7x17 pinhole construction.....

[scootermm]

I posted this over at LFphoto.info but would love any additional ideas you all might have. Im new to this forum.

Im interested in designing/building a 7x17 pinhole camera with the end result being contact printing the images. Im interested in it being a fairly wide angle (of course) and perhaps holding only a single sheet of film at a time or maybe trying to design a way to mount a 7x17 film holder. does anyone have any experience with creating and making cigar box cameras and/or pinhole cameras in the larger than normal formats (7x17 etc)?

The basics Ive been able to determine are that a pinhole creates an image circle of about 150degrees therefore an image circle of 20inches would be created if the focal length (dist from pinhole to film plane) is about 6inches. the pinhole (from reading some links and websites) should be about .5mm in size. does this sound correct or even close to anyone? I realize that because of the large size of the film there may be dramatic light fall off and vignetting in the corners and edges of the resulting negatives but this is partly the endearing quality of it for me. I like the resulting look.

basically Ive come up with a design that would employ a 20inch wide by 7 inch deep by about 7-8 inch tall box with the abiliity to change out the pinholes on perhaps a removeable holder of some simple design. what are anyones thoughts on this or perhaps similiar experience in creating something like this...... also.... in regards to actually using a lens what are good focal length lenses that might work for a fixed focus box camera like this in the 7x17 format? Im thinking along the lines of barrel lenses and the like because the exposures will like need to be fairly long I would assume.
any thoughts on this would be appreciated.
thanks in advance.

 

[glbeas]

With such a format you might try a camera with a curved back that the film is clipped to in some fashion. This will get the panorama effect without the distortion and light fall off of a flat film plane.

 

[shinn]

At Mrpinhole.com you’ll find a great calculator, it gives coverage, f-stop and exposure information. Lenoxlaser.com carries a variety of pinholes that are laser drilled and crisper than hand punched or drilled pinholes. I think they are worth the money unless one desires a softer image.

You should be able to get good coverage with 7X17 as long as your focal length and pinhole size is correct. I’m not sure that 7inches deep will provide the coverage you need (10-12in may work) you’ll have to punch the numbers into Mr. pinholes calculator to find out. I’ve also found that the exposure calculator works well.

I use film holders with my pinhole cameras and think one might be disappointed with only one shot. There are many ways to build these things, I have 5 and their all different. Normally though, I’ve used a hinged back with latches on the camera and foam in between the hinged back and another thin sheet of wood (this keeps the foam from pushing on the dark slide) to keep pressure on the film holder and works great for me.

Happy Days

 

[removed account4]

hi there -

i saw your post on lf.info, i'm glad you posted here too

i began building a 8x20 pinhole camera out of black foam core. it is about 7/10 finished . like you, i surfed a bit to fine info, and i also contacted someone when i was doing my research on the pinhole size &C. i was told that a pinhole projects an image about 3.5 x its focal length.

my camera is kind of based on the mandelette post card camera ... it includes a way to remove exposed paper in the field and slide it under the camera's base where there is the equivalent of a tank and a place to store unexposed paper within the camera. there is a long sleeve with a glove at the end which is rolled up when the camera is being used --- my arm is in it when i am doing the "exposed under & unexposed paper loaded shuffle" ... i don't have a tripod mount, but a barrel vault of corrugated material under the camera - so i can set it down and it stays put, even at an angle ( like a big bean-bag)

while it is really not too hard to make pinholes, i never made them, instead i bought a set from minute aperture ( you can also get pinholes or a zoneplate from eric renner at http://www.pinholeresource.com). the pinholes are laser cut to a specific diameter / focal length, and there is an f-stop relative to f64 so you can get a light meter reading and expose your film or paper accordingly.

sounds like a fun project -
good luck
john

 

