APOD: Sunspot at Sunset (2014 Jan 08)

Comments and questions about the APOD on the main view screen.
User avatar
Chris Peterson
Abominable Snowman
Posts: 14669
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Sunspot at Sunset (2014 Jan 08)

Post by Chris Peterson » Thu Jan 09, 2014 2:46 pm

Nitpicker wrote:This is from the safety pages of my DSLR's manual:
...
I think the second warning is a pretty good warning, but the first one may be over the top, even when the sun is high and even if the camera is on a fixed tripod. I wonder if the risk of damage to the camera is greater with the shutter closed, or the mirror down, or even to the perimeter of the sensor? As for damaging the sensor itself, I imagine a wider image might be worse, in terms of concentrating the direct photons from the Sun onto fewer pixels. But I really don't know. I keep thinking about when I was a kid and setting fire to paper with a magnifying glass.
I think that both warnings are exactly what I'd put in a similar product I was selling. And personally, I'd not observe either of them very diligently.

What matters isn't the FOV of the lens, but the lens aperture. You aren't going to set fire to paper with a lens a few millimeters across; one a few hundred millimeters across can melt aluminum. As far as your eye is concerned, magnification is an important factor. A small image of the Sun on your retina doesn't easily cause damage because the heat can be carried away. A large image (with the same surface brightness) can almost instantly cause permanent damage.

One indicator that having the Sun in the FOV of the camera is generally harmless is the fact that even when the Sun's image isn't on the sensor, there's a good chance it's on some internal surface of the camera. And that doesn't cause any problems.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
neufer
Vacationer at Tralfamadore
Posts: 16535
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Sunspot at Sunset (2014 Jan 08)

Post by neufer » Thu Jan 09, 2014 3:02 pm

Chris Peterson wrote:
As far as your eye is concerned, magnification is an important factor. A small image of the Sun on your retina doesn't easily cause damage because the heat can be carried away. A large image (with the same surface brightness) can almost instantly cause permanent damage.
I've always thought the primary damage from looking at the (non-sunrise/sunset) sun was due to UV not heat.
Art Neuendorffer

User avatar
Chris Peterson
Abominable Snowman
Posts: 14669
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Sunspot at Sunset (2014 Jan 08)

Post by Chris Peterson » Thu Jan 09, 2014 3:16 pm

neufer wrote:
Chris Peterson wrote:
As far as your eye is concerned, magnification is an important factor. A small image of the Sun on your retina doesn't easily cause damage because the heat can be carried away. A large image (with the same surface brightness) can almost instantly cause permanent damage.
I've always thought the primary damage from looking at the (non-sunrise/sunset) sun was due to UV not heat.
UV is associated with long term damage to the retina from simply being outdoors a lot. It causes various retinopathies. Curiously, many older people who wore sunglasses most of their lives are seeing these problems now, because until about 20 years ago sunglasses didn't block UV, but they did block visible light, resulting in larger pupils and more UV exposure than with no sunglasses at all.

But if you stare at the Sun while it's high in the sky, thermal damage will probably kick in before permanent damage from UV (although the latter can cause temporary localized blindness lasting up to several weeks).

A real concern is that a certain percentage of the population have underlying pathologies that predispose them to retinal phototoxicity. Much shorter exposure to bright light can cause permanent damage. It's a major source of complications from otherwise simple eye examinations and procedures that depend on the use of a bright source to illuminate the retina. Most of us just see a bright light for a few seconds; in a few percent of people, there is temporary or even permanent damage. That's not a thermal effect at all.

When I was a laser safety officer at Beckman Instruments many years ago, I saw two kinds of retinal damage from laser exposure- thermal and chemical. The thermal burns were visible on the retina; the photochemical damage wasn't visible, but could only be detected with specialized vision tests.

