Triband Erf

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Derek Klepp
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Triband Erf

Post by Derek Klepp »

Just wondering if I can get one of these.I have got a 152 mmf5 petzvyl scope and can mount an Erf. In front of the lense in the last baffle.Otherwise I will mount an Erf for Ha in there and try a quark.
Cheers Derek


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Re: Triband Erf

Post by marktownley »

There was not many made initially (6 I think) - I have 2, walter has one, Andreas Murner has one and michael wilkinson has another, that leaves one unaccounted for...

You could contact Oliver at Beloptik and see what he says...


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Re: Triband Erf

Post by swisswalter »

Hi Derek

yes contact Oliver. May be he still has the last one and is eager to sell it ;)


Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

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from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)
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Pablito
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Re: Triband Erf

Post by Pablito »

Nope. Last one owns my friend who lives in UK ;)


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Re: Triband Erf

Post by pedro »

There is one 4 sale (UK B&S):

http://www.astrobuysell.com/uk/propview.php?view=80336

ERF triband filter/ Now sold to Michael
Very well suited for safe solar observation with Daystar filters, SolarSpectrum or other Ca, Ha, Coronado PST mods. and herschel wedge .
Keeps primary telescope focus cooler.

- Diameter 85mm (82mm free aperture)
- Thickness 8.25mm
- Schott N-BK7
- Triple bandpass coating (transmission in Ca, Continuum and Ha)
- Substrate precise polished
- New and unused without cell
- Made in Germany

The coatings are multi-layer hard coatings.

New and unused. The beloptik.de filter. Collection from London only, £195.00. John
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Re: Triband Erf

Post by swisswalter »

thanks Pedro, I forgot that add


Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)
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Re: Triband Erf

Post by michael.h.f.wilkinson »

I got that last one. Planning to use it myself, first in front of my 80mm APM, later inside a 5 or 6" scope.


Solar kit: GP-C8 with Thousand Oaks Solar filter, APM 80mm F/6, Lunt Herschel Wedge, Solar Spectrum 0.3Å H-alpha filter, Beloptic Tri-Band ERF (80mm free aperture), Thousand Oaks 90mm ERF, Coronado SolarMax II 60mm with Double Stack Unit. Lunt straight B1800 Ca-K module.
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Re: Triband Erf

Post by swisswalter »

Hi Michael

congrats. Have fun with the new toy


Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

from 7 am - 7 pm http://www.nanosys.ch

from 7.01 pm - 6.59 am http://www.wastronomiko.com some times vice versa ;)
mdwmark
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Re: Triband Erf

Post by mdwmark »

What you guys call a triband ERF is not much different then a three channel Neb filter like Andover makes. I would be concerned about the amount of heat at the petzval lens at the back of that type of scope. You still have the other wavelengths getting through.
If you are going to use that style of scope block as much energy as possible.
When it came to designing telecentrics the optical engineer told me to stay away from that design for solar scopes. It may have been that we didn't have the Baader type ERF's to keep the heat down, but I don't think you can make a true telecentric design work with a petzval designed scope.
Mark W.


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Re: Triband Erf

Post by Astrograph »

Have to second MarkW

Petzvals will not work well with telecentrics and should never be used without a front mounted ERF.


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Re: Triband Erf

Post by Derek Klepp »

Thanks guys as the scope only cost $300 dollars it can be modified as the front lense is f10 just need a longer tube.It still works OK with the Lunt wedge.
Cheers Derek


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Re: Triband Erf

Post by michael.h.f.wilkinson »

I fully understand why Petzvals are generally avoided in solar work, in particular when combined with Herschel wedges, and I can also see how they would clash with telecentric systems (I suppose you cold compute one, but that would be a pain (and expensive)). However, I am not quite sure I understand the requirement of front mounted ERF in the case of dielectric ERFs. A front-mounted dielectric ERF will reflect a certain percentage of the incoming energy. The remainder enters the Petzval lens after going through the first lens groups. If the same ERF is mounted between first lens groups and Petzval lens, it reflects the same percentage of energy back towards the main objective, and the same amount of energy impacts on the Petzval system.

Maybe someone more knowledgeable than I can explain it


Solar kit: GP-C8 with Thousand Oaks Solar filter, APM 80mm F/6, Lunt Herschel Wedge, Solar Spectrum 0.3Å H-alpha filter, Beloptic Tri-Band ERF (80mm free aperture), Thousand Oaks 90mm ERF, Coronado SolarMax II 60mm with Double Stack Unit. Lunt straight B1800 Ca-K module.
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Re: Triband Erf

Post by Astrograph »

Hi Michael

Front mounted ERF's are Energy ABSORPTION filters not reflection. When you pick one up it rattles because the glass is loose in the mounting to allow it to expand as over time it will get warm. These filters are normally made to block UV light which causes the most heat build up.

A dielectric ERF (i.e. a UV/IR cut filter) is basically a mirror that REFLECTS light back out of the telescope.

When light enters a telescope, it is unfocused so the front objective is not affected by long term exposure. It does not heat up. The rear of a telescope is another matter. In a Petzval the rear cell will encounter concentrated light and therefore get hot. This will make it expand with predictable results. A front mounted filter prevents.

You must also avoid using a dielectric ERF with an oil spaced refractor. Because the dielectric mirror encounters converging light it is reflected back still converging. Therefore as it exits the scope it will be more focused. This can cause the oil to heat and possibly separate.


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Re: Triband Erf

Post by michael.h.f.wilkinson »

I know the difference between an absorbing (which should also absorb a lot of NIR) and dielectric ERF, and the problems of heat concentration in the rear element of a Petzval, hence my remark. I still do not see why a dielectric ERF could not be used in a Petzval scope (with non-oil-spaced front element, as you rightly point out). With a Petzval, you would still face the telecentricity issues, so maybe it is a moot point


Solar kit: GP-C8 with Thousand Oaks Solar filter, APM 80mm F/6, Lunt Herschel Wedge, Solar Spectrum 0.3Å H-alpha filter, Beloptic Tri-Band ERF (80mm free aperture), Thousand Oaks 90mm ERF, Coronado SolarMax II 60mm with Double Stack Unit. Lunt straight B1800 Ca-K module.
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