Relay lenses II: Pocketscope Relay Lenses

19 Jun, 2026

Introduction

In the early 2000s, there was a plethora of night vision "pocketscopes" which are small monoculars meant to be handheld or tripod-mounted for nighttime surveillance use. Many of these pocketscopes came with fast optics and used a common ocular thread pitch (the same one as the AN/PVS-5) and were either c-mount or threaded to take the AN/PVS-15 objectives (which also shares a common ocular thread pitch with the pocketscopes and the PVS-5.)

These housings were almost all designed for autogain tubes and were very simple, with a battery compartment, power switch, and some had IR illuminators. Most had the aforementioned PVS-5 ocular threading, and they were either C-mount, threaded for PVS-15 objective assemblies, or had proprietary optics. The designs varied, but there is one that I personally like: the Litton M944A.

My Litton M944A, modified with an ANVIS lens cell and a cut-down ENVIS eyepiece.

Both the Litton M944 and ITT 6010 have the same objective and ocular threading, however they have very different optical assemblies. The M944 comes with PVS-15 threaded optics, and a PVS-5 ocular assembly, where the ITT 6010 comes with a c-mount PVS-14 lens, and a PVS-14 ocular with the old PVS-5 threading (these appear to be the same as the ENVIS, a c-mount pocketscope also made by ITT.)

As mentioned in my last blog post, I acquired a Litton 1x relay lens system for use with the M944. The litton relay was the best performing of all 3 relay lens systems i tested, so I kept it in my personal collection. I then found out that ITT made a comparable relay lens system, for the ITT 6010 so I picked one up on Ebay. The Litton 1x lenses appear to be a bit more desirable than the ITT ones, and their used prices tend to reflect that.¹

These lenses are very optically similar. The distortion profiles are very close, the image is very flat, and the lenses both have the same threading (PVS-5 thread to pocketscope, T-mount thread to camera) and the optics appear to be coated with some anti-reflection coating. The optics appear to be a single element on the tube side, an achromatic doublet on the camera side (deduced by adequate chromatic aberration control and delamination on the Litton relay,) and both projecting a 1x image circle; 18 mm in diameter.²

Litton 1x

The Litton 1x is manufactured by Fujinon, according to CNoct and confirmed by Rossi777.^3,4 It is 73.8 mm long, with a diameter of 56.0 mm and weighing 252 grams. It has a turquoise-blue coating on both front and rear elements.

Front and rear view of the Litton 1x relay lens.

The relay lens is quite large on the M944, and is relatively stiff to turn. There are no locking elements to set the focus, so I scored two hashes on the lens body, to serve as an alignment point to fine-tune the focus of the relay.

The Litton relay in my M944A.

This relay lens is nice to use. The stiffness of the focusing ring led to the rubber grip to fall off, so I had to glue it back in place. However, of the three relay lenses i evaluated in my last post, it had the best optical performance, projecting an even, flat image. The front element is recessed and has a deep groove, allowing one to cram in filter elements with 3D-printed spacers to correct for the chromatic aberration of the lens.

Rear view of the Litton relay in my M944A.

This lens paired with the M944 has single-handedly improved my NV photography by a huge amount, and enabled me to shoot astrophotos with a telescope and filter wheel. Any relay to surpass this lens is clearing a very high bar.

Delamination of the rear elements in the Litton relay lens. The delamination is the ring of haze seen in on the lens; up close it has visual texture.

Unfortunately, the Litton relays have one glaring fault: delamination with age (see above.) This is a known problem for old Litton optics (such as the PVS-15/PVS-18/M944 objectives, and the PVS-7A/C eyepieces) and is caused by the adhesive off-gassing and separating the lens elements. My personal lens has relatively mild delamination, though CNoct mentions several of his lenses are severely delaminated and very hazy.³

ITT 1x

The ITT 1x is likely manufactured by Qioptiq, according to CNoct.³ It is 73.8 mm long, with a diameter of 51.4 mm and weighing 247 grams. It has a purple-orange coating on both front and rear elements.

Front and rear view of the ITT 1x relay lens.

The relay lens is not explicitly designed for the M944, and the knurling does cut into the threads of the 944 body. There are two set screws to lock the focus, so the system can essentially be set and remain in focus for the most part, which is a nice quality of life improvement over the Litton 1x.

