Tak TOE - finally able to report back

[JeremyS]

10 minutes ago, Deadlake said:

I have the Baader prism. Depending which review you read on CN the Baader BHSS or prism wins. From my understanding a prism diagonal actually introduces a small amount of chromatic shift. It cannot do any other as light entering a prism will disperse due to refraction. Ironically this trait can be used to correct some chromatic shift in other devices such as binoviewers. In real terms a prism cannot be as good as a pure mirror and will always be less efficient with light due to dispersion.

The prism may have a beneficial  affect on certain telescopes and introduce a chromatic shift on others. 

Would you need a good nights seeing to observe the chromatic shift or just different diagonals to try out?

I'm planning on getting the 2" BHSS for a new APO scope, due to the faster cool down and the ability to use with EP field stops > 33 mm prism version I have. The cost difference between the Baader 2" prism/BBHS is not that much.

I also know some dealers favour the BHSS for collimation of APO's.

Martin

Yes I’ve read loads  of reviews in Baader prism vs mirror. There do seem to be a few cases where ppl prefer the prism and maybe it’s in specific scopes with specific targets.

At least to me the balance was tipped towards the mirror which is why I bought it. But then there’s the nagging doubt about whether the prism might be better.

It’s this nagging doubt in many areas that leads to £££ being spent on scopes, eyepieces, mounts etc etc

[jetstream]

Thanks guys... now I want a Baader BBHS lol!

 

Edited January 30, 2021 by jetstream

[Deadlake]

1 hour ago, JeremyS said:

Yes I’ve read loads  of reviews in Baader prism vs mirror. There do seem to be a few cases where ppl prefer the prism and maybe it’s in specific scopes with specific targets.

At least to me the balance was tipped towards the mirror which is why I bought it. But then there’s the nagging doubt about whether the prism might be better.

It’s this nagging doubt in many areas that leads to £££ being spent on scopes, eyepieces, mounts etc etc

I could see the value of a prism for your Tak doublets or bino-viewers, but I suspect for your APO the mirror is best.

I was wondering if the prism came out best in the first CN review  due to Baader improving the BHSS over time?

[Deadlake]

1 hour ago, jetstream said:

Thanks guys... now I want a Baader BBHS lol!

 

I have a full set of Vixen HR's due to JeremyS , similar path being taken here...

[JeremyS]

2 minutes ago, Deadlake said:

I could see the value of a prism for your Tak doublets or bino-viewers, but I suspect for your APO the mirror is best.

I was wondering if the prism came out best in the first CN review  due to Baader improving the BHSS over time?

That’s not what I wanted to hear

[Deadlake]

2 minutes ago, JeremyS said:

That’s not what I wanted to hear

Well I bought the prism without seeing the 2nd CN review favouring the BHSS. I might of bought the BHSS, however the chromatic shift with the prism might actually help out the doublet I use it in, by luck.

Edited January 30, 2021 by Deadlake

[jetstream]

6 minutes ago, Deadlake said:

might actually help out the doublet I use it in, by luck.

My feeling is that it can in the right scope.In the 120ED on Jupiter it splits off "red" a tiny bit out of focus. The APO triplets are not affected like that.

[johninderby]

Some usefull info.

https://agenaastro.com/articles/guides/diagonals/choosing-a-baader-diagonal.html

And this review

https://www.baader-planetarium.com/en/downloads/dl/file/id/160/product/1237/testreview_mirror_vs_dielectric_vs_prism_diagonal_comparison_w_paolini.pdf

And from the conclusions of the review.

”Quality prisms are prime candidates for the diagonal component in telescopes with focal ratios of f/7 or greater. Prism diagonals tested did not introduce any visually apparent chromatic aberration or spherical aberration in f/7 or f/8 telescopes and showed views just as brightly while notably higher in planetary contrast and notably lower in scatter on all celestial targets than similar high quality aluminum or dielectric mirrors. At f/6.25 chromatic aberration became apparent, but was inconsequential on all but the very brightest targets.”

 

Edited January 30, 2021 by johninderby

[JeremyS]

14 minutes ago, johninderby said:

Some usefull info.

https://agenaastro.com/articles/guides/diagonals/choosing-a-baader-diagonal.html

And this review

https://www.baader-planetarium.com/en/downloads/dl/file/id/160/product/1237/testreview_mirror_vs_dielectric_vs_prism_diagonal_comparison_w_paolini.pdf

And from the conclusions of the review.

