Teleplus MC7 DG works with beercan and A900

[David Kilpatrick]

I decided to obtain a new Kenko 'for Digital' Teleplus MC7 DG - the latest eight-contact version for Sony, but not the 'top of the line 300 model which has come in for some criticism elsewhere (and costs almost as much as an s/h Minolta converter, or a Sigma Apo). I used the MC7 20 years ago with the 70-210mm, and I thought that it retained focusing despite the result being f8.

Well, I was right - it does. On the A900 and A700, it focuses reasonably fast but the A900 is far better at locking on the target even in extremely dim and difficult conditions. The A350 focuses slowly and has real trouble locking on to lower contrast subjects, but can hit obvious ones well enough. The quality retained is surprisingly good - it will throw off purple fringes if aimed at a subject like a small prism hanging in the sun in my window, but otherwise with the 70-210mm f4, a setting of f10 (2/3rds of a stop down) is enough to clean the image up.



AF on the chicken's head - at 100% - at 400mm setting wide open



Quick hand-held full aperture shot at 360mm:



100 per cent section:



The Kenko does not disable AF on ANY lens incuding even the 500mm f8 mirror, but most simply won't focus though the camera will try. The 70-300mm SSM behaves erratically, jittering around, and was removed very quickly. The 28-105mm f3.5-4.5 RS, a recent acquisition (yesterday!) which so far is proving to be superior to the 24-105mm D when used on the 900 and a decent walkaround substitute for the more limited 28-75mm D, AFs at all focal lengths including 210mm at f9. The 35-200mm xi will not operate at all despite the 8 contacts, the converter's chip is clearly not compatible. Overall, the quality from the converter is surprising. Even the 500mm yields good detail at 1000mm f16, but manual focusing is tricky and the light forces ISO 1600 which really doesn't show the best results.

David

[Yagil Henkin]

Not only with the 500 mirror. Just one question - David, How would you rate the 28-105 for the A900? I have one (not A900, the 28-105...) And wonder how good it'd be optically, and especially how better is the 28-135.

[David Kilpatrick]

I have not used the 28-105mm much yet, I got a mint one yesterday (as new, as if never opened from its packaging). It seems to be extremely good, maybe not quite as good as the 28-135mm in the corners. I have only used it for a few shots so far and it seems to be just a little softer centrally than the 28-75mm, in contrast rather than resolution, and a bit better to the edges. It is far superior to the 24-105mm and has just a hint of CA, with hardly any distortion at the wide end. It holds f3.5 from 28 to 35mm, then f4 from 35 to 50mm, then f4.5 from 50mm on.

I got mine on a Buy It Now from a dealer with a VAT receipt for £120, which to me is £101 with the VAT removed, and I felt that was a very fair price. I sold my 24-105mm D for £149 which was a good price for the buyer, and I know the 28-105mm RS is much older and not a D model, and does not do 24mm... but it appears to be a much better lens all round.

David

[Yagil Henkin]

Also, the focus is quite fast, at least on my Minolta 7 & 5 (Film) and sony A700.

[David Kilpatrick]

Also, I have been looking at the 28-105mm and it seems to be a very advanced design. It does not vignette or distort significantly, and the field stays flat for close-ups. It is also very well made, much better than the 24-105mm or the 16-80mm CZ. The extending front barrel stays really firm and does not wobble when pressed. As you say, the focus is fast too. From memory of the 24-85mm, I didn't like that lens much at all, but mainly because the close focus seemed restricted. The 28-105mm only goes to 50cm but the close-up area covered is acceptable. Not close enough for a butterfly, but close enough for a portrait of a single rose.

David

[sparaxis]

I find the general disregard for this lens odd.

Most of the reviews I have read over the years rate it better than the 24-85 which in turn was generally better regarded than the 24-105.
Perhaps some people think it to be similar to the 28-105 Xi, which gets a generally poor review.

Although the 28-105 Xi and subsequent 28-105i and Rs share the same nominal construction there may well be differences.
If one studies the patent literature, one of the great advantages claimed for the "Xi" design was that since both zooming and focus were under the control of the camera, radically varifocal designs could be used and appear to the user as a "zoom"

You can see this with the 35-200. Switch it to "manual zoom". Turn the zoom ring and you see the lens is very far removed from a zoom lens. a relatively small change in focal length results in major defocus. Perhaps the reason this lens never re-appeared as a "normal" lens is that is was simply not mechanically possible.

The Xi and subsequent versions of the 28-105 share the same nominal elements/groups arrangement. However in converting it from a "radical varifocal" to a zoom, they may have changed a mediocre lens into a good one. (I am assuming the 28-105 Xi shares some of the characteristics of the 35-200. I have never used one but that is implied by the patents.)