The ITT relay in my M944A.

Due to the smaller sizer and set screws being able to lock the lens in place, the lens is even nicer to use than the Litton 1x for regular photography. The lens focuses smoother, and just seems to work a tiny bit better than the Litton 1x. Unlike the litton relay, filters need to be inserted on the rear element rather than in-front of the lens as there is no cutout that could accommodate the filters AND fully seat the lens into the M944

Rear view of the ITT relay in my M944A.

Upon inspection of the lens, I did not notice any delamination. Since the lenses were quite similar optically, with a flat image across the image circle and very close edge distortion, further evaluation needed to be done using a resolution test target to really push the lenses to their limit.

Methods

Litton relay on the left, ITT relay on the right. The teflon tape on the ITT relay is present to widen the barrel diameter so the same filter and filter holder could be used on both systems.

Imaging

To test the relay lenses on their own merits, imaging conditions are standardized. The target is the USAF 1951 resolution test target, printed on a 600 DPI laser printer.⁵ The camera is my EOS RP, using my canon EF 200 mm f/2.8 L II shot wide open at 1/50" exposure time and ISO 1600. White balance was set to 6542 K for all shots. The image intensifier system used was my C-mount M944A with my L3Harris 18UM image intensifier tube.⁶

The three setups compared are the native image of the relay lens, one with a 470 nm long-pass (LP) filter and a 2x T-mount teleconverter attached to the t-mount threads on the relay lenses. The test target was set 3 m from the camera and tripod and the illumination was from the streetlights past astronomical darkness through blinds, and was consistent for the duration of the imaging.

Images were shot in RAW format, and immediately converted into .png images without any image processing . They were labeled in MS paint, and then compressed to <10 Mb using Caesium image compressor and uploaded to bearblog. Analysis of the images was done with the raw image, under digital magnification. Resolved elements are defined as elements that have some degree of contrast, and line pairs are visible, even if poor in contrast. Unresolved elements appear as a block without identifiable line-pairs.

Native Optical Performance

The optical performance is qualitatively evaluated by scrutinizing the limiting resolution of the test target under digital magnification. The images are also qualitiatively evaluated om edge distortion and overall exposure. Chromatic aberration in night vision relay lens systems is typically seen as a blue haze using P45 white phosphor image tubes, as these optics were primarily designed around the 545 nm P43 peak and the three other major wavelengths in P43.

470 nm LP Filter

The fastest and most rudimentary way to address chromatic aberration is to filter out the frequencies that the lens elements cannot focus. The selection of such a filter requires examining spectra of phosphor emissions.

P43 (green) and P45 (blue) spectra, overlaid.⁷

P43 and P45 have similar spectra up to ~470 nm, however P45 has additional emission peaks from 390 to 470 nm in the blue region, forming a blue-white image to the eye. To address the chromatic aberration, a 470 nm LP filter is used. Previously, I used a VG9 filter⁸, which had absolutely atrocious transmission (~70% at 532 nm peak) and was losing a huge amount of light using it. Then I found a 470 nm LP filter ⁹ with a relatively broad transmission (~98% at 540 nm peak) and figured it'd be better. The lenses are also qualitatively compared using the 470 nm filter, using digital zoom to note the limiting resolution.

2x Teleconverter

Due to the relatively small image circle, a 2x Teleconverter could double the image size to ~36 mm, and thus the image could be stretched across most of the sensor similar to the GEM-II. A 2x CPC teleconverter was used for the duration of the testing. The same qualitative comparison used in scrutinizing the native lenses is then done.

Results

The resulting images are shown below, sorted by the optical configuration.

Native Lens

Litton 1x relay. Note the visible blue fringing, and element 6, group zero is not resolved.

ITT 1x relay. Note the substantial reduction in blue fringing, and element 6, group zero is resolved.

470 nm LP Filter

Litton 1x relay with 470 nm LP filter. Note that group 1 elements are not resolved.

ITT 1x relay with 470 nm LP filter. Note that elements 1 and 2 in group 1 are resolved.

2x Teleconverter

Litton 1x relay with 2x teleconverter. Note element 1 in group 1 is resolved.

