Re: [pinhole-discussion] camera conversion question
Murray, I hope I understood your description (sometimes my ESL comprehension fails me miserably). You are considering (first) the 4 side of the bellows frame opening: Since the bellows do not end at the center of the lens (or pinhole for than matter) but beside the shutter, the angle between them and a perpendicular to either side of the 4 opening is irrelevant, the bellows will not vignette your image unless they sag beyond a line from the end sides of the 4 opening and the pinhole. If the aim is to get a 4x5 image by building an extension box, you should analyze the 3 size first, as the ratio 4 intended image size to 3 opening is greater than 5 image side to 4 opening. If you lower a perpendicular from the pinhole to the film plane, you'll have a triangle (let's call it A) with corners at: pinhole - middle of the 3 opening - end side of the 3 opening, you also have another triangle (let's call it B) with corners at: pinhole - middle of the 4 image size - end side of the 4 image size, since this 2 triangles have equal angles, we can write that: Base of A divided by Base of B = height of A divided by height of B Base of A is half the 3 opening = 1.5 = 38.1mm Base of B is half the image size width of 4 = 2 = 50.8mm height of A = bellows extension = 130mm height of B = height of A + extension box deepness EBD = 130 + EBD So you have: Base of A / Base of B = height of A / height of B 38.1 / 50.8 = 130 / (130 + EBD) EBD = (130 * 50.8 / 38.1) - 130 EBD = 43.33mm An extension box of 43.33mm will give you an image width of just 4, since my skills and tools to make cameras or modifications to existing ones aren't that great, I'd make it at least 46mm deep instead. A similar analysis can be made for the other side and the result would be 1.28 (close to your finding of 1.25), but since it this result is smaller, you have to use the larger one of 43.33mm, which is equal to just above 1.7 All the above could have been explained fast and nice with a simple drawing, but this is just an ascii posts only list. Guillermo - Original Message - From: Uptown Gallery mur...@uptowngallery.org Gutted some Polaroid rollfilm cameras with 130 mm lens/bellows. Extends a little farther than that due to 3.5 feet to infinity focus adjustment. Pulled lens, kept shutter for experimentation on one. Rear opening of bellows frame is a hair larger that 4 x 3. I took some measurements along 4 axis and calculated a 22 degree angle for the bellows. From this I figured I need a 1.25 entension box to get a 5 image. I didn't calculate or measure the short side yet...might be different due to aspect ratio of 4:3 differing from 5:4. Gonna try ground acrylic instead of glass. Question is, with a pinhole I should have adequate coverage, but do you think my anticipation of angle will prevent 'vignetting' by the bellows or rear of the camera (existing opening?) Thanks Murray ___ Post to the list as PLAIN TEXT only - no HTML Pinhole-Discussion mailing list Pinhole-Discussion@p at ??? unsubscribe or change your account at http://www.???/discussion/
[pinhole-discussion] camera conversion question
Hello: Gutted some Polaroid rollfilm cameras with 130 mm lens/bellows. Extends a little farther than that due to 3.5 feet to infinity focus adjustment. Pulled lens, kept shutter for experimentation on one. Rear opening of bellows frame is a hair larger that 4 x 3. I took some measurements along 4 axis and calculated a 22 degree angle for the bellows. From this I figured I need a 1.25 entension box to get a 5 image. I didn't calculate or measure the short side yet...might be different due to aspect ratio of 4:3 differing from 5:4. Gonna try ground acrylic instead of glass. Question is, with a pinhole I should have adequate coverage, but do you think my anticipation of angle will prevent 'vignetting' by the bellows or rear of the camera (existing opening?) Thanks Murray
Re: [pinhole-discussion] Guillermo's 5 lp/mm optimum design
Hi all, Speaking of small pinhole cameras: a manufacturer of laser drilled pinholes once sent me a 0.001 pinhole good for an optimal focal length of under 0.5mm!! I couldn't possible make a camera with such focal length. I just read Michael Crichton's new novel called 'Prey' in which there is a company trying to manufacture pinhole cameras using nanotechnology. Needless to say it all goes horribly wrong, worth a look though if you like that type of thing. Cheers, Tim _ Help STOP SPAM: Try the new MSN 8 and get 2 months FREE* http://join.msn.com/?page=features/junkmail
Re: [pinhole-discussion] Guillermo's 5 lp/mm optimum design
- Original Message -
From: HypoBob hypo...@pacbell.net
Guillermo,
In a posting on 13 December you stated that an 8x10 pinhole image rivaling
the resolution of a lens image (i.e., 5 lp/mm) could be obtained with a
focal length of 120 mm or less and the optimum pinhole.
