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PostPosted: Thu Mar 13, 2008 7:04 pm 
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Hi folks,
    Summary: Full-frame sensors only have an advantage in landscape photography if longer exposure times can be used.
OK, that's a little simplistic and only really applies when you need to maximise depth of field but it captures the essence of my point.

I was having a little rootle around the Net today in an effort to discover a definitive text discussing the pros and cons of full-frame vs cropped sensors for landscape photography and came up with very little. Maybe my search strings were poor or maybe the answer is considered so obvious that nobody has bothered to write about it.

Recently, over in this thread, I tried to explore the technical advantages, or otherwise, of full-frame sensors compared with cropped sensors. For sensors with the same pixel count, the main points were that:
  • Full-frame sensors have better dynamic range.
  • Full-frame sensors give better image quality.
  • Full-frame sensors can work at higher ISO numbers.
  • Full frame sensors can be less demanding on lenses.
  • Full-frame sensors can more easily offer a shallower Depth of Field but they don't have to.
So it would seem to be game, set and match to full-frame sensors. After all, even without considering the above bullet points we know that many of the best landscape photographers use 5x4 inch film cameras so a larger digital sensor must also be better.

I'm not sure it's completely clear-cut though. The big deal with film is that if you double the size of the film you double the resolution while essentially leaving all the other characteristics unchanged. When considering digital sensors with the same pixel count, in order to obtain the largest depth of field while still avoiding diffraction issues, it turns out that the full-frame camera has to be stopped down further when using a lens giving the same angle of view as a given lens on a cropped sensor camera. As an example, if 20mm and f/8 gives best DoF on a 1.5x crop factor sensor then 30mm and f/12 (1.5 x 20 and 1.5 x 8 ) gives the equivalent DoF and sharpness on a full-frame sensor with the same number of pixels. The problem then is that the rate at which light is gathered by the lens on the full frame camera is exactly the same as the rate at which it is gathered by the shorter lens on the cropped one. In the example above, both lenses have an entrance pupil of 2.5 millimetres. So each of those big fat full-frame pixels actually has exactly the same amount of light falling on it as the smaller pixels on the cropped sensor.

As mentioned, a full-frame sensor isn't having to work it's lens so hard. But when operating near f/8 (cropped) or f/12 (full-frame) you don't necessarily need mega-expensive glass to obtain sharp results. Of course, for the same wide angle of view, full-frame cameras can use lenses with longer focal lengths and those lenses are likely to be cheaper but that has to be set against the increased cost of the camera. In this context, I am not suggesting that the tiny sensors on compact cameras are as good for landscape work as those in DSLRs because the demands on the lenses become extreme as diffraction limited apertures of the order of f/2 are needed (in the example above a 1/8" sensor would need a diffraction limited lens of 6mm focal length working at f/2.3).

I have come to the conclusion that, with the same pixel count, a full-frame camera has only one advantage over a cropped sensor camera when shooting landscapes where depth of field must be maximised. It has to work with the same amount of light entering its lens as diffraction limited best DoF demands the same entrance pupil but, using the same ISO number, that light is integrated over a longer time (smaller f-numbers mean longer shutter times). That can be done on a full-frame sensor without blowing the highlights because of the deeper wells so we gain reduced image noise and/or better dynamic range. The longer exposures aren't usually an issue with landscapes though they probably indicate a greater need to use a tripod. If the subject demands the same short exposure time as would be needed on a cropped sensor camera then the advantage of the full-frame sensor disappears (increased ISO and the same f-number means increased sensor noise).

So much for my theoretical ramblings. Would any forum members fortunate enough to have shot landscapes with both full-frame and cropped sensor cameras care to comment? Then, of course, there is the added complication of the higher pixel counts usually associated with full-frame sensors!

Bob.

