There will be a transit of Mercury Monday morning. I have some binoculars and a set of eclipse viewing specs. If I tape the eclipse filters over the binocular objective (big) lenses, will that be enough to safely view the transit? I guess I could fold the specs and double the filter and then just look through monocular style. I’ve read that putting the filters over the ocular (eyepiece) lenses will heat up the filters too much.
Would my idea work OK or not?
Eclipse filters are not intended for looking at a sun whose light is being concentrated by binoculars. If you are determined to see it “first hand,” I suggest using a pinhole projection system. If your aim is to see it magnified, I suggest finding one of probably several websites that will show it through a telescope.
That’s why california jobcase said to tape the filters over the objective lenses.
The technique works fine, and I used it for the Venus transit a while back. There is some risk in that if the tape fails and the filter falls off, you now have the sun beaming in your eye. But it’s really not that hard to make sure the tape is secure. The reduction in brightness works exactly the same as an unmagnified image.
There is definitely something to be said about watching it directly instead of through a projection system.
Unless you have VERY powerful binoculars, this discussion may be moot. I watched the Transit of Venus through a 500mm lens, and it still looked pretty small (though I got some really great photos). Mercury is much smaller than Venus and is farther away. Good luck finding it.
A pinhole projection would be way too small.
Another option is to find an observatory in your area that is opening up for public viewing of the event. That is my plan, weather permitting.
Hmm. I found that the transit of Venus could be easily seen without any magnification at all, and that with a modest 12x magnification (12x36 binoculars) I got a very good view. Mercury is about 1/300 the diameter of the sun, so it’s not large, but I’m still thinking it should be pretty visible with decent binoculars.
I guess I could also try putting the filters over my digital camera lens and using its zoom feature. If that isn’t enough magnification, maybe I could combine it with the binoculars with the filters over the objective lens. It would be safe either way since I wouldn’t be viewing directly.
I covered the lens of a Canon with a 30X zoom and got great photos of the August 2017 eclipse. I would be careful with binoculars. Any screw-up could burn your retina.
While I think this is better (putting the filter in front of the binoculars), I don’t think it is correct. You are still condensing the area of the outer lens into your pupil or even smaller area. So sure you are blocking 99% of the bad radiation. But then you are multiplying that area back up over 100x the area. <note that math is estimation for the purposes of demonstration>
Just to test this out right now, I have welding glass (7cm x 15cm- purchased for the transit of Venus and the then-upcoming solar eclipse) and with 3 welding glasses overlaid I can’t see the sun staring straight at it (it is very very dim but viewable with 2). However, I can see the sun through binoculars (8x40) with the 3 welding glasses on the front. So the binoculars are absolutely and logically condensing the light that is allowed through the filters.
So putting the filter in front of the binoculars does not equate to safety.
It is physically impossible for a passive optical system to change the surface brightness of an object. An optical system can change the apparent size of an object, but not the brightness.
So for the purposes of blocking light, it doesn’t matter if the filter is in the front or back. Any magnification the optics perform is exactly counteracted by a change in the collection area. The same amount of light will pass through the system either way.
The reason for putting the filter on the objective side is for heat dissipation purposes–the filter has to do something with the blocked energy, and the larger the area this is spread over the better. An eyepiece filter is likely to melt or crack with that amount of energy. The same filter on the objective side is not being heated any more than leaving it out in the sun.
I’m not sure what’s up with your experiment, other than that maybe the magnification (as compared to an increase in surface brightness) is making the difference.
While I can’t speak to the safety of using welding glass filters in front of the lenses of a pair of binoculars for solar observation, as Dr. Stranglelove correctly points out above, placing filters at the objective end of a telescope (or binoculars) is standard practice for the heat dissipation reasons he states. I have an 8 inch Celestron telescope, the solar filter for it is a thin sheet of aluminized mylar in a metal collar that fits over the front of the scope. Interestingly, the view through the scope is quite clear even though the mylar is quite wrinkly.
I used eclipse glasses taped over the objective lenses of a pair of binoculars for the 2017 eclipse. I can’t say for sure that I suffered no ocular damage, but I did not noticably fry my retinas. Also, I purchased a reputably made set of low magnification eclipse binoculars (basically a fold up cardboard deal) and they had built in filters on the objective side.
Well, I tried it with the eclipse filter over the binocular lens. No eye damage, but not enough magnification. I guess my life will probably finish without having personally seen a Mercury transit!
I tried with my 8x42 binocs projecting on to a piece of paper – didn’t see anything other then a bright circle. I watched some of the live streams instead.
I did use this method for a recent Venus transit successfully
Brian
To be clear, I used the binocular projection system to view the Venus transit, not the watch online system 
Brian
I tried using a 50x scope projecting onto a piece of paper. Got a sharp image the size of a nickel. But …
We are surrounded by trees. No matter where I moved there were shadows of branches and leaves on the image. Trying to spot a tiny dot on that was impossible.
I would have to go a considerable distance up the street to a clear area with the gear to hold things.
When I was taking the scope out I wondered to myself “Gee, I haven’t used this in years. I should bring it out more often.” And now I remember why it’s not all that usable.
My wife has a coupe of scopes w/ the appropriate filters - but little use when it is cloudy and FUCKING SNOWING OUT! :mad:
hmmmm.
I’m sensing a [DEL]potential scam[/DEL] business opportunity here. Filters for your 'phone, monitor etc. that you need when watching eclipses via youtube or similar.
$39.99 for 1 or $75 for 3, guaranteed organic, made by artisans high in the Himalayas.
Runs to get it onto kickstarter
Dinsdale, you just had a really, really effective solar filter.
ha! :d