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D&G 8" F/12 Refractor
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D&G 8" F/12 REFRACTOR
The pursuit of amateur astronomy is a largely personal adventure and no area of our pastime is more personal than the choice one's telescope(s). Since receiving my first telescope as a kid- a 50mm refractor- I have been a visual observer, primarily planetary and lunar. Over the years I have spent a fair amount of time looking for the best planetary scope and while I have had stunning views of the planets through various reflectors, I keep coming back to refractors. While this article centers on my current large refractor, a D&G Optical 8 F/12, it also includes information on other telescopes I have owned. I guess I should mention that I have no affiliation with D&G Optical other than enjoying the performance of their scopes and their top level customer service.
DECISION TO GO WITH A LARGE REFRACTOR
Aperture fever strikes us all. Mine came after a night out with my trusty D&G 6 F/15 and a Coast Instruments Treckerscope 8 F/8 Newtonian. After a few hours of planetary viewing, Jupiter and Saturn in particular, I went to sleep thinking If only I could combine the contrast and resolution of the refractor with the light grasp of the 8 reflector. Within a few days I had an order placed with D&G for a new 8 F/12 OTA, with coatings on all surfaces, Astro Physics focuser (now standard on D&G scopes) and Parallax rings.
D&G is an excellent outfit and dealing with Barry Greiner is a pleasure. Over the years I have asked D&G to evaluate and repair/refurbish several refractors I have owned. In each case the work performed was of excellent quality, the costs reasonable and the turn around time rapid. When I was ready to place the order for the 8 F/12, Barry answered all of my questions about the scope and various options. He responded quickly to e-mails and phone messages and his estimate for completion of the project was accurate. During the fabrication of the lens he kept me updated as it progressed through polishing and figuring. And since receiving the scope, I can honestly say Barry's customer support is superb.
Since the wait was going to be roughly a year, I settled back to find an appropriate mount. One day a Parallax HD-150 popped up on AstroMart and I bought it. When it arrived I was stunned to find out how large the darn thing was. But was it tall enough? My pal and mentor Al George ( 15 F/12 D&G ) suggested it might not be, so I called Joe Nastasi at Parallax Instruments to see what he suggested. Joe also enjoys achromats and had great recommendations concerning appropriate pier height and big achromats in general. In the end I placed an order for a 60 tall portable pier. Joe had it out to me in short order and it was perfect for my needs. After a couple of years experience with the HD-150 mount, I can highly recommend it for large scopes of all types. Not only is it a large and beautifully designed mount, Joe's product support is second to none. The only change I would make at this point would be to have Joe fabricate a permanent pier of the same height.
I kept using the 6 F/15 D&G until the year passed and my new 8 was delivered. The scope arrived in several different packages. The tube assembly was carefully protected in bubble wrap inside a length of Sonotube. The Sonotube did its job as the only apparent shipping damage was a minor crease in the tube. The objective was packed very securely inside a large box and required only three screws to attach it to the tube assembly. The Astro-Physics focuser simply threaded into place. The tube sports a nice paint job, not Takahashi but nice. Three wooden baffles grace the very dark interior of the tube. The dew cap slips into place held by friction. Physically the scope is impressive. The combination of white tube, black focuser and lens cell is strikingly classic in appearance.
Frankly, when I saw the OTA assembled, I realized I'd finally bitten off more than I could chew- this thing is huge D&G's website ( http://www.dgoptical.com/) listed the stats as: overall length- 102 ; OD of tube- 9.00 and weight- 37 lbs. Add the Takahashi 11x70 finder (no wimpy 8x50 on this beast ) and a 2 AP Maxbright diagonal and you are just over 40 pounds. Easy to lift but rather awkward for one person, especially when the saddle is over 7 1/2 feet off the deck. This is definitely a two-person setup. If I am going to observe for several days in a row, I leave the mount set up and simply remove the OTA each morning. The mount rests under a Desert Storm cover until needed. Otherwise, I disassemble the mount too.
Collimation was a bit off after the scope was assembled. I pulled out my Takahashi collimation scope (that company thinks of everything) and with my girlfriend's help had collimation adjusted in a matter of minutes. There are several articles describing refractor collimation. D&G refractors use the nearly universal push-pull arrangement with three sets of screws placed at 120 degrees around the face of the lens cell. All screws are hex-head making for easy and safe adjustments. Using either a Cheshire eyepiece or the Tak collimation telescope, one can readily see two rings reflected from the lens elements (note: the lens cover must be in place over the objective). Collimation is a simple matter of centering the reflections by adjusting the appropriate push-pull screws. The process is done one screw at a time and is a snap with two people - one to loosen the lock screw and carefully turn the adjustment screw while the other looks through the collimation tool. Once the reflections are centered relative to one another, a careful tightening of the lock screw is all that is needed. Since I do not leave the scope set up, I check collimation each time I am out. If it needs a touch up, it can be done very quickly.
