Number of aperture blades

Lens specifications are not complete without detailing the number of aperture blades. But what does it mean in practice?

Of course, the shape of the aperture blades is important for the out of focus highlights, the bokeh. I have previously seen that the Lumix 45mm f/2.8 1:1 macro lens has somewhat more rounded aperture when stopped down than the Olympus 45mm f/1.8. When not stopped down, i.e., at the largest aperture, the diaphragm blades move out of the way, and the opening is usually perfectly round.

Adding a higher number of diaphragm blades can make the aperture opening more rounded when stopping down. However, lenses seldom go beyond nine blades, probably for the reasons of cost, complexity, and the risk of having one of them break down.

It turns out that the number of blades is also related to the rendering of flare, strong light sources inside the image frame. I'll look at that later in this article.

Samyang and Lumix fisheye lenses

There are currently two fisheye lenses available for the Micro Four Thirds system, the Samyang 7.5mm f/3.5 and the Lumix G 8mm f/3.5:



Of course, the major difference between these lenses is the price (the Samyang is the cheaper), the image quality (the Samyang is better, in my opinion), and the focus mechanism (only the Lumix lens has autofocus). But in addition: The Samyang has six aperture blades, and the Lumix has seven. These close up pictures show the rear exit pupil at f/5.6 for both lenses. The Lumix G 8mm lens has more rounded aperture blades, but you can still make out seven segments:

Samyang @ f/5.6	Lumix @ f/5.6

Here is a video showing how the aperture blades open up on the Samyang lens:



Affecting the flare

It turns out that the number of aperture blades affect the flare in a fundamental way. It is common to get a star shaped flare when using small apertures. And the number of spikes in the star is the number of diaphragm blades (when that number is even), or twice the number of diaphragm blades (when that number is odd). Hence, using the Samyang should give us stars with six spikes, and using the Lumix should give fourteen. Let's check, by taking pictures at f/22:

Samyang @ f/22	Lumix @ f/22

To see this more clearly, here are enlargements at f/22 and f/11:



It's not so easy to count the number of spikes on the Lumix image to the right, but I think it is still quite clear that it is fourteen.

Conclusion

To my experience, most lenses have an odd number of aperture diaphragm blades, which produces the most spikes on the star shaped flare around bright objects, e.g., the sun. I guess this is because a larger number makes the flare look more blurred, whereas a small number makes the flare more distracting.

A bit of trivia is that Canon has chosen an even number for most of their lenses, while Nikon is going for an odd number. Hence, it is often easy to guess what brand a photographer uses, based on an image where the sun is inside the frame. However, the aperture also needs to be fairly small to see this effect, e.g., f/16 or f/22.  So you might not be able to make this out based on any picture.

Lumix Leica 25mm f/1.4 and clicking sounds

The Lumix Leica DG Summilux 25mm f/1.4 is a premium large aperture prime lens for the Micro Four Thirds system. It is designed to work as a "classic" bright normal lens for a 35mm SLR system, which was typically rated as 50mm f/1.4. With the 2x crop factor associated with the 4/3 format, the Leica 25mm f/1.4 lens becomes equivalent to a classic normal lens in terms of field of view.

Many users have complained about clicking sounds when using this lens. This has left them worried: When they buy a premium lens, they expect it to function smoothly.

First of all: Don't worry, the clicking sounds are completely normal.

Having said this, let's look at why you experience these clicking sounds.

What's causing the clicking sounds is the change of aperture. In normal operation, the camera leaves the aperture at its largest value when using the camera, and only stops it down just before taking a picture. The aperture is opened up again afterwards. Since the sound of the shutter is louder than the actual aperture change, you don't normally notice the sound of the aperture changing.

I have examined the loudness of the aperture change with a number of lenses here. Generally, most lenses have a similarly loud aperture change. The Lumix G HD 14-140mm superzoom is marketed as a video lens, and is supposed to have more silent aperture change than usual.

