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Merijn
13-Jun-2016, 23:16
Hey guys, I'm interested in building an 8x10 camera for portrait photography. This will be the first time I'm doing anything like this. I have access to a wood workshop and a laser cutter which is why I'm considering laser cutting many of the parts out of poplar plywood. I want the camera to be suitable for polaroid 8x10 since I live in the town where Impossible produces their film, it's an easy access source. Ideally the camera will also be useable with regular film or photographic paper though.

Anyway before I'm getting ahead of myself I'd like to identify all the parts of the camera that have an actual effect on the final image (assuming the basics of a light tight, shake free setup). I've been reading lots of old articles and watching lots of YouTube videos but there's always that gap between what you see and what you need to know to get it right.

As I understand it, the following parts will influence exposure, shutter speed and focus:


The lense and shutter assembly on the front
The length of the bellows (I actually understand how moving the lens back and forth focusses the image, I'm unclear on how bellows length affects shutter time)
The plane of the ground glass and the plane of the film need to be in exactly the same place. I've seen so many different setups ranging from combined fresnel lenses + hand sanded glass to people just using baking soda paper for a test. If you're using a 2mm plate of glass, does the film need to be flush with the front plane of the glass or the rear plane?
The pitch and yaw of the lens assembly affect depth of field


Another thing I'm wondering about is how does the film back ensure a light tight seal with the camera itself? In videos it usually just looks like a drawer that get's pushed into the camera. An overlapping edge covering the seams between the film slide and the camera. Is that really sufficient for a light tight seal?

Anyway I'm at the information gathering stage right now so any pointers you have are welcome. I'm also really interested in sourcing a suitable lense / shutter assembly, bellows and ground glass plate since I doubt I'll be making those myself.

LabRat
14-Jun-2016, 03:07
Building a LF camera for the first time can be difficult if you don't have a basis of the traditional features + design of cameras that has evolved over almost two centuries... And not having used one, it will be difficult to predict what features/ergonomics will be required to make the camera work for YOU...

I mentioned this here before, but is easier/faster/cheaper to use your skills to restore a existing camera, use it for awhile, and then start the design process to make your own once you know what you like/don't like from experience using the first camera...

The process will take awhile, and you can at least shoot/learn while the process evolves...

But don't let this stop you!!!

Steve K

jnanian
14-Jun-2016, 03:34
you might look at posts made by JoeV ( JoeVanCleave).
he has made 8x10 portrait cameras.

you might not have to deal with bellows and front standards with pitch/yaw but nested boxes.
i've made my fair share of cameras and none were more than a box
with a lens, with a focus screen with hand made film/paper holders.
portrait cameras don't have all the movements that view cameras have,
(look at examples of home portrait graflex, as well as rembrandt cameras )
camera movements are mostly for correcting for distortion ... sometimes portrait cameras had
rise and fall, sometimes, the back tilted a little bit to foreshorten a large nose but usually they
were just a box with a lens.

have fun !

Tim Meisburger
14-Jun-2016, 03:36
The length of the bellows (I actually understand how moving the lens back and forth focusses the image, I'm unclear on how bellows length affects shutter time)

Lenses are described by their maximum aperture and focal length at infinity. For example, a lens might be described as an f/4 200mm. What that means is (more or less) that when you focus a 200mm lens on a far object (more than 60 meters or so) the lens will be 200mm from the film plane (the focal length is 200mm).

Aperture is defined as focal length divided by the diameter of the hole in the lens. So, in our example, that would be 200/x = 4, so x (the diameter of the hole) = 50mm.

To focus on something closer than infinity, you need to move the lens farther away from the film plane. That clearly changes the focal length. Say, for example, we focused on something close, and then measured the distance between lens and film plane and it is now 400mm. At infinity focus the lens is an f/4, but if we have a focal length of 400mm, and a hole of 50mm, then our aperture for this case is f/8 (400/50 = 8). Keeping the same hole size, you will have to adjust shutter speed one stop less than shooting a subject at infinity distance to get the same exposure. There are tables available to tell you how much addition exposure you need to provide for a given bellows extension (called bellows factor table), but they are based on the change in aperture described by the simple equation above.


The plane of the ground glass and the plane of the film need to be in exactly the same place. I've seen so many different setups ranging from combined fresnel lenses + hand sanded glass to people just using baking soda paper for a test. If you're using a 2mm plate of glass, does the film need to be flush with the front plane of the glass or the rear plane?

