How to get to F/30 with fast scope and mica etalon

[Highbury Mark]

Unlike the Quark with its 4.2x telecentric, the new Baader/Solar Spectrum Sundancer II only features a 3x inbuilt telecentric. So with a typical F/7.5, 120mm refractor (in this case a Tak TSA-120), I’m only going to get to F/22.5 - well short of the F/30 needed with mica etalons to achieve desired contrast. If a full aperture Baader D-ERF is used, would it be effective (or more importantly safe) to add a focal extender (Tak 1.5x extender) on the telescope side of the diagonal? This would bring the total F/ratio to a decent F/33.75. Would work perfectly with 55mm and 40mm plossls, so overall power wouldn’t be too high.
Or is the only answer to stop down the aperture to slow down the speed of the system?
Primarily, I’m unsure of the protection offered by D-ERFs. But I also wonder if there might be any optical degradation?

[marktownley]

I would stop down, or get an f10 native scope if you want to use a sundancer.

[Highbury Mark]

Hmmm, thanks Mark. Baader apparently have plans for a 4x Sundancer at some stage in the future, but could be a long wait.

[christian viladrich]

You can use a Taka 1.5x ED or equivalent to get f/33.75. There will be no problem for the extender (or any other 1.5x Barlow lens) thanks for the ERF.

As long as you use the 3x inbuilt telecentric, the resulting light beam falling on the mica etalon will be telecentric.

[rsfoto]

Hi and WOW,

Just saw the price of the Baader Sundancer which equals to about US $ 3,200.00 German VAT NOT included ...

Same size as a Quark

That must be really a tremendous piece of technics ...

What if the result turns out to be a possible flop like the Quarks in hot weather like I have in Summer = My best imaging time ...

US $ 3.200.00 is for me in Mexican pesos around MXN $ 65,500.00 plus shipping and Import taxes around MXN $ 78.600.00. 50% of what I would pay for a small car ...

OK, is it worth ? Maybe ... but do I get my money back if it does not work ?

Anyhow, I can not afford it anymore ...

[Highbury Mark]

You can use a Taka 1.5x ED or equivalent to get f/33.75. There will be no problem for the extender (or any other 1.5x Barlow lens) thanks for the ERF.

As long as you use the 3x inbuilt telecentric, the resulting light beam falling on the mica etalon will be telecentric.

Ok - that’s good news. Thanks Christian.

[Highbury Mark]

Hi and WOW,

Just saw the price of the Baader Sundancer which equals to about US $ 3,200.00 German VAT NOT included ...

Same size as a Quark

That must be really a tremendous piece of technics ...

What if the result turns out to be a possible flop like the Quarks in hot weather like I have in Summer = My best imaging time ...

US $ 3.200.00 is for me in Mexican pesos around MXN $ 65,500.00 plus shipping and Import taxes around MXN $ 78.600.00. 50% of what I would pay for a small car ...

OK, is it worth ? Maybe ... but do I get my money back if it does not work ?

Anyhow, I can not afford it anymore ...

No decision made yet Rainer. Apart from anything, I would have to sell quite a lot of kit first. It’s not cheap, but it’s a Solar Spectrum etalon for less than the entry level filter in the Solar Spectrum range - at least at UK prices. I wouldn’t buy any solar filter without a clear return policy from the retailer, but am hoping the consistency with this product will be higher than the competition……

[rsfoto]

Hi and WOW,

Just saw the price of the Baader Sundancer which equals to about US $ 3,200.00 German VAT NOT included ...

Same size as a Quark

That must be really a tremendous piece of technics ...

What if the result turns out to be a possible flop like the Quarks in hot weather like I have in Summer = My best imaging time ...

US $ 3.200.00 is for me in Mexican pesos around MXN $ 65,500.00 plus shipping and Import taxes around MXN $ 78.600.00. 50% of what I would pay for a small car ...

OK, is it worth ? Maybe ... but do I get my money back if it does not work ?

Anyhow, I can not afford it anymore ...

No decision made yet Rainer. Apart from anything, I would have to sell quite a lot of kit first. It’s not cheap, but it’s a Solar Spectrum etalon for less than the entry level filter in the Solar Spectrum range - at least at UK prices. I wouldn’t buy any solar filter without a clear return policy from the retailer, but am hoping the consistency with this product will be higher than the competition……

Hi,

I am now more then 20+ years in this Amateur Astronomy business and still have the impression that we amateurs now in Year 2022 are theT&E, R&D and QC department of all the Astronomy stuff producers ...

[Highbury Mark]

Baader replied to my question about using an extender after the D-ERF but before the diagonal/etalon. Interestingly, they say it would not be safe, though they refer to a ‘barlow’ rather than the extender I was proposing. Here’s what they said:

“we do not recommend to add a Barlow lens in front of the SunDancer.
First of all, even behind a D-ERF, there is quite some energy left, so if the Barlow isn't designed for solar projection, the cement of the Barlow may delaminate.
And second: Instead of converging (as expected by the TZ), the light beam behind the Barlow is diverging, when it enters the telecentric system. This will result in a deteriotion of image/filter quality.
So, at the moment we would recommend to use the SunDancer with the D-ERF at your f/7.5-telescope, and maybe reduce the aperture - if necessary - e.g. with a piece of carton in front of the telescope to judge the effect until the dedicated TZ-4 becomes available.