However, the Lumix Leica 25mm f/1.4 is the brightest Micro Four Thirds lens so far. When using the camera, it is seeing the outside world through the lens, and relaying the information to you through the LCD screen, or the viewfinder. Unlike your eye, which is very flexible in terms of the dynamic range it can see, the camera sensor can only see a more limited range of brightnesses. When using a bright lens like the Leica 25mm, in combination with a bright surrounding, the light is simply too much for the sensor to process. It needs to stop down the aperture to show you a sufficiently good viewfinder image. Stopping down the lens causes a clicking sound.

Further, the camera cannot accurately focus with the lens stopped down. When stopped down, the depth of focus (Dof) is wider, hence the lens appears to be in focus in a large focus distance range. And this can cause misfocus.

So before focusing, the camera must open up the aperture fully, and then close down again afterwards, if the surroundings are very bright. Both opening up the aperture and closing down cause the clicking sounds. Hence, every time you focus the lens in a bright light, you will experience the click before and after the camera has achieved focus.

If you operate the lens in a dim environment, you should not normally experience the clicking sounds upon focusing the lens.

This can happen with any Micro Four Thirds lens, even relatively slow zoom lenses, given that you point the lens towards a strong light source. But since the Leica 25mm f/1.4 is unusually bright, it happens more often with this lens.

So to conclude: The clicking sounds are a normal part of the lens operation.

Noise comparison, aperture change

I have previously compared the focus noise of various lenses. The conclusions from my analysis were hardly surprising, for example, the Lumix G 20mm f/1.7 pancake lens had a rather loud focus noise, due to the traditional focus assembly which moves all the lens groups back and forth.

The lenses with an internal focus mechanism generally featured lower noise, with the Panasonic Leica Lumix DG Macro-Elmarit 45mm f/2.8 1:1 Macro and Lumix G HD 14-140mm f/4-5.8 as exceptions. In the latter case, I believe the microphone was too close to the lens, giving biased results.

You could ask why worry about the aperture change noise. After all, the aperture is generally stopped down just before the shutter is released. And for all Micro Four Thirds cameras, the shutter noise is rather high. So the aperture noise is simply drowned by the shutter noise anyway.

However, there are times when you don't trigger the shutter. This could be when using the new high speed, low resolution mode of the Panasonic GH2. Or, quite simply, when recording videos.

Also, some time in the future, we are going to get cameras without mechanical shutters. When the global shutter technology is mature enough, we will see this in Micro Four Thirds cameras. Then, the only noise we will hear is the focus noise and aperture noise.

To measure the aperture change noise, I placed a mobile phone near the camera, running the "Decibel Ultra" app, to measure the noise level. While I don't trust the absolute measurement of the phone, I think it is good enough to look at the relative levels of noise.

The GH2, and many other Micro Four Thirds cameras, has the feature of stopping down the aperture to preview the depth of focus (DOF). This is very useful, especially for macro photography. I use this feature to toggle the aperture between maximum and f/7.1.

The test



Results

I have only noted down the peak decibel measurements. The results:

Lens	Measurements	Average
Lumix G 8mm fisheye	77 76 77	77 dB
Lumix G 14mm	79 77	78 dB
Lumix G 20mm	76 75 73 76	75 dB
Leica Lumix DG 45mm macro	80 82 81 83	82 dB
Lumix G 45-200	83 80 81 84 83	82 dB
Lumix G 14-42	75 76 75 75	75 dB
Lumix G HD 14-140	78 78 81	79 dB

Conclusions

According to the marketing material, the HD designation of the Lumix G HD 14-140mm f/4-5.8 superzoom lens means that it should have fast autofocus, low noise autofocus, and near stepless low noise aperture.

After my analysis of the AF speed, the AF noise and now, the aperture noise, I cannot see that the lens is that special. It performs pretty much like the basic kit lens. What I haven't looked at, though is the aperture change, which is quoted as "near stepless". Accurate to 1/6 stop, is what I have seen quoted.

