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Antares 150mm f/6.5 Achromat
Dec 05 2005 03:03 AM |
Mr. Bill
in 140mm + Refractors
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ANTARES 150MM f/6.5 ACHROMAT REFRACTOR
by Bill Faatz ( Mr. Bill)
After owning a Synta 120mm f/8.3 achromat and building my own folded refractor with a 6 inch f/8 lens set, I have become a confirmed refractor junkie. The announcement a few months ago of the impending release of the new Antares refractors from China with fast optics well corrected both in color and spherical aberration naturally piqued my interest. When the release was announced, I "pulled the trigger" and bought one from Island Eyepiece in Vancouver.
My observing is mainly low power wide field views of the Milky Way star clouds and large diffuse and dark nebulae associated with them. The benefits of unobstructed optics without the problems of fast reflectors make fast achromat optics ideal for the task. The superior contrast that refractors offer is of supreme importance in viewing the dim, low contrast features that characterize this class of objects. The pinpoint star images further contribute to the aesthetic.
The telescope arrived well packed in a double carton with Styrofoam inserts and noodles. Included in the OTA configuration are the rings, integral dew shield, a dustcap and a standard rack and pinion 2 inch focuser with a 1 1/4 inch adapter (a Crayford focuser is offered as an optional upgrade.) Also included is a well made 7x50 finder with crosshairs. The rings have a mounting bar attached for an unspecified mount. No instructions were included, so your guess is as good as mine which one.
The first thing I did was to remove the mounting bar and secure the ring assembly with socket head screws to a Losmandy universal mounting plate. The holes on the ring assembly are tapped for 1/4-20 which certainly is more convenient then the metric thread that I expected.
The overall appearance of the OTA is striking with well-applied white paint to the main tube assembly and dew shield. The focuser and the lens cell collar are an attractive dark gray crackled finish that contrasts nicely with the tube. The OTA weight including rings without finder is about 22 pounds. The focuser and ring assembly and tube appear to be identical to the Meade AR5 and AR6 series. Ron at Moonlite confirmed the Antares tube is the same as the Meade and indeed the threading on the focuser drawtube is the same as Meade (different than Synta) as I discovered when I replaced the original visual back with an after market from Mercury Systems.
The focuser is a pleasant surprise; much better then the "legendary" Synta focuser with its slop and grease. Disassembling the focuser reveals several Teflon strips for the focuser tube to ride on as well as a plastic strip that can be adjusted for tension. The overall good impression of this focuser is dampened somewhat by the fact the groove milled in the focuser body the rack rides in is oversized which allows a small amount of radial motion when the rack direction is reversed. This in practice was not a problem as there was no noticeable backlash when the tension screw was properly adjusted. The focuser knobs are brushed aluminum and very nice indeed considering the price point of this scope. There is a handle mounted on the bottom of the focuser casting that proved marginally useful in practice.
The dew shield is fixed and seems up to the task with a flat black paint applied to the inside. The dust cap fits snugly.
The lens cell can be collimated with three push/pull screw adjustments. The lens appears to be mg fl coated rather than the advertised multi coatings. The coating is well applied with no noticeable blemishes. The lens edges are blackened.
Tube is well baffled with 4 knife-edge baffles and the drawtube has an additional 3 baffles.
Initial observing side by side with my 6-inch f/8 showed noticeably dimmer views of DSOs. This puzzled me until I did a closer examination of the optics... drawing a ray trace revealed vignetting of the light cone by an overlong drawtube. I removed about 2 1/2 inches off the front of the drawtube (originally 10 inches) and this immediately "opened up" the views. I suspect that the vignetting is deliberately done to make the color correction appear better than the full aperture would deliver.
Even after the drawtube mod, the optics delivered impressive views with both color and spherical correction better than my 6 inch f/8 Synta optics could deliver. The inside/outside focus diffraction patterns on star test are close with a small amount of under correction noted. No astigmatism was seen. I would characterize the optics as a "well corrected achromat" and a sign that the Chinese are improving the quality of their product. The optics along with the mechanicals are in my opinion a definite step up from the Syntas that I have looked through.
Unable to leave things alone, I did several things to improve the original telescope (see pictures.) I added 1 1/2 pounds to the inside of the focuser casting by epoxying lead fishing weights. This shifted the weight center rearward allowing the tube to be balanced at midpoint.
I also painted the inside of the focuser casting first with an undercoat of textured paint with an overcoat of ultra flat black.
The inside of the focuser tube was further blackened with paint as well as a collar of flocking paper between the last two knife-edge baffles.
The inside of the dew shield was lined with 3 M adhesive flocking paper. All these easy fixes gave noticeably better contrast over the original version. As mentioned before, the original visual back (marginal at best) was replaced with an after market that gave a much more rigid lockup of the diagonal to the focuser. This greatly contributed to a rock solid eyepiece alignment that allowed precise and repeatable collimation alignment. On these fast systems that is critical for the best possible images.
To sum up, this is a very good scope for the money (about $650 US OTA) and a good choice for someone looking for a reasonably portable rich field refractor. At 990mm focal length, it is a good compromise in providing both wide field low power views and higher magnification without the need to use a Barlow. I would NOT recommend this for the serious planetary observer; you would be happier with say the Antares f/8 with its better color correction.
