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A Synergistic Combination

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#1 Jeff B

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Posted 22 September 2019 - 09:41 AM

I have called my CFF 160 F6.5 an excellent scope in search of a good Bino-viewer/corrector combination.

 

Well, I found one.  Big time.

 

I had the CFF out last night principally to align my AP900 GTO (using the daytime technique but at night with a star).  Having done that I turned the scope first to Jupiter, then Saturn.  I started with the "Zeiss Biggest" viewer with Baader 1.25X and 1.7X GPC's with my AP diagonal.  I mounted the GPCs down in to the 2" adapter and quick changer assembly that Denis Levatic provided.  The seeing was really rather calm and I started with the 1.25X GPC but quickly ramped up to the 1.7X jobbie.  Wow, Jupiter was engrossing and I quickly maxed out my available eyepiece power with my humble 9mm UO orthos (~195x).  Lots of belt detail when the seeing locked in.  Went over to Saturn.  Very, very nice with that etched quality Saturn has with Cassini, the globe shadow and the ring boundary against the blackness of space.  Belt detail on the globe too.  Very nice.

 

So off to Vega which displayed surprisingly good color correction, better than when using the Zeiss with my Denk power switch.  Spherical correction was first rate too but there were obvious color differences between the inside and outside of focus ring patterns.  But focus, was better than expected with just a bit of red/blue splashing around the stellar core (which was rather white) during moments of unsteady seeing (which was typically induced by my air conditioner's plume when it came on.  I had to look over it).  The double/double was superb.

 

Still retaining the 1.7X GPC, I then swapped out the Zeiss "biggest" for the Zeiss "sharpest", also from Denis.  This viewer has a mirror with a shorter prism light path but an overall slightly lower light path than the "biggest" viewer.  In previous comparisons I've noted the "sharpest" viewer was indeed sharp (but not all that sharper really than my Denks or other Zeiss viewers but still very, very subtly sharper).

 

Oh my!  The double double was very sharp with hard white stellar cores with very faint first diffraction rings. Just wonderful.  So, back to Vega. 

 

BAM!  I was taken a bit aback by the lack of any color splashing and the intense white stellar core.  Ramping through focus showed notably less color tint difference than with the Zeiss "biggest" (or my Denk II which I tried later).   Turning to Saturn, it was very, very sharp and even a tad more "etched" with a tiny bit less lateral color than with the Zeiss "biggest".   Inserting the 12mm Claves brought the magnification down to the point where I found it difficult to detect any differences in color rendition between the viewer with no differences in sharpness.

 

I then covered the scope, came inside and got back up this morning to look at the Moon.

 

BOOM, BAM!!!

 

Wow (!), just an amazing view with the "sharpest", 1.7 x GPC, AP diagonal and 9mm UO orthos.  Very steady seeing.  The scope and optical train had all settled down during the night and what really struck me front and center were the sharpness and total lack of color tinting, refraction, fringing, splashing or whatever on the brightly lit rims of crater walls or their central peaks.  I find this to be a very demanding test, right up there with Vega and Sirius.  Speaking of which, I was struck again by the lack of color splashing and the intense whiteness of Sirius's stellar core.  Racking in and out of focus did show some color but of the same tint on each side with identical rings and an excellent collapse down into focus from each side.  Wow, true APO performance.  I found myself looking around for my 7mm UO pair but couldn't find them. 

 

Speaking of Sirius, the Pup was easy.  However, due to the older coatings inside the viewer, Sirius had two other "companions" due to internal reflections (Vega was a triple system wink.gif ).  This annoys some, but I ignore it.

 

One more final treat was that there was a tight double star just off of the lunar northern terminator line, maybe 1/10 a degree or so.  Just beautiful with a white core to the primary and blue/purple for the much fainter companion. 

 

So, after this long dissertation, I have indeed found the "right", synergistic, high power bino-viewer system for this scope:  Zeiss "sharpest" from Denis Levatic and the Baader 1.25 and, especially, 1.7x GPCs.

 

I had suspected this might happen as I had similar experiences with my old AP 178 F9, pre-ED Starfire and TEC 160 ED, using the Zeiss Biggest and the GPCs, but not to the "degree" I experience with the CFF and the "sharpest."  I will have to revisit those scopes with this combination.

 

So when Baader and AP say the correctors compensate, for the slight spherical over-correction and color errors the prisms in the viewers create when using fast APOs, they seem to be spot on, and, in some cases, such as with my CFF 160 F6.5 (which is very fast for the aperture), it's rather obvious.

 

Like in my audio hobby, I love finding the right combination of components that really lets the music out and helps keeps the nasties in the background.  I found such a system for the CFF last night and this morning.  Visual "music".

 

Jeff


Edited by Jeff B, 22 September 2019 - 09:43 AM.

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#2 denis0007dl

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Posted 22 September 2019 - 11:02 AM

Thanxs for that nice writeup, Jeff, again!

 

You really ARE very demanding observer, who delivers and share your very detailed observation experiences with comunity!

 

I can feel nd see your LOVE, and ENERGY you have in hobby we all enjoy!

 

Stay like that buddy!

 

All best from Croatia,

Denis, binoviewers expert



#3 Eddgie

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Posted 22 September 2019 - 11:33 AM

Good report.

 

Yes, people I think dismiss the spherochromatism induced by the BVs, but the faster the scope, the more of a concern that it should be.  The Baader GPCs do a great job of correcting it.