[christian viladrich]

Hello Mark,

Interesting answer of Baader to this question ;-)

1) Regarding safety : I understand why they answer this. They want to be on the safe side and do not what to get involved in any problem ;-)

2) Regarding the second part of the question relative to the divergent beam : there is some flexibilty in the use of a telecentric system.

What makes a light beam telecentric is mainly the "telecentric unit" (i.e. TZ-2, TZ-4, etc). Still, the optical setup up in front of the telecentric system has some influence on telecentricity (in particular the focal length of the telescope). If you use a Barlow lens in front of a "telecentric unit", you will still have a beam close to telecentric

An example of this is given by Schmid-Cassegrain telescope : from the optical point of view, the secondary (convex) mirror acts just like a Barlow lens. Still, there is no problem to use a "telecentric unit" at the focus of a SC telescope (such as TZ-3).

This being said, if we want to get the very best results from a telecentric unit, this is true that :
- a telecentric system is optimized for a telescope of a given focal length (see discussion at the bottom of this page :
http://astrosurf.com/viladrich/astro/in ... lar/FP.htm),
- also, a telecentric system is optimized (or not) for a given telescope design (refractor, Newtonian, Schmidt-Cassegrain). For example, AiryLab telecentrics are optimized for Schmidt-Cassegrain telescopes. This optimization is mainly related to the correction of aberrations (spherical aberation, astigmatism, etc.) and a litlle to "telecentricity".

This being said, the light beams after the Barlow lens is convergent, not divergent. Probably, what Baader meant was that the angle of the "chief ray" (ie. ray of light passing though the center of the lens) is larger when using a Barlow lens.
https://www.eckop.com/wp-content/upload ... 68x340.png

In any case, this is an interesting question :-)

[Highbury Mark]

Hello Mark,

Interesting answer of Baader to this question ;-)

1) Regarding safety : I understand why they answer this. They want to be on the safe side and do not what to get involved in any problem ;-)

2) Regarding the second part of the question relative to the divergent beam : there is some flexibilty in the use of a telecentric system.

What makes a light beam telecentric is mainly the "telecentric unit" (i.e. TZ2, TZ4, etc). The optical step up in front of the telecentric system has some influence on the telecentricity. If you use a Barlow lens in front of a "telecentric unit", you will still have a beam close to telecentric

An example of this are Schmid-Cassegrain telescopes : from the optical point of view, the secondary (convex) mirror acts just like a Barlow lens. Still, there is no problem to use a "telecentric unit" at the focus of a SC telescope (such as TZ-3).

This being said, if we want to get the very best results from a telecentric unit, this is true that :
- a telecentric system is optimized for a given focal length of the telescope (see discussion at the bottom of this page : http://astrosurf.com/viladrich/astro/in ... lar/FP.htm),
- also, a telecentric system is optimized (or not) for a telescope design (refractor, Newtonian, Schmidt-Cassegrain). For example, AiryLab telecentrics are optimized for Schmidt-Cassegrain telescopes. This optimization is mainly related to correction of aberrations (spherical aberation, astigmatism, etc.) and only a litlle to "telecentricity".

Thank you Christian. Much better informed now. so if I go ahead with the purchase, I’m clearer about how to experiment with different set ups.

[christian viladrich]

Mark,
As a general information on telecentric assembly, I have updated a web page here:
http://astrosurf.com/viladrich/astro/in ... icity.html

Starting from the middle of the page, there are some optical simulations describing the role of the different elements of a telecentric assembly.

[vkx86]

I think it can be used with ole good TZ-4 without problems if you have full-aperture D-ERF - it's modular design and it's native 3X telecentric has same T2 connection as TZ-4.
Baader states in SunDancer manual that forthcoming TZ-4 will be additional accessory and blocking filter from TZ-3 must be screwed into new TZ-4 (I assume, that if it will be used in small bore scopes).
SunDancer II is Solar-Spectrum's etalon used in their Suna series in Baader's packaging without TEC unit and with tilter - so you can consider Suna + TZ-4 instead of SunDancer II packaged with TZ-3.

[Highbury Mark]

Thanks Christian and vkx86 for your excellent responses.

[mdwmark]

I think it can be used with ole good TZ-4 without problems if you have full-aperture D-ERF - it's modular design and it's native 3X telecentric has same T2 connection as TZ-4.
Baader states in SunDancer manual that forthcoming TZ-4 will be additional accessory and blocking filter from TZ-3 must be screwed into new TZ-4 (I assume, that if it will be used in small bore scopes).
SunDancer II is Solar-Spectrum's etalon used in their Suna series in Baader's packaging without TEC unit and with tilter - so you can consider Suna + TZ-4 instead of SunDancer II packaged with TZ-3.

Hi group,
The SunDancer 2 uses 1n 1" etalon , so it has a 18mm CA and are in the .5-.6Ang range. The Suna uses an 38.1mm etalon with either an 25mm or 32mm CA versions . They are designed to be in the .7Ang range. The Suna uses an TEC controlled oven and is tiltable.
Mark W.