The FX Sensor
FX vs. DX
So we’ve heard the terms “FX” and “DX” a lot, but what does this mean exactly? In simple terms, “FX” is Nikon’s name for a sensor format that’s roughly equivalent in area to 35mm film (”full frame”). “DX” is Nikon’s name for a reduced-size sensor, also often called “APS-C”.
Sensor fabrication
All current sensors are fabricated using the same types of process as other computer chips. Multiple sensors are made on a single silicon “wafer” in high-tech and hugely expensive — we’re talking billions to construct — fabrication facilities.
Now, as FX sensors are physically larger than their DX counterparts, you can fit less of them on a wafer. On a standard 8-inch silicon wafer you might fit approximately 20 FX chips, compared to around 200 for DX. As the cost of a production run is in terms of cost per wafer, you can summise that FX chips are 10 times more expensive than DX.
However… of course, it’s not that simple. Chip fabrication isn’t perfect - a single spec of dust inside the facility that gets in the way of sensor production, and that’s one sensor from a wafer that simply ends up not working. This might not be a huge problem for DX, where you have another 199 - but for FX, you only have 19. Now imagine that twenty specs of dust get in, or that there are some scratches on the wafer before or after fabrication. That’s a possible 180 vs… a possible 0. FX is therefore many times more expensive, and it helps to explain why FX sensor production hasn’t hit the mainstream until now.
So, when everyone was shooting film, we all had “FX” sized sensors. However, when digital came along it was hugely difficult, and hence expensive, to produce sensors of that size and SLR manufacturers therefore chose to move forward with “DX” sizes. These have the advantage that they’re easier to produce (see box, right) and hence cheaper.
However, DX does have several disadvantages. As the sensor area is lower, so are it’s light-gathering capabilities - meaning lower resolution and/or more image noise. Also, as DX covers a smaller portion of the image projected by a lens, a “crop factor” of 1.5x is introduced. This means that a wide 24mm lens on FX will become something more akin to a 36mm lens when used with a DX sensor. This has been somewhat countered by the introduction of DX-only lenses that project a smaller image circle, such as the standard 18-55mm kit lens supplied with the D60.
On final “issue” with DX sensors is that, due to the reduced coverage, apparent depth-of-field is affected. It’s much harder to get a low DOF to isolate subjects with DX. However, the inverse is also true - if you want large DOF, perhaps for landscapes, it’s easier with DX (until the diffraction limit of your lens, at least).
So, how about a visual comparison between DX and FX? See the comparative image below - you can see just how much larger the FX sensor is.
| FX (D700) | DX (D300) | |
|---|---|---|
| Size | 36.0 x 23.9mm | 23.6 x 15.8mm |
| Pixels | 12.87 million (12.1 million effective) |
13.1 million (12.3 million effective) |
| Image Size | 4,256 x 2,832 | 4,288 x 2,848 |
| Pixel density | 1.4 million pixels / cm2 | 3.3 million pixels / cm2 |
| Pixel pitch | 8.45µm | 5.5µm |
FX Advantages & Disadvantages
The FX sensor format has many advantages, and some disadvantages. Which is best for you may be dictated by your shooting style an usual subject matter.
Advantages
- High Sensitivity
As each physical pixel on an FX sensor is much larger than a pixel on an equivalent-megapixel DX sensor, the FX version has more area from which to capture light. This translates into a higher sensitivity, or, to put it another way — lower noise. Where the D700’s sensor is concerned, this means it outputs amazing high-ISO images far beyond those of DX and indeed other 35mm full-frame chips.
Additionally, the larger light-gathering capability of an FX pixel also helps to improve dynamic range and allow for finer tonal graduations. - No crop factor
As described above, the DX 1.5x “crop factor” means that what used to be wide angle is no longer quite so wide - eg. your 24mm becomes equivalent to a 36mm. With FX, this is no longer a problem - wides become properly wide again. Of course, this is somewhat mitigated by newer DX-only lenses such as Nikon’s own 12-24mm, but for many this is a great return to what we learnt photography with. If you mainly shoot telephoto - wildlife, perhaps - then the DX sensor may actually be a better choice for you, as it’s 1.5x crop factor brings you that much closer to your subject. - Large, bright viewfinder
The FX sensor size means that a larger mirror is used, which in turn means that a larger viewfinder prism is used. This has the result that your view through the eyepeice is large, bright and detailed - which can be quite a revelation if you’re used to DX tunnel-vision!
