A great price for a great lens - I'm tempted and I've already got one!

I recently came by one of these as part of an outfit I bought (for some Takumars):



Pictures, samples and info can be found here

It's a Sigma 12mm f/8 fish eye in T2 mount. I didn't pay much attention to it at the time, as I had read that full frame fish eyes may not be very 'fishy' on a crop sensor DSLR.

I fired off a couple of shots yesterday and found that the projection is actually not bad on APS-C.

f/16 on K200d, resized JPG straight out of the camera.



It's a fixed focus design and in view of this, centre performance stopped down is OK:

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But at the edges, there's some spectacular CA!

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I think that some judicious PP using ptlens or similar may improve the CA and sharpenss so it could be a viable, low cost option to try out fish eye (and is certainly more fisheye like than the Zenitar 16mm on APS-C)

I didn't think I would be in to fisheye, but I quite like it and now find myself tempted by a 10-17!

One advantage if the PK/A mount is that it can be used with multi-segment metering, whereas only spot metering is supported for PK mount lenses, as I understand it. It's debatable whether this is an advantage worth the additional £30-40 over a PK mount, but it may help make the metering with your K10D more consistent.

I briefly had a Samsung GX-10 (sister to the K10D) with the intention of using it with my old MF lenses (including a few Adaptalls) but found it easier to get good results with my K-m, both in terms of consistent metering and also in-camera JPEG processing.

If it's any consolation, I tend to check the metering using the histogram, as Kris described above, with my K-5 when using PK mount lenses, as it is quite often a couple of stops out from where I'd like.

I've got a spare A50/1.7 in good condition - drop me a PM if you're interested

I've had a Chinon 50/1.4 in PK mount which offered respectable IQ and I sold for £30. It is rumoured that the Chinon PK mount lenses were made by Tomioka, who are pretty well respected. The XR Rikenon is believed by some to have been manufactured by Pentax and has a pretty good reputation.

The alternative 'cheap' way of getting a Pentax F/1.4 lens is to buy one with some damage that won't affect IQ, but will affect its value. I got an SMC K 50/1.4 for about half the going rate because it had a dent to the filter ring but with a but of judicious straightening, I can now mount a hood or filter. It's not cosmetically perfect, but has superb IQ.

You could even contemplate one with damage to the front element. There are a number of people over at mflenses.com who have tested lenses with pretty spectacular scratches to the front element that have minimal impact on IQ. I have a Super Takumar 135.2.5 with a single, 10mm scratch on the front and can find no evidence of this in the pictures. The consensus of opinion is that a small number of big scratches is better than abrasion or cleaning marks, which may increase flare.

Having recently rationalised my lens collection, I ended up with some funds burning a hole in my PayPal balance and, in the way of LBA, now have a range of lenses covering a fast APS-C 'normal' focal length.

Most I have bought for a specific reason or application (or a price too good to pass up), but in an idle moment yesterday, while making sure my kids didn't drown themselves (or each other) in the paddling pool, I did a quick comparison.

The lenses:
- Sigma 24-70mm f/2.8 @28mm (to give a comparison with a decent zoom)
- Sigma 30mm f/1.4 (a favourite for low light and portraiture)
- Vivitar (Komine) 28mm f/2.0 CF (one of my first primes and very good value for money)
- Pentax SMC 28mm f/2.0 (K series developed in cooperation with Carl Zeiss - I'm a big fan of the K series lenses and had always wanted a copy of this one)
- Pentax FA 28/2.8 (modern AF Pentax prime)

What I looked for:
- Sharpness
- Out of focus rendering
- Colour and contrast

The process:
I took 3 images with each lens, which were taken as JPGs straight out of the K-5:
- Close up of some apple blossom wide open (sharpness and tricky bokeh on the shed in the background. This isn't a fair comparison as the lenses have different maximum apertures, but the other two images should redress this a bit)
- Same close up of apple blossom at f/8 (sharpness and general quality stopped down)
- General landscape shot at f/8 (sharpness, contrast and colour rendering)

The camera was tripod mounted, using the 2s self-timer at 100 ISO. I focussed manually using live view to verify the focus - there was slight movement of the flowers in the breeze, but I think that the focus is as good as I could have got it in each case.

I haven't done any PP on the images here, mainly because I wanted to make it as fair a test as possible (assuming that the camera does roughly same processing on each one) and also because it's not something I'm very experienced at yet. Also it would have taken much longer, as I can easily script resizing renaming and cropping!

Disclaimer
I'm not what I think is referred to on the other forum as a 'measurebator'; test charts, MTF figures and pixel peeping isn't my cup of tea. I thought that the results here were interesting and I've learned quite a lot from doing this, my results are pretty subjective/empirical and any constructive input is welcome!


Close up, wide open

Sigma 24-70mm f/2.8 (~28mm at f/2.8 )


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Sigma 30mm f/1.4 (at f/1.4 )


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Vivitar (Komine) 28mm f/2.0 (at f/2.0 )


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Pentax SMC K 28mm f/2.0 (at f/2.0 )


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Pentax SMC FA 28mm f/2.8 (at f/2.8 )


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Close up, f/8
Sigma 24-70mm f/2.8 (~28mm at f/8 )


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Sigma 30mm f/1.4 (at f/8 )


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Vivitar (Komine) 28mm f/2.0 (at f/8 )


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Pentax SMC K 28mm f/2.0 (at f/8 )


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Pentax SMC FA 28mm f/2.8 (at f/8 )


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Landscape, f/8
Sigma 24-70mm f/2.8 (~28mm at f/8 )


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Sigma 30mm f/1.4 (at f/8 )


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Vivitar (Komine) 28mm f/2.0 (at f/8 )


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Pentax SMC K 28mm f/2.0 (at f/8 )


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Pentax SMC FA 28mm f/2.8 (at f/8 )


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Conclusions
It's very subjective, but I think they're all pretty good! The Vivtar is spectacular value for money, but the Pentax K and Sigma lenses have better contrast and bokeh that I find more pleasing.

The Sigma 30/1.4 is impressively sharp side open and has really smooth bokeh.

One of the real surprises is how good the Sigma 24-70 is; it's sharp and has surprisingly good rendering for a zoom.

However, there is something special about the colours from the Pentax lenses and I really like the smoothness and subtlety of the bokeh from the K28/2.

I don't know, but I think the key is the 'resistant' bit of weather resistant, not weather proof. I think that the WR sealing is good enough to prevent most water ingress, but not perfectly sealed, so it isn't air tight and probably wouldn't survive immersion in water for long.

Good advice - I have done it in the past and really wouldn't recommend it unless you have dexterity, patience and time in abundance! I did a Takumar 200/4 which failed to yield to being soaked in solvent. It took several hours and a couple of attempts at reassembly (the first time around they still stuck), but it did work in the end.

If you're interested in repairing lenses, I'd say that it's worth a go on a lens you can afford to write off if it doesn't work out (doesn't sound like it, in your case), otherwise it's best to leave the diaphragm mechanism intact if possible.

How about FA* and DA* then?

I think being named after a high end lens would be OK. Preferable to a kid in my daughter's class who is called Acer; it always struck me as a bit unfortunate to have a name that most people will associate with either a laptop or a tree.

I think it's quite a tribute to Pentax's lens designers that even after the advances in technology of nearly 20 years, the FA* still holds its own. Perhaps even more remarkable is the fact that some of the Takumar and SMC-K series designs still hold up pretty well.