Herschel wedge do I need one

[Stu]

6 minutes ago, Rob Sellent said:

Again, experienced observers argue that either a) it makes no difference, b) the risk of cracking a €2.5 - 6k scope is just not worth even contemplating, and c) thermal expansion, fracturing and shock of the lens is augmented in Fluorite.

On this point, I can only rely on personal experience Rob, in using my Fluorite FC100 for regular solar observing since I bought it a number of years ago with no ill effects. I guess I feel relatively safe given the lack of crazy hot sun in the UK, although I have used it on a number of very hot (for the UK) summer days. I think the argument is that the objective is (by definition) nowhere near the focal point so the light hitting it is not concentrated at all.

[Hallingskies]

6 minutes ago, Rob Sellent said:

Re: Solar viewing & Petzval fracs....(@Hallingskies)

I also find it quite confusing.

On the one hand, it's acknowledged from experienced observers on sites like Solar Chat, SGL and Cloudy Nights that using Petzval fracs and a wedge is fine. On the other hand, we get warnings from the wedge manufactures like Baader and Lunt categorically stating that they're not suitable for such scopes.

Similar kind of thing happens with Quark's solar eyepieces. Quark makes no mention but again, experienced observers argue that either a) it makes no difference, b) it only becomes a concern if you're tracking for a long time, c) they canot be used in oil-spaced Petzval's d) but can be used in air spaced Petzval's.

Icing for proverbial cake comes in the form of using Fluorite fracs for white light. Again, experienced observers argue that either a) it makes no difference, b) the risk of cracking a €2.5 - 6k scope is just not worth even contemplating, and c) thermal expansion, fracturing and shock of the lens is augmented in Fluorite.

It’s not just me, then!  I must admit I stick to Baader film on the front of the frac on the rare occasions I do any solar observing or imaging.  First off, it’s cheaper than a Herschel wedge, but mostly it’s because I really am not all that comfortable with the idea of funnelling 100w or so of solar heating down through frangible precision optics....😱😱😱🔥🔥🔥

[Alien 13]

3 minutes ago, Hallingskies said:

It’s not just me, then!  I must admit I stick to Baader film on the front of the frac on the rare occasions I do any solar observing or imaging.  First off, it’s cheaper than a Herschel wedge, but mostly it’s because I really am not all that comfortable with the idea of funnelling 100w or so of solar heating down through frangible precision optics....😱😱😱🔥🔥🔥

I feel the same too, its not just the optics either that get blasted with heat, the focusser and grease within it also gets hot and worse problems sill if there are any plastic bits in there...

Alan

[Hallingskies]

1 minute ago, Alien 13 said:

I feel the same too, its not just the optics either that get blasted with heat, the focusser and grease within it also gets hot and worse problems sill if there are any plastic bits in there...

Alan

Good point!

[Stu]

10 minutes ago, Hallingskies said:

It’s not just me, then!  I must admit I stick to Baader film on the front of the frac on the rare occasions I do any solar observing or imaging.  First off, it’s cheaper than a Herschel wedge, but mostly it’s because I really am not all that comfortable with the idea of funnelling 100w or so of solar heating down through frangible precision optics....😱😱😱🔥🔥🔥

Obviously we should all do what we feel most comfortable with. I think I've said before in this thread that I used to be scared of Herschel Wedges, mainly the older ones where the heat and light used to be directed downwards out of them. The latest units are safe, and to my mind give a much more enjoyable view than solar film. It's the difference between finding a boring blank disk, vs still being able to enjoy granulation cells and tiny pores at high power. If done correctly then it is quite safe for scope and observer, I've not experienced any of the difficulties mentioned and really enjoy my solar viewing.

[johnturley]

24 minutes ago, Rob Sellent said:

Re: Solar viewing & Petzval fracs....(@Hallingskies)

I also find it quite confusing.

On the one hand, it's acknowledged from experienced observers on sites like Solar Chat, SGL and Cloudy Nights that using Petzval fracs and a wedge is fine. On the other hand, we get warnings from the wedge manufactures like Baader and Lunt categorically stating that they're not suitable for such scopes.

Similar kind of thing happens with Quark's solar eyepieces. Quark makes no mention but again, experienced observers argue that either a) it makes no difference, b) it only becomes a concern if you're tracking for a long time, c) they canot be used in oil-spaced Petzval's d) but can be used in air spaced Petzval's.

Icing for proverbial cake comes in the form of using Fluorite fracs for white light. Again, experienced observers argue that either a) it makes no difference, b) the risk of cracking a €2.5 - 6k scope is just not worth even contemplating, and c) thermal expansion, fracturing and shock of the lens is augmented in Fluorite.

In my own case solar viewing is important. I'm not out everyday but I reckon we get an average of around 300 clear days a year. For white light I finally settled on a portable TV-76 + Wedge. A Lunt 60mm for H-alpha (ease of use, no cables, no faff) and a fluorite strictly for those delicate and tender photons of the night .   

I think that's a very sensible approach, I recently purchased an Es Reid tested Esprit 150, and I asked Es (who incidentally does quite a bit of solar observing, but with a dedicated solar scope) about using A Quark solar eyepiece with the scope, and his opinion was that he wouldn't risk it.

