Though I usually work with 4"x5" format film. Unfortunately It is a complex medium for experimenting, So I coupled a 2 1/4 inch black tube to my digital. My objective was to compare the images at f 180 against f 240 images that were obtained by focal length and aperture changes.
The focal plane location is marked on my camera body, so by setting a .018" (.475 mm) pinhole about 3.23" (82 mm) from the focal plain, I obtained by f 180 goal. Next I moved the .018 aperture to 4.315" (110 mm) to the end of the tube for about my desired f 240. This is about one full f stop smaller.
Photo DB 180 cls shows the .018" pinhole adjusted for an f 180 image.
DB f 180 cls
Photo DB 240 ext shows the .018" pinhole extended to an f 240 image.
DB f 240 ext
You will note that moving the .018 pinhole to the end of the tube increases the projection distance so a smaller portion of the image falls on the digital sensor. This gives a pseudo telephoto image.
With some difficulty I was able to make a .014" (.346 mm) pinhole.
DB f 240 cls
When set at the f 180 distance of the .018" pinhole, the .014" pinhole also makes an f 240 in photo DB f 240 cls.
I will let you be the judge. But when enlarged to full image; I believe as expected, both of the f 240 images are sharper than the f 180. I also think the f 240 made with .014" pinhole is a tad sharper than the f 240 made by extending the .018" pinhole to the end of the tube. However, cropping the f 240 image of the .014" pinhole, to match the image size of the f 240 of the .018" pin hole might make a difference.
All these photos are "as shot" from about the same position in my yard on a variable cloudy day. I used my Cannon digital set on a tripod with a 2 second delay and the Auto setting. The ISO was 3200 the exposure varies around 1/25 sec.
I hope you find this helpful.
The focal plane location is marked on my camera body, so by setting a .018" (.475 mm) pinhole about 3.23" (82 mm) from the focal plain, I obtained by f 180 goal. Next I moved the .018 aperture to 4.315" (110 mm) to the end of the tube for about my desired f 240. This is about one full f stop smaller.
Photo DB 180 cls shows the .018" pinhole adjusted for an f 180 image.
DB f 180 clsPhoto DB 240 ext shows the .018" pinhole extended to an f 240 image.
DB f 240 extYou will note that moving the .018 pinhole to the end of the tube increases the projection distance so a smaller portion of the image falls on the digital sensor. This gives a pseudo telephoto image.
With some difficulty I was able to make a .014" (.346 mm) pinhole.
DB f 240 clsWhen set at the f 180 distance of the .018" pinhole, the .014" pinhole also makes an f 240 in photo DB f 240 cls.
I will let you be the judge. But when enlarged to full image; I believe as expected, both of the f 240 images are sharper than the f 180. I also think the f 240 made with .014" pinhole is a tad sharper than the f 240 made by extending the .018" pinhole to the end of the tube. However, cropping the f 240 image of the .014" pinhole, to match the image size of the f 240 of the .018" pin hole might make a difference.
All these photos are "as shot" from about the same position in my yard on a variable cloudy day. I used my Cannon digital set on a tripod with a 2 second delay and the Auto setting. The ISO was 3200 the exposure varies around 1/25 sec.
I hope you find this helpful.
