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Paul Kay

Member Since 27 Nov 2003
Offline Last Active Yesterday, 12:51 PM
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Posts I've Made

In Topic: Expose to the right?

06 June 2015 - 01:20 AM

When digital information is underexposed, chips will strain to record information in the deeper values, and in doing so will produce digital noise.

Ummmm. The darkest areas in the image will be just that - dark. Noise is only produced when you increase the gain (i.e. amplify the signal), so brightening/lightening shadow areas will increase their noise level - very simple. If they are important (more so than highlights) then underexposing them will lead to increased noise when adjusting later. Its got nothing to do with ETTR and lots to do with exposing for your preconceived requirement of output. ETTR in itself is in essence overexposing and as I have said before, can lead to tonal anomalies. So correct exposure must be made on the basis of the subject. Until we get sensors able to record much wider contrast ratios we are always going to be compromising somewhere. I don't see any real advantage to ETTR even in the low contrast conditions (which we compensate for by using flash) underwater. Gurus are great but actual practice is even better IMO.


In Topic: Clean a domeport inside?

31 May 2015 - 11:06 PM

Selvyt cloths are handy for glass domes (try ebay).


In Topic: Expose to the right?

30 May 2015 - 12:02 PM

I have tried experimenting with ETTR and 'normal' exposure. My personal conclusion is that ETTR offers little if any advantages in practice. My opinion FWIW, is that any increased information supplied by the biased exposure is IMO often undermined by subtle but often irritating shifts in tonality produced when readjusting exposure in post, which then require additional adjustment and on occasion I have found that they cannot be thoroughly compensated for. Blown highlights on the other hand are blown. In situations where the contrast is far too high for the sensor to handle I tend to try to decide what can be blown, if anything, and expose accordingly.

 

On the subject of ISO, I tend, on my land cameras (digital Leicas), never to adjust from base ISO (160) and adjust/compensate underexposure in post. If you think about it, increasing ISO is pre-setting another adjustment in-camera - in this case 'gain'. Software has become good enough to allow 'gain' to be applied afterwards, to an underexposed shot. In many circumstances anyway. Problems do occur if too much ''gain is applied to the deepest shadows where banding can occur. With the Leicas this is almost negligible, on my Canons it can be a problem - clearly they are slightly different somehow (CCD vs. CMOS?).

 

And when all is said and done I've also tried experimenting with 'inadequate exposure' and find that post processing can actually produce very acceptable results from mis-judged exposures. My own personal rules on photographic technique are that there are no rules. Photography is practical, if in doubt about what something will produce, try it and be objective about the results. It can be surprising and disconcerting.  


In Topic: Seacam Silver Housing outfit - Canon 5D Mk1

10 April 2015 - 11:11 AM

SOLD


In Topic: Second thoughts about vacuum systems

28 March 2015 - 07:36 AM

is the force that'll move the o rings not just the pressure difference?

Exerting a force by sucking the 'O' ring inwards from decreased internal pressure when the exterior is subject to air pressure may not be the same as increasing liquid pressure applied from the exterior - I say might, I'm not sure what if any the difference is. Also you would need to take into account the physical 'pre-load' on the 'O' ring due to the housing fastening system. As I said it intrigues me. Sounds simple, but is it?