Saturday, January 26, 2013

Digitising old negatives - Part 1 - kit

Over the past year or so I've been investigating how to transfer a set of old slides and negatives to the computer.  I was looking for a method that would provide reasonable quality, be fast, and fairly cheap.  And thanks to some information from herehere and here, I think I've found it.  (I'm very grateful to the authors of those articles for posting about their experiences, and it's in the same spirit that I've decided to document what I have done).

Although I have a scanner - one of those cheap HP all-in-one scanner / printer / copier devices - it isn't very good and scanning film is, by all accounts, a slow process.  Instead I looked into using a slide copier (sometimes called a slide duplicator), a piece of kit that was common a few decades ago.  Slide copiers are basically tubes with a lens inside, one end has a holder for slides (and often negatives), the other end screws into a compatible SLR camera body.  Most copiers used the M42 lens mount which meant that they were compatible with a wide range of cameras.  There was no need to set focus because the slide would always be a fixed distance from the camera. Secondhand copies are quite easy to find on ebay.  My Digital SLR, a Sony, can use M42 lenses with the help of a cheap adapter (most other brands of DSLR can too).  So why not go down this route?

The reason is that these copiers were designed to produce a 1:1 copy of the slide on the 35mm film of an old SLR.  Most Digital SLRs have a sensor - often called APS-C size - that's smaller than 35mm film; they aren't true "35mm" cameras at all.  Only "full frame" DSLRs have a sensor of the right size, and they are expensive (£2000 upwards at the time of writing).  I don't have one. The effect of using a slide copier on a camera with an APS-C sized sensor would be to crop the slide; the outer edges would not be copied (about a third of the total area).

Instead, I've opted for a different kind of duplicator that doesn't have its own lens and has some flexibility in its set-up, the Accura Variable Magnification Duplicator. This dates from the late 1960s / early 1970s and was also sold under the Miranda and Panagor names.  It is much rarer than the standard slide copiers but does turn up on ebay (usually from USA sellers) every few weeks.  It consists of a slide and negative holder which screws into a set of metal rings, the assembly then (possibly with the help of a filter ring step-up or step-down adapter) screws onto your camera lens.

My copy of the duplicator came with the holder, two rings labelled "6 Japan", an unlabelled one, and one with "49F7". The "6 Japan" rings screw into the slide copier itself; they are extension tubes with a diameter matching the old  "Cokin Series 6" (sometimes Roman numeral - VI is used) filter size.  The unlabelled ring is an adapter between this  and "Cokin Series 7" (or VII) size and the final ring is an adapter between Series 7 and a 49mm filter mount.  What this means in plain English is that by screwing all of these bits together in the correct order you can then screw the assembly onto a lens with a 49mm filter thread and - just as importantly - put a bit of distance between your lens and the slide holder.  If your lens has a different filter thread size (55mm is common), adapter rings to convert between the two are common on ebay or photography shops; if your lens filter is more than 49mm (and most will be) then you'll need to search for a step down filter ring of the correct size (xxmm to 49mm).

The set-up I have just described is how the Accura was originally meant to be used; the slide would be of more or less the right distance from the lens to ensure that the whole slide was captured when a lens of the standard 50mm focal length was used to photograph it.  There is an adjustment screw on the Accura which allows for fine-tuning of the distance; the manual that came with it suggests that using this adjustment you can compensate for your lens having a focal length of anything between 50 and 58mm.

However, using this arrangement with today's DSLRs (unless they are full-frame) leaves us with two major problems to solve (and a minor one concerning exposure which I'll cover later).

  • In order to capture the full slide (or negative) on an APS-C size DSLR sensor you either need a lens with a shorter focal length (around 35mm), or you need to put more distance between your lens and the slide holder
  • Unless you have a specialist macro lens to hand, it's unlikely that you will be able to focus on the negative - the distance between it and the lens will be too short for the lens' optics to cope
 Turning to the second problem first, the cheapest way to set up a close focusing lens was to use an old M42 manual focusing / aperture lens with an adapter for my DSLR and some extension tubes.  Extension tubes fit between the back of the lens and the adapter, and their effect is to dramatically shorten the minimum (and maximum) distance over which the lens will focus.  My M42 lens and extension tubes (which I already had - another reason for going down this route) cost around £20 in total and are widely available secondhand or on ebay.

My M42 lens had a 50mm focal length so I still needed to solve the first problem.  35mm M42 lenses are comparatively rare and expensive, and I was concerned that one might introduce a slight degree of "barrel distortion" on the final picture, so I chose to put more distance between the lens and the slide holder.  The easiest way to do this was to hit ebay (one last time) and buy a whole set of those filter step up / step down rings I mentioned earlier; for £10 (from a Chinese seller) I got a set that would adapt from 49mm all the way up to 82mm and back again.  All the rings screw together; by a bit of trial and error I found that I could achieve the right distance by putting the rings that went from 49mm to 62mm and back again between my lens filter thread and the "49F7" adapter.

The final piece of kit to add in was a flashgun - again I was able to make use of one I already owned.  Using that to control exposure will the the subject of Part 2 of this post.

I've described a set-up using a Sony DSLR and manual focus lens, but there's no reason why this shouldn't work for other DSLRs or even for compact digital cameras that take standard filter sizes on their lenses (or can fitted with an adapter to do so).  A native fitting macro lens of around 50mm focal length could be used (dispensing with the extension tubes); alternatively Canon, Nikon and Pentax DSLRs can use M42 lenses with an adapter.  The combination of Nikon and M42 isn't usually recommended because you can only achieve close focusing (ie not beyond a few metres) but since closer focusing is what we want for this exercise it shouldn't matter.

No comments: