Are separate etalons better than a solar scope using the same etalon?

[paulastro]

I've been observing the Sun in H Alpha for some years and it seems to me (and to many others apparently) that an etalon used with a blocking filter on a refractor, of the users choice, will out-perform the same etalon and blocking filter incorporated into a complete solar telescope from the same manufacturer.  If this is accepted as being true, I'd like to know why this should  be the case?  The two usual reasons I've heard cited are 

 (A)  The  complete solar telescopes optics are usually  inferior to that of a telescope chosen by the user to be the host refractor for an external etalon and BF.

(B )  The quality of the etalons made for complete solar scopes are made to a lesser standard than those used when the etalon is for use on the users own telescope.

I also wander why the cost of separate etalons and BFs is generally more expensive than the same components incorporated into a complete solar telescope.  An example is that a Lunt solar scope of 60mm aperture with a B1200 and a Crayford focuser is around £1700 while a separate Lunt 60 etalon and B1200 to use on your own telescope costs around £2440.  Common sense would tell you that it should be the other way round - unless the complete telescope's etalon and BF really are not up to the same quality?

I'd like to hear other people's thoughts and views on this.

[paulastro]

I've been trying to edit out the emoticon where there should be a letter 'B' in the original post.  For some reason every time I edited out it come back!!  Sorry about that.

[Ibbo!]

because B with the ) after it is the code for

[Peter Drew]

Paul. I think one of the answers is that a 60mm front etalon is just that, a 60mm diameter etalon whereas many 60mm solar telescopes in reality have a smaller etalon further down the system but operate as a 60mm solar telescope. Size is expensive with etalons!.    

[paulastro]

Thanks for that ibbo, I'd never have worked that one out in a million years!!  It's cleared up a mystery for me.

[paulastro]

Thanks for that Peter.  Don't any of the manufacturers use the same size etalons as the size of their solar scopes objectives?

So presumably, for those manufacturers that don't , the separate etalon used on a separate refractor will always give a superior performance to one of their own solar scopes of the same diameter? 

If this is the case I think all manufacturers should state the size of the etalons used in each of their solar scopes.   It seems a bit like advertising a refractor as a six inch and then only putting a four inch objective in it to me !!

[Zakalwe]

Paul. I think one of the answers is that a 60mm front etalon is just that, a 60mm diameter etalon whereas many 60mm solar telescopes in reality have a smaller etalon further down the system but operate as a 60mm solar telescope. Size is expensive with etalons!.  

Its very much that. For instance, the Lunt L60 has a 30mm Etalon. However, that shouldn't matter that much as the light cone is pretty close to the Etalon size.

Smaller scopes like the Lunt L50 have a bigger Etalon (35mm IIRC), but the bandpass is a bit wider.

[paulastro]

Peter and Zakalwe.  Just to be clear about this, I'm interested in how this actually affects the final image.  It's obviously true that if we were talking about the position of the ERF in the light path of a PST mod, it doesn't affect the image  if there is a full aperture ERF over the front of the lens or a smaller one down the tube - as long as the latter fully intercepts the light cone.  In the case of the Lunt 60mm scope with the 30mm etalon, will the image be exactly the same quality as if the etalon was 60mm and right at the front of the telescope?

If the answer to this is 'yes' then I think my questions have been answered and it is reasonable that a full 60mm etalon and BF costs more than the 60mm scope with its 30mm etalon.  Also the 60mm etalon (along with its extra cost over a 30mm) will be necessary because on a third party telescope it has to be placed at the front end.

[Pig]

I cant say that I am surprised .... crazy fools .... Is it a given that you have to be so deceitful to be in business

[Merlin66]

A good quality smaller etalon correctly positioned will give excellent results. This is well proved by the very successful PST mods using apertures up to 150mm.......

The manufacturing costs rise exponentially with the size of the etalon: larger etalons are always more expensive.

[Zakalwe]

Peter and Zakalwe.  Just to be clear about this, I'm interested in how this actually affects the final image.  It's obviously true that if we were talking about the position of the ERF in the light path of a PST mod, it doesn't affect the image  if there is a full aperture ERF over the front of the lens or a smaller one down the tube - as long as the latter fully intercepts the light cone.  In the case of the Lunt 60mm scope with the 30mm etalon, will the image be exactly the same quality as if the etalon was 60mm and right at the front of the telescope?

If the answer to this is 'yes' then I think my questions have been answered and it is reasonable that a full 60mm etalon and BF costs more than the 60mm scope with its 30mm etalon.  Also the 60mm etalon (along with its extra cost over a 30mm) will be necessary because on a third party telescope it has to be placed at the front end.

