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I'll get right to the point: This is my solution for adding a third-party lens hood and cap to the DA 35mm f2.4 AL lens.
1) DA 35mm f2.4 AL lens
2) Kalt 49mm metal screw-on lens hood
3) Pentax 58mm pinch lens cap
One of the minor drawbacks, in my humble opinion, about the DA 35mm f2.4 AL lens was the lack of an included lens hood. Pentax made the lens extremely compact, and in doing so they eliminated the typical grooves and bumps found on other lenses that would accept a reversible lens hood.
Adding a third-party hood is no problem at all, provided you purchase the right kind for the lens' angle of view. Some hoods will allow you to attach a lens cap, others do not appear outright to accept a cap. I was irked because I did not want to use a generic collapsible lens hood; I think they are ugly, add way too much extra bulk to the diameter of the lens when stored, and it can be difficult to find a rubber lens hood that provides proper shading for a lens at any given focal length.
When I decided to give myself a Christmas present in the form of the DA 35mm f2.4 AL I also did some research into trying to find the appropriate hood and lens cap combination. I had to take a calculated risk because there was no guarantee the pinch cap I purchased would match the hood. I read a few messages around the web that seemed to indicate 58mm would do the job, but nothing definitively said one way or another. Well, here it is.
The Kalt 49mm metal lens hood screws on easily enough. It looks good and seems to provide the right amount of shade for the lens to prevent flare.
Because the user can no longer access the filter threads the native lens cap does not work. Luckily, a 58mm pinch cap does the job. I suppose any generic cap would do, however I went with the Pentax-branded variety because I want my gear properly represented! The Kalt lens hood has some ridges scored on its inner surface which match up nicely with the ridges on the pinch cap. The cap grips nicely to the inner edge of the hood, much the same way it would on the inner rim of a filter thread. The cap mounts flush with the surface of the hood little effort. There is no indication that the cap would come off very easily if the lens and hood were stored with the cap in place.
A soft "push-on" cap that grips the outer edge of the hood might do the job quite well, however I was not willing to experiment with something I couldn't play with at my leisure.
Another nice thing about this particular hood/cap combination is the fact that if you lose your grip on the cap and accidentally jam it into the lens hood opening it can not ever touch the front lens element. The diameter of the cap is too large for the narrowing tube of the hood.
Some might think this is all too much to worry about for a lens, that a rubber hood is fine. If that does the job for you, well, cheers! Granted, a regular 49mm rubber hood would allow you to use the native 49mm lens cap and avoid an extra purchase. I simply do not like the garish look of a rubber hood. Plus, the act of collapsing such a hood could be a lot of effort exerted on the end of a delicate lens like the plastic DA 35mm f2.4 AL. Don't get me wrong, the lens feels well made, but it's no tank, either.
In all I paid about $20 total for the metal hood and pinch cap.
P.S. This little gem of a lens is pleasantly sharp wide open. I look forward to taking some formal test shots once my neck of the wood warms up a few degrees.