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 Post subject: Question ....
PostPosted: Thu Jun 17, 2010 12:23 pm 
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Hi All

I am back to my trusted site..

I have a problem with high resolution..

For ex: i have taken a photo with ISO 3200 in Av mode.. it has taken its own shutter speed value.. it looked good on camera LCD , when i copied that file to my system which is LCD screen aswell i can see fair amount of noise , yes i know with ISO 3200 you cant help this.. but will it make sense if i increase the shutter speed here to 1/500 or so will i overcome this problem?

Cheers
Mano

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 Post subject:
PostPosted: Thu Jun 17, 2010 2:42 pm 
Hi Mano,

When yo use the Av mode - Aperture Priority - you tell the camera that you prioritize the aperture setting over everything else.

Elsewhere in your camera you have specified how the camera should handle auto-ISO - i.e. what the max. ISO you will allow should be.

Between these two sets of instructions, the camera has automatically set the shutter-speed to get you equivalent exposure.

The - in my opinion - simplest way to address this is to change your auto-ISO setting. Tell your camera that you will not allow a higher ISO than..say 1600 or 800...to reduce the noise.

Of course you have to be cognizant of the shutter-speed, focal length and the movements (if any) of your subject or you may be trading noise with blur.

If you are shooting indoors in dim light and insist on F/16 and do not use a flash, the camera will give you a shutter speed where you cannot hand-hold your camera and where any moving objects in the frame will be blurred, for example.

As for your suggestion: when you say you will "increase the shutter speed to 1/500 the effect will be the opposite of what you intend. Assuming that you change to Shutter Priority mode and increase the speed of the shutter, you are reducing exposure time, forcing the camera to compensate by increasing the ISO (all else being equal). This will give you even more noise. Conversely, if you decrease the shutter speed, you MAY get a lower ISO - assuming that the camera doesn't instead change the aperture for you and keep the ISO high. Which is why I suggest you change your auto-ISO settings.

To be pragmatic, you could ask yourself how often you will EVER allow ISO 3200? The answer is probably close to NEVER lol..so you may as well limit the range of the auto-ISO to the threshold you will accept.

On my Nikon D300 - even though it can be decent at ISO1600 - I still keep ISO800 as my max 99.999% of the time. On my Nikon D40 I don't even bother with ISO above 400.

Cheers :-)


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 Post subject:
PostPosted: Thu Jun 17, 2010 3:57 pm 
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Location: Chennai
Hi

SO you mean to say keeping ISO to AUTO will solve my problem....

Hmm.. will try and get back to you..

Thanks for your help mate..

Cheers
Mano

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 Post subject:
PostPosted: Thu Jun 17, 2010 4:04 pm 
Hey Mano,

yep - just define the upper threshold/max ISO to something less than 3200.

Cheers :-)


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 Post subject:
PostPosted: Thu Jun 17, 2010 4:56 pm 
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If image noise is a problem then using lower ISO will help. How low you can go depends on the acceptable shutter and aperture settings too so it is a balancing act.

LahLahSr, one of the weaknesses of Canon's are they don't allow a user set auto-ISO range, at least not on any model I've used. The auto-ISO on 50D is 100-1600 unless they changed it in a newer firmware after I sold mine. Therefore to get ISO3200 it has to be specifically selected. Personally I found the ISO1600 limit to be good enough for general use, although for critical quality I would manually go lower.

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 Post subject:
PostPosted: Thu Jun 17, 2010 7:01 pm 
Hi popo,

I wasn't aware of this and I'm rather surprised that Canon would not allow user-dictation of the thresholds..thanks for teaching me something new!

If I understand you correctly, you then can specify that it is auto-ISO, but it will only operate with a 100-1600 ISO range.

Assuming I understand that correctly, Mano could try that first. If that isn't enough, he would then have to manually specify one single ISO value? Say ISO800 and then also manually remember to switch it back to auto-ISO or set another lower value if the light increases?

Cheers :-)


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 Post subject:
PostPosted: Thu Jun 17, 2010 7:12 pm 
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That's right (for 50D). I have no idea why Canon are not more generous as even the E-P1 lets you set the auto-ISO range. On Canon, note the auto-ISO range can be different depending on the model. Maybe the 1 series is more generous, but I haven't seen it in lower models. At least the range they give is quite well chosen and matches my own expectations of a usable level (good enough).

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 Post subject:
PostPosted: Thu Jun 17, 2010 7:48 pm 
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The 7D allows for an auto ISO in M-mode...set the shutter speed, aperture, the limits of the auto-ISO, and that's it. Then again, that's a professional model, so Canon indeed does not offer a true user-set auto-ISO for consumers (although when I look at some 'consumers' they more resemble professionals as far as gear is concerned!).

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 Post subject:
PostPosted: Thu Jun 17, 2010 7:57 pm 
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Maybe I'm missing something, I don't see how the auto-ISO in M mode on 7D fits in with the original question. Auto-ISO certainly is selectable in other modes, the Canon limitation being you can't set the range that Auto-ISO works in, like the A350's auto range of 100-400 or user set fixed value.

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 Post subject:
PostPosted: Fri Jun 18, 2010 5:04 am 
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Hi All

Thanks for your suggestions..

But its a shame on 50D i cant set the AUTO ISO range even in M mode as it can be set in 7D(as said bye Joris Van den Berghe) ..

As said by peers here , i think i have to set it to AUTO ISO(which i have already done) in any mode by which the camera not allowing more than ISO 1600.. if i have problems with low light conditions then i have to select it manually to high ISO again...

BTW is using built in flash a SIN as we no longer get the originality of the scene? This is always tricky question for me which i have never asked here... thinking it as a sin i rarely use built in flash and because of the most of the times in low light conditions i get images in blurry .... next to GOD only you guyz can save me on this.. pls help me on this.

Cheers
Mano

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 Post subject:
PostPosted: Fri Jun 18, 2010 5:27 pm 
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It indeed doesn't fit within the original question, but as you did not seem to know about the 7D's auto ISO limits which can be set by the user, I considered it interesting for you to know :). Heard about it from a 7D-user, so...

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 Post subject:
PostPosted: Fri Jun 18, 2010 5:37 pm 
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If you're saying the auto-ISO limits can be set in M mode on 7D, I'd like to know about it cos I don't see it on mine. I am aware that that auto-ISO functions in M mode, but it is the same range as in any other mode, unlike earlier cameras which default to some fixed value (400?).

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Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
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 Post subject:
PostPosted: Fri Jun 18, 2010 5:55 pm 
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Well, I don't know how it works (not being a 7D owner), I just heard it worked that way: setting aperture and shutter speed, and letting the auto-ISO work out the exposure, to get the desired effect of the shutter speed and aperture. I'd consider it kind of silly to have that kind of a function on a professional camera but not being allowed to set the limits :roll:.

Could be wrong of course - to err is human, after all...:)

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 Post subject:
PostPosted: Sat Jun 19, 2010 11:05 am 
Hi,

Going slightly off topic, would over-exposure sometimes help reduce noise? I read that with the Olympus 4/3 cameras, there can be terrible noise when underexposed, but with some exposure compensation the results can be pretty decent. Has noise got any relation with exposure?

Thanks,
Jinay.


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 Post subject:
PostPosted: Sat Jun 19, 2010 11:20 am 
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It has indeed.

Just try getting the shadows right in Lightroom or Aperture...when you use it the shadows feature too much, you'll get a lot of noise. The trick I use is turning it into black & white or sepia :). It's indeed easier to just overexpose it a bit and lower the exposure afterwards to get it right. Or you could use HDR.

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