We received a veritable firestorm of commentary following our post on Tony Northrup's video. In that video, he challenged the industry — and conventional wisdom — about the true nature of differences in performance among full frame and crop sensor cameras and lenses. Now, dpreview.com has weighed in along essentially the same lines as Mr. Northrup: not all f/stops are created equal.
Their style is different — dpreview.com's tone is perhaps more palatable to some — but in any event it is fascinating that they have taken the step of reporting not just focal length equivalents in their reviews, but now depth of field equivalents as well.
The subject — essentially, when is 1.8 not 1.8 and everything that goes with it, from focal length to light gathering — is garnering the attention it deserves. This is a good thing!
Makes you think Cosina is clearly on to something with its set of f/0.95 Nokton lenses (it isn't about bragging rights); ditto with Leica for its Nocticron and for Metabones with its SpeedBooster. Can the rest of the MFT field be far behind in deepening their optics offerings?
And what does this bode for the full frame giants?
What is equivalence?
Equivalence, at its most simple, is a way of comparing different formats (sensor sizes) on a common basis. This is already the way most lenses are talked about: it's quite common to say that a compact camera includes a '28-120mm lens' but the key and (often unspoken) word in that description is ‘equivalent.' It's a simple way of describing the range of fields-of-view that the lens offers, cancelling out the effect of sensor size by using a common reference point.
A 100mm equivalent lens on a small-sensor camera will give the same framing and perspective as an actual 100mm lens does on a full-frame camera, regardless of sensor size, because they are equivalent.
It's this logic that the idea of ‘crop factors' is based on. The ‘Four Thirds' sensor format has a diagonal very close to half that of a ‘full frame' sized sensor. And, sure enough, if you calculate the angle-of-view of a 50mm lens on a system with a crop factor of 2, it's the same as for a full frame camera with a 100mm lens.
Continue reading about equivalence in DPReview's article “What is equivalence and why should I care?”
|Note: it is our policy to give credit as well as deserved traffic to our news sources – so we don't repost the entire article – sorry, I know you want the juicy bits, but I feel it is only fair that their site get the traffic and besides, you just might make a new friend and find an advertiser that has something you've never seen before|
(cover photo credit: snap from DPReview)