43 replies to this topic

[betacygni]

Was fortunate to get drawn for a Stowaway recently and had been hoping to do an ultimate 90mm class shootout between it and my old Vixen FL-90S f9 fluorite doublet. Had the opportunity tonight to finally put them head to head.

 

The setup:
Dual mounted on a Rowan AZ75
Diagonals: Each had a Baader t2 BBHS mirror
Binoviewers: Each had Binotron with powerswitch.
Eyepieces: Tak 25mm TPL on the Vixen, 18mm TPL on the AP.
Exit pupils used via identical powerswitch settings: AP 1.2mm and 0.77mm, Vixen 1.23mm and 0.79mm

 

So everything was setup for as fair a contest as  I could manage.

 

First thing I noticed was the AP was notably brighter. The nebulously of Orion had more pop, Jupiter and stars were a bit brighter.

 

Both scopes were color free, but the Vixen had a warmer tone. I’m not sure I would have noticed this without the ability to immediately swap back and forth between scopes, but Jupiter was warmer, star colors ever so slightly muted on the Vixen in comparison to the AP. It certainly put to bed the fluorite vs (at least top shelf) triplet debate on star color as far as I’m concerned. Though I suppose there is room for newer fluorite doublets having better coatings (in fact I’m not sure the fluorite element on these were coated at all).

 

This is where it got odd. I was adjusting focus on the Stowaway a lot more. The stars initially didn’t seem quite as sharp. I started the test without any cooldown time (important factor to me with my typical limited observing time), so perhaps the doublet had better cooldown characteristics. Wasn’t a very extreme temp differences though, went from a 70s house into 60s outdoors. I found myself adjusting focus on the stowaway less as the night went on, but still more than the Vixen. Perhaps just the Vixen’s f9 depth of field being more tolerant.

 

This was another odd one, the Vixen just felt “more relaxed.” Despite the slightly dimmer view and more muted star colors (I don’t want to overemphasize this, it wasn’t huge), the Vixen just always felt for a lack of a better term more consistent. Again maybe the debated greater depth of focus of the Vixen was handling the seeing conditions better. Maybe the slightly dimmer view was less jarring to the eye, I don’t know. This is the observation I’m least confident in, as it was more a feeling than objective. It could have also very well been related to my binoviewer setup, less than perfect IPD setting or diopter being slightly off. Either way I noticed it throughout the night.

 

The only obvious performance difference I found was at the very end of my session. Came across a dim and fairly tight double. The Vixen split it, but the AP was cleaner and easier to consistently make out. I’m not convinced this wasn’t just due to the Stowaway’s slightly brighter image, as the stars were just within the scopes reach. If they were brighter with the same separation I’m not sure there would have been a difference.

 

Overall the comparison was a bit annoying, as I was hoping it would be obvious which to sell. It wasn’t. The differences I saw never would have been noticed if not directly side by side and were small enough they could simply be other gear confounding variables (newer diagonal, binoviewer sample variation, eyepiece variation, etc).

 

My ultimate takeaway was I’m going to have to choose if I want essentially a f6.65 or f9 Stowaway (or to the credit of the Vixen, an f9 or f6.65 FL-90S).

 

From the value perspective the Vixen is an absurdly good deal if you can find one. About a third of the price of the Stowaway, and I dare say its equal. It’s really too bad they are no longer made (Takahashi, are you listening?).

 

The plus side of all this is I’m really looking forward even more to my upcoming TEC 140 f9.6 fluorite doublet. This was a nice confirmation a top shelf doublet can give a triplet a run for its money.

 

 

Attached Thumbnails

• 

[Jay_Reynolds_Freeman]

Interesting. A friend of mine who is an experienced planetary observer and I once did a side-by-side comparison of my Vixen 90 mm f/9 fluorite doublet and his earlier model (92 mm f/4.9) Stowaway, and we both concluded the Vixen was a hair better. I do not draw any conclusion other than that Vixen and Astro-Physics both make fine telescopes.

 

I have since acquired one of the later-model Stowaways but have not done a side-by-side with the Vixen 90 mm fluorite. I certainly have found no fault with either model Stowaway.

 

 

Clear sky ...

Edited by Jay_Reynolds_Freeman, 21 April 2025 - 03:14 AM.

[Psion]

The advantage of the F9 doublet will be faster thermal stabilization and a more stable image in poorer seeing.

