I like the idea of Pentax having a 35mm lens for this camera but a fisheye has very limited use. What are some opinions about Pentax producing a rectilinear(no distortion)35mm? SR

-- Steve Rasmussen (srasmuss@flash.net), April 15, 1999

Answers

A rectilinear 35mm could be produced but because this lens would be even more asymmetrical than their moderate wide angle lenses, correcting distortion would be difficult. Thr easiest way to correct distortion is to make the lens symmetrical. This of course is not possible in SLRs with mirror boxes that need to be cleared(for wide angle only). The 135, 165, 200 and 300mm lenses actually perform fairly well once you get used to their limitations. Color correction at those focal lengths is not all that hard to solve. The 500, 600 and 800 f/4 are another story. If the 300 were redesigned to be ED, it would be very expensive. Pentax may change this lens though. As far as contacting Pentax, try writing them via snail mail. Rectilinear means straight lines are rendered straight. Falling back effect will still happen with rectilinear lenses; these are two different things. The 45mm is rectilinear but does have what is called mustache distortion. This is the attempt by the designer to correct distortion and what you end up with is a slightly wavey, almost straight line. Have not heard that the 35 fisheye has optical vignetting. The correction for optical vignetting seems to be secretive among the optics companies. It is not considered an aberration so my guess is that designers use a trial and error method to some degree. They design several iterations for the same focal length, all corrected for the normal aberrations and pick the one with the least vignetting. I've heard that distortion is treated the same way because it also is not considered an aberration. In the LF world, center filters are used for optical vignetting. SR

-- Steve Rasmussen (srasmuss@flash.net), April 17, 1999.

Marcelo & Tapas: If Pentax's short telephotos seem a bit awkward in portrait/studio/fashion work, I feel it is because this camera system was not primarily designed to do that. The 90 and 165 leaf shutter lenses seemed like an afterthought for a camera that was originally designed for nature and outdoor work. The slow flash synch is more evidence of this. Pentax probably tried to cover too much subject matter in order to draw more customers.

-- Steve Rasmussen (srasmuss@flash.net), April 23, 1999.

Hi Steve

Could they do it ? Mamiya claim that they couldn't produce the 43mm for an RZ/RB because of the retrofocus design limitations (presumably they mean a sufficient quality 43mm).

Would a 35mm rectilinear lens could pair up with a 55mm lens, wheras now we end up choosing between the 45mm and 55mm. I went for the 45mm because I tend not to use wide angles as general lenses.

What I think Pentax should do it improve their short telephoto lenses in the 135mm to 300mm range. Why do they bring out 400mm and 800mm star lenses but neglect the most used telephoto range ?

Maybe the new 200mm ED IF lens for the 645 means they are going to update some 67 lenses as well.

How de we apply pressure on Pentax ? I e-mailed their comments site for the UK but got no response.

Tapas

-- Tapas Maiti (tapasmaiti@hotmail.com), April 17, 1999.

Steve, Tapas; in response to the original post,

What exactly is a rectilinear lens? Does that mean that lines are straight and not curved?

Does a lens still qualify as rectilinear if lines near the edges are slanted, for instance a building on the right of the frame would look sheared (slanted) to the right? Does the 45mm qualify as a rectilinear lens?

If so, I agree with you that a rectilinear 35mm would be much more useful. Also, I hear that it has problems with light falloff at the edges. Is there any solution for this? It seems that by the design of the lens, attaching a neutral density filter (the ones that correct this kind of defect) is impossible.

Tapas, why do you think that the lenses in the 135-300mm range need to be worked on? I agree that the 300mm would need some redesign because of the difficulty of setting it up on a tripod, but aren't all the other lenses in that range optically (and ergonomically) excellent?

regards, Marcelo

-- Marcelo P. Lima (MPL4@cornell.edu), April 17, 1999.

Marcelo

My view on the 135mm to 300mm is a general point about modernisation. I've used both 165mm lenses and I am not making a complaint about their quality but if you try and pick lenses for an aplication the range seems a bit peculiar.

An example is portraiture, pentax promote the 165 2.8 as their "portrait lens" yet it incapable of doing a full frame headshot. My personal view is that it is too short as well for that. If you look at other lens line ups, Bronica has the 180mm that focuses down to 1m, the Mamiya has the same (though it uses bellows focusing), the blad has a 250mm focusing down to 2.5m. We have the 300mm that focuses down to 5m, is a old design and according to all the opinions floating around then net is one of their worst lenses. Another example is macro, I've used the 135mm and though it is an excellent lens it is hardly macro. The new 100mm is but is very expensive and a very short focal length - in 35mm we tend to want macros in the 60mm to 105mm lengths.

What we end up with is 3 normal length lenses and 3 short telephotos - is this logical ?

I guess my main winge is because I want a 300mm with good wide open performance (else just make it a f5.6 lens and lighter) and focusing down to 2~2.5m and a 165mm-180mm focusing down to 1.0m (dreamland - preferably a 2.8 version) to complement it and I want it for the Pentax 67II.

The longer length lenses obviously need the special glass etc more but the short telephotos are the most purchased and generally useful and should be where Pentax's design efforts should go IMO.

Tapas

-- Tapas Maiti (tapasmaiti@hotmail.com), April 18, 1999.

Tapas,

I completely agree with you that these lenses need major redesign. Although I'm very new to MF, the opinions I've seen around the web aren't that positive, as you said. I bought the 200mm/4 as a general purpose short tele, thinking about using it as a portrait lens too. I was a bit disappointed with its close-focusing abilities, though. It seems that to do serious portrait work (if you're working with fashion, for example) you need the auto extension tube set, which will allow you to crop a bit of the model's head and get a REALLY close shot. I find Pentax a somewhat bizarre company. It seems that there are "Big Brothers" in Japan that control the entire affair, with no regards to what is happening in the USA (I don't know about Europe, you could tell us). You've probably read posts of people who called Pentax in Colorado and it seemed like they really didn't know what they were talking about, or they told you that Pentax in Japan "does not release that kind of information.." I also find it interesting that there are still no ad campaigns for the 67II in the US.. My point is that I get the impression that it is hard to make oneself "heard", and that in this respect, Pentax might not be a very "friendly" company. Maybe we should all try snail-mail, as Steve suggested.

regards, Marcelo

-- Marcelo P. Lima (MPL4@cornell.edu), April 18, 1999.

Well, there is a way to get a rectilinar 35mm lens. But it requires quite a bit of work.

Get a 35mm tilt shift lens designed for 35mm cameras, like the Canon FD 35mm TS lens. or Nikon 35mm PC lens. Remove the lens elements from the helical assembly and fit them to a spare Pentax 67 mount. Design the mount so it holds the mirror up after exposure.

You will have to use the lens with mirror up and for the P67II you will have to remove the lens after each exposure so the mirror can go down all the way and can be recocked. Add to the fact that the corners will probably vinginette and a viewfinder will have to be used and focusing will be by hyperfocal distance it doesn't sound that appealing.

I've been thinking of doing this with my Nikkor 28mm f/3.5 PC lens, but haven't gotten around to it yet. It only has an image cicle of about 70mm, so the corners would vingenette, but after cropping it would still be extremely wide.

Food for thought.

Peace, Rolland

-- rolland (relliott@nasheng.com), February 09, 2001.