Making my own 5x7 camera. HELP!

[ckpj99]

I've been shooting professionally for almost a decade. I have a degree in photojournalism, and understand the physics of light pretty well. I own too many film cameras.

That being said, I've never used anything larger than a 6x6 slr.

I started building a camera, not from different parts from major manufacturers, from wood and nails and glue. It's going to be a box camera, the type common in Cuba, India and Afghanistan. The basically have a tiny darkroom inside of them: a box of photo paper which is used as the "film," a tray of developing chemicals, and a tray of fix. You can get a lot of details on the cameras here - http://www.afghanboxcamera.com/ - if you haven't already heard of them.

I'm designing mine to shoot 5x7 piece of photo paper. I'm building everything myself except the trays and the lens. Needless to say, I have a few questions.

1) I'm thinking about mounting a 210mm lens in the camera. So my first question is this, will a typical 210mm designed for a 4x5 camera cover a 5x7? Keep in mind that my camera will have absolutely no movement. I believe most 4x5 lens account for movement. I'm asking now because I can still redesign the camera to shoot 4x6 is necessary. (Side question, is the 210mm an OK choice, I want a "normal" lens, like a 50mm on a 35mm camera)

2) These cameras have a built in copy stand. You expose the first image of your subject on photo paper which appears as a negative, then you take another exposure of that negative using a copy stand. I'm having trouble calculating two things. First, how far away copy stand must sit from the lens? It can't be too far away or too close, it needs to fill up another 5x7. Basically, I need the lens to subject distance for a 1:1 macro reproduction.

3) Furthermore, what is the distance required between the lens and the film for a 1:1 reproduction. I have at least 300mm of space for the lens to travel, but I want to make sure that's enough. (To restate in a different way, the minimum distance from lens to film will be 210mm, the maximum could be 510mm, is that enough?)

3) I'll be focusing on a groundglass and then putting my paper directly on to the groundglass to expose. So the surface of the paper will be slightly forward of the plane of focus. I'm also building the this focusing/film holding mechanism, so I'm wondering how perfect it needs to be. If the photo paper is leaning backward for forward say 2-3mm, am I going to get an extreme tilt-shift effect or is 2-3mm not a huge detail. I'm not looking for Linhof sharpness or accuracy, but I'd prefer the thing not to be a giant Holga.

4) Lastly, I need to buy a lens. I don't want to spend more than $300 and would prefer to spend half that. It doesn't need a shutter though it would be nice, and an attached board would be helpful (and if it doesn't have a shutter, it needs a good lens cap). KEH has a good selection of lenses in my price range, but it seems most have a DB mount and I'm not sure if that will work for my purposes. If the lens doesn't have an attached shutter, it just needs to be open so I can use a lens cap as the shutter (like back in the old-timey days).

The main purpose of this is to be something fun and perhaps to be used as an education tool. If it ends up producing really nice images, I may use it for a portrait series or a landscape series (hence the initial 50mm-equivalent lens).

You're welcome to call me crazy in your responses. I hope to have this thing knocked out in the next month. All of these problems are arising because all of the cameras I've seen in use produce small images, maybe 2x3 inches, so I'm upscaling a design and running into math problems. The build already has some blood and sweat poured into it. I was using a hole saw and it about ripped my arm off, lol!

Thanks in advance for all your help!

[polyglot]

Look at the info at the root of LFPF, ie not the forum. There are links to all the information you require, eg coverage circle diameters, extension/magnification formulae, etc.

For 1x magnification, the lens-film (and lens-subject) distance will be 2x the focal length. Do you plans to use the same objective lens to do the copying? If so, you might need to have a lot (210mm) of focusing throw to switch between objective (approx infinity) and copying (1x). Almost certainly simpler to do a contact print illuminated through the back of the original print/neg.

[sully75]

I know that I read about someone doing exactly the same thing, maybe on APUG but I'm really note sure. Probably 1 or 2 years ago, somewhere online. Like...exactly the same thing.

[ckpj99]

@polyglot - Thanks for the info. I'm obviously new to the forum/site. That info will be really helpful. I will be using the objective lens to do the copying. The idea is that this is supposed to be an "instant" camera. Doing a contact print to go from negative to positive is interesting, but seems like it would be extremely hard to do on site right after making the initial print. While my purposes may not require this, I'd like to stay true to form.

The way this camera works is that the focusing plane moves, not the lens. The focusing plane is on rails inside the camera. The camera is quite long to accommodate the developing equipment, so moving the focus plane from 210mm to 420mm isn't an issue. And now I have a really good idea of how long the copy stand needs to be. It will collapse and slide under the camera when not in use.

