Aperture speed - a practical question

[Colin Southern]

Assuming i understand correctly, your math is way off ;p
That would be 1/25
f/1.4 - f/2 - f/2.8 - f4 = 1/200 - 1/100 - 1/50 - 1/25

Um, no. We started at 1/20th, not 1/200th so 1/20th -> 1/10th -> 1/4 -> 1/2

[Sunray]

When reading this thread it reminded me of my Nifty Fifthy lense.
Many of you may know it but for the ones that stumble across this thread without it this might be helpful.
Some DSLR manufactorers offer 50mm primes lense at a speed of f/1.8 at very affordable prices. Personally I got one Canon EF 50mm /f1.8 so I can only tell my experience with this lense. I use it on a camera with APS-C sensor size. During low light conditions or indoor shootings it did help me a lot. For indoor shooting it might be already too long on a APS-C sensor camera if you do not have much space around. The sharpness of this lense is pretty good. Bokeh tends to be a bit nervous, depending on the background and aperture. It is missing some features like ultrasonic AF, fulltime manual or a range scale but it has a street price of about 90-100€. It was the first prime lense I bought and I still use it regulary.

Robert

[groovesection]

Um, no. We started at 1/20th, not 1/200th so 1/20th -> 1/10th -> 1/4 -> 1/2

I could have sworn your original post stated 1/200, Boy do i feel a fool now
I do apologise Colin

[Mark von Kanel]

i hope the fool your feeling is a pretty one

[rpcrowe]

I was intending to take two lenses tomorrow to my b in law's birthday dinner at a pub (going via train so no intention of bringing a tripod); a 18-55mm min f stop 3.5, for some focal length flexibility and a 16mm prime, min f stop 2.4, for dinner table shots and because it's indoors, for low light.

Here's the thing...theory tells me that the prime will let x2 more light in, but so what in practical terms? I've just taken a couple of practice shots with both lenses, at the same ISO at max aperture at home, in low light conditions and the only difference I can see is that the shutter speed goes from 1/5th for the 18-55mm to 1/10th for the prime. In practical terms, i.e. being able to hand hold the camera rather than tripod, there's no real difference.

The reason I'm posting this is because, as a relative newcomer, I keep reading about how 'fast' lenses are 'wow' for low light situations etc. My question is, given the above, why???

Cheers

Adrian

#1: Neither of these two lenses is particularly fast nor is either of these lenses one which I would pick for low light photography.

#2: The zoom lens in reality DOES NOT provide a focal length flexibility in a low light environment because of the variable aperture. As you increase the focal length, the f/stop becomes smaller. Until at 55mm the f/stop is f/5.6 which is pitifully slow for low light shooting.

#3: Kit lenses (of all manufacturers) are fairly decent, especially for the price but, where they lack is in low light shooting capability. The 16mm f/2.4 lens which might be good for brighter conditions is also not particularly adequate for low light. Even with stabilization, neither of these lenses are really suitable for low available light shooting. A shutter speed of 1/5 or 1/10 second is too slow for most shooting, especially hand-held. Even if you could brace your camera against a wall or on a table, the stabilization would not freeze any motion of the subjects. Inceasing the ISO "may" help shooting in lower light levels but can impact your IQ considerably...

#4: If a person desires to shoot in low light conditions, I would strongly suggest that flash is considered as a viable (and perhaps the only option). Flash will allow you to shoot at a smaller f/stop which will increase the depth of field and which will produce better image quality. The flash will freeze most motion of your subject. Bounced flash can provide natural looking lighting. I use a bounced hotshoe flash in conjunction with a Joe Demb Flash Difuser Pro ( www.dembflashproducts.com ). The Flash Diffuser Pro is versatile and can provide decent lighting even when there is not a ceiling or wall off which to bounce. The Flash Diffuser Pro has a variable angle FlipIt reflector which comes into play when you cannot bounce off ceilings or walls.

However... Fast lenses can be used in lower light situations but, they need to be fast... Under the circumstances you mentioned @ 1/10 second for a f/3.5 lens, if shooting with a lens such as an f/1.4, which is what photographers normally mean when talking about a fast lens, you can use a shutter speed of 1/60 second. A shutter speed of 1/60 second will be sufficient to get a sharp image in most situations when your subjects are not moving fast.

However again... using an f/1.4 aperture provides razor thin DOF and will often result in OOF imagery.

I stick with my original point! When shooting in very low lighting conditions, a hotshoe flash that is bounced using a reflector diffuser is the best way to go...

[Colin Southern]

I could have sworn your original post stated 1/200, Boy do i feel a fool now
I do apologise Colin

No need to apologise. I wish is WAS 1/200th -- would have made the shot a lot easier to get!

[Colin Southern]

i hope the fool your feeling is a pretty one

You must be feeling lucking today Mark to make such a comment!