Building my own camera

[Robin H.]

Today, out of curiosity, I took an old zoom lens apart that I had lying around. While doing this I was thinking "what if I would build a camera around one (or more) of these separate elements?". So I have a few questions about how I should approach this.
First of all, how can I determine the focal length of these lenses?
I'd like to build a simple box camera with a fixed focus. I'm not looking for technically perfect images so vignetting, soft images and a wide array of aberrations aren't a concern, I would just like something that is fun to build and use!
I also would like to use 5x4 (if the lenses would cover it) so any tips about making the film insert lightproof would be great. I think I'd like to add a ground glass too, which I'll probably be making myself.
This is the first time I'd build a camera and I don't really know what I should specifically ask, so all kinds of advice are welcome!

 

[John Koehrer]

Jbrunner has a youtube about determining focal length. You could use paper negatives to experiment with exposure since you're looking at 4X5.
The ISO of paper tends to be around 3-6.
Check the forum about pinhole cameras and f295.com What you're doing is basically that type camera.

 

[Poohblah]

It's super easy to determine focal length. In a dark room, open up a window that has a view to the horizon or else something very far away (effectively infinity) and focus the lens onto an index card. When the horizon or other distant object is in focus, the distance between the lens and the index card is the focal length. Of course, if the lens is several millimeters thick, you won't get an exact FL, but it will be close enough. Also, this won't work for concave lenses, only convex, but I doubt you'll be incorporating convex elements anyway.

If you're making a fixed focus camera, a simple viewfinder like the fold-out style on Speed Graphics might be easier, unless you're already going whole hog and using film holders & darkslides.

This sounds like a fantastic project, have fun!

 

[Robin H.]

John, I really enjoyed that video! So it turns out that the focal length is ~ 115mm and the aperture around F2.1. There are already a few more things that I'm considering to add to the design such as the ability to use waterhouse stops, which should be very easy to make myself. Do they have be inserted at the nodal point, or doesn't that really matter?

There's also a way that I could somehow have a limited focus range. In the pictures you'll see a threaded cylinder which screws into the barrel that holds the lens. Now if I were to attach this piece to the lensboard I would we able to move the lens an inch further away from the film plane, thus allowing me to focus to a closer distance. Could anyone tell me how I can calculate the distance to which I would then focus? That way I can decide if it's worth the trouble or not to use this piece.

As a final question, can anyone recommend a good place to buy cheap film holders? (yes I checked eBay) Or if someone has some extra holders lying around that could use a loving home, I'm willing to adopt!

If I keep adding more features, I'll probably end up building a fully featured field camera...

 

[Denverdad]

There are already a few more things that I'm considering to add to the design such as the ability to use waterhouse stops, which should be very easy to make myself. Do they have be inserted at the nodal point, or doesn't that really matter?

I don't think the precise location relative to any of the cardinal points is going to matter much. Instead it all comes down to a more basic choice - whether you place the stop in front of, or behind the lens. My understanding is that one will give you barrel distortion , while the other will give you pincushion distortion. It is mostly an aesthetic choice as to which is preferable, although there may be mechanical reasons why one or the other ends up being easier to implement for your particular case.

This link has some discussion of the effect of the aperture location for a meniscus lens.

 

[Mark Fisher]

I made a simple sliding box camera doing pretty much what you are doing. I took the general ideas from Alan Greene's book, Primitive Photography and improvised. I made it to use standard 8x10 holders and ground glass focussing. Here are the images of the camera and an image or two taken with it (you may need to log into flickr to see the link.....not sure). If you open the individual pictures, there is a description of what the image shows.