214 replies to this topic

[Starman1]

Silver is flat well into the infrared, so if it is to be used on the sun, whatever filter is used should cut the IR as much as possible.

If an H-alpha chromosphere filter is used, like the Daystar Quark, that isn't an issue.  But if a white-light photosphere filter is used,

you should definitely check into the amount of IR filtration is there.

[BillP]

Baader makes that contention as well and recommends dielectrics for white light solar.  I personally prefer prisms for when I do white light solar. Not sure how much of the contention though is worrying about nothing or has some actual merit.  Not sure if any medical studies have been done on this. Probably not.  But always better to be save than sorry. But for night time...dielectrics are still a diagonal of last resort for me 

[TH1]

So after reading Bill's report I immediately recognized this Sitall design as a game changer for refractors. But I also picked up the SCT adapter for my C14, after selling more stuff, and then I started to think that this mirror is doing nothing for SCTs.

 

First question: is the scopes secondary silver?

 

When the light hits the secondary hasn't the damage already been done? Or can this improved mirror still pull out the better using whatever light it recieves? And what about a binoviewer? With a corrector? Does this corrector even allow the silver to work? Or does binoviewing omit this mirror altogether?

 

Will definitely not use this mirror for solar! Shows how fragile it really is. I give it 2-3 years use.

Edited by TH1, 28 March 2016 - 01:54 PM.

[astrophile]

So after reading Bill's report I immediately recognized this Sitall design as a game changer for refractors. But I also picked up the SCT adapter for my C14, after selling more stuff, and then I started to think that this mirror is doing nothing for SCTs.

 

First question: is the scopes secondary silver?

 

When the light hits the secondary hasn't the damage already been done? Or can this improved mirror still pull out the better using whatever light it recieves? And what about a binoviewer? With a corrector? Does this corrector even allow the silver to work? Or does binoviewing omit this mirror altogether?

 

Will definitely not use this mirror for solar! Shows how fragile it really is. I give it 2-3 years use.

 

I'm not understanding.  What shows how fragile it is?  And if the diagonal's silver is completely coated and sealed by the dielectric over-layers, how is the silver going to deteriorate?

[Starman1]

It will still deteriorate.  It will just take much longer.  Even overcoated aluminum eventually corrodes.

 

By the way, it seems the Zeiss prism Baader 90° diagonal #2456117, labeled BBHS might have a protected silver coating on the reflective surface after all.  Yet another reason it's so expensive (~$499.)

 

Bill,

For white light solar, you could just add an IR filter if you feel uncomfortable with the IR transmission characteristics of silver.

[TH1]

It has been highly recommended to not use this mirror for visual light solar due to IR. I was going to sell off my diagonals but kept one Dialetric for this reason. The mirror has been absolutely incredible and I haven't even been able to use it properly. Seeing has been the worst all year and I can still make out richer color in my 152 on Jupiter, plus the view will generally include red and blue on the disk when seeing is this bad.

But there is no stray color!

Moons would shimmer violently before with red and blue around their disks. Now there is significantly less scatter and a trace of red and blue.

Can't wait for a decent night!

Add this creation to the Lunt 152, Denk Binotron/LOA being the most revolutionary products for us in astro.

Edited by TH1, 01 April 2016 - 12:27 PM.

[TH1]

It will still deteriorate.  It will just take much longer.  Even overcoated aluminum eventually corrodes.

 

By the way, it seems the Zeiss prism Baader 90° diagonal #2456117, labeled BBHS might have a protected silver coating on the reflective surface after all.  Yet another reason it's so expensive (~$499.)

 

Bill,

For white light solar, you could just add an IR filter if you feel uncomfortable with the IR transmission characteristics of silver.

Which is better for planetary?

 

I would return the mirror for the prisim.

[BillP]

Bill,

For white light solar, you could just add an IR filter if you feel uncomfortable with the IR transmission characteristics of silver.

 

 

I have zero concerns.  UV would be more of a problem IMO.  IR you will know when it is excessive.  But at the tiny transmission levels of the ASTF filters should be zero issues.  I have not yet tried the BBHS for white light solar...I use my Zeiss prisms for that typically, plus I only do solar a few times a year at most.

Edited by BillP, 01 April 2016 - 08:54 AM.

[BillP]

Which is better for planetary?

 

I would return the mirror for the prism.

