Megapixel question (and D40 vs. D40x)

Discussion in 'Digital Discussion & Q&A' started by KevinDks, Jul 9, 2007.

  1. KevinDks

    KevinDks TPF Noob!

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    Hello

    I'm very new here, and fairly new to digital photography. I bought a Canon G7 digital compact for general purpose photography and although it is great to use and very convenient, I have been a little disappointed with the image quality sometimes, especially at higher ISO settings, with too much noise evident when conditions are a little on the dim side.

    From what I've read the issue could be too many pixels on too small a sensor (10 Mpx in this case). Apparently this means that the individual photosites on the sensor are smaller than on, say, a 6 Mpx camera with the same size sensor. It seems that sometimes less really is more.

    This leads to my question. Nikon is offering £60 cashback on various dSLRs purchased with a kit lens. This makes the D40 just £270 (double that number to get the US dollar figure) with the 18-55mm lens, which is quite a lot less than I paid for the G7. I understand it is an entry level dSLR with a limitation on lens compatibility, but I assume the lower number of pixels (6 Mpx), on a larger sensor than the G7, should mean that noise is less of a problem and I should get a bit more dynamic range. In addition, from what I've read the ability to shoot in RAW is very attractive. At that price it is hard to resist.

    However, for £390 (after cashback) I could get the D40x, which is almost identical except that it has 10 Mpx and the lowest ISO is 100 rather than 200. I'm wary of the higher pixel count because of my experience with the G7, but the lower ISO might be worth having. This also seems like quite a bargain, and my budget doesn't really stretch to anything more than that.

    Can anyone help me with this decision? I don't think I need 10 Mpx, but if there isn't much of a downside then I wonder why I shouldn't get the D40x for the lower ISO.

    Many thanks

    Kevin
     
  2. astrostu

    astrostu Guest

    I can't help you with your decision because I'm not a Nikon guy, but I can help explain pixel noise to you.

    ISO effectively boosts the gain by the sensor. This means that even if the same amount of light is recorded by a pixel, it will be output as a higher number. Photon noise is governed by Poisson statistics where the uncertainty is given by the square root of the average. This means that if the pixel records 100 photons, the uncertainty is ±10 photons (10%). If it records 10,000 photons, then the uncertainty is ±100 (1%). So while a higher ISO will boost the signal, making it appear brighter, it will also boost the noise by the same amount. And this is in addition to other noise in the detector (such as Gaussian noise from the heat of the electronics).

    This is why a smaller pixel size will - all other things being equal - give you a noisier detector: If the pixels are half the size in detector A as detector B, then they will only record 25% of the amount of light, each. This will result in 2x as much noise (sqrt of 0.25 is 0.5). Plus the Gaussian noise.

    So that's why - everything else being equal - more pixels in low-light situations is not the best thing to have unless you have still subjects, a tripod, and a fast lens.
     
  3. fmw

    fmw No longer a newbie, moving up!

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    The difference in the pixel count is actually relatively unimportant. I think the 10mp version would be fine, assuming it has the same sensor as the D80 which works very well. I don't think pixel count is the best reason to choose a camera but, if it is the same camera, then there are few disadvantages to having more resolution. I would probably choose the 10mp version myself in your shoes.
     
  4. NikonD40x@Denver

    NikonD40x@Denver TPF Noob!

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    I'm Looking at the Nikon D40x I found the Body for $300.00, Now I need help choosing a great Lens that does not cost a lot but will do enough for me....
     
  5. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    If the deal looks too good to be true...it probably is.
     
  6. NikonD40x@Denver

    NikonD40x@Denver TPF Noob!

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  7. Garbz

    Garbz No longer a newbie, moving up!

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    Kevin pixel density is actually a small part of a much larger system that causes noise. Yes the Canon Powershot G7 has a small sensor that really doesn't help. But if we go exclusively by pixel density then the very first 1mpx digital cameras would be the ones with the least noise.

    The noise is contributed by pixel desity, the way they are aligned, the way their individual amplifiers (MOSFETs for CMOS sensors) are setup and powered, the way the data is read off the sensor and many more all the way to the final Analogue-Digital Conversion.

    The D40x may have smaller pixel density than the D40 but the noise should be similar, probably even better depending on what internal changes were made.
     
  8. KevinDks

    KevinDks TPF Noob!

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    Really useful answers, thanks everyone. Last night I found detailed technical reviews of the D40 and the D40x which found that noise is slightly more evident on the D40x, but mostly at higher ISO settings and not by much. On the upside, they said that the newer model has better dynamic range, and overall the sensor is similar to that in the D80 and D200. That information plus your replies point towards the D40x as the obvious choice, so I think it's time to go shopping.

    Thanks again for replying!

    Kevin
     
  9. PatriK-b

    PatriK-b TPF Noob!

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    Hello,

    If you are not familiar with DSLR, keep in mind that they are very different from compact cameras, do not compare them, any 6Mp, old DSLR will perform better, in any fields (except size and budget :D), than the last 10Mp compact.

    I mean that on actual DSLR:
    - pixel count is not issue, 6,8,10,... will not that much difference until you are planning to make professional use of giant prints. (for example lens quality will be more an issue ;))
    - noise is not an issue until you are planning very special use at very low light condition. (and once more, lens' speed may also be more an issue ;))

    Regarding pure noise performance only, Canon is a little bit better than Nikon.

    If you are new to DSLR world, you don't have bags of lens to reuse, you should take both cameras in hands, pay attention to ergonomic, have a look at prices for accessories, for lenses,...
     
  10. Don Simon

    Don Simon TPF Noob!

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    Sorry but I'm confused now... B&H are not selling the D40x for $300. Even that other site you linked to, which is probably running a scam, is not claiming to sell it for $300 but $400... I'm not sure what we're supposed to be looking for in that link.
     
  11. KevinDks

    KevinDks TPF Noob!

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    Hi Patrik

    Yes, I'm sure you are right. I've ordered a D40x now, so I'll be able to prove this to myself very soon!


    Well, I don't have lots of lenses, but I've been shooting with a manual Nikon film SLR and 50mm 1.8 for almost 20 years, and I'm sure that the company that produced the F series know enough to make a decent dSLR. I hope so anyway, as the money has already been spent! Next time I have some cash I'll probably get the 50mm 1.4, even though the autofocus won't work on the D40, because I love prime lenses.

    Kevin
     
  12. Garbz

    Garbz No longer a newbie, moving up!

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    If you actually intend to dive into this world of lenses I HIGHLY suggest saving for a D80 or seeing if you can get a second hand D70. The lack of autofocus mirror is the reason I try to talk many would be hobbyists out of the D40 in the first place.
    Note that there's no penta-prisms in modern DSLRs. Manual focus becomes not so much a hassle but an epic battle between the camera and the photographer.
     

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