”Quality prisms are prime candidates for the diagonal component in telescopes with focal ratios of f/7 or greater. Prism diagonals tested did not introduce any visually apparent chromatic aberration or spherical aberration in f/7 or f/8 telescopes and showed views just as brightly while notably higher in planetary contrast and notably lower in scatter on all celestial targets than similar high quality aluminum or dielectric mirrors. At f/6.25 chromatic aberration became apparent, but was inconsequential on all but the very brightest targets.”

 

He has a more recent review which extols the virtues of the BBHS mirror diagonal

https://www.cloudynights.com/articles/cat/user-reviews/the-baader-bbhs-sitall-silver-diagonal-r3038

[Deadlake]

22 minutes ago, johninderby said:

Some usefull info.

https://agenaastro.com/articles/guides/diagonals/choosing-a-baader-diagonal.html

And this review

https://www.baader-planetarium.com/en/downloads/dl/file/id/160/product/1237/testreview_mirror_vs_dielectric_vs_prism_diagonal_comparison_w_paolini.pdf

And from the conclusions of the review.

”Quality prisms are prime candidates for the diagonal component in telescopes with focal ratios of f/7 or greater. Prism diagonals tested did not introduce any visually apparent chromatic aberration or spherical aberration in f/7 or f/8 telescopes and showed views just as brightly while notably higher in planetary contrast and notably lower in scatter on all celestial targets than similar high quality aluminum or dielectric mirrors. At f/6.25 chromatic aberration became apparent, but was inconsequential on all but the very brightest targets.”

 

I forgot that part, but the scope this is for is F6, so makes even more sense to get the Baader BBHS now. However for a Tak 120 would the prism be the better choice?

[johninderby]

I’ll stick with the prism for long focal length scopes and the mirror for shorter focal lengths.

Prism works rather well in my ScopeTech 80 f/15 though.

Edited January 30, 2021 by johninderby

[mikeDnight]

I use a Baader/Zeiss BBHS prism with my FC100DZ and can tell you with hand on heart, there is zero visible CA. With mirrors you'll always have light scatter, but not so with a prism. At 500X star images are textbook perfect and set against black velvet, with no light halo due to scatter. The downside is that you pay all that money and end up with a colour free view, like black and white tv from the 60's, but in HD.

[jetstream]

21 hours ago, Deadlake said:

However for a Tak 120 would the prism be the better choice?

Can't really answer this but I will tell you a certainty- if I felt hindered in any way by this prism I would already have the BBHS... even on extremely faint objects the prism works well in the TSA120.Barnards Loop, California, Pleiades Bubble, Flaming Star etc etc no filter. Works well on galaxies too.

I want a BBHS for one reason- I have a weakness for owning good glass. And who knows-maybe I'll own a TEC 140 one day! and need another diag.

[Deadlake]

12 minutes ago, jetstream said:

Can't really answer this but I will tell you a certainty- if I felt hindered in any way by this prism I would already have the BBHS... even on extremely faint objects the prism works well in the TSA120.Barnards Loop, California, Pleiades Bubble, Flaming Star etc etc no filter. Works well on galaxies too.

I want a BBHS for one reason- I have a weakness for owning good glass. And who knows-maybe I'll own a TEC 140 one day! and need another diag.

Indeed if you own a premium APO what else can you tweak.

[jetstream]

 @JeremyS @Deadlake

"However, the Baader Zeiss 2" prism diagonal still slightly less scatter than the BBHS."

"the nebulosity of M42 extended notably further when observed through the BBHS or Zeiss prism than through the Astro-Physics dielectric.  The Zeiss prism showed the furthest extent of the nebulosity, but it was only very slightly more."

https://www.cloudynights.com/articles/cat/user-reviews/the-baader-bbhs-sitall-silver-diagonal-r3038

[JTEC]

Both Baader-Zeiss prisms perform beautifully in my scopes (TEC140 and C11) at all useable mags.  Visibly less scatter than the ‘best in class’ AstroPhysics Dielectric I previously used, and sold. No discernible unwanted colour whatsoever at these focal ratios (f7 and f10).  Work perfectly with binos, where same applies. BillP seemed to prefer the 1.25 prism slightly over the 2” for planetary views. Can’t say I really notice any difference; that said, my best ever planetary views have indeed been with the TEC, Zeiss-Baader binos and the 1.25 prism.  

