Off axis Baader film and fire hazard

[squeaky]

Eek!

I'm waiting for a front to pass over which should have clear skies behind it. So I've been setting up for shots between the clouds.

Just went back out after sorting some emails to see a wisp of smoke coming off my Baader Safety Mask (home made).

It looks as though the few bright moments while I was emailing drifted off axis (I wasn't auto tracking) and focussed the sun onto my cardboard bits. Despite the huge reductions the film makes - this is what I found...

Well, the basic offset mask fitted (needs making tidy - but works)

And this was what it looked like inside...

I count three separate cloud free "events".

Moral of the story - never ever leave a scope unattended when pointed at or near the sun!

Can you just imagine the repair call... "Hi, this new telescope I bought needs a repair - I set fire to it!"

Luckily - scorching my mask was the only damage.

[jgs001]

have you used that mask yet ? I'd be wondering why it is, that the piece of cardboard on the inside mounted to the OTA got burnt... there shouldn't be any way sunlight could enter the OTA except through the safety film, and no other way I can see you'd get focused sunlight onto the inside of the card like that.

It it were me, I'd be thoroughly checking for 'leaks' and sealing them before use.

I do agree about not leaving them outside in sunlight though, especially in that lovely heat absorbing black ...

[squeaky]

I checked it thoroughly against a halogen spotlight. No leaks, no gaps, no micro dots.

Hmm... a thought... mine is a Flex... so could the sun have peeked through the truss section onto the mirror...? Hang on, I'll go look...

YEP! I can stand beside the tube and see part of my primary through the truss section.

That'll be it then. Phew! I say phew because I'd much rather it was this than a dodgy film!

OH, and the weather forecast is wrong - I should have clear skies now. Still dodging clouds.

[jgs001]

that's good that the filter and holder is not leaking... I think I'd want a shroud around that flex, and some way to seal the top too... I can't think of a good thing in not doing so...

[Cath]

I like to know how light managed to become focused onto the cardboard like that. It doesn't make sense to me. Something is not quite right there.

[RogerTheDodger]

If the light is coming in off-axis, the focal point will also be off-axis. The end of a newt tube will be close to the focal point, and as it's not focusing on the secondary, it will focus on the cardboard mask.

[squeaky]

If the light is coming in off-axis, the focal point will also be off-axis. The end of a newt tube will be close to the focal point, and as it's not focusing on the secondary, it will focus on the cardboard mask.

Yep, that's my thought too. Think of the distance from the secondary to the focal point of an eyepiece - and the distance from the (missed) secondary to the end of the flex-tube... and they're not too different. The scorch marks are about 1" (25mm) across - so it's a good job it didn't manage a point focus at that distance!

[Moonshane]

this is an important post and confirms one of the reasons for having a shroud on an open truss, especially when observing the sun.

[Cath]

Eek, using a none enclosed scope on the sun!

I would suggest rapping the scope in something or other when used on the sun. I would never use an open scope on the sun.

[squeaky]

Yeah, I kinda worked that one out

[Cath]

After said event

Maybe this thread should be made a stickly?

[pajr777]

At least with a truss the ash from the cardboard didn't end up on your primary

[squeaky]

At least with a truss the ash from the cardboard didn't end up on your primary

Yeah, lucky me

[squeaky]

Maybe this thread should be made a stickly?

If a mod decides to do that I reckon the title should be changed...

Using off axis solar film with an open truss

Or something. Maybe with - (Fire hazard)

[rfdesigner]

After said event

Maybe this thread should be made a stickly?

I'd second that.. c'mon mods!

[squeaky]

Give them some time - I haven't put the fire out yet

Might need a new user name - Firebug

[661-pete]

One other risk just occurred to me, and this applies to a closed tube as well as a truss.

What if sunlight gets in through the focusser?

If there's no EP present, parallel rays will be reflected, by the secondary, down to the primary, and will then be brought to a focus at the top. If part of the focus cone misses the secondary (or if the scope is out of collimation)...

This could happen while you're setting up, having deliberately pointed your scope 90° 'away' from the Sun...

[jgs001]

I've raised the question of stickyfying the post in the office... we have a lot of stickies, and with the new software things work differently. I'll let you know.

[squeaky]

I've raised the question of stickyfying the post in the office... we have a lot of stickies, and with the new software things work differently. I'll let you know.

Or have a general safety tips sticky...?

Or have a Welcome sticky, then a Main Index Sticky and just link to all the Important Threads/Posts...?

TBH I think the majority of stickies on the majority of boards could simply be listed in a single post. Might be easier for users to trawl as well?

[E621Keith]

You are lucky it was the cardboard which get burnt. If it can burn cardboard it can burn retina.

[squeaky]

You are lucky it was the cardboard which get burnt. If it can burn cardboard it can burn retina.

Yep. Definitely time to make a shroud before I try Solar viewing again.

[Macavity]

Direct sunlight on the mirror all has to "focus" somewhere.

I've always imagined rolling out one of these:

http://www.optcorp.com/cart/productimages/OrionMonsterDob13-L.JPG

during daylight hours must constitute a hazard.

[661-pete]

Surely truss Dobs all come with a mirror cover, which fits directly over the primary? Certainly I've seen such a thing in the shops (never owned one). Else how do you protect the primary from dust? So the safe thing to do is keep the mirror covered if you're manoeuvring the 'scope around in daylight...