Fast lens? Slow lens?


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jsbn

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Jul 24, 2002
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#1
I was told that a lens f/2.8 can be considered a 'fast' lens and any lens f/3.5 onwards can be classified as a 'slow' lens.

I'm still a little confused with the f-stop markings on the lens despite reading so many articles. So do correct me if I'm wrong.

1) Lenses with f/2.8 markings (and below) allows for bigger apertures and thus good for night shots, indoor shots, low light shots then 'slower' lens with f/3.5 markings.

2) Lenses with f/3.5 markings can also be used to take night shots, however, due to the smaller aperture allowed, one will need a tripod or a very steady hand to take reasonably good nightshots.

So, am I right to say this?

BTW, I'm looking for a good lens for both night and day shots (seriously on a budget and I'm a newbie to begin with. So L lens is definitely out for me) with good telephoto zoom of ranges frm 18-200mm, any good lens u guys can recommend? :)
 

Cyberian

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Mar 22, 2002
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#2
jsbn said:
I was told that a lens f/2.8 can be considered a 'fast' lens and any lens f/3.5 onwards can be classified as a 'slow' lens.

I'm still a little confused with the f-stop markings on the lens despite reading so many articles. So do correct me if I'm wrong.

1) Lenses with f/2.8 markings (and below) allows for bigger apertures and thus good for night shots, indoor shots, low light shots then 'slower' lens with f/3.5 markings.

2) Lenses with f/3.5 markings can also be used to take night shots, however, due to the smaller aperture allowed, one will need a tripod or a very steady hand to take reasonably good nightshots.

So, am I right to say this?

BTW, I'm looking for a good lens for both night and day shots (seriously on a budget and I'm a newbie to begin with. So L lens is definitely out for me) with good telephoto zoom of ranges frm 18-200mm, any good lens u guys can recommend? :)
1. Yes
2. Depends on the shutter speed. For me 1/30 sure no problem.

Tokina or Tamron is not bad... no so sure about Sigma.
 

jsbn

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#3
Alright!

Thanks for clearing up my confusion. I usually shoot in Aperture-priority mode in my 300D, how does Aperture values affect the shutter speed? One thing I do know (perhaps I'm wrong. Plz correct me if so):

In Aperture-Priority mode:
Manual setting to Smaller Aperture value = larger Aperture opening = automatic slower shutter speed
Manual setting to Larger Aperture value = smaller Aperture opening = automatic faster shutter speed

Is my deduction correct?
 

ST1100

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Jun 18, 2003
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#4
jsbn said:
In Aperture-Priority mode:
Manual setting to Smaller Aperture value = larger Aperture opening = automatic slower shutter speed
Manual setting to Larger Aperture value = smaller Aperture opening = automatic faster shutter speed

Is my deduction correct?
You got it reversed.

A smaller aperture value, eg from from f2.0 to f1.0, with give you faster shutter speeds, eg 1/30s to 1/60s.
 

mervlam

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#5
jsbn said:
Alright!

Thanks for clearing up my confusion. I usually shoot in Aperture-priority mode in my 300D, how does Aperture values affect the shutter speed? One thing I do know (perhaps I'm wrong. Plz correct me if so):

In Aperture-Priority mode:
Manual setting to Smaller Aperture value = larger Aperture opening = automatic slower shutter speed
Manual setting to Larger Aperture value = smaller Aperture opening = automatic faster shutter speed

Is my deduction correct?
it's the other way round
 

StreetShooter

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Jan 17, 2002
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#6
jsbn said:
Alright!

Thanks for clearing up my confusion. I usually shoot in Aperture-priority mode in my 300D, how does Aperture values affect the shutter speed? One thing I do know (perhaps I'm wrong. Plz correct me if so):

In Aperture-Priority mode:
Manual setting to Smaller Aperture value = larger Aperture opening = automatic slower shutter speed
Manual setting to Larger Aperture value = smaller Aperture opening = automatic faster shutter speed

Is my deduction correct?
No, not really. A larger aperture opening (smaller f-stop number) will give you a faster shutter speed, not a slower one.

The F-stop value used to indicate aperture size is a reciprocal value (ie 1/whatever). Technically speaking, it's the focal length of that lens divided by the actual diameter of the aperture. eg for a 50mm f1.0 lens, the diameter of the maximum aperture 1/1.0 x 50 = 50mm. For a 50mm f2.8 lens, the diameter of the maximum aperture is 1/2.8 x 50 = 17.85mm (roughly). You get the idea.

Each exposure requires a certain amount of light. You can let in the light two ways - either through a big hole for a very short period of time, or through a small hole for a longer period of time. Comprehendo?

So if your lens is able to have a very big hole (ie large aperture f2.8 and below), your shutter speeds will be very fast. That's why it's called a fast lens - allows you to have shutter speeds high enough to handhold.

