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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