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RELEASE 1 JULY 2015 DORIAN BIF-107-50.960-68 

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Total Pages: 3 

26 July 1968 

To: M. Gibbs/E. Jones 

From: B. Siegel 

Subject: Field Curvature Bench Test Results 

Attached is a list of comments on the field curvature tests conducted at Itek 

on the Bench. The major points to note are: 

1. The matrix of points taken is insufficient and not compatible with 

the GE/SPO agreed upon matrix as per TWX 3409, March 27, 1968. 

2, Data taken at the reticle plane is invalid due to a poor relay. 

3. Resolution data is not compatible with previous data taken during 

qualitative testing. 

4. Field curvature at the reticle and eyepiece planes is unacceptable 

for proper ATS simulation. 

5. There is severe loss in resolution off axis. 

It is recommended that a meeting be held with GE/Itek personnel to review the 

results of this test. I would also recommend sending a copy of the attached 

comments via TWX to GE. 

B. Si gel • 

Attachment 

cc: D. L. DuMond 

J. A. Abrahamson 

F. F. Doppelt 

HANDLE VIA BYEMAN 

CONTROL: SYSTEM ONLY 
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BIF-I 07-50060-68 

Page 2 of 3 

Attachment 

COMMENTS ON FIELD CURVATURE TEST - 7/12/68 

1. The test conditions/procedures are defined in an Itek document of 4/9/68 

which we never saw or agreed to. 

2. Precise location of measurements across field at reticle and eyepiece 

planes are not defined. 

3. Measurements at the eyepiece plane were taken with a 3X telescope. At 

our review in May, this scope was so poor that better results were obtained 

with the unaided eye. 

4. The explanation is given that the depth of field is so great that it is difficult 

to define the best focus location. If this is the case, how come the "best quality 

focus" locations, which are within the depth of field range, give different 

resolution readings than the best focus position. 

Itek ran a photographic test to determine if the photographic depth of field 

was comparable to the visual depth of field. They compared one case on axis 

on a subjective basis (see p. 26) and concluded they were comparable. We 

need an explanation of p. 26 comments and the meaning of the resolution readings 

on that page. 

5. Itek took data on what was called "best quality focus" as well as "best 

focus". Need explanation of criteria for "best quality". 

6. At the reticle plane, how does one convert from "micrometer reading" to 

diopters? Subsequent data appears to indicate that the micrometer readings 

are in inches. Is this correct? 

7. In general, for all figures, curves are not faired through data points, see 

especially p. 22. 

8. Based on the data, the following conclusions can be drawn: 

Reticle Plane 

a. This field is not flat nor symmetric. For no anamorph, the field is 

right/left symmetric in the horizontal plane, but apparently skewed up in the 

vertical plane. For 1: 1 anamorph, the field is skewed to the right in the 

horizontal plane. Going to 2: 1 anamorph flattens the field and skews to the left 

in the horizontal plane. Changing objective lens changes field curvature 

substantially. Initial calculations indicate a reticle plane curvature of several 

diopters. Such curvature is clearly unacceptable. 

-SECRLT OUNAN 
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BIF-107-50060-68 

Page 3 of 3 

b. There is great variation in resolution off axis with best resolution 

usually not obtained on axis. There is also significant variation between 

tangential and saggital readings off axis. In general, higher resolution is obtained 

in the horizontal plane than in the vertical plane. It is disturbing to note that 

previous off axis readings taken during the qualitative test give much better 

resolution readings than this test. 

c. It should be noted that all reticle plane data was taken with a relay 

lens that was later shown to be performance limiting. 

d. Recommend that all reticle plane data be taken again and, in addition, 

measurements be taken of the complete vertical plane. Also, data should be 

taken with both objective lenses. 

Eyepiece Plane 

a. This field is highly curved and non-symmetrical. Decreasing 

magnification increases symmetry. Even for low magnification, the curvature 

from on axis to the field edge is close to 5 diopters. Such curvature appears 

unacceptable. 

b. There is severe off-axis resolution loss. In addition, the resolution 

results for 3. 6X are incomprehensible. Resolution values 7-8 times those 

obtained in the qualitative test are shown. Not even a 3X telescope can do that. 

c. Recommend this test be repeated with a full matrix of points 

including no anamorph, 2: 1 anamorph, horizontal and vertical plane, etc. 

9. For information prupose, this test was run April 20-24, the document 

was published May 20 and signed June 4. We received the data around mid- ) 

June. 

--SEGRET- DORIAN