"DX CODING. WHAT`S IT ALL ABOUT?

BOB LEWIS (Area 9)

After reading this article by Bob Lewis, I strongly suspect that the C.R.C. will give him the equivalent of being 'drummed' out of the Brownies, because after spending a fortnight at Tenerife, he comes back without ANY SLIDES WHATSOEVER!

My excuse is that I have already made an audio-visual slide show for Tenerife a few years ago and I don`t want to do the same thing again, and what`s more, being older I was not looking forward to load myself down with the usual gadget bag full of SLR's, lenses, flashguns, tripods etc. I wanted a holiday!!

So I got some Fuji Colour negative film and treated myself to a compact camera just for happy snapping; a Pentax Zoom-70, which is auto-everything, including auto film-speed control. So for the new camera, I had to find out what "DX" CODING meant. I took the camera untested and I was surprised that my holiday snaps were first class, and did not loose a single shot under difficult conditions such as flash, daylight-sync flash and never lost focus even when people walked rapidly towards the camera; and I never had to think about exposures either!!

Now, Compact cameras and 2 DX" films are mainly intended for colour prints for the novice but there is no doubt that "DX" coding is coming to stay for all films and all new cameras. Don`t skip this article thinking that "DX" is of no interest to you. You will be involved in some way sooner or later, especially if you spool your own cassettes!!

"DX" coding was invented by Kodak in 1983. The "DX" system allows very accurate processing for prints and slides for the Labs but not for the amateur. All film manufacturers are now doing "DX" just as they did when Kodak introduced E6.

What about reversal films which seem has much less latitude than colour negative films? I am going to look into that aspect later but first of all I am trying to say what "DX" is all about. On a new 35mm film the first thing you will see is the legend "DX" on the box and on the film cassette.

There are two sets of patterns printed on the metal cassette, one set is a row of bar-code (for the D & P Labs) near to the film lip and the other set is a pettern of clear silver squares (conducting) against the none-conducting black paint of the cassette. These squares are for camera use.

The square patterns are to allow electrical contacts to mesh with the camera electronics inside, providing of course that your camera has been designed for "DX" control. On the 2 DX" cassette the black and silver squares contain two rows, as on my sketch, from 1 to 6, near to the film lip, and 7 to 12, which are adjacent to the 1 to 6 row. Square 1 & 7 are always conductors, acting as an "earth return" to the other squares.

A "DX" cassette can be used on any 35mm camera regardless. If the camera is a "DX" type the metal squares on the cassette will make contact on a row of contacts inside the camera body. The pattern of squares on the cassette carries information on the "works" in the camera circuits as follows:-

Above is a typical example of the "squares", as perhaps indicating a Fujicolour Super HR 100, 24 exposure cassette. Squares 2, 3 & 4 indicate 1/3rd stops and 2/3rd stops. The next row is on squares 7 to 12. Squares 8 & 9 measure the length of the film in the cassette, and squares 11 & 12 indicates the film latitude required for the type of film in use, ie, to "DX" CODING allow the camera more exposure latitude for negative film rather than reversal latitude.

How much of the 2 DX" code control can be used depends on the camera manufacturers. Compact camera makers appear to be mainly interested for colour negative prints, (the market for colour prints is many times more than colour slides) so 1/3rd stops and 2/3rd stops are not necessary and only four contacts in the camera is needed to cover from ASA 50 to ASA 1600 (ISO, if you like). For a Compact camera for colour reversal slides it will be necessary to use films of exact stops of ISO 100 such as Fujichrome 100 and Ektachrome 200; films such as Kodachrome 64 will not be correctly exposed.

More expensive SLR cameras will have more contacts fitted inside the film chamber to cater for 1/3rd stops from ISO 25 to 5000, as well as indicating the film speed. Length of film and frame numbers are displayed on an LCD panal on the top,of the camera and even with compacts there is a window at the camera back to show details of the cassette. You don`t have to fix bits of the cardboard box on a frame at the back of the camera as previously.

At this point C.R.C. members may say that they have been using a camera with great success for "donkeys years" without any 2 DX" altogether, than you! fair enough, but I am afraid that 2 DX" coding will soon be rearing it's ugly head at most of us, whether you like it or not! Especially at those people who use colour-slide bulk films and spool their own cassettes, such as me, and possibly most of the C.R.C. members. All film makers are rapidly changing-over to "DX" cassettes, even with long established films such as Ilford FP4, and of course there is exellent reason. (for some!).

As well as the camera sensing squares there is another code on the film cassette. It is a "Bar-code" near the film lip on the cassette, something like the bar-codes used on most products nowadays, Library books, tins of Lager, cat's meat; you name it!

The purpose of the bar-cod in the "DX" system is to let the processing-labs (not us) know exactly what type of film, length of film and no doubt, the batch number etc, they are gong to process.

Now, the labs do not which to have people spooling-up any old film into any old none `DX` cassette. Using the wrong film or the wrong code on the cassette may ruin the results. In addition, some people post films not in a cassette container, because they like to keep those dinky little tubes! Thus the film people (and you) don`t like it if the cap of a "naked" cassette comes adrift when dropped on transport.

