The Apex ED reducer fits into a standard 2″ focuser. It has M42 T-threads on the camera side, and it can accept a standard 2″ (M48) filter on the telescope side for easy use of light-pollution or other filters.
There are two different APEX units available. An “S” and a “L” model. The S model is for refractors with a focal length of between 300-500mm. The L model is for 500mm and longer focal lengths. My Esprit 100 is an F5.5 (550mm) so I am using the L version.
Backfocus for the APEX-ED is very tight at just 0.5mm and this requires some adapters and spacers to be fitted together to reach optimal backfocus. I’ve been working on this backfocus spacing for a few imaging sessions now. I am continuing to tweak it trying to achieve round stars in the corners of the field-of-view. Currently the stars are still slightly elongated (comet like) which indicates the spacing between the reducer and the camera sensor is a tad off. I’ll continue to work on it and update on how things are progressing here on my website and on my YouTube channel.
Check out this video for more on the Starizona APEX-ED reducer/flattener.
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