What follows are notes from my observing log in which I compared the D&G to other scopes, mostly APO refractors. The notes were written to help me decide which scope actually performed best for my own use. As such, I was not trying to convince anyone of anything. Rather, I simply wanted to see where best to put my own money for my own viewing pleasure. I have included a comparison or two in which scopes compared to the D&G were compared to one another to help extrapolate overall performance of the D&G against the other scopes tested.
August 27th 2003
Set up the D&G 8 F/12 and the 10 PortaBall (PB) for a casual evening showing Mars to friends. Both scopes were allowed to cool down for nearly an hour and a half before observing. Right from the gate I preferred the image in the big refractor. Not to say there were not problems with color, at F/12 it is something to contend with, but the image detail was a notch above the normally top-seeded PB. The image was also more solid in the D&G, probably due to tube currents in the PB. The unfiltered image of Mars provided a more detailed image giving it the edge. Once I added a #21 orange filter, the advantage was even more pronounced.
Part of the edge is no doubt due to the greater depth of focus enjoyed by the long focus refractor. Focus is a far more critical issue in the F/5 reflector, it was harder to hit sharp focus and stay there while the D&G held firm images throughout. And what images Syrtis major and minor were stunning and the nearly dot-like polar cap sharply presented. Plus the longer focal length allows the use of more relaxed eyepieces: I was running a 14mm Pentax XL in the D&G and an 8mm Clave in the PB. Unfortunately, conditions were not settled enough to use really high power and image quality decreased noticeably above 225 power in both scopes.
The Moon was also present and gave the opportunity to hit powers that were silly under the conditions: 5mm TMB mono in the D&G for roughly 480x. Surprisingly nice image The PB did not show any more detail but the lack of color gave it the more aesthetically satisfying image. Power was limited in the PB to 315x with the 4mm TMB.
Around 4:00 AM I had a chance to view Saturn through both scope. When I was a boy, probably 10 or so, I attended a series of lectures on astronomy at Griffith Park Observatory. After one of the lectures I had a chance to view Saturn through the Zeiss 12 refractor and it was the most impressive view of the planet I have ever had. The memory of that view has stayed with me and after owning many excellent scopes it still remained unmatched. Until early this morning that is: I had the 8 set up with the new TMB Supermonocentrics in 10mm and 8mm focal lengths and that long cherished memory lived again. The detail was stunning even under less than perfect conditions. The TMBs and a 12mm Pentax SMC Ortho really let the lens loose and it just nailed Saturn. I think I even saw Ecknes though the somewhat unstable atmosphere made it difficult to be sure. I can not imagine owning a larger refractor, this one is beast enough, but boy am I grateful to Barry for the quality and performance of this scope The PB was turning in it's usual excellent image of Saturn as well but I kept going back to the D&G. The lack of diffraction spikes was a decided plus and Saturn is not a problem as far as spurious color.
4 October 2003
Had the D&G set up alongside the Tak FC 100 for informal Mars viewing. Conditions were marginal. Lots of fleeting high clouds and heat waves. Both scopes were allowed sufficient cool-down time and then turned toward Mars. There were five folks relatively new to observing and their impression of the scopes and eyepieces was interesting.
MARS- the favorite image was that of the D&G. Initially I had a #21 orange
filter on the 12.5mm UO ortho in the D&G. Nice image given the conditions.
I could easily pick out the greatly diminished polar cap and several surface
features. One of the folks asked how much power I was using and when I said
200x he asked what the same view would be like in the Takahashi at 200x.
We dropped a 4mm TMB Mono into the Tak and upon focusing he immediately said I prefer the image in the bigger scope. The detail is easier to see. I
explained about the filter and then removed it to show the effect of the achromat's
color. Interestingly, as Mars has decreased in magnitude since late August,
the secondary spectrum was very muted and no bother at all. Again, the preferred
image was in the D&G. Nothing Earth shattering, aperture wins again given
excellent optics in each scope.
I found the image in the Tak to be quite pleasing. It showed a surprising amount of detail and was sharp. Given essentially the same image scale, it was apparent that the detail was simply easier to pick out in the larger scope, with or without a filter. The D&G is fast becoming my favorite planetary scope.
20 October 2003
Set up the Meade 178 ED and 8 D&G for a round of planetary viewing. Unfortunately, the air was extremely unsteady due to unseasonably hot weather today and twinkling would be a mild description of what was occurring. I tried Mars but neither the scopes nor the atmosphere had settled down enough to view. Finally gave up and left the scopes to cool overnight for an early morning bout with Saturn.
