=====Cooke Speed Panchro Series II 40mm f/2.0 (T2.3) ===== 
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==== Summary ====
The aptly named lens designer Gordon Cook began working at Taylor-Hobson in 1948 and embarked on redesigning the Speed Panchro line. In 1953 the 25mm T2.2 was released and by 1958 a complete set of the Series II was available from 25mm to 100mm with stops from T2.2 to T2.8. The Series II lenses shared much of the DNA of the original Panchro lineage but there was more inclusion of rare-earth glasses and new coating techniques to minimize reflections and increase contrast/transmission performance. Thorium dioxide was added to a silica mixture and helped create glass with high refraction and low dispersion which was massively beneficial in removing chromatic aberration. This ionizing radiation created “color centers” on the glass – areas that absorbed some wavelengths of light instead of just passing them through and over time this resulted in a color cast. Usually this presented itself as a yellow/brownish color that looked like a tea stain, especially towards the center of the glass. The 75mm S2 was particularly susceptible to this. The S2s also marked a transition point from hand-calculations for the optical design of each lens, which could take as long as a year to perfect, to computer aided calculations – albeit on massive computers – which only took days to complete. These lenses also covered the full negative area of 18.63mm x 24.89mm, which was very close to what would become known as Super35. In 1959, as a compliment to this lens set, the Cooke Telepanchros were released – a 5 way lens set covering from 152mm all the way up to 558mm with T-stops from T2.3 to T6.2.
==== Tech Specs ====
| Manufacturer    |Cooke|
| Series          |Speed Panchro|
| Model           |Series II|
| Focal Length    |40mm|
| Max Aperture    |f/2.0 (T2.3)|
| Min Aperture    |T22|
| Format          |Full Frame|
| Image Circle    |37mm|
| Minimum Focus   |12 in.|
| Focus Rotation  |-|
| Iris Blades     |-|
| Optical Design  |-|
| Squeeze         |none|
| Front Diameter  |-|
| Filter Thread   |-|
| Focus/Zoom Rod  |none|
| Native Mount    |Arri/Mitchell|
| Data Protocol   |none|
| Length          |-|
| Weight          |-|
| Body Telescope  |none|
| Body Material   |Aluminum|
| Focus Drive     |Manual|
| Iris Drive      |Manual|
| Zoom Drive      |n/a|
==== History ====
Country of Origin:  \\
Release Date:  \\
Launch Price:  \\
Design Revisions:\\

==== Service ====
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Service Manual: [[staff:servicedb:csp|Disassembly/Re-assembly]] \\
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Full CLA: **5 hrs.**\\
<wrap note>Enter relevant notes here</wrap>\\
Spray threads: **+ 1 hr.** \\
Optics only: **2-3 hrs.**\\
</nodisp>

==== Notes ====
==== Media ====
https://cookeoptics.com/news-and-events/the-history-of-panchro-part-1/\\