As Rob suggested, a Hershell Wedge probably ok with refractors up to 80-100 mm, for larger sizes  a full aperture solar filter such as the Baader or Seymour is a safer option, or best of all a dedicated solar scope. 

John 

[johninderby]

With a regular frac up to 150mm heat is no problem with a wedge. The glass at the front doesn’t get warm as  the Sun's light is not yet concentrated/focused at the objective end. Neither does the focuser. All the heat such as it is goes into the wedge. When I’ve used a wedge  no part of the scope except the wedge gets even warm.

Yuri from TEC telescopes recommends using a wedge with TEC refractors.

Edited November 20, 2019 by johninderby

[John]

I use my Lunt HW with my Tak FC-100 DL. The views are really excellent, when there has been any detail to view

[Rusted]

I use a Lecerta 2" wedge with my 180mm [7"] f/12 and often have it tracking the sun for many hours at a time. [iStar R35 achromat.]

The hot, light cone should fall just inside the baffles and pass straight though the deliberately oversized focuser drawtube.
The baffles at the "hot end" of the light cone and focuser should be shielded by the earlier baffles even when the sun is slightly off axis.
Only grazing incidence over a short arc should occur in the earlier baffles and block access to the later baffles.
I ought to check this myself with the sun off axis. Though I know the baffles are thin aluminium, painted matt black, because I made them.

My 150mm, 6" f/8 H-alpha scope suffers from refocused light reflected off the internal Baader D-ERF.
This is a very hot conical beam focused on and refocused sharply by the objective itself.
Again this instrument points at the sun all day long on most sunny days.
The post D-ERF beam is still hot near focus. Which is a bit of a worry for the etalon group and later filters.
I rely on more experienced solar observers having used even larger apertures with an internal Baader D-ERF and standard PST etalon/filtration.

[Rob Sellent]

You certainly have grown yourself a bigger pair than I have, @John. I find the Spanish Sun does no favours for gorgeous couplings of white flowers or delicate pairings of shrubs 😁 Oh, and there's no way I'd have the courage to use the Vixen for white light. You're a brave man with your Tak 😀

[John]

The Tak is an astro scope so I use it as such. I use my Vixen ED102SS with the Lunt HW as well and it's very good, but the Tak is even better. My understanding is that the Suns light passes through the objective and is bought to focus either 900mm or 633mm away and thats where the heat is and also where the componant that is designed to cope with it is located  

Thanks for the comments on the borders - they are my other half's doing rather than mine !

 

 

 

[Hallingskies]

It seems that a lot of experienced observers are quite OK with letting the full power of the sun shine down their exquisite optics.  So if it’s good enough for you guys, then it’s good enough for me!  Maybe it’s like Stu said, a lot of the older Herschel wedges were maybe a trifle dubious in design, something I certainly recall seeing in action.  Maybe I will invest in a modern one sometime, as the “team thinks” that they do seem to offer improved views - if the Sun ever pulls out of its current prolonged state of quiescence....

[Paz]

On 19/11/2019 at 11:17, PEMS said:

Have read of the Lacetera being at the Brewster angle, not sure what extra that adds.

The Brewster angle applies a stronger polarising effect meaning that with a polarising filter you can adjust the brightness over a wider range.

I think from about 1/12,000 to about 1/2,300,000 or thereabouts.

A solar film dims to about 1/100,000.

An advantage of a wedge is that you can turn up the brightness to just the right amount - useful at higher magnifications, or for binoviewing, or if using colour filters.

[Paz]

On the topic of whether wedges are safe I think everyone needs to do what they are comfortable with or else observing would not be enjoyable due to the worry.

I am happy using a wedge after reading up on it first. However I will secretly admit that put a uv/it cut filter in the path. This is not really necessary but it means I relax and enjoy what I'm doing.

I've used a wedge extensively with a 120mm refractor with no problems.

I've also used a film and still have it but it doesn't get used unless I am observing with a maksutov. That doesn't happen because (for me) a 120mm f5 achromat plus a wedge and a green filter beats a 127mm mak plus solar film.

[Stu]

A few of my Tak in solar action....

[Steve Clay]

On 19/11/2019 at 11:38, Steve Clay said:

This TS wedge seems the cheapest of them all. Can the continuum filter be removed so that the image is white and not green and does the back get very hot?

Thanks

Steve

Steve

I contacted Astroshop.eu re replacing the stacked NB and ND3 filter and replacing it with just an ND3 filter. 

Their reply was under no circumstances should the wedge be used like that. 

So I think I will go with the Lunt 1.25 wedge as it will give me more options

Thanks for all the advice.

Steve

[johninderby]

Astroshop doesn’t know what they are talking about or misunderstood your question.  Contact TS directly and they will tell you it is fine to replace the combined filter with an ND3 filter

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p9409_TS-Optics-1-25--Solar-Prism-with-Polarizing-and-Narrowband-Filter.html

Edited November 25, 2019 by johninderby

[Rusted]

John,

If you read the TS blurb they do state quite clearly that the narrowband filter must not be removed.
It sounds as if they are relying on the unnamed narrowband filter to further reduce the risk.

