[ PINHOLE CAPTURE BEHIND THE SCENE | RSS 6X17F + ND64 + ACROS II / 510 PYRO ]
The main challenge for all pinhole photographers is achieving the correct exposure. Because of the teeny-tiny hole that lets light through, pinhole photography requires longer exposure times, making it difficult to get the perfect exposure without clear guidance. Some manufacturers provide exposure tables to work with light meters, and there are phone apps that can help with this.
However, this article is for minimalist pinhole photographers who prefer a simple approach without extra gadgets. This article will guide you through a straightforward process using a light meter reading and a simple conversion factor to calculate the correct exposure for all your pinhole cameras. Let’s get started!
Know The Focal Ratio of Your Pinhole Camera
- The focal length for your camera is from the back of the camera to the rear of your pinhole, measured in millimeters and designated as ‘F.’
- The size of the opening of the pinhole itself is called ‘d‘.
- F/d = focal ratio
- You need to know this number to figure out your exposure.
- Example: 200mm (focal length) / 0.5 (pinhole opening size) => 200/0.5 = F/400
- If you purchase a ready-made pinhole or pinhole camera, the maker will supply its d-number.
- For example, my pinhole d-numbers for my pinholes and cameras are:
- RSS 6×17 = 0.30
- 4×5 Titan (2 lens cones) = 0.30 & 0.50
- CCB Hasselblad Pinhole Caps = 0.25, 0.30, 0.35, 0.40 & 0.45
- Suppose you do not know your d-number for your pinhole, xerox a copy of the pinhole and measure from the copy with a millimeter ruler. If it is too small to measure, make several copies, paste them together, and then measure and divide by the number of copies (ex: 3x copies = (1+1+1)/3 = N). If you can scan the pinhole and measure it in Photoshop, that may also work.
Ready Made Pinholes & Supplied Focal Ratio Numbers
- The maker will supply its F-Number if you purchase a ready-made pinhole camera.
- I have two pinhole cameras and various Hasselblad V pinhole lens caps; all F-Numbers were supplied:
- RRS 6×17 = f/233
- 4×5 Titan (2 lens cones) = f/230 & f/290
- CCB Hasselblad Pinhole Cap + 0.35 pinhole = f/220
[ THE RSS 6×17 CAMERA BACK MARKED WITH EXPOSURE FORMULA ]
How to Calculate Exposure Once You Have The Focal Ratio
- Most light meters can read @ f/128, but typical pinhole cameras need a larger focal ratio.
- This method uses your light meter reading at f/128, the largest f/stop meters have.
- I will show how I got to the conversion factor of @F/128 x 3.3 for my RSS 6×17 camera above.
- I set my ISO and took a meter reading at f/128 (2 sec)
- The formula is: (focal length/128)² x N => where N is the light meter reading @ f/128
- Using focal length f/233, we divide by 1/128, square it, then multiply by 2 sec
- Here is the formula again: (focal length/128)² x N
- Math inside the parentheses first, then square result, multiply by N
- (233/128)² x 2 = (1.8203)² x 2 = (3.3135) x 2 = 6.627 sec
- (233/128)² = (3.3) is the conversion factor for this camera only and will not change
- The light meter reading of 2 used in this example will change with each different light value
- On my camera, I have taped: @F/128 x 3.3
- Conversion factor 3.3 applies only to this camera; run through the equation for each camera.
[ CUSTOM CAMERA BUILDING HASSELBLAD PINHOLE CAP & PINHOLES ]
Ready Made Pinholes for Hasselblad V Cameras
I have been a Hasselblad V shooter for decades. It was my workhorse system in the portrait and special event business. It is only natural for me to keep using these cameras for other than commercial work. They have excellent quality Zeiss lenses, and I can count on the Hasselblad system to perform. When I found pinholes made for the V system from Custom Camera Building (CCB), I had to try them out. The set includes a body cap that holds interchangeable pinholes in diameters of 0.25mm, 0.30mm, 0.35mm, 0.40mm, and 0.45mm pinholes—0.35mm is the average size for the set. CCB supplied this data: focal length with 0.35mm pinhole is 77mm, and f-stop is 220 => (77/0.35). = 220.
The Hasselblad 500 series cameras’ flange focal distance is approximately 74.9mm. Now to convert my 501cm camera into a pinhole camera, this distance would be roughly the effective focal length of the pinhole “lens,” assuming the pinhole is situated where the lens would normally be mounted, which it is when it is installed on the supplied body cap. It looks like the CCB cap and pinhole insert add 2.1mm to the focal length bringing it to 77mm. Where am I going with this …
I calculated the compensation factor for 0.25mm, 0.30mm, 0.40mm, and 0.45mm pinhole f-stops for meter readings taken at f/128 using the conversion equation (f-stop / 128)². I printed them on card stock, mounted them to thin cardboard, added “meter @ F/128” on the reverse, and placed it in the case containing all the pinholes. When I shoot my Hassy with a pinhole installed, after setting up the shot using my CFE 80/2.8 lens, I take a meter reading at f/128 and then adjust the light meter reading by the conversion factor on the card for the specific pinhole. I average conversion factors to the nearest whole number without exposure consequences. My standard technique for black & white film development is semi-stand, and using an average factor for exposure works for my development method. YMMV.
|PINHOLE SIZE||FOCAL LENGTH ÷ PINHOLE SIZE||(F/STOP ÷ 128)²||CONVERSION FACTOR|
|0.25||77/0.25 = f/308||(308/128)²||5.79 = 6|
|0.30||77/0.30 = f/257||(257/128)²||4.03 = 4|
|0.35||77/0.35 = f/220||(220/128)²||2.95 = 3|
|0.40||77/0.40 = f/193||(193/128)²||2.27 = 2|
|0.45||77/0.45 = f/171||(171/128)²||1.78 = 2|
[ HASSELBLAD CCB PINHOLE KIT ]
NOTE: Long Exposures
Long exposures are a typical aspect of pinhole photography, and reciprocity failure often comes into play. Reciprocity refers to the relationship between exposure time and the film’s sensitivity. In many films, extended exposure times require adjustments for decreased sensitivity, a phenomenon known as reciprocity failure. In my practice, I use Fujifilm Acros precisely because it doesn’t require any adjustments for reciprocity time. This characteristic of Fujifilm Acros eliminates the need to factor in any additional considerations for reciprocity, simplifying the process of achieving the correct exposure in pinhole photography.
Suppose you will be using film other than Fujifilm Acros. In that case, you must familiarize yourself with the extra time (N) your film may require for longer exposures and calculate N for the time necessary after using the conversion factor. Then you will add the extra time to the after-conversion value => (after-conversion value) + (reciprocity value) = (total exposure time).
Reciprocity Example: exposure time after applying conversion factor = 2 minutes. The film manufacturer states the reciprocity value is 100% more for exposures of 1 minute to 4 minutes. The total time required for the exposure now becomes (2 minutes) + (2 minutes) = (4 minutes).