Last year I used iBooks from Apple to make a book of my images and also the ADAPS Year Book. The quality was superb, but the price quite high.

This year I am trying out www.blurb.com having seen some very nice examples of their printing at the NEC.

I'll let you know how it goes, but if you want to preview the first 15 pages of the book I have just done, then it's here:

http://www.blurb.com/bookstore/detail/600429

Comments are welocme!

With Pentax macro lenses I wouldn't worry - they are all excellent.

Only the DA lenses will focus manually whilst in AF, and it is a very useful feature.

The F and FA macro lenses are very big and very heavy compared with the DA, but they are superb performers.

No problem, but I thought I'd covered enough without bringing in Movie lenses as well...as far as amateurs and still cameras go they are obsolete.

I suppose some collectors will use cameras with T stops though, and some will use cameras with non-standard aperture values and shutter speeds. It gets more and more complicated the more you think about it.

It's like all knowledge, it's interesting. But as to why in practice, well I've never referred to a DOF table yet. If I had a very specific DOF requirement that might be different, but I don't.

The rule of thumb to use a small aperture and focus one third of the way into a scene is as much as I ever use. I even use that for small product shots - look at my eBay page for over 100 current examples!

Every lens will have a Depth of Field table and someone recently gave us a link to the Pentax website which apparently has them all.

Older instruction manuals used to contain DOF tables.

No.

The f stop is a ratio, f1.4 is one stop wider than f2 and we know that the square root of 2 is 1.4 (OK, 1.414 or so before someone jumps on that!) so that shows the mathemeatical relationship.

If you have a simple lens of 25mm diameter and a focal length of 50mm this nice easy example is f2. (50 divided by 25)It's as simple as that. The beauty is that it holds true for any lens of any foacl length. If the same 25mm diameter lens had a focal length of 100mm it would be f4. (100 divided by 25). So to make a f2 100mm lens we would need a lens diameter of 50mm...much larger glass.

This is why long fast lenses are enormous and wide angle fast lenses can be much smaller. This latter point falls apart because SLR wide angles have to be retrofocus in design to clear the flipping mirror, so the front glass can be quite large, but the actual exit aperture (look through the back of the lens) is small.

Apertures like f3.5 are half values. The full sequence is 1.4, 1.7, 2, 2.3, 2.8, 3.5, 4, 4.5, 5.6, 6.3, 8, 9.5, 11, 12.5, 16........etc. Some photographers (and Canon) will "simplify" things by calling apertures things like "f 8 and a half" but that doesn't really help to clarify!

T stops are transmission stops, sometimes found on old cameras. A four element uncoated lens might lose 35% of its light to internal reflection, so a physically sized f2.8 lens might have an actual transmmission of T3.5 or T4. This isn't a problem with SMC lenses, but even 0.2% per surface loss can mount up in a 15 element lens. Auto exposure takes care of any slight error because of light loss. So T stops are now obsolete.

I should have made this an article....

6x6, 645, 6x8, 6x9 are all medium formats using 120 roll film. A 6x6 lens could in theory be used on a 645 camera (the focal length would be slightly longer) because the image circle will be the same.

In the Days of Film photographers understood that different formats needed different focal lengths and it was never a problem. For example, the standard lens for Minox is 15mm, for 110 is 24mm, for 35mm is 50mm, for 645 is 75mm, for 6x6 is 75 or 80mm, etc.

The reason that "35mm equivalent" came about is probably because there was not just one format when digitasl cameras arrived, but a multitude of different CCD sizes. Only by giving a "35mm equivalent" could any sensible comparison between different cameras be made.

With film it was simpler because we knew that a 24mm was a standard on the Pentax 110 but an ulra-wide on a ME Super. Nobody was confused by that. But then again people were familiar with medium format as well, which is no longer quite as true.

If we are settling on APS-C then the "35mm equivalent" can fade away - it's causing more confusion than clarity now because so many new photographers have no idea what 35mm looked like anyway.

In the case of compacts it may still have a function. I have no idea what a 6.5mm lens on my compact might mean....

Perhaps it refers to the use of zooms, where the set aperture value could be say f8 but the actual f stop will vary as you zoom.

If this is the case, with a prime the values should always be the same.