 

The Baaders are fine for scopes that can reach focus using one of them, but for others that can't reach focus with either of these, I recommend the Televue 2x amplifier.  This is also designed to correct the spherochromatism from the binoviewer.

 

BV with TV.jpg

 

Particularly for solar (both white light and H-a) I recommend the Baader GPCs or the Televue 2x.  While you can't see the color shift when doing H-a, the spherochromatism is probably at its worst at 650nm.   For white light, using a wedge, you can really see the difference the prisms make. GPC is like going from a well corrected ED scope to an Apo.   

 

Here is my Lunt 80 with 1.7x GPC (which actually only gives about 1.5x or so).

 

post-14923-0-05193400-1565226094_thumb.jpg

 

So, yes, I think that either the Baader GPC or the Televue 2x Amplifier should be used for the most demanding high resolution observing. 

 

 


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#4 Jeff B

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Posted 22 September 2019 - 05:21 PM

Good lead on the TV 2X Amp Eddgie.   Another option.

 

Also:

 

"Here is my Lunt 80 with 1.7x GPC (which actually only gives about 1.5x or so)."

 

Interesting you should say that as I certainly felt it did not give 1.7X, especially compared to the 1.25X GPC, when installed in the standard way by screwing it into the bottom of the Mark V dovetail.  Also, I found that installing the things the way I did here results in them being a little more forward in the light path and I got the impression of increased magnification.  If I can dig up a graduated reticle eyepiece, I can certainly check this stuff out.  How did you determine the reduced magnification?

 

Jeff



#5 Eddgie

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Posted 23 September 2019 - 08:03 AM

I have not measured the power of the 1.7x, but many others have and that figure has been provided by people that have, and I have no reason to doubt it.  I easily get a full disk view of the sun even using zooms with a tiny apparent field of view.

 

Moving the GPC does raise the power however the spacing of the GPC for the best spherochromatism is important, though I don't know exactly how important, meaning I don't know how far ahead of the entry prism you could put it and still get effective correction.  The designer though (Roland Christen) says that it should be placed at the entrance of the binoviewer.  The Mark V puts it inside the dovetail, and the Maxbright puts it in essentially the same position, with the lenses mounted immediately adjacent to the front aperture.   

The actual increase in magnification is not that big.  Remember, the working distance of the GPC is the light path length of the binoviewer.  If it is more like a Barlow in operation, then given 1.25x at a spacing of 100mm would mean that moving it forward by 50mm would probably not change the magnification the same way that moving a shorty Barlow designed for 50mm of spacing would.   

 

Again, I do not know how critical the spacing is, but as with so many things like this, what we know for sure is that the designer says that for best performance, it should be kept as close as possible to the front aperture.  At some distance, my guess is that it simply provides less correction, or possibly over corrects in the opposite direction.  


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#6 Eddgie

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Posted 23 September 2019 - 08:14 AM

And the Televue 2x amplifier is expensive, but it works quite well. 

 

I only just found out from the solar forum that it has the same thread as the earlier Denk binoviewers so can be screwed directly into the nose threads. 

 

Now most people using the Denks probably have power switches, but for someone that does not, I think the TV 2x is the way to go (if they can't reach focus with the 1.7x GPC). 


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#7 Jeff B

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Posted 23 September 2019 - 11:22 AM

Good stuff Eddgie and thanks.

 

So I measured the difference in position of the convex side of the element when mounted the standard way in the Mark V and the "biggest" viewers and when mounted down in to the top of either the T2 diagonals or the 2" adapter, both with the quick changer (I had to flip the element around for that).  It came out to 18mm.   Not much difference really compared to the total prism path length of a typical viewer, but about double the "stock" distance to the entry prism front face.  But without question it does work well there in the context of this CFF system. 

 

The GPCs also worked very well in correcting my early AP 178 F9 pre-ED Starfire using either the Mark V or the Zeiss biggest viewers with the "standard" GPC install position inside the dovetail:

 

https://www.cloudyni...r-nights-dream/

 

Based upon my CFF experience, I really do want to do a lot more messing around with these GPCs, the Zeiss Sharpest, my older Christen Triplets and my TEC 160 and 200ED's.  

 

This is fun.

 

Jeff



#8 elwaine

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Posted 24 September 2019 - 09:48 AM

There seems to be contradictory statements regarding the placement GPCs and resultant magnifications. Thomas found:

 

 

1. 1.25x GPC, used in top of Zeiss T2 prism: 1.24x. Close to the listed figure.

2. 1.25x GPC, used in front of Zeiss T2 prism: 1.31x. No surprises. Difference very slight and barely visible, yet clearly gives more extra back focus.

3. 1.7x GPC, used in top of Zeiss T2 prism: 1.51x. What the hey?

4. 1.7x GPC, used in front of Zeiss T2 prism: 1.65x. What? Not even 1.7x here?

 

And this comes from Company 7’s website (in which the first figure is the mag. factor from placing the GPC directly into the Mark V, between the binoviewer and the diagonal):

 

- factor 1.25x - alternatively installs before the Baader 90 degree prism diagonal to provide 1.45x
- factor 1.70x - can be installed before the Baader 90 degree prism diagonal for 2x

 

Neither Thomas nor C-7 state whether they used a standard 2” diagonal or a T-2 diagonal with its shorter light-path. If Thomas used a T-2, and C-7 used a 2” diagonal, that might explain the differences in the mag. factors when the GPC was positioned between the diagonal and the telescope. But it shouldn’t make a difference when used between the binoviewer and the diagonal. Or is that not the case?


Edited by elwaine, 24 September 2019 - 09:55 AM.



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