35mm Movie Lens Specifications
I have couple of good Russian reference books with specifications of some lenses. The books are quite old, so there are no most modern lenses in them, unfortunately. But there are many lenses listed in them that are still in use by many DP's all over the world. So, this technical info can be useful for them.
Explanation of parameters and measuring methods
Values of basic lens parameters listed in this section - focal length, back focal distance, front focal distance, flange focal distance and distance from rear end of the lens block to focal plane - were measured accordingly to GOST 1395-67 and GOST 13096-67.
Effective relative aperture value (1:ne) was determined accordingly to mechanical engineering normal MN 63-59. It is value of relative aperture of an ideal lens (1:n) that has light transmission factor (τ) equal to 1, and that produce same average brightness of the circle in the center of the frame as tested lens.
Denominator value of the effective relative aperture (ne) for a lens with round aperture was calculated by the following formula:
ne = n/√τ,
where n – denominator value of geometrical relative aperture ;
τ – light transmission factor expressed as a relation of the light beam that passed through the lens and has 10mm diameter in the image plane to light beam that would pass through an ideal lens with same geometrical relative aperture in the same condition.
In the Soviet lens specifications, there are target diagrams pictured for spherical and chromatic aberration, astigmatism and distortion. For non-Soviet lenses these diagrams have been built based on measurements conducted accordingly to RTM-KINO 149-64, RTM-KINO 151-64, RTM-KINO 153-64 и RTM-KINO 154-64.
Remaining aberrations serve as relative quality of lens corrections. But these aberration values can't provide full info on the lens image quality.
Most common way to estimate quality of a lens is measuring its resolution that is expressed in quantity of lines per mm of image.
These reviews show resolution over the frame area in form of graph.
There are also brightness distribution graphs. Measurements have been done accordingly to RTM-KINO 156-64 on the special photometric device with light sensitive element and galvanometer.
As you probably know, brightness consists of two parts. First part is useful light producing an object image. Other part is parasite light that doesn't take part in the image producing.
This adverse part of the light flow falling onto image plane is important factor that decreases image quality. It can be expressed as light scattering.
The light scattering factor is relation of the brightness of the black object placed on evenly bright background to the background brightness. It is expressed in percents.
The reviews contains light transmission factors as well. It is relation of the output light flow (F) to incoming light flow (F0) expressed in percents. This value has been measured directly with aid of light source, collimator, photometric sphere, selenium photocell, and galvanometer.
The light transmission factor (τ) of the most lens samples has been determined simultaneously with measuring of the effective relative aperture. Its formula is:
where τ value relates to central light flow of 5mm diameter for 16mm lenses and of 10mm diameter for all other lenses.
The last listed parameter is spectral transmission factor (τλ) graph. It shows relation of the specific wave length light flow F1λ passed through the lens to the incoming light flowF0λ of the same wave length.
Spectral transmission factor formula:
τλ = F1λ/F0λ = E1λ/E0λ ,
where E1λ and E0λ – energy of the light flow falling onto photo cell freely and through the lens at same wave length.