| Hardware Test | Last revised: 06/22/02 |  |
Celestron Eyepieces Test Report |
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This report looks at a selection of Celestron eyepieces as used on the Celestron 5" series of SCTs. All eyepieces are sold by Celestron and are of the 1¼" barrel diameter size. Manufacturer specifications and eyepiece test results from field measurements with a C5+ are presented. Calculation of various types are made from these numbers. To reflect typical usage all field measurements are given for the eyepiece through a star diagonal with and without the Celestron Reducer/Corrector. Results are reported in table form.
Table Sections
The following explains what each section of the table means.
| Eyepiece Designation and Model #: | Celestron eyepiece designation and model |
| Manufacturer's Specs | Specifications from the Celestron catalog |
| Measured Field Stop (mm) | The field stop was measured using a micrometer. In all cases it was in front of the field lens. This value is important in the calculation section of the table. |
| Measured FOV (deg) | Measured field-of-view using "star drift method" timings on a Celestron C5+. First row is with a star diagonal alone and the second with the addition of the Celestron Reducer/Corrector. The third row is the percentage increase in field due to the Reducer/Corrector. |
| Calculation Sections | Each section here uses the above numbers to determine a quantity. Results are given for eyepiece through a star diagonal and with the addition of the Reducer/Corrector. |
| Image Scale (deg/mm) | This is the image scale at the field stop. If you were to put a reticle marked in millimeters at the field stop, the number reported would be the degrees spanned by each 1-mm on the reticle. |
| Telescope Focal Length (mm) | This is the telescope focal length to the field stop. |
| Telescope Focal Ratio (f/#) | F-stop of telescope with this eyepiece calculated from above focal length divided by 127-mm objective size of the 5" series of Celestron SCTs. Objective size from NexStar5 specs and derived from Oct. 1993 Sky & Telescope C5 report. |
| Telescope Magnification (#x) | Magnification of the eyepiece. Calculated telescope focal length divided by manufacturer's reported eyepiece focal length. |
The Table
Notes follow after the table for fields marked with an asterisk "*."
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Table: Celestron Eyepiece Specifications/Measurements and Calculated Values when Used on a C5/G5/NexStar Telescope |
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| Eyepiece Designation and Model #: | SMA 25-mm #93007-A | Cross Hair Kellner 20-mm #93304 | Ultima 12.5-mm #93352 | Ultima 5-mm #93350 | |
| Manufacturer's Specs | Focal Length (mm) | 25 | 20 | 12.5 | 5 |
| Apparent Field (deg) | 52 | 43 | 51 | 50 | |
| Measured Field Stop (mm) | 22.1* | 13.9 | 10.8 | 3.8* | |
| Measured FOV (deg) | w/Diagonal | 0.94 | 0.58* | 0.44 | 0.18 |
| +Reducer/Corrector | 1.43 | 0.88 | 0.68 | 0.27 | |
| % Increase | 52% | 53% | 55% | 50% | |
| Calculations | Calculations | Calculations | Calculations | Calculations | Calculations |
| Image Scale (deg/mm) | w/Diagonal | 0.0425 | 0.0414* | 0.0407 | 0.0474* |
| +Reducer/Corrector | 0.0647 | 0.0633 | 0.0630 | 0.0711* | |
| Telescope Focal Length (mm) | w/Diagonal | 1347 | 1385* | 1406 | 1210* |
| +Reducer/Corrector | 885 | 905 | 910 | 806* | |
| Telescope Focal Ratio (f/#) | w/Diagonal | 10.6 | 10.9* | 11.1 | 9.5* |
| +Reducer/Corrector | 7.0 | 7.1 | 7.2 | 6.3* | |
| Telescope Magnification (#x) | w/Diagonal | 53.9 | 69.2 | 112.5 | 241.9 |
| +Reducer/Corrector | 35.4 | 45.3 | 72.8 | 161.3 | |
| Eyepiece Designation and Model #: | SMA 25-mm #93007-A | Cross Hair Kellner 20-mm #93304 | Ultima 12.5-mm #93352 | Ultima 5-mm #93350 | |
"*" Notes:
SMA 25-mm field stop on tested unit did not have a consistent rim distance from the edge of the barrel. It gave the impression of being off-center. This is the eyepiece that came with the telescope.
Cross hair Kellner 20-mm field-of-view without Reducer/Corrector was not measured but derived from the Reducer/Corrector reading. This will be addressed in a future update.
Ultima 5-mm eyepiece field stop is small and close to the field lens. Value given is a a ballpark estimate. All quantities derived from this measure are also flagged with an "*". On the model tested black manufacturing spots (flat black barrel paint?) were evident on internal glass surfaces. Viewing with a 6x loupe revealed the edges around the glass elements to be ragged (paint again?). Construction quality does not match that of the Ultima 12.5-mm at all.