That said, the Lumix G HD 14-140mm f/4-5.8 zoom lens does have a softer sound when changing aperture.

In terms of aperture noise, the lenses appear to perform quite similar. And this is not strange: The aperture diaphragm mechanisms are probably rather similar between the lenses.

A tale of a broken Lumix kit lens

Contrary to much of the online opinion, I think that the basic kit lens from Panasonic, the Lumix G 14-42mm f/3.5-5.6, is rather good. Considering the price, the size and the weight, I think it gives a good performance. The autofocus is fast, the sharpness is generally good.

However, when evaluating the bokeh characteristics of the lens, I noticed that the out of focus highlights were non-round. This is found for some lenses, for example the Lumix Leica 45mm f/2.8 1:1 macro lens has elliptical out of focus highlight rendering outside of the centre of the frame. But I found that the Lumix G 14-42mm lens had more like potato shaped highlights.

A closer examination revealed that the aperture diaphragm was indeed misaligned, giving non-round out of focus highlights for all stopped down aperture sizes. If found this to be so bad, that I took the lens back to the shop where I bought it in the first place.

The store keeper has some problem verifying that his off the shelf lens did not exhibit the same non-round aperture. I helped him by taking a photo with the lens mounted to the Panasonic GF2 camera at f/9, 2 seconds, and removed the lens during the exposure. Looking towards the light through the lens showed that his copy had a round aperture.

So he accepted my lens as defective, and sent it for repair.

After one month, I started enquiring about the lens. I always got the same answer: "The lens is just around the corner, should be in our store the beginning of the next week."

It was not until after three months that the lens finally did arrive in the store. When I went to pick it up, I was told that they simply replaced the lens with a new one. Why let me wait for three months when they would just give me a new copy?

Coming home, I once again checked if the aperture was rounded. See for yourself, this image was taken with the Lumix Leica 45mm f/2.8 1:1 macro lens:

In fact, my new lens exhibits exactly the same problem as the one I returned in the first place. I did check that the new lens has a different serial number, so it is not the same lens that I returned.

Letting me wait three months for a new lens is bad. But giving me a new lens which has the same problem as the one I returned is simply appalling.

Epilogue

I took the lens back to the retailer again. This time, they offered to change my lens directly from their stock. We tested two lenses, and neither had completely round apertures. One was as bad as my own lens, and the other was pretty rounded. So I took the best one.

I don't expect perfectness from a lens this cheap. So I am happy with the near round aperture opening.

Bad aperture diaphragm in Lumix G 14-42mm f/3.5-5.6

When investigating the bokeh of some Panasonic Lumix lenses, it came to my attention that out of focus highlights using the Lumix G 14-42mm f/3.5-5.6 kit lens was irregularly shaped when stopped down. I decided to take a closer look, to see what the problem is.

First, I took a picture in which I set the lens to tele (42mm), focused as close as possible, and placed a flashlight in the background. The flashlight renders out of focus. Here is the full image at f/5.6, the maximum aperture. The flashlight is placed in the centre of the image:

To see how the roundness changes when stopping down, I have made 100% crops from the centre at various apertures:

This verifies the problems I saw when studying the bokeh. The out of focus highlights are definitively not circular. It looks like the aperture diaphragm blades are misaligned.

Micro Four Thirds lenses are always wide open when powering the camera down. This means that normally, you cannot look at the diaphragm blades from the inside, since the aperture is wide open.

However, a trick is to stop down the lens, and then remove the camera battery. That way, you can remove the lens while stopped down. This procedure is not exactly recommended by the manual, so use with caution.

Using this trick, I could photograph the back side of the lens when stopped down:

Here it is clear that some of the blades are misaligned. Thus, the resulting image has non-round out of focus rendering.

I've made a video showing the stopping down of the aperture blades. The apertures goes from f/3.5 down to a full close in 1/3 stops.



I filmed it using the Panasonic Lumix GH2 and the Leica Lumix DG 45mm f/2.8 macro lens. To get the needed magnification, I used the new Extra Tele Converter (ETC) mode.

