Happy Sunday All -
So I've wanted a lightweight 6x12 for a hiking trip I'm taking to Norway coming up. After lots of work, I've gotten most of the items sorted and I took ahold of my first printed prototype. The printing process used is laser sintering. I've found the resolution to be superb (granular to below 0.3mm) and it's also very strong (for items printed with a thickness of over 2mm).
My main concern now is testing it to produce consistent results.
Curent Lens: Mamiya Press 50mm F6.3
Back: Horseman 6x12
I'd like to solicit some help with what and how to test. Testing is incredibly difficult. You've really got to be systematic and rigorous. I'd love feedback and criticism.
Some thing's I'm actively testing:
1) Distance from Focal Plane to Film Plane
My general philosophy here has been to use a longer lens, shooting at a short focal length and a fast aperture. Overall the goal is to have a very narrow DoF so that you can measure how far off you are.
I shot some preliminary shots and I could see that @ infinity, many of the items in front were in focus but infinite was not, so I knew that the lens to focal plane distance was too long.
My first real test - shoot a subject measured @ 8 feet away using my Mamiya Press 150mm F5.6. I setup a table with a black box against a white background (the box is an empty 4x5 box
). Then have a tape measure on its side. Have little black items mark each half foot in front of the black box. Shoot the first shot at 8 feet (which, if everything is perfect, then the black box should be in focus). Then focus the lens @ 9 feet. Then 10. Then 15.
Here's the first shot with the lens focused at 8 feet.
Here's the second shot at 9 feet.
I also shot with the lens at 10 feet and it's now out of focus.
Conclusion: Pretty sure 9 feet nails the focus here. The distance the lens travels from 8 to 9 feet is 1.3mm. So if I shorten the film plane to lens by 1.3mm, then my focus should be sharp. If my logic is off here, I humbly ask for criticism
2) Light Leaks
There are a few places where light could come in from:
1) Where the lens meets the body.
2) Where the horseman back meets the body.
3) The plastic that is being printed is porous. It looks black on the outside, but the inside is white (Shapeways paints it black for me). Direct sunlight could simply penetrate the body itself.
So I've come up with some a way of taping over certain parts, to potentially isolate where light is coming in. From my early photos, I can't detect any light leaks, which is good thing. I ran some more rigorous tests to isolate these, but every frame came out 100% overexposed (even when covering up the cracks from places #1 & #2 with gaffer's tape). So I suspect that place #3 is at play here.
I'll have to cover the entire body with gaffers tape to see what happens and if I've missed something. This is pretty disappointing though (just got the film back a couple of minutes ago). I suppose it's noteworthy that this only really happens in direct sunlight. Indirect sunlight won't do this.
Some thought for a remedy:
1) Cover the entire body in gaffers tape (ugly but easy and practical)
2) Cover it in some other material.
3) Add flocking (something I plan on doing) to the inside.
3) General structural strength
Overall it feels really solid. I designed an Arca swiss style plate into the body to act as a "foot" on the front so that it doesn't fall over and I can attach it to my ballhead. This is working well but it's a bit flimsy at the corners of the baseplate. I've redesigned and beefed up the mounts from the baseplate to the body.
4) Odds n Ends
I put a bubble level on the cold shoe and found that it wasn't dead center (using the bubble level on my tripod for that). What I think is happening is that the graflok style back is pushing up against the cold shot and flexing it (pointing it downward). I've changed that in my design. The good news is that when I put the bubble levels on the lens and on the back, they match, so I feel more confident that the film plane and the lens are perpendicular.
Thanks for the reading! If there are other methods of testing I should be doing, please let me know.