 

 

 

Planetary is often filled with personal preferences.  That being the case, only you will be able to determine which.  I don't have enough seat time with planetary comparisons with both so cannot say which I would prefer.  Anecdotally though the BBHS seems to be staying in the focuser more...but I would never let go of the prism.  Not an either-or thing for me as both are excellent and both have their strengths.

[BillP]

Even overcoated aluminum eventually corrodes.

 

That is true.  While I often hear of folks re-aluminizing and coating their mirrors, I seem to rarely come across threads saying similar for the secondaries.  Seems odd as they would deteriorate similarly correct?  So things like the TV Mirror diagonals and the Tak 2" Mirror diagonal would all have limited life times.

[Max Power]

The differences between diagonals are so small as to be un-
noticeable if BillP hadn't brought it up.
Kinda like the differences between eyepieces at the top level,
or scopes.

The best+ the best+ the best= a significant difference. Maybe.

[BillP]

Yes...many of the differences are not so overt.  However, a difference being small does not mean it is necessarily insignificant.  Small levels of scatter can often mean the difference between seeing a feature and not being able to see it at all.  I would never have believed or known this had I not done all these comparative tests over time.  Examples that come to mind are small barges on Jupiter, orthographic clouds over Olympus Mons on Mars, storms in the belts on Saturn, subtle colorations and hues on double stars, etc. 

 

I personally attach more importance to the optimization of the accessories, like the eyepieces and diagonals, rather than the main objectives.  Reason being is that over time I inevitably upgrade the objectives as I may be able to afford, so the scope is a little more transient.  The things like diagonals and eyepieces and such though, once you have a winner it tends to stick around.  So more likely for me at this point in my journey for the accessories to go through a bunch of scopes over time rather than for a scope to go through a bunch of accessories.

 

From a diagonal perspective now I have the BBHS, the 2" Zeiss Prism, and the 1.25" Zeiss Prism.  IMO these three represent a range of optimized diagonals.  And of course on the eyepiece side I have the XWs and XO and ZAO for planetary so nothing going to top them for my observing needs.  So for me now, the main objective is all that gets varied as the accessories are now fixed (unless something new comes along that can supplant them, but doubtful). 

Edited by BillP, 01 April 2016 - 12:46 PM.

[Starman1]

Bill,

I presume you know how to do a star test of a telescope.

You would find it illuminating (pun intended) to do a star test on a scope without a star diagonal and then again with the diagonal.

Over the years, I've owned many scopes that used star diagonals--Maks, SCTs, refractors--and many star diagonals from many companies, but only 2 star diagonals that had NO visible effect on the star test image.

The #1 problem, as is the case for secondary mirrors, is a slight convexity to the star diagonal's mirror, which imparts a slight magnification to the star diagonal, usually a bit of astigmatism, and a touch of spherical aberration.

Alas, I own neither of those star diagonals today.

I should buy a dozen different ones and do a comparison again.

 

Light scatter is just one problem, and it's far from unique to dielectric star diagonals.

[BillP]

Why would a guaranteed flat Newtonian Secondary or a Diagonal have a slight amount of convexity?  First I've heard of this.

 

I've not done a star test on the varying diagonals.  However, when doing testing with very tight doubles, I was surprised that the doubles showed split with the BBHS and touching with no black space at all between them when using the Dielectric.  Sure didn't expect that.  Was able to repeat that performance too on various evenings.  Have no idea why that would be.  Surprising though.

Edited by BillP, 01 April 2016 - 03:59 PM.

[TH1]

 

Which is better for planetary?

 

I would return the mirror for the prism.

 

 

 

Planetary is often filled with personal preferences.  That being the case, only you will be able to determine which.  I don't have enough seat time with planetary comparisons with both so cannot say which I would prefer.  Anecdotally though the BBHS seems to be staying in the focuser more...but I would never let go of the prism.  Not an either-or thing for me as both are excellent and both have their strengths.

 

Care to share these strengths/differences Bill? Thank you.

[Starman1]

The substrate could simply be flatter on one than the other.  A distinct possibility not related to the coating material.

 

First: the process of making a flat can have the unintended effect of rolling off the edge of the mirror.  They're held on the edge in a fixture that is not PERFECTLY rigid on the nanometer level.  So the rotating table under the mirror can tilt the mirror ever so slightly.

 

Second: the process of coating the mirror with a large number of cavities of dielectric coatings also tends to roll off the edge of the mirror.

