Wednesday, August 27, 2008

Pentax 135mm Lens Comparison

Got one of these for a pretty good price. It's not the famous M42-mount Pentax Super-Takumar 135mm f/2.5, but rather the downscale, made in Taiwan, Takumar (Bayonet) 135mm f/2.5. This lens is pretty downscale as Takumars go, being from the budget line. It has four elements in four groups, and was made from 1980 to 1988. Not a classic by any means.

As if I don't have enough 135mm lenses already: I have an excellent Pentax SMC-M 135mm f/3.5, a Carl Zeiss Jena 135mm f/3.5, a Pentax Auto-Takumar 135mm f/3.5, and a creepy plastic $2.00 Hanimex 135mm f/2.8 which is extremely bad. But the Takumar (Bayonet) is a K-mount, not an unhandy M42 mount, and is a stop faster than the SMC-M, so more light and shallower DOF.

But how does it stack up? here are the contenders:



I took some photos of our housing development's water tower, comparing it to the SMC-M. The color cast is different, as the Takumar (Bayonet) lenses did not have Pentax Super-Multi-Coating, but rather an ordinary multi-coating (they are not single-coated, a common rumor, but probably single-coated on the inner surfaces).

Anyway, the full frame:



And comparisons:

f/2.5f/3.5 or f/4f/8
 


The Takumar (Bayonet) shows some obvious CA wide-open but shapes up admirably at f/4. I cannot really say that the SMC-M (which has a great reputation) wide-open is really that much better than the Bayonet at f/4 (one stop down). At f/8 of course they're pretty much identical.

A good buy, if I may say so myself. That f/2.5 could prove handy sometimes.

Thursday, August 07, 2008

Sub-pixel Anti-Aliasing on Linux

After my accident with the Linux Oracle Binary Image last week, I've been using Linux exclusively on my notebook. It has been somewhat of a pain, but I'm surviving! (quite a feat, after two years of a Windows desktop). I even got the wireless working.

But something has always been bugging me about Linux: how to optimize the Cairo font-rendering engine to get really good anti-aliased text.

Now this may be old hat to the hardened Linux crowd, but it's a sufficiently major discovery for me.

First of all: what is the sub-pixel order? it turns out that the vast majority of LCD displays have RGB pixel order, which is why this is the default.

You can determine the sub-pixel order for your particular LCD by going to this: Lagom LCD test. Windows users don't have to do this, as they have the ClearType Tuning Wizard (not installed by default on XP, but you can get it from MSDN somewhere).

A second important note: (and I just learned this five minutes ago) do not enable full hinting! for some reason, full hinting make sub-pixel anti-aliased text look worse than regular full-pixel anti-aliased text. Although do note that on a CRT, full-pixel AA is the only game in town.

The Lagom site recommends to use "slight" or "medium" hinting. After I switched from full hinting to medium hinting, there was a huge improvement in visual clarity, it's so not funny.

Have fun with your LCD!

Sunday, August 03, 2008

Adjusting Infinity Focus on the Pentax Super-Takumar 35mm f/3.5



I have a Pentax Super-Takumar 35mm f/3.5 lens in M42 mount which I got some months ago. It has been sitting in my drawer all this time because on the 1.5X DSLR it's equivalent to a 52.5mm, which would be interesting except it's slow at f/3.5.

I suddenly got interested in it because of this thread on the MFLenses forum. One of the posters opined that this lens (along with the Mir-1b 37mm f/2.8 which I also have and which also just sits in a drawer) are some of the top wide-angle lenses.

Update: the Mir-1b, which won the Grand Prize at the 1958 Expo in Brussels, is actually a Russian clone of the Zeiss Flektogon.

So I decided to take some photos (out the window) with the Pentax, and quickly discovered that it doesn't focus to infinity. Here's a photo I took with the Super-Tak, the Mir-1b, and the SMC-Pentax DA 16-45mm f/4 ED AL:



The Mir-1b at f/2.8 was sharper, and so was the SMC-DA at f/4. Also it was obvious (from the split-image focusing screen as well as from focus confirm on the K10D) that the Super-Takumar was not properly focused at infinity. Apparently this is a common woe of wide-angle old Pentax lenses.

I found this blog post which details how to adjust infinity focus on a similar lens. The fellow used a sink drain plug to get the front ring off, but I didn't have such a drain plug, so I used a pair of pliers with rubber grips:



Everything else was exactly the same as in the original blog post. Took only about 20 minutes of fiddling to get the right adjustment.

Before and after (100% crop):


Much better!!

That said, I got to try the neglected Mir-1b and it's unexpectedly good! It's extremely flare-prone so I screwed a Pentax hood to the front, making it look quite impressive (almost like a small Canon 17-40mm f/4 L):



It also has pretty good ergonomics, and seemingly better bokeh than the Super-Takumar.

Mir-1b 37/2.8Super-Takumar 35/3.5