Baader M48 Fine-Adjustment Aluminum Ring - 0.3/0.5/1mm

You need a Baader M48 Fine-Adjustment Ring when your camera, filter wheel, or other accessory tightens down in the wrong rotational orientation. These rings add a tiny, precise amount of space—as little as 0.3mm—to change where the threads stop, allowing you to perfectly align your imaging train.

Yes, but minimally. Each ring will add its thickness (0.3mm, 0.5mm, or 1.0mm) to your total back focus distance. For most flatteners and reducers with a +/- 1mm tolerance, this is a negligible change. However, for systems requiring very high precision, you must account for this added distance.

To rotate an accessory by 180 degrees (a half turn), you need to add half the thread pitch in spacing. The standard M48 thread pitch is 0.75mm, so half of that is 0.375mm. The 0.3mm ring will get you very close, and the 0.5mm ring will rotate it slightly past the 180-degree mark. Starting with the 0.3mm or the full set is the best approach.

If your off-axis guider (OAG) body tightens with the guide prism misaligned with your camera's sensor corners, you can insert a 0.3mm ring between the OAG and the camera. This small adjustment is often all that's needed to rotate the OAG prism into the optimal position for finding a guide star without obstructing the main sensor.

Yes, you can stack the rings to achieve intermediate spacing. For example, stacking the 0.3mm and 0.5mm rings will give you 0.8mm of spacing. This is a reliable way to fine-tune both rotational alignment and back focus distance simultaneously.

No, they are not threaded. The Baader M48 Fine-Adjustment Rings are flat, precision-machined shims designed to sit between a male and female M48 thread. The threads of your existing equipment pass through the center of the ring.