THE ZD40-150mm KIT LENSES
how do they compare and do they work with the ec14 teleconverter?
|Side by side - no mistaking these two lenses! The miniaturization of the compact version is quite an achievement.|
I've had several requests to take a closer look at the performance of both the original version and compact version of ZD40-150mm kit lenses to see where the differences lie, and also to answer the much asked question 'do either of these lenses work with the EC14 Teleconverter?'
For those unfamiliar with Zuiko Digital telephoto zoom kit lenses, the original and larger version appeared with the E-300 and the compact version appeared with the E-400.
The original version is a quite a large lens with maximum aperture range of f=3.5~4.5, 13 elements in 10 groups (no ED glass) weighing 425g. The more recent edition has a maximum aperture range of f=3.5~5.6, 12 elements in 9 groups including one ED lens and a true circular aperture (for better bokeh) weighing 220g. It is lighter, more compact and slower. ED (as far as I know stands for Extra Dispersion) glass is supposed to increase sharpness by cutting down aberrations.
The EC14 is a teleconverter with 6 elements in 5 groups which increases the focal length of the lens by a factor of 1.4. This means the ZD 40-150mm becomes a 56-210mm lens. Of course extended focal length benefit comes at a price because the aperture is subject to a 1.4 times factor too, increasing the ZD40-150mm native lens aperture spread to f=4.9~6.3 in the original version and f=4.9~7.8 in the compact version.
The EC14 is the only teleconverter I have ever used that does not appear to affect resolution to any significant degree. This is achieved by very careful optical design and construction and some heavy coatings applied to the special glass elements used. It may also account for it being rather expensive.
But, you can see that using the EC14 with any lens reduces the amount of light entering the camera.
According to Olympus in their lens handbook/spec sheet for the both versions of the ZD40-150mm lens states these will only work in combination with the EC14 in manual focus (MF) mode. I also note the specs for the 10X zoom ZD18-180mm f=3.5~6.3 says exactly the same. Why?
Because the auto focus system employed in Olympus DSLR cameras relies on light, the company is concerned that where innately slow lenses are used in conjunction with the EC14 - which slows them even more - that the AF system may not work in all circumstances. Olympus are truly 'playing safe' here.
AUTO FOCUS SYSTEM:
Olympus' auto focus relies on Through the Lens (TTL) passive phase contrast detection system. Simply put this means part of the light entering the camera is split into two beams and allowed to pass through the mirror. This is directed to the AF unit in the base of the mirror box. The AF unit has twin prism detectors which measure and compare the light intensity between the beams (similar principle to a rangefinder) and determine if the area measured lies in front or back focus. This information is fed to the AF motors in the lens which adjusts the position of the elements in the lens to bring the subject into sharp focus. When focus is achieved the AF points on the screen illuminate.
Obviously the system requires both light and contrast to function, the more the better. If there is no light the system does not work. In restricted light the system endeavours to work but may 'hunt' (winding in and out of the lens mechanism). Or it may simply do nothing when the shutter is half pressed because the unit cannot sense sufficient light. If the latter occurs normally no picture can be taken unless you over-ride this in the cameras menu by enabling manual focus only or single AF plus MF (S-AF+MF).
I'm sure you will have experienced both these situations where the AF system refuses to lock. The same happens if you try to focus on a plain wall or a subject with little contrast. This is nearly always observed when shooting indoors. Normally increasing ambient light and/or contrast fixes the problem. For this type of situation the focus assist light (either flash strobe or red AF beam) may resolve the problem but this light is restricted in reach and intensity and may also be defeated by the lens itself. Large lenses such as the ZD 35-100mm effectively shade off the flash strobe emission from the subject.
When Olympus engineers test the systems they will ascertain how much light is required to enable the AF system to work in most conditions. Their designers will factor this in when designing any new lens as it would be madness to produce a lens that will not pass sufficient light to allow the AF system to work. Their current slowest lens is the ZD18-180mm that has a maximum aperture at 180mm of f=6.3 and for the purposes of this article I'm using the arbitrary value of f=6.3 as the ceiling for satisfactory AF function in most conditions. (NOTE: this is for the purpose of this article only).
The engineers are concerned that in certain situations there will be insufficient light for satisfactory AF. One of these situations occurs when the user decides to slow down a lens' aperture by using it in conjunction with the EC14. I believe that where the aperture is slowed to less than my arbitrary f=6.3 due to adding the EC14 it is safer for the company to tell us the AF will not work and to use manual focus. As said the company is playing sfae but it's a quite reasonable stance to take.
LOW LIGHT AF - REALITY:
All that said (and it had to be explained) it's my experience that both the ZD40-150mm lenses work with the EC14 in most situations even when the ambient light is poor. All this means is the AF system Olympus has chosen works at lower light intensities than they acknowledge. I can also tell you that the AF function works with the ZD18-180mm f=3.5~6.3 when used with the EC14 (gives this lens an ultimate reach of 252mm at f=9). We should be very happy with this!
But naturally, (and remember we are ignoring the company's recommendations) it does mean that AF lock failure is more likely as ambient light drops and this manifests mainly in a shutter button press achieving no AF. If the situation occurs outside when using the lens at maximum focal length we have little choice but to rely on manual focus. This being so, it makes sense to have your camera set to S-AF+MF in any case. Where the situation occurs indoors (unlikely to be using the EC14 indoors) then the AF assist light should, or might, remedy the problem.