I am curious to hear the real world results as I have been thinking of getting one to use on one of my maxxum 7s.

[Yagil Henkin]

I have one, and It's my main walkaround lens with the film camera. Good quality, fast, accurate.

[Vidgamer]

I find the general disregard for this lens odd.

Most of the reviews I have read over the years rate it better than the 24-85 which in turn was generally better regarded than the 24-105.
Perhaps some people think it to be similar to the 28-105 Xi, which gets a generally poor review.

Although the 28-105 Xi and subsequent 28-105i and Rs share the same nominal construction there may well be differences.
If one studies the patent literature, one of the great advantages claimed for the "Xi" design was that since both zooming and focus were under the control of the camera, radically varifocal designs could be used and appear to the user as a "zoom"
....

I got a used 28-105xi recently, and am curious what you're referring to. I just tried zooming (which is only manual, of course, on my A100), and it becomes out of focus, and the camera quickly refocuses. I tried a couple of other lenses, and they both seem to need re-focusing after zooming, but to different extents. (So, I'm not sure that any I tested were parfocal.) How much is too much?

And if the 28-105xi isn't a real zoom, what is it doing with the tube moving in and out so far?


As for teleconverters, I have an old Promaster 1.7, and I realize that it is not great to begin with, but I keep trying it once in a while, with mixed results. It is prone to blooming/purple fringe, particularly depending upon what lens is used (and I suppose, how many highlights you have). Also, I have had poor results with panning -- I suspect that because it is not chipped, that SSS does not work well with it.

[01af]

Although the AF-xi 28-105 mm and subsequent [non-xi] AF 28-105 mm share the same nominal construction there may well be differences. [...] The xi and subsequent versions of the 28-105 share the same nominal elements/groups arrangement. However in converting it from a "radical varifocal" to a zoom, they may have changed a mediocre lens into a good one.

Indeed. When looking at the section drawings of the AF-xi and the AF 28-105 mm lenses then you'd be hard-pressed to see the differences. You have to look pretty carefully to notice them. Even though the change from a vari-focal to a parfocal design seems a major one, the section drawings hardly reflect that---they look very similar, almost equal.

The AF-xi 28-105 mm is a very soft lens at full aperture. The images look as if they were taken through a Softar filter, with a fairly obvious flare but still good core sharpness. When stopping down an f-stop or two, the image will clear up considerably. The lens is not bad but neither it's very good. At full aperture, the AF-xi 35-200 mm is a much better lens. So I am surprised to learn here that the non-xi AF 28-105 mm is praised so highly ... I only have the xi version (which I don't like).

And if the AF-xi 28-105 mm isn't a real zoom, what is it doing with the tube moving in and out so far?

'Real zoom' means parfocal---which the AF-xi 28-105 mm clearly isn't; it is varifocal. So it's not a zoom lens in the narrower sense of the word but a vario-focal lens.

-- Olaf

[sparaxis]

A clarification for Vidgamer:

A parfocal lens, as is commonly found with zoom lenses, maintains focus as you zoom. Most zooms today use mechanical compensation, in which various cams, (really differently curved slots in some of the moving barrels), move the various different groups of lenses by different amounts as you zoom to maintain focus. Usually these days some of these elements are moved during the "focussing" process, so called "internal focussing". (This actually changes the focus by changing focal length without compensating for focus shift.) Older zooms would focus by only moving the front few elements of the lens. Once of the bizzare side effects of internal focus is that the focal length changes quite a lot as you focus closer. (Gets shorter) Which explains why that 200mm lens may have the field of a 120mm lens at minimum focussing distance.

All of this is mechanically complex. Varifocal lenses do not attempt to maintain focus as you change focal length. Minolta hit upon the idea of simplifying the mechanical design of the lenses by making all the focus shift compensation "electronic". By using power focus, the camera knows exactly how far to shift the focus to compensate for the amount that it has zoomed. Very clever. This is the sort of trick that made 4-element zoom lenses possible for point and shoot cameras. However even the best "true zooms" are not entirely parfocal.

The power zoom function seems to work fine with every body I have tried it with so it should work with the A100. With the zoom ring in the forward position twisting it to the one side or the other will zoom, pull the ring back towards the body and twisting it gives power focus. Depending on how far you twist the ring if works slower or faster. With the Xi lens I have, the 35-200, the camera shifts the focus fast enough to maintain focus as I zoom.

Perhaps as part of the "cheapening" process that the Xi design allowed, the lenses were cheapened as well. The whole experience was a disaster for Minolta as everyone hated the idea and sales were slow. They followed up very quickly with the Si series cameras but by then Canon had moved to No 1.

Of the Xi lenses, the only one that has a good reputation seems to be the 35-200. However it must be remembered that it was wickedly expensive in its day.

