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A-L-E-X
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Total Solar Eclipse 2017

03 Sep 2017 23:58

midtskogen wrote:
A-L-E-X wrote:
Source of the post Actually astigmatism might HELP.  Since it causes you to see double, in effect you see something twice- and it becomes easier to notice.

Well, there's no more light entering the eye, and things depend a lot on contrast.
A-L-E-X wrote:
Source of the post Mid, how do you carry such heavy lenses around?  I bought  a big lens and then returned it right away because it was simply too heavy- I do not do well with anything over 200mm.  Rather do digiscoping with a telescope.

When I fly to SFO I usually do it without checked-in luggage for convenience, but since I obviously wanted to bring some stuff with me this time, I simply filled up a suitcase with gear till it weighed slightly above 20 kg (I think my ticket allowed 2x23 kg, but I didn't want to drag two suitcases).  The heavy stuff was tripods.  The 1000 mm (and I also had a 1.6x teleconverter which together with the DSLR's sensor size gave 2400 mm effectively, perfect for having the sun fill the entire frame) is light and small, because it's a reflex lens (like Newtonian telescopes).  The lens weighs 1.9 kg, but probably around 2.5-3 kg with the case.  Some stats here.

You can see the lens at 4:35 in my video.  It's even more compact than most telescopes.

Oh that explains it- you have a mirror lens!  I like those.  It's like a catadioptric telescope, the mirrors fold the path of the light, making it possible to have a long focal length in a short tube.
 
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midtskogen
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04 Sep 2017 00:28

A-L-E-X wrote:
Source of the post Oh that explains it- you have a mirror lens!  I like those.  It's like a catadioptric telescope, the mirrors fold the path of the light, making it possible to have a long focal length in a short tube.

Yes.  It has a few drawbacks, though.  You can't change the aperture and the focus depth (which is extremely shallow - we're talking millimeters at the closest focus around 8 m).  And the focus in general is extremely sensitive.  It doesn't even stop at infinity, probably due to manufacturing issues and that the temperature can cause expansions large enough to influence the focus ever so slightly.  I bought this lens used in Tokyo ten years ago (a good place for finding exotic lenses at reasonable prices).  It's not something I use often, but it's a very nice thing to have,
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Total Solar Eclipse 2017

04 Sep 2017 00:53

midtskogen wrote:
A-L-E-X wrote:
Source of the post Oh that explains it- you have a mirror lens!  I like those.  It's like a catadioptric telescope, the mirrors fold the path of the light, making it possible to have a long focal length in a short tube.

Yes.  It has a few drawbacks, though.  You can't change the aperture and the focus depth (which is extremely shallow - we're talking millimeters at the closest focus around 8 m).  And the focus in general is extremely sensitive.  It doesn't even stop at infinity, probably due to manufacturing issues and that the temperature can cause expansions large enough to influence the focus ever so slightly.  I bought this lens used in Tokyo ten years ago (a good place for finding exotic lenses at reasonable prices).  It's not something I use often, but it's a very nice thing to have,

Does it have low CA (usually mirror lenses are good with keeping false color to a minimum.)  The TC probably enhances the shallow depth of focus- you could try focus stacking there. At long focal lengths atmospheric turbulence or haze also becomes a factor.  I read that the maximum that should be used is around 3000mm.
 
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midtskogen
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04 Sep 2017 01:10

A-L-E-X wrote:
Source of the post Does it have low CA (usually mirror lenses are good with keeping false color to a minimum.)

I might see some if I use it with the teleconverter.  But compared to my two simple telescopes, I'd say that the chromatic aberration is very low, for most practical purposes non-existent.  The main issue is to get proper focus.  And also, things out of focus get a ring effect due to the secondary mirror.  They're not evenly blurred, which may look odd.
Nikon also has a 2000 mm f/11 reflex lens, but that one is a monster and extremely expensive.

