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Messages - neuroanatomist

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6181
EOS Bodies - For Stills / Re: ISO 50
« on: January 21, 2013, 10:53:28 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?

LOL. Earlier, it was suggested that it means 'Half The Photons' - that seems to be Mikael's definition, anyway.

Really, it's Highlight Tone Priority, which is a way to preserve one stop of highlights in an image (at the cost of an extra stop of noise in the shadows). 

6182
EOS Bodies - For Stills / Re: ISO 50
« on: January 21, 2013, 10:50:48 AM »
My point was in reference to using ISO 50 and ISO 100 at the same aperture/shutter speed - in that case, there's no difference in the highlights in the RAW image files, and ISO 50 would not blow any more highlights (the meter would show a stop of underexposure). In your example, you are talking about changing aperture or shutter speed when going from ISO 100 to ISO 50 to maintain a metered exposure. It's that change in aperture/shutter that's causing the blown highlights, not setting ISO 50, per se.

@sanj - the reason this is relevant, at least to me, is that many times (usually, in fact), I choose aperture and shutter speed for a reason. Aperture is chosen for the desired DoF so I can include/exclude what I want to be sharp in the image, shutter speed is chosen to stop or show motion, as desired.  If those values are dependent variables (fixed for the shot, ISO becomes the independent variable.  In that case, there is no benefit to ISO 50, which was my point.  Of course, given the constraints of my personal range of acceptable ISO values (which is pretty broad on the 1D X!), I still cannot achieve the exposure I want, then I decide where to compromise.

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.

6183
EOS Bodies - For Stills / Re: ISO 50
« on: January 21, 2013, 10:32:00 AM »
i have been writing about shutter speed/ f-stops read back

You have been writing about HTP affecting the amount of light that hits the sensor, read back.

If you spew enough drivel throw enough darts, some are bound to hit the target.

6184
EOS Bodies - For Stills / Re: ISO 50
« on: January 21, 2013, 10:14:15 AM »
Neuro is wrong about 50iso not you.

No, you are wrong about me being wrong.  You often seem completely unable to distinguish between changing aperture and/or shutter speed, which change the actual amount of light reaching the sensor, and changing ISO, which changes only what the sensor does with the light that falls on it, but has no effect on the amount of that light. For someone who professes to understand the principles of photography, that's a key point - one that seems beyond your comprehension.

There's a reason ISO 50 needs to be unlocked to be used. It's not actually ISO 50. It's ISO 100 being reduced in camera to ISO 50. The same as shooting ISO 100 and then in post bringing the exposure down a stop. I would never shoot with it.

Exactly.  There's no real benefit to ISO 50, except perhaps convenience if you're shooting in Av mode and want a stop slower shutter speed.  But if a highlight would be blown at ISO 100 with a given aperture/shutter combo, it'll be just as blown at ISO 50.

Neuro, my tests indicate differently to this. Iso 50 highlights are clearly more blown. I can never contradict you, so please tell where I am going wrong here..

You're not contradicting me at all, and we are both correct.  What I stated was, 1) there is no benefit to ISO 50 and, 2) if a highlight is already blown at ISO 100, using ISO 50 won't help.  Both of those are true (despite Mikael's seeming inability to comprehend them).  What you're showing simply goes further - not only can ISO 50 not save highlights that would be blown at ISO 100, it can actually cause highlights to blow that would not have blown at ISO 100. 

My point was in reference to using ISO 50 and ISO 100 at the same aperture/shutter speed - in that case, there's no difference in the highlights in the RAW image files, and ISO 50 would not blow any more highlights (the meter would show a stop of underexposure). In your example, you are talking about changing aperture or shutter speed when going from ISO 100 to ISO 50 to maintain a metered exposure. It's that change in aperture/shutter that's causing the blown highlights, not setting ISO 50, per se.

6185
EOS Bodies - For Stills / Re: ISO 50
« on: January 21, 2013, 09:46:19 AM »
My 5dmk2 starts at 200 iso if  I enable HTP= 1 stop under 100iso= let fewer photons hit the sensor

Why are you perseverating on this?  Please explain: when the HTP is enabled and ISO 200 is set, the camera is actually exposing at ISO 100...how does that in any way alter the number of photons hitting the sensor?  You seem completely unable to comprehend the simple facts. 

