November 25, 2014, 05:35:07 PM

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Messages - Lee Jay

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196
The reason ISO 100 on a Canon has roughly the same DR as ISO 400 is because the read noise drops by about a stop with each progressive increase to ISO. Hence the flattening of the DR curve on Canon sensors.

Well, it's not that the read noise drops, it's just that all other data & noise off the sensor is amplified 4x compared to ISO 100, which lowers the impact of the read noise. So even though you're throwing away 2 stops of highlight range at ISO 400, 4x (2 EV) darker signal is now being amplified to be brought up to your SNR = 1 (or what have you) threshold, leaving DR largely the same. Cameras with very little downstream read noise don't need the sensor signal amplified to overcome the 30+ electrons of read noise in a Canon camera.

I think there is more to it than that. There is something else going on that flattens the curve relative to read noise at lower ISO, because once your past ISO 400, then you get that linear fit that matches the ideal DR curve. ISO 100 on a 5D III has 33.1e- RN. That is noise added to the signal AFTER the pixels are read (well, after they are amplified and shipped off the sensor, during read). At ISO 200, the pixels are amplified, then read. Since the RN is added down stream, logically, you should still have 33.1e-...the signal was already amplified, so it's still the same strength at this point as an unamplified ISO 100 signal. Similarly, at ISO 400, the pixels are amplified even more, then read. Since RN is added down stream, logically, you should still have 33.1e-. The information coming off the sensor always effectively represents a signal with the same strength, since it's being amplified there before readout.

Your explanation doesn't really explain why read noise drops with higher ISO settings. I don't know exactly why it drops, ...

Yeah, it does.

Let's say, for sake of argument, that 1V = 10,000e- at ISO 100.
Let's say the analog noise is 10mv.  10mV * (10,000e-/1V) = 100e-

Now, let's say that 2V = 10,000e- at ISO 200.
We still have 10mv of analog noise.  10mV * (10,000e-/2V) = 50e-

Got it?

197
It looks like the sensorgen.info domain has expired, so I can't provide any references.

https://web.archive.org/web/20140708054926/http://sensorgen.info/

Case in point:

7D: 8.3e- (4.3µm)
70D: 13.5e- (4.11µm)

6D: 26.8e- (6.6µm)
5DIII: 33.1e- (6.25µm)

Cameras with smaller pixels sometimes have more read noise. Read noise doesn't really have that much to do with pixel size...it has to do with downstream electronics, like the ADC.

https://web.archive.org/web/20140715201224/http://www.sensorgen.info/CanonPowershot_G15.html

The reason the read noise scales with pixel size is that well capacity does.  If you need more range to capture a larger voltage, you get more noise at the smaller voltages.

199
Read noise aside, larger sensors have more dynamic range.

Yeah, but that's misleading, because read noise scales (down) along with size (well capacity), so DR isn't strongly affected by pixel size.

200
Back up a second. So even if you shoot RAW the histogram in camera is only displaying the color space you've chosen?

And the in-camera processing (especially contrast and saturation) you've chosen.

201
I was not going to make a big case out of this, but what you see on the camera is what you see on the camera. You need to be able to read that properly. And yes, what you see there is nor correct, but you need to judge your settings based on what it tells you. At least that's what I do. The histogram I referred to was LR, looking at the Raw files. If that is incorrect also, I'd appreciate a clarification.

The default conversion gives you much less dynamic range than is available in the raw data.  Even if both highlights and shadows are clipped in the default conversion, using -highlights and +shadows may recover several stops of DR from the ends of the histogram.

202
I am still amazed over the number of posts this topic is able to produce. I hope Canon is paying us some attention.

To me it is rather simple. If I shoot images and the histogram shows I have covered what I wanted covered, I am, from a DR perspective, good. If the histogram shows that I hit either the floor or ceiling, I'm either irritated over a poor exposure setting, or, especially when I'm in the basement and through the roof, with shadows black and highlights blown, in the same picture, I want more DR. I have quite a few of those, where I have to choose which end I want to give priority and have black shadows or blown hightlights in the other end.

