Panasonic GH1 Optics

Panasonic GH1 Optics

Lumix Vario G HD Lens

While the Panasonic GH1 is compatible with any Micro Four Thirds lens (and even standard Four Thirds lenses via an adapter), a new series of Vario G lenses have been designed especially for the GH1. These new "HD" lenses are designed for movie recording by incorporating a nearly silent inner focus direct-drive linear motor for continuous auto focusing, as well as seamless aperture adjustment. In fact, autofocus is not supported without an HD lens when shooting movies in AVCHD FHD mode. At the time of writing (May 2009), only one HD lens has been released, and it's bundled in the GH1 kit. The Lumix G Vario HD 14-140mm/F4.0-5.8 ASPH./MEGA O.I.S. has a 10x zoom and features optical image stabilization. As this review is being written, we've just tested it for SLRgear.com, and those results should be posted by the time this full review of the camera goes live on our main Imaging-Resource.com site.

Overall, the 14-140mm lens does very well, particularly for one with a 10x zoom ratio. It's particularly good from 14mm out to about 50mm, being quite sharp from corner to corner, even wide open. At longer focal lengths, its images are slightly softer, but still very good when compared with any other long-ratio zooms we've seen to date. (In fact, it's one of the best long-ratio zoom lenses we've seen, on any platform.) Some of its superior performance is doubtless due to the optical correction Panasonic applies in-camera: The camera itself corrects for a lot of the chromatic aberration, vignetting, and geometric distortion produced by the lens itself. Panasonic's own SilkyPix RAW converter and Adobe Camera Raw both also make these same corrections, so you should see similar performance when working from RAW with either of those two converters. Other RAW converters may or may not provide similar results.

Also announced at the same time as the Panasonic GH1 was the Lumix Vario G 7-14mm f/4 ASPH. We've also tested this lens on SLRgear.com, and it also did very well.

Micro Four Thirds

Given that the Panasonic GH1 is only the second Micro Four Thirds camera to be announced, it might be good to take a quick look at just what Micro Four Thirds is all about. (This section taken from the Panasonic G1 review, so you can skip it if you've already read that review.)

Panasonic and Olympus' Micro Four Thirds standard is aimed at allowing a significant reduction in the size and weight of interchangeable lens digital cameras, achieved by eliminating the bulky mirror box from the design. With the mirror box gone, the "back-focus distance" (or back focal length) of compatible lenses can be reduced. Technically, back focus distance is defined as the distance from the vertex of the lens's rear element to the sensor, but for practical purposes, it's easier to speak in terms of the distance from the lens-mounting flange to the sensor surface. In the existing Four Thirds system, this dimension was 40mm; for Micro Four Thirds, it has been slashed to just 20mm. Obviously, this change allows for a significant reduction in the size and weight of the camera body while retaining the same sensor size.

That's not the only benefit, though. As well as smaller and lighter camera bodies, Micro Four Thirds offers the possibility of a significant reduction in the size and weight of the lenses, too. While the physical size of a lens depends somewhat on the size of the image circle it must produce, it turns out to depend even more strongly on the back focus distance the lens was designed for. Reducing the back focus distance can significantly decrease the length of the lenses needed to cover the area of a Four Thirds image sensor. Lenses for the new system can also be somewhat smaller in terms of diameter as well, and indeed the new mount is some 6mm smaller (44mm vs 50mm) than that called for in the original Four Thirds standard.

Removing the mirror box does have some potential disadvantages, though. Obviously, it removes the possibility for any Micro Four Thirds camera to offer a true through-the-lens optical viewfinder, with no way to divert the optical path to the viewfinder between exposures. Hence, Micro Four Thirds cameras will be limited solely to using a Live View function as seen on certain recent digital SLRs, where data streaming from the image sensor can be displayed on an LCD display, electronic viewfinder, or both. For similar reasons, with nowhere to put a phase detection autofocus sensor, Micro Four Thirds cameras are limited to using contrast detection autofocus. While this can offer higher focusing accuracy, and negates problems with front or back focusing, contrast detection has in the past always been slower than the phase detection systems found in digital SLRs.

Still, the Micro Four Thirds system promises interchangeable-lens cameras with good performance at significantly smaller overall sizes. With the Panasonic G1 and now the GH1, early indications are that the platform is off to a solid start.

Using your current Four Thirds lenses

This brings us to the issue of using current Four Thirds lenses on the new Micro Four Thirds system. It is indeed possible to use all your old glass, by virtue of the MA1 mount adapter, although there may be limitations with some lenses.

The shots above show the MA1 adapter by itself, and attached to the 14-50mm lens that shipped as the kit optic with the Panasonic DMC-L10 SLR. The adapter is quite easy to use, just attach it to the lens and then attach the combination to the camera. Since all it's doing is adapting between the different flange sizes and adding 20mm of increased back focus distance, the mount adapter needs no optics in it, so it has no effect on image quality, lens speed, or any other optical characteristic.

