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10-04-2009, 12:15 AM   #1
Nubi
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A very trivial info about DA 40 ltd

First of all, I love this lens. It is somewhat of a funky focal length, but nonetheless I think it is a fantastic lens.

Initially during the development, they wanted to make it as thin as possible. The engineer department, after much calculations and experiment, figured out if they were to make the lens as thin as they possibly can, the focal length will be at 38mm. But the product development team felt that that particular focal length reminded them of a cheap P & S lens from the film era. Also, as you know, the older pancake, the M40mm, f/2.8 was also 40. So they settled on 40mm, even though they could have made the lens even a bit thinner.

I know who give a flying lick about that, but I thought I would share it with you, because I like this lens sooo very much. I think this is one of the most "interesting" lens ever made by Pentax.

Sorry to take up the precious virtual space....

10-04-2009, 01:27 AM   #2
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both the M40 and DA40 are optically the same and are pancakes. though the manual focus could be bought at much cheaper price around 70 bucks, it is a concern also when you use it for digital since the metering would only be centerweight. in other words, you cannot utilize the other two metering options. so it's more like handicapped in a way. this is one advantage the DA LTD has over the M40. other advantage is more optimized for digital slr use, built and etc...
10-04-2009, 05:05 AM   #3
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as far as I know, as stated above, the M40 and the DA40 are optically identical. so I dont know what exactly you are referring too when talking about not making it 38mm. they are quite different in other aspects, of course, and I can see the engineering challenges, fitting the electronics and AF gears into the body and still have it basically the same size. of course they did drop the aperture ring.
10-04-2009, 05:09 AM   #4
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If they would gone for the thinnest lens ever, then the focal length would have been 38. That's all I am saying. They decided against making it as thin as they can make it for the reason stated above.

10-04-2009, 08:51 AM   #5
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Curious where you heard that story about initially considering 38mm. Seems detailed enough to be plausible, but it's a new one on me.

As for the M40 and DA40 being the same optically, I've seen this debated by knowledgeable people, and the consensus seems to be that they are *not* the same optically - the DA40 is a marked improvement. The basic optical formula in terms of # elements & groups is known to be the same, but given the DA40 has a short minimum focus distance, it does seem likely something significant changed.
10-04-2009, 09:21 AM   #6
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Darn... just 2 milimetres! So close..

If it was 38mm then x1.5 would make it 57mm which in hand is almost identical to 58mm, that is a focal length of Helios-44 (and some other 50's i think) which already qualifies as fast fifty normal kit lens.

So to make it sound better Pentax at the same time made it into 60mm short-tele, when they could make the smallest possible normal focus lens.

I wonder how deep inside the camera lens can protrude on APS-C bodies. The mirror is smaller than FF. Could it be possible to make fast 30-35mm DA lens without retrofocus element, just placing more of it inside of the body?
10-04-2009, 11:31 AM   #7
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QuoteOriginally posted by ytterbium Quote
Darn... just 2 milimetres! So close..

If it was 38mm then x1.5 would make it 57mm which in hand is almost identical to 58mm, that is a focal length of Helios-44 (and some other 50's i think) which already qualifies as fast fifty normal kit lens.

So to make it sound better Pentax at the same time made it into 60mm short-tele, when they could make the smallest possible normal focus lens.

I wonder how deep inside the camera lens can protrude on APS-C bodies. The mirror is smaller than FF. Could it be possible to make fast 30-35mm DA lens without retrofocus element, just placing more of it inside of the body?
So short as the image is "in focus" 45.46mm behind the lens
10-04-2009, 11:47 AM   #8
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QuoteOriginally posted by Nubi Quote
If they would gone for the thinnest lens ever, then the focal length would have been 38. That's all I am saying. They decided against making it as thin as they can make it for the reason stated above.
Maybe I'm interpreting you wrong, but the thinnest Pentax lens ever probably goes to the Takumer 18mm f11 fisheye lens. It makes the M 40mm look like a stack.

