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Messages - TrumpetPower!

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511
"As I already explained, it is a question of how much enlargement is necessary for a print."

this is about pixels, no film, as long you have 1,6 times better lenses and use f8  and the signal/noise is equal
from the  APS 24 mp  and the  24 mp 24x36 there is no enlargements advantages with 24x36
It is a pure optical question= we need 1,6 better lenses on the APS

Mikael, if what you wrote were true, then a 4000 ppi, 22 megapickle scan of a 35mm negative would produce just as good an 8" x 10" print as a 500 ppi, 20 megapickle scan of an 8" x 10" negative from a view camera. Or, that a 5DIII would make as good a print as a 20 megapickle 8x10 view camera back.

It would also mean that this 18 megapickle toy:

http://www.amazon.com/Cybersnap-1018-Micro-Digital-Camera/dp/B007PVMKPU/ref=sr_1_35?s=photo&ie=UTF8&qid=1358787121&sr=1-35

would beat the pants off of the original 1Ds with its wimpy 11 megapickles.

And that assertion is so laughably idiotic that there's no point in further discussion with you.

Seriously, dude. Get a clue. You're in more need of one than any I've seen here in a looooooooong time.

Cheers,

b&

512
EOS Bodies - For Stills / Re: ISO 50
« on: January 21, 2013, 11:38:28 AM »
Regardless of camera brand I often recommend using 'HTP' or whatever acronym a particular brand has chosen to signify a more gentle contrast curve towards the clipped highlights when shooting outdoors in sunny weather. -But for jpg shooters only!.

There's some slightly better and simpler advice you could offer JPEG shooters: do whatever you have to to make the image on the back of the camera look the way you want it to. Those on-camera knobs are the only ones you have to fiddle, so fiddle with them until you're happy with the result.

And HTP is an excellent in-camera implementation of "ETTL" (expose-to-the-left) post-processing, and perfect for situations where you care about highlights and won't see noise in shadows. Similarly, ISO 50 does a great job of doing exactly what ETTR does, when it's shadow noise you're worried about and don't care if the highlights blow. If you're shooting JPEG, you should know what each does and when to use either -- as well as when not to use them.

But, if you're shooting raw (and, generally, you should be if your post processing is much more than picking keepers), you should also understand what HTP and ISO 50 are doing, and why you're better off doing what they do yourself. Maybe it's an especially contrasty scene, and a single stop of ETTL isn't enough to keep those highlights you're so interested in, so you'll want to underexpose not by one stop but by two stops, for example.

Cheers,

b&

513
I think S/N based on area (where number of photons captured per unit time is proportional to area) varies fundamentally as the square root of ratio of areas. So increasing area by 2.5x improves S/N only by 1.6x. (I do know other factors do come in, but the basic statistics of S/N is a sqrt relationship).

You're correct about the actual numbers, of course. I didn't mean to imply a specific numerical relationship, which is why I tried to phrase it as loosely as I did.

With each standard increase in format, you gain an effective (roughly) one stop of ISO performance. If you're happy with ISO 400 on 4/3, you'll be happy with ISO 800 on APS-C, and with ISO 1600 on full frame, and ISO 3200 on medium format -- with a big, honkin' caveat that different manufacturers are using different technologies with their sensors in each segment. In the real world, it's more like ISO 100 on APS-C has half the noise as ISO 100 on 4/3, and so on...your MF back might not actually do all that well at ISO 3200, but its ISO 200 will be at least as clean as ISO 100 on full frame.

And, of course, we're also talking about actual prints, not pixel peeping or other meaningless measures.

Cheers,

b&

514
EOS Bodies - For Stills / Re: ISO 50
« on: January 21, 2013, 10:56:44 AM »
But the key point is that ISO 50 offers no benefit, and can in some cases result in a detriment - therefore, I see no reason to use it.

I, too, have no use for ISO 50 nor HTP. But I would find it useful if I were shooting JPEGs with no intention of post-processing, or if I were planning on doing ETTR or ETTL (respective) exposure and wanted a closer preview image on the back of the camera -- say, if a clueless client were looking over my shoulder.

Cheers,

b&

515
EOS Bodies - For Stills / Re: ISO 50
« on: January 21, 2013, 10:53:18 AM »
Here is the dumbest question in the thread, but since I am the one that made the test, could I please ask what is HTP?

Not dumb at all. I've tried to expand the acronym at appropriate places, but obviously not everywhere it's appropriate.