@sully75 - I'll look around APUG. This is definitely not an original idea. Finding someone who has built a 5x7 version would be extremely helpful. Thanks!

I've decided to vary the design a little. Instead of a door on the back and a "light-tight" sleeve on the side, I'm doing light-tight sleeves on both. The back one will have a bit a flare to it, so it can be rolled up and peered through for focus. My last design hurdle is creating a movable stop on the rails, I need to find some sort of little clamp or something.

Thanks for all your advice!

[E. von Hoegh]

http://www.largeformatphotography.info/

[Jim Jones]

It sounds like an interesting and time consuming project. My choice of lens would be a Kodak Ektar (or the older uncoated Anastigmat) f/7.7 203mm. This ancient design makes sharp images of both distant and near subjects. It is usually in a shutter, but sometimes available at low cost in barrel mounts for use on copy cameras. A shutter should be unnecessary. Exposures on photo paper might be around 1/4 second in bright sunlight with the lens wide open. This is easy to time by hand or with an improvised shutter. However, a 203mm lens would require about 812mm between negative and photo paper for a 1:1 copy. The 170mm version of this f/7.7 lens was used on large Kodak folding cameras, and may provide barely adequate coverage for your use in a more compact camera. Similar design lenses were available from other makers under other names. Many modern lenses in a convenient focal length have more than enough coverage, but cost more. The longer lenses make portraits that may be more pleasing to some customers.

Focusing on a ground glass is precise; but for such portraiture, focusing by scale may be adequate and certainly quicker. Use a scale for subject distance and another for focusing the lens. The scale for the subject need be no more than a string with markers at the distances for full length and head-and-shoulder photos. Fixed focus also works well for copying the negative.

[ckpj99]

Jim,

Thanks for the tips. There's a camera swap this weekend in my area, and I hope to find something there to test the system with. I can always upgrade to a better lens later.

812mm is not a problem. I can make the copy stand as long or as short as I need. The camera itself is 560mm (~22 inches) deep. The film/carrier will be able to slide all the way back to that distance, well, not quite, but within a cm of that distance. In theory, the camera could support a 280mm lens and still make a 1:1 reproduction.

As for focusing, this will all be done on the groundglass. My question was about the needed precision of the groundglass and carrier. I'm using wood and only moderately accurate tools. I'm curious as to how important it is to have the film plane perfectly parallel to the lens board. How drastically will the focus be affective if the film is tilted, say, 5 degrees.

Also keep in mind, that the 5x7 will be the final print size. There will be no enlarging.

I'm going to keep an eye out for that Ektar. I'm curious to see what turns up at the swap. I may end up buying something ridiculous just to get the lens out of it.

I'll keep everyone posted on this. I've designed and built several 35mm pinhole cameras, so I'm pretty sure I can get it done, this is just on a completely different level.

[sully75]

I think this process is not going to be super sharp...so I think you could get away with a little slop.

[TheDeardorffGuy]

Nails??? Really? Nails??
http://www.microfasteners.com/

[ckpj99]

Hey y'all. So construction is underway. Yes, I'm using nails, lol.

Here's what I came up with:



It's close to 24 inches long about about 12 inches tall and wide.

There are currently three holes in the box. You can see two in the photo. The one on the right/front is the lens hole, the one on the side is the access hole to move the focus plane. There's a third in the back opposite the lens hole. It's traditionally a door that opens for focusing. I'm making it a sleeve just like the side hole traditionally is.

The film/paper carrier will be a modified picture frame. I bought a 5x7 wooden frame that I'm going to cut to a size that fits in the camera. I took the glass out the frame and acid etched it to turn it into a ground glass. For those of you who are interested in acid etching this type of glass, leave the paste on for 5-8 minutes, not the recommended 1 minute. I know acid etching is not a good way to make ground glass, but it will work for my purposes.

What you can't see in this picture is the rails that run along the inside. The ground glass/film carrier deal sit atop and slide along those rails. You can see part of it through that side whole. Under those rails sits three things: the developer tray, the fix tray and the box of photo paper.

I'm not sure if anyone cares to read about my progress, but I'll probably keep posting things here. As I said, I'm heading to a camera swap on Saturday and I'm hoping to pick up a lens for this beast. My next goal is to make the film carrier thing. After that, I'll be added the collapsible copy stand to the bottom of the camera and hopefully added the lens soon!

Wish me luck!