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Astro-Physics 6” f/8 Telescope Review

Posted by Ed Moreno   02/13/2008 12:00AM

Astro-Physics 6” f/8 Telescope Review
I call this one “Buffy.”

Buffy is a very old Astro-Physics 6” f/8 APO triplet APO telescope, manufactured probably in the 1986 to 1987 time frame. So, let’s call her 20-something.

I bought Buffy used, and paid a rather princely sum of $3200. Now this seems like a LOT of money for a 20-something year old telescope, and some may wonder if it was worth the price? I mean lets face it, there are more and more choices (though very few in the 6” APO segment today) for APOs, and competition is indeed bringing some prices down. And yet the old AP could be said to be appreciating! How can that be? I mean I think these scopes only sold for about $1500 when new. So, the question still begs to be answered… Is it WORTH it?

My first 6” refractor experiences were with a couple of Celestron CR150s. The first (non-adjustable cell version) had superb optics. Being a reflector guy (SCT mostly), the color really bothered me when viewing bright solar system objects, but the low power cluster viewing was beautiful. But the color bothered me, so I sold it. About a year later though, I missed the lovely sharp star fields, so bought another one. The optics were not quite as good as the first, but still, the view was beautiful. But this time, the mount got to me. It was simply hard to mount these big nose heavy scopes and get them high enough to view at zenith. So off it went.

Over the next few years, I found myself once again missing the wonderful crisp big refractor views. I was on a wait list for a large APO for some very very long length of time, and finally, I decided that I just wasn’t willing to wait anymore, so I purchased a Meade 152ED. The Meade proved to be a really EXCELLENT scope, and I used it for a year or so before getting the urge for a C14. Life is like that, you know? Also, the Meade was under-mounted on a Go-to Atlas (EQ6), and since I was going to have to buy a new mount for the C14, I sold the Meade and the EQ6 to finance the CGE 1400.

But once AGAIN, I found myself missing the beautifully crisp refractor views. I have to tell you, they really do get under your skin. I ADORE my C14. I have logged hundreds of targets in the last 18 months or so with the C14. Hundreds and HUNDREDS of targets. I ADORE my C14. I had my trusty Vixen 140 for wide field viewing… The 140 has a superbly flat field and was very complimentary to the C14, but at the same time, it didn’t present nearly as bright or sharp of a viewing experience as the Meade 152ED had. I liked it though because it DID go wide, and it COULD be mounted on a CG5. Taking out two big mounts wasn’t something I though I would do. In the end though, the memory of seeing the double cluster in the Meade 152ED, or M35, or any one of the really big open clusters (beautiful in the Vixen, but STUNNING in the Meade 152ED) really haunted me.

Astromart to the rescue. A “Vintage” Astro-Physics 6” f/8 was on sale for $3500. The price seemed a bit steep to me, but some email and phone calls, and a negotiated price of $3200, with me personally going to the seller to pick up made it a bit more appealing.

I decided that the AP 6” would at the very least have optics that were in all practical aspects, perfect. This in itself was worth a great deal to me. I have learned over the years that optical perfection DOES show at the eyepiece. In every telescope where I have owned two of the same telescope, I could always tell that there were variations in quality. This is ESPECIALLY true with SCT. But again, I owned two Vixen 140s, and two Celestron CR150s, and in both cases, one of the scopes performed a bit better than the other. Not much, but ENOUGH FOR ME TO SEE! So I knew that the 6”had to have optics that were as perfect as possible to make me happy, and I was confident that even these old Astro-Physics scopes would be uniformly excellent in terms of optical quality.

The scope was a bit faster, shorter, and lighter than the Meade 152ED, but I learned my lesson and knew that the Atlas would not be enough mount, but I COULD put it on the CGE mount.

The AP was in rough shape when I picked it up. The lens coatings were showing some very slight scratches. A lot of people would have totally freaked out, but I know that these almost invisible scratches do very little damage to the image.

The tube was in rough shape cosmetically. I had really severe ring rash. I spent hours with automotive polishing compound rubbing the finish out. I suspect that sometime in its life, it has been repainted. Anyway, “Buffy” got her name from the amount of effort that I put into making the finish look smooth and glossy again.

