Author Topic: pinhole minimum focal length..  (Read 6690 times)

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db

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pinhole minimum focal length..
« on: May 22, 2007, 07:25:44 AM »
So, how low can you go??

Before the image starts to fall apart I guess. I know that a pinhole is capable of stupendous wide angle, but at what point does it all start to go pear shaped.

I'm a pinhole novice, but theres nothing like pushing the envelope, so for example, if I was to make a 5x4 film box (what's that.. maybe 1/2'' deep??) into a camera, for 5x4 obviously, am I just being silly?


Francois

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Re: pinhole minimum focal length..
« Reply #1 on: May 22, 2007, 08:02:08 AM »
I guess with such dimensions, you're bound to get plenty of vignetting... and a very wide angle of view.

I used the Pinhole Designer (http://www.pinhole.cz) to calculate it would give you a picture taking angle of 162?14'50" :)
(by the way, the program is freeware)
But on the upside, pinholes don't theoretically induce distortion in the image (but if your pinhole isn't round, it will)

Now, for the vignetting issue... lets do a bit of geometry ;)
We all know light gets weaker the further it has to travel (inverse square law anyone)...
But lets not get into calculations but more into drawings.

Take a used sheet of paper, a ruler and a compass. Draw on the sheet your camera's size viewed from the side (side view of the film to one side, pinhole on the opposite). Put an X where the pinhole would be. Use the compass and draw a half circle in the rectangle with a radius the equivalent of the box thickness (pinhole to film distance) having its central point in the pinhole. Notice anything? The circle is very small in the center. This is where exposure would be evenly distributed. A large part of the sheet would be pitch black, but you would get an extreme wide angle.

Now do the same thing with a different size box. The results would be different. In extreme pinhole telephoto lengths, light falloff will be negligible if the film size is relatively small.

I hope the demo explains the workings of the camera more clearly... (at least, that's how I calculate the stuff)
You'll also get to understand why many like curved film surfaces (it minimizes the vignetting)
Francois

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al

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Re: pinhole minimum focal length..
« Reply #2 on: May 22, 2007, 09:03:07 AM »
As the focal distance gets smaller, the optimum pinhole diameter gets smaller too and it gets tricky to make an accurate enough hole (maybe easier with a laser, but we don't have one of those in our sewing box).  The matchbox pinhole is about half an inch deep, and that requires a pinhole less than 0.2mm to be optimal.

Someone made a matchbox pinhole with a slim box which I think was 8mm, which gave a massive angle of view on 35mm film. I'll try to find a link to the photos on flickr.

I once tried a pinhole made from a 5x4 film box about 1/2" deep, ended up with a circular image around 1.5" diameter in the middle of the sheet, the vignetting was so severe that most of the film area was wasted. 




astrobeck

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Re: pinhole minimum focal length..
« Reply #3 on: May 22, 2007, 11:46:48 AM »
I once tried a pinhole made from a 5x4 film box about 1/2" deep, ended up with a circular image around 1.5" diameter in the middle of the sheet, the vignetting was so severe that most of the film area was wasted. 

I've had similar experiences with short focal lengths and homemade boxes. The shallowest 4 x 5 box I've managed well is 1.5 inches.
Another consideration is how fast the shutter speed needs to be for such a short distance....but I use my finger or tape and not a mechanical shutter to  allow the experience of pinhole to be even more organic.

 :)

db

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Re: pinhole, and aust foto festival
« Reply #4 on: May 22, 2007, 07:18:42 PM »
Great answers- thanks pinholers!

Yes, I expected severe fall-off, but didn't know how large it would be. The curved film plane is a very good point. I'm now thinking of trying a small can, and perhaps even a paper neg for lower sensitivity..

I have enrolled in a pinhole workshop at next month's Daylesford Foto Biennale- I can't wait. http://dfb05.tripod.com/07/

This is a month long festival of workshops, seminars and endless exhibitions, set in picturesque rural Victoria. As well as obligatory digital subjects, many topics focus on alternate wonders such as Pinhole, Cyanotypes, Vandyke, Bromoil, Photogravure, Ziatype, Ultra large format, Fine art printing etc... If you're thinking of a trip down-under in a year or two, maybe look out for the '09 program before you book.

Ed Wenn

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Re: pinhole minimum focal length..
« Reply #5 on: May 23, 2007, 03:34:47 AM »
Don that festival sounds like a LOT of fun. Another reason for me to get my shapely butt back to Australia. Do let us know how you get on...and of course post some pinhole efforts here in due course.
Ed's Blog: Filling a Sieve -:- Ed's Bands: edwenn.com

filmwast

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Re: pinhole minimum focal length..
« Reply #6 on: May 25, 2007, 05:59:02 PM »
Don that festival sounds like a LOT of fun.

