When you want one rifle to run both a daylight and a thermal optic there are two options: either switch between a day-scope and a dedicated thermal or keep the former permanently on-board and attach a front-mounted add-on (a.k.a. “clip-on”) when wanted. The first route requires repeatable, quick-detachable mounts for all optics and rifles involved; the second, only a single consistent interface between the day-scope and the thermal. Clip-ons also alter nothing except how you see the world downrange: everything else (hold, eye-relief, reticle, and adjustments) is unchanged. Additionally, their compact dimensions, versus a dedicated sight make for greater portability and ease of use as a spotter while stalking.
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As for constraints, the principal ones are (a) how much the day-scope view crops your view of the thermal’s display; and (b) how quickly the pixels in the display become intrusive as you zoom in. Consequently, some day-scopes make better clip-on hosts than others. To minimise or eliminate cropping, choose a base magnification of 2x or less; and to reduce pixelation, a resolution of 1024 x 768 or larger. A further consideration (literally) is how far you may have to stretch to reach the clip-on’s focusing ring. So, it’s out with the big, high-power variables, and in with a new generation of compacts with a low base magnification and an ample zoom factor to give a top end of 12x/16x for daytime precision.
Parameters set, let’s consider the Spectra TI35 thermal clip-on from German Precision Optics (GPO, kindly supplied by UK distributors Raytrade. First impressions are of a smart, but somewhat familiar-looking, unit. Smart, thanks to a titanium-coloured focusing ring, GPO’s understated branding, and a premium Tenebraex flip-up objective lens cover; familiar, because the body shape and controls are those of a HIK Micro Thunder. This shouldn’t surprise us: GPO design and QC their optics from Germany, but source them –as many brands do- from Asia. Familiar, too, is the mounting ring, though here the source is Croatian firm Rusan, leaders in thermal day-scope adapters.
The Spectra’s vital statistics include a 35mm/f1.0 objective lens, a 384 x 288 px/17 μm uncooled Vox sensor running at 50 Hz, a 1024 x 768 full-colour OLED display, and an advertised NETD figure of <35 mK (lower numbers indicate an image with more tonal detail). Overall, a creditable mid-range spec with a betterthan- average display.
Also in the box are an eyepiece with a rubber eye-cup for use in “spotter” configuration; and a 2-part adapter, one half of which screws into the device, while the other mates with the female thread inside the objective bell of the day-scope. Finally, you get a pair of CR123A batteries, a carry case (insufficiently spacious to accommodate the adapter and eye-piece at the same time), a lens cloth, instruction booklets and a C-spanner for tightening the adapter in the day-scope.
The instructions are decent, with only the odd moment of Chinglish, but squintingly diminutive. More importantly, neither states that it is essential to zero the clip-on before shooting, or how to do it. Fortunately, GPO’s website provides a well-written, clearly-illustrated and downloadable “sighting-in” manual. We’ll get to zeroing later.
First, powering-up. The battery compartment is clearly marked for polarity and closes securely with a thumb-screw. Next to it, a rubber flap covers a USB-C port for attaching a power bank or data transfer. Note: a menu option lets you choose between 3V and 3.7V power sources. Don’t select the latter when running off the CR123As or the device will shut down on you and you’ll need to connect a power bank to get it going again. GPO claim a run-time for a pair of CR123As of 4.5 hours, which proved about right, though running the Wi-Fi when using the T-Vision app, or activating the “hot-tracking” function cut this significantly.
But I’m running ahead of myself. To get started, push and hold the Power button for a couple of seconds. six seconds later the device is booted and ready to use… almost. Strangely, it takes another 15 or so, before the menu is accessible, via a long press on the Menu button. Once in, you can use the four satellite buttons (Mode, Camera, Shutter and Zoom) to scroll to your preference before using the Menu button to select it. A long press on the Power button activates a 5-second countdown to standby, or reactivates the device thereafter. Absent, a visible indicator of standby mode, it is advisable to remove the batteries between uses.
