What does "FRA" mean for the Askar FRA400?
FRA stands for Flat-field Refractive Astrograph. This means the Askar FRA400 is designed with a built-in optical element that corrects for field curvature, so you do not need a separate field flattener. It produces a flat, sharp image across its entire 44mm image circle natively.
Do I need to buy a separate field flattener for the Askar FRA400?
No. The quintuplet (5-element) objective lens design provides a corrected 44mm image circle without any additional accessories. You can attach your full-frame or smaller camera directly and achieve sharp stars across the field.
How does the Askar FRA400's 44mm image circle work with a full-frame camera?
A standard full-frame sensor has a diagonal of approximately 43.3mm. The Askar FRA400's specified 44mm image circle fully illuminates these sensors, preventing vignetting (darkening of the corners) and ensuring your entire frame is usable for imaging large targets like the Andromeda Galaxy (M31) or the Veil Nebula complex.
Is the Askar FRA400 suitable for a portable "grab-and-go" setup?
Yes. With an optical tube weight of 2.56kg and a total weight of 2.88kg with rings and dovetail, the Askar FRA400 is extremely lightweight. Its compact 317mm length makes it easy to transport and mount on lighter-duty equatorial mounts, making it an excellent choice for field imaging.
What is the benefit of the 140mm back focus on the Askar FRA400?
The 140mm back focus provides extensive space for accessories. This is critical for imagers who use:
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Filter Wheels: Easily fits large filter wheels for LRGB or narrowband imaging.
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Off-Axis Guiders (OAGs): Provides enough room to place an OAG in the optical path for precise guiding.
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Rotators: Accommodates electronic rotators for automated framing.
This flexibility allows you to build a sophisticated imaging train without worrying about running out of focus travel.
Can I use the Askar FRA400 for visual observing?
Yes. While designed as an astrograph, the Askar FRA400 performs very well for visual use. The included 2" and 1.25" adapters allow you to use standard diagonals and eyepieces for wide-field views of star clusters and nebulae.
