ultra wide aperture lenses

[failingretina]

What's the use?

I've got a 50mm f/1.8.

I understand having a lower f number allows more light in but also produces a much shallower depth of field.

I've never found i've needed to go lower than f/2.5. i tried some at f/1.8 but i would find say eyes in focus and the tip of those out.

So is there a need for these expense f/1, f1.2 etc. lenses? any photographic examples?

sorry if this is a very noob question. i've only had my camera 2 and a bit months.

cheers

 

[bradleysmith]

Sometimes there is a need for them yes. Very dark locations, no tripod, ISO maxed out image stabiliser on the cusp of being workable and f/1.4 comes to the rescue. To use your example you can either have your friend's eyes sharp and a slightly out of focus ear or you can have no photo at all.

 

[P20]

My very limited understanding, hopefully will confirm or shoot his down:
The lower f number will allow faster shutterspeed. So a F1.4 will be quicker than the F1.8 even if both running at the same F number (say F8) on the camera. Also should be better in low light situations.

(sits and waits to be shot down by someone who knows what they're on about):bonk:

 

[mr_pants]

My very limited understanding, hopefully will confirm or shoot his down:
The lower f number will allow faster shutterspeed. So a F1.4 will be quicker than the F1.8 even if both running at the same F number (say F8) on the camera. Also should be better in low light situations.

At the same f-number, the shutter speed will be the same.

 

[Voyager]

The lower f number will allow faster shutterspeed. So a F1.4 will be quicker than the F1.8 even if both running at the same F number (say F8) on the camera. Also should be better in low light situations.

(sits and waits to be shot down by someone who knows what they're on about):bonk:

OK. Bang!

f8 is f8 whatever the maximum aperture of the lens is. It will make no difference at all to the shutter speed if the lens is a f1.4 or f2 if it is stopped down - only if it is wide open where you get to shoot at a higher speed in a lower light.

 

[Voyager]

Leica make (made?) an f1.0 for their rangefinder cameras - not uncommon but @£5000 last time I looked! They now make one that is f0.95 (as Canon did for their old 7's back in the '60's)

While I think the 'fastest' 35mm film lens ever was the specialist (and very rare) 35mm f0.9 Nikkor.

That must have a DoF measuring in millimetres.

 

[P20]

At the same f-number, the shutter speed will be the same.

OK. Bang!

f8 is f8 whatever the maximum aperture of the lens is. It will make no difference at all to the shutter speed if the lens is a f1.4 or f2 if it is stopped down - only if it is wide open where you get to shoot at a higher speed in a lower light.

Thank you guys

 

[Canon Bob]

Bodies focus at the lens' max aperture so AF in poor light is going to be far more successful with a faster lens.

I think this is one of those questions that you'll figure out yourself in a couple of years time.....with more experiemce you'll begin to appreciate why they exist.

Bob

 

[V8burble]

DoF is also dependant on distance to the subject (and focal length but as a prime that is fixed here). Try taking a full length portrait shot with your 50mm f/1.8 and you will see a very usable DoF.

 

[danbroad]

This is both a common source of confusion and a photography hot-topic. In summary:

The faster lenses are often associated with higher-end glass, and offer pleasing bokeh and good contrast/sharpness one stop off maximum. For example, the Nikkor 85mm f/1.4 or the 200mm f/2.0, both excellent one stop down [and pretty darned good even wide open..]

Plus, the camera auto focuses and views at maximum aperture [i.e. wide open.] A smaller f-number means both a brighter viewfinder and faster autofocus in available light.

However, the depth of field issues are restrictive - remember depth of field is relative to both f stop AND focal length. Try it for yourself at DOFMaster. Therefore, a 300mm f/2.8 has a DoF measurable in milimetres, whereas a 14mm lens is fairly 'deep' even at f/2.8.

[That's why you're more likely to get a great landscape with a 17mm lens at f/8-f/11, or why street shooters can get away with hyperfocal distance pre-focusing for waist-high candids on low-focal length lenses, but don't fret this point if it confuses..]

With cameras such as the D3, 5D and D700 which can shoot reliably noise-free at high ISO's, there's little need for f/1.4's unless you specifically need the wafer-thin depth of field, individual lens pleasing bokeh or the faster autofocus; and remember the D700/D300 will autofocus an f/5.6 lens as quickly as an older body with a fast lens in most conditions. That's just technological advancement. Plus, in the case of the longer 1.4's, the sheer size of the glass to move makes the focus slower; take the 85mm f/1.4 vs the 85mm f/1.8 as a case in point.

