Explore Scientific 8x50 Helical Finder-Guider 1.25″ T2

Explore Scientific 8x50 Helical Finder-Guider 1.25″ T2

Overview

The Explore Scientific 8x50 Helical Finder-Guider is a high-quality, versatile optical instrument combining the functions of a finder scope and a guide telescope. With a focal length of 220 mm, it features a precision helical focuser and a detachable eyepiece unit equipped with an illuminated reticle crosshair. Thanks to its 1.25″/31.7 mm barrel connection and T2 thread (M42x0.75 mm), it is an ideal tool for autoguiding in long-exposure astrophotography. The instrument can also be used as a compact travel telescope for visual observation.

Optics and Field of View

This 8x50 finder scope with helical focuser delivers a bright, sharply defined image with an exceptionally wide field of view of 6.96 degrees - significantly exceeding the capabilities of typical finder scopes in the same class. This makes it much easier to locate and center objects in the field.

• Illuminated reticle crosshair with scale markings at 1-degree intervals for reliable reference when estimating distances between objects
• Open center of the crosshair for precise centering of a star or other target object
• All optical surfaces feature FMC (Fully Multi-Coated) anti-reflection coatings for maximum light transmission and bright field of view even under adverse conditions

Helical Focuser and Focusing System

Focusing of the objective lens and the reticle crosshair operates independently, giving each observer full control over the image:

• The main objective is focused via a large, knurled ring of a precision helical focuser with a travel range of 28 mm
• A laser-engraved millimeter scale from 0 to 28 mm allows easy reproduction of the focus position
• Minimum focusing distance is 3 m, making the finder usable for terrestrial observation as well
• The eyepiece unit allows independent focusing of the reticle crosshair directly at the eyepiece, so each observer can adapt the image to their own eyesight without compromise

Autoguiding for Astrophotography

One of the primary strengths of this instrument is its use as a guide scope for autoguiding in astrophotography. Autoguiding works by having a smaller guide telescope with an attached tracking camera continuously measuring mechanical deviations of the mount and correcting them in real time - ensuring pinpoint star images even during long exposures.

• The finder-guider fits into the existing finder shoe of the main telescope and aligns parallel to it
• If the existing shoe is not compatible, a replacement finder shoe is included in the package and can be attached with four M5 screws
• The tracking camera connects via the 1.25″/31.7 mm barrel or the T2 thread (M42x0.75 mm) at the rear of the finder
• The camera is secured by a brass clamping ring and three thumbscrews
• The focal plane is located approximately 22 mm behind the T2 thread - the required back focus of the tracking camera should be taken into account
• Maximum permitted camera weight is 550 g, covering the vast majority of commonly used guide cameras

Visual Observation - Compact Travel Telescope

The Explore Scientific 8x50 Finder-Guider can also be used as a compact mini travel telescope for visual observation. With optional eyepieces, magnifications from 8x to 40x can be achieved:

• Compatible with virtually all 1.25″/31.7 mm eyepieces with focal lengths from 5 to 26 mm
• Specially recommended: Explore Scientific 52° series (Art. 02195xx) and 62° LER series (Art. 02196xx) eyepieces
• Please note: the finder supports direct viewing only - a zenith prism or diagonal mirror cannot be used

Build Quality and Mounting

The entire finder mounting assembly is made of aluminum, ensuring durability combined with low weight:

• The finder shoe is compatible with many common telescope models, including Explore Scientific and Bresser Messier
• Six large adjustment screws with anti-slip knurling allow easy and precise alignment of the finder - even with gloves on or in adverse weather conditions
• All adjustment and clamping screws feature plastic tips to protect the finder body and mounting surfaces from scratching
• Finder shoe bore axes: 31.7 mm in both longitudinal and transverse directions

Technical Specifications