[Louis D]

16 hours ago, JTEC said:

Both Baader-Zeiss prisms perform beautifully in my scopes (TEC140 and C11) at all useable mags.  Visibly less scatter than the ‘best in class’ AstroPhysics Dielectric I previously used, and sold. No discernible unwanted colour whatsoever at these focal ratios (f7 and f10).  Work perfectly with binos, where same applies. BillP seemed to prefer the 1.25 prism slightly over the 2” for planetary views. Can’t say I really notice any difference; that said, my best ever planetary views have indeed been with the TEC, Zeiss-Baader binos and the 1.25 prism.  

Not surprising.  Dielectric coatings are known to have a certain surface roughness absent in prisms and even silver coatings.  I wonder if the BBHS dielectric protective overcoat ruins the smoothness of silver.

[JTEC]

39 minutes ago, Louis D said:

Not surprising.  Dielectric coatings are known to have a certain surface roughness absent in prisms and even silver coatings.  I wonder if the BBHS dielectric protective overcoat ruins the smoothness of silver.

I have wondered the same thing, Louis.  BillP’s review of the BBHS made it sound very tempting. I’d like to give one a try but can’t justify the expense of doing so. 

[John]

Does this spell the end of the dielectric dominance of the diagonal world ?

 

[Deadlake]

Has anyone used either the Baader BBHS or prism in a F6 APO scope? 

Edited February 2, 2021 by Deadlake

[Don Pensack]

19 minutes ago, John said:

Does this spell the end of the dielectric dominance of the diagonal world ?

 

Not at all. 

First, silver coatings are expensive, and even more so when the necessary UV enhancement dielectric coatings are added to silver.

Second, the long term durability of silver coatings is still a question.  The jury is still out, so to speak.

Third, having a high output above 650nm is essentially unimportant for scotopic vision.

Fourth, diagonals get dirty and scatter light easily.  We know about the durability in cleaning of pure dielectric coatings.  We don't know about silver.

Fifth, a lot of high end scope manufacturers like TeleVue and AstroPhysics offer dielectric coated diagonals for sale with their refractors.  Takahashi offers prisms.

Sixth, the reflectivity at long visible wavelengths is close to the same.

Ultimately, should enhanced silver coatings prove durable, they could be another choice for high end stuff.

But they won't replace the dielectric coated ones in the more affordable range.

[johninderby]

16 minutes ago, Deadlake said:

Does anyone know how the BBHS or prism works in a F6 APO scope, I presume the BBHS is the one to go for? 

The prism is recommened for over f/7.

[jetstream]

18 minutes ago, Deadlake said:

Does anyone know how the BBHS or prism works in a F6 APO scope, I presume the BBHS is the one to go for? 

What scope are you getting exactly?

[Don Pensack]

19 minutes ago, Deadlake said:

Does anyone know how the BBHS or prism works in a F6 APO scope, I presume the BBHS is the one to go for? 

The prism also is available with the hypoteneuse surface BBHS coated, So there are both mirror and prism BBHS diagonals.

A prism is not recommended below f/7, but I'd put it at f/8, because I saw a lot of prismatic chromatic smear at f/7 with the prism.

The BBHS mirror prisms were all recalled last fall due to a bad quality on the mirrors.  Baader has yet to replace the stock with good ones,

so finding one might prove impossible right now.  If you find one, you want to be sure it is not from the batch made in the Fall.

The quality of the mirror after coating is the truly critical factor, which is the reason for the high cost of the AstrPhysics MaxBright and TeleVue EverBrite.

 

[Deadlake]

1 hour ago, jetstream said:

What scope are you getting exactly?

I have an APM LZOS 130 mm / F6 on order (an AP130GTX you can buy without waiting for your lottery ticket to come up , the TSA120 is F7 and a 130 TOA is too slow to cool and too bulky).  F6 due to being able to use it with a televue compressor for NV in case you where wondering why not go for the F9.2. 

Edited February 2, 2021 by Deadlake