[Tyson M]

Nothing about your review seems odd.

Fluorites seem to have warmer tones. And longer focal length scopes seem more stable than shorter focal length scopes.

Both are beauties.

[25585]

My choice would be to keep both for now. More comparisons, and sort out how you feel. If I had to make an on the spot choice, I would keep the Vixen.

[starman876]

Was fortunate to get drawn for a Stowaway recently and had been hoping to do an ultimate 90mm class shootout between it and my old Vixen FL-90S f9 fluorite doublet. Had the opportunity tonight to finally put them head to head.

 

The setup:
Dual mounted on a Rowan AZ75
Diagonals: Each had a Baader t2 BBHS mirror
Binoviewers: Each had Binotron with powerswitch.
Eyepieces: Tak 25mm TPL on the Vixen, 18mm TPL on the AP.
Exit pupils used via identical powerswitch settings: AP 1.2mm and 0.77mm, Vixen 1.23mm and 0.79mm

 

So everything was setup for as fair a contest as  I could manage.

 

First thing I noticed was the AP was notably brighter. The nebulously of Orion had more pop, Jupiter and stars were a bit brighter.

 

Both scopes were color free, but the Vixen had a warmer tone. I’m not sure I would have noticed this without the ability to immediately swap back and forth between scopes, but Jupiter was warmer, star colors ever so slightly muted on the Vixen in comparison to the AP. It certainly put to bed the fluorite vs (at least top shelf) triplet debate on star color as far as I’m concerned. Though I suppose there is room for newer fluorite doublets having better coatings (in fact I’m not sure the fluorite element on these were coated at all).

 

This is where it got odd. I was adjusting focus on the Stowaway a lot more. The stars initially didn’t seem quite as sharp. I started the test without any cooldown time (important factor to me with my typical limited observing time), so perhaps the doublet had better cooldown characteristics. Wasn’t a very extreme temp differences though, went from a 70s house into 60s outdoors. I found myself adjusting focus on the stowaway less as the night went on, but still more than the Vixen. Perhaps just the Vixen’s f9 depth of field being more tolerant.

 

This was another odd one, the Vixen just felt “more relaxed.” Despite the slightly dimmer view and more muted star colors (I don’t want to overemphasize this, it wasn’t huge), the Vixen just always felt for a lack of a better term more consistent. Again maybe the debated greater depth of focus of the Vixen was handling the seeing conditions better. Maybe the slightly dimmer view was less jarring to the eye, I don’t know. This is the observation I’m least confident in, as it was more a feeling than objective. It could have also very well been related to my binoviewer setup, less than perfect IPD setting or diopter being slightly off. Either way I noticed it throughout the night.

 

The only obvious performance difference I found was at the very end of my session. Came across a dim and fairly tight double. The Vixen split it, but the AP was cleaner and easier to consistently make out. I’m not convinced this wasn’t just due to the Stowaway’s slightly brighter image, as the stars were just within the scopes reach. If they were brighter with the same separation I’m not sure there would have been a difference.

 

Overall the comparison was a bit annoying, as I was hoping it would be obvious which to sell. It wasn’t. The differences I saw never would have been noticed if not directly side by side and were small enough they could simply be other gear confounding variables (newer diagonal, binoviewer sample variation, eyepiece variation, etc).

 

My ultimate takeaway was I’m going to have to choose if I want essentially a f6.65 or f9 Stowaway (or to the credit of the Vixen, an f9 or f6.65 FL-90S).

 

From the value perspective the Vixen is an absurdly good deal if you can find one. About a third of the price of the Stowaway, and I dare say its equal. It’s really too bad they are no longer made (Takahashi, are you listening?).

 

The plus side of all this is I’m really looking forward even more to my upcoming TEC 140 f9.6 fluorite doublet. This was a nice confirmation a top shelf doublet can give a triplet a run for its money.

Thanks.  Will keep my Vixen 90mm Fluorite.  Was ready to put it up for sale.   

[Scott99]

For me these Vixen FL refractors are awesome because of the light weight of the tube and the high-quality f/9 FL lens.  They are telescopes of their time though.  There is no way to overcome the back element of the lens being uncoated.  I ran a 102FL against my FS102 and was surprised that the FS102 seemed better on all counts.  Not only slightly brighter and more contrasty but also a little less false color, which was the opposite of my expectation.   I had expected to replace the FS102 with the Vixen to get the f/9 focal length.  The 102FL was still a wonderful small apo though.