Im not an optician by any means so thke this with a pinch of salt. In a perfect setup, a sub-aperture Etalon will produce the same results. However, there will be manufacturing tolerance, so the Etalon may be positioned to allow for that.  The flipside is that a full aperture Etalon is MUCH harder to make. Are the manufacturing tolerance more or less detrimental to the views than the manufacturing tolerances on a full aperture Etalon? I cannot answer that question. However, the cost difference means that a mere mortal like me can have access to technology that less than 20 years ago was the preserve of the professionals.

I cant say that I am surprised .... crazy fools .... Is it a given that you have to be so deceitful to be in business

Thats harsh IMHO. I don't see any deceit. in fact, Lunt get nothing but high praise from me...they delayed the shipping of the Lunt 50 for months to ensure it was correct. Other manufacturers seem more than happy to let users beta test their kit.

[ollypenrice]

Another thing is that, because of the tiny bandpass and near-monochromatic light involved in Ha imaging, there is no need for colour corrected compound objective lenses.

I don't see the slightest deceit in having a smaller etalon than objective. It's routine, for instance, to put 1.25 or 2 inch filters in 20 inch telescopes. They remain 20 inch telescopes.

Olly

[paulastro]

There's a lot to ponder there Zakalwe, thank you.  As all you good folks reading this can probably tell, I have a decision to make.  I have a PST and a Quark I use on an Equinox 80.  The Quark clearly gives a wonderful view of the chromosphere, and I know full well that if I wanted to achieve the same using an etalon, either inside a complete solarscope or as an external etalon on my Equinox, I'd have to be looking at something far outside my price range.  This is not what I'm after.

I use my PST as a grab and go on an altaz mount and can get it in use within a minute - it's always ready to carry outside and I can carry it in one hand.  Because I keep my Quark, scope, binoviewers and mount etc etc  inside (no alternative) it clearly takes a little while to set up.  Hence I use my PST when it would be impossible to get the Quark into use and therefore probably use it at least ten to fifteen times more often.  My PST is a very good one, but as I use it so often I want something with a bit more umph for my grab and go..

Hence the decision I'm coming to terms with is whether to get a 60mm Lunt scope (possibly a 60mm Coroanado scope but I'm a bit concerned about Meade's service record if I have to ever have it repaired) or a separate 60mm Lunt or Coronado etalon and blocking filter.  If I was convinced the solarscopes would give a good an image as a separate etalon I would go that way but I'm not as yet.  Also I am well aware  that the quality of both Lunt and Coronado scopes do vary and those nice people on the Isle of Man are too costly for me.

I have been keeping my eyes out for something likely second hand but anything suitable seems to be as rare as hens teeth.

[Pig]

I do.... I think its disgraceful

[JamesF]

I wonder if the "energy density" at the etalon makes a difference?

James

[Merlin66]

James,

Unless you're pushing an aperture >60mm the "internal etalon" certainly has no issues with "energy density"!!

I do recommend (mandatory!) using an ERF with 80mm and above....

[Zakalwe]

I think that you need to go back to your original premise and revisit it. Why do you think that an external Etalon and BF are superior? Perhaps the difference is nothing more than the focal lengths of the host telescope compared to the solarscope?

 (A)  The  complete solar telescopes optics are usually  inferior to that of a telescope chosen by the user to be the host refractor for an external etalon and BF.

(B )  The quality of the etalons made for complete solar scopes are made to a lesser standard than those used when the etalon is for use on the users own telescope.

Are any of the above actually the case?

The best way would be to compare an external Etalon on a donor scope with the same aperture and focal length, side-by-side with a solarscope. For example, a 60mm Etalon on a 60mm f5 refractor alongside a 60mm Lunt. Perhaps a nearby retailer would set such a comparison up for you?

You're about an hour away from me...I'm more than happy to let you have a comparison with my Lunt L60 pressure-tuner if that would help?

[michael.h.f.wilkinson]

I wonder if the "energy density" at the etalon makes a difference?

James

Not unless the energy density melts things . These optics are essentially linear

[michael.h.f.wilkinson]

Quality of the components is generally the key issue. My 19mm free aperture etalon in the Solar Spectrum H-alpha unit gives WAY better results than the full aperture 35mm unit of the LS35, because it has a narrower bandwidth, and a 75mm aperture "feeding" it. The downside is that I cannot see the entire disk.

[JamesF]

Not unless the energy density melts things . These optics are essentially linear

That's fair enough.  It was just a random idea that I couldn't answer myself.  It struck me that a small internal etalon might be subject to more thermal stress than a full aperture etalon and the required tolerances are obviously really very small.

James

[paulastro]

I think that you need to go back to your original premise and revisit it. Why do you think that an external Etalon and BF are superior? Perhaps the difference is nothing more than the focal lengths of the host telescope compared to the solarscope?

Are any of the above actually the case?

The best way would be to compare an external Etalon on a donor scope with the same aperture and focal length, side-by-side with a solarscope. For example, a 60mm Etalon on a 60mm f5 refractor alongside a 60mm Lunt. Perhaps a nearby retailer would set such a comparison up for you?

