Lesson 16 The Underwater Photo Course
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Duplicating and copying


Sooner or later you will need to provide high quality copies of important slides to protect your original transparancies from loss or damage. By duplicating your important slides, you can safely store the original and use the duplicate on a day to day basis. If you are ever sending slides to anyone, perhaps a publisher or magazine, then always send duplicates, and pack them in plain, not glass mounts.

Duplicating involves taking an exact copy of your slide, and can be done in a number of ways:

It is worth mentioning that there are various levels of quality in duplicating, there being differences in costs between projection quality and reproduction quality duplicates.

Doing it yourself

The economics of doing it yourself are very questionable. With specialist duplicating bureaux charging from 30 pence a copy, you will be hard pushed to do this much cheaper yourself, with a film costing about UKP6.00 and developing an additional UKP3.00. However, it is worth experimenting with, as it will help you develop the skills required to enhance slides - copying - which we will discuss in the next section.

There are probably as many ways to duplicate a transparency as you have transparencies to duplicate, but in this section we will avoid all the professional techniques and concentrate on what is probably the cheapest and most effective for an amateur on a limited budget.

One of the realities of duplicating is that you cannot make a perfect copy of a slide just by photographing it. Doing this results in vastly increased contrast in the copy primarily due to the design of normal films, which try to expand their sensitivity range by darkening underexposed areas and lightening over-exposed areas. The low exposure latitude of slide film is also relevant and adds to the effect.

If we want accurate copies, then we must use special copying film. The one I would recommend is Kodak SO366, as it is the only one I have found that is balanced to daylight (or electronic flash), and comes in rolls of 36 for 35mm cameras, rather than rolls of 10 metres or longer.

The equipment you will need is:

The approximate arrangement of equipment is

Photograph here

Setting up

SO366 does not come with an ISO rating, but instead is given a starting EI (exposure index), printed on the film cassette box which amounts to much the same thing. In addition, the colour balance of the film at time of manufacture is not perfect, and for each batch of film Kodak print, again on the box, a starting colour correction pack which you must make up yourself from the Ilford Colour filters, and place in front of the strobe.

Perfect exposure, especially considering the high degree of magnification is extremely difficult to calculate, and because you might have a mix of dark and light slides, and because when copying (see below) you might want to adjust the exposure, TTL strobe exposure is not really recommended.

I run off a test roll, bracketing exposures by moving the strobe further and further away from the diffuser, starting perhaps at 3 inches, and repeatedly doubling the distance each time. By recording the distance for each exposure, then examining the results against my subject slide, I can obtain a good approximation of the best distance to place the strobe to achieve the best results.

If your strobe has variable power (as my SB25 does) then you can keep the same distance, and alter the power setting instead (within the 5 stop variation of the strobe before you have to start moving it). Remember to set your camera on manual at the recommended strobe sync speed, and set your macro lens at the midpoint aperture to obtain the best possible quality from it.

Especially if you already have a lens that will focus down to 1:1, this is a reasonably cheap place to start, and all it will cost you is a sync cord and the correction filters as a set-up cost.

Be careful to include the complete image, bearing in mind that many camera viewfinders only show about 92 percent of the final image. You do not want to make the image smaller than necessary, or include parts of the slide mount in the duplicate. Be also aware that the slide mount will mask a small portion of the slide, and if you want to be particularly exact, you should remove the slide from the mount before duplicating.


Of course copying includes duplicating, but I tend to think of copying as permitting in addition:

Copying permits you to correct those naughty little errors in composition, or to close in on a subject which you were really too far away from. It will permit you to correct a multitude of little errors, and end up with a fine result rather than a mediocre one, within the bounds of the fact that there will always be some loss of image quality when copying, especially if you are enlarging to any degree.

Exposure adjustment

Due to the design of the duplicating film so that it can maintain contrast, it has a much higher exposure latitude than your original film. If you have assessed that your original is one stop under-exposed, then you will need to duplicate the slide with a two stop over-exposure in order to compensate for it. The same applies to over-exposure of the original.

As always, it will do no harm to bracket your exposures in order to end up with the result that you want.

Cropping and Enlargement

Your first obstacle is the fact that your macro lens cannot focus down further than 1:1. You will therefore need some form of additional extension, in the form of either extension tubes or bellows. Realistically, you will want to work somewhere between 1:1 and 2.5:1. The recommended options available to you, with Nikon equipment are therefore.

Realistically, the price of the PB-6 bellows (and preferably the matching PS-6 slide mount) is such that you need to take a much wider look around at other options available to you to achieve the same result, such as

all of which may come in cheaper than Nikon bellows and attachments. Even using a professional lab to produce custom slide enlargements is going to work out cheaper unless you have a vast amount of slides to copy.

Some companies manufacture zoom slide duplicators which are capable of returning 1:1 to 2.5:1 copies of slides at a reasonable price. My experience of one (not all of them) is that while they will duplicate effectively, there is a considerable loss of sharpness in the result. Whether this is due to my own technique or design limitation of these pieces of equipment, I do not know, but would recommend that you try to obtain some sample results from a sharp slide before committing your money. They may work excellently, but this is not my experience.

However, if you do go ahead and 'do-it-yourself', copying will always result in a different degree of magnification than you were using for 1:1 duplication, and you must therefore either estimate the increase in exposure required, or take another sample roll, bracketing exposures for each magnification level.

This is a complicated subject, and much further information is beyond the scope of this book, so readers should refer to the reading list for further details on this matter.

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This page was last updated on 11 August 1998
Please address any comments to Mark Mumford