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PostPosted: Thu Mar 13, 2008 10:29 pm 
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May I put my 2cents in although I don't have a APS-C plus a FF body, Bob?
I think your analysis is right if you compare the D300 and the D3.
But if you look at a D3x or D4 with (hopethetical) 24MPix sensor things may change a bit. If namely the sensr just has more of the same photocells, you just get more image of the same quality captured with one shot. And the only limitnig factore is the quality of the lens used here in the corners.
So you come to a totally different conclusion based in the assumption on pixel-densitiy of the sensors compared.

Summary:
1. Sensors of different sizes but equal pixel count are equally capable of shooting ladscape
2. FF-sensors with the same pixel-size as smaller sensors have a clear advantage of their smaller cousins.

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PostPosted: Fri Mar 14, 2008 1:12 am 
If you will permit me an irreverent addition to this:

It would then follow that a DX sensor with only 6MP (instead of 10 or 12) would be able to produce better results on it's 6MP image than any 6MP crop from a DX sensor with more pixels.

(shameless D40 plug, I know)


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PostPosted: Fri Mar 14, 2008 1:41 am 
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No problem. You can be as irreverent as you like, my son. :lol: :lol:

You can see why I have deliberately avoided the megapixel considerations as it's a minefield. One thing that full-frame sensors offer is a modest increase in the number of pixels whilst still allowing each of those pixels to be bigger, with the advantages referred to above. As you know, your D40's 6 MP would scale to 13.5 MP on a full-frame sensor. Add in a few incremental advances in fabrication technology and the 15.3 MP of the 5D MkII rumour (and it is most definitely only a rumour) sounds sweet. So yes, if you don't need or want the extra pixels then a 6MP sensor has the potential to produce the same IQ as the central portion of a full-frame sensor with over twice the pixel count. 8)

Bob.

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Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
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PostPosted: Fri Mar 14, 2008 1:13 pm 
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As an Olympus-owner I would like to put in my two cents as well;
I realize that in terms of image quality, a sensor almost can't be big enough. Still I think there are situations (like mine) where smaller sensors like the four thirds have a lot going for them. As a beginning photographer on a tight budget (I'm just a poor student ;) ) I chose to accept the smaller sensor quality because as a counterbalance it allowed me to spend more on lenses that I think more than compensate for the IQ-loss sensor-wise. In the end IQ is a combination of many factors, The most important being the lenses and probably second most important the sensor size.
My knowledge of camera's is at most a month old though, and pretty much comes from this forum, so please feel free to correct me. :)

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PostPosted: Fri Mar 14, 2008 2:03 pm 
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Hi Paukl,

You make excellent points. This thread is designed, hopefully, to inform and certainly isn't meant to suggest that anything other than a full-frame sensor isn't good enough. In fact I have been quite surprised that it appears that for those types of landscape photography where best depth of field is paramount the full-frame sensor has to accept the potential compromise of longer shutter times, everything else being equal. Of course, the FF sensor still wins out in terms of better sensor noise etc. but that is probably taking us into areas of concern that only pros trying to sell their work worry about. Addendum: I suppose one ought to replace "pros trying to sell their work" by "pros trying to sell their work and those of us who love our toys even if we still can't use them to best effect". :lol: :lol: :lol:

Bob.

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Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
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PostPosted: Tue Mar 25, 2008 11:35 am 
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Hi folks,

There is a rather long read here which is relevant to this thread. The conclusions drawn don't, I believe, differ in any way from my own thoughts above but I liked the way the section Partial Equivalence highlighted the way ISO works. There is also a great deal of discussion about depth of field and much wider issues such as lens quality.

Bob.

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Olympus OM-D E-M1 + M.Zuiko Digital ED 12-40mm f/2.8, Lumix 7-14mm f/4, Leica DG Summilux 15mm f/1.7 ASPH, M.Zuiko Digital 45mm 1:1.8, M.Zuiko Digital ED 75mm 1:1.8.
Leica D Vario-Elmar 14mm-150mm f/3.5 - f/5.6 ASPH.
OM-D E-M5, H-PS14042E, Gitzo GT1541T, Arca-Swiss Z1 DP ball-head.
Astrophotography: TEC 140 'scope, FLI ML16803 camera, ASA DDM60 Pro mount.


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