118 replies to this topic

[Scott in NC]

I didn't really set out to buy one of these, but the buyer of my FS-152 offered me this in trade as partial payment, and of course I wasn't about to say no!  I had never gotten the opportunity to use one of these fine astrographs before, as I don't do AP, and had always considered a scope like this to be overkill for visual use.  

 

For those of you who are unfamiliar with the Tak "Baby-Q," the FSQ (which stands for "Flatfield Super Quadruplet") -85 is an 85mm f/5.3 Petzval refractor (focal length 450 mm) containing two doublet optical groups, each containing a single FPL-53 ED element.  It has a very nice, beefy, yet very smooth and precise 80mm (3.15") focuser.  And at 4 kg (8.8 lbs.), it's much heavier than the average 80mm-class scope.  It looks and feels like a serious scientific instrument.

 

I haven't yet had the opportunity to view through it, but took the opportunity to DPAC test it today.  And it passed with flying colors!  Although I really shouldn't use the word "colors," as it had no chromatic aberration to speak of.

 

Here's the scope set up for testing.

 

 

[Scott in NC]

Before posting the DPAC images, I'll have to warn you.  Even if you're not already bored with the subject of DPAC testing, these images will absolutely put you to sleep. There's really nothing to see here. Now I know why these scopes sell for around $4000. And mine didn't even come with the extra flattener that APers use to take "over the top" flat images, as if the images from this Petzval quadruplet weren't already perfect enough. But I know that dedicated imagers have different standards than us visual users, especially since the lenses in our eyes can easily accommodate for minute levels of field curvature that won't play nicely with a camera sensor.

 

As usual, I'll start off with green light, as that's where our eyes are most sensitive.

 

(Edit: images redone in post #59 https://www.cloudyni...85/?p=12744869)

 

Green inside focus:

 

 

Outside focus:

 

 

Red inside focus:

 

 

Outside focus:

 

 

Blue inside focus:

 

 

Outside focus:

 

 

 

Edited by Scott in NC, 14 June 2023 - 07:45 PM.

[Scott in NC]

I really don't see any significant spherical aberration in any of the three colors above.  Maybe a faint hint of overcorrection in blue, but I had to blow the images up pretty large in order to try to bring out any SA that might have been there.  If the minute amount of SA seen above in blue had been noticed in green (where our eyes are most sensitive), this would still be a phenomenally well-corrected scope.  The other thing of note is that all three colors come to focus at almost the exact same points.  This is a true apochromat, well corrected for both SA and CA.

[Scott in NC]

For completeness sake, here are the white light images.  These are the best images for showing off any chromatic aberration that exists, and I really don't see much at all other than a faint hint of blue at the edges of the bands.  
 

(Edit: images redone in post #59 https://www.cloudyni...85/?p=12744869)

 

 

 

Edited by Scott in NC, 14 June 2023 - 07:46 PM.

[Scott in NC]

In a nutshell, this appears to be a fantastic scope.  Obviously it's wasted on a non-imager like me, but I still can't wait to see how it will do for visual use under the skies.  Alas, I won't get to find out tonight.  It's been sunny all day, and now at 4:30 p.m., I just looked out the window to see that it's totally overcast.  Oh well--that can await another day.  At least DPAC'ing gives me something fun to do with my scopes when I can't view through them!

[Scott in NC]

In case anyone is wondering why the image circles above are a little oblong and aren't perfectly circular, that's not related in any way to the optics of the scope.  I'm still learning to take these Ronchi images using a new camera tripod (rather than my previous method of hand-holding the camera), and I didn't have the camera perfectly lined up with the scope.  I'll get better with practice!

[CHASLX200]

Jack it up to 350x on the moon and see how it looks.

[Scott in NC]

Jack it up to 350x on the moon and see how it looks.

At an exit pupil of 0.24mm, I guarantee I won’t like the view, as I have floaters much larger than that.  Alas, the scope is capable of much more than my eyes can appreciate.

[CHASLX200]

I never really cared for triplets but i bet it is good as a low power sweeper. Bet it can take high powers on Venus and the moon fine. About 250x is the max for Jupiter on a 85mm scope as you start getting a dim image, but Venus can keep on going.  I am lucky floaters don't bother me. Always wanted to try One of them TAK'S but the collimation probs scare me.

Edited by CHASLX200, 03 June 2023 - 04:42 PM.

[Kitfox]

Scott, as we discussed earlier, all your other 3”-class scopes are going into long-term storage…at least until you decide to trade this wonderful TAK with me for the “spare” Vixen ED130s 

 

I have certainly found that the big sister 106 is a wonderful “sweeper”, as Chas put it. And it will take a little power, too. 

Edited by Kitfox, 03 June 2023 - 04:58 PM.

[Erik Bakker]

What a great scope the FSQ-85 is.

 

And no, it is not wasted on a non-imager like you (or me).

 

It is a superlative instrument for allround visual use!

[Reid W]

A colleague here has the 106.  I limited my time to three minutes.  Any longer, it would have been in my lineup.