Alan

[jcoffin]

Even though the change from a vari-focal to a parfocal design seems a major one, the section drawings hardly reflect that---they look very similar, almost equal.
-- Olaf

The difference between a varifocal and a zoom design isn't necessarily on the lens elements at all. Rather, it's in the rates at which the elements are moved as you change the focal length.

A simplified version of a zoom lens is a relatively short focal length element at the front, and a reducing lens behind to give the effect of a longer overall focal length. To focus the lens, we move both elements relative to the film plane. To change the focal length, we change the distance between the two elements. As we change the distance between the elements, the distance that's in focus changes at the same time as we change the focal length.

To create a zoom, therefore, we have to change the distance between the elements to change the focal length, and at the same time change the distance of both elements from the film plane to maintain the focus.

In a typical case where you zoom by twisting a zoom ring, it has angled grooves/slots cut on the inside to translate your twisting movement into forward and backward movements of the elements. In a zoom lens those angles have been calculated to maintain focus as the focal length changes. In a varifocal lens, little or no attempt at such compensation is made.

Of course, practical lenses aren't nearly that simple -- a fixed focal length lens typically has a half dozen or so elements of different shapes, using different kinds of glass, etc., to reduce distortion, spherical and chromatic aberration, etc. A practical zoom lens may easily have a dozen elements or more, usually arranged into half a dozen groups or so. As such, instead of just moving two elements relative to each other, the slots/grooves have to be arranged to move all six (or whatever) groups of elements relative to each other. Especially when dealing with relatively short zooms, you often have groups that move in one direction during one part part of the zoom, and the opposite direction through the remainder of the zoom range.

The long and short of it, however, is that there isn't necessarily any optical difference between a varifocal and a zoom lens. Most of the difference is in the care that's put into calculating and cutting those angled grooves/slots that translate your twist of the zoom ring into forward and backward movement of the element groups.

This also tends to explain why a zoom design will often be better than an otherwise equivalent varifocal: the zoom is simply a result of greater care in both design and manufacture.

P.S. it's also worth noting that a fixed focal length lens with internal focus uses the same principle. The difference is that instead of moving the elements to maintain focus while changing focal length, it moves the elements to maintain focal length while changing the focus.

[sparaxis]

A very good description.

The point I was trying to make (indirectly with respect to lens elements) was that the Xi series of varifocals had cheaper to manufacture lenses as one of the goals. Obviously one of the ways to cheapen lenses is to use less elements as well and a generally lower level of correction and mechanical precision.

Two of the lenses that made it into post Xi versions have no great reputation as zooms either, namely the 28-80 f4-5.6 and the 100-300 zoom. The first generation 28-80 3.4-5.6 (62mm filter) was greeted as a great improvement at the time.

The 100-300 Apo is quite a lot better than the non-apo version.

Alan

[Vidgamer]

...
The 100-300 Apo is quite a lot better than the non-apo version.
....

Tell me about it!

I HAD a 100-300xi for a while, but exchanged it for a 100-300 APO. Much happier now. I bet that the design of these lenses are very different, but I dunno.

I haven't used the 28-105xi enough to have firm conclusions about it, aside from agreeing that it seems a bit messy when used with a wide-open aperture -- from a quick test, it looks better stopped down only a bit. I'm not convinced that it's so horrible, but I can get better results with a wider aperture with, for example, an inexpensive 55-200. I want to try it more in good light and see what it does. From what little I used it, I think it has a pleasant look.

Interesting explanation of the xi design. (My previous experience with the word "parfocal" is swapping eyepieces on my telescope. Two eyepieces are said to be parfocal if you can swap 'em without having to refocus the telescope, so it's the same usage.) I didn't realize that zoom = parfocal -- I always assumed zoom meant simply the changing of focal length (as opposed to a prime lens). Certainly, the xi lenses are labled as "zoom" lenses.

[01af]

Certainly, the xi lenses are labled as "zoom" lenses.

Sure ... because from a marketing point of view, they are parfocal zoom lenses. The focus compensation is not accomplished optically or mechanically but electronically. The camera will compensate through the AF mechanism ... and the point is: this compensation is carried out without using the AF sensor. You can put the camera with an AF-xi lens on a tripod, auto-focus, put the lens cap on, change the focal length, and remove the cap without re-focusing. The image will remain in focus because when shifting the focal length setting, the lens will send focus compensation data from a look-up table to the camera which will actuate the AF motor to accomplish the compensation according to the data received from the lens. No focus metering involved! The lens won't get re-focused but the focus shift will directly and immediately get compensated for.

So in a way, the AF-xi 28-105 mm and AF-xi 35-200 mm lenses are zoom lenses indeed.

-- Olaf