Disadvantages
- Larger, more complex lenses
As the image circle that is projected by DX lenses is smaller than that project by FX lenses, the DX versions can be made somewhat smaller and lighter. This isn’t always the case - the Nikkor AF-S 17-55mm f/2.8 DX lens is quite a beast - but is a valid consideration if you want a small, light package to carry. - Image Uniformity
The FX sensor really does stress the lens being used. If you use an FX lens on a DX body, you’re just using the “sweet spot” in the centre of the lens. On FX, you’re also using the edges of the lens, which a never as sharp as the centre. This has been a problem recently, as people who snapped up the D3 found some corner issues with the pro Nikkor AF-S 70-200mm f/2.8 lens.
The result of this is that the CMOS FX sensor used in the D700, and the D3 before it, became an instant classic. It blew the doors open for low-light and high-ISO photography that simply wasn’t possible with a DSLR before. In the past, Nikon had always lagged behind their main competitor Canon in the high-ISO stakes. With the D3 that changed overnight.
Integrated Dust Reduction System
Dust issues have plagued digital SLRs since their introduction. Although not always visible, all sensors have some level of dust on their surface. Most of the contamination is caused by dust particles as small as just one micrometre (0.001mm), which stick to the sensor through an electrical charge. The sensor is negatively charged and the particles carry a positive charge; hence they attract each other. This is the same mechanism by which you see dust collect on a vertical television screen.
Dust can more readily be seen at small apertures. You’re unlikely to notice anything at f/2.8, but stop down to f/22 or further and you’re sure to see many dark dots and splodges on your images, all caused by dust sitting on the sensor of your DSLR. Traditionally, this dust had to be removed by blasting it with air or by “wet cleaning” with a suitable liquid.
In an attempt to combat this, Nikon’s new Integrated Dust Reduction System employs quad-frequency ultrasonic sensor cleaning every time the camera is turned on or off. The competition have had similar systems for a while; Olympus were first with their SSWF on the E-1 in 2003. Sony, Canon and Pentax introduced their own variants in 2006, and Nikon followed in 2007 with the dust reduction system in the D300.
Of these, none have proven completely effective - they won’t remove all of the dust on a sensor. From anecdotal evidence, the Olympus system is widely considered to be the best, perhaps followed by Nikon’s.
However, there is one downside to the sensor cleaning mechanism - according to Nikon themselves, it’s the reason for the reduction in viewfinder size from 100% on the D3, to a quoted 95% on the D700. (It was originally assumed that the D700’s built-in flash was the reason for the coverage reduction, but Nikon say this is not the case).
Note that Nikon say this is 95% - in reality this appears to be a measure in linear terms of the sides of the finder, so the actual coverage is 90% of the frame (0.95 * 0.95 = 0.9025). Only you can know if this is going to be a deal breaker for you - probably not, I’d guess - but it’s surely the reason that the D3 has no anti-dust shaker.
| <—— Photos of the D700 | The Nikon DSLR Range ——> |
July 25th, 2008 at 2:48 pm
I’m confused by this 95% (or 90%) viewfinder coverage situation.
Does the viewfinder show you precisely what you will get in the photo?
If not, does the viewfinder show more image than you will really get or less?
If you get more than you see in the viewfinder, I don’t have a problem with it because I could always crop later in Photo Shop. But if I get less image that I see in the viewfinder, that could be a problem because potentially something I see on the edge of the frame might be cut-off on the image file.
Can anyone explain exactly whether this 95/90% means getting more than I will see in the viewfinder, or less?
Thanks to anyone who can explain this clearly and simply.
July 26th, 2008 at 1:41 am
Hi Mike,
you’ll get more than you see in the viewfinder. Consider it as a kind of safe frame or room for cropping. I’d like to see it this way. Of course, if you do very carefully arrange your picture, you can end up with something on the edges you did not see and have to crop away (which means throwing away some of your 12 M Pixel). Haven’t tried yet, but I think these issues do not apply if you use live view, which should show exactly 100% on the screen.
July 26th, 2008 at 7:54 am
Thanks for that Volker. I now think this is certainly the camera for me.
Losing a few of the 12m pixels in order to crop later is not something that concerns me. I’ve done just fine with only 6M px for a long time now.
My only regret will be leaving behind my coveted 18-200mm Nikon DX format lens. Any replacement for FX format is likely to be expensive but maybe a third party zoom will do the job.
July 27th, 2008 at 3:04 am
“Can anyone explain exactly whether this 95/90% means getting more than I will see in the viewfinder, or less?”
Yes, you will get more than you see through the viewfinder,
For cost saving reason, small size is one of the major consideration in camera design stage,
reducing 5-10% in depth size that will cause viewfinder coverage reducing if that trimed the design from D3.
