Questions about a so called "Solar Wedge".

[WilliamAstro]

So as I ditched the solar filter since it is still risky as it can be prone to minor scratches and pinholes which leads to risk of damaged eyesight, I went on SGL months ago discussing a way to image/observe the sun without any risks. And one person suggested me a solar wedge. Here are questions about this product.

 

Q: If the material inside the solar wedge (that blocks out the sun light and you see the sun's disk) gets scratched, is there any risk to that?

A: (Here)

Q: It is said that it heats up overtime when it is pointed to the sun, if I use any imaging cameras or lenses is there a chance that will melt/burn the materials on them? Does it also have a risk of burning your skin too if your not careful?

A: (Here)

 

What I know from this product so far:

I know that it is only compatible for refractor telescope up to 150mm in diameter. In solution of that I will get myself an Evostar 72-ED and use my Nexstar SLT Mount since that mount only can be attachable to dovetail bars from an OTA.

Hypothetical equipment used dedicatedly for Solar/Lunar imaging.

OTA: Skywatcher Evostar 72-ED
Mount: Nexstar SLT or even my Skywatcher Star Adventurer (experimentally)

Cameras: ZWO 120MC-S, Canon 600D

Other: Lunt Herschel Wedge 1.25 Inch (for Solar imaging)

 

Feel free to give back advice as much as needed as I go along with this project.

Cheers!

William

[Gfamily]

Afraid I can't give any information about your specific queries, but personally I'd not be too concerned about minor scratches and pinholes in a Baader filter,  they're not going to admit any more light than your normal pupil unless they have a total area exceeding 5-10mm^2, and standard magnification is going to disperse even that over a larger area of your retina than your naked eye would give.

I would though be concerned about any defects that are very obvious.   

Edited July 15, 2022 by Gfamily

[wulfrun]

Just to point out, a Herschel wedge doesn't work by blocking light as such. It reflects a small amount toward the eyepiece and "dumps" the rest elsewhere by redirecting it.

[Mr Spock]

A wedge works by re-directing light and heat. There's no danger from scratching.

Only the back of the wedge gets hot. The red bit on a Lunt. Everything else is cool and there's no danger to eyepieces or cameras.

[Louis D]

I've been using Baader solar film in a homemade cell since it came out over 20 years ago.  It's an incredibly tough film.  A forward-back shake while viewing the sun or an incandescent filament will reveal any damage if you move the sun/filament around the entire aperture.  Tears would be immediately apparent from the shake as air would flow through the gap.  The bigger concern for me would be the filter falling off due to a poorly made cell.  Mine is a very snug, custom fit and doesn't come off without coaxing.

My Hercules 1.25" wedge looks nearly identical to the Lunt above except that the white ceramic heat sink is visible like the Altair wedge.  When used with my 90mm APO under the Texas sun, the white disk doesn't get any hotter than mildly warm.  I can keep my thumb on it with no discomfort.

If you're concerned about that residual 5% light going up to the eyepiece or camera, don't be.  It gets further attenuated by a 1:1000 neutral density filter (ND3) below the eyepiece holder.  There just isn't much heat energy left at that point.  It's still too bright for your eyes, so you'll need a variable neutral density filter or similar on the eyepiece.  Some wedges have this functionality built in.

My bigger concern is the focused sun's energy striking the interior side wall of my focuser over time if I walk away from my scope on my non-tracking alt-az mount.  I'm concerned it will scorch the interior blacking paint/material.  As such, I always cap the front of the scope when walking away for any reason.  I have enough experience as a child with a 2" magnifying glass to know that it doesn't take much to ignite combustibles with the focused energy of the sun.

BTW, 1.25" wedges are generally only rated up to 125mm scopes.  For 150mm scopes, a 2" wedge is recommended due to the larger heat dissipation capacity.

If the prism wedge itself got scratched, although I don't know how that would happen because it's hard to get to, you would have some loss of image contrast due to scattered light.  Let's say the scratch does somehow lead to prism failure and it shatters.  That's the beauty of the design right there.  100% of the light dumps out the back instead of the normal 95%, and none of it goes up to the camera or eyepiece.  The failure mode leads to a safe condition.

[Pete Presland]

The replies above have pretty covered everything, i have used my Lunt wedge on an Evostar for some quite long sessions, no problem with heat at all.

[Cosmic Geoff]

I wouldn't worry about pinholes and scratches on the full-aperture filter. With a 127mm scope, a pinhole 0.127mm in diameter would let through one millionth of the unfiltered light.

I did however have an accident with my home-made solar filter, where the pistoning effect of putting it on and taking it off displaced the inadequately secured film so that some unfiltered light got around the edge of the film.  It made a nasty glare, but fortunately I realised something was wrong before my eyesight suffered any damage. 

To repeat what others have said, the Herschel wedge does require a supplementary filter. 

The Herschel wedge system, unlike the full-aperture filter, has the potential for overheating parts of the telescope, as noted.

The projection method is probably safest of all for one's eyesight, but has the potential for overheating parts of the telescope, especially eyepieces with plastic parts, e.g. the basic eyepieces supplied with many Skywatcher and Celestron kits. Bits melt.  I also have an eyepiece cap with a hole melted in it.

Edited July 16, 2022 by Cosmic Geoff

[david_taurus83]

The 1.25" Lunt wedge used to come without the ND filter in place. I had this version and it required screwing the an ND filter into the eyepiec each time. I believe the newer ones now come with it already installed in the wedge. Just a thought if your buying second hand so you know what to look for. 

[Carbon Brush]

I use a 102mm scope with a Lacerta wedge. This design projects the 'wasted' light on to an aluminium slab.
It doesn't get hot even when left all day - and (given a bit of effort) can function as a finder.
The wedge includes the ND filter -that won't unscrew.
No reservations about using it.

[Gabby76]

I have a Baader herschel wedge which I have used for around 15 years now, excellent views.

The older Baader like mine uses a multi folded metal screening inside a enclosure as the heat trap. 

Observing with a 150mm f/8 refractor during the 2017 solar eclipse in USA, I observed for a total of 4 hours (sunspots-eclipse-sunspots)  and the temperature difference between the telescope tube and the light trap averaged 3°C. Never more than warm and no danger of anyone being tattooed by hot metal. 

[IB20]

I have a 1.25” Lunt Herschel wedge which I use in a 3” refractor, it has never even got slightly warm to the touch.