Which ISO setting do you use for UW?

[SuPrBuGmAn]

I always shoot RAW, ISO does impact image quality. I don't know, or care to be honest , the science behind it - but the results are obvious at full resolution in large steps, not so much in smaller ones.

ISO100 - ISO200 is noticable on my PnS, ISO400 is very noticable.

ISO 100 won't show noticable degradation in image quality until ISO400 with reasonably sized images, even then, its more than workable/saleable from my E500 or E1. ISO800 and even ISO1600 can be cleaned up fairly well if exposed correctly with noise reduction software. DSLRs are much more capable of handling noise than PnSs.

 

[victor]

I always shoot RAW, ISO does impact image quality. I don't know, or care to be honest , the science behind it - but the results are obvious at full resolution in large steps, not so much in smaller ones.

ISO100 - ISO200 is noticable on my PnS, ISO400 is very noticable.

ISO 100 won't show noticable degradation in image quality until ISO400 with reasonably sized images, even then, its more than workable/saleable from my E500 or E1. ISO800 and even ISO1600 can be cleaned up fairly well if exposed correctly with noise reduction software. DSLRs are much more capable of handling noise than PnSs.

Have you compared the files or just the images produced by the software you are using to interpret the image?

It is quite possible that changing the ISO value does enable amplification of the raw data from the CCR, however then the data is not truly RAW. Any amplification will introduce noise, differing attenuation for different frequencies so color shift, etc.

I suspect that different camera manufacturers will address this problem in different ways. It would be better to leave the raw data alone when it is saved and leave any amplification for post processing in the software.

 

[HowardE]

Have you compared the files or just the images produced by the software you are using to interpret the image?

It is quite possible that changing the ISO value does enable amplification of the raw data from the CCR, however then the data is not truly RAW. Any amplification will introduce noise, differing attenuation for different frequencies so color shift, etc.

I suspect that different camera manufacturers will address this problem in different ways. It would be better to leave the raw data alone when it is saved and leave any amplification for post processing in the software.

I shoot in uncompressed RAW on a Nikon D200, and YES the ISO changes (amplifies) the signal at higher ISO settings. There is definitely noise, and it's not created by the software. When viewed in Nikon Capture, Photoshop CS2, or Windows RAW viewer, I see the same results.

 

[Darnold9999]

As I read it the signal is amplified between the CCD and the digitizer when ISO is increased beyond the CCD's "natural" sensitivity. If below then the signal is reduced post the digitizer. This from the article I quoted earlier.

Wether this amplification produces a better result than post processing amplification is something I am waiting for someone with more expertise in such things to comment on.

 

[HowardE]

As I read it the signal is amplified between the CCD and the digitizer when ISO is increased beyond the CCD's "natural" sensitivity. If below then the signal is reduced post the digitizer. This from the article I quoted earlier.

Wether this amplification produces a better result than post processing amplification is something I am waiting for someone with more expertise in such things to comment on.

The article you posted is interesting for sure.

I would have to say that the "natrual" sensitivity is probably the lowest ISO setting, and the amplification explination sounds valid.

It's easy to see - topside, when shooting outdoors on a cloudy day. For example -

I set up to shoot an outdoor photo.

I use the meter (just did this a minute ago), and set the camera to F10 and 1/100th at 100 ISO. I have a properly exposed photo.

Leaving F stop at F10

If I change to ISO 200 - I can shoot the same shot at 1/200th

and at ISO 400 - I can shoot it at 1/400th.

The real question (which I'll take test shots right now, and post results) is - does amplifying the exposure and adjusting the levels in the RAW imager yield the same results (noise) as increasing the ISO on the camera body? Which would involve taking an underexposed shot at ISO 100 @ 1/400th and boosting the exposure in RAW.

 

[HowardE]

cropped for maximum magnification of the image -

1/800th F10 ISO 400

1/400th F10 ISO 200

1/200th F10 ISO 100

1/800th F10 ISO 100 - Boosed the Exposure in Photoshop

IMHO - it looks like the boosted 100 ISO photo is very similar in the amount of noise as the ISO400 photo.

These were shot in RAW, and converted to JPEG.

 

[Diver Dennis]

Yes, its called silhouette when the subject is dark against a lighter back ground. Yes, you would need a strobe to properly light the dark areas, increasing the ISO to correct the the dark subject only overexposes the background to the overexposure round file.

Underwater is like turning on a high power blue light coming from above, at that depth everything has a blue cast. The questions is how did the under belly of the lead hammerhead shark come out as pure white, without artificial light? Plus I have seen Mr. Hall's video on TV, as I recall he was using rebreathers and taking those pictures at a depth of 100ft or more. The light from the strobe did not reach the sharks in the background.

I disagree. The strobe must have reached the lead shark to light up the belly unless he did a lot of work in editing the shot.

It may have helped your friends out if they seen Howard Hall's hammerhead shots with a strobe and shooting in an upward direction. Shooting upwards will give you more than enough light to properly expose an image at the lowest ISO, even without a strobe.

This statement is incorrect. You said yourself the subject would be in silhouette.

 

[Darnold9999]

Thanks howarde - my intuition tells me that they should be very similar - i.e. boosting post production (photoshop) and a higher ISO as they are both working with the same result from the CCD device. The difference would be that the enhancement done prior to digitizing might be better because it works with the signal pre digitizing and is "camera specific" i.e designed to work with that CCD in that camera. I suspect the difference is marginal either way so will use whichever is more convenient at the time.

 

[Wayfarer2]

An excellent explanation of exactly what a RAW file is.
Wow could I get another Ex word in that sentience LOL
http://www.luminous-landscape.com/tutorials/understanding-series/u-raw-files.shtml

 

[Darnold9999]

An excellent explanation of exactly what a RAW file is.
Wow could I get another Ex word in that sentience LOL
http://www.luminous-landscape.com/tutorials/understanding-series/u-raw-files.shtml

Interesting article, but doesn't say anything about ISO which if I understand it does change the RAW file because the boost in sensitivity to light is done by boosting the voltage from the CCD before digitizing and creating the RAW file.