 

More recently I've seen color curve diagrams for Tak's old FC series and the FS series and the FS actually had improved color correction over the FC series, which I didn't know.  I've read that the Vixen fluorites are the same design as the FC series so that might explain what I saw with the FS102.

 

As for asking Tak for more - they made two runs of f/9 FC100-DL's over 4 or 5 years I think?  That was your chance Or get the current DZ.  I see these as the old Vixen fluorites made in 2025 with every possible modern advantage. 

 

For me the f/9 length is critical, I love it over f/6.65.  It's just better.  It's better for everything except the largest possible FOV.  Eyepieces all like f/9 over f/6 and perform better.  You get to used longer-fl oculars at the same powers.  This is probably the "relaxed" factor mentioned above.   I prefer the longer FL and ED doublets over short triplets.

Edited by Scott99, 21 April 2025 - 12:03 PM.

[Reid W]

Try white light solar.  I found my 90F to show the grainulation … better, and as far as focus- yes the f9 is set and forget.

 

I found the V90 performed better with a prism diagonal- either the Baader basic or Tak 1.25” vs using a (premium) mirror.

 

The 92 has a shorter moment arm and pairs nicely in my super light go-to rig.

[bobhen]

I would guess that the slight jumpiness in the Stowaway triplet is because the Vixen doublet acclimated quicker than the triplet.

 

I would also guess that the warmer tone in the Vixen is due to slight imperfect or some residual color error. The cooler the view the better the color correction is until you get a dead cold view with a mirror's perfect color correction.

 

I also think that Tak should make a 90mm. But I would be looking for a TSA 90mm triplet. But since they already have an 85mm and a few 100mm refractors, I guess there's probably not a chance at that In any event, for visual only, I'll take my Takahashi FS-100DF 100mm F7.4 Fluorite doublet over either of these. More aperture and with the same quick acclimation properties as the Vixen 90mm and the Tak 100mm OTA is only 6.3 pounds and is available now and much less expensive than the AP Stowaway. For visual and imaging pursuits, it would definitely be Stowaway.

 

I've seen some suggest that the longer focal length and greater depth of field of the Vixen is the reason for the slightly calmer view. That might seem logical but it is incorrect. HERE is a link to a website that goes into great depth on the subject. For those that just want the conclusion, here it is...

 

"Telescopes of equal aperture are affected the same by atmospheric turbulence, regardless of focal ratio. The error in the hypothesis is that it was assumed that the same atmospheric distortion will cause the same shift in the best focus position in the two telescopes, and this is not true. While the high f-number telescope does enjoy a greater depth of focus, unfortunately the shift in best focus caused by turbulence is also greater. In fact, the two are locked together; the instrument with four times greater depth of focus also has a four times greater linear shift of the best focus position."

 

Both the Vixen and the AP are great refractors. As to which would be preferred, it just comes down to (as it usually does) how they are going to be used. 

 

Bob

Edited by bobhen, 21 April 2025 - 01:37 PM.

[turtle86]

My choice would be to keep both for now. More comparisons, and sort out how you feel. If I had to make an on the spot choice, I would keep the Vixen.

 

Agree. I would definitely keep both for now if possible, since the initial shootout was somewhat inconclusive. After a few more comparisons are done, with more objects and varying viewing conditions, a favorite might then emerge.  As Bob says, the choice likely comes down to how the scope will be used.

 

I have the Stowaway myself and must say that its optical quality never fails to astonish me.  Just a wonderful scope.

Edited by turtle86, 21 April 2025 - 07:57 PM.

[weis14]

Great comparison!  I've never looked through one of the Vixen FL refractors, but I have no doubt that its stellar reputation is well deserved.  

 

My Stowaway is the best 90mm scope I've ever owned, but I've never put it against a top end competitor.  The closest competitor was the Astro-Tech AT92 I had immediately before it.  In a quick side-by-side, the AT held its own pretty well, but its shorter focal length resulted in significant field curvature that was unable to be forgotten once I looked through the Stowaway.

[Lagrange]

I would guess that the slight jumpiness in the Stowaway triplet is because the Vixen doublet acclimated quicker than the triplet.

 

I would also guess that the warmer tone in the Vixen is due to slight imperfect or some residual color error. The cooler the view the better the color correction is until you get a dead cold view with a mirror's perfect color correction.