The controls are pretty intuitive. Blipping the Camera button captures a JPG image; while a long press starts recording video, and another saves the clip as an MP4. The Shutter button recalibrates the display, though an automatic setting is available. With the eyepiece attached, the Zoom button speeds you from 1X, to 2X, 4X, 8X and back to 1X again with each press, but in clip-on mode, it automatically switches to navigation-only - a neat feature, as accidental zooming at the wrong moment could cost you a shot.
Now familiarised with the device, we can mount it to the day scope. Raytrade supplied a GPO Spectra 4-16x50i, whose objective bell is a perfect fit for the TI35’s adapter. If you run a different scope, you can specify an alternative Rusan unit that slides over the objective bell and locks with a cam lever. Mounting was initially hindered by a blanking plate on the bottom of the device not clearing the barrel, but this was easily removed, revealing 2 tripod-compatible sockets.
Now I could assemble the adapter, align the Spectra by squaring the day scope’s reticle against the graphics in the menu, and lock everything into place with the C-spanner. That done, removing/ refitting is as simple as loosening/ tightening a locking collar. A similar collar secures the day-scope adapter or eyepiece. Nevertheless, it takes practice to transition rapidly and silently from spotting to shooting mode when hunting. In this context, slide-on/cam-lock adapters are preferable.
Before shooting, as mentioned, the clip-on needs to be zeroed. GPO recommend (1) fixing the rifle firmly in place (i.e., strapped down in a rest on a solid bench), with the day-scope’s reticle centred on the target (2) without moving the rifle at all, fitting the clip-on, and (3) using the control buttons to align the display to re-centre the target in the reticle.
If using a day scope of 3x or greater, before fitting the clip-on it’s worth activating the Spectra’s Wi-Fi, connecting the device to your smartphone, and opening up the T-Vision app, so as to see the alignment co-ordinates in full. As with many device apps, I had to deactivate the SIM on my phone first, after which the connection was fast and stable.
Simultaneously pressing the Camera and Zoom buttons opens the alignment screen, where X- and Y-axis scales let you centre the image. The zeroing manual notes that each number represents 2.5cm @ 100m. Testing proved this to be accurate. Knowing this figure also makes it possible to zero the Spectra without a fixed rest. Start at 0 on each axis and you won’t be far off. Repeated removal/refitting of the Spectra showed no zero shift. Nevertheless, GPO advises marking the adapter’s position on the day-scope for consistency.
Out and about
In the field, the Spectra gave a good image in both hand-held and clip-on modes, enabling potential quarry to be detected at distance, identified well beyond shooting range, and easily contextualised in the landscape. Having seven palettes just a button-press away is nice, but for simpler scrolling I would settle for White Glow (a.k.a. “white hot”: some Chinglish here!), Black Glow, Red Glow and the green “NV” settings: dispensing with the psychedelic Fusion Glow, Urban Colour and Nature Colour options. I could also do without having to enter the menu to adjust brightness and contrast, or to change between the Jungle, Forrest [sic], Stone, Urban and Discovery presets.
Also in the menu is an angle-based distance-measuring function. Once activated, it prompts you to select a target size (Brown Bear: 3m, Deer: 1.2m, Grey Wolf: 0.8m or Custom: 0.1m-9.9m), then blip the top and bottom of the target, before displaying the range in the top L/H corner for about 5 seconds. Ingenious, but tedious, too: since it’s hard to make two precise inputs, and the rangefinder automatically defaults back to the main menu after each reading.
Ergonomically, things are so-so. As a hand-held spotter, neither the boxy cross-section and protruding batterycover screw, nor the lack of a handstrap or a lanyard attachment-point are ideal. Whilst as a clip-on, trying to focus the Spectra with my arm fully extended with the 369mm long 4-16x50i scope, had me wishing for a focusing dial instead of a ring.
These things aside, the TI35 really grew on me during testing, especially once I swapped the 4-16x50i for GPO’s 2-12x50i, which gave me a full view of the display and more satisfying results up to 6X. My conclusion? Teamed with the right scope, GPO’s clip-on has enough performance, polish and pedigree to make it well worth a look.