Large Format Projection Camera

meet the current iteration of my large format experiments. here is the basic idea:

frame

my current version consists of main body frame that the bellows bolt on to. the most recent improvement is the way the projection screen is held.

the previous iteration was two halves screwed together at the corners:

which meant that i basically had to dismantle everything to change the projection screen. the current version is in one piece that can take a projection screen frame sliding in from the side. here it is before before the second face is assembled. the dimensions of the recessed area are slightly over 30×40 to accomodate projection screens of those dimensions.

now, it can be slid out with everything else mounted. you can see here the fresnel lens. also, since this is an old screen, it has the old frame still attached and is covered in dust and glue residue.

here is the file containing pretty much all the pieces used in here.

all_parts.svg_Download

rigging

the rest of the frame is made from standard rigging components:

for rigging parts, avoid the cheap (< 5 EUR) 90 degree rod clamps. they suck. from left to right – smallrig (18 EUR, good), BGNing (3 EUR, total garbage), CamVate (11 EUR, perfectly acceptable)

also, there are relatively cheap “minifocus” branded 15mm rods available. those do NOT have the same threading as all the other ones. i have smallrig, lanparte, camvate, and a bunch of other 15mm rods and rod connectors, they are all happily compatible. the minifocus ones are not:

they still work fine in places where no extension is needed. i am using them for the horizontal crossbars like in this picture (this is the front with the lens board removed):

in the back, i am using a simple GFX cage mounted similar to the front- and back plate mounts the PU-leather is connected to the backplate and can be wrapped around the lens. this is more or less light tight. If you need absolute darkness inside, then you may want to check if this needs modification.

the back plate opening is 140mm – which should be plenty for most cases – for reference: the diameter of the laowa 17mm is 90mm, the zhongyi speedmaster 65mm is 82mm.

bellows

i got my bellows custom made from a shop in china. they were absolutely brilliant, and helped me a lot when i miscalculated some of the dimensions (and they refused to do it, saying that this probably was a mistake – and they were absolutely correct).

the bellows come without a frame. for mounting them, i have glued them to a frame, and this frame is screwed to another frame. so on top of the glue, the end of the bellows is held between these two frames (red and orange in the picutre). the second frame has the holes to mount it to the main body (green in the picture)

this here is the OLD screen holder with fuji gfx 50r and a zhongyi speedmaster 65mm. note that the back is extended quite precariously:

recording

I now mostly use the laowa 17mm lens. when misaligned, this gives much weirder effects, but when done corrently, it makes the overall thing a lot more compact (the distance between screen and lens can be <20cm, this lens is really amazing). however, this is not always good. consider this:

this is done with fresnel and ground glass – but the only change between the left one and the right one is that the left one was done with the laowa 17mm, the right one with the zhongyi speedmaster 65mm.

the laowa exaggerated the uneven illumination of this combination, and it also lead to more weirdness caused by inner reflections in the glass.

the zhongyi (the shot on the right) has none of these issues, but i had to extend the camera rods to get far away because of the speedmaster’s relatively long minimum focusing distance of ~70cm, so this is not possible without a second tripod to hold the end steady.

projection screen

i have tried different options – ground glass, ground glass + fresnel, frost filter, frost + fresnel. the last one has a tiny downside, which is that the lens pattern is sometimes visible (please ignore the fact that it is also very dusty, i am aware of that):

ground glass is by far worse than i was expecting. it does have a very nice grain-like texture:

but it also has very directional brightness, leading to very strong vignetting:

here is the assembled version of the frame with a fresnel / frostfilter projection screen. front bellows and a lens are mounted, but no bellows in the back.