TEC 140 APO

Theoretical characteristics are the following:

- diameter 140mm, focal length 980mm (F/D=7),
- objective optimized for 546 nm line (theoretical strehl 0.99 for that line),
- chromatic correction 0.02% F between 436 nm and 1000 nm,
- polychromatic strehl of 0.92 for 436, 480, 546, 656 nm,
- seven layers of anti-reflection coating optimized for 400-700nm: loss 0.25% (or less) for one air-glass surface
- 4" focuser
- fully illuminated field with diagonal 2" = 1.5°
- fully illuminated field with FF corrector (6 X 7 cm) = 2°5 (draw tube end cap removed)
- FF not required below 20mm diameter (CCD chip)

According to TEC, color balance has been optimized for the 450-650 nm range that matches the sensitivity of the human eye and gives the best planetary views. A less correction is applied below 450 nm (blue) without any drawback for visual use. Also F/D ratio is chosen to the minimum in respect to the Abbe's criteria.

Practical characteristics (according to TEC) are the following:

- typical optical accuracy: lambda/10 PTV (mini lambda/8) lambda/50 RMS (interferometry)
- chromatic correction: true chromatic correction has been measured by TEC (018, x1x, x3x) and an independent Japanese optician (x5x).

Measured and theoretical corrections (given design) are very close. This comes from the fact that TEC mesures the refractive index for each blank of ED Glass (FPL-53) in order to optimize the final triplet and explains the excellent results "in the field".