Zeiss DTI 6-40 Thermal Imaging Monocular
- By Chris Parkin
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- Last updated: 17/09/2023
The latest Zeiss thermal monocular is available with 20 or 40mm interchangeable lenses to cater to the needs of woodland or open-land hunters. The main body is made in Germany and the lenses are from China. You can buy both lenses if you want, with the only difference being the field of view. The unit can also become a scope-mounted clip-on, offering further versatility across worldwide markets.
Zeiss’ aim is to seamlessly blend the DTI into the current hunting culture, and as such, the first thing I noticed about the unit was its superb ergonomics. The twist-up eyecup is similar to the design found on the brand’s binoculars and it offers four positions to suit your eyesight, head position, and spectacles. Eyepiece focus lies ahead to give a sharp picture on the internal 1024 × 768-pixel HD display. There are three control buttons on top; the front is for power, and the rear two control the colour palette as well as photo or video activation. A roller sits centrally, controlling digital zoom up to 10x beyond a baseline optical 1.5x (20mm) or 3x (40mm) magnification, imparted by the f1.0 germanium lens and image processing software. Image focus is controlled with a tactile rubber collar behind the objective lens, and a securely fitting rubber lens cap is hinged below. The unit is supplied in a Cordura case with a neoprene sling, and this fits on either side of the ocular lens, with a lens protector cap slotted along it.
Ergonomically speaking, this is one of the best thermals I have ever used, as it hangs without excess bulk, flat to your chest. The lens caps stay in either state exactly where you left them, and everything feels very well made. If you do have both lenses, these can be swapped in less than 30 seconds, as they thread into the front of the body, with a secure collar for grip. I would imagine secondary lenses are supplied with their own individual lens caps.
The DTI uses a removable battery that fits in a compartment underneath. This has an approximate 6.5-hour battery life and charges using a supplied USB-C cable. The port sits under a rubber cover. This cable needs a 20w power supply, so make sure your USB source is up to the requirements. It takes about 3 hours to charge.
In use, the longest I used the unit was four hours and the internal display showed 50% remaining. I never found it to give false readings, nor did it seemingly dump its charge, but I was using the unit in battery-friendly 10 °C air temp. The heatsinks are tactile on the sides and they do feel warm when charging, which is a known factor and of no concern. There is a ¼” thread on the underside for tripod mounting, and if you really want, the DTI can also track GPS data. It also offers the usual time/date functions.
Zeiss has shown me the data of analysed market needs and looked at competitors’ exact specifications to directly combat them with an equivalent 640 × 480-pixel sensor resolution at 12μm pitch. There’s a 50Hz refresh rate for a smooth image on the screen, but no NETD rating is published.
The menu structure is truly intuitive, with easily controlled functions and menu screens, plus large, easily visible icons. Low-energy Bluetooth and Wi-Fi connectivity are available, and you can use the Zeiss app to alter the setup. However, I prefer to do everything on the unit alone, as I go hunting to escape my phone.
Familiar functions like screen brightness, contrast, and colour pallets are easily selected. You can customise functions like the colour palettes and an automated battery timer that switches the display off when the eyepiece is taken away from your face. This saves masses of battery life and also prevents the unit from lighting up your face when hanging around your neck. It’s so quick to react, you hardly even notice it in use.
So, what’s it like to use? Well, the functionality is breathtakingly intuitive compared to many peers, and the ergonomics are exceptional, with no need to search for buttons or dials, as they fall automatically at your fingertips. ‘DynamicZoom’ enables fast zooming to improve identification and you can select your preferred zoom speed as part of five customised observation profiles.
When switched on, the unit comes to life immediately with a visible and usable thermal image. However, it takes nearly 30 seconds for other functionality to come online. This is a factor being addressed by Zeiss, as although it doesn’t restrict use, it’s quite unnerving at first.
Scrolling through the menus allows you to select Universal, Fog, Detect, or Identify modes to suit your needs. Detect was my preference. My colour palette preference is usually white/hot, or very occasionally black/hot in open spaces, but I really liked the red/hot, which as well as remaining generally white, really ‘pops’ when something comes into your field of view. It’s not as distracting as the red tracker dot dancing all over, which is used by other brands. It was also noticeable that with fine depth of field control focusing the f1.0 lens, you could perceive a more three-dimensional perspective of an animal’s detail. This isn’t as easy to show in a photo, but it’s visually distinct on recorded video. On that topic, a long hold on the rearmost control button swaps from stills to video, or vice versa. Whilst in either mode, a single press initiates either function, so you don’t need a long hold to catch the action!
For a user with experience with a lot of thermal devices, Zeiss’ ‘ZSIP Pro’ three-stage image processing algorithm is noticeably beneficial. The first processing stage removes unwanted electronic noise from the sensor’s output signal, while the second divides the entire image into 12 sections that are individually optimized with respect to contrast. The last step optimises sharpness. Marketing spiel aside, this eliminates the problem of large, cold areas, like the night sky, auto-dimming the display and concealing closer quarry that would otherwise be visible.
‘Made in Germany’ is apparent, with solid build quality and smooth, precise mechanical components. The interchangeable 20 or 40mm lenses allow users to swap for a wide field of view in woodland or max magnification over longer ranges. The electronics are predictably reliable and the ZSIP processing is good. However, one thing disappointed me slightly. Given Zeiss’s rich optical history, I found the ocular lens quite critical to positioning and it was easy to lose screen focus within the generous exit pupil. The battery system is reliable, and I like the option to carry a spare, although the unit can be run with a power bank. It’s also noticeable that with Bluetooth and Wi-Fi, there is an almost undetectable latency between the DTI’s image and a smartphone display. I loved the speed with which the controls operate and especially the fluidity and immediacy of the zoom, which, incidentally, can be set to give increments between 0.1 and 1x for each tactile click of the roller. Increasing zoom, as always, shows escalating pixelation, but I liked the fact that the roller control took minimal mechanical effort, so there was less disturbance to the unit’s stability.
I imagine that Zeiss has invested heavily into sensor technology, so further evolution in their range has started on a decent level, with superb ambidextrous controls, an easily navigated menu system, and total reliability. I didn’t experience any system crashes, so maybe that long warmup time is worth it. I don’t think I got to see the best image capability, due to the warm, spring daylight, when compared to the cooler winters, but regardless, I never failed to detect and identify quarry. Also, I never had to switch the unit off to save battery life, and it was always secure and available in the centre of my chest.