At 4:00 AM I gave it another look. The sky was still unsteady but much better than before so I pointed both scopes at the Trapezium. I had placed an MV-1 filter on the 2 diagonal in the D&G earlier which seems to work on atmospheric turbulence as well as color: the six stars stood out clearly in the D&G while the Meade was struggling with them. The 178 ED easily nailed all six a few nights ago so it was clearly atmospheric instability. In moments of relative calm I could see all six in the ED but the D&G was much better.
Saturn was a push: the 178ED was giving a sharp, contrasty image with a 10mm TMB mono. No false color evident, just a sharp, clear image. In calmer moments I thought I was picking out Encke's but there was too much agitation to be sure. The only negative with the 178 is the focuser. It has a “hump” in its movement and causes the image to jump when I hit it. The D&G was sharp but so bright that I noticed false color for the first time on Saturn. I am sure the atmosphere had an effect and wonder if it was the culprit. ( I should note that I had removed the MV-1 prior to turning to Saturn). Adding my Denkmeier binoviewer with a pair of 18mm UO orthos was a definite cure : gone was any false color and the image was bright and clearly defined. One could get use to this I tried running up to 12mm UOs but the conditions would not support the increase. Settling back with the 18mm's was a wonderful experience. The gibbous Moon was just rising so I swung both scopes to it. The air was decidedly worse near the horizon so I kept the power reasonable: 10mm TMB (160x) in the 178ED and a 20mm UO Erfle (120x) in the D&G. Nice images but too much turbulence for fine comparing fine detail. The binoviewer with 18mm UOs was a treat in the big scope though Like being in a space ship cruising over the surface.
I like the 178 ED as it's length is nearly perfect for the G-11 and it is a nice bino scope. The color in the D&G is noticeable but not offensive. There is something classic about having it to use especially as I am reading Mars and It's Canals by Lowell. Like a time machine of sorts. I can't wait to try the 12.5 Portaball with the new curved diagonal holder against the D&G.
13 November 2005
Out with the D&G 8 F/12 and 12.5 Portaball. I have been curious for a while now about how these two stack up against one another, especially as the PB has the curved secondary support. Unfortunately, the seeing has been unstable for the last while. Plus the dew has been terrible.
I spent most of the time on Gassendi and the area around Mare Humorum. The PB was running at 160x with a Pentax 10mm XW and the D&G about 170x with my favorite Meade 14mm UWA. The level of detail was very close- the D&G was giving a tighter image at first and I was able to see finer detail inside Gassendi. I could see everything in the PB as well but focus was far more critical. I am convinced that the reason is the refractor’s longer focal length and greater depth-of-focus. The PB image of a white Moon against a nearly black background was very pleasing. The D&G has a slight bluish tint to the shadows around the edges of the crater and rilles. Razor sharp, but a bit of color. Both scopes were showing great detail inside Doppelmayer as well, very sharp in the D&G, slightly more fleeting in the PB. About 2/3rds the distance between Gassendi and Schiller a small peak near Lacus Timoris caught my attention (can not find the name in Rukl’s). It was quite detailed through the D&G exhibiting what looked like a small craterlet along one of its ridges. I could see the craterlet in both scopes, but easier in the refractor.
D&G is having problems with dewing, hard to keep it clear. When it is, sharpness and the level of detail is essentially the same though I prefer the image in the PB esthetically. Dewing hit the PB I have owned PBs for five years and never had to turn on the anti-dew heater until tonight. PB- 5mm XW at roughly 320x, D&G a 9mm Nagler at 266x. Finally gave in to let the dew heater do its job.
Seeing is more stable as a light fog has rolled in. Both scopes are soaked and the D&G is streaming water, so much that my leg was soaked from it dripping onto me. Excellent image in both scopes Using a 9mm Pentax SMC ortho in the PB ( 177x) and the 14mm Meade UWA in the D&G (172x) I would describe both images as “razor sharp.” Both scopes are showing essentially the same level of detail in the rings and on the planet itself. In fact, it seems to me that on all three objects, the Moon, Mars and Saturn, the D&G and PB are very evenly matched. The differences: I can see the three inner moons easier in the D&G which I assume is due to the lack of central obstruction and spider-induced diffraction. But there is a very slight bit of color too. In moments of best seeing I do not notice it, but add slight atmospheric instability and it is just barely present. I don’t know if I would notice it if the PB image was not color free.
Just for kicks, I started running the power up to see how the image held. I plopped a 3mm Radian into the D&G (800x). I often read folks state when using very high magnification, “no image break-down” and still am not sure what they mean. This image was soft and had lost a lot in contrast. But it was nicer than I would have guessed. Ring structure, Cassinis division and the Crepe were present as was some detail on the globe. Under excellent seeing this scope would be a high-power killer. Dropping back to a 4mm TMB monocentric (600x) the image looked slightly better. Frankly, I was not happy with the contrast and detail until I hit 240x with a 10mm TMB mono. In fact, 175x to 250x tends to be my favorite planetary range regardless of scope.
