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So we'd have to ask you to check the manual or consult your TeleVue-dealer. If the telescope can be used for projecting the sun, it can also be used with a Herschel wedge.
If this is the case, please also clarify if the 1.8 ND filter should be placed where the Continuum filter was with the 3.0 ND behind it closest to the eye piece, the other way around with the 3.0 ND closest to the prism with the 1.8 ND closest to the eye piece, or whether it makes no difference.
*The documentation specifically mentions Astro Physics, TEC, and Zeiss. I am using a Tele Vue-85 which claims APO performance.
To be straight! The Herschel wedge warrants for a safe solar viewing experience, with only the ND 3.0 filter in place! However, the photopic reception of brightness is very different for different eyes (and related to age as well!).
When adding a solar continuum filter, the user has the same amount of transmission reaching the eye as without such a filter - but only within a 10 nm wide part of the spectrum at 540 nm. For this reason the "overall brighness" is perceived as being less. But if the Herschel wedge (w. ND 3.0 filter in place) were transmitting a dangerous amount of energy - even the small 10 nm "window" would constitute a "danger".
So for a 99.9 % majority of people it is not "necessary" from the aspect of safety, to add another ND -filter on top of the necessary ND 3.0 filter. But - a small number of people do inherit raised sensitivity for brightness, leading to eventual phototoxic reactions in the eye during prolonged and repeated exposure to light levels that would be perceived as normal by others.
Effects of phototoxic overreaction have been exhaustively investigated for the new generation of LED and CREE light sources which can compete in their radiation intensity with solar brightness in the meantime - when stared into at close distance. So the same precautions as valid for direct intensive LED illumination must be observed for Herschel-wedge operation just as well.
Fortunately most people have a "built in" aversive-reaction, to avoid excessive amounts of light falling onto the retina. So everyone observing the sun should be attentive to constantly observe his own "comfort feeling". If the visual brightness is experienced as causing strain on the eye, or an "afterglow-experience" will remain for some time when lifting the eye from the eyepiece, - in these cases a further added 0.9 ND filter will largely help to have a comfortable seeing experience. Adding a 1.8 ND filter though onto the 3.0 ND-filter will dim the solar image to a degree that fine solar details become invisible (unnecessarily).
Do test the Herschel brightness experience in good faith for a few seconds with only the ND 3.0 filter in place (always!). Depending on your age then maybe add a 0.9 ND- or even 0.6 ND-filter, until the image brightness is perceived as comfortable even at viewing sessions of up to 3 minutes. After each 3 minutes a short pause is mandatory, to check for any "afterglow"- effects, for dizzyness or for impaired vision. This is because brightness strain on the eye can bring out hidden retina damages or very early retina dislocation that went unnoticed before.
Only for imaging purposes, the ND 3.0 filter may be taken off the light path and replaced with one of the photographic ND-filters (0.6/0.9 or 1.8 ND) - so as to arrange brightness in a way that the shortest available camera exposure time can be made use of.
We recommend to put them flat on a rubber mat (e.g. sponge rubber) and put another piece of rubber on top of it. Then put your flat hand on the upper rubber mat and rotate it - this way, the pressure is distributed on the whole filter cell, and the the two parts shut come off easily.
Larger telescopes are a bit of a problem as there aren't many of them, so we can't really test it. However, we recommend take do some breaks during the observation so that everything can cool down.
Please also note that not only aperture is a problem, but also the f/ratio - a fast telescope has got a smaller image of the sun close the the Herschel and will get hotter, while a telescope with a long focal length will produce a wider beam of light - this distributes the energy onto a larger space (so that it doesn't get too hot), but there is a higher risk that the light will not completely hit the prism when you center details at the edge of the sun for better observation. For each meter of focal length, the image of the sun is about 1 cm large, and it should fit fit completely into the 2" nosepiece ot the Herschel - which has got a free aperture of about 48mm. Otherwise, parts of the focuser may become very hot when the sun is not centered.
So please take both focal length (diameter of the beam of light) and f/ratio into account when you think about larger telescopes.
Baader Adapter 2" (male) / T-2 (male) # 1508035
Then you have a T-2-thread, onto which you can mount the binoviewer or the T-2 QuickChanger as described in the manual (page 18 in the manual of the MaxBright II); the 2"-filters of the Herschel wedge fit into the 2"/T-2 adapter. We recommend a T-2 quickhanger, so that you can insert the glasspath correctors for T-2 into the binoviewer; be careful with the 2.6x gpc as it may hit the filters in the Herschel.