You're about an hour away from me...I'm more than happy to let you have a comparison with my Lunt L60 pressure-tuner if that would help?

Many thanks Zakalwe. 

Re my premise that an external etalon and BF are superior.  Over the years I've had the chance to use quite a few solar scopes and also the same manufacturers etalons used externally.  I've certainly come across some solar scopes which are certainly below par - giving images clearly inferior to lesser spec and size scopes that they produce themselves.  Though I've used fewer external etalon setups, I've not seen any in action that don't perform as well or better than I'd expect and certainly none that would be out performed by lesser spec systems.  Many people I've spoken to have voiced similar experiences and hold similar views - though granted this isn't proof it's true of course! 

You make an interesting point that the reason could be the difference between the focal lengths of the different systems, it's not something I'd considered.  Having said that, even if this is true, it might still be a good reason for using an external system as you can then choose what focal length scope you use with the etalon to get the best out of it.

As you say this could be tested out by comparing the solar scope with the same size etalon on a scope of the same focal length.  It's something I'd love to do, though I'm not sure if I have a 'local' supplier who even keeps any of the scopes and etalon sets in stock.  Most suppliers now seem to order the things in and drop ship.  Also if they did have the necessary stock they may not be happy about opening up one of the boxes and let me use them unless they have additional 'demonstrators'.

It would be my dream if there was a dealer somewhere I could go and test out the various systems side by side.  Though this is possible on occasions at some star parties the scope to do it is very limited. 

I would love to come and try out your Lunt 60 and the PT as at least it would give me the chance to see what one can do.  I have not used a Lunt 60 for a while, and not one that had a PT.  Also I'm afraid the last one I used wasn't very good even compared with a good PST and it put me off them rather.  This is probably really unfair to Lunt and it would be good to see one that performs well.  I'm afraid though that I can't see me being able to come up with a 60mm Lunt etalon on a scope of the same focal length to bring along with me as I haven't got access to either. 

[Merlin66]

Paul,

Check out the results being obtained with various solar scopes over at the excellent solar chat group....

http://solarchat.natca.net/index.php

[paulastro]

Thanks Merlin.  I do actually use solar chat, and agree with you it is indeed excellent.  To me though, as an almost purely visual observer, it does seem to offer far more  to the imager.  Though there are visual reports and reviews on it,  the quantity is only a fraction of the  imaging content.  I must say though, I'm not complaining about this, it's a wonderful facility and there are few days I don't have at least a look at it.  I would say though, to me at least, the images people produce are a very poor guide to what the various instruments used offer visually.  Many of the imagers are hugely talented and skilled and it's hard to think how many of the images can be bettered.  The problem is the images are so good  that there is a huge gulf between what the most eagle eyed and talented visual observer can see and the detail seen in images taken using the same instruments by the similarly talented imagers.

So in summary, while I think the images clearly show what images can be obtained and aspired to with various instruments, they offer very little to indicate to any visual observer (and particularly to inexperienced solar observers) what they will be able to see visually through the same instruments.

Of course this is not limited to solar observers.  The difference what can be seen visually on Jupiter and what can be imaged with the same  telescope for instance is just a big a gulf.

[jetstream]

I am finding that the Quark is giving views that are equal to or better than some processed images- not all though. Seeing makes a huge difference as does optimizing the set up, magnification is critical. In recent VG seeing the views have been 3D and stunning. I am pondering now that maybe the eye can make out detail that I thought was the realm of cameras given a chance...many imagers have huge knowledge of Ha and use optimized equipment whereas a lot of us visual people do not ( speaking for myself) and this could account for some of the difference.

[Zakalwe]

I am finding that the Quark is giving views that are equal to or better than some processed images- not all though. Seeing makes a huge difference as does optimizing the set up, magnification is critical. In recent VG seeing the views have been 3D and stunning. I am pondering now that maybe the eye can make out detail that I thought was the realm of cameras given a chance...many imagers have huge knowledge of Ha and use optimized equipment whereas a lot of us visual people do not ( speaking for myself) and this could account for some of the difference.

The more that I use the Quark (and I have only had a handful of chances) the more I realise some of it's limitations. Namely, the length of time to change the bandpass. I can't imagine trying to use it visually....waiting 7-10 minutes for the tuning to change would drive me nuts!

I would love to come and try out your Lunt 60 and the PT as at least it would give me the chance to see what one can do.  I have not used a Lunt 60 for a while, and not one that had a PT.  Also I'm afraid the last one I used wasn't very good even compared with a good PST and it put me off them rather.  This is probably really unfair to Lunt and it would be good to see one that performs well.  I'm afraid though that I can't see me being able to come up with a 60mm Lunt etalon on a scope of the same focal length to bring along with me as I haven't got access to either.

Anytime you fancy, just drop me a line. I've also got a 50mm external Etalon...some Duct tape and a bit of ingenuity and it could be cobbled onto a refractor?