Are those bright f1.4 lenses realy tat gud?

http://www.dxomark.com/index.php/en/Our-publications/DxOMark-Insights/F-stop-blues
Tuesday November 23 2010

F-stop blues
For years, lens makers have fought hard to market lenses of wider and wider aperture. Wide apertures (e.g., f /1.4 instead of f /2) but a series of measurement published on dxomark.com cast some doubts on the real benefits, for digitally equipped photographers, of these progresses.

Loss of light at wider aperture

“We have been very surprised,” explained Frédéric Guichard, chief scientist at DxO Labs, “to find out that some of the gain from wider lens openings seems to be offset by the present state of sensor technology. Our measurements all point in the same direction: as you go further than f/ 4 – to f /2 and wider, the accrued quantity of light falls marginally onto the sensor. A stronger and stronger part of this additional light is blocked or lost. I am therefore inclined to question the real benefit of faster lenses.”

This loss seems to increase when the pixel size decreases, as shown on the figure below.

ΔEV at f/1.4 function of pixel pitch

Some sensors can have a loss of more than 1 Ev at f/1.2.

ΔEV at f/1.2 function of pixel pitch

Raising ISO to compensate light loss

A further assessment is still more troubling. It seems that many camera makers are raising the ISO sensitivity when the lens opening is at its widest, probably to cover up the lack of efficiency. “We have ascertained,” explained Guichard, “that on many cameras, the ISO is pushed up on the order of 1/3 to 1/2 stop when the lens opening comes close to its upper limit.

Sensor gain function of f/# (expressed in Ev)

“Accordingly, the photographer has no way to detect that he/she has not benefited from the increase of light transmitted. Of course this increase in ISO translates into other downfalls – mainly in accrued noise. But these remain unknown to the operator,

“We can suspect,” Guichard continued, “that sensors collect the incoming light all the more improperly, in that this light comes from a more oblique angle. Since faster lens have, by definition, a wider opening, they raise the proportion of oblique light, hence the proportion of lost energy which never lands on the pixels.”

DxO Mark measurements are based on an assessment of the effective T-stop for every camera-lens combination. T-stop, a measurement widely used in the industry, especially the motion picture industry, is a measurement of the effective quantity of light transmitted by the lens at a certain f-stop. Thus, T-stop takes into account every reflection or absorption due to the lens. It can be considered as an effective (versus theoretical) way of measuring the aperture.

A possible conclusion of DxO Labs’ measurements is that photographers should consider with caution the maximum f-numbers advertised for lenses. Indeed, depending on the performance of their camera body and sensor, they may not effectively benefit as they expect from such wide apertures.

Read about this before buying my first f/1.4 lens. But after buy also still no regrets haha.

but i stil dun quite get what they are trying to say...

does tat mean we get underexpose pics if we shoot a f1.4 in aperture mode?

I'll try to explain based on my explanation.

They are just trying to highlight that f/1.4 -> f/2 -> f/2.8

Basically f/1.4 is 1 stop faster than f/2, and 2 stops faster than f/2.8 right? But actual condition it is not that. A little lesser due to light loss on big aperture.

What the company does is they secretly increase ISO to compensate. Meaning, let's say 200 ISO, it is actually 400 ISO or something (I don't know the right amount, but ISO is increased) to compensate for the light loss.

icic...now i understand edi...just nw i gt google a bit on this...thanks ya CY..

So this news is spreading and letters hv been sent to companies that are involved to get the truth on this...

This is just a guess from Dxolab anyway...lets wait for the truth n see how...

Looking back, i got quite a number of underexposed pics when using my f1.4 lens at aperture mode without any flash...if we use flash we wont even notice anything...