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Agena 50mm Deluxe Straight-Through Finder / Guide Scope with Helical Focuser

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  • 50mm f/3.8 fully multicoated compact finder / guidescope with 190mm focal length
  • Precise dual-focus mechanism makes it easy to achieve and hold focus without play or wiggle and without rotating the eyepiece or autoguider in the focuser
  • Compact and lightweight scope won't take up much space or weigh down your mount
  • Moderate aperture reveals many guide stars not accessible with smaller guidescopes
  • Ideal for guiding long-exposure imaging with refractors and reflectors up to focal length of 1500mm
  • Serves as a large finderscope for bright views of stars and deep-sky objects using 1.25" eyepiece (not included)

Ideal for autoguiding long-exposures with DSLR or CCD cameras, this moderate-aperture 50mm guidescope gives bright images and puts within reach many guide stars not accessible with smaller-aperture scopes. With an overall length of 8.1" (205mm) to 10.5" (267mm), and a weight of 1lb-6.2oz, this f/3.8 refractor with a focal length of 190mm won't take up much space or weigh down your mount. It works best for imaging with refractor or reflector telescopes with focal length up to 1500mm.

Precision Dual-Focus Mechanism

The focuser includes a drawtube with a total travel of 32mm for coarse focusing. It is marked in 1mm increments. Once set, the drawtube locks in position with a single thumbscrew (please note that only one screw is required and included, even though there are 3 threaded holes on the tube).

Precise, fine-focus adjustment comes from a newly-engineered helical focusing mechanism with 10mm of travel. The fine focuser has a knurled focusing collar and a 0-10 scale on the drawtube with 0.05mm increments. A thumbscrew is also provided to lock down the helical drawtube where desired. The design of the precision helical focuser eliminates any play in the drawtube over its entire travel range.

The total focus travel range is thus 42mm.

The helical focuser also incorporates a fixed-orientation design. That means your autoguider only moves in and out during fine focusing and does not rotate, so the camera orientation and field of view of the guide stars remains fixed.

The focuser is machined with male T-threads to securely attach an autoguider that has a removable nosepiece and female T-threads. Or if your autoguider has a fixed 1.25" nosepiece, you can insert it directly and lock it into the focuser's accessory holder. A compression ring makes sure you don't mar your autoguider or eyepiece.

Alignment Rings and Versatile Dovetail Mounting Options

The scope includes dual mounting rings with three nylon-tipped collimation screws per ring. The rings are attached to a 1.23" (31mm) wide by 3.5" (89mm) long dovetail mounting bar which fits into Vixen/Synta-style dovetail finder bases (not included) found on many telescopes. The dovetail bar also includes three threaded through-sockets for other attachment options (one 1/4"-20 threaded hole in the middle and two M8 threaded holes, one on either side). For example, it can be mounted on one of the pre-drilled holes on the tube rings of many refractor and Newtonian reflector optical tubes, or on the rear of most Schmidt-Cassegrain telescopes using a suitable optional dovetail base.

An Excellent Large-Aperture Finderscope

The guidescope also makes an excellent large-aperture finder. It accommodates many 1.25" eyepieces, including illuminated reticle eyepieces such as the Agena 1.25" Wireless Illuminated Reticle Eyepiece with Focusable Single Crosshair (not included). This 24mm focal-length 50° AFOV eyepiece, for example, turns the scope into an approx. 8x50 straight-through finder with a wide 6.3° field of view that gives bright views of faint stars and deep-sky objects not visible in smaller stock finders.

  • Main tube diameter = 54.5mm
  • Dewshield diameter = 60.7mm

Please Note:

  • All these finders have, or will soon develop, light indentation marks on the finder tube from the delrin-tipped screws on the finder bracket. This is not an indication of a defective or used finder.
  • This finder cannot be used with a diagonal to make it a right angle finder. You will not have sufficient in-focus travel.


Note: Occasionally, the product you receive might have a slightly different cosmetic appearance or labeling than what is shown. This can often change from batch to batch according to the whims of the manufacturer. However, you will always receive a brand new, original product as described above.

Description copyright: Agena AstroProducts - Reproduction without permission prohibited.

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Filed under: Eyepieces & Accessories