INTRODUCTION AND THOUGHTS:
Sorry about the low contrast photos, it was getting dark out and I shot them with a tablet. For those who skoff at small fracs like these, let me tell you that if you don't know what to observe with them, then you should think twice. These tiny scopes are an absolute boat-load of fun for those who truly appreciate observing many multiples and showpiece doubles within their resolving limits. Ask Derek Wong what happened the first time I tried his Nikon 65ED. This is the 65 achromat version, but I use these scopes alot because they're so easy and quick to set up. Having a 2 year old and a family doesn't exactly allow you time to go off, doing all you want at any time. Also, these little scopes require little time to acclimate. Using Dawes Limit, the Nikon comes in with a theoretical resolving power of 1.78" while the baby Tak comes in at 1.93". I barrowed this very rare Nikon refractor from Derek, along with some very rare Nikon .965 eyepieces he has. For those not familiar with these Nikon refractors, keep reading. I really love achromats, especially when their lenses are figured so beautifully. This is a world class sample and you will probably not find a finer achromat, anywhere in the world. Often, when I compare or evaluate telescopes, I don't concern myself too much with what glass is being utilized and often prefer not to know but may investigate later. Just hand the sample over, and I'll determine whether or not I like it under ideal seeing and it helps me keep an open mind. This night of seeing revealed stars which appeared exactly as you see in #8 and #9 of this Pickering scale for a frame of referance.
http://www.damianpea...m/pickering.htm
You have to be careful when using this because it can be deceiving, depending on the brightness of the stars and the aperture being used. For example, Rigel, which is a very bright star, made the star image appear more like #7 on the Pickering scale. So, remember that when I use the Pickering Scale, it is primarily being used as a frame of referance as to how the stars "appear" to look on a particular given night through the eyepiece. I'd also like to briefly touch-up with others regarding the quality of optics and splitting double stars, because this too can deceive observers if they spend a great deal of time reading about optics and less time observing with them. There are a few ways one could interpret splitting double stars. One red flag I often see in the forums is when observers argue that a larger telescope is better for doubles because they have greater resolving power.This may often be true or not true in practice for several reasons, but don't forget too that observing doubles doesn't "always" demand, taxing out the resolving limits of your telescope. There are many multiple star systems you can enjoy observing without using a large telescope. In my opinion, a good 4" refractor can provide a lifetime of enjoyment for these applications. Another red flag I often see in the forums is that the quality of optics is not important for doubles because in theory, more energy is removed from the central airy disc and placed into the surrounding diffraction pattern, allowing the optics to resolve tighter doubles. So, imagine a really good optical system places roughly 85% of the light in the central airy disc while the remaining 15% goes into the diffraction rings etc.
Okay, so the prior comments sound all fine & dandy, BUT, remember too that the more junk that gets removed from the airy disc and thrown into the outer diffraction pattern also means you hurt the contrast around the central airy disc as well. That means by comparison, when you magnify the stars in the eyepiece, you will often see more extraneous junk, hanging around the airy disc, particularly when the seeing fluctuates in and out. Not only that, but you also Inherit a small loss of light for seeing slightly fainter stars. And finally, this goes back to what I mentioned before, and that is, the pleasure of enjoying doubles doesn't always mean taxing the limits of the telescope. I will be doing that specifically for this review, but I would much rather prefer a high quality optic that presents the stars as cleanly as possible than worry about splitting the tightest stars the telescope can handle and besides, you can just use a slightly larger aperture for that. Often in practice, having a smaller airy disc doesn't always mean you will split finer doubles anyway. In theory you might, but don't get so wrapped up in all this hype. Overlaps are a beautiful sight anyway and if it all really bothers you that much, then make yourself a central obstruction and suspend it in front of the objective. In practice though, it's not going to do all that much. In the end, it's more about appreciating what it is we are seeing and how beautiful it appears to the eye. So, like "Hal" put it..... "I honestly think you ought to sit down calmly, take a stress pill and think things over". People in the forums often get really pumped up about optics. I'm actually more curious to hear what others have to share about those theories in the field during practice.