I also own the 500 mm f/8 reflex which I've used quite a bit.  It's only slightly larger than my 80 mm f/1.4.
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04 Sep 2017 02:52

midtskogen wrote:
A-L-E-X wrote:
Source of the post Does it have low CA (usually mirror lenses are good with keeping false color to a minimum.)

I might see some if I use it with the teleconverter.  But compared to my two simple telescopes, I'd say that the chromatic aberration is very low, for most practical purposes non-existent.  The main issue is to get proper focus.  And also, things out of focus get a ring effect due to the secondary mirror.  They're not evenly blurred, which may look odd.
Nikon also has a 2000 mm f/11 reflex lens, but that one is a monster and extremely expensive.

I also own the 500 mm f/8 reflex which I've used quite a bit.  It's only slightly larger than my 80 mm f/1.4.

I get that same effect with the secondary on my scope- it's "secondary shadowing" :( I dislike it intensely because it causes uneven illumination of the image- funny thing is you don't see this effect with optical viewing, it only happens when pictures are taken.
Focus is also a big worry with telescopes, because what visually seems to be in focus, looks soft after the image is taken, and ends up being a process of trial and error (mostly error lol.)
Maybe a focusing mask would also help with long lenses?

Fascinating, although that lens is very expensive, if it performs as well as an 80mm APO refractor, it would be worth it.  As you know, aperture (lens diameter) is most important when it comes to gathering light for AP, just like it is for visual use.
 
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04 Sep 2017 03:09

I think I paid something like $700 for the 1000 mm used and something similar for the 500 mm brand new.  For something more expensive, like the 2000 mm which is more a collector's item probably at the price of a decent car, I probably get much more for the money if I get a nice telescope and a matching camera.  But I would use this too little to be worth the investment.  The 500 mm is nice because of the physical size, not much larger than a normal length, and with a teleconverter and my DSRL I get 1200 mm effectively.
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04 Sep 2017 03:32

midtskogen wrote:
I think I paid something like $700 for the 1000 mm used and something similar for the 500 mm brand new.  For something more expensive, like the 2000 mm which is more a collector's item probably at the price of a decent car, I probably get much more for the money if I get a nice telescope and a matching camera.  But I would use this too little to be worth the investment.  The 500 mm is nice because of the physical size, not much larger than a normal length, and with a teleconverter and my DSRL I get 1200 mm effectively.

plus 500mm is much better for general use (like birding and sporting events), I find that specialized lenses just sit there gathering dust.  Even telescopes- it's a lot of work to set them up and frame the image just the way you want it.
 
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04 Sep 2017 05:52

Manual focus is a pain for birds and near hopeless for sports, but there might be a way around that with autofocus in a teleconverter.  I'm not sure.  So these are basically my eclipse lenses.

Here's a bird shot with the 500 mm, note the out of focus parts (a 20 year old photo, and >15 years old scan, so limited quality):
► Show Spoiler


We might want to take further discussions on photography to another thread.
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04 Sep 2017 07:47

Watsisname wrote:
Source of the post Added: It could also depend on when you look, as the prominences on the western side will be more exposed near the end of totality while the eastern side gets more covered.


That might explain it, I was using my camera a but more towards the end as I wanted to snap pictures before turning the unprotected lens away from the sun.  Wasn't really looking with my eyes much anymore at that point.

midtskogen wrote:
Source of the post We might want to take further discussions on photography to another thread.


Show off your work thread seems to be the talk about stuff you do thread, so that would probably be best.




This is interesting

r/Space Moon illuminated by Earth during eclipse

They show the Moon's face as visible which apparently was my memory playing tricks and yet the same thing is happening in the comments.  One user goes so far as to say they couldn't recall, then edited their post saying this picture looks close to what they saw.  Human memory really can't be trusted
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04 Sep 2017 11:16

Yes, I suspect something else might be at work here, Doc.  It could be we "saw" what we expected to see when we look up at the moon, and usually when we look at the moon so there is some detail to see, so our brain superimposed what we usually see when we look at the moon.  But memory itself can't be trusted, unless it's on a silicon chip of course :-)  I've read some fascinating stuff about false memories and how the more you try to access a given memory the more it gets altered- it's the mental version of the Heisenberg Uncertainty Principle- the more you try to measure something the more you alter the measurement.
 
