For those that don't know, the history behind the green button is as follows:

When automation was introduced to Pentax cameras, the 'auto' settings were usually identified by green text (at least as early as the K2). The idea being that the user would select the green settings to get a good shot. This is why the 'A' on the aperture ring of KA lenses is green.

When Pentax launched the SFX there were concerns that users could get the camera into a state that they didn't understand. Pentax provided a 'C' (clear) button, which when pressed put the camera onto the basic program line and reset most other options to the default settings.

When the Z-1 was released, the green button became the 'IS' button (Interactive something), which when pressed would set the camera back to the selected program line (or if in manual mode - one shot aperture priority).

On the K-5 the default options are picked out in green (AF-S, matrix metering, auto AF selection etc.) and pressing the green button sets the selected program line.

In manual mode, the green button is great because it sets the selected program line. Once there if you hit the AE lock button, it will hold this EV value and you can shift the shutter speed or aperture with a dial and the camera will change the complementary value to maintain that EV value.

The benefit of this is that you can leave the camera in manual (for those artistic shots...) but if you suddenly need to capture something quickly, simply press the green button and you're in program, then press the the 'AE-L' and spin a dial and you're in HyperProgram.

Hi Horst,

You don't need to program anything into the green button (on the K-5 at least). When using manual (non-KA) lenses in manual exposure, it stops the lens down momentarily to meter and sets the shutter speed corresponding to the stopped-down aperture.

John.

Hi Oso,

Having fired up the clip-on meter (the later square one), I'm quite surprised how 'frisky' the needle is (far more than my old Leningrad 8 meter). It also slides onto the viewfinder accessory slot, which has the effect (for me at least) of moving my glasses further away from the finder and hence reducing eye relief.

I really bought it because I felt it made the camera look cooler

John.

For me it depends on the cost of the lens and the size/vulnerability of the front element. When I use filters it is usually to keep dust off the front element so I don't need to clean it off the lens, only the filter. I'm more likely to damage a lens through trying to clean it (or putting a thumb print on it) than banging it into something.

Then again I hate damaging stuff, even if it was one of my half dozen M 50/1.7's that I use as body caps.

If the debate is UV over clear, I'd go for UV simply because they cut through haze better (and if it isn't hazy you probably won't notice the difference).

Nah they won't, they've a big line in (expensive) VR lenses instead.

A couple of months ago I bought an SMC-Tak 135/3.5 for £50 (optically mint but some 'brassing' of the aperture ring) and another £12 for a hood. Both But-it-now's and slightly more than the auctions were running at the time.

I've only seen the 35/2 in buy-it-now's, usually silly prices. I've seen Super-Tak 55/1.8s for around £30-40, but I paid that for an S1a + 55/1.8. There are a lot of Spotmatics with Super-Tak 55/1.8s that go for £20-30.

John.

I have an old Sigma 70-300 f/4-5.6 APO Super from the late '90s which has pretty much the same profile, markings etc. I suspect this is basically the same lens but with one less 'APO' element?

I haven't really tested my 'APO' version but would say it was OK optically for this type of zoom. The AF isn't brilliant either but I can't compare to comparable screw-driven zooms of similar lengths.

I don't know how much these are compared to other options, but if I was looking at Sigma's, from these links from Sigma's website, I'd go for the DG APO as you have SR, it looks better MTF wise, has two SLD elements instead of one and should be cheaper:

APO DG info: link
APO DG MTF: link

DG OS info: link
DG OS MTF: link

Or there's a Sigma 135-400 APO for sale in the classifieds (not mine).

John.

Thanks Algi,

The orange marks on the aperture ring & focusing scale line up the hyperfocal distance at f/8. Line three marks up and you have everything from 6ft(ish) to infinity if you check the DOF markings (on 135 film).

John.

My only gripe is that it is in a slightly different position on the battery grip than the camera.

I use it all the time in manual, it sets the currently selected program line (without having to scroll through shutter speeds) or with K lenses for stop down metering and didn't know it did anything else.

A lesson for budding wedding photographers perhaps: link