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Re: APOD: M27: The Dumbbell Nebula (2021 Jul 12)
Posted: Tue Jul 13, 2021 8:33 am
by stefanz
Chris Peterson wrote: ↑Tue Jul 13, 2021 1:37 am
stefanz wrote: ↑Tue Jul 13, 2021 12:37 am
But that magnification limit does not mean that color vision is "
A matter of biology, not optics", as Chris stated. (BTW, that limit explains why you wont find 50mm binoculars with a magnification of less than 7).
Visually, the only value in a larger aperture is that you can operate at a higher magnification. Not that you collect more light.
A 7x50 binocular cannot collect more light than a 7x20 binocular? A 7x50 binocular cannot project more light to the retina than a 7x20 binocular? This is what you you are stating here.
I mentioned the magnification limit due to the pupil size which means a 7x80 binocular wouldn't be brighter than a 7x50 binocular and which also means that an object in a 11.2x80 binocular is as bright (and larger) as in a 7x50 binocular --
if the object is extended. More exact: if the object is extended if seen with both kinds of optics (this also includes the unaided eye at magnification 1)
As long the object cannot be resolved it has to be treated like a point source, which means it becomes brighter if we increase the aperture at magnification above the mentioned limit.
Re: APOD: M27: The Dumbbell Nebula (2021 Jul 12)
Posted: Tue Jul 13, 2021 4:15 pm
by neufer
stefanz wrote: ↑Tue Jul 13, 2021 8:33 am
Chris Peterson wrote: ↑Tue Jul 13, 2021 1:37 am
stefanz wrote: ↑Tue Jul 13, 2021 12:37 am
But that magnification limit does not mean that color vision is "
A matter of biology, not optics", as Chris stated. (BTW, that limit explains why you wont find 50mm binoculars with a magnification of less than 7).
Visually, the only value in a larger aperture is that you can operate at a higher magnification. Not that you collect more light.
A 7x50 binocular cannot collect more light than a 7x20 binocular? A 7x50 binocular cannot project more light to the retina than a 7x20 binocular? This is what you you are stating here.
I mentioned the magnification limit due to the pupil size which means a 7x80 binocular wouldn't be brighter than a 7x50 binocular and which also means that an object in a 11.2x80 binocular is as bright (and larger) as in a 7x50 binocular --
if the object is extended. More exact: if the object is extended if seen with both kinds of optics (this also includes the unaided eye at magnification 1)
As long the object cannot be resolved it has to be treated like a point source, which means it becomes brighter if we increase the aperture at magnification above the mentioned limit.
Indeed:
- 1) Chris was not talking about point sources.
2) Chris does not consider apertures
so small that (for a set magnification)
one's 8mm dilated pupils are not fully utilized by all point sources.
(A 7x20 binocular makes use of only one eighth of available dilated pupil area.)
Goldilocks/optimal faint object magnification: aperture/8mm.
Re: APOD: M27: The Dumbbell Nebula (2021 Jul 12)
Posted: Tue Jul 13, 2021 6:24 pm
by stefanz
neufer wrote: ↑Tue Jul 13, 2021 4:15 pm
- 1) Chris was not talking about point sources.
If you assume that Chris considers objects like M27 purely as extended objects the following statement from Chris means that they wont become brighter if you use a telescope.
Chris Peterson wrote: ↑Tue Jul 13, 2021 1:37 am
The reason it is a matter of biology and not optics is that the individual rods and cones will never receive a greater flux of photons through a telescope than they will unassisted.
(Photon flux is the amount of photons per area and per time. Thus, this statement indeed addresses extended objects. The question is whether you can apply this for unresolved object ...)
neufer wrote: ↑Tue Jul 13, 2021 4:15 pm
2) Chris does not consider apertures
so small that (for a set magnification)
one's 8mm dilated pupils are not fully utilized by all point sources.
Chris' thesis, that
Chris Peterson wrote: ↑Mon Jul 12, 2021 9:34 pm
The number of photons a rod or cone receives does not increase with aperture.
and that it is
A matter of biology, not optics
was general and without any constraints (at least I cannot find ones). That would mean, a 7x20 binocular is as good as a 7x50 binocular ...
neufer wrote: ↑Tue Jul 13, 2021 4:15 pm
(A 7x20 binocular makes use of only one eighth of available dilated pupil area.)
Wow, you have 20.9mm (=20mm/7*8) pupils
I shared my arguments and I won't do that again.
I explained up to which limit aperture increase makes sense on how it is related to magnification. I also explained why a small object that cannot be resolved with unaided eye becomes brighter if you use a telescope.
Re: APOD: M27: The Dumbbell Nebula (2021 Jul 12)
Posted: Tue Jul 13, 2021 6:56 pm
by neufer
stefanz wrote: ↑Tue Jul 13, 2021 6:24 pm
neufer wrote: ↑Tue Jul 13, 2021 4:15 pm
(A 7x20 binocular makes use of only one eighth of available dilated pupil area.)
Wow, you have 20.9mm (=20mm/7*8) pupils
Parallel red lines 20mm wide would ideally generate
eyepiece parallel red lines 8mm wide to fit a dilated
pupil resulting in an ANGULAR magnification of 2.5.
An ANGULAR magnification of 7 results in eyepiece
parallel red lines only 
20/7 mm wide to fit
a nominal daytime pupil watching a sporting event.
