F-stop blues - being duped into fast lenses

Started Jul 4, 2012 | Discussions thread
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inasir1971
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F-stop blues - being duped into fast lenses
Jul 4, 2012

Apologies for vague title but wanted to share an article that I came across with everyone. Have seen this issue referenced but just got the full article. Since the D800, I know at least I am using fast primes more than I have before. One of the questions that often comes up is which one - the 1.4 or the 1.8?

An article by DXO labs (Nov 2010) sheds some light (pardon the pun) on how modern sensors do not benefit as much as we think from fast lenses. To compensate for this (so we keep buying expensive fast lenses) manufacturers have been boosting the gain (ISO) at larger apertures so fast lenses seem faster. This gain is unknown to the user - you might think that you are shooting at ISO 100 but the camera sees f1.4 and has cranked up the ISO to 140 to give the illusion that the sensor is getting more light.

Here is a graph (from the article) showing a few models and the gain implemented:

The most egregious offender seems to Sony, but everyone would seem to be doing it. The applied gain is very pronounced faster than f2 for 3 of the above, and by even f2.8 for Sony.

Loss in efficiency seems correlated to pixel size - smaller pixels (higher resolution), benefit less from fast glass. Since that is the direction we are headed (see D3200) this is of relevance.

This issue is not academic and it directly affects shooting and glass choice.

  • selecting faster apertures may be counter productive leading to noisier images (as the additional gain applied would be unknown to the user).

  • faster lenses may not give you the gains that you think you are getting.

This is not arguing against fast lenses - the benefits of better optics, DOF control, and build will still be there, the sensors are simply not able to collect much of the additional light.

The full article: F-stop blues
http://www.dxomark.com/index.php/Publications/DxOMark-Insights/F-stop-blues

Nikon D3200 Nikon D800
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