Intrepid pinhole focal length

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Nebular89

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Just got the intrepid pinhole for the 4x5. It says it’s a 150mm focal length. Just to double check, does that mean that the pinhole has to be 150mm from the film to work as intended?
 
I suppose it does. I'd never really thought about the technicalities of focusing something where nothing is actually out of focus; on the other hand, if they give you an approximate aperture, that would be based on 150mm distance,
 
Nebular89 said:
Just got the intrepid pinhole for the 4x5. It says it’s a 150mm focal length. Just to double check, does that mean that the pinhole has to be 150mm from the film to work as intended?
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At 150mm from the film it will give a relatively normal FOV (similar to a 150mm lens) but it will work at other distances. The optimum diameter of a pinhole is a function of it's distance from the film, so it will work best at 150mm, but it should be reasonable over quite a range, possibly showing issues by 100mm bust give it try.
 
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StephenM said:
I suppose it does. I'd never really thought about the technicalities of focusing something where nothing is actually out of focus; on the other hand, if they give you an approximate aperture, that would be based on 150mm distance
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Yea, I’ve never really thought about it. I’ve had a zero 2000 before, it didn’t occur to me when I bought it
 
Petrochemist said:
At 150mm from the film it will give a relatively normal FOV (similar to a 150mm lens) but it will work at other distances. The optimum diameter of a pinhole is a function of it's distance from the film, so it will work best at 150mm, but it should be reasonable over quite a range, possibly showing issues by 100mm bust give it try.
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That’s what I thought. I did message them but they never got back
 
My intrepid pinhole has a diameter of 0.5mm (the design may have changed since I got mine). At 150mm the f number is 300 (focal length / diameter) and at 90mm it is 180. So the focal length will have a significant effect on the required exposure. I make sure to take this account but don’t worry too much about whether I’m using the optimum length. If I wanted maximum sharpness, I wouldn’t be using a pinhole.
 
Kevin Allan said:
My intrepid pinhole has a diameter of 0.5mm (the design may have changed since I got mine). At 150mm the f number is 300 (focal length / diameter) and at 90mm it is 180. So the focal length will have a significant effect on the required exposure. I make sure to take this account but don’t worry too much about whether I’m using the optimum length. If I wanted maximum sharpness, I wouldn’t be using a pinhole.
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Im glad you mentioned the f stop being 300. On their website its listed as being 280 at 150mm even though it says its 0.5.
Yes the exposure was my biggest concern. I dont want a lot of sharpness, I've a soft spot (no pun intended) for pictorialist landscapes. I like how it they can look like drawings. I've had similar results from my 120 pinhole camera but I found it too wide, I think it was about 20mm on full frame
 
Nebular89 said:
I've had similar results from my 120 pinhole camera but I found it too wide, I think it was about 20mm on full frame
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One of the things I like about using the Intrepid as a pinhole camera is the ability to use longer focal lengths / narrower angle of views compared to most commercially available pinhole cameras. I've never understood why there is such a trend for having very wide angles of view on pinholes.
 
Kevin Allan said:
One of the things I like about using the Intrepid as a pinhole camera is the ability to use longer focal lengths / narrower angle of views compared to most commercially available pinhole cameras. I've never understood why there is such a trend for having very wide angles of view on pinholes.
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Best get a tape measure so I can get the f stop right!
Maybe so it’s easier to get what you want in frame. I was able to find a 20mm viewfinder for a hot shoe that used to use
 
I came across the bit in my 'camera reference' spreadsheet that covers pinholes on Friday but then couldn't find this thread again (the link to TP seems to have disappeared from the computer at work...)
Having got back home the thread is easily found but I don't have the spreadsheet!

One factor I didn't see on Karl's link above is that the optimum pinhole size is actually wavelength dependant. It's usually determined for ~555nm (the wavelength the human eye is most sensitive to) I'm considering trying to take UV & IR photos with a pinhole, so the difference might be useful :)


Now I've been able to combine the the right url with access to my spreadsheet, I can give a tiny bit more info in case it's useful to others.

The optimum focal length is apparently the square of the pinhole diameter multiplied by a fiddle factor based on wavelength.
The factors I have noted are:
750 for 550nm (normal vision)
1124 for 370nm (UV)
647 for tungsten lighting
561 for 750nm IR
443 for 950nm IR

(Units for focal length will be the same as those used for the diameter).

My notes also suggest pinholes with a focal length of 90mm should cover 5x4 & coverage appears to be linear with focal length.
 
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