I've not looked at the calculator, but that can't be right. However, it depends on how closely you look into the matter and does potentially become extremely complicated.

For all practical purposes, there is more DOF on smaller formats, and if you think about it it has to be so. An 80mm lens has the same DOF because it is always an 80mm lens. But it is a telephoto on a smaller format, and for that given field of view has the DOF of an 80mm but the filed ofview of say a 120mm. The 120mm on the larger format gives the same picture at the same distance but has less DOF.

An extreme example would be a Minox with a format of 8x11mm (huge compared to some digital compacts!) and with a standard lens of 15mm. because it is a 15mm lens you don't even need to focus there is so much DOF, but the angle of view is what you would expect of a standard lens.

In a similar way, digital compacts have enormous DOF for the very same reason, and their lenses are very short focal lengths (7mm anyone?)

The digital SLR is not so extreme, having a sensor of maybe around 22x15mm, but I'm sure that it is at least one stop more DOF that we have compared to 35mm, for a given field of view.

I think I'll leave it there for now before we get any deeper into it!

There's a fair bit we agree on there, George.

Just to explain more clearly what I meant, if I may I will use an analogy. If we take the M series of cameras, then my feeling is that in terms of the ergonomics, they match perfectly with the smaller and lighter M series lenses. This is not to say that other lenses are no good with these cameras, just that from a design standpoint I feel M bodies and M lenses gel together particularly well.

The digital (DA) lenses are also physically much smaller and lighter, partly because of the materials used, but also because they are designed to only cover the APS sized sensor and can therefore be either more compact or more adventurous in specification. On the *istDS that I use, the SMC Pentax-DA 18-55mm is perfect - light, compact and efficient. The SMC Pentax-FA 24-90mm works just as well, but is huge and heavy by comparison.

That's all that I meant!

I think you've hit on an important point there - give the users what they want. But what do the users want? The best quality at any price? The cheapest mega-zoom for 6 x 4 prints? Somewhere in the middle is the compromise, and although there will be some takers at both ends of the spectrum I suppose it's where the perfect trad-off between quality and price lies.

Somewhere ages ago on this forum I said I was waiting for a full size 10MP sensor from Pentax before I felt the quality level would be right. In the event, I am happy with my A3 prints from an APS sized 6.1MP sensor. OK, if there was higher resolution I would take it, but it would be a subtle difference for my applications and I can wait.

That only leaves the question of wide angles, and I need about a 12mm lens to make things perfect again. So I will probably be a taker for the new 12-24mm zoom.

I have also found that digital SLRs handle IMHO better with the lenses they are designed for. So the DA zooms are pretty good anyway. The only exception is that for studio use I like a constant f number, so there is a use for my A series manual focus zooms. The 35-70mm makes a fantastic portrait lens!

The new DSLRs are really fantastic to use, maybe you could borrow one to try out? It might be better than you think....

A friend of mine called round today because he was unhappy with the quality he was getting from his Fuji S2 Pro and Nikon lenses, so we ran a whole battery of tests to see if we could fathom out the problem. I used the SMC Pentax-DA 18-55mm on my *istDS as a reference comparison for the tests.

The Nikkor lenses were a 50mm f1.8 and a 24-85mm zoom that cost around £300.

The results were interesting, and the outcome was that the Pentax produced crisper pictures than the more expensive Nikkors. With the Fuji/Nikkor combination there were also issues over focusing accuracy, but when we achieved like-for-like situations the pentax had a distict edge.

If this is so, and it's not just that I'm lucky to have a good Pentax lens and he is unlucky to have some under-par Nikkors, then what is the value in a "Pro" designation?

This is one reason I have never gone for leica - if you spend £1800 on a lens and get a poor one it's a disaster. If I haven't liked (occasionally) a Pentax lens I have been able to afford a different one. Pentax products are consistently of a professional standard, whether they are pitched as such or not.

You're right that Pentax lenses are up there with the best, and in terms of quality and design are hard to beat. Their design for me actually is better than some of the Nikon and Canon lenses, and the feel of the Pentax lenses surpasses even Contax and Leica.

The bodies are very nicely designed and manufactured, but are probably less reliable than the lenses. This might well be true of all marques, as the camera body is a more complex bit of kit.

The Pentax marque is, I think, aimed at a high quality enthusiast level, with some aspirations to pro use (otherwise why make 15mm lenses, shift lenses, mammoth telephoto lenses...) and I think they are aiming to have a decent urnover at that level. There's no point IMHO of trying to compete in the leica market, and even Leica seem to be finding that out the hard way. Equally, there's no satisfaction in manufacturing cheap and nasty cameras, it does little for the reputation! So somewhere in the middle is a good compromise, and my feeling is that Pentax sit there very comfortably.

Full frame pro spec DSLR? I think they were going to do that, and realised that the costings didn't fit their profile.

There are limitations to using zoom lenses on the SP500. The Pentax zooms of the period were large and heavy and very restricted in terms of focal length. It wasn't really until the M series that zooms of quality and compact dimensions started to appear. Independent zooms of the period can be dire in quality and subject to flare and other defects.

I don't know how many modern zooms are available in M42 mount, but these would probably be your best bet. Possibly Cosina/Vivitar, Tamron, amybe Sugma. You might also find some Russian lenses in M42.

In many ways it would vbroaden the possibilities if you were to buy a K mount body, and if you want one very similar to your SP500 then the Pentax KM would be as close as it gets.

Then all the K mount zooms are at your disposal. The ones with constant f numbers are best for manual exposure measurements, so the SMC Pentax-M 24-35mm f3.5 and the SMC Pentax-A 24-50mm f4 and 35-70mm f4 lenses are excellent choices.

So do I, Matt, so do I!

As you already know, a 28-80 Macro zoom is not a true macro lens, but it may well focus quite close.

The aperture ring can be set to any of the marked apertures, and usually this will mean that the camera will set the shutter speed (aperture priority or Av) or you could use manual settings of the speeds.

The "A" setting is used when you want the camera body to control the aperture. So, for example, you could set the shutter speed and let the camera set the aperture (shutter priority or Tv).

Some bodies require the lens to be set on "A" to be able to function correctly.

Some Pentax bodies are unable to use the aperture ring on lenses, and if the MZ60 is one of them then the lens needs to be set on "A". If there is no A setting on the aperture ring, the lens is an M or K lens that is not compatible.

Is the aperture ring on the lens set correctly to "A"? Or is the camera trying to tell you that the Aperture value is incorrect?