Monday, August 23, 2010

Advantages of a Full-Frame Camera

photographyLast September I wrote the article Thinking Outside The Frame: Sensor Sizes Explained. In this post I want to discuss more specifically the advantages of full-frame (FF) over APS-C cameras. The four photographic reasons to choose FF are lower noise, narrower depth of field, wider lens coverage and less diffraction. I will discuss each of these in turn, keeping the discussion pitched at the beginner.

Lower noise at high ISO
Except for a few freaks who yearn for the days of film grain (hey, I love grain!) we all want less noise in our images, since noise is the enemy of detail and sharpness. FF cameras have less perceived noise at higher ISO settings. This allows us to take clearer pictures in less light.

In actual fact, noise has nothing to do with the sensor size, but instead with the pixel density of the sensor. But since a full-frame camera can have lower densities for the same mega-pixels rating (it's larger, remember?), it will have the lower noise, all else being equal.

However, as sensors and the cameras built around them improve, this advantage of FF decreases. If an APS-C camera is noisy at ISO 800 then one might yearn for full-frame. But if it is not noisy until ISO 12800, the advantage is less appreciable. Mathematically, FF might give us the same one or two stop improvement, but there is a point of diminishing return. Especially if there is so little light one can no longer compose an image properly in the viewfinder!


Narrower depth of field
Do you need more DOF control than that provided by f/1.2 on APS-C? Then move to full-frame and have even less of your image in focus! Personally, I rarely want anything faster than f/2 on APS-C; I have plenty of DOF control.


Correct field of view
A 50mm lens on FF behaves like a 50mm should... at least for those raised on 35mm film. A 50mm on APS-C captures only the cropped central part of the image, behaving like a 75mm focal length lens. This matters little throughout most of the focal range, but limits how wide you can go.

But again, let's consider the practical reality. Pentax provides a zoom down to 12mm. You can buy a third-party 10mm rectilinear and 8mm fish-eye. There are few applications where this would not be wide enough.

(This advantage in the wide end is a disadvantage for those who enjoy shooting telephoto. A 300mm lens on APS-C covers the same field of view as a 450mm on FF, giving more "reach" for less money.)


Less diffraction
Lenses with a longer focal length have a larger aperture for a given f-stop. The larger the aperture, the less diffraction. Because, as we have just seen, full-frame requires a larger focal length lens for the same field of view, it follows that they produce less diffraction, all else being equal. Landscape photographers might find this significant, but I'd suggest a tilt lens for even more control.


Conclusions
There are also non-photographic reasons people prefer full-frame. Among these are the prestige factor, the fact that FF bodies may have more or better features (since they are aimed at "professionals") and the familiarity of using focal lengths that produce the same results as 35mm film.

My personal take on all of this is that APS-C sensors are a good compromise for the vast majority of photographers. It also doesn't hurt that APS-C bodies are cheaper and smaller. The evidence is in the marketplace. While Canon, Nikon and Sony provide full-frame cameras, these sell a minuscule amount compared to their cropped sensor models.

Nonetheless, certain vocal Pentax fans feel left out in the cold, since their favourite brand does not produce a full-frame camera. They should be satisfied that Pentax has the 645D, with its cropped medium format sensor. This trumps even full-frame in each measure we have just examined.

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5 comments:

Anonymous said...

"They should be satisfied that Pentax has the 645D, with its cropped medium format sensor."

Robin, I fail to see the logic in this, even though the 645D is often suggested as the answer to the people wishing for a Pentax FF camera. Most Pentax DSLR users have a lot of lenses and other accessories that could be used on a FF camera. The 645D system is not only more expensive, but also mostly incompatible so they would have to start from a clean slate. And starting from scratch, there are many other brands and technologies to choose from. Like a FF CaNikon which would not be as good as the 645D but much cheaper.

robin said...

Those who have Pentax FF lenses from the days of film could simply sell them and buy into a Canikon FF system. Or the 645D when it is available in their territory.

Only those who prize certain lenses above all those from any manufacturer would need a Pentax FF. This is certainly not "most Pentax DSLR users", only the few vocal ones who gather online. I do not think that is a strong economic basis for Pentax to produce a new camera line.

Full-frame offerings from Canikon are not actually "much cheaper" -- and certainly the difference is not vast if one is investing for business purposes. The Pentax 645D line will obviously come down in price as have other brands, once it is established further.

Anonymous said...

Robin,
Thank you for an even-handed and down-to-earth analysis.
A point that you might stress in your reference to the 645D system is the factor 'prestige'. Many of those who request a FF from Pentax seem to do so because they require proof that Pentax is a top company, which is able to deliver innovative, high-end products just like Canikon. (In other words, these insecure voices require proof that they've not opted for a loser).
But the 645D is precisely the innovative high-end product that establishes Pentax' professional prestige.

robin said...

I should add that were Pentax to release a full-frame camera as small and cheap as the K-7, modelled after the Limited line of lenses, I would buy it as soon as my bank account said "hi there!" That's because I believe the FA Limited line has no equivalent in any other brand. Thus I do fall into the exclusive category I outlined in my previous category. But, unlike others, I think it is fantasy to suppose this might happen.

I will also gladly buy the 645D immediately after my first successful bank heist.

fRANK d said...

aps C is also cheaper to manufacture adn yeilds higher profits so it will never go away. Aps C is getting better we are at iso 25000 and i'm sure it will get to 50k and then 100k iso. I forget where I read but a sensor for apsc cost like 40bucks... fullframe sensore cost like 400 dollars. The cameras are also bigger not coutning Leica's offering. This creates more cost and yeilds less profits unless companies charge like 8000 like the new Nikon. This new k5 should really give FF a run for its money as well as the other Sony based cameras...Nikon..Sony.
We should all send Sony a thank you card for such fine work with semiconductors.

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