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Total Solar Eclipse 2017

04 Sep 2017 16:12

A-L-E-X wrote:
Source of the post  It could be we "saw" what we expected to see when we look up at the moon, and usually when we look at the moon so there is some detail to see, so our brain superimposed what we usually see when we look at the moon.

At least in my case I felt the opposite.  It looked dramatically different from what I expected.  If I understood nothing of the astronomy I would not have guessed I was seeing the Moon in front of the Sun at all, but rather that the Sun had been stolen away and replaced by something dark and alien.  I intimately understood why people in ancient times would have thought the world was ending.

DoctorOfSpace wrote:
Source of the post This is interesting

r/Space Moon illuminated by Earth during eclipse

Oh neat, they were based in Madras as well!  Their composite is beautiful, but it doesn't really look like what I saw.  If the Earthshine on the Moon were that apparent I think the cause of eclipses would have been obvious in ancient times.

If I take my longest exposures (which get the middle corona) and bump the exposure by about 4 stops in lightroom, I can just start to make out the details in the Moon's disk.  It would have taken much longer exposures like theirs to make it clearly visible.  This is six shots with +5 exposure boost, aligned and stacked to reduce noise.  A little bit of lunar surface detail appears, but all but the farthest rays of the corona are blown out.

► Show Spoiler


DoctorOfSpace wrote:
Source of the post They show the Moon's face as visible which apparently was my memory playing tricks and yet the same thing is happening in the comments.  One user goes so far as to say they couldn't recall, then edited their post saying this picture looks close to what they saw.  Human memory really can't be trusted

Yeah, I think this shows how prone the mind is to suggestion.  Reflections/comments made during or immediately after the eclipse are likely more correct than those made days or weeks afterward, or upon seeing photographs.

I really can't imagine being able to see any of the moon's surface with the eye with the bright corona right next to it, but who knows, maybe you and some others did.  People do see things differently. :)
 
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Total Solar Eclipse 2017

04 Sep 2017 16:31

Wat, even things in our surrounding seemed a different color.  We do take the sun for granted but when special events like this occur it becomes apparent how dependent we are on it.  In a way it's like being in outer space and seeing things we could normally only see from there.  In space there is no such thing as "day" and "night" and no atmosphere to create blue skies.  I feel like during the eclipse we really get to see what the universe is like and not the everyday illusion we live in because we are isolated on a miniscule rock of a planet.
 
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04 Sep 2017 22:09

People who have seen a lot of eclipses generally say that they see nothing but blackness in the disc, so seeing the earthshine is extremely hard.

Yes, seeing an eclipse must have been a frightening experience in ancient times, though in Europe the cause of solar eclipses was early known amongst educated people (Pliny, 1st century AD, calls it obvious (ah, I love the expressiveness of Latin in few words): "manifestumst solem interventu lunae occultari lunamque terrae obiectu" - "it's obvious that the Sun gets occulted by the Moon's passage between and the Moon by the Earth's position in front").  Pliny has a fairly good description of eclipses explaining the cause, the conical shape of the shadow (stars and planets are not darkened) and how that proves the relative sizes of the Sun, Earth and Moon and the shape of the Earth.  According to him the cause and first successful prediction of a total solar eclipse was made by Thales of Miletus in 585 BC.
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05 Sep 2017 00:23

Now that is kind of scary, do you think people who have seen a lot of eclipses say that because they might've damaged their eyesight somehow?  Thanks for the history on eclipses, do you think we could model that in SE?  I was going through SNPP trying to find things I want to suggest be added to SE and I saw an eclipse in there from 585 BC and wondered what was so special about it.  Now I know! :-)
 
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05 Sep 2017 01:40

A-L-E-X wrote:
Source of the post do you think people who have seen a lot of eclipses say that because they might've damaged their eyesight somehow?

No.
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