A Fast Lens??

donkeymusic

donkeymusic

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Morning,

have read a few times about needing a faster lens. could someone enlighten me as to what this means?

thanks
 
Larger aperture.....lets more light in and gives artistic narrow DOF :thumbs:
 
And if you have a wider aperture you can take the shot....faster.
 
so like an f1.4? would be classed as a fast lens? or would there be quicker?
 
Bout as fast as your gonna get.

looking at some pretty pennies though!
 
Yes, fast because a wide aperture lens would give you fast shutter speeds.

Its a bit of an old school term to be honest.
 
makes sense now when i read posts.

so basically when looking at new lenses the smaller the f number the faster the lens
 
just looking at a lens i got, it was Sony DT 50mm f1.8 SAM Lens, if the smaller the f number was, surely this should be more then £130, new.

or am i missing something else?

thanks
 
"when looking at new lenses the smaller the f number the faster the lens"

Yes, but most of the time you'd be using more sensible apertures otherwise all your shots are going to have next to no dof and look a bit soft.

There's a place for "fast" lenses but you wont want to be at f1.4 all the time unless you've got some pretty specific shooting needs.
 
Yup cos a smaller number is a wider(larger) aperture


A larger number is a narrower (smaller) aperture

not confusing is it.:)
 
donkeymusic said:
makes sense now when i read posts.

so basically when looking at new lenses the smaller the f number the faster the lens
Click to expand...

Correct.

It's also worth bearing in mind that some zom lens provide a constant throughout the range whereas others will only provide the largest aperture (smallest f number) at the lowest focal lengths :)
 
donkeymusic said:
just looking at a lens i got, it was Sony DT 50mm f1.8 SAM Lens, if the smaller the f number was, surely this should be more then £130, new.

or am i missing something else?

thanks
Click to expand...

50mm lenses are generally cheaper than just about any other focal length for the same maximum aperture, also the lens you mention is APS-C only which makes it simpler and cheaper to make than an equivalent full frame lens.

To compare prices of f/1.4 lenses that will fit your camera (note, these are all full frame):

Sony 50/1.4 = £275 ish
Sony 35/1.4 G = £900 ish
Zeiss 85/1.4 = £1000 ish
 
Here's how I see it.

f/5.6 and above - dog slow (but usually for good reason, i.e., a super tele at anything below f/5.6 would be as big as the hubble telescope and probably as heavy)
f/4 - slow
f/2.8 - quite fast - generally considered the beginning of the range of 'fast glass'
f/2 - and f/1.8 - very fast but surprisingly cheap
f/1.4 - faster but often considerably more expensive
f/1.2 and f/1.0 - usually thousands of pounds worth of lens and quite large, but allows one to take pictures in virtually candlelit conditions.

The 'faster' the lens, the more you can open the aperture, letting more light in and allowing higher shutter speeds. With my 50 f/1.8 I can take most shots, handheld, even in a room lit only by a lamp. Fair enough I might have to use ISO 800 or 1600 (my camera's maximum) but because I can expose correctly the high ISO noise is minimal. Trying to do the same kinds of shots with my kit lens was barely even possible despite having IS!
 
trencheel303 said:
Here's how I see it.

f/5.6 and above - dog slow (but usually for good reason, i.e., a super tele at anything below f/5.6 would be as big as the hubble telescope and probably as heavy)
f/4 - slow
f/2.8 - quite fast - generally considered the beginning of the range of 'fast glass'
f/2 - and f/1.8 - very fast but surprisingly cheap
f/1.4 - faster but often considerably more expensive
f/1.2 and f/1.0 - usually thousands of pounds worth of lens and quite large, but allows one to take pictures in virtually candlelit conditions.

The 'faster' the lens, the more you can open the aperture, letting more light in and allowing higher shutter speeds. With my 50 f/1.8 I can take most shots, handheld, even in a room lit only by a lamp. Fair enough I might have to use ISO 800 or 1600 (my camera's maximum) but because I can expose correctly the high ISO noise is minimal. Trying to do the same kinds of shots with my kit lens was barely even possible despite having IS!
Click to expand...

It's worth pointing out that it's all relative to the lens in both performance and price, for instance a 200mm f1.8 is hardly cheap, and you won't get a 500mm lens faster than f4.
 