Re: APOD: M27: The Dumbbell Nebula (2021 Jul 12)
Posted: Tue Jul 13, 2021 7:51 pm
by stefanz
neufer wrote: ↑Tue Jul 13, 2021 6:56 pm
Parallel red lines 20mm wide would ideally generate
eyepiece parallel red lines 8mm wide to fit a dilated
pupil resulting in an ANGULAR magnification of 2.5.
That's the magnification limit I mentioned yesterday. (I noticed you use different font colors and weights. Does this have a meaning?)
According to my calculation
neufer wrote: ↑Tue Jul 13, 2021 6:56 pm
20/7 mm
= 2.85mm (diameter of exit beam of a 20x7 Keplerian telescope, see your image). If that is
neufer wrote: ↑Tue Jul 13, 2021 4:15 pm
only one eighth of available dilated pupil
the dilated pupil diameter has to be 2.85mm*8=22.9 mm.
I think there was a small mistake in your statement that's why added a smiley (the winking one:
).
The consequence of this thread is that I won't participate in discussions in this forum anymore. That will save a lot of energy. But I think you won't miss me.
Re: APOD: M27: The Dumbbell Nebula (2021 Jul 12)
Posted: Tue Jul 13, 2021 8:10 pm
by johnnydeep
stefanz wrote: ↑Tue Jul 13, 2021 7:51 pm
The consequence of this thread is that I won't participate in discussions in this forum anymore. That will save a lot of energy. But I think you won't miss me.
Please don't feel that way. I for one have appreciated the discussion. Your contributions so far have been worthwhile. Stick around!
Re: APOD: M27: The Dumbbell Nebula (2021 Jul 12)
Posted: Tue Jul 13, 2021 9:09 pm
by neufer
johnnydeep wrote: ↑Tue Jul 13, 2021 8:10 pm
stefanz wrote: ↑Tue Jul 13, 2021 7:51 pm
The consequence of this thread is that I won't participate in discussions in this forum anymore. That will save a lot of energy. But I think you won't miss me.
Please don't feel that way. I for one have appreciated the discussion. Your contributions so far have been worthwhile. Stick around!
Stefanz arguments have certainly helped to clarify that:
- Chris's blanket rule of thumb that: resolved/extended nebulae are only magnified when looking thru telescopes while brightness levels are basically unaffected is somewhat limited in practice
In fact, resolved/extended nebulae are always made somewhat dimmer when looking thru telescopes ... especially for magnifications that are significantly larger or smaller than the Goldilocks/optimal faint object magnification of aperture/8mm. (Note: extended clusters of unresolved stars turn into a more dispersed array of individually brighter stars.)
Re: APOD: M27: The Dumbbell Nebula (2021 Jul 12)
Posted: Wed Jul 14, 2021 4:30 am
by alter-ego
neufer wrote: ↑Tue Jul 13, 2021 9:09 pm
...
In fact,
resolved/extended nebulae are always made somewhat dimmer when looking thru telescopes ...
especially for
magnifications that are significantly larger or smaller than the
Goldilocks/optimal faint object magnification of aperture/8mm. (Note: extended clusters of unresolved stars turn into a more dispersed array of individually brighter stars.)[/list]
The eye is a complicated animal (biology matters here
). The optimal magnification for faint object visibility depends on the objects surface brightness and background sky contrast. You may find the link en
lightening. There's more discussion than just this plot, and some points of controversy included. I've not kept up with updates if there are any. Roger is an old star-party partner and compadre of mine prior to writing the book.
Optimum Magnified Visual Angle Visual Astronomy of the Deep Sky
Re: APOD: M27: The Dumbbell Nebula (2021 Jul 12)
Posted: Wed Jul 14, 2021 9:15 am
by XgeoX
orin stepanek wrote: ↑Mon Jul 12, 2021 1:05 pm
M27_Falls_3557.jpg
Just beautiful; Don't want to experience it here on Earth while I am
still here!
70cec30919aefe50ada3bd8e0e6239e6.jpg
These guys are about to figure it out!
Orin,
Love the pugs. I grew up with one “Tiny”. She was great, lived to 15 1/2 on chicken gizzards and chocolate (we didn’t know it was bad for dogs back then, sure didn’t seem to affect her).
Once again your post made me smile!
Eric
Re: APOD: M27: The Dumbbell Nebula (2021 Jul 12)
Posted: Wed Jul 14, 2021 11:09 am
by orin stepanek
XgeoX wrote: ↑Wed Jul 14, 2021 9:15 am
orin stepanek wrote: ↑Mon Jul 12, 2021 1:05 pm
M27_Falls_3557.jpg
Just beautiful; Don't want to experience it here on Earth while I am
still here!
70cec30919aefe50ada3bd8e0e6239e6.jpg
These guys are about to figure it out!
Orin,
Love the pugs. I grew up with one “Tiny”. She was great, lived to 15 1/2 on chicken gizzards and chocolate (we didn’t know it was bad for dogs back then, sure didn’t seem to affect her).
Once again your post made me smile!
Eric
I love Dogs; they seem to like me too! I remember as a kid when we went to Grammy's & Gram pa's farm; they had 6 or 7 dogs that always came to greet me! I guess I was going to the dogs!
I like most critters!
Re: APOD: M27: The Dumbbell Nebula (2021 Jul 12)
Posted: Thu Jul 15, 2021 3:22 am
by RocketRon
OK, lets shift the question about a bit and go off track a bit.
How many times are we likely to have gone through supernovas in a previous life ?
And we'll sidestep if going supernova is less 'enjoyable' than going planetary nebula ...
neufer wrote: ↑Mon Jul 12, 2021 1:20 pm
We are all made of ancient
supernova stardust not recent planetary nebula stardust.
I like most critters!