Tag Archives: autofocus

Pentax’ PLM and DC lenses explained

2 Mar

DC (“direct current”) is a kind of focus motor that has been used in Pentax lenses for some time. While it is quiet, it’s not entirely silent. Pentax’ most recent 55-300mm lens features a new type of motor branded as PLM. Here is what Pentax representatives had to say about it in an interview:

The PLM design can quickly activate and allow for faster focusing, but the lens element must be low weight due to limited power (torque).

The DC motor can generate high power (torque) with deceleration mechanisms, which is better for lenses with larger focusing elements. A DC motor can be driven at high speed, but there is an issue that a little sound is generated.

Generally, we use the what we feel is the best focusing mechanism for each specific lens design.

It would be reasonable to suspect that the 55-300mm’s new optical formula and narrower aperture were needed to allow the faster, silent motor to be used, although it should be noted that, like the recent 18-50mm kit and non-kit zoom lenses, the new 55-300mm lens is collapsible to a somewhat smaller size, with the difference between collapsed and uncollapsed size being more pronounced in the 18-50mm.

In the interview, the representatives went on to explain that they do not expect to see PLM in a large aperture lens any time soon, instead putting their money on researching other kinds of motors as well as algorithms to improve autofocus.

Sony a99 II: No C-AF in manual video?

15 Feb

Here’s the relevant section of Kai Man Wong’s review of the a99 II, discussing its video capabilities, the f/3.5 caveat, and the missing option to have continuous autofocus when video exposure is set manually:

 

I take my hat off to Kai for delivering a more thorough review of this camera, and in a shorter space of time, than other frequented outlets.

Will Canon eliminate viewfinder black-out?

13 Aug

Viewfinder blackout is one of the most upsetting limitations of current camera technology. So far, it affects all cameras that produce a viewfinder image through the same lens that is subsequently used for image capture.

Canon now has a patent on switching from the traditional phase-detect autofocus (PDAF) sensor to its dual pixel on-sensor PDAF. Like many patents, this is in itself so obvious that it doesn’t, in my opinion, justify a patent. However, Imaging Resource has mused whether this means that there is a sister patent that will explain how a viewfinder image will continue to be generated during such capture. Obviously, this would point at some kind of hybrid viewfinder, but Canon might, in the process, succeed in eliminating black-out. Ironically, one way to implement such a viewfinder would be through another additional pellicle or reflex mirror.

It certainly is bloody time that somebody eliminated black-out. Aptina’s sensors can be read out at 60 Hertz to record a full resolution image. In spite of Nikon’s 1 series supporting such a framerate, something is clearly wrong with the electronics design since even those cameras still have black-out.

One has to wonder whether Canon will eventually bowl itself out of the game with its apparently steam-punk approach to this problem. At the same time, one wishes that Nikon electronics and software engineers would get their hands out of their ***** and produce a better processing pipeline. I have no doubt the Germans could do it if they put their minds to it. Hey Leica, are you listening?

Source: Egami (Google Translate Link Warning: LINK)

Nikon readying V3? Feels like long wait.

29 Nov

The Nikon 1 V2 has been with us since late 2012, shortly followed by the S1, which, even though a lower-priced model without viewfinder, offered a sensor with markedly improved dynamic range and colour depth. As a result, the V2, shortly after its introduction, soon became a much less attractive proposition, added to which, there was initially an issue with limitations placed on the available autofocus modes when used with the FT1 L adapter for Nikon F-mount lenses (no AF-C available), which was later resolved with a firmware update.

Now, we hear that a V3 may be finally on the way, but it may have its accessory port removed and replaced with a “legacy” flash hotshoe that will give access to a larger range of existing flash models for DSLR cameras. This would allow Nikon to retreat from providing a separate flash accessory range for the 1 series, a range of cameras that despite its fast and accurate on-chip phase detect autofocus hasn’t been selling very well.

While I personally noticed the 1 series’ slightly unusual design, it doubt this would ever stop a truly revolutionary camera from also being declared a design classic. I, for one, would love to be blown away with a more complete mirrorless vision from Nikon. (Pun noted.)

The more megapixels, …

6 Oct

…the sharper your lens has to be.

…the more accurate your focus has to be.

…the faster your shutter has to be OR

…the better your image stabilisation has to be (IBIS, OIS or tripod).

…the bigger your hard disk has to be.

…the faster your computer has to be.

What’s the deal with the Canon 70D?