Since one could place any size negative material in such an arrangement,
aren't you in effect saying that a 120 mm focal length is the maximum for
obtaining 5 lp/mm resolution?
Yes, but those 5 lp/mm are on the film which is more often than not and
intermediate step to the final result, the latter being, more often that
not, a positive print. So although the resolution you may have on your
35mm format made with the optimum size pinhole 50mm body cap is better than
5 lp/mm when you enlarge it to 8x10 you will get a print with just about 1/8
the resolution on film. If you didn't have to enlarge and view the print at
the normal distance of comfortable vision, then, the 5 lp/mm are enough.
Now, if you make a 16x20 pinhole camera and view that print at a distance
equal to twice the normal distance of comfortable vision, you will then
only need 2.5 lp/mm on the print, in which case 480mm focal length would be
the maximum.
Is there also a minimum focal length for this resolution?
Not mathematically, but practically there is. For a given format, there is
a minimum limit of the focal length that would acceptably cover the film
format, as well as there are practical limits forced by how small a camera
we can make, a manufacturer of laser drilled pinholes once sent me a 0.001
pinhole good for an optimal focal length of under 0.5mm!! I couldn't
possible make a camera with such focal length.
Do you have some equations you can share with us that give the
relationship between resolution, focal distance, and pinhole size? I'm
guessing
that this all may be based on the usual equations with a properly chosen
value for the circle of confusion.
Resolution = 1 / (1.22 * wavelength * fstop)
if you use wavelength = 0.00055mm, it becomes:
Resolution = 1490 / fstop
Assuming you know the resolution and want to know what fstop would give you
that resolution:
fstop = 1490 / resolution
but, fstop is also equal to:
fstop = Focal length / pinhole diameter
and:
pinhole diameter = 0.03679 * SQRT(Focal length) {units in mm}
therefore:
fstop = Focal length / (0.03679 * SQRT(Focal length)
or also written as:
fstop = 27.1813 * SQRT(Focal length)
therefore:
Focal length = ( fstop / 27.1813 )^2
How did I get 120mm as the maximum focal length I talked in my post?:
I started with the need of 5 lp/mm, therefore:
fstop = 1490 / resolution
fstop = 1490 / 5
fstop = 298
Focal length = ( fstop / 27.1813 )^2
Focal length = ( 298 / 27.1813 )^2
Focal length = 120mm (aprox)
In any event, it seems that the conditions will hold only 'near' the
center of the image because the corners and edges are beyond the optimum
focal
distance.
That is true, but you could have a semicircular film plane with the pinhole
in the center of the semicircle, in which case the distance pinhole film
would be constant (in one axis, at least). Make the film plane half an
sphere and you will get same distance everywhere on the film plane :-)
Also, I'm thinking that you may be assuming a certain viewing distance for
the observer since smaller images tend to be held closer to
the eye than do larger ones. That is, the 8x10 size may be necessary to
get the viewer to hold the 5 lp/mm print about 20 inches from his eyes
rather than the 12 inches at which he may hold a smaller 5 lp/mm print.
That is correct.
Thanks for getting me off onto this tangent. I always enjoy your posts,
Thanks, I enjoy posting them, it keeps my brain from getting rustier.
BTW, corrections to the above are welcome.
Guillermo
[pinhole-discussion] Guillermo's 5 lp/mm optimum design
Guillermo, In a posting on 13 December you stated that an 8x10 pinhole image rivaling the resolution of a lens image (i.e., 5 lp/mm) could be obtained with a focal length of 120 mm or less and the optimum pinhole. Since one could place any size negative material in such an arrangement, aren't you in effect saying that a 120 mm focal length is the maximum for obtaining 5 lp/mm resolution? Is there also a minimum focal length for this resolution? Do you have some equations you can share with us that give the relationship between resolution, focal distance, and pinhole size? I'm guessing that this all may be based on the usual equations with a properly chosen value for the circle of confusion. In any event, it seems that the conditions will hold only 'near' the center of the image because the corners and edges are beyond the optimum focal distance. Also, I'm thinking that you may be assuming a certain viewing distance for the observer since smaller images tend to be held closer to the eye than do larger ones. That is, the 8x10 size may be necessary to get the viewer to hold the 5 lp/mm print about 20 inches from his eyes rather than the 12 inches at which he may hold a smaller 5 lp/mm print. Thanks for getting me off onto this tangent. I always enjoy your posts, Bob
Re: [pinhole-discussion] Human eye
