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DX v FX Format

Malcolm Evans , Aug 10, 2009; 06:53 a.m.

Apologies for raising this old chestnut again.
I am in the market over the coming 12 months for a second camera body (also a couple of lenses, including one longer reach than my 18-200 (27-300) and the question arises FX or DX? I have read the various posts on this forum and also an article by Ken Rockwell, unfortunately I am still a little perplexed on which direction to head. I have a DX format SLR at the moment at 12 mp. I cannot justify or afford a D3 or a D3X so I was waiting to see what was launched and given the D300S is still 12 mp I will hang on a bit longer and canvas some more opinion and input.
Firstly I understand nearly all that I have read, due to educational background, in terms of why FX gives better detail, the cropping effect the demands on the optics and also the longer reach etc. But what does concern me is the matter of mp v optical resolution. This lead to the following questions in my mind.
a) Is there any point in waiting for DX to go beyond 12MP, or infact could such a step in terms of photoreceptor size be a backward step (thinking of Mr Rockwells essay and comments in a book I also have).
b) At what MP size will FX format have photoreceptors the same size as DX now and hence offer no advantage of todays DX (allowing for the reduced challenge on the optical part of the system) , again thinking of Mr Rockwells piece and the book I have.
c) Is a 35mm sensor optimal or is it just emotional/nostalgic or driven by a desire to leverage old glass. When will photoreceptor size cause us all to demand a bigger sensor again so we can get more MP at todays FX photoreceptor size. Probably driven by stock agencies and publishers upping their minimum acceptable image MP size as there first line of defence to being swamped.
d) I did not fully understand the point/explanation made about a DX sensor leveraging the sweetspot of a non-DX lens. Is it that only the central portion of the lens is leveraged (I understand why this would be an advantage) If so, does that mean the wide open F value of a non DX-lens is changed when used on a DX format body?
I photograph mainly wildlife and archaeology (buildings and close ups), some landscape.
It seems my decision is around and element of future proofing and image quality.....
Go for a D300S as going beyond 12mp will not be an improvement on DX.
Await a DX format camera @ greater than 12 mp.
Await a D700 replacement/refresh @ greater than 12 mp (but how big before I am no better off than my current DX)
The above factored by a general consideration of would it be better to have an FX and a DX.
Many thanks in anticipation


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Matthew Brennan , Aug 10, 2009; 07:31 a.m.


You ask a lot of technical questions of current bodies, most of which I'd care to answer by saying unless you are going to expect truly massive prints from your camera then pixel count, pixel size, sensor size and type and resolvable detail from avail. lenses are mostly moot points. I have some great Nikkor glass but unless I can keep the whole camera/ lens combo absolutely still whilst the mirror/shutter actuates then the resolution of either the lens or sensor is limited by the support offered. Of course a medium format sized sensor will yield more detail, given it's used properly but at what cost & as a means to what end?

Current technology dictates that too many pixels on a given sensor spoils the broth via noise etc. Until the technology improves where by resolution gain is improved without exposure penalties we are left with the current Nikon 12 MP FX and DX CMOS sensors which provides arguably the best results with the least penalties. At least this is my line of thinking and I voted with my bucks and purchased the D700.

By mounting FX format lenses on DX format bodies one can eliminate any soft edges / vignetting that the lens might otherwise exhibit on an FX format body. In other words, only the light from the centre of an FX lens illuminates the smaller DX sensors thus using the 'sweet spot' and not projecting light from the outer limits of the lens. Typically (but not always) a lens will have best sharpness in it's centre and will suffer sharpness and light fall off etc around the outer proportions of the lens. I used several FX based lenses on the D200 & D300 and found this to be so.

If you are wanting to purchase a 300mm / 400mm lens or longer and you already have a DX body on which to get the DX crop factor gain then perhaps the D700 body is the one for you. I have no need to make a print any larger than 14 -18 inches long and my current set up will do that for me to my desired standard, I'm sweating over what may or may not be around the corner.

Although I have shifted to the Nikon FX format I'm a firm believer that Nikon intends to maintain it's DX format in both D-SLR bodies and DX lenses well into the future. I'm also of the opinion that why should you wait for the next model if your opportunity cost is missing out on current photographic opportunities ........ Grasp your photographic opportunites now! Buy a currently avail. body or better still invest in a lens which is far more likely to stay with you longer than a camera body will.

Wouter Willemse , Aug 10, 2009; 12:12 p.m.

First of all, a little warning: Ken Rockwell has some really good articles, some really bad and a lot of very biassed ones (like: we should all shoot JPG, because real photographers get it right the first time). Not all he says is all that true. So take his findings with a pinch of salt.

