Ugly Hedgehog - Photography Forum
Home Active Topics Newest Pictures Search Login Register
Main Photography Discussion
Pinhole lens information.
Page 1 of 3 next> last>>
May 19, 2018 15:28:17   #
DaveC1 Loc: South East US
 
I've been playing with a pinhole lens I made from a 0.35mm pinhole I purchased from EBay, a M42 metal screw on body cover, and a Nikon M42 to F converter. What I'm going to present is the math to determine the f stop of an pinhole lens and an easy way to use it with a light meter.

First of all the focal length is the distance between the point of convergence in your lens to the sensor or film in your camera. In the case of a pinhole lens that point of convergence is the pinhole. So in the case of the Nikon F mount the focal length of a pinhole mounted as I have is approximately 50mm, give or take.

So what does that make the f stop # for this pinhole lens? The f stop is equal to the focal length divided by the aperture. In my case with a 0.35mm pinhole and with a 50mm focal length its 143.

So how do I use that with a light meter since none of my light meters go up to f stop 143? If you do a 1/2 stop series spreadsheet starting at 1 you find 143 falls in between f stop 128 and the next 1/2 stop of 152.2. Rounding up to 152.2 I have found that there is a conversion factor between f2 and f152of 5400 so if your light meter gives you a reading of f2 at 1/60" multiply that shutter speed by 5400 resulting in 5400/60=90" By the same token a light meter reading at f22 has a conversion factor of 45. So if your light meter gives a shutter speed of 2 seconds at f22: 2"*45=90". Both readings are EV 8 by the way.

I'm certain that there are other ways to arrive at shutter values for such high f stops this is just one way. This method works for me and results in good exposures.

Comments welcome.

Reply
May 19, 2018 15:42:04   #
RWR Loc: La Mesa, CA
 
DaveC1 wrote:
I've been playing with a pinhole lens I made from a 0.35mm pinhole I purchased from EBay, a M42 metal screw on body cover, and a Nikon M42 to F converter. What I'm going to present is the math to determine the f stop of an pinhole lens and an easy way to use it with a light meter.

First of all the focal length is the distance between the point of convergence in your lens to the sensor or film in your camera. In the case of a pinhole lens that point of convergence is the pinhole. So in the case of the Nikon F mount the focal length of a pinhole mounted as I have is approximately 50mm, give or take.

So what does that make the f stop # for this pinhole lens? The f stop is equal to the focal length divided by the aperture. In my case with a 0.35mm pinhole and with a 50mm focal length its 143.

So how do I use that with a light meter since none of my light meters go up to f stop 143? If you do a 1/2 stop series spreadsheet starting at 1 you find 143 falls in between f stop 128 and the next 1/2 stop of 152.2. Rounding up to 152.2 I have found that there is a conversion factor between f2 and f152of 5400 so if your light meter gives you a reading of f2 at 1/60" multiply that shutter speed by 5400 resulting in 5400/60=90" By the same token a light meter reading at f22 has a conversion factor of 45. So if your light meter gives a shutter speed of 2 seconds at f22: 2"*45=90". Both readings are EV 8 by the way.

I'm certain that there are other ways to arrive at shutter values for such high f stops this is just one way. This method works for me and results in good exposures.

Comments welcome.
I've been playing with a pinhole lens I made from ... (show quote)

Pinhole lens??

Reply
May 19, 2018 16:07:08   #
DaveC1 Loc: South East US
 
RWR wrote:
Pinhole lens??


Yes, check it out. This is the lens (and I use that term loosely) that many of the early, and home brew, cameras used.

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2060353.m570.l1313.TR0.TRC0.H0.Xdslr+pinhole+lens.TRS0&_nkw=dslr+pinhole+lens&_sacat=0

Reply
 
 
May 19, 2018 16:14:46   #
DirtFarmer Loc: Escaped from the NYC area, back to MA
 
Personally I think that when talking about pinholes, the words "lens" and "focal length" should be in quotes since they are virtual parameters for a pinhole. Probably "f/ stop" also.

Reply
May 19, 2018 16:20:02   #
DaveC1 Loc: South East US
 
DirtFarmer wrote:
Personally I think that when talking about pinholes, the words "lens" and "focal length" should be in quotes since they are virtual parameters for a pinhole. Probably "f/ stop" also.


If that were the case I would not have any measurements on which to base the math which works nicely. You do have a point of convergence and you have a distance from that point to the sensor. You also have a ratio between the aperture and that distance. Just because its much more simple than a glass lens does not mean it doesn't function as a lens, which it does.