THE EYEPIECES:
As you can see, I have a slurry of .965 Nikon's and 1.25" Tak LE's. I'm a big admirer of small, light weight, narrow field eyepieces which help focus your attention on what's being observed. The barrels are also smooth, so I can switch them out quickly and easily. This is the type of observing where wide field eyepieces are less important and are actually, sometimes distracting because they're often heavier and present other unrelated objects in the FOV I don't need to see.
THE DIAGONALS:
i used the stock Nikon prism which has easily proven to be incredible. The same goes for the Tak prism which I always use in the little Tak. In case others ask, I do like the Tak prism as a premium diagonal, even in the larger Taks as well. Where the compression ring resides, often falls into the safety bevels of eyepieces, forcing the observer to have to make additional rotations to secure remove eyepieces. My suggestion is either some sort of parafocalling ring, or you can use smooth barrel eyepieces or elevate the eyepiece. I have a rare parafocalling ring with a compression ring an drew thumb screw for this.
THE TARGETS:
The Trapezium
Rigel
Sigma Orionis
h3945 CMa
Epsilon CMa
Zeta Cancri
THE NIGHT JUST PRIOR TO THIS:
Since John Volk, Derek Wong and I were observing Orion's Trapezium with a 5" f12 Apomax and a Tak FS128 just the night prior, we were enduring a night of about 5 out of 10 with seeing. It was barely enough that we could only see the E star trickling in and out of focus and that's how bad the seeing was. Seeing is more important while viewing the E and F components and can definitely be seen in lesser apertures easily if the observer knows where they're looking. This night was certianly no night for a reliable comparison of these two wonderful scopes.
COMPARING THE TWO BABY FRACS:
I set both scopes out side by side at sunset for about an hour, prior to observation. I first fired both scopes at the Trapezium, switching between 99x and 127x in the baby Tak while switching between 111x and 156x in the Nikon. The first thing I noticed in the Tak is that all four stars were absolutely razor sharp! Perfect airy discs with an extremely faint, ill-defined diffraction ring around each star. It looked textbook perfect and the contrast was stunning! The appeared just like #8 on the Pickering scale, far surpassing the evening we had at Derek's the previous night. There was a good deal of space between all the stars and they were crystal clear and very still. I'm in extremely light polluted skies and even so, I tried to use averted vision to see the E star just for fun and even with averted imagination I could not make it out. In this particular instance, aperture would have helped. I then played with the two magnifications using the Nikon, and right away I could detect some subtle scintillating around each star. I immediately attributed this to tube currents, because at this level, the seeing was so rock stable that subtle aberrations, whatever they were, would be evident. After about another 20 minutes more had gone by, I was in awe at how incredible the Nikon was. Sure, it's a small scope and chromatic aberration is easier to suppress in this aperture, but good heavens this scope was standing right up there with the baby Tak, it was that good. At this point, I would say the Tak appeared to have about 10% or 15% more contrast in my visual estimation.
I then decided to fire both scopes at Rigel and of course as expected, there was trifling evidence of false color in the Nikon, but the secondary component was slightly more evident in the Nikon compared to the baby Tak. I figured this was because I was running out of magnification at 127x with the eyepieces I had while using the baby Tak. I decided to drop the Nikon down to 111x and then the issue made more sense. Sometimes you have to play with the magnifications and exit pupils a bit to see what's going on. Between these two close stars, I gave a slight nod to the baby Tak, but not by much. Also, there was just a hair amount of false color in the Tak as expected on such a bright star at these magnifications. Both of these telescopes were already working beyond their theroretical limits, so no issues worth bothering with there. This just comes to show what an incredible achromat this Nikon truly is. I then pointed both scopes at Sigma Orionis which is one of the most breathtaking multiples in the entire heavens. Four stars stood out absolutely textbook in both scopes and subtle color shadings in each scope were visible. I just got the slightest hint that the appearance of the star colors although subtle, seemed to have just a tad bit more pop in the baby Tak, probably most likely from the slightly better color correction, but there was absolutely nothing that objectionable about the Nikon, it was really that good.
