View Full Version : Penny drops! Book plate holders and Film Sheaths

Steven Tribe
11-Feb-2013, 03:11
I am sure most will have realised this before now - but it took me a couple of years for the penny to drop.

I have a number of field cameras (9x12, 13x18, 18x24 and 30x40cm) most which came with book form (opening in the middle with releasable central metal plate) plate holders. A few of these came with film sheaths as adapter to sheet film - but many without.

Although sheaths work excellently, there is always the problem of checking and adjusting the ground glass position as the raised edges of the sheaths do increase the film plane depth in most holders by around 1 mm.

Eventually I have realised that these book holders do not need sheaths, as the internal mahogany framing is less than the nominal size. This means that film can be "placed" into a precise square "hole" from the rear. All that is needed is a stiff plain cut out which covers the film and is pressed against the film by the single or double spring on the central metal plate.

After this discovery, I have used the metal film sheaths I have in a reversed position as a temporary (expensive, but a forgotten expenditure!) measure. Experience in a changing bag says that the system would be easier/quicker with specially made "pressure plates" which fit the "square hole" exactly. There is some difficulty in ensuring the pressure plate has "fallen down" with these slightly indersized sheaths.

I also note that 5x7" sheet film can be used in the same way with the 13x18cm book holders I have - there is enough film overlap.
The side with central latch should be done first and it is easy to mistake negative side of the film when working from the inside out, so to speak.

I will post again when I have found a suitable replacement for these, rather heavy, steel sheaths.

Roger Hesketh
11-Feb-2013, 04:02
The edges of the plates sat on that internal frame that you speak of. The emulsion surface is located at that point.
Cut film is slightly narrower than the plates to allow for the edge of the film sheath but their is still sufficient overlap for the edge of the film to sit on that frame.
In terms of finding a backing for the film. Rigidity is more important to avoid flex than thickness. Picture glass cut to the correct size for the holders is probably favourite if you can stand the weight.
If you measure from that inward edge of that internal frame to the front face of the holder you are in for an interesting surprise. That distance is between 5 and 6 mm it varies depending on the size of the holders but their will generally be less than the proverbial thickness of a hair on a flies bollock difference between that measurement and the current ANSI specifications for modern film holders.
You are correct about the use of film sheaths placing the plane of focus too far back. You might just get away with it though depending on your choice of lens and aperture .Depth of focus is greatest for long lenses stopped well down and focused at shorter distances. The worst case scenario from a depth of focus point of view is a short lens used wide open focused at infinity. So for instance using a long portrait lens at portrait distances the depth of focus will be be more than sufficient to outweigh a mm or so misplacement of the emulsion surface.

Roger Hesketh
11-Feb-2013, 06:00
To illustrate my point as to whether it matters depends upon the use of the camera.

If one were to consider the use of a half plate camera. You might choose to use lenses of 4 inch focal length for wide angle work, 8 inches as a normal lens and one of 12 inches focal length for portraits.

Looking at a worst case scenario for each focal length lens used here on half plate. Focused at infinity and at the widest possible aperture depth of focus is as follows. (Circle of confusion 0.025mm)

With a 4 inch lens used at f11 the depth of focus extends 1mm either side of the point of principle focus, 1.3mm either side at f16. You may wish to consider placing the emulsion surface in the correct plane If you are careful you might just get away with it. If you use a wider aperture than f11 you definitely need to consider doing so.

8 inch lens at F4.5 also 1mm either side of principle plane of focus but you are unlikely to be using an aperture that wide with a lens of this length other than at portrait distances when depth of focus is much increased. Depth of field is 2mm either side if you stop down to F11 at that aperture a sheet of film placed 1mm away from principle plane of focus as in a film sheath would be acceptably sharp.

12 inch lens at f4 Depth of focus 1.1mm either side. A t f8 it is 2.2mm depth of focus either side of the principle plane of focus . Clearly their is no great need to be too fussy about where the emulsion surface is placed when using a lens of this focal length.

Given that it is so much more of a faff to load the book form holders with sheet film if you are not using a film sheath. Unless you are looking to take pictures with very fast wide angle lenses focused at infinity. Something I cannot ever remember doing. I personally would be inclined to to take a pragmatic view and use them and to rely on the depth of focus to take up the slack whilst mindful that the technique being used is not ideal but good enough.