A. With the current technologies, there is no point in waiting for more than 12 MP on DX. The steps will be very very small. Maybe some new noise reduction trick will change the game, but I have no crystal ball to tell that for sure...
And ask yourself: do you need more than its 12 megapixel resolution? A lot of your questions boil down to the amount of megapixels, but frankly, more megapixels does not always mean more quality, or whatever you might like to call it. As megapixels rise, so do the requirements to lenses. Your 18-200 is not the sharpest lens, so try a good prime/pro zoom on your current body, and now evaluate whether 12 megapixel is enough or not.
Going from 12 to 25 megapixels, the long side goes from 4200 tot 6000 pixels. That's how much you really gain... it's double the resolution, but only ~125% increase for each side. Is that really going to change that much? I, like many here, believe 12 is really enough for all normal practical uses.

B. Individual photosites size, to compare 12Mpixel DX to FX it would be around 30 MP, I believe

C. It's just a size. Yes, old lenses are their old self again, and if you shot film a lot and are used to specific primes giving a specific look, that matters a lot.
But if you are relatively newbie like me, and have no serious experience with film, all of that suddenly means nothing. To me, super wide angle is 12 to 16mm. A normal lens is 35mm. My 24 f/2.8 is a great very moderate wide angle... The point is, I've always shot DX camera, and given my liking for long lenses more than for wide angle, will continue to do so. 300 f/4 or 450 f/4...I'll take the last one, thanks :)
So again, think for yourself: does it have any meaning to you?

D. Indeed, DX only uses the central portion of the lens, which is the best bit with the least issues. So lenses designed for FX/Film tend to perform better on DX than on FX when it comes to vignetting, corner issues and such. But this is all rather fractional, good lenses are good lenses regardless of DX or FX, and some DX lenses have great performance too.

So FX or DX? Well, unlike what your post seems to imply, it is not a decision based on megapixels. The current advantages of FX are in other things:
1. Larger recording medium means less depth of field. So the depth of field with a 50 f/1.4 on FX versus DX will be less on FX. Great for portraits and such, a bummer for macro.
2. High ISO performance. Since the D700/D3 have far bigger photosites (12 mpixels on a bigger sensor, compared to the D300/D90 etc.), thheir pictures contain less noise. ISO3200 perfectly usable on a D700, on a D300 ISO3200 looks pretty crappy.
3. More wide angle options. Though, with the arrival of 10mm wide angle zooms for DX, the gap is not that big anymore.
There are more, smaller, differences, but this is what makes people want D700 over a D300(s).
So, the big question is: do you really believe you need more megapixels, and if so, please explain us why you'd need them? So we can help you decide whether that is a logical wish or wishful thinking. Because the way your posting sounds, you refuse to have another 12 MP camera as second body... but as it is, the current 12 MP Nikon bodies all deliver a pretty amazing performance - so they do make an excellent choice.
(tip: compare EOS 50D pictures to EOS40D pictures - 10 versus 15, and otherwise pretty similar cameras. Does the extra 5 MPixel bring a lot?)

Oskar Ojala , Aug 10, 2009; 12:20 p.m.

a) No, it needs to go to 20 mpix or more to make a difference and then you need new lenses.
b) Roughly 27 mpix or in practice a D3X will do it. But what would it matter, only the final picture and its quality matters.
c) No, the larger the better. Medium format kills 35 mm quality wise.
d) the image quality tends to be the best at the center of the picture and since DX only uses the center then it's said it uses the sweet spot of the lens. Personally I don't buy much into this, as it's easier and better to optimize a lens directly for DX. Otherwise people would be using MF lenses on 35 mm due to their "sweet spot" characteristics. The F value has nothing to do with the format.
Don't worry about photoreceptors sweet spots and such; only the quality of the final image counts. Don't about future proofing, both DX and FX will be around for a while longer. If you want to wait for a DX that offers real image quality improvement over a D300 then you're not buying a new camera in 2009 or 2010, maybe not even in 2011.
FX (D700) is better image quality wise than DX (D300), but for macro a subjects requiring long reach (wildlife) DX has an advantage.

ross b , Aug 10, 2009; 12:23 p.m.

You could look at this website and compare the D700 and D300 and see if there is anything of value to your needs. The D700 does provide a wider dynamic range and lower noise. The D3x topples the competition but at a huge price. It has ISO 100 which helps a lot.

Matt Laur , Aug 10, 2009; 12:25 p.m.

Indeed. I recently delivered another 30-inch print produced from a slightly cropped D300 exposure. I used a good lens (the 70-200/2.8), and had enough light for a slightly stopped-down, high shutter speed exposure. The results - even stretched out to thiry inches - were very, very good when printed by a pro lab that knows what they're doing.

I will rarely be printing anything that large. Smaller than that, even somewhat marginal shots can produce excellent prints. I could wish for those same 12mp to behave better at higher ISOs when working in worse light, but right now I'd rather buy more lenses, lights, and light modifiers than a D700 or D3. Resolution itself simply hasn't been a practical problem for me, at all. It wasn't with the D200, and it certainly isn't with the D300. I'll wind up with an FX body at some point, but not because I'm waiting for higher resolution - that will be all about low, low light. Other than that, I know that even for quite large prints, the limiting factors in quality for me are generally lenses, technique, and getting up early enough in the morning to be where I need to be to have something interesting to shoot in the first place.