 

I also think that Tak should make a 90mm. But I would be looking for a TSA 90mm triplet. But since they already have an 85mm and a few 100mm refractors, I guess there's probably not a chance at that In any event, for visual only, I'll take my Takahashi FS-100DF 100mm F7.4 Fluorite doublet over either of these. More aperture and with the same quick acclimation properties as the Vixen 90mm and the Tak 100mm OTA is only 6.3 pounds and is available now and much less expensive than the AP Stowaway. For visual and imaging pursuits, it would definitely be Stowaway.

 

I've seen some suggest that the longer focal length and greater depth of field of the Vixen is the reason for the slightly calmer view. That might seem logical but it is incorrect. HERE is a link to a website that goes into great depth on the subject. For those that just want the conclusion, here it is...

 

"Telescopes of equal aperture are affected the same by atmospheric turbulence, regardless of focal ratio. The error in the hypothesis is that it was assumed that the same atmospheric distortion will cause the same shift in the best focus position in the two telescopes, and this is not true. While the high f-number telescope does enjoy a greater depth of focus, unfortunately the shift in best focus caused by turbulence is also greater. In fact, the two are locked together; the instrument with four times greater depth of focus also has a four times greater linear shift of the best focus position."

 

Both the Vixen and the AP are great refractors. As to which would be preferred, it just comes down to (as it usually does) how they are going to be used. 

 

Bob

 

The most plausible explanation I've read for people finding the view to be more stable in longer focal ratio scopes is that the longer tube puts the objective further away from the heat plume from the observer.

[betacygni]

The most plausible explanation I've read for people finding the view to be more stable in longer focal ratio scopes is that the longer tube puts the objective further away from the heat plume from the observer.

The difference in distance wasn’t much in this case, but then I imagine our heat plumes are most intense at these relative close distances then drop off substantially.

My guess would be the objective cooling, but more specifically the slight change in focus point as this happens. The greater depth of focus (and faster cooling) of the doublet perhaps both contributed to the focus point staying more consistent.

Edited by betacygni, 21 April 2025 - 09:34 PM.

[starman876]

My lust for a Stowaway is somewhat diminished and my appreciation for my 90mm Vixen fluorite has  increased

Edited by starman876, 21 April 2025 - 09:47 PM.

[betacygni]

My lust for a Stowaway is somewhat diminished and my appreciation for my 90mm Vixen fluorite has increased

Yes, I was honestly surprised the Vixen did so well. I knew from reports and my own experience these are special scopes, but putting it side by side with an essentially perfect triplet is something else entirely.

I suspect which scope I keep will come down to portability (the stowaway definitely wins there) and focal ratio, the Vixen just can’t do the wider FOV. That said I’m not sure I care about those two factors much.

But I’m in no hurry and as other have suggested I’ll give it more time to get to know he qualities of both. It was quite informative to see the differences first hand we often theoretically discuss.

Edited by betacygni, 21 April 2025 - 10:08 PM.

[Jay_Reynolds_Freeman]

[...] the Vixen just can’t do the wider FOV. [...]

With a two-inch focuser adapter and a two-inch barrel eyepiece, the Vixen 90 will provide a field width approaching 3.5 degrees, and a 55 mm Plossl or a wider-field type down to perhaps 30 mm will show it.

 

Clear sky ...

[Dr Arnheim]

Great comparison!  I've never looked through one of the Vixen FL refractors, but I have no doubt that its stellar reputation is well deserved.  

 

My Stowaway is the best 90mm scope I've ever owned, but I've never put it against a top end competitor.  The closest competitor was the Astro-Tech AT92 I had immediately before it.  In a quick side-by-side, the AT held its own pretty well, but its shorter focal length resulted in significant field curvature that was unable to be forgotten once I looked through the Stowaway.

Yes the AT92mm is great. In good seeing I have pumped up the magnification to over 290x already without any image break down (I know that this makes little sense but I just wanted to try it). I would love to test it side by side with a Stowaway or Vixen one day.

I think that differences between good scopes are pretty small, however, I also think that the members of this forum (and I include me here) are subject to a strong self-selection bias for the biggest astro nerds out there. So these small differences can mean a lot to us : ). I mean just try to explain a normal person that one scope is better than the other and that you know that because you jumped from one scope to the other for several hours while there were mounted in parallel.

 

I love these comparisons. Keep them coming!

 

Btw, This Vixen looks beautiful!