Here's a photo of the setup for capturing the video:

Conclusion

My lens most certainly has a bad aperture mechanism. Whether this is a one-off bad copy, or a systematic problem with the lens line is hard to say. I would guess it's an example of poor quality checking, and that most lenses are ok.

This problem annoys me a bit. I've previously found the basic kit lens to be a good one, despite the mixed reception it generally gets online.

Now, this is not really a big issue. Generally, you don't get much bokeh with kit zoom lenses anyway. So the problem is not very likely to show in images. If using the camera at full auto, it generally chooses the maximum aperture anyway, in which case the aperture opening is round.

This problem might affect the exposure correctness. The defective aperture blades could cause slight exposure irregularities. But again, this is not likely to be a big problem

Epilogue

If found the aperture to be so bad, that I took the lens back to the shop where I bought it in the first place.

The store keeper has some problem verifying that his off the shelf lens did not exhibit the same non-round aperture. I helped him by taking a photo with the lens mounted to the Panasonic GF2 camera at f/9, 2 seconds, and removed the lens during the exposure. Looking towards the light through the lens showed that his copy had a round aperture.

So he accepted my lens as defective, and sent it for repair.

After one month, I started enquiring about the lens. I always got the same answer: "The lens is just around the corner, should be in our store the beginning of the next week."

It was not until after three months that the lens finally did arrive in the store. When I went to pick it up, I was told that they simply replaced the lens with a new one. Why let me wait for three months when they would just give me a new copy?

Coming home, I once again checked if the aperture was rounded. I found that my new lens had exactly the same problem, the aperture blades are misaligned. I did check that the new lens has a different serial number, so it is not the same lens that I returned.

Letting me wait three months for a new lens is bad. But giving me a new lens which has the same problem as the one I returned is simply appalling.

Lumix G 14-42, new kit zoom

For the introduction of the Panasonic Lumix G2 and G10 cameras, a new kit zoom was launched. Much to the dismay of Micro Four Thirds users, since on first sight it looks like a dumbed down version of the old kit zoom.

First of all, it has slightly worse technical specifications: The long end of the zoom is 42mm, while the old had 45mm. Next, the new kit lens has got a plastic mount, while the older has a metal mount. The new zoom also lost the OIS switch: Switching OIS on or off is now done through the menus.

In terms of ergonomy, the new lens also lost the rubber zoom ring. It now features a plastic zoom ring, which gives somewhat less friction when operating it with your fingers.  Some users of the old lens experienced that the rubber zoom ring came loose.  This will not be a problem with the new lens, since there is no rubber ring.

Now, the change of the long end focal length doesn't bother me. 42mm and 45mm is basically the same field of view, there is no significant difference here. Also, the plastic mount, if done properly with good quality materials, is probably solid enough. After all, this is a very light weight lens, and in normal use, it doesn't need as strong support as larger lenses.

What about other aspects? Some reports indicate that the sharpness of the new lens is not as good as the original Lumix G 14-45mm lens. I cannot comment this, since I haven't used both.

Here's an analysis of the sharpness and bokeh of the lens.

The GH1 kit lens, the Lumix G HD 14-140mm, is specified with an aperture range from f/4 to f/5.8. However, while zooming from wide to tele, it closes down very quickly. So it is fair to say that this is essentially an "around f/5.6" lens, with a bonus brightness in the short end.

What about the other kit lenses? This diagram shows the relationship between the focal length and the maximum aperture for the three kit lenses:

For the 14-42mm and 14-140mm kit lenses, these values were sampled by using the actual lens. For the 14-45mm lens, I took the values from various reviews off the Internet.

It looks like the new kit lens has slightly better speed at f=25mm: f/4.6, compared with f/4.9 for the old kit lens.

