Originally posted by adwb if I take a series of shots with a k5 in raw saved as whatever highest quality,and with a 645 and 6x6 with, same subject and lighting and as near as possible lenses that are equal in focal length and the same ISO, shutter speed aperture as dictated by a hand held light meter incident light on the subject.
Question;
if I have this image printed out to A3+ size will there be a discernible difference in the image quality between the formats if they are cropped to give as near as possible the same image when viewed at say 1-2 meteres away?
You mean relative focal length - as a 75mm normal for 645 or 6x6 won't be for the K5.
I won't comment on possible image quality in the pixel/grain peeping sense - pinholecam is right, with film the weak link is the digitization of the film.
However, say you have a 35mm on the K5 to get an approximate 'normal' equivalent to the lens on, say, a good TLR's 75 or 80mm. (I know I'll get into trouble here with optical/geometrical experts) The perspective and depth of field / how it is rendered will be different. The larger lens/film will tend to do better with tone gradations as well. You'll get something of a classic look... when everything goes well.
This does not mean the images are 'better' than the K5, as digital does a lot of things better than film, or at least more reliably.
I'll put it this way, 120 film is way better and easier to digitize than 35mm film; there's less latitude for error with 35mm, the lenses have to be better, etc. to approach even mediocre 120 in most respects. But 35mm cameras tend to be smaller, faster to use, and more flexible. Personally, I get more consistently good images from my K100D than from my 35mm film cameras...
Quote: the reason I ask is that I was thinking of buying a 645 or 6x6 but have been very surprised by the high second hand prices. Given market forces etc I would have though the demand was low and lower prices for "old technology"
so what more can I expect get by spending this money against say a good piece of glass for the K5?
Demand depends on which camera you look at. There are hot cameras that everyone looks for, and there are perfectly fine ones that go without bids. That said, there is a large 120 subculture these days... which I hope continues so the film remains available!
With 120, you don't have to start with the 'best' - though the Pentaxes are very nice! With the P645, lens prices started going up before the digital version was released.
However, there are lots of 'lesser' TLRs from, say, Ricoh (Diacord), and various other brands. Except for the real cheapos with poor lenses, they will do a good job. But you may not like the camera format.
Another way to go is with a vintage folder. Here you pay up for ones with RF, or don't and go primitive (which is a terrifying thing!) But it isn't too difficult to learn focus estimating... Again, the hot cameras are bid up, while perfectly fine ones languish. Despite the usual advice to go for 4 element lenses, triplets are perfectly fine, often better than the 4's even, as you'll tend to shoot stopped down.
But if these aren't your cup of tea, there are some cheaper alternatives to the P645 - Mamiya for example tends to be cheaper and more plentiful.
But the real crux of the matter: what do you get from going 120 vs new glass for the K5? Here, I have to go for the fun / exploration factor, the enjoyment of the hobby.... I find it enjoyable to work with antique technology (i.e. no automation)... I rarely use my P645 even, preferring cameras from the teens to the 50s. This is photography with the emphasis on the experience itself, with the result being important but not critical to the enjoyment. If the result, i.e. the image, is critical, with 'image quality' being a primary goal, then I'd say 120 will deliver, but the process will be long and expensive. The K5 lens in that case may bring the more immediate joy.