Steven Tribe
11-Feb-2013, 07:11
Thanks for the analysis!

I have never found loading sheet film into sheaths larger than 5x7" that easy and keeping surfaces away from sticky fingers, even in a Harrison tent! Loading back plates behind the film was easier - but could have been easier if they fitted without some up and down and sideways movement. But there are differences in clearance between different book designs for the same format.

Roger Hesketh
11-Feb-2013, 09:06
Steven you are right for larger sizes a backing plate is much easier. Just a shame you cannot buy sheet film cut to the right size for book form holders only that cut for sheet film holders . I suppose you could always cut your own. I wish 5x7 film would fit in half plate ones. 5x7 is I think just a little smaller than 13x18 which is why it will fit in 13x18 holders.

I was wondering if I might ask a favour please. Would you mind measuring your 13x18 book form holders for me. As I am sure you know modern block form holders in half plate , 5x7 and 13x18 have the same external dimensions they just differ in their internal dimensions. They are all 150mm in width so can be used interchangeably in cameras that they will fit.

I am now for instance pretty sure that my '5x7' Gandolfi Precision made in 1970 was actually built to take half plate Eastman pattern double dark slides. The 150mm dimension came about as I am sure you know because that was the size used for the construction of half plate holders by Gandolfi ,Houghton and a number of other manufacturers .Thornton Pickard pattern holders are narrower.

I would be interested to know the size of the 13x18 holders to see if the size relationship extends further back in time. If they are the same external size as Gandolfi pattern half plate ones it might allow the use of 5x7 film in half plate cameras with book form backs as you say 5x7 will work in 13x18 holders. I have never heard of any 5x7 book form holders.

I have a half plate Sanderson built by Houghton which takes Gandolfi pattern holders . It really is an academic exercise at the moment as the camera is an early one with a square folded bellows and I need to sort the holes in the corners before I can use it. I would be interested to see if 13x18 book form holders might possibly fit it. Though I strongly suspect they wont. You never know till you try.

Steven Tribe
11-Feb-2013, 09:58
I have various 13x18 book holders and will do the exercise for you.
I know there are some differences in external sizes and engagement systems - but have never measured the "film/glass" square.
On a similarly note, I bought a couple of full-plate holders recently which have exactly the same external measurement of my most common 18x24 book holders!
So I have added a full plate camera to my ownership.

Steven Tribe
11-Feb-2013, 13:18
I found three sets, but I have more .... somewhere!

Basic external mahogany sizes are:

depths are: 17.5, 18.5 and 18.5mm.
widths are 154, 155 and 155mm.
Lengths are more varied - 207, 210 and 216mm.

Roger Hesketh
11-Feb-2013, 17:02
Thank you Steven for going to so much trouble, it is appreciated. Never mind. Nice result though for you with your new WP camera. Another benefit of your success is that I do not feel quite so daft as I might have done at this juncture for suggesting the possibility that the 13x18 cm holders might be the same external size in the first place. Cheers.

Steven Tribe
12-Feb-2013, 02:43
There is a very sensible e**y seller in the UK who has sold a lot of orphan mahogany plate holders recently. He has quite a lot of insight and measures up very well. This is where I found my 1/1 plate holders - made on the basis of an 18x24cm design.
It is obvious from his carefull measurements of, perhaps 20 different varieties, that there was an import of Continental holders, designed for tailboard/reisekameras originally, that have altered internal dimensions to meet UK requirements of 1/2 plate, 5x7" and full plate.

These book types are quite easy to modify for slightly different widths - the light-tight system is just velvet strips without light traps.

Roger Hesketh
12-Feb-2013, 08:09
I suspect I may know who you mean. Active on here and also on the UK forum?

A 5x7 DDS holder is an interference fit in that camera.

Whenever I get round to fixing up that camera to use seeing as the film register is just a little less than a mm out I will probably just use the 5x7 holder anyway and thicken it by sticking layers of tape on the bearing surface.

Once again thanks.

P.S. I also have a new whole plate camera. I found a WP insert in a 10x12 holder whilst unearthing forgotten treasures when up in the loft last night.

Steven Tribe
15-Feb-2013, 02:09
I have now developed 20 or so 18x24 and 13x18cm films mounted as mentioned.

Edges are certainly more attractive than sheet film holders and film sheath mountings.

Surprisingly square and the minimum edge "clamp" was just 1 mm - but enough!