Bolsey Model B2

The Bolsey Model B2 is a Bolsey Model B with the addition of flash synchronization and double exposure prevention.  The camera takes standard 35mm film in cassettes.  The B2 was introduced about 1948.  Peerless Camera Stores (New York City) advertised them in the October, 1948, issue of Popular Photography for $65.90.  The camera was discontinued in 1957.

Front

Rear

Top

Bottom

Interior

Ready to take a picture

After taking a picture

The body of the camera is made from aluminum and the dimensions are roughly 4-1/4 inches wide by 2-3/4 inches high by 2-1/2 inches deep. The camera has the controls on the lens, which was normally the case on leaf shutter cameras.  The lens is an f/3.2-f/22, 44mm, coated Wollensak Anastigmat.  The shutter is a Bolsey Wollensak Synchromatic leaf shutter.  The back of the camera comes off for loading film.  The path between the film cassette and the take-up spool is shorter than usual, and Bolsey ads claimed that you could get four extra pictures on a roll of film if you were careful about loading film.

The shutter release sets and releases the shutter in one motion.  The shutter has a moving peg that pops up to stop the shutter release from resetting after you take a picture.  The peg retracts when the film is wound and this allows the shutter release to reset.  To make a deliberate double exposure you push in the peg to allow the shutter release to reset.

The back of the camera has a depth of field calculator based on a circle of confusion of 0.05mm or 1/500 inch, which was typical for a miniature camera at the time, and a film reminder dial for Panatomic X (Kodak), Daylight Anscocolor, Tungsten Anscocolor, Daylight Kodachrome, Type A Kodachrome, Ultra Speed Pan (Ansco), Super XX (Kodak), Supreme (Ansco), Plus X (Kodak) and a blank space for when there is no film in camera.  None of the films are still in production.

The flasholder plugs into the openings on the left rear of the camera and takes a #5 or #25 flash bulb.

There are no strap lugs.  If you want a neck strap you need to use the leather camera case.  You also can use a strap that screws into the tripod socket.

A filter kit with a lens hood was available.  The lens takes a 24 mm series V adapter ring.

The Bolsey B2 is small and cute.  According to "Brass, Glass and Chrome" the camera was especially popular with women photographers.  You need to be careful with the shutter release to avoid camera shake.

Cimberland Mountain State Park, Crossville, Tennessee.  Ilford HP5 film.

This example has a very stiff (basically impossible) rewind.  Curiously it rewinds better with the back off. I need to give it a DIY CLA.

Diffraction and Circle of Confusion

Because of the wave nature of light, the image of a distant point of light is not an infinitesimal point, but a finite disc surrounded by a series of concentric rings.  The Royal Astronomer Sir George Airy worked out the mathematics of the effect of diffraction on an image in 1835.  The size of the disc depends on the diameter of the lens and the wavelength of light and is given by the approximate formula 

r = 1.22 * l * f / d  

r is the radius of the disc

l is the wavelength of light

f is the focal length of the lens

d is the diameter of the lens.

f / d being the focal ratio of a lens, we can use the focal ratio, N, instead of f / d.

r = 1.22 * l * N

In photography the diameter of the circle of confusion is usually used, so the diameter of the circle of confusion produced by diffraction is twice the radius of the Airy disc.

c = 2.44 * I * N

The wavelength of visible light ranges from about 400nm to about 700nm.  Using the middle of the range, 550nm, we get

c = 0.0011342 * N (in millimeters)

or

N = 882 * c

For an image to be seen as sharp in the final print the largest circle of confusion should be no more than the resolving power of the human eye viewing the final print at a comfortable distance.  Diffraction producing that much blur begins to affect the image quality.

On a 36x24mm, full frame sensor, c is typically given as 0.03mm.

N = 882 * 0.03

N = 26

Most full frame lenses stop down only to f/16.  A few stop down to f/22 or even f/32 (to increase depth of field).    

On a 17.3x13mm, Micro 4/3rds sensor, c is typically given as 0.0.15mm.

N = 882 * 0.015

N = 13

Under ordinary circumstances you would not stop down the lens on a Micro 4/3rds camera to more than f/11.

Sensor Size and Bokeh

Photographers like to call the blurred quality of a background in a portrait "bokeh."  You can get a numerical value for the size of the blur circle (circle of confusion) from an out of focus point of light at infinity starting with the thin lens formula:

1/f = 1/u + 1/v

f is the focal length of the lens, u is the distance from the lens to the object and v is the distance from the lens to the image.  When u is infinite 1/f = 1/v.  The distance from the lens to the image is equal to the focal lens of the lens.  You could express 1/v as 1/(f+e), with e being the distance the image moves as you focus on objects closer than infinity.  With a little algebra you can derive a formula for e as

e = f^2 / (u - f)

The amount of blur you get for an out of focus distant object is 

b = e / N

where N is the focal ratio of the lens.

Finally, the blurriness of the image on the final print depends on how much the image is enlarged. A Micro 4/3rds image has to be enlarged twice as much as a full frame image to make the same size print.

Let's aim our cameras at a subject 3m (10 ft) away.  We'll use a full frame digital camera with a 50mm lens set at f/2.8 and a Micro 4/3rds camera with a 25mm lens set at f/1.4.  The 50mm lens on a full frame camera has the same field of view as a 25mm lens on a Micro 4/3rds camera.  Both cameras see the same perspective because both are at the same distance from the subject.

Full Frame (36mm x 24mm)

f = 50mm

u = 3,000mm

N = 2.8

b = 50^2 / ((3,000 - 50) * 2.8)

b = 0.30

Enlarge the image 8 times to make an 8x10 print and you get a 2.4 mm blur circle.

Micro 4/3rds (17.3mm x 13mm)

f = 25mm

u = 3,000mm

N = 1.4

b = 25^2 / ((3,000 - 25) * 1.4) 

b = 0.15

Enlarge the image 16 times to make an 8x10 print and you get the same 2.4mm blur circle.

When you set up for the same perspective and field of view, to get the same background blur you need to open the aperture twice as much on the Micro 4/3rds camera as on the full frame camera.