2 Jul

Canon has just released its new mid-range APS-C camera, the 70D, following on from a line-up traditionally situated between the entry-level “rebels” such as the 700D and the more recent flagship, the 7D. But rather than look at the new camera’s position in the line-up, let’s explore its features.

For some time now, Canon has continued to produce great glass alongside cameras with mediocre sensors. Particularly, Nikon has overtaken in terms of resolution, sensitivity/noise and dynamic range, the latter being particularly hurtful to Canon’s reputation, utility, and business.

Canon EOS 70D

Promotional image of the 70D from Canon

Along comes the 70D – what can we expect? It’s clear that Canon has made this model matter, placing it as a deliberate game-changer with all the features thrown in that could win it top awards in reviews – a swivel and touch display of high resolution, a tiny increase in capture resolution for still images, and WiFi connectivity. This alone won’t be enough to silence the critics, since, as Samsung recently reconfirmed, what matters most to people is the quality of the resulting image. Image quality could be said to consist of a combination of resolution, sharpness, dynamic range, and colour and brightness fidelity. Unfortunately, with the camera having just been announced, we may have to wait a little to see if the new sensor can deliver improvements in any of these areas.

The headlining feature, however, will be its on-sensor phase detection technology, which, in contrast to previous such attempts, allows examining sharpness at each pixel within an 80% window of the overall frame. I have to admit that while this is an improvement on all current implementations of on-chip phase detection autofocus, it rather reminds me of Canon’s dogged determination to give its users an inferior 95% frame coverage pentamirror viewfinder, where Pentax gives you 100% view at entry level – and even the 70D delivers only 98%. But enough of partisanship – I rightly shot down Canon’s 100D as a gimmick, and will give credit where it’s due. That said, it will be difficult for Canon to convince me that they’ve obsoleted the optical viewfinder by providing an admittedly versatile rear display.

Canon EOS 70D with active WiFi link

Canon promotional image showing active WiFi link in top display

Canon is clearly keen to get the word out and salvage what fans haven’t averted their eyes, minds and wallets at the over-two-year lag in sensor performance. The EOS M hasn’t made a huge impact either, so what can the 70D bring?

There is no word yet on how fast this new live view autofocus is, and remember that it competes with a 19-point traditional phase detection autofocus that is active when using the optical viewfinder. The statement seems to be that the on-chip autofocus is preferable, as it evaluates many more focus points than the traditional sensor. However, the same DIGIC 5+ imaging processor that fulfils a more traditional role in the 5D Mk III seems to have been tasked with this new load, and is presumably slowed down by it, much as the Pentax K-5 II, according to some test data, is struggling to provide snappy autofocus amid the new AF sensor capabilities and presumably CPU-intensive algorithmic improvements.

I would therefore expect the on-chip autofocus to be slow. This, presumably, is the reason why no electronic viewfinder was provided, leaving the 70D as a bit of a half-way horse, and explaining why these advances weren’t introduced in a flagship model. I suspect the best route for interested users would be to wait for test data, and probably a successor model that perhaps leverages a DIGIC 6 or 7 for fast on-chip phase detection autofocus and electronic viewfinder. If such a combination could result in less AF hunting and fewer false catches or “snags”, it would be a true revolution deserving of amateur investment. (But pick your lenses carefully because the optical stabilisation – denoted IS or IS II in Canon jargon – is still going to cost you a lot extra!)

Sharpness

21 Feb

Photography at its core revolves around the challenge of obtaining a sharp and colour-accurate image of a scene. Once we’ve achieved sharpness, we can modify the image in any way we like, even removing the sharpness in creative ways. However, we cannot yet easily move in the opposite direction. Therefore we’re obliged to obtain a sharp image as a first step.

What, then, are the factors that determine the sharpness of the image we obtain?