The 2.7 inch focuser was a Byers replacement. Apparently, early Astro-Physics focusers were not all that great. The Byers is massive and a good match for the OTA. It easily carries the 31mm Nagler.

I have only had five or six nights of observing with Buffy, and here is my report.

This telescope is incredible. It is EASILY the best quality optics I have ever looked through. The quality of the view is IMMEDIATELY apparent. Swing it at any point in the sky, and WHATEVER it lands on will look SUPERB.

My first targets were bright stars. This was to do some star testing. Inside and outside of focus showed beautiful Fresnel patterns. You could see color in the out-of focus patterns, but the overall evenness of the light distribution looked literally perfect. The edge of the bright outer ring showed a level of smoothness that I have not observed before in any telescope I have ever tested.

One of my first in focus targets was Castor. This is a trivial split for the 6” AP, but an important frirst affirmation for me. I can spit castor easily in the C14, even at very low power. But it is never all that pretty because seeing usually fuzzes up the star patterns.

In the 6” AP, even with less than excellent seeing, Castor was PERFECTLY split. The optical correction is SO perfect, that I could not even SEE a first diffraction ring on either component. Now a really perfect refractor will put MOST of the energy at the center of the Airy disk (there is some debate on the web as to the nomenclature, but I like calling it an Airy disk). The Airy disk is NOT uniformly illuminated. In an obstructed telescope it is a dulled spike. But a perfect refractor puts MOST of the energy at the center or POINT of this spike. In the obstructed telescope, enough of this energy is shifted to the first diffraction ring that even a perfect reflector will show s faint first ring. But a PERFECT refractor should have a first diffraction ring that is almost imperceptible except on the very brightest stars. Even here though, it will be hard to see because of the contrast ratio between the brightness of the Airy disk and the brightness of the first ring. Castor in the 6” AP was just two bright little spikes with no diffraction ring visible. PERFECT. I have NEVER seen it shown so utterly perfectly.

I went to several more challenging doubles, and in every case, I was rewarded with the best splits I have ever had.

On to Sirius… Oops.. Some color. The seller told me that this would be the case. I could see some violet fringing, and some deep purple in the field around Sirius.

But… I could also see the PUP(Sirius B)! My first time! The color didn’t bother me really, but it was a bit more than I had been expecting… I initially thought that the color correction wasn’t that much better than the Meade 152ED. This is what I discovered though… The AP needs to cool. A few nights later, I went BACK to Sirius, but this time, I have placed the OTA out two hours before to acclimate. On THIS occasion, the color correction was almost perfect. So there you go. A 20-something 6” AP oil spaced triplet has to cool down to deliver peak performance.

Anyway, over the years, I have become a much bigger double star observer. The first 6” achromats did that to me. I learned that on nights with a full moon, or nights with haze, I could still do a lot of observing if I wanted, but the trick was to pick targets that were good targets for the conditions. And double stars are EXCELLENT targets for those bright nights out… The AP was clearly presenting the best double-star observing I have ever seen.

On subsequent nights, I started hunting clusters. Ok.. A 6” telescope, even a PERFECT 6” telescope, is no match for a C14. There were lots of clusters that I have bagged in the C14 that were barely visible as faint glows in the 6”. But when I looked at most of the bigger clusters, the view in the AP thrilled me. I almost fell out of my chair when I stuffed in the 31mm Nagler and slewed to the Double Cluster. Oh, I have framed it beautifully in the Vixen 140, but the stars were somewhat dim for a 5.5” aperture (extra lenses and less than perfect optics). When the Double Cluster slid into the field of the AP, the view was freaking GLORIOUS. I have NEVER seen it as strikingly beautiful as this.

In the 6” AP, the ENTIRE FIELD was FLOODED with stars. In my 5” SCT, the effect of the field curvature and the smooth falloff of field illumination means that the view is brighter in the center, and the nucleus of each cluster is prominent, but as you move your view to the edge of the field (with both clusters framed in the center of the field, the stars seem to thin out pretty dramatically. In the 140 refractor, you see more stars at the edges of the field, but the light transmission and less than perfect optics conspire to once again suppress the field of faint stars that is lurking all around the double cluster. You have to remember that the Double Cluster is IN the Milky Way. The field SHOULD be COVERED with very faint background stars. And in the 6” AP, it WAS! Even from my Mag 3.5 VLM back yard, the area around the clusters was literally CARPETED from field stop to field stop with infinitesimally tiny an faint pinpricks of starlight. And in the 31mm Nagler, they were pinpoint RIGHT TO THE FIELD STOP of the eyepiece. I couldn’t BELIEVE how beautiful the view was. Right here… Right at this very moment, the question of whether the old girl was worth the money was unequivocally answered to my complete and utter satisfaction. WOW!

