Lacerta Brewster-angle Herschel Wedge with 48mm Prism, ND3.0, 2" Nosepiece and 2" Rotator Eyepiece Holder
Made in Europe!
Lacerta White Light Herschel Wedge Solar Wedge with large prism with 48mm optical window with Brewster-angle and accessories included, M48-thread on telescope side, M54-thread on eyepiece side, 2" Rotation-Adapter to eyepiece or camera and 2" ND3.0 filter
The Herschel-LAC2s version of this series comes with a large prism with 48mm optical window, M48-thread and 2" nosepiece on telescope side, M54-thread and 2" rotation-adapter to eyepiece or camera on eyepiece side, and a 2" ND=3.0 neutral density filter is also included
Please read the SAFETY NOTES at the bottom of the page!
Most commercially available Herschel wedges (like INTES, Lunt, Scopium, Baader...) come in a 90-degree variant.
The Lacerta Herschel-wedge features a significant, 56.6-degree angle, so called Brewster-angle that provides a special benefit when compared with other 90-degree Herschel wedges.
This befenit is coming from the fact that nearly 100% of light is polarised under this angle; this means that the Lacerta Herschel wedge offers continuous or even complete dimming with the mandatory ND=3.0 filter and an additional (optional) polarising filter. In reality a dimming range between ND=4.07 and 6.37 or even more can be achieved.
Without the polarising filter the Herschel prism operates at ND 4.07 that is very good for photography. The 90° "traditional" Herschel prisms can achieve ND=4.24 to 5.00.
As seen on the below image, the difference in visual perception is significant, so this unique, patented design offers real improvement in visual observations as well as photography of the Sun in white light.
It can be seen that the granulation in traditional Herschel prisms is well observable only with an additional third filter in addition to the ND3 and polarising filters. Herschel prisms with Brewster angle do not need an extra filter, because the dimming range here continues to until ND=6.37.
How to use the Herschel prism?
- The ND3 filter must be placed on the eyepiece side, not the telescope side to avoide overheating and cracking of the filter. In the case of the Herschel LAC2s, the 2" ND3 filter glass is removed from the filter frame, and fixed directly into the fixed, bottom part of the Rotation Adapter (using the filter's own fixing ring from the filter frame).
- Then the polarasing filter is screwed into the bottom side of the rotating, top part of the Rotation Adapter. When we use this Herschel prism without the top, rotating part of the Rotation Adapter, the Polar filter must be screwed into the eyepiece. The overall brightness then is adjusted by the rotation of the eyepiece.
- Please note, that the optical elements strictly need to have the following sequence: Telescope - Herschel prism - ND3 filter - Polar filter - additional filter (e.g. IR block filter or contrast filters of your choice (i.e. Baader Solar Continuum filter)) - eyepiece (or camera)
- Be aware that when switching eyepieces, all the filters must be used again in the correct order. When observing with eyepieces, you have to "re-use" the polarising filter only as the ND3 filter stays inside the fixed, bottom part of the Rotation Adapter. Then you can regulate dimming by rotating the eyepiece (as it holds the polarising filter).
Note: The Herschel-LAC2s version takes up about 110mm of back focus. If there is still an additional 50-60mm back focus on your telescope, you could possibly add a Baader 2" ClickLock Clamp and screw the polarising filter into the bottom part of the ClickLock clamp instead of the eyepiece. This would make swapping eyepieces very easy as both the ND3 and polarising filters would stay in place all the time. Then dimming would be regulated by rotation of the ClickLock clamp.
Why is the Lacerta Herschel prism open at the bottom?
- The open design enables a much better ventilation than other designs that are available on the market
- The amount of stray light that enters through the open part is totally negligible compared to the bright sun entering from the telescope
- no light escapes through the open part, so your shoes wont be on fire!
WHAT'S IN THE BOX? (Herschel-LAC2s):
- Lacerta Herschel prism (component / core product) with Brewster angle, telescope side with M48 thread and eyepiece side with M54 thread,
- M48M48 37mm barrel as telescope side nosepiece adaptation,
- RotaM54p Rotation Adapter with internal M48 thread to take 2" filter glass
- ND3 filter (2"), incorporated into the fixed RotaM54p rotation adapter,
- RoteM48 Rotation Adapter with 2" filter thread on both sides (positive and negative).
Recommended optional products:
- 2" polarizing filter for continuous dimming.
Attention: Herschel prisms are generally relatively bright - an ND3 filter needs to be used mandatory! Continuous dimming is only possible if a polarizer is taken. But as many Astro friends have these two filters already, we offer the "naked" prism also solo as "core product". Please refer to the "recommended products" below!
ATTENTION: HERSCHEL PRISMS ARE GENERALLY RELATIVELY BRIGHT!
THE INCLUDED ND=3.0 FILTER MUST BE USED ALL THE TIME, PLUS IT MUST BE USED WITH A POLARISING FILTER AS WELL FOR VISUAL OBSERVATIONS!
CAN BE USED ONLY WITH REFRACTOR TELESCOPES!
All filters must be screwed in after the Herschel wedge, not before. If you screw in a filter in between the telescope and the Herschel wedge, the filter will most likely overheat and crack that is also dangerous for your eye...we cannot take any responsibility for any improper use. Use it responsibly and if you don't know what you are doing, ask a professional or don't use it.
IR/UV Blocking filter and Baader Solar Continuum Filter is also recommended, especially when used for photography.
When additional polarising filter is used, continuous dimming is possible.
Due to the fact that many amateur astronomers would already have a polarising filter and possibly even a ND=3.0 filter, we also offer the "naked down" prism as a component item.