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Using CDs/DVDs as a solar filter - safe for reflector?

fragmonkey

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fragmonkey

fragmonkey

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I found this here guide for a DIY solar filter for your DSLR: http://www.instructables.com/id/DIY-Solar-Filter-for-Camera/

I'm wondering if that same thing could work on a newtonian reflector. Mine has an aperture that is completely covered by a CD or DVD, though I'm concerned that maybe too much light can still get through and damage the reflecting mirror. Should I be concerned about sunlight ruining the mirror? I thought I read somewhere that direct sunlight can damage the internals. Maybe I can use two such DIY filters for even less light coming through?

As an aside, I have a proper filter arriving in the mail sometime next week but this seems like something fun to do in the mean time.

Thanks

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John

John

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Don't risk it !!!!!

Use a proper filter in the proper way, ie: fully covering the aperture of the scope at the front end.

The risk of damage to your eye is far more grave than the risk to the mirror - you can buy a new mirror for a few £'s.

Proper solar filters made from Baader Solar Film are really not expensive and block 99.999% of the light from the Sun which is what you need to make viewing safe.

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KeironKK

KeironKK

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Even if you managed to make it, I am sure something similar would happen. Your eyes are more precious and valuable than a cheap CD disk. I wouldn't even risk it. Bide your time reading up on what you could expect to see with a proper solar filter.

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fragmonkey

fragmonkey

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I totally neglected to mention, but this is for IMAGING with a dslr, so I'm now too worried about my eyes getting any sunlight whatsoever :)

I'm far more concerned about any impact on my telescope. I tested it out briefly just by holding one of these CDs in front of my eyes outside and it blocks significant light. Using two makes the sun appear like a solid white ball without any extreme light.

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Luke

Luke

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Baader say to not use the Herschel Wedge (also at the eyepiece/camera end) with a reflector, so I'm sure the same goes for the CD/DVD:

"Only use the Herschel Solar Prism with refracting telescopes. Reflecting telescopes may be damaged by the concentrated energy at their secondary mirrors."

I personally wouldn't use the CD/DVD even with a refractor, as the Baader film is high quality, cheap and readily available :laugh:

Have fun when it arrives, white light can get quite addictive :smiley:

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fragmonkey

fragmonkey

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Baader say to not use the Herschel Wedge (also at the eyepiece/camera end) with a reflector, so I'm sure the same goes for the CD/DVD:

And personally I would wait for the safety film even if you had a frac rather than use the CD/DVD.

Of course this would be a terrible idea to use it at the eyepiece end with a reflector. The idea here is to use it at the opening, and this stuff really does seem to block out a lot of light. I'm just not sure how it blocks other wavelength, or if that's even an issue. The main thing with looking at the sun with an unprotected reflector is the heat generation, and from my basic testing it certainly feels like heat is not getting through

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Luke

Luke

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Ah, sorry, your text is fairly clear, not sure why I misread it, I was thinking you meant the full beam will focus on the camera :confused:

I have heard about people using CDs/DVDs (which is not to say it is safe) and as far as I recall the Baader film is superior optically. If you're going to get better results with the film anyway, is it worth any risk?

Of course this would be a terrible idea to use it at the eyepiece end with a reflector. The idea here is to use it at the opening, and this stuff really does seem to block out a lot of light. I'm just not sure how it blocks other wavelength, or if that's even an issue. The main thing with looking at the sun with an unprotected reflector is the heat generation, and from my basic testing it certainly feels like heat is not getting through

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John

John

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Of course this would be a terrible idea to use it at the eyepiece end with a reflector. The idea here is to use it at the opening, and this stuff really does seem to block out a lot of light. I'm just not sure how it blocks other wavelength, or if that's even an issue. The main thing with looking at the sun with an unprotected reflector is the heat generation, and from my basic testing it certainly feels like heat is not getting through

I'm all for experimenting but not where the Sun is concerned. There are so many things that you and the originator of the article you linked to above are "not sure" about I just can't understand why you would risk either your equipment or, worse, your eye when a tried and tested and most likely optically better performing solution is not only available for a low cost but you have already ordered it :undecided:

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Bizibilder

Bizibilder

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Again a definate NO from me. These things are NOT solar filters and are dangerous - even for photography. Get some Baader ND5.0 film and make a completely safe filter for visual or photographic use.

Playing with CD's / DVD's is not a "fun thing to do". Sorry to sound so firm but you only have one pair of eyes and it takes less than a second to blind yourself - permanently.

By the way, the reason you don't use a Herschel wedge with a reflector is that the sunlight would first be partially focussed onto the secondary mirror - and that would be enough to shatter it with the heat created. The wedge itself is specially designed and made from materials that will withstand the heat of the focussed Sun.

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Luke

Luke

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I've also heard that some CDs/DVDs have much thinner layers than others...

I think the bottom line is that the answer to the question, is it safe, is no.

These are not designed for solar viewing/imaging, have not had extensive safety testing, so it's impossible to say they are safe. And you do need to be *very* careful with solar. Any modding etc. should only be done at your own risk being fully aware of what you are doing and what the consequences are if anything goes wrong.

My Herschel Wedge comes with big warnings and pages of instructions, which you won't get with a CD. There is such a simple, affordable, better and safer alternative in the Baader solar film. :)

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Naemeth

Naemeth

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I totally neglected to mention, but this is for IMAGING with a dslr, so I'm now too worried about my eyes getting any sunlight whatsoever :)

I'm far more concerned about any impact on my telescope. I tested it out briefly just by holding one of these CDs in front of my eyes outside and it blocks significant light. Using two makes the sun appear like a solid white ball without any extreme light.

A second of unfiltered, concentrated light is easily enough to completely destroy your camera sensor. If the CD breaks (which can happen during normal use) then you will quite quickly get the secondary mirror holder melting, and anything you've got in the light path.

Don't risk it.

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Zakalwe

Zakalwe

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At best, you will get an absolute rubbish image of the Sun, such as the one in the link:

FTRWVR1H6DWQCPG.LARGE.jpg

A £20 Baader solar film would beat that image hands down.

You could easily end up killing your DSLR. The disc might block visible light, but what about infra-red? It could easily kill the shutter curtains.

At worst, you could knacker your eyes. A beam of focused sunlight coming through the viewfinder would do a lot of damage. Especially from a full aperture scope (the link shows only a piddling little disc to cover a camera lens).

In short, there's a lot of unknown risk with this. You might be OK, you might end up blind. It would be crazy to risk it just to save £23 on some Baader film.

Of course, if you do have a go, then have a read of the Darwin Awards page. it won't kill you, so you won't win a Darwin Award, but you might as well have a read about people that do dumb things whilst you still have eyes!

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AlexB67

AlexB67

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Solar observing is not something I'd want to try I think without seeing a setup. They do solar observing sessions here in Bristol, must go sometime and see the setups, have a chat about it :).

I've seen/read articles where people manage to burn the inside barrel coatings of eyepieces with insufficient protection in place with Newts. IMO, this is one of those cases where the "risk and experiment and see what happens" approach cannot be afforded in any form whatsoever.

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ScottS

ScottS

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My scope doesn't even get taken outside until the sun has left the sky. I know the dangers, but I also don't want someone else coming along and pointing it at the sun without knowing. Not into solar or imaging work but if I did I wouldn't do it in any way other than the proper tried and tested way.

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