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Sky-Watcher Esprit 150 0.77x Reducer/Flattener
The Sky-Watcher Esprit 150 0.77x Reducer/Flattener is a dedicated optical corrector that transforms the Esprit 150ED and 150EDX refractors from f/7 to a much faster f/5.4. This 0.77x reduction shortens the telescope's focal length from 1050mm to 810mm, cutting required exposure times by about 68%. It flattens the field for pinpoint stars to the edge and delivers a 36mm fully illuminated field suitable for full-frame sensors, with a 90mm back focus, or 55mm with the supplied M48 adapter and back focus spacer.
From f/7 to f/5.4: A 68% Reduction in Exposure Time
By converting the Esprit 150's native f/7 optical system to f/5.4, this reducer cuts the exposure time needed by about 68% compared with the native configuration. You can collect more data in a single night or capture faint detail in shorter sub-exposures.
A 36mm Corrected Field for Full-Frame Sensors
This corrector not only reduces focal length but also flattens the field for pinpoint stars to the edge. Its 36mm fully illuminated field is large enough for full-frame sensors.
90mm and 55mm Back Focus Options
The reducer has 90mm of back focus. By installing the supplied M48 adapter and back focus spacer, the required back focus becomes 55mm, making it straightforward to attach cameras and filter wheels with M48 threads.
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90mm Native Back Focus: Back focus of the reducer without the adapter and spacer.
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55mm Back Focus: Achieved with the included spacer and M48 adapter, for cameras and filter wheels with M48 threads.
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Dedicated Design: This corrector is matched to the Esprit 150ED and 150EDX refractors. Sky-Watcher states its Esprit reducer flatteners are not compatible with other telescopes.
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What is the correct back focus for my setup with the Esprit 150 Reducer?
The reducer's back focus is 90mm. With the supplied M48 adapter and back focus spacer installed, the required back focus becomes 55mm, which makes it straightforward to attach cameras and filter wheels with M48 threads.
Is the Esprit 150 0.77x Reducer compatible with my non-Sky-Watcher telescope?
No. This reducer/flattener is a dedicated corrector for the Sky-Watcher Esprit 150ED and Esprit 150EDX refractors. Sky-Watcher states that its Esprit reducer flatteners are specifically designed for their telescope and are not compatible with other telescopes, even refractors with the same aperture and focal length.
What does the 68% exposure time reduction mean for my Esprit 150EDX imaging sessions?
A 68% reduction means an exposure that would take 10 minutes at the native f/7 takes about 3 minutes and 12 seconds at f/5.4. This lets you gather about three times as much data in the same amount of time.
Will the Esprit 150 Reducer work with my full-frame camera?
Yes. The reducer delivers a 36mm fully illuminated field, which retailers describe as large enough for full-frame sensors.
How do I achieve the 55mm back focus with the Esprit 150 Reducer?
The reducer ships with a back focus spacer and an M48 thread adapter. With both installed, the required back focus becomes 55mm instead of the native 90mm.
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| Manufacturer SKU |
S20215 |
| Compatible Telescopes |
Sky-Watcher Esprit 150ED & 150EDX (1050 mm f/7) |
| Reduction Factor |
0.77x |
| Reduced Focal Length |
810 mm |
| Reduced Focal Ratio |
f/5.4 |
| Native Focal Length / Ratio |
1050 mm / f/7 |
| Exposure Time Reduction |
68% (vs. f/7) |
| Fully Illuminated Field |
36 mm |
| Back Focus (Native) |
90 mm |
| Back Focus (with Adapter) |
55 mm |
| Camera Connection |
M48 (with supplied adapter) |
| Weight |
910 g (2.0 lb) including end caps |
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0.77x Reducer/Flattener
× 1
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Metal Thread-on Caps
× 1 set
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Sky-Watcher 2-Year Warranty