OTOH, for casual views of the planets and moon the f/6.5 works fine, especially with a minus violet filter.
Two thumbs up!
by Bill Faatz ( Mr. Bill)
After owning a Synta 120mm f/8.3 achromat and building my own folded refractor with a 6 inch f/8 lens set, I have become a confirmed refractor junkie. The announcement a few months ago of the impending release of the new Antares refractors from China with fast optics well corrected both in color and spherical aberration naturally piqued my interest. When the release was announced, I "pulled the trigger" and bought one from Island Eyepiece in Vancouver.
My observing is mainly low power wide field views of the Milky Way star clouds and large diffuse and dark nebulae associated with them. The benefits of unobstructed optics without the problems of fast reflectors make fast achromat optics ideal for the task. The superior contrast that refractors offer is of supreme importance in viewing the dim, low contrast features that characterize this class of objects. The pinpoint star images further contribute to the aesthetic.
The telescope arrived well packed in a double carton with Styrofoam inserts and noodles. Included in the OTA configuration are the rings, integral dew shield, a dustcap and a standard rack and pinion 2 inch focuser with a 1 1/4 inch adapter (a Crayford focuser is offered as an optional upgrade.) Also included is a well made 7x50 finder with crosshairs. The rings have a mounting bar attached for an unspecified mount. No instructions were included, so your guess is as good as mine which one.
The first thing I did was to remove the mounting bar and secure the ring assembly with socket head screws to a Losmandy universal mounting plate. The holes on the ring assembly are tapped for 1/4-20 which certainly is more convenient then the metric thread that I expected.
The overall appearance of the OTA is striking with well-applied white paint to the main tube assembly and dew shield. The focuser and the lens cell collar are an attractive dark gray crackled finish that contrasts nicely with the tube. The OTA weight including rings without finder is about 22 pounds. The focuser and ring assembly and tube appear to be identical to the Meade AR5 and AR6 series. Ron at Moonlite confirmed the Antares tube is the same as the Meade and indeed the threading on the focuser drawtube is the same as Meade (different than Synta) as I discovered when I replaced the original visual back with an after market from Mercury Systems.
The focuser is a pleasant surprise; much better then the "legendary" Synta focuser with its slop and grease. Disassembling the focuser reveals several Teflon strips for the focuser tube to ride on as well as a plastic strip that can be adjusted for tension. The overall good impression of this focuser is dampened somewhat by the fact the groove milled in the focuser body the rack rides in is oversized which allows a small amount of radial motion when the rack direction is reversed. This in practice was not a problem as there was no noticeable backlash when the tension screw was properly adjusted. The focuser knobs are brushed aluminum and very nice indeed considering the price point of this scope. There is a handle mounted on the bottom of the focuser casting that proved marginally useful in practice.
The dew shield is fixed and seems up to the task with a flat black paint applied to the inside. The dust cap fits snugly.
The lens cell can be collimated with three push/pull screw adjustments. The lens appears to be mg fl coated rather than the advertised multi coatings. The coating is well applied with no noticeable blemishes. The lens edges are blackened.
Tube is well baffled with 4 knife-edge baffles and the drawtube has an additional 3 baffles.
Initial observing side by side with my 6-inch f/8 showed noticeably dimmer views of DSOs. This puzzled me until I did a closer examination of the optics... drawing a ray trace revealed vignetting of the light cone by an overlong drawtube. I removed about 2 1/2 inches off the front of the drawtube (originally 10 inches) and this immediately "opened up" the views. I suspect that the vignetting is deliberately done to make the color correction appear better than the full aperture would deliver.
Even after the drawtube mod, the optics delivered impressive views with both color and spherical correction better than my 6 inch f/8 Synta optics could deliver. The inside/outside focus diffraction patterns on star test are close with a small amount of under correction noted. No astigmatism was seen. I would characterize the optics as a "well corrected achromat" and a sign that the Chinese are improving the quality of their product. The optics along with the mechanicals are in my opinion a definite step up from the Syntas that I have looked through.
Unable to leave things alone, I did several things to improve the original telescope (see pictures.) I added 1 1/2 pounds to the inside of the focuser casting by epoxying lead fishing weights. This shifted the weight center rearward allowing the tube to be balanced at midpoint.
I also painted the inside of the focuser casting first with an undercoat of textured paint with an overcoat of ultra flat black.
The inside of the focuser tube was further blackened with paint as well as a collar of flocking paper between the last two knife-edge baffles.
The inside of the dew shield was lined with 3 M adhesive flocking paper. All these easy fixes gave noticeably better contrast over the original version. As mentioned before, the original visual back (marginal at best) was replaced with an after market that gave a much more rigid lockup of the diagonal to the focuser. This greatly contributed to a rock solid eyepiece alignment that allowed precise and repeatable collimation alignment. On these fast systems that is critical for the best possible images.
To sum up, this is a very good scope for the money (about $650 US OTA) and a good choice for someone looking for a reasonably portable rich field refractor. At 990mm focal length, it is a good compromise in providing both wide field low power views and higher magnification without the need to use a Barlow. I would NOT recommend this for the serious planetary observer; you would be happier with say the Antares f/8 with its better color correction.
OTOH, for casual views of the planets and moon the f/6.5 works fine, especially with a minus violet filter.
Two thumbs up!
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