Ahh, thanks for the explanation. g Cheers - george (knuckle dragger) --- Alan Cangemi ac-t...@msn.com wrote: Ahhh, George, Now I see the confusion. The old style brains (those used before 1985) did in fact see lights as individual frames. But the modern brain, especially those in people born after 1986, see light as a continuous stream. Even though the old style brains are still manufactured and used (mostly for economic reasons.the new styled brains cost 4 times as much) most people nowadays are using the new brains. It's easy to spot those with new and old styled brains.the old style recipients tend to drag their knuckles when they walk upright. Sorry for the confusion, George. Best regards. Alan (old style) Cangemi - Original Message - From: George L Smyth glsm...@yahoo.com To: pinhole-discussion@p at ??? Sent: Monday, January 06, 2003 8:56 PM Subject: Re: [pinhole-discussion] Human eye Well, you'll need to speak with my Physiological Psychology teacher of 30 years ago, as that is what our textbook said. We do not see things as continuous streams, but as frames. Cheers - george --- Alan Cangemi ac-t...@msn.com wrote: George. The brain DOES NOT take in light similar to a movie camera's film mechanism. It sees light as a continuous stream. It is only through mechanical processes that wheels appear to be turning backwards whilst the vehicle is moving forward. So there! sreehC Alan - Original Message - From: George L Smyth glsm...@yahoo.com To: pinhole-discussion@p at ??? Sent: Monday, January 06, 2003 5:53 PM Subject: Re: [pinhole-discussion] Human eye While light does stream in continuously, the brain takes it in similar to a movie camera's film. This is why you may see a bicycle's tires appear to move backwards as it goes forwards. Cheers - george --- erick...@hickorytech.net wrote: Another thing occurs to me. The camera analogy is also limited by the fact that camera shutters open and close, while light streams into the human eye continuously. The operative 'shutter speed would have to be the duration of exposure to the rod or cone required to trigger nerve conduction. I don't know whether there is a trasmission period followed by a refractory period, which would equate to shutter speed, or not. - Original Message - From: erick...@hickorytech.net To: pinhole-discussion@p at ??? Sent: Sunday, January 05, 2003 11:30 AM Subject: Re: [pinhole-discussion] Human eye Here is some information I have. How it applies I'm not sure. The eye is only the aperture, lens and sensing apparatus. Because the eye is attached to the brain it would make more sense to use a digital camera as a model rather than film camera. The mind can read an image and give a response in as little as 0.04 seconds- a professional pingpong players response time, for instance. Nerve transmission time mind to brain can be measured by measuring cortical evoked potential responses to visual stimuli. I might have once know the limiting values but I don't recall them. A big name in research in this area is Meichenbaum, if you want to look it up. As for aperture, the lens to retina distance is roughly 25 mm. Maximum pupil size, i.e. aperture diameter, is maybe 8 mm in an adult, so the maximum F stop would be 25/8= 3.1. Minimum aperture would be about 25/2 for 'pinpoint pupils, an F stop of 12.5. I think that the eye processes light sensation somewhat differently at low light levels, so film speed would be a guess. Remember too that the eye and brain cannot distinguish as separate images any sequence more rapid than about 14/second. That is the basis for movies and television, sequences of still images projected faster than the eye can distinguish, thus blending them into apparent continuous motion. I- Original Message - From: George L Smyth glsm...@yahoo.com To: pinhole-discussion@p at ??? Sent: Sunday, January 05, 2003 10:53 AM Subject: Re: [pinhole-discussion] Human eye On 22 Jul 2002, at 11:16, eco...@aol.com wrote: I know this is not strictly pinhole, but I wondered if anyone had access to the average human eye values for the camera variables. ie Respective - film speed, shutter speed, aperture, focus range, depth of field etc. Thanks Ellis When I looked into shutter speed many years ago, I came upon the conclusion that the eye's shutter speed is approximately 1/100 second. You can verify this by taking
Image Vision was Re: [pinhole-discussion] eye camera
Hello Pete, Believe it or not, I had the intuition 2 days ago, reading the Human eye thread, that you, Pete, would post something about it and here it comes ! Why did I think of the intervention of a blind photographer ? Just because the discussion was slowly but surely expanding from a question about the Image to a question about the Vision , and when it comes to Vision we all know that visually impaired and/or blind people have a lot to say... While writing this , I just cannot prevent myself from quoting some lines of the back cover of Evgen Bavcar' s book Le voyeur absolu. Evgen Bavcar is a Slovenian born (Vojke Flis, if you are still on this list, you probably know him!) blind photographer living in France since the 70's; he is also a universitary researcher in philosophy and aesthetics. Here is my translation for the question he rises in his book : This exceptional experience [a blind man taking photographs] leads to this essential question : Would not be - before any other thing - photography, a mental image of the world, and only that ? An effect of sensuality, for which the print would only constitute a secondary phenomenon ? Human eye ? Pinhole camera ? Image ? Vision ?... 2003 begins with all these questions and, I'm sure, 2003 will end with all these questions ;-) Let's share our Visions, let's share our Images Cheers from France Jean - Original Message - From: pete eckert peteeck...@mindspring.com To: pinhole-discussion@p at ??? Sent: Monday, October 14, 2002 5:10 AM Subject: [pinhole-discussion] eye camera Hello All, The discussion comparing the eye and camera has been interesting. Here is a spin on it for you. There has been some projects going on to replace damaged retinas with implants. A few of these projects involve sending pictures to a receiver in the eye. The projects have the blind community very excited. I as a blind photographer may someday be able to see my own work. Pete ___ Post to the list as PLAIN TEXT only - no HTML Pinhole-Discussion mailing list Pinhole-Discussion@p at ??? unsubscribe or change your account at http://www.???/discussion/