Roland Christen had a good article on this. It's because the coating thickness is not uniform over the mirror's surface and because of heat applied during coating.

 

Third: if you look at a lot of Danny's (PINBOUT) posts here on CN, he has run into a lot of secondary, flat, mirrors with slightly convex surfaces.

It is not uncommon.  He shows the interference fringes on a lot of them, and it isn't pretty.

 

Fourth, one of the reasons a 2" diagonal is recommended on scopes small enough that the entire clear aperture of the diagonal is not illuminated is simply to avoid the edges of the mirror, where the majority of the optical problems (like TDE) lie.  So, a good reason to use a slightly oversized secondary mirror in a reflector and an oversized mirror in a star diagonal.

 

If you hung out on the ATM Forum or REFLECTORS Forum a bit, you'd see all the reports on bad mirrors, mostly secondaries, but also star diagonals.

 

And, as I mentioned, a star test done with and without them usually reveals the problems caused by the star diagonal.

 

One of the reasons I recommend Antares Optics secondary mirrors is that they are tested AFTER coating, so WYSIWYG.

As for star diagonals, if you get a chance to test 4 of the same brand/model some time you'll see there is a variation from unit to unit just as there is with primary mirrors.  All too often, people blame the primary mirror in inexpensive scopes for poor image quality when it is really the secondary at fault.

[Neptune]

 

Which is better for planetary?

 

I would return the mirror for the prism.

 

 

 

Planetary is often filled with personal preferences.  That being the case, only you will be able to determine which.  I don't have enough seat time with planetary comparisons with both so cannot say which I would prefer.  Anecdotally though the BBHS seems to be staying in the focuser more...but I would never let go of the prism.  Not an either-or thing for me as both are excellent and both have their strengths.

 

Bill, I am the lucky owner of a AP175 APO.  Could you do a list of strengths (pros) and cons for each.  I am wondering if I am missing out on something here!  Maybe it is time to replace my 2" quartz dielectric.

Edited by Neptune, 01 April 2016 - 05:36 PM.

[jrbarnett]

The substrate could simply be flatter on one than the other.  A distinct possibility not related to the coating material.

 

First: the process of making a flat can have the unintended effect of rolling off the edge of the mirror.  They're held on the edge in a fixture that is not PERFECTLY rigid on the nanometer level.  So the rotating table under the mirror can tilt the mirror ever so slightly.

 

Second: the process of coating the mirror with a large number of cavities of dielectric coatings also tends to roll off the edge of the mirror.

Roland Christen had a good article on this. It's because the coating thickness is not uniform over the mirror's surface and because of heat applied during coating.

 

Third: if you look at a lot of Danny's (PINBOUT) posts here on CN, he has run into a lot of secondary, flat, mirrors with slightly convex surfaces.

It is not uncommon.  He shows the interference fringes on a lot of them, and it isn't pretty.

 

Fourth, one of the reasons a 2" diagonal is recommended on scopes small enough that the entire clear aperture of the diagonal is not illuminated is simply to avoid the edges of the mirror, where the majority of the optical problems (like TDE) lie.  So, a good reason to use a slightly oversized secondary mirror in a reflector and an oversized mirror in a star diagonal.

 

If you hung out on the ATM Forum or REFLECTORS Forum a bit, you'd see all the reports on bad mirrors, mostly secondaries, but also star diagonals.

 

And, as I mentioned, a star test done with and without them usually reveals the problems caused by the star diagonal.

 

One of the reasons I recommend Antares Optics secondary mirrors is that they are tested AFTER coating, so WYSIWYG.

As for star diagonals, if you get a chance to test 4 of the same brand/model some time you'll see there is a variation from unit to unit just as there is with primary mirrors.  All too often, people blame the primary mirror in inexpensive scopes for poor image quality when it is really the secondary at fault.

Personally I wish they'd gone with fused quartz or Zerodur rather than Sitall.  Sitall quality has been a roller coaster over the last few decades.  Zerodur has been much more consistent.  Fused quartz polishes smoother than either and is harder.

 

But honestly a high quality aluminum coated with quartz overcoat Pyrex or Supremax mirror, in my experience, when clean and new, surpasses prisms, and dielectrics on any substrate.  Not so much after some use and years though.

 

Regards,

 

Jim

Edited by jrbarnett, 03 April 2016 - 07:20 PM.