Andy L , Aug 10, 2009; 12:27 p.m.

My favorite Ken Rockwell article is the one where he explains that real photographers don't use lens caps. But anyway.

Don't sweat the megapixels. Yes, there are higher MP DX cameras out there (made by Canon and Pentax, for example) but higher MP doesn't necessarily yield better results - even with large prints. If you have a 12MP Nikon right now you have... a D90 or D300? Don't expect any current DX camera (from any manufacturer) to improve your image quality results over either of those models, not even a new D300S. The Nikon 12MP CMOS models are the current top of the line. So if you want another body, you want either FX (you'll need new lenses too!) or a second body for the sake of having a backup, in which case, since you already seem to have AFS, look at the D5000 as a money and weight saving option.

Peter Hamm , Aug 10, 2009; 01:49 p.m.

too much thinking. too much philosophizing. How big do you print? For most people, if you don't KNOW you need FX, you most likely don't. If you print below 8 x 10 or 11 x 14, then a well shot photo on DX and the same well shot photo on FX will probably look identical to the trained eye.

Why do you NEED more than 12MP? Why might you NEED FX? Most of us need neither.

RL Potts , Aug 10, 2009; 02:30 p.m.

IMHO, better sensors mean better prints. But you do have to pay attention. When I upgraded from a D80 to a D300, I got more mp's and better photos, because the new sensor was just better in a number of ways and short-comings are magnified in enlargements that may have little to do with pixel count.

For buildings and landscapes, the D700 should be better. There is noise with the D300 period.

For wildlife, the dx crop, the high pixel density, and the ability to crop severely from long lens shots is indispensible.

I think you need to decide what your priorities are.

Ilkka Nissila , Aug 10, 2009; 03:33 p.m.

Essentially an FX sensor records about twice as many photons for a fixed set of exposure parameters (ISO, shutter speed, and aperture). This information can be used for additional detail (i.e. D3X's 24 MP) or to improve the SNR of the data recorded by each photosite (i.e. D3, D700) vs. a camera using the DX sensor (e.g. D300).

If your FX camera has as many pixels as the DX camera being compared to, the pixel quality will be different. In the image recorded by the FX camera, the tones look deeper and you can do more post-processing, use higher contrast curves or greater saturation without the image breaking apart. If you've tried to adjust the tone curve (in curves in photoshop) of a point and shot image with a midtone contrast increasing s-curve, you can see that the image basically breaks apart, there are about as many tones as there are in a selection of Lego bricks. DX vs. FX, FX vs. medium format, a bit of the same thing except that the differences are more subtle as the sensor size difference is not as great, relatively speaking (point and shoots use really tiny sensors).

Now, what about 24 MP FX vs. 12 MP FX? Does one "lose" something as the pixels get smaller? Yes and no. The individual pixels are more noisy but in a print of the same size from both cameras, the tonality is comparable as the eye/brain tends to average the small pixels together (increasing SNR and tonality of the D3X approximately to the level of the D3/D700, give or take a little due to technological implementation differences) when you look at the image as a whole. When you look at the details though, you'll see more detail with the 24MP image assuming a good lens at or close to optimum aperture and large enough print size. So in this sense the higher resolution imager is better if we just look at basic photon noise as key determinator of SNR. But in practice there are additional implementation factors which put the D3X ahead at base ISO and the D3/D700 ahead at high ISO.

Other factors favouring FX over DX: 1) bigger viewfinder so you see your subject more clearly. I can't help wonder what kind of garbage is sold on consumers in terms of viewfinders. How do the people even tell what the subjects' expressions are at the moment before the exposure, if the view is about as good as looking through water? Ok, the better DX viewfinders are fairly decent but the pentamirror types are fuzzy and they are all quite small. 2) Greater variety of high end and special-purpose lenses available. 3) Better image quality at wide apertures with fast primes (this is due to the lower MTF spatial frequency required by FX to get similar detail in the final print; essentially you get better detail contrast with FX, 4) Better image quality with wide angle lenses (assuming top-of-the-line lenses are selected for each format), 5) More room for improvements in the future, 6) the full image circle is recorded which means that you don't get unwanted flare and ghosting effects if you have the light source within the FX area but not seen in the DX viewfinder directly, 7) greater range of apertures that yield high quality results, 8) Nikon's high end lens development seems to be exclusively FX now. Do you want the whole image to be recorded, or just half?

Advantages of DX include 1) small size of bodies, 2) compact zoom lenses like the 16-85, 3) greater reach with telephotos, 4) greater reach and working distance with macro lenses, 5) signficantly lower cost. For me factor 4 is of interest, as I am drawn more to close-up photography these days, and I have no illusion here: DX has a significant practical edge here, though I make do with FX (the limitations are fairly subtle).

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