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06-08-2010, 12:59 PM   #1
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Grainy shots with k-x at ISO 400

Guys,

I need help. I was using a Panasonic FZ18 all this time and one of my motivations to upgrade to a DSLR was "low light" photography. I obviously chose the best one according to reviews, which is the K-x....

Imagine my consternation when I took some sunset photos at just ISO 400 (reviews seem to say 1600 is pretty noise free) and I got some grainy shots which my wife literally laughed at...

Exif settings are below, and so is the shot....

What did I do wrong? Please spare me the photoshop line as I know very well I can get it to work that way. Or raw!

I was expecting good ISO 1600 jpegs at low light out of the camera.

Thanks All,
Rwik


EXIF:
ExposureTime : 1/100Sec
FNumber : F9.0
ExposureProgram : Program Creative
ISOSpeedRatings : 400
ComponentConfiguration : YCbCr
ExposureBiasValue : EV-2.0
MeteringMode : Division
Flash : Not fired(Compulsory)
FocalLength : 55.00(mm)
Software : K-x Ver 1.01

Attached Images
View Picture EXIF
PENTAX K-x  Photo   

Last edited by rwik78; 06-08-2010 at 01:40 PM. Reason: Added 100% crop
06-08-2010, 01:24 PM   #2
hcc
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Rwik
I followed a similar path as you, coming from a FZ20 (that I still use occasionnally) to a K-7.

Looking at your shot, my main criticism would be that the photo is very dark, rather than grainy. I am surprised by the short exposure time (1/100s). For a sunset (or sunrise), I would use 1/20 to 1/40s to get more light into the camera sensor.

Could you indicate :
- what lens was used (kit lens ?),
- what dial mode did you use ?

I often use the P-mode, and, if needed, lower the shutter speed to get more light into the sensor.

Lastly, most Pentaxians would agree that it takes a few weeks (at least) to master a dSLR camera. My first shots with the K-7 were no better than my shots with the FZ20, that I know by heart after 5 years. A few months later, off course, this is a different story: my shots with the K-7 are much, much better that I could achieve with the FZ20 or any P&S: I am not going back to a P&S unless I do not have the K-7.

Hope that the comments will help....
06-08-2010, 01:29 PM   #3
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Yes it look a bit dark to me (and dark images will look a bit grainy).

Is this a 100% crop or a scaled full image?

Also I see that there is some negative exposure compensation (making it darker) - was this deliberate?
06-08-2010, 01:31 PM   #4
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Thanks Hcc, this forum is just great, people are so helpful and constructive

Actually, I wanted the dark effect, as you can see it is not "really" a sunset. You can see in the exif I actually set the exposure to -2. Using the 18-55 kit lens at the slow end (did give a go with the 50-200, same results). I tried both the sunset in scene mode and the P mode.... Again, similar results.

06-08-2010, 01:32 PM   #5
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Jonathan, it is a scaled version.
06-08-2010, 01:44 PM   #6
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It is too dark and seems to have shake/motion blur.

Usually for "dark effect" you should do it in post processing after all. With any digital camera, there IS some constant level of noise. When you make the image darker, noise "increases" proportionally to image.

Practically you should try to expose every shot correctly or a bit brighter (unless highlights are blown) if needed. Always avoid darker exposures, than normal, if not absolutely necessary (e.g. to preserve highlights). Then if dark effect is needed, you darken the image in post processing (either by curves or "exposure"/gamma adjustment - simply adjusting birghtness does not produce the same effect as taking darker picture in camera).

Note for shake: for SR to activate, you have to wait for the hand to light up in viewfinder. I didn't knew this a the beginning. Otherwise the SR system wont be active when you take the shot, even if enabled.

Here is an example taken with much older and a lot noisier camera k200d at ISO800:

Since it has been exposed more or less correctly, the noise is not that visible even at this high ISO setting.

P.S. Your image is also mostly in blue to violet tones. Digital sensors are least sensitive to the blue light, and produces most noise in blue tones.
P.P.S. Usually when i want to show the special mood of some event, i always DO take one "incorrectly" exposed and "wrong" white balance'd shot. Just to remember what i was after, when processing the technically qualitative image.