My observations conclude that the AF continues to work and there is no noticeable slowing of the AF system as light fails. When light drops to the level where it is insufficient the lens either 'hunts' or the shutter button does not respond. But this occurs only at surprisingly gloomy light levels anyway - levels where you will recognize you are going to run into problems - being almost dark.
In fact I have tried the slow combinations indoors in a 40 foot long passageway lit (for this purpose) at one end only by a 60W bulb and the AF function works just fine. To give you some idea how gloomy this test situation was, the exposure recommended by the camera was f=8.0 @ 4 seconds but the AF system worked quickly and accurately. It is far more likely to be defeated in gloomy conditions not by the absence of light but by having little contrast to measure.
You can see the dilemma faced by the company. There will be situations where a slow lens + EC14 will not auto-focus whether this is because of the ambient light or the deliberate slowing of the lens. Olympus has chosen the safe option and told us that innately slow lens will only work in MF in that situation. The reality is they will work, just be aware of why they might not and what to do if they don't.
COMPARING THE LENSES:
I had a brief look at the performance of the both ZD40-150mm budget lenses (and the ZD50-200mm) in my review of the E-400; you can read that piece here and concluded that general optical performance (in terms of sharpness and rendition) was reflected in the price. By far the best performer was the ZD50-200mm with the old style ZD40-150 second and the latest newcomer, the compact ZD40-150mm coming third. The test was basic, consisting of only my standard 'stone pillar' images and did NOT include use of the EC14 with either of the budget telephoto kit lenses.
Here I shall extend the original tests and for this session I'm using my E-400 tripod mounted with the following settings; A mode, ESP, ISO = 100, WB AUTO, NR= OFF, ESP-AF, S-AF, File = SHQ, CONTRAST = 0, SHARPNESS = 0, VIVID, COMP -0.3, tripped by remote control.
The day is 100% grey. This means the sky is an even dull grey colour and the light is poor but diffuse. I took a reading with my EuroMaster V light meter and it recommends f5.6 at 125th at ASA 100. This is not a sunny 16 day.
Original (old) lens set at f=5.6 throughout FL range; usual pillar target:
Compact lens set at f=5.6 throughout FL range; usual pillar target:
OBSERVATIONS ON THE ABOVE:
There is not much to put between the two lenses in my usual pillar test. I'd give this test to the older version of the lens but by a small margin. To my eyes the older version displays a slightly more pleasing contrast level and is sharper as the telephoto winds out. The newer version is slightly softer at the short end, very similar in the middle and for whatever reason is softening at maximum telephoto.
COMPARING THE LENSES WITH ADDITION OF EC14:
Old version lens + EC14; Lens set to f=5.6 throughout FL range; usual pillar target:
Compact lens + EC14; Lens set to f=5.6 throughout FL range; usual pillar target:
OBSERVATIONS ON PILLAR TESTS:
At this sort of range the new compact version of the 40-150mm is an excellent lightweight alternative offering almost as good resolution, colour rendition and just a tad less in contrast than the original version. Yes, it is slightly slower at the long end but the benefits to those conscious of weight and bulk are considerable. However, it has to be said it cannot equal the older version in this test.
As said the day was dull with diffuse light. With the addition of the EC14 the AF system worked flawlessly throughout. Before moving to the next part I'd like to show you this grab shot taken with the older version of the lens + EC14 when a female pheasant walked past my tripod within three feet. I quickly released my camera and took this:
Crop: (no pun intended)
MORE TESTS SHOTS:
I decided to choose a brighter day to show the results from both lenses on their own only. This endeavours to show which lens is best at full telephoto in good conditions. For this series I'm using my nearest neighbours house which is being renovated at the moment. My usual pillar target is about 260 foot away from the camera. This new target is approx. 1500 feet away (6 times the distance). This should determine which lens is better at long distance details. No camera settings have been changed.
Old version lens at full reach wide open at f=4.5, then at f=8.0
Compact version lens at full reach wide open at f=5.6, then at f=8.0
OBSERVATIONS ON ABOVE:
At longer distances and in any conditions the superior optical build and specification of the original version of the 40-150mm stares through. It is sharper by a good degree, has better colour rendering and finer contrast. No doubt about it in my mind; the older version may be larger and heavier but if you want image quality over convenience, it delivers.
There's little further to add. The results from the compact version would benefit from a touch of post processing to lift the contrast and sharpen the details whereas the original version is adequately good enough straight from the camera.
It boils down to how much emphasis you place on less bulk and lightness versus pure image quality. In many circumstances each lens will deliver good images, almost on a par with each other. In most areas the older and better specified model will give you the edge in brightness, resolution and contrast, but is it twice as heavy and almost twice the size. At the end of the day it is your call.
As far as the lenses working with the EC14 I can find very few circumstances where they do not work in ordinary AF mode. As insurance, if you are using any slower lenses in combination with the EC14 then set your camera for S-AF=MF to ensure you never miss a shot. Other than that just go out and enjoy the extra reach the EC14 gives you but remember it slows the lens down so you may have to increase the ISO to compensate.
NOTE: This article seeks nothing other than to inform. Only you can decide what equipment you want/need for your use. Bear in mind I own both cameras and lenses, out of my own pocket; I have nothing to gain or lose by publishing this article, photographs, examples or opinion.
|Posted October 2007||Copyright © 2004/5/6/7 John Foster|