Edited by Dr Arnheim, 22 April 2025 - 09:59 AM.

[SandyHouTex]

I'd keep the Vixen and sell the Stowaway.

[Scott99]

Yes, I was honestly surprised the Vixen did so well. I knew from reports and my own experience these are special scopes, but putting it side by side with an essentially perfect triplet is something else entirely.
 

These f/9 FL doublets from Vixen (Optron?) are pretty close to being perfect too.  IMO you don't need to get a Stowaway to improve on your 90FL.  They're just slightly different at the eyepiece.  I think of them as on par with the current Taks with a tiny, barely perceptible loss of contrast from the uncoated element. 
 

I could never get comfortable with the f/5 and f/6 Traveler and Stowaway because of my plossls and other simple eyepieces.  I can't use them at f/5-f/6 but they're excellent at f/8-f/9.  If you're not getting on an airplane or doing exposures there's no reason to go faster than f/9 IMO.

Edited by Scott99, 22 April 2025 - 11:05 AM.

[Spikey131]

These f/9 FL doublets from Vixen (Optron?) are pretty close to being perfect too.  IMO you don't need to get a Stowaway to improve on your 90FL.  They're just slightly different at the eyepiece.  I think of them as on par with the current Taks with a tiny, barely perceptible loss of contrast from the uncoated element. 
 

I could never get comfortable with the f/5 and f/6 Traveler and Stowaway because of my plossls and other simple eyepieces.  I can't use them at f/5-f/6 but they're excellent at f/8-f/9.  If you're not getting on an airplane or doing exposures there's no reason to go faster than f/9 IMO.

Some of us enjoy a wider field than that afforded by an f/9 scope.

[ris242]

and when the 140 arrives, these scopes will collect dust. lol

[25585]

I would guess that the slight jumpiness in the Stowaway triplet is because the Vixen doublet acclimated quicker than the triplet.

 

I would also guess that the warmer tone in the Vixen is due to slight imperfect or some residual color error. The cooler the view the better the color correction is until you get a dead cold view with a mirror's perfect color correction.

 

I also think that Tak should make a 90mm. But I would be looking for a TSA 90mm triplet. But since they already have an 85mm and a few 100mm refractors, I guess there's probably not a chance at that In any event, for visual only, I'll take my Takahashi FS-100DF 100mm F7.4 Fluorite doublet over either of these. More aperture and with the same quick acclimation properties as the Vixen 90mm and the Tak 100mm OTA is only 6.3 pounds and is available now and much less expensive than the AP Stowaway. For visual and imaging pursuits, it would definitely be Stowaway.

 

I've seen some suggest that the longer focal length and greater depth of field of the Vixen is the reason for the slightly calmer view. That might seem logical but it is incorrect. HERE is a link to a website that goes into great depth on the subject. For those that just want the conclusion, here it is...

 

"Telescopes of equal aperture are affected the same by atmospheric turbulence, regardless of focal ratio. The error in the hypothesis is that it was assumed that the same atmospheric distortion will cause the same shift in the best focus position in the two telescopes, and this is not true. While the high f-number telescope does enjoy a greater depth of focus, unfortunately the shift in best focus caused by turbulence is also greater. In fact, the two are locked together; the instrument with four times greater depth of focus also has a four times greater linear shift of the best focus position."

 

Both the Vixen and the AP are great refractors. As to which would be preferred, it just comes down to (as it usually does) how they are going to be used. 

 

Bob

The Sky-90 was Takahashi's most recent 90mm.

[25585]

Yes, I was honestly surprised the Vixen did so well. I knew from reports and my own experience these are special scopes, but putting it side by side with an essentially perfect triplet is something else entirely.

I suspect which scope I keep will come down to portability (the stowaway definitely wins there) and focal ratio, the Vixen just can’t do the wider FOV. That said I’m not sure I care about those two factors much.

But I’m in no hurry and as other have suggested I’ll give it more time to get to know he qualities of both. It was quite informative to see the differences first hand we often theoretically discuss.

I have been asked why I keep my smaller Taks - DL & TSA120 - now I have a TOA-130. 

[Dr Arnheim]

The Sky-90 was Takahashi's most recent 90mm.

Unfortunately the Sky-90 doesn't have such a stellar reputation as you would expect from a Takahashi ...

[Ben Diss]

Great. Now I'll never see a Vixen 90 in the classifieds.