The image in the PB at 300x with a 4mm TMB mono was excellent but tracking
turned into a bear Much better with a 7mm Pentax XW (230x) and its much
Conclusion- I think these scopes are pretty much equal in performance though each has minor differences. As far as ease of use- no contest, the PB wins hands down. But from comparing them side-by-side, from my view the unobstructed 8 system and the 12.5 with its 17% obstruction are equals.
A FEW THOUGHTS:
FALSE COLOR- no way around it, large achromats do throw up false color. Based
upon sharing the D&G with many people over the last few years, it is clear
to me that some folks are more bothered by it than others. If you are one of
those folks, maybe a large Newtonian or an APO would be a better fit. There
are ways to minimize it:
Lots of folks talk about the use of filters to minimize the effects of false color. I have had good results minimizing the “haze” surrounding bright objects when using the Sirius MV-1, Baader Fringe Killer and for Mars particularly, the Televue Mars Type “B”. A while back while talking about scopes with “refractor man” Stan Martin ( 11 F/15 D&G), I learned that he and other D&G users prefer an 85B color filter (light salmon) . To date my best views of Mars have been through a 48mm Hoya 85B I attach to the diagonal.
Another option is the Chromacor which is actually a lens system designed to intercept the light cone and correct for chromatic abberation. Having read many posts from satisfied users, I recently picked one up though I have yet to try it. Doug Peterson (8 F/12 D&G) has given me a lot of help and advice with respect to using a Chromacor, including this note:
I had the Chromacor before I obtained the D&G, I ordered the N version for
maximum flexibility with multiple scopes. The D&G was very close to neutral
without and with the CC. I always thought the damage due to color was
overrated. I was wrong. The difference on Jupiter is staggering, the last
time I can remember so much detail was with a 16 newt.”
And from Stan Martin:
“The 11 is fantastic I just love the simplicity of an observatory setup. This year's opposition of Mars was inspiring. It's one of those things you experience by yourself and know one will ever know. You're right about my initial statements about the chromacor, but I would have to change that. I finally bought my own chromacor and have really gotten to like it on bright planets, namely Mars & Jupiter. After more thorough testing, the results showed close to 60% color reduction.”
I and others have noticed a reduction in chromatic aberration when using a binoviewer. Since I am not an optical expert I can not explain how it occurs, but my experience is that a binoviewer significantly reduces CA. Stan Martin does a good job of explaining it:
“It was also the first time I've heard someone else comment about the perceived color reduction when using a binoviewer. I have often found this effect to be of great advantage in planetary observation with a large achromat. Along with this I have found a HUGE advantage of improving perceived affects of turbulence with the use of both eyes in a binoviewer. These two attributes are worth stressing in your review. If I switch back and forth between the binoviewer and a single eyepiece I would estimate that perceived secondary color and turbulence are almost cut in half (of course this is just a function of the brain processing the combined images and not actual change in turbulence). I think that the false color improvement may be caused by the split images being individually less bright and therefore having less noticeable secondary color.”
APO v ACHROMAT
Frankly, for visual observations of the Moon and planets, I see this as a pointless
debate. It isn't that I do not enjoy APOs, to date I have owned several large APOs including an Astro Physics 6 F/12 Superplanetary, Meade
127 ED, Meade 178 ED, Takahashi FS-152 and a TEC 140 F/7 not to mention
two superb 4 APOs ( Showa 100mm F/10 APO and a Takahashi FC-100) along with several other APOs from 60mm to 85 mm. But from my experience, for planetary
viewing a large achromat is a fine instrument. One of the most knowledgeable
guys on the planet when it comes to scopes, particularly refractors, is Roland
Christen of AP fame. In an article about the best planetary scope he stated:
Refractor, 7 to 9 Apo, F8 to F11, or 8 to 12 achromat, F12 or longer. These scopes will cost the most, although excellent achromats can be gotten at reasonable prices from builders like D&G Optical. Inch for inch, refractors will have more light grasp, and in my own experience, an edge on contrast which is important in making out planetary detail. Achromats will have chromatic aberration effects that turn some people off but others have learned to ignore.
Well I couldn't agree more, large achromats, especially from a top maker like D&G, make fine planetary scopes. Over the years I have tried many scopes looking for the one best matched to my observing habits. Many scopes have come and gone but the D&G remains. I tried to sell it once or twice but each time I had second thoughts, it is just too neat a scope. Yes, I also own a great APO, currently a Takahashi FS-152 (plus I am on the AP 160 list and also coveting the Takahashi TOA 170 due out in a year or two). But there is something special about swinging the D&G around to take a peek at the Moon and planets. The first time I set the D&G up in my girlfriend's backyard she looked at it and said, It looks so majestic just sitting there Couldn't have said it better. As my friend and mentor Al George describes it best, You are a refractor man
- stevew, Serenity Now, StellarOne and 3 others like this