How do I use the Askar Backfocus Adjuster to find the correct spacing?
Start with your theoretically correct backfocus distance, accounting for the adjuster's minimum 16mm length. Take a test image and examine the star shapes in the corners. Rotate the adjuster in small, 0.05mm increments and take new test images until the corner stars are perfectly round. Once set, use the two fixing screws to lock the position.
Which version of the Askar Backfocus Adjuster do I need?
Both versions accept an M54x0.75 female thread from your telescope or corrector. The choice depends on the next item in your imaging train:
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M54 Version: Choose this if your camera, OAG, or filter wheel has female M54 threads.
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M48 Version: Choose this if your camera or filter wheel uses the standard male M48 (2-inch filter) thread.
My flattener needs 55mm of backfocus, but my train is 53.5mm. Can the Askar Adjuster fix this?
No, the Askar Backfocus Adjuster cannot fill a gap that large on its own. Its adjustment range is 16mm to 20mm. You would first need to add extension tubes to get close to the required 55mm, and then use the adjuster to fine-tune the final millimeter or two with its ±2mm range.
How do I lock the position on the Askar Backfocus Adjuster?
The adjuster features two holes for fixing screws. Once you have rotated the barrel to the desired backfocus distance, you can insert and tighten small screws (not included) into these holes to prevent any further rotation, securing your setting for the rest of your imaging session.
Will the Askar M54 Adjuster help with elongated stars on my full-frame camera when imaging M31?
Yes, most likely. Elongated stars in the corners of a full-frame sensor, especially on a large target like the Andromeda Galaxy (M31), are a classic sign of incorrect backfocus. The Askar M54 adjuster is ideal for this, allowing you to make tiny, precise changes to the spacing until those corner stars become sharp and round.
What is the minimum optical path length of the Askar Backfocus Adjuster?
The minimum optical path length added by the adjuster is 16mm when it is fully retracted. It can be extended up to a maximum of 20mm.
