[jase (Jason)]

Yes, the FLT-132 is quite well colour corrected. Actually, I would expect this for generally any type of triplet. The scale on the x axis show the colour shift or deviation, while the y axis shows the focal ratio (from F/0 at the bottom through to F/7 at the top). You could potentially determine what each y axis scale points are by calculation of the focal length as the focal ratio increases. The most important part is how the colour spectrums converge at focus (at F/7). Adding a focal reducer can change this, so we would need to obtain statistics for its optical design too.

If we compare the TOA-130 longitudinal chromatic aberration chart (attached), you will note the colour deviation is much finer. It’s listed as a maximum +/- 0.01mm deviation for the visual wavelengths g 436nm (blue) through to c 656nm (red or h-alpha). Takahashi provide a chart showing the chromatic aberration through the visual spectrum from UV through to infra-red (400nm through to 900nm – actually this should be all the way to 1000nm).

The chromatic aberrations lines are tighter on the Tak compared to the TMB. It would help if they provided identical charts, but it’s not too difficult to make an assessment. As part of the evaluation process it’s important to also look at spot diagrams and the Strehl ratio.