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The MonsterAdapter Pentax Adapter LA-KE1 ($439) bridges the gap between two vastly different camera systems. It works with many (but not all) of Pentax's autofocusing SLR lenses, making them compatible with mirrorless cameras from Sony. It's an especially intriguing adapter for photographers who've moved to a Sony mirrorless system, but held onto a stash of favorite Pentax glass. The LA-KE1 is on the pricey side, no doubt due to its niche appeal, but even with some firmware quirks I found it to be a practical solution to use Pentax's beloved FA* and Limited lenses with Sony mirrorless cameras.

MonsterAdapter is a new name in the photo world, and while the LA-KE1 is the first of its products I've had a chance to use, it's not Monster's first effort. It has already made similar adapters to use Nikon F and Minolta/Sony A SLR lenses with Sony E mirrorless cameras.

The attention is on Pentax lenses with the LA-KE1, one of the few brands out there without its own mirrorless system or adapter solution. It's especially appealing for photographers who've held on to some of Pentax's characterful classic lenses, whether it be a version of the FA 31mm Limited or something rarer, like the FA* 24mm F2.

The adapter itself is a pretty basic concept. Lenses are designed to be mounted at a set distance from an image sensor. Since that distance is pretty short on a mirrorless camera, an adapter is essentially a light-proof spacer. MonsterAdapter recommends you take care when using the adapter with heavier lenses, especially those that weigh more than about 2.2 pounds (1kg). You'll want to make sure to cradle a big lens to support its weight when working handheld, and to use a tripod collar when mounting it.

There's a cottage industry of purely mechanical "dumb" adapters for mirrorless cameras—you can read about them in our guide to adapting lenses. MonsterAdapter goes a bit further, adding autofocus for screw-driven lenses and electronic aperture control. It comes with a premium price, $439 versus $30 or less for a manual alternative. You may find it worthwhile, however, especially if you still use some of your old favorite Pentax glass and want to enjoy the convenience of autofocus.

Not all lenses are supported, though. With its current firmware, the adapter focuses on lenses that rely on a screw-drive, not those with an internal focus motor. Pentax's film-era autofocus lenses use this type of focus. If you're using more recent made-for-digital glass with a DC, PLM, or SDM focus motor, you won't be able to use autofocus, at least not yet—MonsterAdapter promises to update the firmware to expand support to these types of lenses. For now, you're limited to using it with lenses from the list below.

It's also not a good fit for older lenses without electronic aperture control. You can mount them and use them at an open aperture, but they don't stop down, so the LA-KE1 is for open aperture use only. It's not something I see as a real negative, though—a manual Fotodiox adapter works perfectly with older SMC K and M series lenses and costs just $25.

Your choice of Sony camera matters, too. The LA-KE1 really needs one that supports phase detection focus for adapted lenses to work well. For full-frame that's a7 II or newer, and for APS-C the a6100 through a6600 are all supported, but not the a6000 or NEX generation.

I tested the MonsterAdapter LA-KE1 with the Sony a7R IV and several Pentax lenses from the FA and DA Limited series. The screw-driven lenses worked mostly as expected. I ran into some quirks with certain lenses, and noted that autofocus isn't quite as speedy as when paired with a Pentax SLR.

As an example, the HD FA 31mm takes about a second to drive focus from infinity to close-up with the LA-KE1 versus the K-1 Mark II's 0.5-second and the K-3 Mark II's 0.3-second. The adapter's focus motor doesn't drive the lens with quite the same level of power as native SLRs. There's very little delay when focus is set closer to start, though—if the lens just needs to make a small adjustment there's a slight lag.

Focus speed may be a step slower than an SLR, but the adapter allows you to take advantage of Sony's subject tracking and face/eye detection focus modes, just as with an E-mount lens. But focus speed matters for certain types of photography—if you're thinking about using your old Pentax lenses to snap fast-moving action with your quick-firing Sony mirrorless camera, think again. The adapter is good for family snapshots, portraits, and landscapes, not for demanding subjects like wildlife and sports.

I experienced some issues and lockups and overexposure when working at very narrow f-stops with select lenses, but nothing deal breaking. If you're using the lens with its v01 firmware, you might run into some problems working in aperture priority with certain lenses when the f-stop is set to f/16 or smaller—my copy of the SMC FA 43mm Limited had issues with overexposure at very narrow apertures. It's been fixed with the v02 firmware (more on that in the next section), but if your adapter is loaded with v01, you can sidestep the issue by using your camera's manual mode.