Hi Donkey Music,

The best way I found to visualise the F number is I keep in my mind that F means fraction (I'm probably wrong !). So;

F5.6 = 1/5.6 = 0.1785 Decimal (17.8% of available light will hit the sensor compared to an F1) Slooooow

F2.8 = 1/2.8 = 0.357 Decimal (35.7% of available light will hit the sensor compared to an F1) Will have to do

F2.5 = 1/2.5 = 0.4 Decimal (40% of available light will hit the sensor compared to an F1) Better

F1.8 = 1/1.8 = 0.555 Decimal (55.5% of available light will hit the sensor compared to an F1) Better still

F1.4 = 1/1.4 = 0.714 Decimal (71.4% of available light will hit the sensor compared to an F1) Beauty

F1.2 = 1/1.2 = 0.833 Decimal (83.3% of available light will hit the sensor compared to an F1) Just fainted

F1 = 1/1 = 1 Decimal (100% of available light will hit the sensor) I'm in a coma :)


I may be totally wrong, but if I keep telling myself this, I don't feel as guilty buying F1.2 -> F2.8 Lenses instead of feeding the kids ! Simon
 
Simon-Australia said:
Hi Donkey Music,

The best way I found to visualise the F number is I keep in my mind that F means fraction (I'm probably wrong !). So;

F5.6 = 1/5.6 = 0.1785 Decimal (17.8% of available light will hit the sensor compared to an F1) Slooooow

F2.8 = 1/2.8 = 0.357 Decimal (35.7% of available light will hit the sensor compared to an F1) Will have to do

F2.5 = 1/2.5 = 0.4 Decimal (40% of available light will hit the sensor compared to an F1) Better

F1.8 = 1/1.8 = 0.555 Decimal (55.5% of available light will hit the sensor compared to an F1) Better still

F1.4 = 1/1.4 = 0.714 Decimal (71.4% of available light will hit the sensor compared to an F1) Beauty

F1.2 = 1/1.2 = 0.833 Decimal (83.3% of available light will hit the sensor compared to an F1) Just fainted

F1 = 1/1 = 1 Decimal (100% of available light will hit the sensor) I'm in a coma :)


I may be totally wrong, but if I keep telling myself this, I don't feel as guilty buying F1.2 -> F2.8 Lenses instead of feeding the kids ! Simon
Click to expand...

If I tried to remember that I'd miss the shot:)
 
true, perhaps I should have suffixed "...for less than £20k".
 
it would probably be cheaper to artificially light up your entire town and use an f4.
 
Simon-Australia said:
Hi Donkey Music,

The best way I found to visualise the F number is I keep in my mind that F means fraction (I'm probably wrong !). So;

F5.6 = 1/5.6 = 0.1785 Decimal (17.8% of available light will hit the sensor compared to an F1) Slooooow

F2.8 = 1/2.8 = 0.357 Decimal (35.7% of available light will hit the sensor compared to an F1) Will have to do

F2.5 = 1/2.5 = 0.4 Decimal (40% of available light will hit the sensor compared to an F1) Better

F1.8 = 1/1.8 = 0.555 Decimal (55.5% of available light will hit the sensor compared to an F1) Better still

F1.4 = 1/1.4 = 0.714 Decimal (71.4% of available light will hit the sensor compared to an F1) Beauty

F1.2 = 1/1.2 = 0.833 Decimal (83.3% of available light will hit the sensor compared to an F1) Just fainted

F1 = 1/1 = 1 Decimal (100% of available light will hit the sensor) I'm in a coma :)


I may be totally wrong, but if I keep telling myself this, I don't feel as guilty buying F1.2 -> F2.8 Lenses instead of feeding the kids ! Simon
Click to expand...

Wrong unfortunately. :bonk: One stop in f numbers is a doubling of light and the multiplication factor is the square root of 2. (i.e. 1.4)
So f/2.8 will let in twice as much light as f/4.

Also worth noting that f/0.95 lenses exist!
 
Simon-Australia said:
Hi Donkey Music,

The best way I found to visualise the F number is I keep in my mind that F means fraction (I'm probably wrong !). So;

F5.6 = 1/5.6 = 0.1785 Decimal (17.8% of available light will hit the sensor compared to an F1) Slooooow

F2.8 = 1/2.8 = 0.357 Decimal (35.7% of available light will hit the sensor compared to an F1) Will have to do

F2.5 = 1/2.5 = 0.4 Decimal (40% of available light will hit the sensor compared to an F1) Better

F1.8 = 1/1.8 = 0.555 Decimal (55.5% of available light will hit the sensor compared to an F1) Better still

