Failed, shooting the sun

I hope this is the place to post this. If not, feel free to move it. NEWBIE ALERT!

With the new sunspot cycle, I wanted to be able to shoot the sun. I have other reasons to be able to look directly at it, but I thought I would photograph it in the process.

I went to the local welding supply and bought a piece of welding glass. It is marked "optically correct", but I know for this purpose it might not be good enough. At $4, it certainly isn't a costly experiment.

The problem came when I held the glass in front of my 100-400 and tried to focus. I cannot find a focus point at all. It looks out of focus no matter what I do with it. Is this a function of the wavelength of the light? Or what?

Aaargh! You held a bit of glass in front of your £1000 lens while it was pointing at the sun? You do know how much damage you could have done if you'd have allowed that bit of glass to drop?

Here's a link explaining how to make a safe filter.

hollis_f wrote in post #14397786
Aaargh! You held a bit of glass in front of your £1000 lens while it was pointing at the sun? You do know how much damage you could have done if you'd have allowed that bit of glass to drop?

Here's a link explaining how to make a safe filter.

Yep, sure do. It's called being careful.

Thanks for the link.

hollis_f wrote in post #14397786
Aaargh! You held a bit of glass in front of your £1000 lens while it was pointing at the sun? You do know how much damage you could have done if you'd have allowed that bit of glass to drop?

Here's a link explaining how to make a safe filter.

It does damage to the lens as well? I've always heard not to shoot at the sun because it would damage the sensor (or your eyes if you're looking through the viewfinder). I think it mentions that in the manual.

ohata0 wrote in post #14403541
It does damage to the lens as well?

It has the potential to do so. There's a lot of heat being concentrated at the rear of the lens.

Gary - have you tried to just manually focus the lens on infinity? I'd be really nervous about the heat factor Frank mentions. If you must do this, perhaps shooting off a tinted mirror would be safer.

ohata0 wrote in post #14403541
It does damage to the lens as well? I've always heard not to shoot at the sun because it would damage the sensor (or your eyes if you're looking through the viewfinder). I think it mentions that in the manual.

The lens has a viewing angle. Much of the light within this circle will be projected to the image circle in the camera. So if you aim a lens directly at the sun, you project lots of energy at the sensor.

But the front element of a tele lens will pick up light for a much wider angle than the viewing angle of the lens. The lens normally tries to "eat" this light by having it absorbed inside the lens. That is why the sides inside the lens are matte-black. Because reflections inside the lens would result in loss of contrast in the photo. And that is a big reason why we have hoods when shooting towards light sources.

But in the end, the sun pours out about 1kW/m2 of energy. And the lens elements tries to project that light into a quite small circle somewhere inside the lens or inside the camera.

Another thing you should consider is that some light are visible. But lots of the light from the sun are outside the visible range. You have IR and UW light too. Not visible but transmitting energy. So a filter that does only filter the visible light but lets through the short UV light or the long IR waves can project an image that looks ok, while at the same time projecting huge amounts of heat.

That means that it may look eye-safe or camera-safe, while the amount of energy that reaches the camera sensor or your eyes are way above the safe levels.

Lots of people with spotting scopes have had very bad oops moments because they have been carrying their scopes over the shoulder without any lens cap.

In the end, any use of optical instruments requires the user to think twice with regards to the sun.

Having a lose filter held by hand means that the filter is only there when you think about it and intentionally point your lens at the sun. What about when you fool around with your camera while trying to mount it on the tripod? What if you point it at the sun then? In what direction will the camera point before you put the filter in front of the lens and start aiming the camera?

+1 to the warnings. Big, bright, hot, ouch !. Not good.

Aside from that, you need a fairly light-tight seal between your solar filter or welding glass and the lens. Otherwise you get stray light bouncing around between the lens and the filter and it's nearly impossible to get a real image. Your camera was probably trying to focus on that.

C'mon, folks. Let's give a little credit here. The camera is rotated away from the sun by at least 45 degrees during any time the filter is removed. As for leakage, the filter is much larger than the largest element of the lens. Yes, I have manually focused on infinity, on cloud edges, etc. In fact, I've varied the focus all over that end of the range, and it does not work. Someone mentioned the other wavelengths of lights, and that was my original question. Does anyone actually know the answer? Or is everyone just happy saying it is a bad idea? I really feel it must be mostly related to wavelength of the light passing through, because binoculars will focus. They will easily go to hyper-infinity, where the 100-400 won't. Maybe that's what it takes.

Yes, it's no.
You're welcome.

Then what? Anyone know?

Gary McDuffie wrote in post #14407325
...........I really feel it must be mostly related to wavelength of the light passing through, because binoculars will focus. They will easily go to hyper-infinity, where the 100-400 won't. Maybe that's what it takes.

Gary, you've got me stumped here and that's why I'm asking.

How is it than you can manually focus your binocs to hyper-infinity, but you can't manually focus the 100-400 to do the same. Am I missing something obvious here?

The 100-400 won't go beyond infinity like the binocs will.

Gary McDuffie wrote in post #14408324
The 100-400 won't go beyond infinity like the binocs will.

Ok - I see what you're saying now. And even when you set it AT infinity things are still out of focus?

I find my 100-400 does go past infinity......or it appears so. If I set it to past infinity the moon for example is OOF, and I have to pull it back a bit to make it focus.. Is this what is being talked about here?