A smaller quirk, some lenses will report their maximum aperture incorrectly. Both HD and SMC versions of the FA 43mm F1.9 Limited show as F2.0 lenses with the adapter, and the HD DA 21mm F3.2 Limited shows up as an F3.5 lens. Sony doesn't make any F1.9 or F3.2 lenses, so it's likely its cameras cannot recognize these uncommon f-stops as valid settings.

Aside from that, EXIF data translates as expected, so you'll know what lens you've used to make an image, and in-camera IBIS works without issue. Many Sony cameras use stabilized image sensors just like Pentax's SLRs.

Manual focus is supported, too. There's an AF/MF toggle switch on the side of the LA-KE1, and it's necessary to use it to swap focus modes; the option is grayed out in camera menus. Quick Shift lenses like the HD DA 40mm Limited support full-time manual focus override with Pentax SLRs, but the feature doesn't translate to the adapter.

The LA-KE1 is limited to manual focus when recording video, but electronic aperture control is available.

You can set full-frame Sony cameras to always use the entirety of the sensor, or to swap to a cropped view when APS-C lenses are attached. The adapter is smart enough to pass this information on to the camera.

My a7R IV swapped to its 26MP APS-C mode when I attached the DA 15mm Limited and other DA series lenses. There are exceptions—for example, the HD DA 70mm F2.4 Limited and DA* 60-250mm F4 cover full-frame sensors, and the adapter is smart enough to tag them as full-frame lenses. You always have the option to force your full-frame Sony to use either its full-frame mode or cropped APS-C sensor area; a setting is available in the menu to swap between the two.

MonsterAdapter provided me with an early look at its forthcoming v02 firmware. It adds support for loads of additional lenses, including many with internal SDM and DC focus motors. Support for PLM focus motor lenses isn't included.

The update works as promised, fixes some bugs from v01, and adds support for a wider array of lenses—I tried a few with the adapter. The DA* 60-250mm F4, D FA 150-450mm, and DA 20-40mm Limited all worked perfectly.

These types of lenses have their own focus motors, so they aren't limited by the speed of the LA-KE1's motor; the real trick is in the adapter's ability to translate focus commands between a Pentax lens and Sony camera. I noted a slight hesitation for focus acquisition with these lenses, but nothing that kept me from getting a shot.

The v02 firmware is on pace for release before the end of this year. You'll need to have access to a Windows system to run the required software, though. It works with operating systems as old as Windows 7 and a compatible Sony camera; only the very old NEX-C3, NEX-5, and NEX-5N aren't supported.

I updated the firmware using a Windows 10 laptop and my Sony a7R IV. It's a quick update to run—the whole process took about five minutes, including some time fumbling around the a7R IV menu to set the camera to USB Mass Storage mode, a requirement for the update. Windows Defender warns that the firmware update software is unrecognized, but the software worked as expected and loaded the firmware just fine.

Plugging a USB cable into your camera is a cumbersome way to run updates, though, and creatives who prefer to use macOS are left in the cold for updates for now. MonsterAdapter tells me that it's not yet finalized a plan for Apple users. The ideal scenario is a firmware update that can run from a memory card in-camera, but I'd be surprised if that solution was technically feasible for a third-party adapter.

The MonsterAdapter Pentax Adapter LA-KE1 is a real boutique piece of photo equipment, an adapter made for photographers who want to use their favorite Pentax glass with Sony's mirrorless system, without giving up on autofocus. At press time it's the only adapter of its type out there.

The appeal may be narrow, but is welcome for those who fall under its scope. I've been clinging to a couple of my favorite Pentax FA Limiteds for years and often use them with a Sony mirrorless with an adapter. Adding autofocus is a big deal—it turns a lens that I'd use for still-life and tripod work into one that's better suited for handheld photography.

Focus speed isn't quite on the same level as with a Pentax SLR, and not nearly as quick as what you get with Sony lenses with Sony cameras, so I'd think twice about using the adapter for fast action and continuous drive photography. It's up to the task for snapshots and candids.

I encountered a few operational bugs with the v01 firmware, but the forthcoming v02 squashed them, and adds support for more lenses, bringing the total to over fifty. The v02 update is promised for public release later this year.

At $439, the pricing verges on premium—if you've got relatively low-end Pentax lenses, it's worthwhile to think about swapping them out for one made for E-mount cameras. The LA-KE1 isn't meant for kit lenses or bargain bin finds. It's a better fit for photographers who've held onto some unmatched Pentax classics and have an itch to use them with a Sony mirrorless camera. If you fall under that umbrella, and don't mind a splurge, it can give you good reason to dust off your favorite K-mount lens.

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