ITT 1x relay with 2x teleconverter. Note element 1 group 1 is partially unresolved, and the remainder of group 1 is unresolved.

Discussion

These resulting images were then cropped and placed side-by-side.

comparison between the native relay lenses

Between the ITT and Litton relays, the ITT has better chromatic aberration, with significantly less blue fringing. This may also be due to the different coatings on the lens, possibly cutting out more of the high frequency light that contributes to the chromatic aberration. As the white balance is fixed across all images, the yellow cast on the ITT image indicates some blue light is being blocked by internal lens coatings. Futhermore, the purple-orange lens coating is reminiscent of certain PVS-14/ANVIS lens coatings, which have a similar orange-purple coatings.¹⁰ Without using a spectrophotometer, I can't make a quantitative assessment on the specific light transmission, so the qualitative "it's yellower" is the best I have.

comparison between the relay lenses with a 470 nm LP filter

With the 470 nm LP filter, the problem of chromatic aberration in both lens systems is addressed since it matches the spectral output of the tube to what the lens was designed around. Thus, using the 470 nm LP filter, the lenses can be compared as if the intensifier was a high-performance P43 tube,¹¹ which is the best-case scenario for the optics. The ITT relay resolved elements 1 and 2 in group 1, where the Litton barely resolved element 6 in group 0. Knowing this, the ITT has slightly better performance, with higher spatial resolution despite the visually worse contrast.¹²

comparison between the relay lenses with the teleconverter

Oddly enough, when paired with the teleconverter, the Litton relay provides a better image. Teleconverters add additional distortion to an image, especially if they are not optically "matched" to a lens (which this teleconverter is not.) The Litton relay resolves element 1, group 1, where the ITT relay cannot resolve the vertical element. The Litton relay also has slightly better edge distortion, with a flatter image closer to the image edge, indicating a better (but not perfect) optical match with the teleconverter used. The teleconverted does lose a few stops of light, so the resulting image appears dimmer despite being the same objective lens.

Conclusions

Although the relay lenses are very close upon initial inspection, the ITT relay is the optically superior lens, albeit by a very narrow margin. The ITT lens also has some quality of life features and is marginally better to use as a relay lens that can be slapped onto a camera and run with. However, the Litton relay has better performance with the CPC teleconverter. The best part about the ITT relay (and primary detraction from the Litton relay) is that the lenses are not subject to the delamination that old Litton lenses are. Knowing this, I conclude that the ITT relay is the superior relay for my purposes of maximizing detail in astronomical objects and NV photos. However, that doesn't make the Litton relay a bad choice per-se. If you can get one at a good price (< $50 USD) and it's in good shape (very little delam, like my unit) it's worth it. My conclusion from the last post still holds true, and that's with the Litton relay.

This information also applies exclusively to the 1x relay lenses; ITT and litton also made 0.66x lenses that I have not been able to evaluate. The ITT 0.66x lenses externally look extremely similar to their 1x, so if you're buying one, tread carefully. The inner element of the 1x should be relatively large, and should look like the photos shown in this post. I have not been able to acquire any other relay lenses, nor do I have the camera equipment to image an afocal setup using a PVS-14 ocular and fast prime lens. There are also other pocketscope relay lenses. I believe BE Meyers made some, and there are almost certainly others, though those are even harder to track down than the ITT/Litton relays. Going based off availability and cost, I recommend a Litton M944¹³ paired with an ITT 1x relay. The ITT 6010 has at least a half-dozen models and is quite hard to find, unlike the M944. At time of writing, the M944, full optics, relay lens, and adapters can be had less than half the cost of a PVS-14 with optics, so all you'd need to bring is a image intensifier tube and camera.¹⁴

I decided that I would part ways with the Litton relay to a friend of mine, and sold it with the teleconverter. As far as I'm concerned, the ITT 1x relay is here to stay unless someone makes a relay lens threaded for a PVS-14 threads, in which case I will drop everything I own to get one.

Post Scriptum
I'm not making a "next up" post. That silly little note essentially forced me into writing this blogpost, which took two whole months between start to finish. I'm instead gonna leave it open ended, and write what comes to mind.
—Kat

Citations, Footnotes, and Personal Comments