- Commodity name: 91F 0.75x Reducer
- Commodity ID: 91F 0.75x Reducer
The Askar 0.75x Reducer for the 91F is specially optimized to unlock greater astrophotography capabilities.
The 0.75x reducer can bring Askar 91F's focal ratio down to F5, providing not only a faster focal ratio but also built-in field-flattening correction. The shorter focal ratio delivers a wider field of view and a faster exposure time, making it ideal for capturing large areas of nebulae, star clusters, and faint, fast-moving celestial objects.

The 91F 0.75x reducer adopts a triplet design and supports a 44mm full-frame image circle. The back focus from the M48 thread is a standard 55mm. Both end threads are M59*1. The 91F photographic extension tube includes M54×0.75 and M48×0.75 adapters for direct and convenient connection to the 0.75x reducer. The reducer features a built-in M48*0.75 2-inch filter thread, allowing for direct filter installation and use. The entire reducer is CNC-machined and comes with front and rear metal threaded caps to protect against dust when not in use.

Parameter
（After attaching）91F Focal length	455mm
（After attaching）91F Focal ratio	f/5
Lens Number	Triplet design
Back Focus	55mm（from the base of M48 male thread）
Weight	0.3kg
Rear-end thread type	*M591**

Size Diagram

Installation

Optical Path Diagram

Spot Diagram

Product introduction

The 0.75x reducer can bring Askar 91F's focal ratio down to F5, providing not only a faster focal ratio but also built-in field-flattening correction. The shorter focal ratio delivers a wider field of view and a faster exposure time, making it ideal for capturing large areas of nebulae, star clusters, and faint, fast-moving celestial objects.

The 91F 0.75x reducer adopts a triplet design and supports a 44mm full-frame image circle. The back focus from the M48 thread is a standard 55mm. Both end threads are M59*1. The 91F photographic extension tube includes M54×0.75 and M48×0.75 adapters for direct and convenient connection to the 0.75x reducer. The reducer features a built-in M48*0.75 2-inch filter thread, allowing for direct filter installation and use. The entire reducer is CNC-machined and comes with front and rear metal threaded caps to protect against dust when not in use.

Specifications

Parameter
（After attaching）91F Focal length	455mm
（After attaching）91F Focal ratio	f/5
Lens Number	Triplet design
Back Focus	55mm（from the base of M48 male thread）
Weight	0.3kg
Rear-end thread type	*M591**

Size Diagram

Installation

Optical Path Diagram

Spot Diagram

Video

Images

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