[Kurtz9]

So after reading Bill's report I immediately recognized this Sitall design as a game changer for refractors. But I also picked up the SCT adapter for my C14, after selling more stuff, and then I started to think that this mirror is doing nothing for SCTs.

 

 

FWIW we recently (about a week ago) got the BBHS diagonal for our C9.25 Evo SCT- and it produced a very noticeable improvement on the GRS on Jupiter- like Bills review I was surprised just how noticeable a difference...  (for full disclosure- it was replacing a 'cheap' GSO 2" quartz dielectric diagonal)

 

Unfortunately haven't had a chance between time and weather to take the scope anywhere dark yet (Jupiter was observed from an orange-light-polluted back of the house) to comment on improvements for any DSO stuff.

[Disciplus55]

Hi All,

Not quite a feedback on the BBHS diagonal only, but more on an overall set up :

Last night, me and my friends from our astro club made an observation session at a secondary school from 9pm to 11pm, we had 4 scopes and about 20 enthusiastic kids who wanted to see the Moon and Jupiter. I had my TSA 102 with a Leica zoom (with Powermate) and my BBHS diagonal. The other scopes where a SW Mak 180 mm with ES 82 eyepieces and a TS Dielectric diagonal. Then a SC of 250 mm and a 200 mm Newtonian. All the kids where dropping some "wow, awesome, nice, etc..." on all scopes.. but almost all of non shy ones, quite a lot of them actually, when looking at Luna or Jupiter on the Tak where claiming things like : "Wow, here, we see much better, it's much nicer"... it was all said...    : sharper image, way more contrast, a ton of details, vibrant colors, no CA... All 4 magnifications were close, all scopes were on temperature and collimated, but all the rest was different : aperture, scopes formulas, eyepieces and diagonals... but all in all, the resulting image was so obvious that the kids noticed the difference for their first view of the Moon and Jupiter of their lives ! 

I shall compare only the diagonals during some nights in May.

[BillP]

 

...almost all of non shy ones, quite a lot of them actually, when looking at Luna or Jupiter on the Tak where claiming things like : "Wow, here, we see much better, it's much nicer"... it was all said...    : sharper image, way more contrast, a ton of details, vibrant colors, no CA... All 4 magnifications were close, all scopes were on temperature and collimated, but all the rest was different : aperture, scopes formulas, eyepieces and diagonals... but all in all, the resulting image was so obvious that the kids noticed the difference for their first view of the Moon and Jupiter of their lives ! 

 

Very cool    From a design standpoint, the apochromatic refractor is the purest possible with the least impacts to the light.  The resulting character this imparts to the view may be hard to quantify, but subjectively it is an easy tell.  So not surprised at their reactions.  And of course, the TSA is magical anyway.

[SiriusLooker]

Bill..

  Yep, sorry I also would agree strongly with Jim Barnett and his feedback.. As matter of fact, after reading your nice article of testing, and (Before) reading Jim's feedback, I was also going to remark, after having over 40yrs experience, and (Now), observing 325 to 350times each year, that there are too many differences in one unit versus another, not just primary mirrors, but both secondary and diagonals.. My friend recently change out his old Secondary with Antares high quality secondary , and his Starsplitter 18inch performance went up a 3 fold!  I will recommend an Antares secondary for someone (who has a reflector), to upgrade before changing primary, or something else. 

  Just my 2cents input.

  Dennis

[SiriusLooker]

Sorry, (Correction),, I meant to say   ......strongly agree with Starman1 feedback and not Jim B.    sorry for confusion..

[BillP]

Sorry, (Correction),, I meant to say   ......strongly agree with Starman1 feedback and not Jim B.    sorry for confusion..

 

No need to be sorry as this is a hobby of "preferences" and not "facts".  And not I strongly agree with Don also...on some points...on other points less...some points not.  He made a lot of points!    It's all good.  Only one adage I feel stands as a best practice, "To you own eyes be true."  For me, in several areas the silver has been phenomenally better.  Others I have spoken with as well once they brought those aspects into the forefront of their observations.  It's all about what we like once we see it.

Edited by BillP, 28 April 2016 - 09:53 AM.

[MarkCPC11]

So can I gather that this new Baader BBHS diagonal which seems to be ordained as the newest product with mystical powers is not recommended for SCT's because of its optical design?

But to fully articulate my point, is this only viable for a refractor telescope?

 

Mark