Why does zoom effect ap?

[MeGotsACanon]

I've noticed that when i zoom in closer, the smallest app number suddenly increases, this is anoying because i', trying to get qucik shutter shots and i then have to adjust the shutter to compensate.

I'm sure they do it for a decent reason, any one know it?

[stopbath]

The aperture rating is the ratio of light that hits the sensor or film compared to the light in the image before the lens. Thus a f1 will transmit all light. F8 will transmit 1/8 of the light. f.85 will transmit MORE light than what is available (Called a nocturnal lens, the lens has a huge front element, and the image ends up brighter on the film than what's in real life!)

Anyway, your camera has one front lens element. That sets how much light can enter the lens. That is fixed. As you zoom in, you increase the resulting image, and as the image is magnified, the light becomes less intense. This is why the fstop increases as you zoom in. It's the physics of the lens.

[MeGotsACanon]

Thanks stopbath, i new there had to be a reason.

I wanted to use it at a sporting event, and i guess i cant use zoom anymore, would be ok because i have the tele, but has huge vigenniting.

Having a f0.85 would be brilliant for a quick shutter, could be a car going past and still no drag.

[stopbath]

Use higher ISO to attain those shutter speeds while using telephoto.

The A70 tele convertor is not meant to be used in wide mode, only telephoto.

The nocturnal lens is massively expensive (I've only been shown one, never used one.) More reasonable are the 1/1.4 or 1/1.2 lenses that can be had for not too many hundreds. (But then you'ld need an SLR body too!

[MeGotsACanon]

nah, wasn't after oner, just though they would be nice to use.

Higher ISO, is that the 400? or is it like the app and reversed.

Then is its only meant to be used on zoom, how do you achieve really quick shots when zoomed in at full 3x with the tele aswell?

[stduc]

ISO value relates to 'film' speed. ISO 100 is double the speed of ISO 50. ISO 200 is double 100 & 400 is double 200 so 400 is 6 times 'faster' than ISO 50 which gets you the best shots with the least noise. So, if a particular shot requires f4 at 1/60 sec at ISO 50 you can also take the same shot at f4 1/500 sec or f8 at 1/250 sec using ISO 400. You do of course suffer a big rise in noise using ISO 400.

The above assumes I have got my math right!

I tend to raise the ISO no as a last resort when I can't use flash, external flash or keep the camera steady on a tripod or, the subject is moving. I find that the esge preserving smooth feature of PSP is pretty good at removing noise however.

[Ikinaa]

stduc wrote:
ISO value relates to 'film' speed. ISO 100 is double the speed of ISO 50. ISO 200 is double 100 & 400 is double 200 so 400 is 6 times 'faster' than ISO 50 which gets you the best shots with the least noise. So, if a particular shot requires f4 at 1/60 sec at ISO 50 you can also take the same shot at f4 1/500 sec or f8 at 1/250 sec using ISO 400. You do of course suffer a big rise in noise using ISO 400.

The above assumes I have got my math right!

I tend to raise the ISO no as a last resort when I can't use flash, external flash or keep the camera steady on a tripod or, the subject is moving. I find that the esge preserving smooth feature of PSP is pretty good at removing noise however.

hmmm... I may be wrong, but isn't it :
f/4 : 1/500
f/5,6 : 1/250
I think when doubling time, you need to multiply the f/ by sqrt(2) = 1.414... something like : because of the size of the disc of light (lenses are circular) =pi * r^2
(gosh... maths are long past...)
oh and by the way... 400 = 8 * 50

[stopbath]

MeGotsACanon wrote:
nah, wasn't after oner, just though they would be nice to use.

Higher ISO, is that the 400? or is it like the app and reversed.

Then is its only meant to be used on zoom, how do you achieve really quick shots when zoomed in at full 3x with the tele aswell?

I'm not following the question regarding "really quick shots" How does putting the adapter on slow down the camera? Does the camera have a hard time focusing?

I've not got the tele adapter for the a70 camera, but I've used other Canon Tele adapters with no change in performance other than the image change.

[MeGotsACanon]

How does putting the adapter on slow down the camera?

I dont think it slow's it down, i think it speeds it up. The focous only happens once so multi shooting wouldn't have a problem if that does happen, i'm not sure.

The point i was getting at was to take a photo at full 3x without tele would be a higher app = longer shutter than comparerd to with the tele and just enough to stop the vigeniting, lower app needed (less x's on the actual camera) meaning quicker shutter meaning less drag in an action image with the same amount of light.

Could be wrong, dont know. Just what i thought.

[stopbath]

I think I got what you mean.

When you do not use the tele adapter you likely get as shutter speed and aperature settings, and when you put on the adapter, you get the same aperture, but a longer shutter speed. This makes sense (I don't have the adapter to test) as the light is more dispersed.

You'ld have to do some tests to find out exactly what the gains and penalties are.