HTP stands for Highlight Tone Priority. Rather than ISO 100 being the lowest selectable ISO, ISO 200 becomes the lowest selectable ISO. The camera actually exposes at ISO 100 but applies a tone curve to brighten the image. This has the end result of recording more highlight detail, but there's no such thing as a free lunch, so you get nosier shadows at the same time. If you're shooting raw, you can achieve the exact same result by shooting at ISO 100, underexposing by a stop, and brightening the image by a stop in post-production (with, of course, highlight compression to avoid digital clipping).

Cheers,

b&

516
EOS Bodies - For Stills / Re: ISO 50
« on: January 21, 2013, 10:48:18 AM »
The important part where you're talking straight past each other seems to be this:
If you let the camera chose exposure, it will overexpose in ISO50
In manual exposure mode it makes no or very little difference between ISO50 and ISO100
None of you seem to disagree on this, so I fail to see the problem.

TheSuede, your two-line summary is correct (if, naturally, a bit oversimplified), but that's not what Mikael has been writing. And when neuroanatomist and I have been writing that, Mikael has been arguing that we're worng.

Cheers,

b&

517
This assumes that you also always print the full frame. For some cropping is always required.  If you crop the same image to the same composition your results may vary.  We don't always have the luxury of filling the frame especially when using a prime lens in less than adequate quarters.

If you're shooting side-by-side with a 7D and a 20mm prime, a 5DIII and a 35mm prime, and an 8x10 view camera and a 250mm prime, you're going to be cropping away the same proportional amount to get the same composition from each, rendering the cropping point moot.

If you're distance-limited, sure, it can make a difference...but generally not at much as most people tend to think. If that little birdie only fills an eighth of your frame with the 800mm f/5.6 on the 5DIII, you'll get better results putting the lens on the 7D, but not hugely better. The real answer is to improve your tracking skills so you can get closer and fill the frame, with whatever camera / lens combination.

Cheers,

b&

518
EOS Bodies - For Stills / Re: ISO 50
« on: January 21, 2013, 10:23:49 AM »
Mikael, let's try to make this even more simple.

Consider that you've got four cameras and one tripod set up in a studio. All four cameras are 5DIIIs, and all four have 50mm f/1.4 lenses attached. The tripod is fixed and the lighting (continuous, not flash, just to keep things simple), is held constant. All we're doing is swapping out cameras, focussing on the same spot, and releasing the shutter.

All four cameras are set in manual mode to record to raw (no JPEG), with the following settings:

Camera A: 1/100s @ f/8 @ ISO 50
Camera B: 1/100s @ f/8 @ ISO 100
Camera C: 1/100s @ f/8 @ ISO 125
Camera D: 1/100s @ f/8 @ ISO 200 + HTP

If you then examine each of the four raw files, you will find that the only difference is in the metadata.

Now, we shoot as follows:

Camera A: 1/200s @ f/8 @ ISO 50
Camera B: 1/100s @ f/8 @ ISO 100
Camera C: 1/80s @ f/8 @ ISO 160
Camera D: 1/50s @ f/8 @ ISO 200 + HTP

What we now discover is that each raw file is different.

Let's assume that there was a gray card in the scene. And let's pick a completely arbitrary number of 100 to indicate the average pixel value of that gray card in the 1/100s @ f/8 @ ISO 100 exposure.

What we discover is the following values for that gray card in each of the raw files:

Camera A: 1/100s @ f/8 @ ISO 50: 100
Camera B: 1/100s @ f/8 @ ISO 100: 100
Camera C: 1/100s @ f/8 @ ISO 125: 100
Camera D: 1/100s @ f/8 @ ISO 200 + HTP: 100

Camera A: 1/200s @ f/8 @ ISO 50: 50
Camera B: 1/100s @ f/8 @ ISO 100: 100
Camera C: 1/80s @ f/8 @ ISO 160: 125
Camera D: 1/50s @ f/8 @ ISO 200 + HTP: 200

Now, we're going to try another experiment, shooting the last series, but all at ISO 100. This is what we get:

Camera A: 1/200s @ f/8 @ ISO 100: 50
Camera B: 1/100s @ f/8 @ ISO 100: 100
Camera C: 1/80s @ f/8 @ ISO 100: 125
Camera D: 1/50s @ f/8 @ ISO 100 + HTP: 200

Finally, we're going to do one last pair of experiments with a different set of ISO values. Here're the results:

Camera A: 1/100s @ f/8 @ ISO 100: 100
Camera B: 1/100s @ f/8 @ ISO 200 (no HTP): 200
Camera C: 1/100s @ f/8 @ ISO 400: 400
Camera D: 1/100s @ f/8 @ ISO 800: 800

Camera A: 1/100s @ f/8 @ ISO 100: 100
Camera B: 1/200s @ f/8 @ ISO 200: 100
Camera C: 1/400s @ f/8 @ ISO 400: 100
Camera D: 1/800s @ f/8 @ ISO 800: 100

If that doesn't clear it up, nothing will....

