I tested the ToupTek GS-100 PAPO. It’s a 25/100 mm f/4 apochromatic guide scope with four elements and ED glass, which also functions as a wide-field imager. Priced at CHF 149 (including tax) in our store, it’s a three-in-one solution: autoguiding, entry-level wide-field imaging, and a visual observation tool. Here’s what I think of it after using it.
I got the GS-100 PAPO in the GS-100AR version, the one with rack-and-pinion focusing. First impression: the build quality is exceptional. The body is very rigid; nothing moves, and there’s no play in the focusing mechanism. It’s a well-finished piece of equipment that inspires confidence the moment you take it out of the box.
As a guiding instrument, it's really great. The stars are sharp, perfectly round, and there's no purple fringing on the bright ones. ToupTek has reduced the purple fringing compared to the older GS models, and it really shows. Autoguiding locks on without any problems.
In wide-field imaging, it’s definitely worth a try. At a 100 mm focal length and f/4, you can capture wide fields: expansive nebulae, the Milky Way, and large objects. The stars appear extremely fine across the entire field of view. The 1″ flat image circle covers an ASI290, ASI678, or similar sensor without distortion at the edges.
Manual focusing is tricky. The focus point is very precise at f/4—it’s easy to overshoot it. The depth of field is shallow, as with all f/4 lenses. You have to take it slowly, turning the focus ring in tiny increments. But that doesn’t prevent you from using it: once you’ve found the focus, it holds. And with an AAF motor (AR version), the problem disappears completely.
My favorite feature: You can screw a 2-inch filter directly onto the front anti-fog screen. Standard M48 × 0.75 thread. That means you can attach a filter, an IR-cut filter, or an H-alpha filter directly to the telescope, without an adapter or filter wheel. This is very convenient for wide-field imaging with filters.
For a multi-filter setup, a filter drawer or filter wheel can be mounted using an M54-to-M48 adapter. But for a single filter, screwing it onto the anti-fog screen is the simplest solution.
ToupTek offers two lines of PAPO eyepieces: the GS-100 with a 100-mm focal length, and the GS PAPO 150–350-mm series. Here’s how they compare:
The rule: The focal length of the guide scope must be at least equal to the focal length of the main telescope, and ideally longer. For an 80 mm f/5 (400 mm) telescope, a 100 mm GS-100 is too short for guiding, but sufficient for short exposures. For a C8 at 2000 mm, you’ll need a GS PAPO 300 or 350 mm.
But the GS-100 has an advantage that the others don’t: at a 100 mm focal length and f/4, it’s capable of wide-field imaging. The GS PAPO 150–350 mm models are too long for wide-field imaging. The GS-100 is the only one that serves as both a guide scope and an imager.
Two versions: GS-100AC (Crayford) and GS-100AR (rack-and-pinion). I chose the AR version, with the rack-and-pinion mechanism. The rack-and-pinion mechanism is stiffer; it doesn’t slip under the weight of a heavy camera. The Crayford is smoother and sleeker, but it can slip under the weight of a heavy camera. For guiding with a small camera, the Crayford is sufficient. For imaging with a cooled camera, the rack-and-pinion system is more reliable.
The AR version is also compatible with ToupTek's AAF focusing motor. For autoguiding and control, this is the option to choose.
For guiding: a ToupTek G3M or ZWO ASI290 camera on the eyepiece holder, mounted on the main telescope’s Vixen rail. The GS-100 is lightweight and does not overload the mount.
For wide-field imaging: a color or monochrome camera with a 2-inch filter on the dew shield. At f/4 and 100 mm, a 30- to 60-second exposure is sufficient for bright objects. Faint objects require more time, but this is a 25 mm lens: we’re not going to be looking for faint galaxies with this. We’re looking for wide, bright fields.
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The The ToupTek GS-100 PAPO is priced at CHF 149, including tax in our store. Be sure to check out the ToupTek line and PAPO guide glasses, 150–350 mm.
This article is based on my personal review of the ToupTek GS-100 PAPO (GS-100AR version), the official specifications from ToupTek Astro (touptekastro.com), and customer reviews posted on the ToupTek website (Lance McIntosh, Dave Pritchard, Jay Cooper-Groves, 2026). Retail price: CHF 149, including tax.
CBurkhalter
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