books/advice

It would have a front element the size of a manhole cover

An aperture is a ratio and is the same for all lenses. That's why a light reading of say 1/125 sec at f8 will be the same for any lens fitted.

It applies to all lenses but it helps to understand what the fX refers to:

A lens with an aperture of f1 has an aperture equal to the focal length (ie, a 50mm/f1 lens has an aperture with a diameter of 50mm).

A lens with an aperture of f2 has an aperture half the focal length (ie, a 50mm/f2 lens has an aperture with a diameter of 25mm).

A lens with an aperture of f4 has an aperture a quarter of the focal length (ie, a 50mm/f4 lens has an aperture with a diameter of 12.5mm).

And so on and so forth.

Each of the standard apertures (1-1.4-2-2.8-4-5.6-8-11-16-22-32) lets in exactly half as much light as the one before it, so 4 is twice as bright as 5.6, 2.8 is twice as bright as 4, 2 is twice as bright as 2.8, etc.

You'll find lenses in the "normal" range with very fast apertures (like the 50/1.2 John mentions above) but there is always a size/weight penalty. For example, a 300mm/f2 lens would need an aperture of 150mm diameter making it a vast heavy monster - this is why (like George said in his post) fast is a relative term. For a 50mm lens something like f2.8 would be considered pedestrian, whereas a 500mm lens with an f2.8 would be considered lightning fast.

As far as I know, the fastest 300mm lens is made by Olympus for their digital cameras and it has an aperture of f2 - that's the sort of glass that needs a tripod to support it and a bodybuilding course to carry around (not to mention deep pockets!).

It's all about compromise and I stick to the Tamron as my recommendation for your race days - 5.6 is perfectly useable on a lens that length and it's light enough to be hand held and not give you a hernia...

thanks john

i think i'm gettig it now

Aperture (as usually undestood) normally means 'relative aperture' and is in fact the ratio of the actual aperure (the size of the 'hole' when looked at from the front of the lens) to the focal length. Thus a 50mm 1.4 has a maximum aperture of 35mm but a 300 2.8 has a a maximum aperture of 107mm

Because lthe amount of light a lens can gather is related to both its focal length (or more strictly its angle of view) and the actual aperture the relative aperture gives an indication of light gathering ability of the lens which is not related to focal legnth and therefore you don't have to take focal length into account when metering.

With a wide angle lens the 'hole' has to be rather smalller than the front element because of gathering light from a .... wide angle. So large relative aperture wide angle lenses are big, heavy and expensive. This becomes even more the case if it is a zoom.* With telephoto lenses the maximum size of the hole is usually the diameter of the front element - hence a 300mm F1 - if such a thing could be made - would have a front element 300mm in diameter. Hence wide aperture telephotos are also big, heavy and expensive. It is only when it comes to 'standard' or short telephoto that large relative aperture lenses are relatively easy to make and hence can be acquired without breaking the bank - the Pentax 50 F1.4 being a good example

* so the 16-50 2.8 is quite a bulky lens with a 77mm filter thread even though the bigest actual aperture is a mere 18mm - 50/2.8

<edit> PS I was obviously writing this as John wrote his post - sorry to repeat!!

WOW!!!

you guys know your stuff , I'm gonna have to print off this whole thread because I'll never remember it!

mucho mucho ta for the explanations. That last one from you Tony really makes the penny drop.

(hope some other folks are benefiting as well, perhaps the ones that are a bit shy and don't want to show their ignorance like me. )

Jeff,

The list is like a menu in Jamaica - not everything is available. But it does apply universally.

Mid-range lenses are easy to make, and easy to make fast. As you get wider or longer, it is harder to make fast lenses, so the longer/wider the lens, the slower it will be.

But although 1:5.6 (aka f5.6) is slow in absolute terms, it would be considered fast for a very long lens. That is what I mean by "relative".

G

thanks George,

like I said the penny has dropped about the relative diameter of the aperture compared to the length.

Camera has finally arrived and it has the 28 - 70 f4-f22 lens.

First impressions are it so flipping light and the auto focus is just amazing (to me anyway)

The operation/action of the lens seems a bit "scratchy" when you adjust the focus and zoom. Is it possible to lubricate or clean the action?

Have downloaded the manual (it's actually the MZ5-N manual 101 flipping pages) and just trying to work my way through the functions before loading the film.

Don't put any lubricant onto or in the lens what so ever
If any of it gets onto the elements or the aperture blades the lens will be history.
You would probably need to get it professionally cleaned but i don't know if that would be economically viable, the cleaning may cost more than the lens is worth.

If its not too bad you may have to live with it or get another off e-bay. I just ran a search and there are several listed for very little money.

Good luck and don't forget to post a few pics

I've had a few of the SMC-FA 28-70 f/4 lenses. They are all a bit like that, alas. But don't let that put you off
Pentax put some excellent glass in this lens, and it is very capable of superb results. It will come into its own when trying portraiture and the like - shooting at 70mm at f/4 or f/5.6. You'll find the out of focus background all buttery smooth with a very "3D" feel to the image

Unfortunately I have had two of these that "misted" up. One of the rear elements was prone to fogging. However, if you have a clear version it'll probably stay clear. Just keep it clean and dry (ie don't store it in a damp environment!)

Have fun
Matt

thanks for that matt.

had a look at your web site some great pics mate.

How do you get that clarity on those portrait pics?

Thanks Jeff
The fisherman and guitarist were taken with the SMC-F 50mm f/1.4 lens - which is mind blowingly sharp.

The shots of the kids were lit by a remote Pentax flash (camera left) shooting through a brolley and a reflector (camera right). The brolley was very, very close (literally just out of shot), and the combination of light and reasonably small aperture - probably around f/8 or f/11 - means you get plenty of contrast... which results in detail. Full size they are incredibly sharp
(Plus I shoot in RAW and use Silkypix which has some very good sharpening algorithms).

Hope that helps
Matt

Matt (had a look at your photoshop tips) , or anybody else who can answer another one of my stupid questions

When you have a 35mm film developed obviously you can get a cd of the pics. Can you use CS2 to edit those images from the CD?

Reason I ask is because I have got CS2 and would like to have a play around.

Jeff

Yup
The CD normally contains JPG image versions of the 35mm images. Do be aware that the quality of the scanning varies from lab to lab
But, yes, it's a quick way to Photoshop your slides or negatives.
Matt

cheers matt

so far to get my head around is lenses, the camera functions and CS2 plus read through the half dozen books I picked up from the library yesterday.


Think I better just stick a film in and go take some pics.


Doe anyone find keeping a log of what you did when taking pics helps. I'd of thought it is a must ?