10-04-2009, 11:51 AM   #9
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QuoteOriginally posted by Blue Quote
Maybe I'm interpreting you wrong, but the thinnest Pentax lens ever probably goes to the Takumer 18mm f11 fisheye lens. It makes the M 40mm look like a stack.
yup, I know because I own it. its probably thinner than the DA 40 with the lens cap on. however, the 18mm has a simple aperture mechanism and no focus ring.
10-04-2009, 11:53 AM   #10
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QuoteOriginally posted by Nubi Quote
If they would gone for the thinnest lens ever, then the focal length would have been 38. That's all I am saying. They decided against making it as thin as they can make it for the reason stated above.
In optics, it doesn't really matter. Each and every company makes lenses that do not have exactly the same focal length as engraved on the front lens ring. If they made a 38mm lens then it could have been marketed as a 40mm lens. Just like a 135mm lens is never perfectly 135mm, but 133 or 137mm, even though the front ring reads "135mm". It's a marketing thing
10-04-2009, 01:06 PM   #11
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QuoteOriginally posted by Marc Sabatella Quote
Curious where you heard that story about initially considering 38mm. Seems detailed enough to be plausible, but it's a new one on me.

As for the M40 and DA40 being the same optically, I've seen this debated by knowledgeable people, and the consensus seems to be that they are *not* the same optically - the DA40 is a marked improvement. The basic optical formula in terms of # elements & groups is known to be the same, but given the DA40 has a short minimum focus distance, it does seem likely something significant changed.


Actually, there was no reason to hold the source from the beginning. Sorry guys.

There is a Japanese photography magazine called "Digital Photo." In Feb 2008 issue, a there is a section where a each manufacture was to pick out a lens that signified the philosophy of product development. Pentax picked DA 40 ltd. In it, there is a guy named Yasuuki Maekawa. He is a product development manager. He discussed extensively how DA 40 was designed from ground up. According to him the thinnest ever was DA 40 which is 1.5cm without a hood(I actually never measured). The reason I bring this up now is simple. I was just flipping through them and happened to stumbled onto it. In it, he did not talk about whether or not optically these 2 lenses were identical. But he does say that the project started with a clean slate. He also talked about how they paid little attention to numerical values yielded by not so vigorous experiments(because they didn't put too much emphasis on "numbers" as with any ltd lenses including FA). But they debated endlessly in regards to the subtle differences in IQ that the lens demonstrated at each stage of development.

These Japanese magazines often interview engineers who actually worked on certain projects or that, and often times they are very candid, almost to a fault. I believe I have many more that you guys might be interested in, especially about K-7. As for K-7, there were a larger number of people involved than a typical project of this size, due to relatively shorter product cycle compared to years past. Therefore more engineers made numerous comments about the K-7 developement in various magazines. Ooops, going off the topic now. Sorry.

Last edited by Nubi; 10-04-2009 at 01:07 PM. Reason: Because English is my second language
10-04-2009, 01:11 PM   #12
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Interesting stuff! Thanks for sharing.
10-04-2009, 01:22 PM   #13
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The top is the M and the bottom is the DA 40mm. I find it hard to believe that the designer of the bottom wasn't aware of the top one. In addition, as we mentioned it isn't the thinnest Pentax lens of all time either. This is an interesting article. It makes me wonder if there was a translator involved with the Yasuuki Maekawa interview.
10-04-2009, 01:39 PM   #14
Nubi
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Could it be modern Pentax era vs. old takumar?

Dunno.
10-04-2009, 01:45 PM   #15
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QuoteOriginally posted by ryan s Quote
So short as the image is "in focus" 45.46mm behind the lens
Are you sure? Pentax has 45.5mm (K mount and M42 screw) registration distance. Still, even most FA/m42 lenses have their rear element inside of the camera.

And you could probably go even deeper with APS-C camera. Since the lens would be DA anyway, there is no need for it to be mountable on film cameras because of the missing aperture ring and it would vignette being wide-ish.

So i did some measurements:

I just measured the maximum absolutely safe distance (from the mount to the edge of mirror in up position - most closest point to the mount). It's 8.84mm, this gives us 45.46 - 8.84=36.62mm fl (x1.5=54.93).
Unfortunately it would have to protrude even more, because it is somewhere in the centre of the whole lens assembly from where you can measure the focal length.
For example M50/1.4 protrudes 7.96mm in the camera behind the mount, when focussed to infinity. Some primitive logic shows that it has some (50-45.46)+7.96=12.5mm's of glass "behind" it's focal length.
Applying the same value for our minimum distance 36.62+12.5=49.12 (x1.5=67), you get the same 50mm.

What's the situation with 40Ltd. Is it retro focus and how much it protrudes?

Probably you can go even deeper, since the mirror is nearest at its top and goes away when swinging down.
Most likely if you're not making F1.4 lens, and unless there are other compatibility issues (like SDM contacts) i think it could be possible to make a bit shorter and faster (like 33/2) "normal" pancake, with not so much glass (read less price, weight and more quality) as in retro focus design.

Since i've stumbled on such dumb ideas i guess it' s time to bed. Have a good talk!
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