF. The main advantage of RAW over TIFF is that it takes a lot less time to record onto the Compact Flash Card so they don't fill up the buffer for as long. Further if in the future some new whiz bang extrapolation software comes out then you still have the RAW file to start with. Finally competitions accepting digital images are now requesting the RAW file to prove you haven't manipulated the image.

What do I need to do to the image once it is in the computer?

You will need to purchase an image manipulation application. The most common is Adobe Photoshop. There are four basic steps to get your perfect image. First you correct for any under or over exposure and open the image. Then you select 'levels'. This is how much RGB (Red Green and Blue) light the CCD has recorded. You can select each colour channel separately and adjust them until you get the correct overall colour you desire. Next you can 'saturate the image'. This makes the colours more vibrant - a bit like using Fuji Velvia instead of Kodak Ektachrome. Finally the image usually requires some kind of sharpening. A process called 'unsharp mask is really the only fifter you require here. The terminology relates to the reprographic film process whereby a light, soft unsharp negative version of the image is sandwiched next to the original positive during exposure. This technique increases the edge sharpness on the resulting plate. The unsharp mask filter reproduces this ef fect electronically. How much to apply is down to trial and error, a guide would be to start with an amount of 80% with a radius of 2 and threshold of 5 - but experiment. That is it you now have a perfect image. Oh don't forget to press 'save'.

Is the quality as good as film?

For 99% of all uses yes. I have mode AO size posters and no one commented that they were digital. Indeed when I told some, 'erhh - but- it's-not-as-good-as-film-sceptics' they were very surprised. Comments came forward on the lines of 'Oh yeah, you can get away with it underwater - that old chestnut. Let's make an analogy here. When CDs first appeared the majority of us commented that the sound was not as good as vinyl. To the purist this may still be the case but how many of us buy LPs today? If I asked you to tell the difference between a CD and an LP today you almost certainly would be able to do so. The LP crackles, jumps a track every now and then and plays for a third of the time - need I go on?

What are the advantages and disadvantages?


Instant image viewing - it's fast.
More images can be taken per dive - typically over 100.
No scanning and cleaning is required
You can alter ISO and white balance on the fly for individual frames.
Huge exposure latitude - allows you to shoot in manual mode with confidence
Can use manual flash - no over exposed foreground subjects due to TTL
The CCD uses the centre (best part) of the lens
Easily stored, catalogued and retrieved Images are free
The focal length of traditional lenses is increased
No film to worry about, heat, X-ray machines etc
Images can be backed-up on site


CCDs give poorer results when shooting at direct sunlight
My old film camera heavily depreciated
The focal length of traditional lenses is increased

Reproduced from in focus 78 (Sping 2004)

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