I have a Chinon 28/2.8 but don't use it so much because my copy's near-focus is about a yard, while all my other 28's go down to about a foot. It's good for 'scapes but nothing really close.

I wouldn't rate the A35-80 as anywhere near 'OK' when used normally. IMHO it's one of the worst lenses Pentax ever sold. Ah, but put it on a mount-reversal ring, and it's actually sharp! At the 35mm end it reaches 2:1 at ~5cm. At the 80mm end it reaches 1:2 at ~15cm, and will focus past infinity. Yes, an actual macro zoom! But I still don't use mine much.

I have the big heavy expensive Lil'Bigma DG 170-500. I don't use it nearly enough. I also have the lightweight old FA100-300 (silver). I use it a lot. It is very sharp, renders very well, AF's noisily but quickly on my K20D, and cost me US$100. Yes, it looks cheesy. Yes, it is plasticky. And its optics are very very good. Did I mention cheap? Very well -- it's inexpensive, and a great value.

Or, buy older fast manual primes. My used Kiron 24/2, Komine 28/2 CFWA, and Nikkor 35/2 (modded for PK) did not cost much. The Tomioka 55/1.4 and planar Yashica ML 50/1.4 cost even less. Unless I gain another inheritance or rob a minimart, I likely won't be in the market for FA Ltd's in this decade.

ObTopic: When to upgrade cameras? Never. Just supplement. Even though modern cameras are just computers with lenses, the upgrade imperative is different. I need to upgrade computers much more often than supplementing my lot of cameras. Timing isn't much different though. Supplement/upgrade as soon as it can be afforded. Waiting for something better is for suckers -- there will ALWAYS be something better later on, but we don't want to wait forever, eh?

So, my advice: Buy the Kr now. Let your son carry many lenses, that's good training and exercise. And don't forget to wear hats.

I think it was one of the Capa brothers who said, "If your photos aren't good enough, you're not close enough." So I am usually inadequate. Bother.

While gargling for RED FILTER DIGITAL CAMERA DYNAMIC RANGE I found this page on FILTER OPTIONS FOR DIGITAL CAMERAS which tells us almost everything we need to know. Or at least its a good start. Now I don't need to write a filter treatise. Whew.

Well, it does leave out a little. Use a Yellow filter when shooting garish colored neon lights at night. Use a Red filter with B&W shots for greater dynamic range. Use a Blue or Violet-CC filter to replicate early photo emulsions, which only see 'actinic' (UV-violet-blue) light. There are more, but that's enough for now. Have fun!

I should have qualified my "thin DOF is for art, thick DOF is for sales" comment as somewhat of an oversimplification. Of course thin.DOF pics can be sold, and thick.DOF pics can be artistic. But as mentioned, looking at published photos and top photo sites, we see much more thick than thin DOF. Perhaps thin.DOF shots MUST be artistic in order to sell, just as vegan food MUST taste good in order to get anyone to eat the stuff. But I digress.

Mention was made of replicating a Fast Fifty's DOF with a longer lens. To roughly compare degrees (not absolutes) of DOF, I compute the very simple DOF INDEX which is just: FL/AP, focal length divided by aperture. The larger the number, the thinner the DOF. Thus a 135/2.5 (54) has thinner DOF than a 50/1 (50) or 58/1.2 (48.3) but thicker DOF than a 200/3.5 (57.1) or 300/4 (75). Again, FL/AP doesn't give the range of DOF, just the comparative thickness with different FL/AP combinations.

Thin DOF (wide-open) is for art. Thick DOF (stopped-down) is for sales.

That said, I cherish my fast lenses, and use my 24/2, 28/2, 35/2, 50/1.2, 85/2, and 135/2.5 wide-open more often than not, varying mainly with light. But I don't need to sell photos. My K50/1.2 certainly isn't for prestige, as nobody around here knows or cares that I have it. And my FA50/1.4 (my only AF prime) sees use mainly as the gotta-get-the-picture lens when its speed and agility are paramount. It's just gravy that it also shoots well stopped-down.

Why buy a fast lens? FOR THE SPEED! Duh... And why buy a slow lens? For the sharpness maybe, but mostly for the lower price. Those German 35-40-50-100 f/4.5's for under US$15 each are sure sweet. But those are for bright days. No good for vampires.

40mm doesn't float my boat on APS-C. (Mea culpa: I have other 40's, not the DA.) I personally prefer 28 and 50. Some love 40mm as being intimate, others don't as being stand-offish. I find it too in-betweenish. The 21 sounds better for you.

I've many many lenses. My lens-of-the-day rotation is an attempt to use them all. Alas. But the main glass sorts out like this:

Most-used (drivearound): DA18-250
Most-used (walkaround) Komine 28/2 CFWA
Most-under-used: Lil'Bigma 170-500