[scootermm]

john gary and shinn
thank you all so much for all the advice. I ordered about three aluminium pinhole plates from lenoxlaser.com in varying sizes yesterday so they should be in sometime next week. Im thinking of trying to "put" together a mock up of the design I have thus far this weekend. also ordered a box of 25 sheets of 7x17 Efke film from jandcphoto.com so I should be able to hopefully make some exposures in the coming weeks.
the 3.5xFocal length is about the ratio that seems consistant. Im going to have to experiement because I keep reading that there is a magic ratio for pinhole size to focal length that creates the sharpest image. so I may have to adjust my pinhole sizes and focal length until I get a good result. Im contemplating making the design in two sort of boxes, sort of like a gift box..... with the bigger lid being the part with the pinhole and the smaller one fitting inside it to have the film. that way the focal length can be easily adjusted etc.
overall it should be an interesting project and Im anxious to get to the end result to see the outcome.
again thanks for all the advice and info. if anyone has anymore of any similiar experiences Im always open to ideas/critiques/etcetc.

 

[removed account4]

hi again

the gift box idea is really good
my brother made me a 8x10 pinhole kind of like that -
the back end has a handle and slides back&forth within the box of the camera. just make sure you baffle the part that slides with something to keep the light out ...

if you use paper first, a good starting iso is about 6 ( unless you use azo which is something like 6-8 stops slower )

good luck!
- john

 

[Jim Jones]

john gary and shinn
. . . Im going to have to experiement because I keep reading that there is a magic ratio for pinhole size to focal length that creates the sharpest image. . .

The calculator at Mrpinhole.com gives close to the pinhole size I've found to be correct for optimum on-axis sharpness with panchromatic film. The formula I derived from calculation and testing gives the pinhole diameter as the square root of the focal length multiplied by .007 (all diminsions in inches). For 7x17 film a 7" focal length seems awfully short. A 9" focal length will have about two stops less exposure in the corners than in the center, and a considerable fall-of in corner sharpness. The pinhole diameter will be .021" and the aperture f/429.

 

[Joe VanCleave]

Scootermm, this sounds like a neat project. And the link provided by jnanian regarding the Mandallete camera was interesting.

I've built several pinhole cameras using the "falling plate" principle, which may also be a solution to your need for multiple large format negatives in one box. My version of this design uses matteboard film holders, stacked in the rear of the camera. Each holder has a notch, or series of notches, along the top or sides, which alternate with each holder. A light-tight mechanical sliding linkage allows the front-most holder to fall face-down into the bottom of the camera, with a little encouragement by tilting the box forward. The next film holder is thus revealed, ready to shoot.

My 8x8 version, using 8x10 paper negs or sheet film, holds 12 sheets. It has slots on both sides of the holders, interlocked by sliding linkages on both sides, operated by knobs. The problem with this design is if you don't operate both knobs simultaneously (up or down direction), the front holder falls crooked and gets hung up.

My 5x8 version, which holds 10 sheets, corrected this fault by using a single sliding linkage on top, which interlocks slots cut into the top of each holder.

Other operating limitations with the falling plate design is that your focal length has to be longer than the film holders are tall. Which wouldn't really be much of an issue with your panoramic format. The other issue is you've got to transport and handle the box in an upright position, otherwise the fallen film holders could get all topsy turvy in the box and jam the rest of them from falling properly.

Overall, however, I've gotten used to these issues, and find that having a dozen LF negatives already loaded in a box to be a refreshing way to do pinhole, especially scenic locations, where you are far from home.

As to the optimal pinhole size: making it too small - that is, going beyond optimal - doesn't necessarily make the images blurrier, as the increased diffraction from the too small aperture is being made up for by improved geometric effects of the too-small hole. My experience is going moderately beyond optimal you'll find the sharpness platues off, with no real improvement or loss. The real problem is that your exposure times just suffer too much, as reciprocity gets to be a real bear.

Good luck, keep us posted.

 

[Dave Wooten]

Hey Scooterman,

are you going for a more portable set up? Just wondered as you could just make some pin holes for your 7 x 17 camera and have several focal lengths?

A general rule of thumb is multiply the focal distance by 3 to minimum acceptable coverage....150 mm therefore should cover nicely i.e. 6 inch lens should cover 18 inch circle...

To me to curve the film is interesting however, part of the charm of the pinhole camera is its unique perspective, also IMHO positives from curved negs are best viewed as curved...

an interesting comparison project, would be to see one of your 7 x 17 lens photos also taken with the pin hole using the same focal length for both...