UV transmission of some Barlow lenses

Barlow lens UV Transmission
Vixen 2x 58%
APM 1.8x 45%
Takahashi extender 1.5ED 68%
Astrophysics 2x (old model) 64%
2.7x APM coma corrector 75%

Protocole :

- Measurements made with a Mewlon 250, ASI 290 camera and Astrodon UV filter.
- Source of light : Venus high in the sky (> 55°), coronal sky.
- Reference measurement : made at the Mewlon 250 focus (i.e. with no Barlow, only reflective optics)
- Barlow transmission evaluated by comparison with the measurement made with no Barlow lens (difference in effective focal length is taken into account in the calculation).

Accordingly, UV transmission is only valid for :
- the ASI290 response profile  in UV,
- the Astrodon UV filter transmission profile (bandpass = 320 to 385 nm).


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