I also added the aperture data for the premium Olympus standard zoom, the Olympus M.Zuiko Digital ED 12-50mm F3.5-6.3 EZ power zoom. This lens is comparable with the other kit lenses in the short end, but the aperture closes down very quickly as the focal length increases. I think this is consistent with the Olympus M 4/3 design philosophy, which generally puts compactness ahead of maximum aperture.

The main purpose of the kit lens, is to be cheap and good enough for most beginners. I'm guessing that the size and number of the glass lens elements is an important contributor to the price.

The diameter of the front element of the 14-42mm lens is 13% smaller than that of the 14-45mm lens. And that means the area is 25% smaller:

It is quite remarkable that Panasonic has essentially retained the specifications, while shrinking the front element so much.  Of course, reducing the front lens diameter is not necessarily good for the image quality.  It could lead to more vignetting at max aperture, for example.

All in all, I think this will be a pretty successful lens. Some early reports indicate slightly worse sharpness, however, for the target audience that may not be a problem. The cheaper construction means that Panasonic can sell them in kits at a lower price point, which they will need now that the competition has gotten their systems launched.

The autofocus speed of the newer 14-42mm lens is very good.

Nikon to m4/3 adapter

One of the benefits of the Micro Four Thirds format is the short register distance. Since virtually all other formats have a longer register distance, it is possible to make adapters for other lenses to be used on Micro Four Thirds.

Here is one of many adapters available:

It attaches to the camera just as a Micro Four Thirds lens. Here is a video showing how to attach the adapter to the Panasonic Lumix GH1.

It reads "NIK-M4/3", and can be used to mount Nikon F mount lenses to a Micro Four Thirds camera. These kind of adapters are simple, meaning that they only provide a means to mount the lens, and no control over the aperture or focus is possible from the camera. On the positive side, they are rather inexpensive, and can be purchased for around US$30-40.

http://www.amazon.com/gp/product/B002MXFGJI/ref=as_li_qf_sp_asin_il_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=B002MXFGJI&linkCode=as2&tag=micr43rdsphot-20&linkId=47SACJR2BVSJUUPV

When using a third party adapter like this, the camera has no electronic confirmation that a lens is actually connected. For the camera to still operate, you need to set the menu item "shoot without lens". This is found under the "Custom" menu, indicated by a "C" with a wrench icon. Here is the menu item from the GH2 camera:

In the picture below, the adapter is used to mount a Nikkor 200mm f/4 AIS tele lens to the Panasonic Lumix GH1. When using this legacy lens on a Four Thirds camera, the field of view becomes equivalent to a 400mm lens. With a long tele like this, using a tripod is a necessity. While you can choose fast shutter speeds and capture an image without blurring due to camera shake, framing the subject is very difficult when handholding this combination. Recording video without a tripod is virtually impossible with such a long lens.



This lens has an aperture ring. Since the camera cannot control the aperture, it needs to be set manually. The presence of an aperture ring makes this operation easier. Some more expensive adapters have a means for controlling the aperture also for lenses without the aperture ring, e.g., the Nikon G mount lenses.

Many newer lenses do not have aperture rings, and require an adapters with a lever to stop the lens down. This goes for both Nikon and Pentax lenses.

Focus confirmation

There is some talk on the internet about adapters that provide focus confirmation for legacy lenses. To my knowledge, such a thing is not possible with Micro Four Thirds cameras. The cameras cannot confirm the focus when using non-compatible lenses. In fact, with the current cameras, the only way for the camera to know that the image is in focus, is to use a Micro Four Thirds lens, or one of the CDAF compatible Four Thirds lenses.

To be able to confirm the focus, the camera must jog the focus back and forth to find the optimum contrast. This is not possible with manual focus lenses, of course, since the camera cannot control the focus at all. So focus confirm adapters for Micro Four Thirds simply make no sense at all.

Size

A fun fact is that the adapter is larger than the Panasonic Lumix 20mm f/1.7 pancake lens. (The lens to the right below.)


Example images

Here are two example pictures taken at f/4:



And an example video:



I have also looked into an adapter for Pentax K lenses.