Reply
May 19, 2018 16:38:24   #
RWR Loc: La Mesa, CA
 
DaveC1 wrote:
Yes, check it out. This is the lens (and I use that term loosely) that many of the early, and home brew, cameras used.

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2060353.m570.l1313.TR0.TRC0.H0.Xdslr+pinhole+lens.TRS0&_nkw=dslr+pinhole+lens&_sacat=0

Very loosely. Have you seen this one?
https://petapixel.com/2017/05/31/heres-worlds-first-multi-aperture-pinhole-lens-dslrs/

Reply
May 19, 2018 18:12:38   #
newtoyou Loc: Eastport
 
Look up book by Eric Renner. Aquire one. Read it. You now have answers.enjoy

Reply
 
 
May 19, 2018 18:18:41   #
DaveC1 Loc: South East US
 


I have not, interesting.

Reply
May 19, 2018 18:31:21   #
newtoyou Loc: Eastport
 
Shop.Remember, this is a Pinhole less is more. 10$ will get you a fit for .your camera 10$.Go from there.

Reply
May 19, 2018 18:43:20   #
rgrenaderphoto Loc: Hollywood, CA
 
DaveC1 wrote:
Yes, check it out. This is the lens (and I use that term loosely) that many of the early, and home brew, cameras used.

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2060353.m570.l1313.TR0.TRC0.H0.Xdslr+pinhole+lens.TRS0&_nkw=dslr+pinhole+lens&_sacat=0


These are a lot of fun.

Reply
May 19, 2018 18:52:30   #
newtoyou Loc: Eastport
 
THEY TEACH PHOYOGRAPHY. How about Brady work in digital. I think not.

Reply
 
 
May 19, 2018 18:56:06   #
BebuLamar
 
DaveC1 wrote:
I've been playing with a pinhole lens I made from a 0.35mm pinhole I purchased from EBay, a M42 metal screw on body cover, and a Nikon M42 to F converter. What I'm going to present is the math to determine the f stop of an pinhole lens and an easy way to use it with a light meter.

First of all the focal length is the distance between the point of convergence in your lens to the sensor or film in your camera. In the case of a pinhole lens that point of convergence is the pinhole. So in the case of the Nikon F mount the focal length of a pinhole mounted as I have is approximately 50mm, give or take.

So what does that make the f stop # for this pinhole lens? The f stop is equal to the focal length divided by the aperture. In my case with a 0.35mm pinhole and with a 50mm focal length its 143.

So how do I use that with a light meter since none of my light meters go up to f stop 143? If you do a 1/2 stop series spreadsheet starting at 1 you find 143 falls in between f stop 128 and the next 1/2 stop of 152.2. Rounding up to 152.2 I have found that there is a conversion factor between f2 and f152of 5400 so if your light meter gives you a reading of f2 at 1/60" multiply that shutter speed by 5400 resulting in 5400/60=90" By the same token a light meter reading at f22 has a conversion factor of 45. So if your light meter gives a shutter speed of 2 seconds at f22: 2"*45=90". Both readings are EV 8 by the way.

I'm certain that there are other ways to arrive at shutter values for such high f stops this is just one way. This method works for me and results in good exposures.

Comments welcome.
I've been playing with a pinhole lens I made from ... (show quote)


What I do is to assign your f/143 as 14.32 that is 14.32 stops from f/1.0. Now if the meter is reading EV8 I subtract 14.32 from 8 and the answer is -6.32 and it means your exposure time is 6.32 stops more than 1 second. So doing 2^6.32 would give me 79.9 seconds.

Reply
May 19, 2018 19:17:03   #
DaveC1 Loc: South East US
 
BebuLamar wrote:
What I do is to assign your f/143 as 14.32 that is 14.32 stops from f/1.0. Now if the meter is reading EV8 I subtract 14.32 from 8 and the answer is -6.32 and it means your exposure time is 6.32 stops more than 1 second. So doing 2^6.32 would give me 79.9 seconds.


Much more precisely, since I rounded up to the next stop, but yes.

Reply
May 19, 2018 19:25:41   #
newtoyou Loc: Eastport
 
I was fortunate in having a dslr body to assign to pinhole. The math escapes me, but by applying sunny 16, I extrapolated and experimented till I had decent results. The results are worth it.

Reply
May 19, 2018 19:55:25   #
BebuLamar
 
What I am trying to point out is that the math is very simple and it's easier to do than other methods.

Reply
Page 1 of 3 next> last>>
If you want to reply, then register here. Registration is free and your account is created instantly, so you can post right away.
Main Photography Discussion
UglyHedgehog.com - Forum
Copyright 2011-2024 Ugly Hedgehog, Inc.