M54 Threaded Filter Mount (M54 OL7.5)

M54 (OL7.5)

Name: IDAS M54 (OL7.5) Full-Frame Threaded Filters
Brand: IDAS
SKU: IDAS-MOUNT-M54
Availability: InStock

M54 OL7.5 Filter Mount (7.5mm Optical Path / CA 47mm)

*IDAS M54 OL7.5 filter body. Ultra-low profile 7.5mm optical length, generous 47mm clear aperture.

Full-Frame & Large Format M54 Mount Design

The IDAS M54 OL7.5 filter is an ultra-low profile 7.5mm optical path length filter featuring a generous 47mm clear aperture. It minimizes peripheral vignetting across Full-Frame and APS-C sensors on various M54-compatible astrographs, flatteners, and cameras. It also serves as the ideal baseline backfocus setup (7.5mm + 17.5mm = 25.0mm) for Celestron RASA 8 (25.0mm requirement) paired with 17.5mm FB cooled cameras.

7.5mm Optical Length Design 〜 Universal M54 & RASA 8 Baseline 〜

RASA 8 Example (25.0mm) ＝ Filter (7.5mm) ＋ Camera (17.5mm)

As an ultra-slim M54 filter, it consumes merely 7.5mm of optical backfocus across diverse optical trains. As a prime use case, pairing with a 17.5mm FB cooled camera establishes the exact 25.0mm backfocus baseline demanded by Celestron RASA 8.

💡 Mechanical Length (8.1mm) vs Optical Path (OL 7.5mm): The physical flange-to-flange mechanical distance is 8.1mm. Because the 2.0mm filter glass refraction extends the focal point by approx 0.6mm, the net optical backfocus consumption is designed to be exactly 7.5mm.

Massive 47mm Clear Aperture (CA) — Significantly Reduces Vignetting

Large 47mm clear aperture accommodates the steep light cones of ultra-fast optics (such as F/2). Compared to traditional M42 or M48 threads, it suppresses aperture clipping and significantly reduces peripheral vignetting across APS-C and Full-Frame sensors.

Full Coverage for ASI2600MC Duo & Guide Sensors

Generous 47mm aperture prevents frame clipping on outer autoguiding sensors (such as Duo series cameras).

Compatible with M42 Telescopes (RASA 8 etc.) 〜 Dedicated M42-M54 Adapter (0mm Optical Path) 〜

Although this filter utilizes the M54 thread standard, we developed a dedicated 'M42-M54 Adapter Ring' so that systems terminating in M42 male threads—such as Celestron RASA 8 with its standard M42 camera adapter—can readily take advantage of it. Engineered to sit completely flush inside the filter's front threads, it consumes zero additional optical backfocus (0.0mm), preserving your exact backfocus calculation.

💡 Available in Two Lineup Options: 'Set' vs 'Standalone'

[Set w/ Adapter]: Choose this if connecting to RASA 8 standard M42 threads or purchasing for the first time (M42-M54 adapter included).
[Standalone Filter]: Choose this if your telescope already features native M54 male threads, or if you already own an adapter and are adding a second filter.

Simple 3-Step Setup (*Example for RASA 8)

STEP 1 [Example] Thread the dedicated M42-M54 Adapter ring onto the RASA 8 front M42 camera adapter. (*Direct connection possible if telescope terminates with M54 male thread).

STEP 2 Thread the IDAS M54 Filter (7.5mm optical path) into the adapter.

STEP 3 Screw your 17.5mm FB cooled camera onto the filter rear thread to complete the 25.0mm baseline setup.

💡 Operational Advice & Troubleshooting for Ultra-Fast Optics (F/2 etc.)

1. Depth of Focus & Fine Backfocus Shimming Ultra-fast optical systems like F/2 have an extremely shallow depth of focus (tens of microns). Due to cumulative manufacturing tolerances of telescope mounts and camera bodies, the optimal backfocus sweet spot may vary slightly. When fine-tuning corner star shapes, micro-adjusting with precision thin shims is recommended.

2. Asymmetric Corner Stars (Sensor Tilt & Collimation) If star elongation occurs on only one side of the frame or corner focus is non-uniform, it is typically caused by camera sensor tilt or telescope optical axis misalignment (collimation), rather than the filter. These issues cannot be resolved by changing filter spacing; adjusting via a camera tilt mechanism (sensor tilter) or consulting your telescope or camera manufacturer is recommended.

Installation Example (Exploded View)

*Prime connection example: Connected to RASA 8 via M42-M54 adapter with 17.5mm FB camera, establishing 25.0mm baseline.

M42-M54 Adapter (Dedicated Step Ring)

*Precision step ring converting M42 male threads (RASA 8 etc.) to M54 filter. Included in the 'Set with Adapter'. Consumes 0mm optical backfocus.

6-Filter Lineup Overview

*Available in NBZ-II, DTD, GNB, NGS1, HEUIB-II, and ODW clear.

Specifications & Compatibility

Thread Standard	M54 P0.75 (Camera-side Male / Scope-side Female)
Optical Path (OL)	7.5mm (Refraction Factored)
Mechanical Length	8.1mm (Flange-to-Flange)
Clear Aperture (CA)	47mm (Large Aperture / Vignetting Reduced)
Glass Thickness	2.0mm
Compatible Systems	Telescopes, Astrographs, Correctors, Cameras adopting M54; Celestron RASA 8 (Use Case), etc.
Production	Made in Japan by ICAS Enterprises