Yes, I could in some cases use HDR and bracketing, but as Lee Jay also points out, when things are moving I find that to be a poor option at best. People, wind in trees, flowing water etc. requires one-shot images.

For people to form their own opinion, I suggest they go back and study the histograms of some of their more contrasty images and see how many (if any) would benefit from more DR.

The in-camera histogram?  The histogram of the default raw conversion?  What histogram are you talking about?

203
Well I have to say I sure as heck could've used more DR the last few days. On a fast pace, with others some of whom were not into photograph, tons of ground to cover, often fast changing and soon fading light, so much to see, even when multi-shot tripod HDR would've worked only had time to set up the tripod once.

You don't need a tripod to shoot an HDR.  In fact, you don't even need one second.  Just shoot a bracketed burst, and use software to obtain perfect alignment in post.

204
Post Processing / Re: Fast editing of RAWs to "camera like" Jpegs
« on: October 04, 2014, 12:30:54 PM »
I haven't uses Canon's software in many years, but they used to provide something called Raw Image Task which would convert a raw image into a JPEG that was bit-for-bit identical with an out of camera JPEG taken in camera using raw + JPEG.  Do they still do that, or does DPP have similar functionality?

205
...I think in the end the D810 is really going to be the Exmor-equipped camera for landscapes.

I'd personally dismiss it for the lack of an AA filter alone.  I'd never be able to trust it for that reason.

206
Okay, I'll provide an image from a high DR scene, that's actually a picture I wanted, not just a test.  This was taken at ISO 100 on a Rebel T2i and it was exposed such as to reduce, but not eliminate, blow out of the raw data on the bright pixels at the top of the image.  In other words, this was about as much exposure as I could give it without further blowing out the raw data on the top of the frame.

See what you think of the technical performance here, by seeing what you can make of the image.

http://tinyurl.com/neof9y4

207
EOS Bodies / Re: Next Rebel Going EVF? [CR1]
« on: October 03, 2014, 02:06:27 PM »
Canon released a new EF-s lens this year - the 10-18IS STM.  They released two new EF-s lenses in 2013, the 18-55IS STM and the 55-250IS STM.

So, from March 21st, 2013 to now, they've released three lenses that cover a 16mm to 400mm equivalent zoom range for the EF-s mount.

You forgot the EF-S 24 / 2.8 pancake.
On the other hand i would not count iterations of the kit zoom or the 55-250 as "new lenses".

Gee...I didn't even realize the 24/2.8 was an EF-s!  I really pay very little attention to slow primes.

These aren't just version II, III and IV of the kit lenses (like all the 28-80s and so on), they are genuinely new in that they use STM focusing systems.  So I think they're worthy of being "new lenses" especially since they still sell the old ones.

208
EOS Bodies / Re: Next Rebel Going EVF? [CR1]
« on: October 03, 2014, 01:51:59 PM »
I just don't see Canon dumping EF-S any time soon...

But they're probably not advancing it further, either. Look at the last lens releases, esp. at the 16-35L/4 with IS with is just made to be a sturdy "standard" zoom on a 20mp crop camera...

Canon released a new EF-s lens this year - the 10-18IS STM.  They released two new EF-s lenses in 2013, the 18-55IS STM and the 55-250IS STM.

So, from March 21st, 2013 to now, they've released three lenses that cover a 16mm to 400mm equivalent zoom range for the EF-s mount.

209
Do you really believe the goal was to "preserve the view out of the window".

The goal was to do a dynamic range test BY preserving the view out of the window.

210
I see what you tried to do with this thread jrista, and while it does show that the A7R's sensor is superior to the 5D3's at the settings you used, unfortunately the fanboys have gone on the defensive and resorted to borderline bullying.

He has deliberately drastically under exposed to try to prove his theory.

The images are NOT underexposed if the goal is to preserve the view outside the windows.  In fact, some of the pixels from the windows are blown out in the raw data.

Now, if you don't mind all-white windows, then the images are underexposed.

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