Genuine Baader SC filters are very pricey even in 1.25". 
This would seriously raise the retail price of the TS solar prism if provided as standard.
Suggesting, perhaps, that this may not be a Baader SC filter but something similar.
This matters to TS solar prism buyers. At least those with a chromatic phobia.
So greater clarity is highly desirable. IMO.

[johninderby]

I remember someone else asking TS about it and TS telling them it was OK to fit just an ND3 filter. 
So just ask TS for conformation.

[Stu]

1 minute ago, johninderby said:

I remember someone else asking TS about it and TS telling them it was OK to fit just an ND3 filter. 
So just ask TS for conformation.

My understanding is that you should always have the ND3.0 filter fitted, AND one of either a polarising filter or Continuum. Certainly without a Continuum in my Wedge the views would be too bright for comfort.

[Rusted]

"Warning!!!

Never use the Solar wedge without the supplied narrowband filter and the polarizing filter. Otherwise irreparable eye damage can result!!!

TS."

I routinely use a Baader SC in my 2" Lacerta prism along with a single rotatable polarising filter and the fixed ND3.

The polarising filter is really valuable for adjusting a pure white image to a comfortable level.
Note that you only need a single polariser to dim against the polarising effect of the prism.
I have a rotatable collar, but with a 1.25" TS you'd need to move the polariser to each new eyepiece.
Then rotate the eyepiece for comfortable brightness before locking the thumb screws of the receptacle.
Not such a chore in bright daylight compared with fiddling with filters in the dark.

Do we know if the TS "narrowband" filter is green? Any owners present?

[Stu]

6 minutes ago, Rusted said:

Do we know if the TS "narrowband" filter is green? Any owners present?

I believe it is a TS version of a Continuum which is green, combined in one filter mount with the ND3.0.

No reason why it can't safely be replaced by an ND3.0 with separate polarising filter or Continuum.

[Littleguy80]

2 hours ago, Stu said:

I believe it is a TS version of a Continuum which is green, combined in one filter mount with the ND3.0.

No reason why it can't safely be replaced by an ND3.0 with separate polarising filter or Continuum.

That’s exactly what I do with my TS Optics Herschel Wedge. The supplied filter is a stacked ND filter and continuum type filter in the same filter cell. I bought a Baader ND3 filter which I sometimes use instead of the supplied filter. I emailed TS Optics at the time who confirmed that the Narrowband filter is stacked with an ND3 filter. The only reason for doing this would be to lose the green colouration that the narrowband filter adds. Of course, you also loose the benefits of the narrowband filter too. 

[Space Hopper]

On 20/11/2019 at 18:44, johnturley said:

I think that's a very sensible approach, I recently purchased an Es Reid tested Esprit 150, and I asked Es (who incidentally does quite a bit of solar observing, but with a dedicated solar scope) about using A Quark solar eyepiece with the scope, and his opinion was that he wouldn't risk it.

As Rob suggested, a Hershell Wedge probably ok with refractors up to 80-100 mm, for larger sizes  a full aperture solar filter such as the Baader or Seymour is a safer option, or best of all a dedicated solar scope. 

John 

I have the Baader HW with filter kit, and used to routinely use my old WO 132mm with it.

I never had any issues, but i only usually observed for a few minutes at a time, then moved the scope away from the sun for a bit.

The objective was fine, and the window at the back of the wedge never got hot at all ; luckwarm and nothing more.

I always used it with binoviewers, often with only the ND3.0 filter in place. Of course, the ND3.0 MUST ALWAYS be in situ. It can actually be unscrewed, which i think is a serious issue. They should have designed it so it could not be removed, or cemented it in or something.

Sometimes i added another of the ND filters to the 3.0 : the 0.6 if i remember,  to dim the view down a touch more if it was a really bright day.

I tried the green continuum but always found it a rather odd, artificial sort of view  like a HA scope.

I primarily brought the HW for the March 2015 eclipse and the May 2016 Mercury transit and to my amazement it was clear for both events ! 🤗

I've not really used it much since ; the sun at present is pretty bland.  Its stored away in  the garage, and i'd thought about selling it , but i think i will keep it, as its a nice thing to use, and what is nicer than observing in warm sunshine ?? 😀

When i do use it again, it will be with the APM  scope rather than the TEC.

The 140 has a Fluorite element, and i don't want to risk 'thermal shocking it'. It would almost certainly be ok though.

 

 

Edited November 25, 2019 by Space Hopper
typos

[JOC]

On 20/11/2019 at 18:24, Hallingskies said:

It’s not just me, then!  I must admit I stick to Baader film on the front of the frac on the rare occasions I do any solar observing or imaging.  First off, it’s cheaper than a Herschel wedge, but mostly it’s because I really am not all that comfortable with the idea of funnelling 100w or so of solar heating down through frangible precision optics....😱😱😱🔥🔥🔥

I've got a reflector, but I am not confident enough of it's construction materials to want to whack concentrated sunlight about inside it.  At least when you cover the end of an OTA with Baader solar film you know you got it all locked out the correct side of your optics