By using the T-2-connection, you can also use
Baader T-2 Conversion Ring # 2958110 plus
Baader Double T-Filterholder 1¼" # 1508030
to mount a 1.25" filter in front of the binoviewer. Again, this may be problematic with the 2.5x gpc as it faces towards the telescope and not into the binoviewer, so make sure that you have enough backfocus.
Installing a single polarizing filter is tricky, as you can't rotate the binoviewer as easily as an eyepiece. There should be enough place to mount the filter in front of the double stack and use the T-2 quickchanger to access it for adjusting the brightness.
If you have problems with eyepieces, you can try to use the adapter #1508035 to attach another eyepiece clamp with T-2-thread - e.g. #2458100 - or an eyepiece, where the field stop is moved into the 2"-barrel, closer to the telescope.
The Herschel Wedge requires a backfocus of 114mm, of this 47mm are used by the 2" Clicklock clamp. To measure the backfocus of your telescope, point the telescope at the full moon, hold a piece of paper behind it and measure the distance between the drawn-in focuser tube and the sharp image of the moon.
If there is enough backfocus, there are also #2956237 37mm ClickLock extension and #2956247 47mm ClickLock extension, although this may be a bit on the costly side...
If you need only some mm, you could use Baader Hyperion 2" Finetuning Stopring with brass clamping ring & 2 thumb screws # 2958027 to keep the eyepiece a little bit outside of the eyepiece clamp.
Would it work well?
Please also read the instructions for the Herschel Wedge thoroughly and only use this product if you feel well informed about the consequenzes of wrong handling.
I ordered the new wedge from WideScreen-Centre in UK, which appeared to be one of few companies having the item in stock. The wedge arrived late last week. I’ve already been able to test it a couple of times and everything seems to work very well. However, I’m not able to remove pre-mounted ND OD 3.0 in order to install one of the less dense ND filters to reduce the exposure times. The Continuum filter unthreads just fine, but the filter is totally stuck. I’m afraid to apply to much force and are wondering if it might have thread lock (locktite) applied or if there some special “technique” in order to remove it.
Or do I need to get a another Baader Adapter 2" (male) / T-2 (male) # 1508035?
Not being able to swap the ND OD 3.0 for one of the less dense somewhat removes whole point for my upgrade.
Will the unfiltered solar energy entering my(very expensive) air spaced triplet objective possibly damage the lens due to over heating? Could I use the wedge/and refractor continuously for 2 or 3 hours with out worry of damage to either? Thank you. Jon Mayer
Baader 2" Cool-Ceramic Safety Herschel prism, Visual and photographic
There is no better way for uncompromising Solar Observation / Solar Photography in white light
Every Solar Diagonal needs additional neutral density filters since the reflected energy of the first surface prism (4.6%) still is a factor of 1000 too large for the human eye. All Baader Solar Diagonals are delivered with a pre-mounted ND 3.0 Baader precision 2 light reduction filter. The photographic version includes other ND-Filters to achieve shorter exposure times. Use with care!
- Space-Technology: The exiting beam in the Baader Safety Herschel Wedge is fed into a heat cage separated from the prism body. Like on a Space Shuttle a ceramic tile forming the back end of the heat cage absorbs the radiant heat without overheating its surroundings. The closed prism body offers perfect safety for educational work.
- Solar Finder: The translucent ceramic tile acts as projection screen for the unfocused image of the Sun. Aiming the telescope at the Sun becomes very easy.
- ClickLock 2 Clamp: Securely clamp any eyepiece with only the push of a lever. Change eyepieces single handedly even in winter with heavy gloves.
- Filter Holder: A 2/M48 threaded ring couples the 2 ClickLock-Clamp to the body of the Safety Herschel Wedge and acts as a filter holder for 2 filters.
- Solar Continuum Filter (10nm HBW/540nm CWL): Included as standard filter
- Optional recommended accessories:2 Baader Polarizer-Filter (# 2408342) mounts into any 2 eyepiece or 2 to 1.25 reducer for adjusting image brightness simply by rotating the eyepiece. Reducer ring 2to T-2 (#1508035) allows to mount any DSLR-camera T-mount directly on top of the Solar Diagonal body
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