Try to read and study carefully all those other pages you linked earlier.  Let's take it by steps:

  • Enabling HTP does not change the selected shutter speed.
  • Enabling HTP does not change the selected aperture.
  • Therefore, enabling HTP does not change the number of photons collected.
  • (Pause for a moment, and study the above three points carefully.)
  • Enabling HTP results in the camera using a 1-stop lower ISO than selected (although the selected ISO is 'incorrectly' recorded in the metadata).
  • The 1-stop lower ISO means less analog gain applied to the readout from the photosites.
  • The decreased analog gain ('underexposure') reduces blown highlights in the RAW file
  • The RAW converter (in-camera or computer software that recognizes the HTP flag in the metadata) applies a selective tone curve to boost exposure in the low- and mid-tones by a stop, sparing the highlights

What part of the above do you not understand?  In particular, you seem unable to grasp the 3rd bullet point.

It's not complex, yet you fail to understand or acknowledge your errors in comprehension.

6186
EOS Bodies - For Stills / Re: ISO 50
« on: January 21, 2013, 08:15:46 AM »
In HTP  the sensor  has now been hit by  less light/photons



Like I said, clueless.

6187
EOS Bodies - For Stills / Re: ISO 50
« on: January 21, 2013, 07:39:38 AM »
Your statement is only "exactly" right if a sensor's "base ISO" is exactly 100.  For many modern sensors it is close, but even a 5DMk3 is closer to 80 and it appears as though a Nikon D800 is closer to 75.  What this means is that there is some analog gain applied, even at ISO 100... and there will be different analog gain applied at 50.

Sorry to be pedantic... I don't want to derail what you're saying.... I just want people to realize that not everything about a camera sensor is set in stone by a god somewhere... and each and every sensor type has it's own unique aspects... :-)

Sorry, friedmud...you're late to the proverbial pedantic party...my own pedantry preceded yours by about 37 posts...  ;)

TrumpetPower is absolutely correct in his statement that, "ISO 50 and highlight tone priority are two special cases. The exact same analog signal amplification (i.e., none) is applied with all three exposures: ISO 50, ISO 100, and ISO 200 w/ HTP. If you use the same shutter speed and aperture, you'll get the exact same raw file in all three cases." (well, almost correct - the base ISO isn't exactly 100 for all sensors, so even at ISO 100, some gain may be applied - but it is the same gain in all three cases).

6188
EOS Bodies - For Stills / Re: ISO 50
« on: January 21, 2013, 07:10:55 AM »
That's exactly what you said... "HTP. it is a halving of infaling light" are your exact words.  Even this last statement from you is not even internally consistent.
no I said by using HTP it is like underexpose  1 stop, go away from 100iso  by an under exposure which well be equal to a 200iso exposure   and thereby make a head room=  which later can compensates with gain and curves

Really?  You didn't say, "HTP. it is a halving of infaling light," and you're sure about that??

Let's check.  You said:

HTP, here you have exposed the motive 1 stop shorter, halving the number of photons and you get a High light head room and then another curve is  applied with a lift in lower areas/levels and a softer curve at the top / high lights
Here 100iso are exposed as i where  200iso  which means 1 stop shorter exposure , the sensor collect less photons who are converted  in to a charge/signal.

...and you then said:

HTP. it is a halving of infaling light

Sure, you also talked about HTP underexposing by a stop.  But for you to deny claiming the light was halved is stubborn intransigence, and a complete lie...a particularly foolish one, too, given that your previous statement that you deny making is there for all to read, and easily catch you in your transparent lie of denial.  The second one, "HTP. it is a halving of infaling light," I could accept as linguistic confusion...but it followed the earlier statement where you talk about halving the number of photons, the sensor collecting less photons, and a 1-stop shorter exposure being used, all as a description about how HTP achieves the highlight recovery. That's not linguistic semantics and typos as Aglet suggests, that a very concise, understandable description where it's quite clear what you mean...it's just WRONG.

But...not only can you not admit being wrong, you deny you even made the statements quoted above.

Moreover, you also stated:

You Neuro and others seems to have a very hard time  to admit that you are wrong .


It is manifestly clear that YOU are the one unable to admit when he is wrong.

At least you were right about one thing:

it is hard  to discuss HTP etc if you do not know what it means

You are obviously having a hard time discussing HTP, because while you appear to understand the consequences in terms of highlight recovery and increased shadow noise (or at least, you can parrot the statements of others who understand that), you haven't got a clue about the image data manipulations that underlie HTP, as clearly shown by your flat out wrong description of a shorter exposure leading to halving the incident light for the exposure. 

6189
EOS Bodies - For Stills / Re: Canon 5d Mark III Eyepiece cover
« on: January 20, 2013, 11:46:05 PM »
Has anybody managed to found a custom viewfinder with a lever for 5D III?
I'm really annoyed with swapping the cover and eyepiece that came with camera. I'll lose one or another sooner or later.

I used to just hang the lens cap from the eyecup.  Always with you, easy, and blocks the light.