Cheers,

b&

519
EOS Bodies - For Stills / Re: ISO 50
« on: January 21, 2013, 10:00:33 AM »
TheSuede, thanks for the details and corrections on the workings of the electronics!

b&

520
EOS Bodies - For Stills / Re: ISO 50
« on: January 21, 2013, 09:52:37 AM »
50iso is no 50 iso, it is equivalent to 100 iso over exposed 1 stop, what you gain is for example  slower exposure time which can be handy , running water etc but at the same time that the sensor is richer exposed you lose 1 stop of DR and that is in the highest levels= earlier clipping

Thank you for the explanation. To me, when I re examine the photos based on what you saying, it seems like ONLY the whites are getting overexposed, NOT the entire frame. Could I conclude that not the entire frame but only the whites get over exposed?

sanj, I would strongly recommend ignoring everything Mikael is writing in this thread. He's very, very worng.

If you shoot with the same aperture and shutter at both ISO 50 and ISO 100, you will get the exact same raw file. When you open it in Lightroom (or wherever), it's starting with the same raw data, but it sees the ISO metatags are different and so, before doing anything else to the image data, it divides all the numbers in the ISO 50 shot by 2.

When you set ISO 50 on the camera, it tells the meter to change by one stop, so the common workflow would be to expose the ISO 50 shot one stop brighter. When you then open it, Lightroom first divides all the values by 2, which gives you the appearance of a file that looks properly exposed. But it wasn't actually exposed at ISO 50, which doesn't actually exist in the camera; it was really exposed at ISO 100. And, just as if you had actually exposed it at ISO 100 and applied one stop of darker exposure compensation in Lightroom, you'd discover you had lost one stop of highlights, you always lose one stop of highlights with ISO 50.

Cheers,

b&

521
Let us say that you have a APS sensor 24Mp with the same S/N as a  24Mp 24x36 sensor then it is an optical question, it is hard to make a APS  lens 1,5 1,6 times better which is require compared to 24x36mm lens.

This is incorrect.

Because there will be less absolute magnification for a same-sized print with the larger format, even if the sensors have the same pixel dimensions, the larger format will be sharper and have less noise. Again, always assuming all else is comparable, including a longer focal length lens for the larger format.

Cheers,

b&

is it, if the S/N and Mp  is the same from the two sensor areas, then it must be an optical question , and there the APS lenses must be 1,5  1.6 better than the  24x36mm lens.

As I already explained, it is a question of how much enlargement is necessary for a print.

If you're making a 24" x 36" print, the APS-C image will be enlarged 41x from the sensor's original size of 14.8mm x 22.2 mm, but the full-frame will only be enlarged 25x from the sensor's original size of 24mm x 36mm.

Whether you measure S/N in noise per pixel or noise per square mm of sensor, because you've got two and a half times as many square mm of sensor per pixel with the larger format, you're getting that much better of an overall signal to noise ratio.

Imagine you were back in the days of film. You have a 35mm camera loaded with Velveeta on one tripod and an 8x10 view camera loaded with the exact same film on a second tripod. The 35mm camera has a 50mm lens and the view camera has a 400mm lens, both of which give the same normal field of view on the respective cameras.

You'd agree that, since it's the exact same film, the exact same chemistry, that the S/N ratio is exactly the same, right?

Now, let's say we're making an 8" x 10" print from the exposure. The 35mm negative needs to get enlarged 7.5x to make the print, but, for the view camera, it's a contact print.

If you don't agree that the contact print from the view camera will be dramatically sharper and have far less grain than the enlargement from the 35mm camera, then you truly are hopeless.

Now, you might still argue that the pixel dimensions are relevant, but I'll show they're not.

Let's not use traditional printing methods, but rather scan the film. But we want to wind up with the same megapickle files for both, to simulate this contrived example. We're going to scan the 8x10 negate at a lowly 300 ppi, and we're going to scan the 35mm negative at a whopping 2250 ppi. We're still going to make an 8x10 print, and we're going to do it at 300 ppi. And, because of the resolutions I picked, it "just happens" that no interpolation of either file is necessary; both will still print at 300 ppi at 8" x 10".

Once again, if you still don't think that the print from the 300 ppi scan of the view camera's negative will blow away the 2250 ppi scan from the 35mm camera, you're hopeless.