Maybe we need a fw trip to Aus? I might be able to find an excuse to make the journey. I here the beer there is cold at least. As for pinholes? Show us the results! Please...

astrobeck

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Re: pinhole minimum focal length..
« Reply #7 on: May 25, 2007, 08:23:21 PM »
Maybe we need a fw trip to Aus? I might be able to find an excuse to make the journey. I here the beer there is cold at least. As for pinholes? Show us the results! Please...

Yes, I could go for some down under sky myself   :)

db

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Re: pinhole minimum focal length..
« Reply #8 on: May 25, 2007, 10:11:51 PM »
OK. All FW's welcome.  I'll put my hand up to be tour guide. You have two years to get your shekkels together -or two weeks for this year's..  ;)

I'll post up dates for the '09 when the program is released.

db

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Promised results
« Reply #9 on: June 04, 2007, 10:56:39 PM »
Don that festival sounds like a LOT of fun.

Maybe we need a fw trip to Aus? I might be able to find an excuse to make the journey. I here the beer there is cold at least. As for pinholes? Show us the results! Please...

OK, on the sensible advice I receieved here, I backed away from the extreme short focal length and gaffered my 5x4 pol back to a Ilford Multigrade paper box. I also lifted the lid slightly before taping that in place, so the focal length was extended from the original 30mm height of the box, out to nearly 50mm.

Here's  this afternoons first and only sheet of film- old type 59- heh- you'd think it was tungsten balanced! A snap of my office front door.

Note that the angle is pretty wide, (gate just over a metre from the camera) and while it has some fall-off, it covers the whole sheet nicely. Being a Diana shooter, fall-off is a desirable factor in my eyes :)

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artpunk

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Re: pinhole minimum focal length..
« Reply #10 on: June 05, 2007, 01:02:38 AM »
Nice result Don!
You'll be bringing this camera to Daylesford?
Sorry I missed the Q & A session, but it looks like you sorted it.
I found distortion gets more freaky the closer to the subject you are, at least with my Holga pinhole, see below; Tulip from approx 10cm, Eggs from approx 5 cm.

I'll put my hand up to be a  guide in 2009 as well, by then I might have saved enough to attend all the seminars and workshops I wanted to attend this year too!




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Ed Wenn

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Re: pinhole minimum focal length..
« Reply #11 on: June 05, 2007, 03:20:34 AM »
Don/Cameron, lovely shots, thanks for posting.

Don, FWIW from someone as lowly as myself, I really think you should pursue this pinhole thing now that you've proved the setup. I can't wait to see what you do with it.

BTW, what did you use for a pinhole? on thsi shot? I have 3 spare Pola backs and there are always boxes lying around....then there's the pile of 5x4 Pola sheet film under my booze cupboard that I only use in my Graph Check these days. Might be more fun to use some of it in this way instead for a change.
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db

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Re: pinhole minimum focal length..
« Reply #12 on: June 05, 2007, 04:42:13 PM »
BTW, what did you use for a pinhole? on thsi shot? I have 3 spare Pola backs and there are always boxes lying around....then there's the pile of 5x4 Pola sheet film under my booze cupboard that I only use in my Graph Check these days. Might be more fun to use some of it in this way instead for a change.


Now don't go being all techy on me and be asking for my effective f- number or anything. I poked an average sewing needle through a coke can, is all I can tell you. It's on the largish side for a pinhole- maybe .3- .5 of a mm. I like the idea of hand-holding them, just in case they're too sharp ;) The beauty of shooting 'roid of course is you don't have to blow a whole roll at the wrong exposure while you're working it out.... 0only a single sheet is worth almost as much as box of TX :-/

I pinned up a holga body while I was at it an I leave for my pinhole odyssey tomorrow..

moominsean

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Re: pinhole minimum focal length results!
« Reply #13 on: June 08, 2007, 02:06:33 PM »
well, how's this for close. propack back, cardboard and aluminum foil...didn't want it to be fancy, just functional, as i have other plans for the back. i tried a couple different pinhole sizes, and finally used a real pinhole that came with a 35mm kit i bought. that's the shot with me as an alien. interesting experiment and kinda fun, but too hard to control. only wasted 10 bucks worth of polaroid doing this! ugh. distance from pinhole to film is about 3/4-inch (around 1.5 cm). you could get closer, but i think you'd just end up with a very tiny photo surrounded by black. type 664. anyway, now you know...
oh, i blogged my short adventure. http://moominsean.blogspot.com/
sean

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