[Kitfox]

That is a corollary to the rule “Never look thru an eyepiece you can’t afford”…

 

 

A colleague here has the 106.  I limited my time to three minutes.  Any longer, it would have been in my lineup.

[T1R2]

Near perfection.

[Scott in NC]

I have to admit that I’m a bit frustrated that I couldn’t get the camera lined up better to make the Ronchi images look nicer and more circular. To the best of my knowledge, the focuser isn’t off kilter, and I’m pretty sure that I saw a perfectly round image circle when looking though the Ronchi eyepiece.  I’m betting that the steep light cone of an f/5.3 scope makes it harder to get the camera lined up squarely with the focuser.  But if anyone has any other ideas, I’m all ears.

[T1R2]

I noticed that the camera wasn't square in the top pic on the bottom, I would just eye it from the back where you took the pic from to make sure it was pointed in line with the drawtube, Then from the side to make sure its angle up/down was parallel. that should get you close enough.

[Scott in NC]

I noticed that the camera wasn't square in the top pic on the bottom, I would just eye it from the back where you took the pic from to make sure it was pointed in line with the drawtube, Then from the side to make sure its angle up/down was parallel. that should get you close enough.

I’m pretty sure that I moved the camera before taking any images.  That was just a quick photo of the setup. I suspect that if I did it again I could do a better job lining everything up.  Not that it would affect the results any, but I still like having my images look as nice as possible, as I don’t want people to confuse my poor photographic technique for flaws with a scope’s optics.

[Scott in NC]

The OCD in me is really getting annoyed by my oval-shaped Ronchigrams.  I’ve going to have to redo them tomorrow.

[Spikey131]

Did the scope offer any deeper insights into pharmacotherapy?

[Scott in NC]

Did the scope offer any deeper insights into pharmacotherapy?

LOL.  One of my wife’s old textbooks from eons ago, I believe.  It was the largest, flat-surfaced object with a dark background that I could find while scouring the basement for a suitable backdrop for my cobbled-together DPAC rig.

[Kitfox]

Scott, try turning the camera into portrait orientation.  The software in many cameras sometimes does funny things when processing the raw image into .jpg, especially when patterns confuse it inside the field of view. If the oval turns with the camera, the OCD in you may want to start working with RAW.    The rest of us were suitably bored with the pretty straight lines and pure colors 

[dawnpatrol]

What a great scope the FSQ-85 is.

 

And no, it is not wasted on a non-imager like you (or me).

 

It is a superlative instrument for allround visual use!

When I bought my FSQ-85, I bought it to be an imaging scope. Then I stuck an eyepiece on it. It's a multi-talented performer. For imaging, one of its super powers is that it doesn't require a huge mount. As one who doesn't have an observatory, I am happy to take a smaller aperture instead of needing a larger, heavier mount. Optically, it's...well...it's just like Scott's DPAC indicates. Pretty much perfect. For wide fields and high magnification, it's outstanding. Of course there's no substitute for aperture, and it's not inexpensive, but everything in life is a tradeoff.  

[Scott in NC]

Scott, try turning the camera into portrait orientation.  The software in many cameras sometimes does funny things when processing the raw image into .jpg, especially when patterns confuse it inside the field of view. If the oval turns with the camera, the OCD in you may want to start working with RAW.    The rest of us were suitably bored with the pretty straight lines and pure colors 

Thanks for the advice.  See what happens when the Ronchigrams look like perfection, and there’s not really anything to discuss about the optics of the scope?  I have to start finding other things to fret over. But I’ll get this little glitch worked out.  

[Scott in NC]

When I bought my FSQ-85, I bought it to be an imaging scope. Then I stuck an eyepiece on it. It's a multi-talented performer. For imaging, one of its super powers is that it doesn't require a huge mount. As one who doesn't have an observatory, I am happy to take a smaller aperture instead of needing a larger, heavier mount. Optically, it's...well...it's just like Scott's DPAC indicates. Pretty much perfect. For wide fields and high magnification, it's outstanding. Of course there's no substitute for aperture, and it's not inexpensive, but everything in life is a tradeoff.  

It’s talk like that that could end up making me want to keep the scope, against my better judgment (from a financial perspective, that is).  But I guess it couldn’t hurt to keep it for a while, at least long enough to fully test it out under the stars.  And as the skies change season by season, it could take a whole year for me to fully explore what this scope has to offer.
 

On a more serious note though, how long have you had your FSQ-85, and do you still own it?

[dawnpatrol]

It’s talk like that that could end up making me want to keep the scope, against my better judgment (from a financial perspective, that is).  But I guess it couldn’t hurt to keep it for a while, at least long enough to fully test it out under the stars.  And as the skies change season by season, it could take a whole year for me to fully explore what this scope has to offer.
 

On a more serious note though, how long have you had your FSQ-85, and do you still own it?

I've had it for about two years and I still own it with no plans to sell. It makes a tidy package. 

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