Now, came h3945 CMa and what a beauty this winter Alberio is. Unfortunatley, this double was omitted from Bruce MacEvoy's 2nd edition of the Cambridge Double Star Atlas because it is not considered a true physical pair, but it is beautiful nevertheless. Bruce still did a splendid job on the 2nd edition with regard to other matters like organization of the lists by constellation instead of right ascension which I really like, but you just have to go into this atlas, knowing that it is mainly a binary double star atlas. Although this double is labeled as a double in this atlas, the designation is omitted, meaning no name is next to it. Both stars looked absolutely gorgeous in both scopes at 47x in the Tak and 43x in the Nikon. Another thing that's so cool about little scopes like these is how forgiving they are, even when stars are this low to the horizon. The colors stood out be briskly in both scopes. One thing I should also note is that since the Nikon was about twice the focal length of the baby Tak, the focus was a bit more forgiving while focusing the Nikon and I really liked that. The focuser knobs are large and buttery smooth and I wouldn't change a thing.
Next, it was time to fire both scopes at Epsilon CMa and this is where things got really tricky. The primary stands out at magnitude 1.5 with a 7.5 secondary. That's a delta of 6 magnitudes which equates to about 250x fainter for the secondary. At a separation of about 8" it is easily within the limits of each scope, but the brightness ratio is tricky and the secondary appears so darn faint. Under this heavy light pollution, it was no easy task with these little scopes and makes it a very difficult double, despite my comments about using these telescope for wider doubles that are fun and easy. I wanted to incorporate this difficult double, specifically for this review, just for kicks and giggles. At the maximum magnifications I had available in each scope, I could swear I was seeing an extremely faint secondary, trickling in and out, but after checking this this double again tonight, using the 8" Zambuto, there's just no way I could have seen it in either of these fracs. The secondary looked quite faint, even in the 8" just to clarify matters more clearly. The contrast in each frac was really impressive and not that much different though.
Lastly, it was time to point each scope at the legendary Zeta Cancri and what a site to behold it is at high magnification. It required me to spend about two minutes to star hop to it through the finderscopes and Cancer is no easy constellation to see from bright city lights for a frame of referance. The A star is mag 5.3 while the B star is mag 6.3 and finally the C star is mag 5.9. In this case, all the stars are pretty similar in magnitude, but the A and B stars are separated by just 1.1" and beyond the resolving power of either of these telescopes, but what was really cool to see was that the AB stars appeared elongated, while the AC star is about 7.2" apart. This object looked nearly equal in beauty and contrast in both of these fracs at the maximum magnifications I had available without the use of an additional barlow. Zeta in both telescopes took on a light yellowish appearance overall. Only on bright stars does the chromatic aberration in the Nikon become all that noticeable and even then, it still performs as flawlessly as a world class achromat should.
CONCLUSIONS:
Between these two fracs, the color contrast may appear a tad more noticeable in the baby Tak, but it isn't that much. I spend an equal amount of time behind the eyepiece using each scope and really love them both. It's such a shame that these world class achromats are no longer made and it seems like no one puts as much care into them like it use to be during the era of these legendary Nikon's. Truly beautiful indeed and the Nikon's buttery smooth motions and flawless mechanical mount design are simply unparalleled by anything I've ever seen before or present. It is so beautifully built, you just have to see it to believe it. Finally, Derek also has an absolutely incredible Nikon 65ED model and I have no doubt it is the finest 65mm class instrument I've ever tested in my life. It is staggeringly flawless. Oh how wonderful it would be to have Nikon back on the astronomy market. It makes modern mechanics look like toys.
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Edited by Daniel Mounsey, 01 February 2017 - 07:17 AM.