Cheers,

b&

522
EOS Bodies - For Stills / Re: ISO 50
« on: January 21, 2013, 12:10:37 AM »
The so-called analog gain is applied prior to readout[. . . .]

Because the readout is the point where the signal logically leaves the sensor, it should be self-apparent that analog gain must be applied by the sensor itself to the signal before (or as) it is read out.

You're of course correct that expanded high ISOs are again digital simulations and not analog processes, but I suspect your cutoff of ISO 1600 only applies to very old cameras. I may be mistraken, but I'm pretty sure that digital ISO boost only happens with expanded ISO settings. With the 5DIII, native (analog) ISO should extend all the way to ISO 25,600...but I wouldn't bet more than a cup of coffee on that exact number.

Cheers,

b&

523
Let us say that you have a APS sensor 24Mp with the same S/N as a  24Mp 24x36 sensor then it is an optical question, it is hard to make a APS  lens 1,5 1,6 times better which is require compared to 24x36mm lens.

This is incorrect.

Because there will be less absolute magnification for a same-sized print with the larger format, even if the sensors have the same pixel dimensions, the larger format will be sharper and have less noise. Again, always assuming all else is comparable, including a longer focal length lens for the larger format.

Cheers,

b&

524
EOS Bodies - For Stills / Re: ISO 50
« on: January 20, 2013, 11:28:48 PM »
that is not what Im saying, every iso step =is a halving of the number electroner, the sensor has no knowledge of iso at all, it collects photons  and the number of photons / electrons is determined by time and the light inlet.

That is an absolutely incorrect statement.

With the now-beaten-to-death exceptions of ISO 50 and HTP, ISO is entirely a function of the sensor. As I've repeatedly attempted to explain, with increasing ISO the sensor applies increasing amounts of analog amplification, and all this happens on the sensor, well before the analog signal is digitized.

Yes, the number of photons that impinge upon the sensor is dependent upon the aperture and shutter (and, of course, the luminance of the scene as projected by the lens). But the number of electrons that reach the analog to digital converter (ADC) depends on how much analog amplification the sensor applies to the readout -- and the amount of amplification is directly set by the user (or the autoexposure system) with the ISO control.

With ISO 50, 100, and 200+HTP, the number of electrons per photon is the same. With ISO 200 (without HTP), thanks to analog amplification, twice as many electrons per photon make it to the ADC. The number of electrons per photon is doubled again with each additional stop of ISO.

(As a side note, "inbetween" ISO settings, those not powers of two times 100 or whatever the base ISO is, are again, with most camera systems, achieved by digital pushing or pulling from the nearest full-stop ISO. ISO 125 produces the same raw file as ISO 100 but with a metadata flag telling the raw processor to add 1/3 stop of digital push, and ISO 160 is really ISO 200 with 1/3 stop digital pull.)

And just, to further clarify what digital versus analog exposure adjustment means...if you were to write a computer program that translated the data in a raw file into a massive spreadsheet, divide every number in the spreadsheet by 2, and then translate from the spreadsheet back to the original raw file format, you'd do exactly the same thing that ISO 50 does. If you were to translate ISO 50, ISO 100, and ISO 200+HTP (assuming identical scenes, apertures, and shutter speeds) files each into separate spreadsheets, they'd all have the exact same numbers in them. But, if you exposed at ISO 200 (without HTP, but still keeping the shutter and aperture and everything else the same), the numbers in your spreadsheet would be twice as big...but they'd also have a higher standard deviation, indicating additional noise due to the distortion from the higher analog gain applied to the sensor readout. If you then, say, made the shutter a stop faster, the ISO 200 numbers would be back in line with the ISO 100 numbers, but you'd still have a higher standard deviation because of the additional noise from the increased analog amplification.

I really don't know how to express this any more clearly. If you still don't understand, then perhaps you should explain how you think the whole shebang actually functions, rather than just vaguely handwave about photons and electrons with unspecific and irrelevant references to Web pages that actually describe things correctly, and the opposite of what you describe.

Cheers,

b&

525
Once again, all else is clearly not always equal. If all you've got is a 300mm lens and you want to shoot the full disc of the moon, yes, of course, you're going to get better results from that lens with a 7D than a 5DIII. But the guy next to you with a 5DIII and a 1200mm f/5.6 is going to get an image of the moon that puts yours with your 7D to shame. And the guy the next hill over, the one with a 32" Dobsonian? Well....

yeah..... but is the guy on the last hill hand-holding the 32" Dobsinian? And if he is, who's going to argue with him?

The <a href="http://hubblesite.org/">gang down south</a> might be able to give him a good run for the money....

b&

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