August 10th, 2008 at 7:29 pm
Does anyone know if my DX format lenses will be compatable with the d700? I have quite an collection and kinda concerned with upgrading my D200 and D2X for the simple fact that I will have to try to sell 1000’s of $$$ worth of lenses at a fraction of the cost.
August 31st, 2008 at 9:15 pm
To: # 4 Photo2020:
It means you’ll see less off what you will get in the file if you’re talking about how much you see in the viewfinder. On the D3 you’ll see 100%, on the D700 you’ll see about 95%.
# 5 Uncle Jon Says:
They are, but not with the whole sensor active. You’ll need to use the DX-mode, which will give you about 5 megapixels. But if you’re only gonna use those, get the D300 instead. Or use them and 5 megapixels while you save to upgrade to FX (fullframe) lenses.
October 21st, 2008 at 3:22 pm
The 95% thing is how much of the actual picture taken that you can see through the viewfinder. This is also the case with 35mm fiilm cameras. My Canon A1 had I think, a viewfinder that showed only 95 or 98% of the actual picture taken. With film of course you nearly always lost an area around the frame when the negative was printed so with digital you can control this by yourself and not rely on a photo lab.
April 17th, 2009 at 8:21 am
hi
im thinking of buying the d700
but i wont be able to use my 17-55mm f2.8 dx lense
i have some old lenses
such as the 24-85mm afs which i use to use on my f100
can i use this lense with the d700 or will i have to buy new lenses
thanks
June 21st, 2009 at 9:47 am
@nirminder: yes you can use this lens on the D700 and it’s a nice lens too.
July 20th, 2009 at 8:42 pm
You can use DX lenses on a D-700 but it will look like you are looking through a round hole when you look through the viewfinder. A red cropping line appears to show you where the camera will crop the “sweet spot” of the image. The D-700 will do this automatically when you attach a DX lens.
The downside is the maximum resolution of the chip is now only about 5 megapixels. Nikon decided this was the lesser of the 2 evils instead of capturing an image with a dark vignette around it.
Your old Nikkor 35mm lens may work however you may have to shoot by setting the exposure and focus manually.
I would imagine all but the cheapest cameras will soon go to full size CMOS chips and if you’re serious about photography I’d start getting rid of my DX lenses.
The D-700 is a tremendous camera but it’s not so much the camera but the impact of the image that counts.
However it is nice to have good tools to work with.
June 11th, 2010 at 7:52 pm
ive tested this and in my personal opinion it is most certainly more in terms of how much more you get than you see in the view finder but……off on just a mere 5% seems wrong to me more like 20-25% off , people should try this themselves i used dx mode with the words on a piece of paper it was a BIG difference like thisfrom point to point ok!!!
. . <—- Thats around how much it adds on , i think that kinda sucks for a $3000.00+ camera,,, but i still love you nikon!!!
July 18th, 2010 at 10:36 pm
Hi. I’ve recently got the d700. the only lens i have is a 55mm prime (really good, but limiting because of the work i do doing storyboards and prospectuses for sports colleges and schools)
I really want to buy the Nikon 24-70mm f/2.8G ED AF-S Nikkor but dont have the money for it right now but quite keen to start shooting with it or something similar. I got a dx lens from work but didnt like the dx crop thing , dont like the fact that i wasnt able to utilize the camera’s full capability. Anyway, like i said above, i dont have the money to buy it right now and so i’m looking for a tempory, more cost effective equivilent till i get the money saved up. so far, i’v stumbbled across the Sigma 17-70mm f/2.8-4 DC Macro OS HSM. Can someone please tell me what they think? ALSO, would this lens be compatible with the fx sensor of my d700? Your help would be greatly appreciated!
(p.s. sorry if my terminology is a bit rubbish, this is my first digital slr that i’v purchased for my proffesion, i’m still learning some of the basics)
July 18th, 2010 at 11:39 pm
Hi Rehana,
DC is Sigma’s term for lenses that only cover APS-C (ie DX) sensors - so no, on your D700 that lens will only really be usable in DX crop mode.
We’re big fans of the Tamron 24-135mm, a great versatile and high-quality lens, but they’re as rare as hen’s teeth these days. If you can find a used Nikon 24-85 f/3.5-4.5 (NOT the 2.8-4), they are also excellent - unfortunately they’ve been discontinued.
The only other Nikon FX standard zoom is the 24-120 VR, which is best avoided, it’s a bit of a dog.
I don’t have any experience of other manufacturer’s lenses (Tamron and Sigma will both do variable-aperture lenses in the 28-80 range, plus faster f/2.8 24-70ish models). Perhaps someone else can recommend one?