M37, M37, M44, and all of the other big clusters all looked Sublime.

M42. Easily picked E and F from the Trap. This is the smallest scope that I have ever seen them with from my back yard. The Meade 152ED got E all the time, but struggled to show F. The optics of that scope were surprisingly good, but in retrospect, once again, the difference in Very good optics and perfect optics does have a way of showing at the eyepiece.

I invited the assistant astronomer out for a look. She is somewhat Jaded I think. She has seen Saturn in the C14 on a night of perfect seeing, and it is her yardstick for all things astronomical. Now I have to tell you, Saturn in the C14 is inspiring. The crepe ring is so beautiful and silver, and the golden hue of the orb is a treasure visually. Most pictures over-saturate the color. Anyway, when the assistant looks at anything, she is usually comparing it to that perfect seeing night view in the C14. She has SEEN M42 in the C14 on several occasions. As she sat at the eyepiece (17mm Nagler) for her view of the Orion Nebula, I was unsure as to how she would perceive it. I mean it is not as bright as in the C14. And E and F are prominent in the C14. The mottling of the cloud that Theta is embedded in is quite pronounced in the C14. Still, I was quite impressed with the view in the 6” AP…

The assistant took some time to find here eye placement in the 17mm T4. Then, Silence. “Can you see anything?” More silence… Finally…”How come you never showed this to me before. It’s BEAUTIFUL!” Well she has seen it a half dozen times, but once again, I think that there was something about the quality of the view and the sharpness of the stars that really caught her attention. It was cold, and she didn’t stay, but before heading in, she said that it was one of the most beautiful things I have ever shown her….

Mars was poor though the 6” This apparition has not been good it seems. The C14 has struggled with seeing and it seems like I have not hit a night were a more detailed view presented itself. My only attempts to view it with the 6” AP have been only so-so. In fact, the views have been on par with the C14, but that I think is a function of a winter appearance and the associated bad seeing.

The moon was interesting in the AP. The AP presented lunar detail that I felt was maybe on par with the C11 I used to own. Now my 152ED was close on many nights, but patience at the eyepiece in the C11 would usually show more detail. Remember, I did NOT do a side by side comparison between the AP and the C11, but I have to tell you, I am not sure that the C11 would have surpassed it. The amount of detail in the 6” seemed quite similar to what I remember seeing in the 11”. I was really surprised with how much I was seeing. Once again, the C14 showed a bit more on the same night if I was patient (I swapped OTAs), but the amount of detail I was seeing in the 6” was surprising to me. As for color on the moon, at the limb, I could see some very faint yellow tinge just inside the limb, but just outside as black as black.

Ok…Here is the REAL problem with the AP… It has spoiled me from Blade, my Vixen 140. I used to set up the 140 a lot of times with the C14, and now that I have put the 6” AP out there, I KNOW that I will not be happy using the Vixen 140 side by side with it. The PAIN is that the 6” F/8 is going to take ANOTHER FREAKING BIG MOUNT! I just can’t IMAGINE myself wanting to swap OTAs on to the CGE, and I can’t IMAGINE being out on some nights and not wanting to use BOTH telescopes at the same time! So, Bye-Bye Vixen 140 and mount, and make way for a second big monster mount. The assistant astronomer is not going to be pleased I don’t think, but I KNOW that it will be UNBEARABLE for me to be out under the Milky Way and not be able to use both the 6” AP and the C14 at the same time. My life is SOOO hard….

So, the question.. Is it worth it? The answer? After using it, if something were to HAPPEN to it, I would have no reservations about paying MORE for a replacement. MUCH more. It is THAT good.

Summary? Best optics I have ever owned. Not likely to own anything better in my lifetime. A big refractor with the big refractor pain of usage (big mount), but an experience you have to have yourself to understand how good it can be. Quality is timeless.