  1. Lens: Lenses differ in “optical quality”, that is to say, how much heterogeneity in surface structure and material composition there is in the glass. Heterogeneous glass will render blurry images, whereas glass that adheres exactly to the intended design will give sharper images. For this reason, many photographers advocate starting with good glass and a cheap camera body, but this again depends on the intended application – for sports and wildlife photography, you will want to have a camera with a high frame rate in order to avoid missing crucial moments in your scene. This may limit your options to mid- to upper-range camera bodies, and take away from your lens budget.
  2. Sensor: The other piece of hardware that matters is the sensor. As part of the sensor assembly, there will usually be an “anti-aliasing filter”, which adds a small amount of blur to the recorded image to avoid the appearance of aliasing and moiré. Recently, camera manufacturers have tended towards giving a weaker AA filter and render a sharper image. It is partly a matter of personal preference whether to use a stronger AA filter, but keep in mind that this, as well as any other filter you use in front or behind your lens, will influence image sharpness.
  3. Focus accuracy: It is obvious that the autofocus accuracy of a camera will determine sharpness (or focus placement, if you will) when using autofocus. When using manual focus on an SLR, much will depend on your skill, but also on having a large and bright viewfinder that allows you to see your scene accurately as it will be rendered on your sensor. On better cameras, the viewfinder will be adjustable to your preferred way of holding the camera up to your eye, or to your level of near- or far-sightedness. The more customisation your camera offers in this regard, and the more accurately you adjust it, the better your focusing ability will be. When using LiveView, you only need to be able to see whether the image on the screen is sharp. Many now recommend using a camera with “focus peaking” to help with this, which highlights any sharply focused edges in your image.
  4. Stabilisation: If you are using longer exposures (weak light or small aperture), and particularly if shooting at greater zoom lengths (telephotography), you’ll have to consider the merits of stabilising your image to avoid blur, either by using a stabilising aid such as a tripod, monopod, gorillapod, beanbag, window mount, etc., and/or by having a camera or lens that support sensor or optical stabilisation, respectively. So-called digital stabilisation is generally less preferred than the other methods, as it typically “slices” the image into sub-images and re-combines them into your final image following alignment. This process is slower both in the taking and processing of the image, and may increase noise in your image. A widely touted rule of thumb says that optical stabilisation should be preferred for larger focal lengths (zoom distances).
  5. Exposure (shutter) time: As mentioned in the previous section, short exposures require less stabilisation. This is because you’re less likely to shake your camera a sufficient amount during short exposures. On some, especially older, camera models the shutter itself will cause the camera to shake, and in some cases the image stabilisation mechanism is in turn shaken in such a way as to add blur rather than subtract it. It’s good to be aware of such settings and either avoid those exposure timings, or disable the image stabilisation. This will vary from camera model to camera model, so you must do some research on how this relates to your particular camera. Notwithstanding these observations, selecting a short exposure is generally advantageous to the quality of your image, with the following caveat.
  6. ISO level: On digital cameras, you can manually select a virtual “film speed”, which corresponds to what in the old days determined how grainy your film was (grainier film catches light more easily on each grain, but with a loss of detail because the “colour dot” (grain) is larger). Higher ISO levels will cause you to lose detail, and will increase noise in your image. You may then want to remove this noise, which, in addition to the loss of detail already inherent in the high ISO level, will cause your image to become even blurrier. Selecting higher ISO levels will allow you to shoot fast action better, but due to the loss of image detail, you should not always shoot at a high ISO setting, or your sensor will perform far below the capability of the sharp lens I hope you bought.
  7. Aperture: This is a slightly advanced topic, but all lenses are sharper at some aperture settings than others. As a general rule of thumb, f/8 will be quite sharp, but the exact sweet spot will vary from lens to lens. The fall-off in sharpness also varies – some lenses can still be very sharp at f/2.8, and most also generate very acceptable images up to f/11. Changing the aperture is, of course, how we control our depth of field, that is, how “deep” into our image we will reach with the sharpness. A small aperture will give greater depth of field, but in order to obtain a nice “bokeh”, i.e. background smoothness, we need to select smaller apertures. Depending on our personal preferences, a truly great lens might be one that allows us to have a part of the image pin-sharp while rendering great bokeh in the background. The shape of highlights on your bokeh, by the way, is determined by the shape of your aperture. Six aperture blades will give you hexagonal highlights. You can make your own.
  8. Adding light sources (flash): Flash may be a very old and time-tested way to improve sharpness in a moving scene, but I mention it last because flash will definitely change the way your scene appears. When using flash, you will always capture an approximation of what you were looking at in real life. Flash can be a creative medium, and especially in a studio setting, where you have more flexibility over the placement of your light sources, these become an irreplaceable part of your toolkit. However, a camera-mounted flash (with the exception of ring flashes in macro photography) will, in most scenes, cause unsightly shadows to appear behind your subject, so camera-mounted flash should be used cautiously and in small doses when possible. You can offset this effect somewhat by “bouncing” your flash off a nearby matte surface with sufficient reflectivity, which will serve to scatter the light from your flash and make shadows less harsh. However, to cut to the short of it, the added light from a flash allows you to lower your exposure times, giving less shake in your image.