Baader Hershel Wedge

Herschel Wedge

Warning - solar observing requires an understanding of what you are doing and strict observation of safety.  Do not ruin anyone's eyesight by a moments carelessness! (Don't fry your camera either)

I have an Orion glass solar filter that works fairly well and a couple of Baader film filters that work even better.  This blows those away.  It doesn't compare to my PST, but it isn't supposed to, it is a white light filter so sun spots and surface features are its strong suit.  The h-alpha filters typically do their best on prominences, though if you can afford a nice enough one they can show a lot of surface features.  I have had nothing but frustration in trying to obtain good solar photos, the wedge should be a major improvement in my photo taking ability.

Herschel Wedges have been popular solar observing accessories for years.  They consist of a high quality uncoated prism mounted so the prism reflects about 5% of the light towards the eyepiece, the remaining light exits harmfully (hopefully) out the back or bottom of the housing.   Since no filter is used in front of the telescope there is a lot of energy exiting the prism housing, these were always considered a somewhat hazardous item.  Burns, fires and blindness were just some of the possible events if a strict safety protocol was not observed.  Various manufactures have tried to make them safer, some more successfully than others.  Baader has developed a magnesium housing that uses a piece of space shuttle tile to capture and safely dissipate the energy.  The entire unit remains cool to the touch and is extremely safe to use.

You cannot use a Herschel Wedge with any type of reflecting telescope, nor can there be any elements in the back end of a refractor.  A simple achromat works best.   The front lens elements collect a lot of energy, smaller lenses later in the optical train cannot cope with the excess energy and will crack.  Any Barlows, field flatteners, or such much be in the system after the wedge.

The basic wedge comes with a Solar Continuum filter for use with achromat telescopes.  It also has a 3.0 Neutral Density filter permanently installed for visual use.  I have the photo version, it also includes the Solar Continuum filter, along with 3.0, 1.8, 0.9, and 0.6 Neutral Density filters, none are permanently installed.   The object is to get to a 1/1000 second exposure to freeze seeing.  The filters stack between the wedge and your camera - as many and in whatever order you need.  At ISO 200 the 1.8 typically gives me 1/1250 second, the 0.6 gives me 1/3250.  I'm still working out the ideal setup, I've only had the wedge a short while, but stacking the 1.8 and 0.6 gave me something to start with at 1/1000 second.

You MUST use the 3.0 Neutral Density filter for visual use.  Period.  5% of the Sun's energy is still too much for your eye to safely look at for an extended time.

The path of the wedge is 128mm to the top of the eyepiece holder.  It will work fine with most refractor/eyepiece combos.  Cameras, on the other hand, may cause problems since the light path has to come to focus above the top of the eyepiece holder.  To use the wedge for prime focus photography with my Nikon DSLR I had to obtain a different adapter to use in place of the 2" eyepiece holder, I didn't have enough front focus, the ring removes over 20mm from the image path and enables me to image the entire Sun.  If I want to magnify the image I can use the normal eyepiece holder with a Powermate and camera combination, some Barlows will also work.

Back A shot of the back showing the space shuttle tile.  Enough light passes through the tile that it acts as a handy solar finder.  The tile remains totally cool to the touch, the magnesium housing does get slightly warm.
Filters The filters provided are designed and coated specifically for use with the Herschel Wedge.  They are packaged in one of the slickest case systems I've ever seen. Each case interlocks top to bottom, or side to side, to build a drawer system.
Filter stack The filters thread into the bottom of a threaded nipple.  The nipple threads into the diagonal housing and into the eyepiece adapter. 

Filter stack showing here is: Solar Continuum, 1.8, and 0.6 Neutral Density

Using Baader's T2-27 t-ring adapter eliminates the extra 20mm of the eyepiece adapter to bring the camera's chip close enough to achieve focus.  Like the above nipple, the filters thread into the adapter, then it threads into the diagonal body.  Your t-ring then threads on the smaller end.

Changing filters is not quick, but it is a simple and secure system.
Case The wedge and filters are packed in a nice case.  Hard to damage anything here!
AR102 Wedge and camera mounted on my AR102 achromat.  The PST rides here too.  Using Baader's T2-27 t-ring adapter I reach focus with just a few mm's to spare.

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