Saturday 19 December 2009

Fitting a Maxwell Hi-Lux screen to a Chamonix 045N-1

I really have been slack when it comes to Blogging – there always seems to be too much 'other stuff' to do. But the time has come to make more of an effort and get some more words written before Tim Parkin covers EVERY photographic topic. I'll try and make a post or two a week from now on, they might not be overly deep and meaningful but hopefully of some use to some people out there.

So, to kick off I wanted to post some details of how I adapted my Chamonix 045N-1 to fit a Maxwell Hi-Lux screen. My decision to take the plunge and get a Maxwell screen was prompted by the much talked about (in Large Format circles) focusing problems with the standard supplied fresnel screen which was causing out of focus photos when they appeared in focus on the ground glass, particularly at bigger apertures. This is clearly not good! When you choose a to use a large format camera you do so in the hope that your transparencies are going to be as sharp as anything out there, 1mm of error focusing could easily compromise this.

I'd always wanted to upgrade to a Maxwell screen anyway just for the improved overall brightness, having now been out and used the camera with the Maxwell I have to say it's a huge improvement, it's a whole new level of brightness. For me it means I can sell my heavy Nikkor 90mm f/4.5 lens and replace it with a smaller and cheaper f/8 as I don't think I'll have any problem seeing and focusing successfully. The very fine fresnel circles are also much less intrusive than those of the standard Chamonix fresnel which also helps with focusing.

The problem is that the Maxwell screens come with a cover glass which is 1.8mm thick, this means that the replacement Maxwell screen isn't just a straight swap, the problem being that the four metal fittings that hold the glass in place don't lay flat on the new, thicker cover glass. (pic1)

Now it is possible to screw the existing clips in place with the new cover glass fitted – the screws just about bite into the wood and the retaining clips sit at an angle. My advice is DON'T do this! In my haste to get out and try the new screen, I did and two of them ended up falling off without me noticing, resulting in my lovely new Maxwell falling to the ground and getting permanently scratched – not happy! Even if you can get the clips to stay in at an angle you'll find that the screen protector plate won't hold in place because the grooves in the retainers will be at an angle and the protective cover needs these to be parallel to hold. Hugo was kind enough to get me some replacement clips and screws sent over from the Chamonix factory.

So this leads me to this Blog – an explanation of how I converted the retaining clips so they sit properly against the new Maxwell cover glass and hold everything in place securely and we can use the protective cover again.

The answer is to cut a small bit of the metal retainers away to accommodate the new cover glass – a pretty simple job that only took me about half an hour to do.

The first step was to drill a hole in an off-cut of wood which would snugly fit a retainer clip, I drilled it just deep enough to leave the retainer sticking out by the amount I wanted to remove (I had to drill a couple of holes to get this right as you can see from the pic (pic2). I held the block steady in my vice. I used a 12mm forstner bit to drill the holes as they leave a smooth, flat bottomed hole. I used the screw that holds the retainers in place on the camera to hold it in place in the hole (pic 3). I found that there was still a bit of movement to ended up G-clamping the retainer in place too.

Right – time for some butchering!

I used a thin metal cut off disc in my Dremel (pic 4). These things are pretty fragile so expect to get through a couple in the process of cutting the chunks out. If you haven't got a Dremel I suppose you could use a small hacksaw to do the cutting – the Dremel makes it much quicker and easier though.

First I cut downwards – you don't really need to do any precise measuring and marking to determine where to cut, as long as you're removing enough material it doesn't need to be precise. I cut just to the side of the screw hole, leaving just a bit of metal between the cut and the hole (pic 5). I then cut horizontally to remove the chunk – as I'd set the retaining sticking out by slightly under the thickness of the cover glass (which is 1.8mm) I just cut level with the wood block, removing the correct amount to retainer metal (pic 6).

This leaves a rough chunk removed from the clip (pic 7) , the next job was to smooth the cut up, I used an abrasive disc on the Dremel first (pic 8) and finally used a needle file to do the final finishing (pic 9). You can be as neat about this as you like – you can't actually see the new cut surfaces when they are re-attached to the camera so if you're lazy like me, you'll do just enough to take any sharp edges off. That's the clip done – now all we need to do it put them back on the camera.

I filled the existing screw holes with a bit of wood calved down to a point – a match stick will do (pic 10). I then cut it off level with a knife (pic 11). All that's now left to do is put the screen in place and screw the clips back on, leaving a nice level retaining clip and a securely attached Maxwell screen! (pic 12)

An added bonus of using a Maxwell screen in that there's a recess left on the inside of the ground glass where the old fresnel used to be housed. I find this is a great place to slot masks – I almost always shoot square these days so I made a square mask out of some thin black plastic sheet, I can bend it slightly and clip it in where the fresnel used to be – this works excellently as the out facing surface where you focus is free to focus on, unaffected by the mask. The mask is easy to remove by just removing the screen back and popping it out. (pic 13).