What does the Askar F/3.9 reducer do for my FRA400 or FRA500?
This 0.7x reducer shortens your telescope's focal length, making it optically "faster." For the FRA400, it changes the focal length to 280mm and the focal ratio to f/3.9. This results in a wider field of view and significantly shorter exposure times needed to capture faint deep-sky objects.
Can I use full-frame cameras with the Askar F/3.9 reducer?
Yes. The reducer is specifically designed to produce a corrected 44mm image circle, which is large enough to cover standard full-frame sensors (typically 43.3mm diagonal) without vignetting. This ensures sharp stars across the entire frame of your large-format camera.
Is it difficult to connect my camera to the Askar F/3.9 reducer?
No, connection is straightforward. The reducer requires a standard 55mm back focus from the rear mounting flange to your camera sensor. This is the same spacing used by most DSLRs with a T-ring and many dedicated astronomy cameras with their included spacers, making it easy to achieve the correct distance for optimal performance.
How does a 0.7x reducer affect my exposure times?
A faster focal ratio gathers light more quickly. Moving from f/5.6 (on the FRA400) to f/3.9 means your exposure times can be cut by more than half to achieve the same image brightness. A 5-minute sub-exposure at f/5.6 is roughly equivalent to a 2.5-minute sub at f/3.9.
Can I image the entire North America Nebula (NGC 7000) with an FRA400 and this reducer?
Yes, this setup is ideal for such large targets. With the reducer, an FRA400 has a 280mm focal length. Paired with a full-frame sensor (like a Sony a7 series or ZWO ASI6200), this provides a field of view of approximately 7.3° x 4.9°, which is more than enough to comfortably frame the entire North America Nebula (NGC 7000) and the neighboring Pelican Nebula (IC 5070).
What's the best way to use 2" filters with the Askar F/3.9 reducer on my FRA500?
The reducer features a built-in M48x0.75 female thread on the telescope side. You can simply screw any standard 2" mounted filter directly into the reducer before attaching it to your telescope. This places the filter in the optimal position within the light path.
