Viewing the sun with binoculars

[Perikles]

Recently, I tried viewing the sun with some 16 x 70 astronomical binoculars to see if I could see some sun spots. How come I can still see this computer screen, you may well ask. Well, I tried with the lens caps on, with a pin-hole in the caps made with a needle. This gave a blurred image of the sun which was still rather too bright, but not dangerously so. I've been puzzling about this blurred image, and wondering whether the lens caps were too far away from the lenses for the pin hole to act just as a very small lens aperture.

Is this a totally insane method of viewing? I would like to prepare myself for viewing the transit of Venus next month, so any advice would be appreciated.

[John Mendenhall]

Lord only knows how much ultra violet is getting thru. Better is the glass for a welding face shield. Be sure it is firmly attached to the front of the binoculars. I both wire it on and tape it. Keeps the light and heat out of the binoculars. I forget what number welding glass is needed, but I'm sure others can advise you. Be careful! When in doubt, don't.

[chrlzs]

John's right - welders glass is one way to go, but it needs to be high quality stuff - some of it is optically awful. You can buy it in pieces of about 4" square. The recommendation is usually for #14, but you will find grade 13 or even 12 might be better and will still give significant protection for anything other than very long viewing times. Just be careful, take breaks...

Otherwise, pop down to your local telescope shop and get some proper solar film. Do NOT use other homemade intensity reducers eg crossed polarisers, smoked glass, CD's, etc as some of these may just reduce the optical wavelengths and leave the bad (IR/UV) stuff unaffected - thereby making the danger of eye damage much worse than having nothing at all..

I've also used binoculars as a projection method, unprotected (eek!). However there is a danger that you might crack/damage an eyepiece element from heat load (which is why i did this using my cheaper binoculars...they survived ok!)

[Perikles]

Otherwise, pop down to your local telescope shop and get some proper solar film.

Yes, that would be the solution, except that I'm not aware that there is a shop here in Tenerife. Where might I best find this as a mail order from somewhere in Europe?

The welder's glass is a great idea, if only I could find out where.

[chrlzs]

I'll let someone else give you a tip on mail order, but welder's glass should be available at any decent hardware store, or tool shop. Or look up a local welder and ask him/her where they get their supplies.

[glappkaeft]

Yes, that would be the solution, except that I'm not aware that there is a shop here in Tenerife. Where might I best find this as a mail order from somewhere in Europe?

There are lots of online Telescope vendors. I have experience with the three Swedish shops and some German and British ones. Since you are on Tenerife you'd probably want a Spanish shop to simplify shipping. You want something similar to Baader Astrosolar Saftey film (http://www.baader-planetarium.com/so...fi_start_e.htm).

Here is a list of shops i found on www.astronomy-shops.com. The Spanish page was impossible to link to but one of them should have what you need.
Aire libre
Al marsad al andalusy
Alarcon web
Alpha cygni
Amaina
Astrocasion
Astroeduca
Astronautica
Astronomia para todos
Catalana telescopios
Cientifica balear
Hubble lens
Imvo
Industrias pedret
Informatica industrial
Lunatico astronomia
Magnicenter
Microciencia
Moonfish
Observar el cielo
Opticamuka
Opticaorama
Oryx
Tecno spica
Telescoshop
Valkanik esp. astronomia s.l

[Solfe]

I have never tried this with any success, but how about covering one lens on the binoculars and then projecting the image from the other lens to a white surface. Since I have never gotten this work myself, perhaps there is a technical reason it wouldn't work.

[Perikles]

There are lots of online Telescope vendors.

Wow - thanks for the list, I'll have a look

I have never tried this with any success, but how about covering one lens on the binoculars and then projecting the image from the other lens to a white surface. Since I have never gotten this work myself, perhaps there is a technical reason it wouldn't work.

I tried that with a lunar eclipse, and it doesn't seem to work. @chrlzs had a very good point about damaging an eyepiece when pointing at the sun, so I'm going to be very careful.

[profloater]

If only you had a cave pointing the right way you could set up a camera obscura to view the sun as a projection

[Perikles]

If only you had a cave pointing the right way you could set up a camera obscura to view the sun as a projection

I'm working on it, but at this rate, it will be finished for the next transit in year 2117 .

Nobody has yet commented on my use of a pinhole to reduce the lens aperture.

[profloater]

well we have some "leonardo" sunglasses which are an array of pinholes and work very well. It cuts down the light and the eyes integrate all the images somehow. When you draw a ray diagram you pass one ray through the optical axis and one through the edge of the aperture. So do you need at least two pinholes spaced apart?

[Hornblower]

I have never tried this with any success, but how about covering one lens on the binoculars and then projecting the image from the other lens to a white surface. Since I have never gotten this work myself, perhaps there is a technical reason it wouldn't work.

That is how I viewed the 2004 transit of Venus. I mounted the binoculars on a camera tripod and projected the image onto the side of the house. The only technical barrier I can think of is poor aim.

[chrlzs]

That is how I viewed the 2004 transit of Venus. I mounted the binoculars on a camera tripod and projected the image onto the side of the house. The only technical barrier I can think of is poor aim.

Same here.. And yes, unless the binoc's are perfectly aimed, nothing will happen. With a bit of care, you can position your screen (an A4 sheet of paper will work fine) in the shade, then carefully align the binocs (use their shadow to help you), and move the paper back or forward to get the image in focus.

It should work fine - I've done it several times without any sign of damage to the binoc's. But I wouldn't use expensive ones, and I'd keep the viewing times short, say 30 secs at a time, then shade the front lens for a short while.

[agingjb]

I had no trouble in 2004 producing a projection with handheld binoculars onto a piece of paper that showed the planet. Not wonderful, but at least I could say I saw the transit (no telescope available at the time).