May 2001 Archives

In dealing with the Sigma 28-105 lenses, remember that there is the 28-105 4-5.6 UC, the 28-105 4-5.6 UC II, and the just-released 28-105 3.8-5.6 UC III, as well as the 28-105 2.8-4. According to the test results, each new version of the 4-5.6 UC make was better than the last. I have the latest (UC III) and find it quite good for the "if you just have one lens" situations (just shot four rolls with it today). It has a minimum focusing distance of about 19", and does adequatly on an HTsi plus as far as focusing speed. If you have the old UC, you may be quite pleased with the UC III, and it is a lot less expensive than the 2.8-4 version. I would not recommend it over top quality prime lenses, however. It is, after all, an all-purpose zoom.

It is usually rated as one of the top in it's class. But a better question is, how much production variation exists between lenses of the same make and model? If you took 100 different 85mm f/1.4 lenses and ran the same tests for, say, resolution (lines per mm) under controlled conditions, how much would the results vary from lens to lens? 2%? 10%? I find this question important, since so many of us rely on these "objective" tests in buying decisions. From what I have heard, there is little variation among the top lenses: it is the cheap ones that vary a lot. Which probably explains why people have such heated discussions about Sigma and the like (It's great, it sucks! back and forth about the same lens).

I'm sure I've mentioned this before. An adaptor exists. It has a piece of glass in it, kind of like a teleconverter. Why? If you've ever used extension tubes (which are great, by the way!) you would notice that when the lens gets further away from the camera, the focal plane gets closer to the front of the lens, but the lens will no longer focus to infinity (the depth of field gets narrower too). Now this is just what you want for macro photography, but not for much else.

Back to the adapter. The MC/MD and AF mount rings are different sizes (the MC/MD ring is about 30% smaller). So one side of the adapter accepts the MC/MD lens, the other mounts to the AF body. Now an adapter that can do this, purely from the mechanics, is of necessity several millimeters too thick. Without correcting optics, it would become a short extension tube. So to allow the MC/MD lenses to focus to infinity, a pieces of glass is necessary to correct the focus. Now this piece of glass, that is about 2cm in diameter (not ideal for large aperture lenses in the first place) is not of very high quality (reasonable quality, to be sure, but not high) in any of the models that I have seen.

So when you mount your expensive lenses on this $40 adaptor, they all become considerably worse (I've done tests with an MC 58mm f/1.4, an MD 28mm f/2.8 and an Celtic 135 f/2.8). The resulting pictures look pretty bad, when compared to these same lenses on the proper camera body. Put in absolute terms, the results were worse than the cheapest 28-200 AF zoom in every area except distortion. That is, sharpness and contrast suffered noticeably.

If you never enlarge your pictures beyond 3x5" (9x13 cm) then you may not notice. Likewise, if you have never developed an eye for variations in contrast between lenses, and can't see the practical difference between a $100 zoom and an $800 fixed focus lens, then again, you won't have any problem with the results. In my test, a Sigma UC III 28-105 AF zoom gave instantly visually better results than the best lenses through the adaptor, and on 3x5" prints! No magnifying glasses, no getting really close. Lay them all out on the table, and you can pick out the ones from the adaptor vs. the ones from the Sigma zoom from a distance.

Now I don't want to exaggerate the differences, but there was a huge quality difference! The pictures through the adapter are still better than most plastic lens point& shoots, but that is not a very good reference point. Of course, the MC/MD lenses are wonderful on my SRT cameras (and better than the Sigma zoom). Well, I hope that answers your question. Yes, you can do it, but do you want to pay the price? Technical note: The trick to get the adaptor to work on an HTsi is to hold down the spot meter AND self timer buttons WHILE turning on the camera - this will override the shutter-release failsafe, allowing you to take pictures in aperture priority mode.).

The last time I heard of one of those, it was a case of an early Sigma lens that only worked with the first series of Minolta AF cameras (7000 and 9000) but was software incompatible with the later versions. In addition to manual focus, you could only shoot with aperture wide open, because the Minolta AF lenses have no aperture ring, as this function too is software controlled (through a ROM chip in the lens). For details, see this page.

I had written earlier that Sigma's 24mm f/2.8 autofocus lens was sharper than Minolta's, relying on, among others, photodo.com's tests. Someone (I forget who) corrected me, saying that while Sigma was sharper at the center, Minolta was sharper at the edges. I went back to photodo.com and checked the two. Looking carefully at every single measurement for both lenses, I must report that the graphs show the Sigma lens to be sharper than the Minolta at ALL areas of the lens at f/8. At f/2.8 the lenses are closer, but Sigma's is still sharper at every point on the negative. Remember, this test is of resolution only, and says nothing about color, contrast or bokeh. Still, I would like to give credit where credit is due. Photozone.de 's lens survey (not the reader survey, but the average of the magazine reviews) also rates the Sigma ahead of the Minolta version. Lens tests abound, especially on the internet. They can be subjective, a sort of write up/near advertisement, or objective, such as sharpness, and distortion (a la photodo.com).

I should note that samples vary considerably among Sigmas. The good ones are very good, but there are quite a few lesser examples floating around as well. Test any lens you are considering before purchase (or after purchase, and then sell it quick on eBay if it doesn't measure up).

The two you mention are the sharpest pieces of glass Minolta sells! Remember as you get into the lower focal lengths that it becomes more difficult for a manufacturer to make a lens of the same sharpness as 50 or even 100mm. That aside, the 35mm f/2.0 and the 35mm 1.4 are both almost as sharp as the other two you have. Interestingly, Sigma's 24mm f/2.8 is also very sharp (photodo 4.0) and as such well ahead of Minolta's 24 f/2.8 (3.4). The 28 f/2.0 rates better than any other option at 28mm. So, if you like to spend money, and want only the best, consider the 28mm f/2.0 or the 35mm f/1.4. Also, the 20mm f/2.8 is an excellent lens.