Consequently, ALL film makers are starting to do it. I have already got the following staked cassettes in my possession:- Kodak, Agfa, (yes, even Agfa Ortho), and all Ilford films exept XP1, which still seems to stick to the old but easily removed end-caps.

FP4 cassettes have been re-designed and they are not using masking tape to stick the centre any more. They seem to have gone "Continental" with a new fangled clip at the centre, Some of the new Ilford caps can be taken off, but only with great difficulty with a beer-can opener and some are tough as Kodak's caps, and cannot be removed without damage. Times are changing.

Personally, I always liked the old Ilford-type cassettes; easily removed caps, large enough in the body to roll 36 frames without getting too tight and it was easy to open the cylinder to brush-out the velvet lips. The latter facility doesn`t exist with the plastic type; with only one end cap it is hard to brush out the velvet and I always found a plastic cassette is prone to scratch the film.

Luckily, I have a friend who processes special B&W films and prints (including page 3 prints!) from photographers all over the UK and he keeps me plenty of `used` cassettes, so for the moment I am "All right, Jack!". But alas, he reports that the number of old type cassettes are rapidly dwindling. Whether or not some manufacturer is going to make special cassettes for the bulk user we will have to keep our eyes open. was it not a firm called, Shirley-Welland and another firm who`s name escapes me, used to make them? All long dead, I suppose!

Back again to the "DX" specifications. There are two more codes to consider, as well as the first and second codes I have already mentioned. The third code is a pattern of holes punched by the film maker at the start of a film for certain automatic processing machines and the fourth code is a very crafty code that only appears until the film has been developed. After the film has been processed you can see the fourth code located between the edges of the film and the perforations. You will find the code is something like a barr-code. There will be two pattern marks on every frame number. The idea is to give information to the printer so that he can reset his machine to give the best possible processing results from that particular batch of film.

I cannot say which D&P labs have all these facilities. All that I can say is that my "Happy snaps" I was using was ISO 100 and 400 Fujicolor and sent them off (what a cad!) to a new shop, called "SuperSnaps", in my town. With a name like that it was almost enough to put me off, but in fact the prints were ready first thing next morning and the results could not be faulted. Not the cheapest nor the dearest process house, but the results were certainly cheaper, quicker and better than my own colour printing efforts. Of course, if you wan`t a larger print, good enough for exhibitions, you can simply do-it-yourself. and you have a good basis for a start.

As I implied at the beginning, this article may not be aimed at the C.R.C. alone, because there is a lot of colour negative content in the article, but we must keep in mind the changes in photography in general.

I was talking to Colin Powell (our Hon. Treasurer) the other day and Colin considered that "DX" in photography can be likened to "Syncromesh" in the motor industry. When syncromesh gearboxes came out, motoring die-hards who previously changed gears by double-declutching said that synchromesh was "Pansy" and was looked down upon, but how many people nowadays are using a "crashbox"! Those simple gearboxes have all been consigned to the motor musiums!

Now we come to another aspect on the "DX" situation. What if you (or your wife) have a 2 DX" only compact camera and you still have bulk films and you have plenty of redundant cassettes which are not "DX"!

No problem! If you are using none-DX cassettes, most of the "DX" Compact cameras will automatically operate as if you are using ISO 100 stock. So you will be getting exact exposures with the very popular ISO 100 bulk reversal films such as Fujichrome, Konica and Ektachrome 100 with any old none-DX cassettes. I have found that the auto-focus, auto-exposure, auto-flash, auto-zoom, auto-everything Compact is ideal for B&W films for candid sport "DX" CODING and press subjects but an ISO 100 film is not quite fast enough in dull weather.

I have a lot of bulk Tri-X in the fridge and it is very cheap and if I could use the Trix-X on the "DX" Compact camera it would be just the job to carry around at all times. The trouble is, I cannot lay my hands on any empty ISO 400 "DX" coded cassettes. All "DX" coded ISO 400 cassettes that I have come across, such as HP5 and Fujicolor 400, have been "staked" and useless for re-spooling.

I thought, What about fixing home-made "DX" codes to old Ilford un-coded cassettes? After a few failures I have found a method of putting codes easily on old cassettes and the method has worked well. First of all you must have access to a "genuine" "DX" coded cassette to find out the code for the right type of film speed you require. The important bit is the row of black and silver squares, No. 1 to 4 as shown on my sketch.

On your old cassette, fix a piece of kitchen aluminium foil, stuck down with DOUBLE-SIDED Sellotape in the same position as squares 1 to 4 on the 'genuine' "DX" cassettes. For a compact camera there is is no need to place squares 5 to 12 on the old cassette, because those particular connections are not used in the Compact cameras.

Now fix pieces of ORDINARY Sellotape on the aluminium foil to act as an insulator in the same position as the black squares are on the "original" cassette, and Bob`s your uncle! I have tried the above method and it really works! But alas, I have a horrible feeling the days of being able to spool your own bulk film are numbered!

Keep your old type cassettes and look after them like gold!