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Was the Tak Sky 90 a flop?

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#51 BravoFoxtrot

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Posted 15 August 2018 - 12:05 PM

Old thread.

 

I had one of the first versions years and years ago and didn't like it.  I wanted a more portable FS-102, but it had some issues.  I remember an objectionable amount of false color that disappointed me and believe I sent it in for repair for a collimation issue.  I also remember being excited the day I replaced it with a TV-85.  

 

I heard version 2 was much better due to some changes (no idea what they were), but I never considered it again after my first experience.  



#52 nicoledoula

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Posted 15 August 2018 - 07:41 PM

It was only a flop profitability wise. 



#53 t.r.

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Posted 15 August 2018 - 07:59 PM

I believe the "dirty secret" was the first version would not hold collimation.

#54 CHASLX200

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Posted 16 August 2018 - 05:13 AM

I believe the "dirty secret" was the first version would not hold collimation.

Main reason i never bought one.



#55 rolo

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Posted 16 August 2018 - 06:08 AM

Old thread.

 

I had one of the first versions years and years ago and didn't like it.  I wanted a more portable FS-102, but it had some issues.  I remember an objectionable amount of false color that disappointed me and believe I sent it in for repair for a collimation issue.  I also remember being excited the day I replaced it with a TV-85.  

 

I heard version 2 was much better due to some changes (no idea what they were), but I never considered it again after my first experience.  

The Sky 90 at f/5.6 was meant to for imaging. Any flourite doublet at f/5.6 will exhibit some false color and will not make a good high power scope. hoghe f/ratios like the FS102 are much better suited for that.



#56 junomike

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Posted 16 August 2018 - 07:10 AM

The Sky 90 at f/5.6 was meant to for imaging. Any flourite doublet at f/5.6 will exhibit some false color and will not make a good high power scope. hoghe f/ratios like the FS102 are much better suited for that.

This is why IMO these OTA's are best used (visually)  for Wide Field DSO's.  I love my WO88 (498mm) as it easily fits both Veils (NGC6992/6960) as well as NGC7000.

Planetary/Lunar....meh, It's ok for a sub 100mm OTA but I don't find Planets come alive until you reach the 5" mark.



#57 BravoFoxtrot

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Posted 16 August 2018 - 07:51 AM

The Sky 90 at f/5.6 was meant to for imaging. Any flourite doublet at f/5.6 will exhibit some false color and will not make a good high power scope. hoghe f/ratios like the FS102 are much better suited for that.

 

Correct.  The significant amount of false color was due to an issue with the scope.  

 

I think fast refractors make fine visual instruments and especially shine in wide field observing.  



#58 Far Star

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Posted 16 August 2018 - 09:16 AM

 

You can have the same optical design slightly tweaked and improved by the same lens assembly manufacturer in a different body.

 

The Borg 90FL is a doublet fluorite, 90mm F5.6, fluorite at the back of the lens assembly and distance between the elements tweaked. Length with a FTF is 38 centimetres and weight with Borg 80mm rings and Dovetail about 2.3 kilos. 

 

 
 
Alternatively, these show up at reasonable prices both on CN and AM on a not very infrequent basis.
 
The design is an excellent compromise in my opinion of portability Vs optical performance. Field curvature is present and can easily be detected on the moon when it fills the eyepiece or with a Nagler 31mm when panning the skies. Contrast is on par with what one would expect from a fluorite doublet (and yes, IMHO there is a clear and detectable difference vs other optical designs).
 
There is very slight CA in focus on the Lunar limb but does not detract at all from the views. Has shallow depth of field so dual speed Focuser is a must to optimize use. 4.81 degrees TFOV with a Nagler 31mm, 5.58mm exit pupil and 16x magnification. Pair it with a binoviewer and with Pan 24 or Plossl 32mm at native FL you get slightly more than 3 degrees TFOV. 
 
However, despite the glowing comments above, I will state that obviously it does not reach the level of contrast of its longer focal ratio brethren, having compared it to my Tak FC76DC which is a f7.5 doublet fluorite of similar optical design. 
 
