Understanding HDR from a photographer's perspective.

tirediron

Watch the Birdy!
Staff member
Supporting Member
Joined
Jul 8, 2005
Messages
45,747
Reaction score
14,804
Location
Victoria, BC
Website
www.johnsphotography.ca
Can others edit my Photos
Photos OK to edit
Have a nice day!
 

table1349

Been spending a lot of time on here!
Joined
Sep 9, 2006
Messages
0
Reaction score
2,772
As a member of the "Photographic Community," mind you I am only speaking for myself as a member, I have but one thing to say. "Yawn...." ( I must have missed the election of spokesman for the photographic community or was it on the Florida ballot in 2004?)

This whole discussion reminds me of the workings of our sun.

Fusion in the Sun step by step

The overall fusion reaction 4 1H + 2 e --> 4He + 2 neutrinos + 6 photons happens in several steps. (This is not different from methane burning, which also happens in steps.)
Step 1

1H + 1H --> 2H + antielectron + neutrino
fusion1.gif

This step is nearly impossible.
  • The protons repel each other because they both have + 1 charge.
  • They have to get within 10-15 m of each other for the strong interactions to hold them together.
  • One of the protons has to change into a neutron (emitting an anti-electron and neutrino).
    • This requires a weak interaction.
    • But the chance of this weak interaction happening just when the protons are together is almost zero.
This near impossiblity has two consequences:
  1. The gas must be very hot, so that the protons hit each other with high speed.
    • This lets them get near to each other, even though they repel each other.
  2. Even so, the reaction is very rare. That is why the Sun is still burning after 4.6 billion years!
Step 2

electron + antielectron --> photon + photon
fusion2.gif

The antielectron soon hits an electron. They annihilate to make two photons. (These high energy photons will be absorbed in the gas, eventually giving lots of low energy photons.) Step 3

2H + 1H --> 3He + photon
fusion3.gif

The 2H hits a proton and sticks to it, making a 3He and emitting a photon in the process. (This high energy photon will be absorbed in the gas, eventually giving lots of low energy photons.) Step 4

3He + 3He --> 4He + 1H+ 1H
fusion4.gif

Since these reactions make 3He nuclei, there are some of these bouncing around in the gas. When two of them hit each other, the 2 neutrons and 4 protons of rearrange themselves into one 4He nucleus and two free protons. Note that steps 1,2 and 3 each happen twice for each time step 4 happens.
The net result is
1H + 1H --> 2H + antielectron + neutrino
1H + 1H --> 2H + antielectron + neutrino
electron + antielectron --> photon + photon
electron + antielectron --> photon + photon
2H + 1H --> 3He + photon
2H + 1H --> 3He + photon
3He + 3He --> 4He + 1H+ 1H
That is
6 1H + 2 e --> 4He + 2 1H + 2 neutrinos + 6 photons
or
4 1H + 2 e --> 4He + 2 neutrinos + 6 photons
The amount of energy released in each separate reaction has been measured. The net energy release is 26 MeV. There are some other reactions also. They are less significant because they don't produce much energy. [For this reason, please don't try to memorize them.] But they have a special significance because they produce neutrinos, which we will study.
  • 3He + 4He --> 7Be + photon
    • 7Be = (4 p + 3 n)
  • 7Be + electron --> 7Li + neutrino
    • 7Li = (3 p + 4 n)
  • 7Li + 1H --> 2 4He
  • alternatively
    • 7Be + 1H --> 8B + photon
      • 8B = (5 p + 3 n)
    • 8B --> 2 4He + antielectron + neutrino
There is another energy producing cycle that is important in hot stars (temperatures bigger than 16 x 106K). It is called the CNO cycle. In it, carbon is a catalyst. It is needed to make the reaction work, but is not used up. [Again, I would suggest that you not memorize the cycle, but do understand the concept of a catalyst, which is important in practical chemical reactions.]
  • start with 12C
    • 12C = (6 p + 6 n)
  • 12C + 1H --> 13N + photon
    • 13N = (7 p + 6 n)
  • 13N --> 13C + antielectron + neutrino
    • 13C = (6 p + 7 n)
  • 13C + 1H --> 14N + photon
    • 14N = (7 p + 7 n)
  • 14N + 1H --> 15O + photon
    • 15O = (8 p + 7 n)
  • 15O --> 15N + antielectron + neutrino
    • 15N = (7 p + 8 n)
  • 15N + 1H --> 12C + 4He
The net result is that you get the 12C back and you have used up 4 protons to make one 4He, along with two antielectrons and three photons. The antielectrons will annihilate with electrons to make photons. So hydrogen is burned to make helium with carbon as a catalyst.



The bottom line is, sun make light, sun produce heat, sun warm earth and sustain life. Sun good. :D



But I have printed this out for those nights when I am experiencing insomnia. It will help.


P.S. Helen, I still love you.
 

LaFoto

Just Corinna in real life
Staff member
Supporting Member
Joined
Feb 1, 2004
Messages
34,813
Reaction score
822
Location
Lower Saxony, Germany
Can others edit my Photos
Photos NOT OK to edit
You want this thread closed, methinks.
Your wish is my demand.
 

LaFoto

Just Corinna in real life
Staff member
Supporting Member
Joined
Feb 1, 2004
Messages
34,813
Reaction score
822
Location
Lower Saxony, Germany
Can others edit my Photos
Photos NOT OK to edit
Well, hoping that everyone has calmed down some over the issues between yourselves at hand, this thread is being reopened, but also moved to its appropriate forum, i.e. the Graphic Programmes Forum. Please keep it a discussion free from personal insults.
 
Joined
Nov 12, 2007
Messages
122
Reaction score
0
Location
Chicago
Website
www.carolinedixey.com
Can others edit my Photos
Photos NOT OK to edit
I wonder if that dude's pictures get better the more he insults people on the internet. Sheesh.

Close this back up again, and suspend Moglex for starting internet fights like a child. I was hoping to actually learn something from this thread, but it was just a bunch of nit-picking ego-centric people bashing each other, and I actually feel dumber after reading it.
 

Most reactions

Top