Solar Eclipse Filter

RalphLambrecht · Jan 25, 2017

The US has a big total solar eclipse in August 2017 coming up. I was thinking that a simple fully exposed piece of B&Wfilm developed to a density of 3.0 or even 4.0 would make a very effective solar filter for viewing and photographing.any ideas,experience or comments;must be cheaper than buying a solar filtr and just as safe, I hope.

Rick A · Jan 25, 2017

https://www.exploratorium.edu/eclipse/how-to-view-eclipse

Luckless · Jan 25, 2017

If you're going to point optics at the sun or try to look at it, then you need to use real equipment from a reliable company and make sure it is in good repair each and every time.

Remember, the sun is a wide spectrum light source, and large amounts of IR and UV that we can't see reach ground level. Going cheap on filters is a good way to fry important things because you aren't blocking what you can't see nearly as well as you thought you were. - Given that exposed and developed film is often used as a filter when trying DIY IR photography, I'm going to go with "Probably not the best idea" for blocking IR.

Also remember that a big part of why IR and UV light can be so damaging to the human eye is that the eye can't see it and doesn't contract or force blinking, and why cheap sunglasses are so dangerous. - Your eye goes wide open and happily lets all the damaging light it can't see in.

resummerfield · Jan 25, 2017

For unaided viewing (no optics), I’ve used a welding glass filter, shade 12 (shades 13 or 14 would be better, but hard to find). Welding glass filters are pretty common, and cheap at about $10.

Also, I find this site, http://www.mreclipse.com/ very helpful

RalphLambrecht · Jan 25, 2017

Luckless said:
If you're going to point optics at the sun or try to look at it, then you need to use real equipment from a reliable company and make sure it is in good repair each and every time.

Remember, the sun is a wide spectrum light source, and large amounts of IR and UV that we can't see reach ground level. Going cheap on filters is a good way to fry important things because you aren't blocking what you can't see nearly as well as you thought you were. - Given that exposed and developed film is often used as a filter when trying DIY IR photography, I'm going to go with "Probably not the best idea" for blocking IR.

Also remember that a big part of why IR and UV light can be so damaging to the human eye is that the eye can't see it and doesn't contract or force blinking, and why cheap sunglasses are so dangerous. - Your eye goes wide open and happily lets all the damaging light it can't see in.

actually,I'm not doing this to save money, but many commercial sun filters are limited to a density of 3.0 and I think developing B&W film will giveme potentially a higher density and thereby a safer filter. I tried a metal foil filter made for telescope viewing but it creates a mostly fuzzy image!

RalphLambrecht · Jan 25, 2017

resummerfield said:
For unaided viewing (no optics), I’ve used a welding glass filter, shade 12 (shades 13 or 14 would be better, but hard to find). Welding glass filters are pretty common, and cheap at about $10.

Also, I find this site, http://www.mreclipse.com/ very helpful

They also have a heavy color cast, which is unwanted.I'm looking for neutal density.

Leigh B · Jan 25, 2017

My wife has traveled all over the world in the last 50 years chasing eclipses.

She gets viewing filters and photographic filters from these folks:
http://www.thousandoaksoptical.com/
Dead Link Removed

- Leigh

Sirius Glass · Jan 25, 2017

One must be careful not to burn the focal plane shutter [example the cloth shutter in the Leica, metal ones on other cameras] or ones eyes. While replacing a shutter is expense, replacing an eye is even more so. I was riding in a car during a partial eclipse, it started getting dark, I removed my sunglasses and glanced up. That burnt the retina in one eye, luckily it was not a bilateral hit. I was fortunate and the ophthalmologist was able to used [a controversial approach at the time] the side effects of an arthritic drug to cause the swollen cones and rods to shrink in size so that they could properly heal without crushing each other. I had not damage after the recovery. This was only a quick glance. Though a viewfinder could be really bad.

Gerald C Koch · Jan 25, 2017

Whenever the is a solar eclipse people are warned not to look at the sun through ANY filter. This also applies to the viewfinders of cameras even SLR's. They recommend viewing indirectly with an improvised camera obscura made from a carboard box. Having seen the damage caused to cloth focal plane shutters I thoroughly agree. Cameras can be repaired but we have only two eyes.