Re: [pinhole-discussion] Human eye
Ahhh, George, Now I see the confusion. The old style brains (those used before 1985) did in fact see lights as individual frames. But the modern brain, especially those in people born after 1986, see light as a continuous stream. Even though the old style brains are still manufactured and used (mostly for economic reasons.the new styled brains cost 4 times as much) most people nowadays are using the new brains. It's easy to spot those with new and old styled brains.the old style recipients tend to drag their knuckles when they walk upright. Sorry for the confusion, George. Best regards. Alan (old style) Cangemi - Original Message - From: George L Smyth glsm...@yahoo.com To: pinhole-discussion@p at ??? Sent: Monday, January 06, 2003 8:56 PM Subject: Re: [pinhole-discussion] Human eye Well, you'll need to speak with my Physiological Psychology teacher of 30 years ago, as that is what our textbook said. We do not see things as continuous streams, but as frames. Cheers - george --- Alan Cangemi ac-t...@msn.com wrote: George. The brain DOES NOT take in light similar to a movie camera's film mechanism. It sees light as a continuous stream. It is only through mechanical processes that wheels appear to be turning backwards whilst the vehicle is moving forward. So there! sreehC Alan - Original Message - From: George L Smyth glsm...@yahoo.com To: pinhole-discussion@p at ??? Sent: Monday, January 06, 2003 5:53 PM Subject: Re: [pinhole-discussion] Human eye While light does stream in continuously, the brain takes it in similar to a movie camera's film. This is why you may see a bicycle's tires appear to move backwards as it goes forwards. Cheers - george --- erick...@hickorytech.net wrote: Another thing occurs to me. The camera analogy is also limited by the fact that camera shutters open and close, while light streams into the human eye continuously. The operative 'shutter speed would have to be the duration of exposure to the rod or cone required to trigger nerve conduction. I don't know whether there is a trasmission period followed by a refractory period, which would equate to shutter speed, or not. - Original Message - From: erick...@hickorytech.net To: pinhole-discussion@p at ??? Sent: Sunday, January 05, 2003 11:30 AM Subject: Re: [pinhole-discussion] Human eye Here is some information I have. How it applies I'm not sure. The eye is only the aperture, lens and sensing apparatus. Because the eye is attached to the brain it would make more sense to use a digital camera as a model rather than film camera. The mind can read an image and give a response in as little as 0.04 seconds- a professional pingpong players response time, for instance. Nerve transmission time mind to brain can be measured by measuring cortical evoked potential responses to visual stimuli. I might have once know the limiting values but I don't recall them. A big name in research in this area is Meichenbaum, if you want to look it up. As for aperture, the lens to retina distance is roughly 25 mm. Maximum pupil size, i.e. aperture diameter, is maybe 8 mm in an adult, so the maximum F stop would be 25/8= 3.1. Minimum aperture would be about 25/2 for 'pinpoint pupils, an F stop of 12.5. I think that the eye processes light sensation somewhat differently at low light levels, so film speed would be a guess. Remember too that the eye and brain cannot distinguish as separate images any sequence more rapid than about 14/second. That is the basis for movies and television, sequences of still images projected faster than the eye can distinguish, thus blending them into apparent continuous motion. I- Original Message - From: George L Smyth glsm...@yahoo.com To: pinhole-discussion@p at ??? Sent: Sunday, January 05, 2003 10:53 AM Subject: Re: [pinhole-discussion] Human eye On 22 Jul 2002, at 11:16, eco...@aol.com wrote: I know this is not strictly pinhole, but I wondered if anyone had access to the average human eye values for the camera variables. ie Respective - film speed, shutter speed, aperture, focus range, depth of field etc. Thanks Ellis When I looked into shutter speed many years ago, I came upon the conclusion that the eye's shutter speed is approximately 1/100 second. You can verify this by taking successive pictures of a waterfall. We all know that slowing down the shutter speed to a second or more will make for silky water, which is not what we see. From there, take pictures with faster and faster speeds (don't forget to take notes). When