Likewise, there's few photographs which need to go from f/4 to f/2.8 just to regain a handheld shutter if you can double the ISO and get the same shutter speed effect without risk of ISO/ASA noise.

If you want f/2.8 for artistic reasons, then faster glass still stands, but if you're reasoning to get a fast lens for low light, you'd be equally justified in spending the money on a D700 and keeping your [1-2 stop slower] older glass. If you're pushing the boundaries of available light photography - bats by moonlight - then you need the help of both.

 

[Voyager]

Bodies focus at the lens' max aperture so AF in poor light is going to be far more successful with a faster lens.

Plus, the camera auto focuses ...at maximum aperture [i.e. wide open.] A smaller f-number means ..... faster autofocus in available light.

As a person whose only SLR is an old manual focus T90 - is this 'faster' auto focusing actually noticeable in use or one of these things that is only measurable with lab equipment?

 

[Uneducated_Rick]

As a person whose only SLR is an old manual focus T90 - is this 'faster' auto focusing actually noticeable in use or one of these things that is only measurable with lab equipment?

In normal light I think the faster is only noticable in a lab but in low light the extra aperture makes focusing possible where a 3.5-5.6 zoom may not focus at all

Similarly lenses on a canon that have tc added so that the maximum aperture goes beyond f8 will not autofocus at all regardless of the light conditions

 

[Voyager]

In normal light I think the faster is only noticable in a lab but in low light the extra aperture makes focusing possible where a 3.5-5.6 zoom may not focus at all

Ta.

With no experience of either, I suspect that IS/VR is probably more useful (with longer lenses) than a stop or two of expensive, heavy glass.

 

[Uneducated_Rick]

Ta.

With no experience of either, I suspect that IS/VR is probably more useful (with longer lenses) than a stop or two of expensive, heavy glass.

IS/VR won't ever help with a freezing a moving object, the only option is a wider aperture

 

[Canon Bob]

As a person whose only SLR is an old manual focus T90 - is this 'faster' auto focusing actually noticeable in use or one of these things that is only measurable with lab equipment?

I didn't say focus would be faster...it's not. My point was that focus was "more successful" in poor light. Wider aperture lenses can discern the contrast needed to AF in darker situations where the slower lenses can't.

Bob

 

[fletch5]

Depends what you are shooting though voyager

 

[Voyager]

IS/VR won't ever help with a freezing a moving object, the only option is a wider aperture

Or more light.

That's two options....

 

[Voyager]

My point was that focus was "more successful" in poor light. Wider aperture lenses can discern the contrast needed to AF in darker situations where the slower lenses can't.

Are we at the point that the digital ISO is more than fast enough to capture an image yet, with some slow lenses, the AF system isn't good enough to focus?

 

[Canon Bob]

Are we at the point that the digital ISO is more than fast enough to capture an image yet, with some slow lenses, the AF system isn't good enough to focus?

I think we've been there for quite a while.

One other issue is the accurracy of the commanded position. If the lens is 2.8 or faster then the body commands the lens to focus within 1/3 of DOF. If the lens is slower than 2.8 then the target is simply "within DOF".

Bob

 

[danbroad]

IS/VR won't ever help with a freezing a moving object, the only option is a wider aperture

True and false.

True: VR won't stop a moving target - only a faster shutter speed will.

False - there is another way. You can double the ISO, and that will halve your shutter speed. And it gives you the quicker shutter speed back without sacrificing depth of field.

Even as recently as 2 years ago, we all agreed a shot at ISO1600 was a waste - so f/2.8 lenses made sense - it took that 1/25 shot to 1/50 by going from f/4 to f/2.8.

Now, the Nikon FX will shoot well at ISO 6400 - so you can stay at f/4, and bring your shutter speed from, say, 1/10 at ISO 200 to 1/320 at ISO 6400 - 5 stops and a clear picture. Even if you had an f/1.0 lens in that same situation [with all the DoF compromise that would bring], you're only reclaiming 4 stops. Do the math yourself if you don't believe me!

The argument of faster glass for motion-stop over a slower lens isn't applicable to the FX sensor. Newer bodies will focus an AF-S lens at 5.6 faster than an older generation body with good AF-D glass at f/2.8 [AF is a feature of the body, not the lens].

The other arguments - bokeh, contrast, colour - are the remaining reasonable arguments for faster glass.