A-200 lens

A mini-review of the Olympus A-200 teleconverter on the Dimage 7.

 

Introduction:

This lens is one of the few teleconverters that are known to work on the Dimage 7 at this time. The other popular lens is the Olympus B300 teleconverter. Both of these lenses are not made any more, so are hard to find. The A-200 is a 1.5X teleconverter intended for the Olympus IS/L series cameras. Here are some comments on the A-200

Construction: 

The lens is fairly compact. It has 49mm threads and so screws directly onto the D7 with no adapter needed (in fact, if you are in a hurry you can attach the lens without taking the Minolta lens shade off). The rear element of the A-200 is close to but not touching the front lens on the D7; that is good for a teleconverter, it gives maximum field of view. The body of the lens is plastic, and the weight of the lens is 161gm ( for comparison, a set of AA NiMH batteries is about 100gm). Because of the light weight, I don't feel TOO bad attaching this to the D7, although it is harder to operate the D7 zoom with this lens attached, it helps to tilt the camera down to zoom out or up to zoom in. The front element of the A-200 is about 60mm, and the rear element is 34mm. (The front lens on the D7 is 40mm). There are no lens threads on the A-200, so you cannot attach a lens shade to it.

 

Light loss:

The diameter of the A-200 is 60mm, and the diameter of the D7 is about 40mm. The ratio of the areas is 3600/1600 or a factor of 2.25! This should mean that the camera would gather more light when the lens is attached, but in practice I find that the exposures are exactly the same at full zoom with the lens attached; the D7 must not be able to take advantage of the extra light at full zoom. (Ralph Brown points out and rightly so that actually this is the ratio of areas that would be expected for 1.5x since 1.5x1.5=2.25... the lens is designed for no light loss at full zoom.)

However, here is a trick, you CAN get some light gain with this lens by operating it at less than full zoom (but see vignetting below). At about 133mm on the camera, you can get almost half the shutter speed on the camera (factor of 2 light gain, or one stop), while still having 200mm overall focal length with the lens attached. This could be useful for shooting sports in low light.

 

Vignetting: 

The camera does Vignette with the A-200 attached. In fact, there is some slight vignetting at all focal lengths. This is typical of telephoto systems unfortunately. He are some worst case shots of the vignetting...

Vignetting at 200mm (worst case, large aperture)

Vignetting at 125mm (worst case, large aperture)

These are worst case situations for vignetting because they were shot with the lens wide open. With the lens stopped down, as it would be in an outdoor scene, the vignetting is less noticible.

See the outdoor vignetting test in this album

 

 As you can see, the vignetting is fairly constant from about 130mm to 200mm. It is there, and may be visible on some subjects; however on "natural" subjects it is less visible. It is just a light reduction in the corners (upper left the most) rather than full vignetting.

 

Image quality:

See the A-200 image quality album here.

I've uploaded some test shots to an album. I've tried to arrange this test to show several things. a) off axis quality b) chromatic aberration c) vignetting d) degradation due to using the lens.

Note the following.

* In the first shot with A-200 at 200mm (300mm effective) note that you can hardly see the mild vignetting in the corners even on the white paper in the upper left corner.

* On this same shot, note only mild chromatic aberration on the very high contrast test chart. Also check out the image sharpness at the edges which is where most teleconverters have problems. There is some minor degradation at the very edges.

* Compare the resolution of the first shot with the A-200 to the second shot which is the camera at 200mm without the lens. You may have to zoom to the full size images to do this. There is a definite resolution improvement in the center of the chart. Is is a 50% improvement? I don't know, but you can see the improvement, and the center of the chart isn't in the center of the field..

* Compare the last shot to the first. In the last shot, I moved the camera at 200mm 33% closer and lowered it until the image scale matched the first shot which was taken farther away with the lens. Yes, it does not match exactly, but it is really hard to do; it I do it again I'll take the shots on a perfect level so that perspective change is not a factor. Comparing the shots shows you how much the A-200 degrades the image (not much!) Perhaps there is a little more scattered light.

Sorry about the reflection on the olives of my lights, I should have moved them.

 

Scattered light:

   If you zoom the lens out, you can see that there is quite a bit of light being scattered off the inside of the lens barrel in most situations. I feel that this light probably reduces the contrast of your images somewhat, and that the lens could benefit from having the inside painted a better flat black, or having felt or other flocking material glued around the inside. I have not done this with mine though because the only way to open the lens is to unscrew the retainer for the front objective which is going to be a pain. My lens has a couple dust specks on the inside though, so maybe I'll open it some day and give it the treatment.

 

In summary, I'm kind of surprised that this lens is as good as it is... too bad it isn't 2X though. As a lightweight alternative to the B300 lens, I think that it is worth looking at.

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