Askar 111F 0.74× Focal Reducer

Askar 111F 0.74× Focal Reducer — For the Askar 111F Flat-Field Astrograph

The Askar 111F 0.74× Reducer is a dedicated focal reducer designed exclusively for the Askar 111F Flat-Field astrograph. It reduces the 111F’s native f/6.9 focal ratio down to f/5.1, shortening the effective focal length from 766mm to 566mm. This produces a wider field of view and a faster optical system that reduces exposure times — making it ideal for large nebulae, expansive emission regions, and imaging sessions where efficiency matters.

The reducer incorporates built-in field-flattening correction, eliminating field curvature and ensuring sharp, round stars from the centre of the frame all the way to the corners of a 44mm full-frame image circle. No additional flattener is required at the reduced focal ratio.

The optical design features a triplet lens group for smooth, well-corrected reduction. The standard back focus distance is 55mm from the M48×0.75 male thread. Both ends of the reducer body feature M68×1 threads. The 111F’s photographic extension tube connects directly via the included M54×0.75 and M48×0.75 adapter rings. The rear adapter ring has a built-in M48×0.75 standard 2" filter thread. The body is precision CNC-machined and ships with protective metal thread caps on both ends.

Who Is This Product Best For?

• Askar 111F owners who image large nebulae or wide star fields and want a broader field of view and faster exposures.
• Imagers in light-polluted environments who benefit from the faster f/5.1 ratio to shorten sub-exposure times.
• Narrowband and broadband filter users wanting more imaging efficiency from their 111F setup.
• Photographers who want flexibility — switching between the native f/6.9 (for tighter framing and higher resolution) and f/5.1 (for wider field) without a second telescope.

Why Choose the Askar 111F 0.74× Reducer?

• Dedicated design — optimized specifically for the 111F; delivers consistent, well-corrected performance across the full 44mm image circle at f/5.1.
• Built-in field flattening — one accessory handles both reduction and corner correction simultaneously.
• Significantly faster system — f/5.1 vs f/6.9 means roughly 45% less exposure time required for the same signal.
• Wider field — 566mm vs 766mm focal length gives approximately 26% more field width per axis.
• Standard 55mm back focus — no spacing guesswork; direct adapter connections are included.
• Filter-ready — built-in M48×0.75 rear thread accepts standard 2" astronomy filters directly.
• CNC body with protective caps — professional build quality with dust-proof metal end caps.

Recommended Uses

• Wide-field deep-sky nebula imaging with the Askar 111F
• Large emission and reflection nebulae
• Galaxy groups and wide star fields requiring broader framing
• Narrowband and broadband filter imaging
• Efficient imaging from light-polluted sites

Compatibility and Accessory Notes

Compatible telescope: Askar 111F Flat-Field only. Not compatible with the 91F, 131F, or other telescopes.

Connection: Connects via the 111F’s photographic extension tube using the included M54×0.75 or M48×0.75 adapter rings. Both ends of the reducer body are M68×1 threads.

Back focus: 55mm from the base of the M48×0.75 male thread. No additional spacing calculation required when using the supplied adapters.

Filter compatibility: Built-in rear M48×0.75 thread accepts standard 2" astronomy filters directly.

Important Limitations

• 111F only — this reducer is not compatible with the 91F, 131F, or any other telescope in the F Series.
• Not for visual observing — focal reducers are imaging-only accessories.
• 55mm back focus must be respected — altering the back focus distance from 55mm will degrade corner star quality.

Frequently Asked Questions

What does this reducer do to the 111F?
It reduces the focal length from 766mm to 566mm and the focal ratio from f/6.9 to f/5.1, giving a wider field of view and faster exposures.

Does it work on the 91F or 131F?
No. Each F Series telescope requires its own dedicated reducer. The 91F uses the 0.75× Reducer (M59 thread) and the 131F uses a different 0.74× Reducer (M72 thread).

Do I need a separate flattener at f/5.1?
No. Field flattening is built into the reducer and covers the full 44mm image circle.

What is the back focus distance?
55mm from the base of the M48×0.75 male thread on the rear of the reducer.

Our Recommendation

At Ontario Telescope and Accessories, we recommend the Askar 111F 0.74× Reducer as a natural pairing for any 111F owner who regularly images large nebulae or works under light-polluted skies. The step from f/6.9 to f/5.1 is meaningful in practice — combined with the wider field, it transforms the 111F into a noticeably more capable wide-field imaging system. For 111F owners who haven’t yet added a reducer, this is the one accessory most likely to expand their imaging possibilities.