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Pentax SMC 85mm f1.8
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PostPosted: Sat Jan 05, 2008 9:24 pm    Post subject: Pentax SMC 85mm f1.8 Reply with quote
I am progressively working through my manual lenses now that I have a digital camera that can accommodate them. I took this picture this morning in my front courtyard. I am very happy with it. The focus point is the furthest pillar and you can all of the texture in it. I gave it only the smallest amount of sharpening (which I do with all digital shots.) The color is really nice too. I really must use this fella more often.

The one problem is focusing when shooting wide open. My old eyes are not up to it. But if you nail it the image really pops. It has nice bokeh too wide open. I will try to find some shots taken with it set this way.



PostPosted: Sat Jan 05, 2008 9:27 pm    Post subject: Reply with quote
I have this lens with broken !? front lens at edge , takes great captures as well like new Smile


PostPosted: Sat Jan 05, 2008 10:43 pm    Post subject: Reply with quote
Very nice! I love these parameters: 85mm f1.8!


PostPosted: Sat Jan 05, 2008 11:18 pm    Post subject: Reply with quote
I wonder what it is about 85s, 105s and 135s? These focal lengths all tended to have particularly good lenses from the big name designers and manufacturers.

Is it that these were the "signature" focal lengths so they went all out to design good lenses for them, knowing that these would make or break their name in the market place. Or is it because there is something about these short to medium telephotos optically that made them easier to design? Perhaps a bit of both.

Even if they had features that allowed an "easier" design, the designer had choices to make. I have read that the earlier (pre-AI) Nikkor 105s were designed as true telephotos ie they were optimized for medium to long distances based upon the earlier still rangefinder design and lens usages. Later when these were redesigned they realized that many of these were now more likely to be used for portraits so optimized them for shorter ranges.


PostPosted: Sun Jan 06, 2008 12:02 am    Post subject: Reply with quote
peterm1 wrote:
Or is it because there is something about these short to medium telephotos optically that made them easier to design?


You nailed it.

Lenses shorter than 55/58mm need an additional diverging element in order to clear the mirror of an SLR camera (their optical draw is longer than their focal lens). Unfortunately this additional element also adds many aberrations and a lot of distortion. These can be corrected to some extent by adding more glass elements or by using aspherical surfaces. Anyway, the shorter the focal length, the more difficult it is to build a good lens.

Lenses longer than 135mm tend to suffer from chromatic aberrations, which increase with lens magnification. The most common way to deal with the problem is to use low dispersion glass, like glass containing fluorite (e.g. ED glass) but then again, the correction is never perfect and the use of special glasses is limited by the price factor.

Cheers!

Abbazz


PostPosted: Sun Jan 06, 2008 12:08 am    Post subject: Reply with quote
Abbazz wrote:

You nailed it.
Lenses shorter than 55/58mm need an additional diverging element in order to clear the mirror of an SLR camera (their optical draw is longer than their focal lens). Unfortunately this additional element also adds many aberrations and a lot of distortion. These can be corrected to some extent by adding more glass elements or by using aspherical surfaces. Anyway, the shorter the focal length, the more difficult it is to build a good lens.


Exactly, the retrofocus scheme is basically an inverted tele lens that is placed in the bottom of the optical scheme to allow for the reduction of the focal lenght.

Abbazz wrote:
Lenses longer than 135mm tend to suffer from chromatic aberrations, which increase with lens magnification. The most common way to deal with the problem is to use low dispersion glass, like glass containing fluorite (e.g. ED glass) but then again, the correction is never perfect and the use of special glasses is limited by the price factor.


Yes, and special glasses and true-glass aspherical lenses is why those Apo-Tessars and Apo-Elmarits cost a fortune. Sad
-


PostPosted: Sun Jan 06, 2008 12:10 am    Post subject: Reply with quote
Thanks Abbazz. I should have thought about that. When stated that way its obvious. (As most good ideas are.) Cheers.

Certainly I was going to add that I had noticed that longer focal lengths like this often have fewer elements and of course, your explanation is the reason. It is part of the reason too why I respect what I call lenses with "modest" design specs. It seems to be exponentially harder to design a lens with just that extra half a stop or a stop of coverage while retaining image quality. Part of the reason no doubt that Leica glass is so damn expensive, together with the build quality is that these are amongst the lenses that you can shoot wide open without serious degradation.

But it remains that so often the slower lens (ie with a simpler lens element layout) is the substantially better lens when it comes to image making - Not always; there are some excellent faster lenses - the 50mm Nikkor 1.4 and the 50mm Takumar 1.4 being cases in point where they approach the resolution of the 1.8 versions. (Which themselves are regarded as being exceptional.)


PostPosted: Sun Jan 06, 2008 9:46 am    Post subject: Reply with quote
That's the main reason why wide angle lenses for rangefinder cams can be so amazingly good: no mirror. Wink


PostPosted: Sun Jan 06, 2008 12:41 pm    Post subject: Reply with quote
I said I would try to find some wide open shots. Here is one. I did not quite nail the focus correctly (on the glass) but this shot demonstrates the lovely soft bokeh of this lens when shot wide open (the box behind the glass.)

On reflection, the DOF of this lens at this distance, wide open is so small that it may be impossible to get the whole glass in focus. Note that the front lip of the top of the glass is reasonable but the stem is well out of focus.



PostPosted: Sun Jan 06, 2008 1:19 pm    Post subject: Reply with quote
peterm1 wrote:
I did not quite nail the focus correctly (on the glass) but this shot demonstrates the lovely soft bokeh of this lens when shot wide open (the box behind the glass.)


Great shot, Peter.

The bokeh of this lens is indeed lovely. As it is also less prone to purple fringing than the 77/1.8 Limited, I use my SMC-Takumar 85/1.8 a lot more.

Cheers!

Abbazz
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