If if you want ultraportable, the FC76DS is compact and provides a gentler focal ratio. If you don't mind a bit of extra weight, the FC100 provides a bit of extra aperture at again a nice slow focal ratio. If you want something in the middle which is ultraportable with a wide FOV the TAK90 or Borg 90 will do you fine. 
 
I find that I rarely use mine with 2" eyepieces. 3.09 degrees TFOV, 4.32mm exit pupil and 21x magnification with a Pan 24 are plenty enough for me. I will use a 2" eyepieces only when viewing the Veil, North American Nebula and panning the skies from Scorpio to Cassiopeia in the summer. The luxury of a 2" eyepieces is nice to have, but not essential at such short focal length.
 
I have yet to compare the FC76 to the Borg 90 on the planets but my viewing experience with each on separate occasions, show that despite the wider aperture of the Borg, it's shorter focal ratio does impact on the views. Specifically, the color saturation of the smaller and slower scope is appreciably better. 
 
I do realize that there is a small difference in the optics design of the Borg Vs the Tak, but I would venture to say that my experience should mirror the experience of Tak owners. Further feedback from owners of the Tak 90 in terms of their viewing experience would be much appreciated!

 

The fluorite lens of the Borg 90FL is apparently not at the back of the lens assembly (The information in question on the AOKswiss website seems to be incorrect.):

 

The Borg 90FL objective "is also, just like the Sky-90, a front-surface fluorite design....."

 

Source: http://www.scopeview...uk/Borg90FL.htm (Have a look at the first photo in the "Optics" section of this article!)

 

Furthermore:

 

"The 90FL objective is outstanding – Optron have achieved a fast f-ratio without sacrificing optical quality. All aberrations are well-controlled. Off-axis curvature and coma are at F6 triplet levels, even without the flattener. False colour is well suppressed for such a fast doublet. The 90FL may have the optical spec’ of the Sky-90, but it’s free of that scope’s high-power softness and collimation issues. Designed as an imaging scope, it still performed very well on the Moon and planets. Meanwhile, the 90FL gave lovely wide, flat deep sky views with eyepieces designed for fast f-ratios, like Tele Vue’s."

 

Source: http://www.scopeview...uk/Borg90FL.htm

 

Currently I'm waiting for my Borg 90FL, which is expected to be delivered in September. I look forward to make a side by side comparison with my Tak FC-76DC.



#59 jay.i

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Posted 16 August 2018 - 09:46 AM

The fluorite lens of the Borg 90FL is apparently not at the back of the lens assembly (The information in question on the AOKswiss website seems to be incorrect.):

 

The Borg 90FL objective "is also, just like the Sky-90, a front-surface fluorite design....."

 

Source: http://www.scopeview...uk/Borg90FL.htm (Have a look at the first photo in the "Optics" section of this article!)

 

Furthermore:

 

"The 90FL objective is outstanding – Optron have achieved a fast f-ratio without sacrificing optical quality. All aberrations are well-controlled. Off-axis curvature and coma are at F6 triplet levels, even without the flattener. False colour is well suppressed for such a fast doublet. The 90FL may have the optical spec’ of the Sky-90, but it’s free of that scope’s high-power softness and collimation issues. Designed as an imaging scope, it still performed very well on the Moon and planets. Meanwhile, the 90FL gave lovely wide, flat deep sky views with eyepieces designed for fast f-ratios, like Tele Vue’s."

 

Source: http://www.scopeview...uk/Borg90FL.htm

 

Currently I'm waiting for my Borg 90FL, which is expected to be delivered in September. I look forward to make a side by side comparison with my Tak FC-76DC.

I have to go ahead and disagree with Roger on the claim that the 90FL puts up "flat" deep sky views with TV eyepieces. I used my 21/13/8Ethos lineup and saw plenty of field curvature, so much so that it was too much for me. The slight CA combined with a field of which almost half the stars were out of focus led me to return the scope. I wanted to love it but it's just a little too fast. I would love if it got extended just a little bit. It's the perfect travel size... truly. But it felt too compromised to be an enjoyable widefield instrument based on the CA and FC I saw.




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