There are crazy people who believe there are health benefits from staring at the Sun. They tend to go blind. Luckily, there's a blink reflex that protects us from accidental damage. Unless we're observing with some sort of equipment, we can generally trust that if it's uncomfortable, we shouldn't look long, if it's not there's probably little danger. As with many sunrises and sunsets (the setting Sun is usually more attenuated).
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
Nitpicker
Inverse Square
Posts: 2690
Joined: Fri Sep 20, 2013 2:39 am
Location: S27 E153

Re: APOD: Sunspot at Sunset (2014 Jan 08)

Post by Nitpicker » Fri Jan 10, 2014 12:05 am

Chris Peterson wrote:What matters isn't the FOV of the lens, but the lens aperture. You aren't going to set fire to paper with a lens a few millimeters across; one a few hundred millimeters across can melt aluminum. ...
One indicator that having the Sun in the FOV of the camera is generally harmless is the fact that even when the Sun's image isn't on the sensor, there's a good chance it's on some internal surface of the camera. And that doesn't cause any problems.
I suppose if I were silly enough to setup my camera on a tripod, pointed at the midday sun, with my 300mm lens, unfiltered at f/5.6 (aperture ~54mm), it might do some damage to the sensor, shutter or viewfinder. But I certainly wouldn't be able to photograph the sun like that. I'd probably need to set the lens at f/22 (aperture ~14mm) to have a hope of imaging it, which seems pretty harmless. Still, there are people out there who do silly things all the time.

User avatar
Chris Peterson
Abominable Snowman
Posts: 14669
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Sunspot at Sunset (2014 Jan 08)

Post by Chris Peterson » Fri Jan 10, 2014 12:12 am

Nitpicker wrote:Still, there are people out there who do silly things all the time.
That's why there are warning stickers all over things, and manuals are full of them. And smart people generally figure out which warnings matter (and when), and which don't.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
Beyond
500 Gigaderps
Posts: 6889
Joined: Tue Aug 04, 2009 11:09 am
Location: BEYONDER LAND

Re: APOD: Sunspot at Sunset (2014 Jan 08)

Post by Beyond » Fri Jan 10, 2014 1:34 am

Like the warnings pasted all over ladders. IF one paid attention to all of them, one would never, ever use a ladder :!: :lol2:
To find the Truth, you must go Beyond.

User avatar
Chris Peterson
Abominable Snowman
Posts: 14669
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Sunspot at Sunset (2014 Jan 08)

Post by Chris Peterson » Fri Jan 10, 2014 1:42 am

Beyond wrote:Like the warnings pasted all over ladders. IF one paid attention to all of them, one would never, ever use a ladder :!: :lol2:
Ladders and aspirin. Two products that would never be approved for sale if they were invented today.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
Nitpicker
Inverse Square
Posts: 2690
Joined: Fri Sep 20, 2013 2:39 am
Location: S27 E153

Re: APOD: Sunspot at Sunset (2014 Jan 08)

Post by Nitpicker » Fri Jan 10, 2014 1:54 am

Chris Peterson wrote:
Beyond wrote:Like the warnings pasted all over ladders. IF one paid attention to all of them, one would never, ever use a ladder :!: :lol2:
Ladders and aspirin. Two products that would never be approved for sale if they were invented today.
Imagine Neil Armstrong's quote without a ladder:
That's one small step ... whoa ... actually that was a doosie! ...

User avatar
rstevenson
Quis custodiet ipsos custodes?
Posts: 2599
Joined: Fri Mar 28, 2008 1:24 pm
Location: Dartmouth, NS, Canada

Re: APOD: Sunspot at Sunset (2014 Jan 08)

Post by rstevenson » Fri Jan 10, 2014 12:19 pm

Nitpicker wrote:Imagine Neil Armstrong's quote without a ladder:
That's one small step ... whoa ... actually that was a doosie! ...
That's one slow plunge for a man, one giant face-plant for mankind.

Rob

deathfleer

Re: APOD: Sunspot at Sunset (2014 Jan 08)

Post by deathfleer » Sun Jan 12, 2014 5:44 am

is the storm in the sky related to the unusual downpour of the rain in the Earth

User avatar
geckzilla
Ocular Digitator
Posts: 9009
Joined: Wed Sep 12, 2007 12:42 pm
Location: Modesto, CA

Re: APOD: Sunspot at Sunset (2014 Jan 08)

Post by geckzilla » Sun Jan 12, 2014 5:46 am

deathfleer wrote:is the storm in the sky related to the unusual downpour of the rain in the Earth
No. Also, there is nothing unusual about downpours of rain.
Just call me "geck" because "zilla" is like a last name.