Last edited by ytterbium; 06-08-2010 at 02:30 PM.
06-08-2010, 02:06 PM   #7
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Thank you Ytterbium, I arrived at the same conclusion.... dark exposure means less signal for the sensor, so noise will be more apparent. Will not underexpose already dark subjects and use gimp ( ) for post-processing.

Many thanks for the SR tip, will keep that in mind.
06-08-2010, 02:20 PM   #8
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I have found for my camera I am getting better results with SR off at around 1/100 (well for 55mm or less focal length like you are using).

I agree that image quality is much better if exposure is "right" (ie. balanced) and then Post Processed but I can see your point. If it was me I would also try:
  • Upping exposure (even if just a little - it makes a bit difference)
  • Moving focus back a little from infinity (current forground is lot out of focus)

As has been said before the K-x gives a lot of flexibility over a point and shoot but it does take a while to get to grips with that flexibility (it does start to come right fairly quickly though!). I had a similar experience coming for a Super Zoom (although I had had some experience with a SLR in a previous life).

06-08-2010, 06:35 PM   #9
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You have the exposure bias set to -2. This means you have underexposed the scene by 2 stops.
This is an operator error, not a camera error.
06-08-2010, 10:32 PM   #10
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Hi Wheatfield,

I wanted the scene underexposed It was okay if the scene was dark, but the noise took me by surprise. I will follow Jonathan's advice and see where that gets me....

I am not saying the K-x is a bad camera :-)

Thanks,
Rwik
06-08-2010, 11:18 PM   #11
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You'll find, in general, that it is better to give relatively ample exposure and print the image down to where you want it.
06-09-2010, 06:33 AM   #12
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I'm not sure what you used for software to process the image, so this may not apply. What can happen with some software like Picasa is automatic brightening. That would take your underexposed image details and brighten them to make them look "better". The software is effectively increasing ISO, but the image looks worse because the brightened areas were initially underexposed.
06-09-2010, 06:46 AM   #13
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Even if you want the picture to be dark, you can still follow the ETTR (expose to the right) rule to ensure that you obtain proper exposure. You can also adjust the darkness in post processing. Another point to watch out for is the metering - if you have matrix metering on - set the metering dispite the focus point selection - this way, the metering does not change if you focus on the bright spot in the sky.

As some of the forum members pointed out, I do think that you have the EV set to -2 to be in error resulting in an underexposed photo.

Last edited by aleonx3; 06-09-2010 at 06:54 AM.
06-09-2010, 06:59 AM   #14
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I did use the AE-Lock for metering Please note I have set it up using CF to be used as just AE lock (Focus with half shutter)

And yeah, with exposure=0, I did not get appreciable noise.

But I am talking about ISO 400? And all the discussions I see seem to mean that with the K-x, you can pretty much forget about noise till ISO 1600....
06-09-2010, 10:52 AM   #15
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That's because it's assumed you are looking at properly exposed picture. A picture that is underexposed by two stops at ISO 400 is exactly the same picture as far as sensor data is concerned as a properly exposed picture at ISO 1600. And I mean *exactly*. You're using the same aperture and shutter speed either way, so you're giving the sensor the same amount of light either way, so the sensor collects the same number of photons either way, so it produces the same signal. Only difference is whether the signal is amplified two additional stops to get from ISO 400 to 1600 or not. Either way, you've deprived the sensor of the light it needs to get the sort of signal-to-noise ratio it needs for a better picture.

Beyond that, it also appear you didn't focus carefully enough, nor did you hold the camera steady enough, to get a sharp picture. That doesn't help, as noise will always be more noticeable in softer textures than ones that have more detail. And in that respect, by their very nature (soft and largely devoid of detail), clouds and sky will often be the noisiest areas of any picture. Then there is of course the fact that any noise that is present is going to be far more apparent when pixel peeping at 100% than when viewing "normally" - which is to say, on screen, or in prints viewed from a typical distance for the print size.

So if someone were to have produced a recipe for how to see the most possible noise in a picture, I'd say you'd have followed it to a "T".
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