6190
EOS Bodies - For Stills / Re: ISO 50
« on: January 20, 2013, 11:42:55 PM »
that is not what Im saying...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.

...and apparently, by the HTP setting as well, which reduces by half the number of photons reaching the sensor.  Or so you stated earlier, in multiple posts and more than one way:

HTP, here you have exposed the motive 1 stop shorter, halving the number of photons and you get a High light head room and then another curve is  applied with a lift in lower areas/levels and a softer curve at the top / high lights
Here 100iso are exposed as i where  200iso  which means 1 stop shorter exposure , the sensor collect less photons who are converted  in to a charge/signal.

HTP. it is a halving of infaling light

Do you stand by those assertions, Mikael?  ::)

That's exactly what you said... "HTP. it is a halving of infaling light" are your exact words.  Even this last statement from you is not even internally consistent.

Factual consistency does not seem to be one of Mikael's strong suits...  But in other ways, he's quite consistent - his use of bold text, his derogatory questioning of others' understanding coupled with urging others to 'read' and 'try to understand', his repetition of the same statements in post after post, in these and similar areas, he seems consistent to the point of boredom.

6191
Software & Accessories / Re: Black Rapid and dropped camera?
« on: January 20, 2013, 09:46:15 PM »
My use case is, for example, hiking. I've got the big LowePro backpack, and there just is no way to have the camera out while your on the trail without simply holding it with that pack. I'm hoping that the strap will afford some carrying ease, plus be ready for landscape shots.

I often wear a BR strap in conjunction with a loaded Lowepro Flipside 400 AW while hiking. The BR strap goes against my back, under the pack, but in front the BR strap goes over the backpack shoulder straps, and the camera hangs down just under the pack.  With the BR strap, I can easily slide the camera up the strap like that to grab a shot, but since the camera strap is held in place by the pack, a 'fixed' clamp/strap cannot slide.

6192
Software & Accessories / Re: Black Rapid and dropped camera?
« on: January 20, 2013, 09:20:34 PM »
Anyhow just the other day I found a solution I like, the kirk security strap

I've run across this before. The problem I see with it is that you're giving up the 'rapid' part of the Blackrapid - the fact that the strap stays in place and the hardware slides freely up the strap.  That makes raising the suspended camera to your eye fast and easy, without the strap bunching up or friction of the strap/pad trying (or failing) to slide on your shoulder slowing things down. The way Kirk describes it, it's intended for 'keeping a second camera or lens handy' not for a primary strap for the in-use camera.

If you've ever tried just slinging the Canon neck strap over your shoulder, the Kirk strap seems similar, at least in theory.  I'm interested to hear your impressions when you get it!

6193
EOS Bodies - For Stills / Re: ISO 50
« on: January 20, 2013, 08:26:57 PM »
Thanks for explaining Trumpetpower & Dr. Neuro (which I usually trust to be correct), htp & iso50 aren't self-explanatory and hardly documented anywhere - and in other articles there's still the theory that htp does some magic because it's done inside the image pipeline - probably because no one knows the exact tone curve Canon is applying.

Yep.  Most RAW converters see the HTP flag in the metadata, and apply their version of Canon's tone curve. But some RAW converters ignore the metadata flag (e.g. Rawnalyze) and just show you the 1-stop underexposed image as it's actually recorded in the RAW image data.


6194
EOS Bodies - For Stills / Re: My next upgrade...
« on: January 20, 2013, 08:17:20 PM »
I don't know, I've never flown with it. I just stick the pod in whatever carry on bag (clothing) I'm bringing. The rest of my camera gear goes in a dedicated photo bag, from a Lowepro Pro Runner 450 when loaded up, to a Think Tank Urban Disguise 40 v2.0 when traveling light. I save the Pelicans for when I'm going to extreme places cause they be heavy.

Gotcha. I usually pack the gear in a Lowepro Toploader + Lens Case(s), Flipside 300 or 400 AW (depending on how much), then put that in the Storm im2500 for the flight, in case I'm forced to gate-check it (full overheads on airlines where I don't have priority boarding, or regional jets where the bins are too small).  That way, I have protection during the flight, and a way to carry my gear around at my destination. 

6195
Lenses / Re: 24mm 35mm 70mm FoV
« on: January 20, 2013, 07:30:06 PM »
Agree with LostArk as to using one lens vs. another.

But it sounds like you're just trying to get an idea of the different FoVs, framing regardless of perspective, similar to how I often recommend setting a zoom lens to specific focal lengths to help choose the right prime for your needs, but obviously the reverse doesn't work.

This FoV calculator may help: http://www.bobatkins.com/photography/technical/field_of_view.html

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