That all sounds great, so what's the limitation? It turns out that not all lenses are able to move their elements quickly enough to work with the G series' contrast-detect autofocus. Normal phase-detect AF systems are fairly forgiving of focusing speed, because the correct focal distance setting is determined independently of the lens elements' motion: The camera looks at the subject, calculates the correct focal distance, commands the lens to move, and then snaps the shot once the lens reports back that it's moved to the correct setting.

With contrast-detect autofocus, though, the lens has to move multiple times, and must come to rest before the camera can take each "look" at the subject, to determine whether the focus is better or worse than it was at the previous focal setting. In order for the overall focus cycle to be performed quickly, the lens needs to be able to shift focal settings very quickly, multiple times per second. This is a demanding requirement, and not all lenses are up to the challenge. Olympus offers contrast-detect AF on some of their recent SLRs, but the feature only works with a few lenses that have focus motors both strong and fast enough to move the lens elements very quickly. Other manufacturers offer contrast-detect AF that works with any of their lenses, but at the cost of very slow AF times. (It's for this reason that Nikon refers to the contrast detect AF option in their SLRs as "tripod mode.")

So, while some current Four Thirds lenses will work just fine on the new Micro Four Thirds system, with full support for AF operation, other lenses will be reduced to "guided manual" focus, in which the user will need to adjust the focus setting, looking to either the viewfinder (less accurate) or the camera's focus indicator (more accurate) for focus confirmation. And, without a firmware update, some Four Thirds lenses may not work with the Panasonic G series at all, because the camera won't respond to movements of the "fly by wire" focus ring on the lens. Fortunately, Olympus (the biggest Four Thirds lens maker by far) has committed to updating the firmware in their lenses to work with Micro Four Thirds standard cameras: Check with your lens manufacturer to see whether your current Four Thirds lenses are compatible.

Panasonic GH1 Autofocus

Like the Panasonic G1, the GH1 uses a very fast contrast-detect autofocus system, capable of adjusting focus sixty times/second. This fast AF is a key technology that enables live autofocus during movie recording. (Conventional contrast-detect AF systems on most digital SLR cameras are way too slow to perform continuous AF during movie recording, which is why no SLRs offer continuous AF during movie recording, at least as of this writing in late May, 2009.)

The Panasonic GH1 offers on-screen manual focus (with a very nice variable magnification of the LCD viewfinder display to assist in focus determination), as well as three AF servo modes; AF-S (single-shot focus), AF-C (continuous AF), and AF Tracking. In AF tracking mode, the camera will automatically track a subject after you've initially focused on it by half-pressing the shutter button.

Panasonic's AF tracking is unique, in that it uses color and tone to track an object, so its less likely to be confused by a different-colored object momentarily passing between the subject and camera than would most conventional distance-only AF systems. The camera also continuously adjusts exposure as it tracks the subject, so the exposure will be correct, even if the lighting changes between when you lock the tracking and when you trip the shutter.

Besides its various servo modes, the Panasonic GH1's AF system sports several different focusing modes, including Face Detection, 23-area focusing, 1-area focusing, and Direct AF area. Face Detection AF works the way it does in most compact digital cameras, detecting up to 15 faces in a scene, and focusing on the most prominent one. When Face Recognition is enabled, the Panasonic GH1 goes further by trying to recognize individuals. Up to 6 faces can be registered, and the camera will display the person's name when it recognizes the face. In 23-area mode, the camera looks for the most prominent subject that's closest to the camera, even if the subject isn't in the center of the frame. Single-point AF is just what it sounds like, focusing on whatever is in the center of the frame.

Direct AF mode is a useful option that's set from the Custom Menu. When it's enabled, you can move the single AF area around the frame with the arrow keys, and change its size by rotating the front control dial. Size options range from quite small to relatively large, with a total of four sizes available.

As advertised, we found that the Panasonic GH1's AF system worked during video recording. We did notice, however, that the camera's AF system was much more responsive when recording to the Motion JPEG (AVI) file format than when recording AVCHD files, particularly when recording in "Full HD" mode (1920x1080 resolution).

Panasonic GH1 Sensor Cleaning

The Panasonic GH1 features an ultrasonic dust-reduction system, especially important since the GH1's shutter is normally open for full-time Live View. The system automatically runs at power-up, but can also be activated manually via a "Sensor Cleaning" Custom menu option. In the G1, manual sensor cleaning was combined with the "Pixel Refresh" menu option.

The images above were taken from our standardized test shots. For a collection of more pictorial photos, see our Panasonic Lumix DMC-GH1 Photo Gallery .