A useful rule of thumb is the reciprocal rule - you can handhold down to the reciprocal of the focal length without camera shake. So for a 200mm lens, you should not be slower than 1/200s shutter speed. For an 18mm lens, you can handhold down to 1/18s (or 1/20s) without camera shake. But of course you will still have motion blur of your subject.

From this you can see that the 18-55 EF-S lens that came with your 300D is actually quite useful even if it does not have a large aperture. Since you are on a budget, I would also recommend a very cheap 75-300mm lens (but it can be used only in bright sunlight). For low light shooting, you can't beat primes. Get the 50mm f1.8 (which can give you gorgeous portrait shots as well). Later you can get the Sigma 20mm f1.8 (about $600) and the Canon 85mm f1.8 (also around $600).
 

clive

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#7
pls do not use the words "smaller" , "larger" as they are loose terms and potentially confusing.

to describe f2 vs f8, its better to say

"f2 is faster than f8"
or
"f2 is numerically smaller than f8"

IMHO ;-)


"1) Lenses with f/2.8 markings (and below) allows for bigger apertures and thus good for night shots, indoor shots, low light shots then 'slower' lens with f/3.5 markings.

2) Lenses with f/3.5 markings can also be used to take night shots, however, due to the smaller aperture allowed, one will need a tripod or a very steady hand to take reasonably good nightshots."


some points to note:

- there are folks who deem f2.8 to be "slow already". they have stricter standards and thus they personally set the speed limit @ f2... ie they take any lens slower than f2 as "slow". the standard recognition of anything slower than f2.8 as being "slow" is just a widely/commonly/universally agreed upon consensus based on a lot of statistics and a lot of cumulative shooting experience. u can also choose to set your personal speed limit @ f4, or @ f1.4, ie ultimately u have to decide where the cut off point for "acceptable speed " is.

- f2.8 vs f3.5 is only half a stop difference. u can always set the lens to f8 and shoot those dimly lit scenes eg candlelight cocktail party. whatever aperture u set to, whether f1.4 or f16, u still have to ensure proper handholding technique. for this, i can always impart to u the secrets of "the-art-of impossible-handholding"...hehehe! ;-)

:)
 

jsbn

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Jul 24, 2002
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#8
ST1100 said:
You got it reversed.

A smaller aperture value, eg from from f2.0 to f1.0, with give you faster shutter speeds, eg 1/30s to 1/60s.
Oh, guess I'm still a little confused between the 'big and small', 'fast and slow'.

Have to drill this into my skull.

I'm still quite new into this. Still playing around with the Aperture-priority mode first. Haven't got to the Shutter-priority mode yet. Hopefully can go into full manual mode (like u guys) once I'd learnt abt the shutter speed part. I've juz grasped the concept of Aperture.

Thanks for all the tips! I'll read more into it! :)
 

jsbn

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#9
clive said:
for this, i can always impart to u the secrets of "the-art-of impossible-handholding"...hehehe! ;-)

:)
'The Art of Impossible Handholding'.... :bigeyes:

I guess it involves big muscles and lotsa bicep & tricep workout at the gym? :cool:
 

rncw

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#10
jsbn said:
Oh, guess I'm still a little confused between the 'big and small', 'fast and slow'.

Have to drill this into my skull.

I'm still quite new into this. Still playing around with the Aperture-priority mode first. Haven't got to the Shutter-priority mode yet. Hopefully can go into full manual mode (like u guys) once I'd learnt abt the shutter speed part. I've juz grasped the concept of Aperture.

Thanks for all the tips! I'll read more into it! :)
hehehe...go out to shoot more, then you'll learn faster... :)
 

Spyer2

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#12
:bsmilie: I recall one T-shirt printed "If you can't convinced them, confused them". I think now is really confusing.. :confused:
 

jsbn

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Jul 24, 2002
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#13
Spyer2 said:
:bsmilie: I recall one T-shirt printed "If you can't convinced them, confused them". I think now is really confusing.. :confused:
Not so bad, I still can understand streetshooter. :D
 

Astin

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#14
Seriously, there are 3 things to determine the exposure:
- aperture size (f number)
- shutter speed
- ISO value
These 3 things interrelate to each other and determine whether your exposure is correct/over/under.
 

jsbn

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Jul 24, 2002
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#15
Astin said:
Seriously, there are 3 things to determine the exposure:
- aperture size (f number)
- shutter speed
- ISO value
These 3 things interrelate to each other and determine whether your exposure is correct/over/under.
Ok, will bear dat in mind. :)
 

#17
Astin said:
Seriously, there are 3 things to determine the exposure:
- aperture size (f number)
- shutter speed
- ISO value
These 3 things interrelate to each other and determine whether your exposure is correct/over/under.
Oops... forgot one more - flash compensation.=)

Haha... anyways jsbn, I'm quite noob too, but i find shooting in full M mode is also quite good for learning, cos based on your exposure reading in your viewfinder, you are forced to continually make changes and think abt whether u want the frame to be over/under/just nicely exposed.

Yep... again, I'm pretty much as green a noob as u get, but just my 2 cents worth.=)

Cheers

Neil
 

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