Luckless · Jan 25, 2017

I would suggest stepping back and trying to track down specifically where the fuzziness was coming from with the solar filter you were using.
Solar imaging is a challenging technical field after all. The sun is moving along at a fairly decent clip, and its surface is not static. Plus all the chances for equipment issues: Internal reflections, vibrations, precision and smoothness of tracking, etc. Not to mention general seeing conditions of the atmosphere.

If you DIY a solution, then I strongly suggest finding some reliable means of measuring the difference across the IR and UV light levels that your filter is actually blocking. It does not take much of a misstep on something like this to cause some very serious injuries.

tedr1 · Jan 25, 2017

Ralph's fogged film is OK for naked eye viewing, the eye evolved in sunlight

For applications that involve a lens then safety is paramount, improvised filters are just that improvised and uncontrolled and therefore carry risk to the optical assembly (eye camera or telescope).

In astronomy one of the ways of reducing the solar energy is to use a very small aperture, this may be simpler and safer to improvise than a filter.

Gerald C Koch · Jan 25, 2017

tedr1 said:
Ralph's fogged film is OK for naked eye viewing, the eye evolved in sunlight

Looking at the sun directly without some special filtration will permanently damage the retinas. Any doctor of opthamology will tell you that AND that a piece of developed film is not a suitable protection. Remember we cannot see UV radiation even though it will damage the eye. So you cannot personally judge what is safe. We also evolved eyelids for the specific purpose of protecting the eye.

revdoc · Jan 25, 2017

Many years ago, I used the leader of some 35mm b&w film as a solar filter. It produced a noticeable yellow cast, but otherwise worked. Just make sure it's silver-based film and not chromogenic. However, these days I would just get a proper solar filter. They're cheap and easily obtained.

As far as eclipses go, you can watch without filters during totality, but not before or after. I'd actually recommend looking everywhere but the sun until totality. You'll see the light change in a way you've never seen before, you'll see the wildlife behaving strangely, and you might also see shadow bands scooting around on the ground. It is, as young people would say, way cool.

Larry the sailor · Jan 25, 2017

I'm hoping to make a short trip to get to see and photograph the eclipse, already have the time off scheduled.
No problems shelling out a reasonable amount of coin for a proper filter. Still, wondering if a stack of ND filters would be OK.

Leigh B · Jan 26, 2017

Larry the sailor said:
Still, wondering if a stack of ND filters would be OK.

You can buy good safe viewing glasses for about $2 in singles, less than $1 each in quantity > 25.

How much are your eyes worth?

- Leigh

revdoc · Jan 26, 2017

A stack of ND filters? No way. You need to block out IR, which ND filters might or might not do. Thing is, if the IR isn't blocked, but the visible is, you won't have any sensation of discomfort, but your retina will still burn.

zanxion72 · Jan 26, 2017

Try this one:
https://www.amazon.com/Solar-Filter-Telescopes-Binoculars-Cameras/dp/B00DS7IFQS

If you are to record details on the surface of the Sun with a telephoto, then for some more get a Baader filter:
https://www.amazon.com/Solar-Filter-Telescopes-Binoculars-Cameras/dp/B00DS7IFQS

Larry the sailor · Jan 26, 2017

See. That's why I posted that I was wondering, now I'm not wondering anymore and will source and buy a proper filter.

tedr1 · Jan 26, 2017

The outer parts of the eye may be irritated by exposure to large amounts of UV however the sensitive retina lies behind the cornea, lens and fluid filled globe of the eye. Some data on transmittance of these components is available here

http://iovs.arvojournals.org/article.aspx?articleid=2122713

The use of light filtration aids by arc welders may be more related to chronic irritation of the outer parts of the eye, the eye lids and conjunctiva, rather than anything caused by penetration of UV deep into the eye. As the medical paper linked to above shows, the lens of an adult eye is pretty impervious to UV, or at least they were in 1962

PS just to make the point clear, the sensitivity of the outside of the eye to UV is well documented and is the reason welders and mountain climbers wear goggles, because the exposure is prolonged and can result in a chronic condition. This is different from gazing at the sun for a few minutes through a filter, the eye lens blocks most of the UV and prevents it from penetrating to the interior of the eye, and, the exposure is brief. The same data does however seem to show that near IR is transmitted fairly well, that may be of more concern than UV.

Solar Eclipse Filter

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