A. Steadiness check: Particularly when composite photography is contemplated (but valuable in any case), a check for image steadiness is advisable. The subject matter may be simple; for instance, a black background with a simple cross made of adhesive tape. Photograph 20 or 30 seconds of the cross, cover the lens, backwind to the beginning, uncover the lens, offset the chart by the width of the tape, and double-expose the chart. Any unsteadiness will readily show between the offset lilies (Do not re-thread on a different perforation — this introduces the possibility of unsteady perforations and compromises the camera test.) After photographing and processing this and before projecting, examine the negative for perforation damage and scratches.
B. Optical: Lenses should have been calibrated at the factory or by the distributor for exposure and focus and the distributor should have checked the ground glass position with reference to the film plane. If you trust your supplier there is no need for extensive testing. If, however, the equipment is unfamiliar or it is necessary to field test the equipment, following are suggested procedures:
1. Focus and ground glass/film plane:
(a) Set up a focus/definition chart (obtainable from camera equipment suppliers) with center and corner targets; set up at a distance from the camera corresponding to a scale-calibrated distance, filling the aperture as much as possible. Check the eye focus versus scale focus. Repeat for each lens. Repeat at a mid-distance (15 to 25 feet) scale calibration. With a zoom lens, check at several zoom settings.
A consistent discrepancy suggests either ground glass or index error. A discrepancy on one lens suggests error in the setting of the scale ring. (When using Panavision wide-angle lenses, read and follow the Panavision instructions.) In either case, photographic or collimator tests are required to confirm the source of error. (If you have a rental or a newly acquired camera/lenses, send it/them back for correction.)
(b) Set up the definition chart at a scale distance closest to filling the frame. If the index and/or focus scale rings are provided with secondary index marks for adjustments, use these marks as a guide; otherwise:
On a piece of tape on the index, make four additional temporary marks at equal intervals above and below the index. Space the marks to indicate 0.001 in travel of the lens for each interval (see "Lens Formulas"), and label those away from the film "plus" and those closer to the film "minus."
At a wide-open aperture, using either the temporary marks or the permanent secondary marks mentioned above, photograph a short take (just enough to get up to speed) at each index mark: "plus," "N," "minus." Develop and examine with a 10X magnifier. The N exposure should be noticeably sharper than the plus or minus. If it is not, repeat the test to confirm.
Check all lenses, and check also at another mid-dis-tance (say 15 feet), always at a scale-calibrated mark. If any lens is consistently "off the mark" or if there is a pattern of failure between lenses, send the camera/lenses back for recalibration or, in the field, be guided by the focus test results.
2. Sharpness (See also "Lens Selection."):
Because sharpness is a subjective judgment based on the composite of resolution, acuteness, contrast, flare and aberration, a full test of each lens would encompass photography in a number of different situations. A simple comparison may be made between lenses, however, by photographing a definition chart and a simple scene with each lens and comparing them with identical exposures made with a lens of known photographic performance.
(a) The definition chart should preferably be one made for lens testing (available from camera supply distributors) and should have targets in the corners as well as in the center. Exposure should be made at a wide-open aperture, a mid-aperture (one at which you would be most likely to photograph interiors), and at a very small aperture, each lighted for normal exposure. The wide-open exposure should show up aberration and distortion, particularly in the corners, should they be present. The small aperture exposure will tell you (in comparison with the "mid-aper-ture" exposure) if there is lower definition because of diffraction; a lack of definition at wide-open or small apertures can affect apparent depth of field as well as intrinsic sharpness.
(b) The test scene should include a white area, a light area (with detail such as lace), and a dark area with detail, as well as a person or object showing detail in mid-tones. There should be a normal exposure and one each one stop over and underexposed. When printed alike in the mid-tones and compared, this will show up contrast, and if the lens has a tendency to flare, the overexposed scene will be flatter than the normal and will show flare from the white area into the surrounding area. Care should be taken not to exceed the printer scale.
(c) Comparison of (b) normal exposure with a like exposure made with a known lens is a subjective sharpness test.
3. Exposure (T-stop), color shift:
Photograph a short length of film of a gray scale at the same T-stop and illumination with each lens. The negative gray scale may be read with a densitometer, if available, to determine uniformity. If a print is made of the negative it may be projected to see if there is a color shift between lenses. In most instances small differences in color can be corrected in printing and will affect only the rush prints. If you are photographing on reversal film, you may wish to use color correcting filters to balance the lenses.
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