F1.4 = 1/1.4 = 0.714 Decimal (71.4% of available light will hit the sensor compared to an F1) Beauty

F1.2 = 1/1.2 = 0.833 Decimal (83.3% of available light will hit the sensor compared to an F1) Just fainted

F1 = 1/1 = 1 Decimal (100% of available light will hit the sensor) I'm in a coma :)


I may be totally wrong, but if I keep telling myself this, I don't feel as guilty buying F1.2 -> F2.8 Lenses instead of feeding the kids ! Simon
Click to expand...

are you sure, theres a nocton f0.95 :p
 
Helios 44/2 (58mm f2) M42 screw fitting = £15 on ebay
Adapter M42 to Sony =£20ish, may be cheaper (canon are £4.49 from Amazon!)

Ok you will have to manually focus but it's a cheap way of getting quality glass at a low price. I use live view to focus as you can zoom in to the subject for pin point focusing.
 
donkeymusic said:
just looking at a lens i got, it was Sony DT 50mm f1.8 SAM Lens, if the smaller the f number was, surely this should be more then £130, new.
or am i missing something else?

thanks
Click to expand...

50mm primes are cheap because it's just about the easiest focal length to make. Most 'nifty-fifties' are also known as 'legacy primes' that were standard issue with film SLRs for decades, made by the million. They also tend to be cheapy made with basic focusing and no image stabilisation.

Generally speaking, making low f/number lenses is the most difficult optical design challenge, which is why consumer zooms tends to be limited to around f/4, and f/2.8 costs a heck of a lot more. Only primes can manage f/1.8, f/1.4 or f/1.2.

Simon-Australia said:
Hi Donkey Music,

The best way I found to visualise the F number is I keep in my mind that F means fraction (I'm probably wrong !). So;

F5.6 = 1/5.6 = 0.1785 Decimal (17.8% of available light will hit the sensor compared to an F1) Slooooow

F2.8 = 1/2.8 = 0.357 Decimal (35.7% of available light will hit the sensor compared to an F1) Will have to do

F2.5 = 1/2.5 = 0.4 Decimal (40% of available light will hit the sensor compared to an F1) Better

F1.8 = 1/1.8 = 0.555 Decimal (55.5% of available light will hit the sensor compared to an F1) Better still

F1.4 = 1/1.4 = 0.714 Decimal (71.4% of available light will hit the sensor compared to an F1) Beauty

F1.2 = 1/1.2 = 0.833 Decimal (83.3% of available light will hit the sensor compared to an F1) Just fainted

F1 = 1/1 = 1 Decimal (100% of available light will hit the sensor) I'm in a coma :)

I may be totally wrong, but if I keep telling myself this, I don't feel as guilty buying F1.2 -> F2.8 Lenses instead of feeding the kids ! Simon
Click to expand...

Yes, I'm afraid that's wrong. As pointed out above, the relationship between f/numbers is the square root of two, ie 1.414.

The f/number is just a ratio between the focal length and the diameter of the aperture. Somewhat confusingly, f/1.4 is double the light passing area of f/2, which is double f/2.8, which is double f/4 and so on, f/5.6, 8, 11, 16, 22 etc.

david1701 said:
are you sure, theres a nocton f0.95 :p
Click to expand...

Zeiss made a 50mm f/0.7, famously used to create the 'look' of the Kubrick film Barry Lyndon. Some say it was soft and dreamy, others that it was just blurred.
 
HoppyUK said:
50mm primes are cheap because it's just about the easiest focal length to make. Most 'nifty-fifties' are also known as 'legacy primes' that were standard issue with film SLRs for decades, made by the million. They also tend to be cheapy made with basic focusing and no image stabilisation.

Generally speaking, making low f/number lenses is the most difficult optical design challenge, which is why consumer zooms tends to be limited to around f/4, and f/2.8 costs a heck of a lot more. Only primes can manage f/1.8, f/1.4 or f/1.2.



Yes, I'm afraid that's wrong. As pointed out above, the relationship between f/numbers is the square root of two, ie 1.414.

The f/number is just a ratio between the focal length and the diameter of the aperture. Somewhat confusingly, f/1.4 is double the light passing area of f/2, which is double f/2.8, which is double f/4 and so on, f/5.6, 8, 11, 16, 22 etc.



Zeiss made a 50mm f/0.7, famously used to create the 'look' of the Kubrick film Barry Lyndon. Some say it was soft and dreamy, others that it was just blurred.
Click to expand...

There you go. I knew I was wrong ! :)
 
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