Normally the frosted face of the ground glass will be against the frame, so thickness of glass does not matter. When you put the film holder in, the face of the film should be in the same plane that was occupied by the frosted face of the glass.


The pitch and yaw of the lens assembly affect depth of field

Not really. They change the plane of focus. Normally the plane is parallel with the film plane, but when you apply tilts you can modify the plane of focus so that it is tilted as well. In the most common application, this allows you to get a foreground and distant background in focus. A true plane has no thickness. Depth of field is the zone of acceptable sharpness on either side of the plane of focus, and you can think of it as adding thickness to the plane. When you tilt the plane of focus that thickness goes with it, but remains perpendicular to the plane.
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Another thing I'm wondering about is how does the film back ensure a light tight seal with the camera itself? In videos it usually just looks like a drawer that get's pushed into the camera. An overlapping edge covering the seams between the film slide and the camera. Is that really sufficient for a light tight seal?

Yes, its just a lip and a rebate. Light will not go around corners unless you have a reflective surface.

Anyway I'm at the information gathering stage right now so any pointers you have are welcome. I'm also really interested in sourcing a suitable lense / shutter assembly, bellows and ground glass plate since I doubt I'll be making those myself.

Randy
14-Jun-2016, 09:26
Merijn, I really think you need to get your hands on an actual large format camera. Size is not that important (that's what she said) as a 4X5 camera is just a smaller version of an 8X10. It would be very, very helpful to you if you could look at an actual camera on a tripod and play with it, perhaps observe an experienced photographer in action with one so you can ask questions about it's operation as it is being performed. I think you would come to a much better understanding that way.
Just my thoughts.

Merijn
14-Jun-2016, 10:08
Merijn, I really think you need to get your hands on an actual large format camera. Size is not that important (that's what she said) as a 4X5 camera is just a smaller version of an 8X10. It would be very, very helpful to you if you could look at an actual camera on a tripod and play with it, perhaps observe an experienced photographer in action with one so you can ask questions about it's operation as it is being performed. I think you would come to a much better understanding that way.
Just my thoughts.

Oh I plan on that. I don't intend to just design one from scratch without having ever seen one in person. I'm just unlikely to see one in action, I've found a few in my town but they're pretty much ruined. Metal work rusted shut, bellows so ragged I can see right through them, lenses looking more like fog than glass. Good for seeing the moving parts, useless for figuring out how each part affects the final result or calculating exposure.

Leszek Vogt
14-Jun-2016, 15:39
Unless your poplar is well seasoned (low moisture like about 8%), I'd look towards cherry or mahogany, which are more stable woods for this kind of project....even under weird humid conditions. But, the mahogany from Phillipines is not as stable as the one from Honduras. The best mahogany would be from Dominican Republic, but I have some doubts that you could get your hands on any of that.....urr, unless you dismantle an old Chippendale antique.... ;)

Les

Merijn
14-Jun-2016, 22:35
Unless your poplar is well seasoned (low moisture like about 8%), I'd look towards cherry or mahogany, which are more stable woods for this kind of project....even under weird humid conditions. But, the mahogany from Phillipines is not as stable as the one from Honduras. The best mahogany would be from Dominican Republic, but I have some doubts that you could get your hands on any of that.....urr, unless you dismantle an old Chippendale antique.... ;)

Les

Poplar plywood isn't a solid wood. It's basically layers of poplar glued together with each layer crosswise to the previous one. It tends to warp less than regular wood. Besides it's dirt cheap and I want to see if I can make something functional before dropping a bundle on exotic wood.

barnacle
15-Jun-2016, 11:00
Merijn, there are a number of build threads in this section which people have found useful as guides. Here's mine; smaller than you're looking for but the idea is the same. I don't claim it's perfect (in fact, I'm planning its replacement already) but it might be worth a look.

http://www.largeformatphotography.info/forum/showthread.php?128525-DIY-5x4-in-Sapele

Neil

jp
15-Jun-2016, 12:57
The length of the bellows (I actually understand how moving the lens back and forth focusses the image, I'm unclear on how bellows length affects shutter time)

It does not affect shutter time, but does affect exposure. Simple inverse square law in effect; move the lens away from the film and there is less light falling on a given area. There are calculators for bellows compensation.

I'll throw in a vote for buying a beater camera and using skills to fix it or build something based on it. The back which holds the groundglass and spring for holding the filmholder and not letting in light is best experienced not built double-blind.