My Celestron 150mm f/8
Posted: Sat Sep 28, 2019 4:55 am
Synta 150mm f/ 8 Refractor
The short tube version seems to be getting popular of late so some thoughts on my refractor.
The Synta yard cannon, sold by Celestron, Skywatcher, Omegon, Saxon, Kson and various other retailers since it first became available in 2000.
If you have not seen one of these in the field, the first impression from people is usually “That is a really big telescope!”
They are an impressive looking piece of kit when set up and always seem to gather a crowd at outreach nights.
Showing new people views of the planets or lunar surface are memorable moments.
The C6-R is a mid focal length 150mmaperture Fraunhofer achromatic refractor made in China under the Suzhou Synta Optical Technology Company name.
It comes packaged with the standard Synta rack & pinion focuser, cast aluminium tube clamps, 200mm extruded Vixen style dovetail plate, a 9×50 straight through finderscope, plastic bodied 31.75mm mirror diagonal, a 20mm Plossl eyepiece and collimation eyepiece finish the accessories package.
The C6-R when first released seemed to have a noticeable lack of consistency in lens quality and spacing with them arriving under-corrected, neutral or over-corrected.
It was akin to a lottery at times and some people reported having to return 2-3 telescopes before finally receiving a good one.
Consistency progressively became better over time at least, the chances of getting a poor one are quite minimal now.
The Advanced Series Go To mount with slightly re-designedCG -5 was packaged with a tripod that now used 50.8mm/ 38.1mm stainless steel legs and capacity was supposed to be 13.6 kg!
The tripod/ mount and telescope are packaged in three very large boxes with moulded styrofoam and accessory boxes holding everything in place.
The instruction manual was written reasonably well and the mount had the ability to do a one or two star alignment, quick align, or last alignment.
What was in the boxes with some weights:
C6-R: 8.6 kg
ASGT mount: 5.44 kg
Counterweight Shaft: 0.932 kg
Counterweight(s): 5.244 kg (theCG -5 has 1 counterweight included)
Tripod: 7.455 kg
Spreader Bar: 0.340 kg
Hand Controller: 0.228 kg
Power Cord: 0.225 kg
Total weight of the C6-R/ ASGT: 33.708 kg
The C6-R performs better than one would first expect, chromatic aberration is present of course but less than what would normally be expected with a larger mid focal length refractor, spherical aberration is also well controlled, and contrast and sharpness are very good. Chromatic blur is approximately 6.9
Strictly on a view per cost basis it is an excellent option for a largeaperture refractor package.
Using this refractor I was able to have my first views of Scorpii B.
It works extremely well for splitting close double stars or viewing globular clusters, and puts up great lunar and planetary views.
A light yellow filter or one of the various Minus Violet filters does a reasonable job of curbing the chromatic aberration the telescope produces on bright objects and with the telescope capable of a 2.3° field of view it shows good views of various deep sky objects.
Having a mid focal length off/ 8 it is reasonably easy on eyepiece selection in use as well.
When seeing the images of these on various websites you will see the tube rings centered or slightly to the rear of the tube.
These images are strictly marketing images.
The telescope is very lens heavy and the actual balance point places the rings almost directly behind the lens cell.
This places the eyepiece low to the ground and can make viewing in some positions a bit uncomfortable.
There are a few things to do to get the eyepiece into a more convenient position such as:
1. Add weight to the focuser end of the tube. 2.3-3.5 kg of ankle weights are usually sufficient to get the telescope more centered.
2. Remove and replace the factory dewshield with a lightweight one.
The factory dewshield is made of steel and weights 1 kg.
3. Use a heavy CNC 50.8mm diagonal.
4. Replace the factory focuser with a stronger model.
Besides adding needed weight to to the back of the telescope, I consider this upgrade a bit of a necessary one as the factory focuser is not very good.
5. Replace the straight through finderscope with a heavierRA / RACI finder.
6. Use a heavy eyepiece adapter for 31.75mm eyepieces.
TeleVue still makes a heavy adapter called the “Equalizer”, but taking a regular aluminium adapter to a mill shop and having a copy made from brass is usually not an expensive option and is slightly heavier than the TeleVue.
It will also most likely cost less than the normal 72,00 € that TeleVue charges as well.
7. Metal focuser knobs. There were various places you could buy 24.5mm, 38.1mm or 50.8mm Brass or Steel knobs for this purpose.
A mill shop can also make them for a reasonable cost.
8. This is a tripod mount modification but helps place the eyepiece in a more accessible location.
Orion Telescopes in USA sells a 405mm half pier that fits any standardEQ -5 mount top plate and it can also be modified to fit the AVX mount top plate.
This also adds a bit of weight and stability to the tripod since the legs do not have to be extended much.
Comfortable observing should never involve gymnastics!
In all the C6-R is an excellent telescope to have and use though some things should be considered.
As I stated already the package is large and heavy so can take 4-5 trips to get set up.
The included ASGT mount is just adequate for visual use with the large refractor on it, a Hypertune of the mount does help get rid of most mechanical slop but many recommend aEQ -6 mount instead.
There are some modifications as stated above and improved accessories that will enhance the telescopes use considerably so budgeting 1/3 of the overall original cost for this would not be out of line.
So best done over time instead of at once.
I have had my C6-R since 2005 when I purchased it at an estate sale and have made numerous changes to it over the years, some due to necessity as our relationship did not start out well.
This is how it currently is:
1. The aluminium tube was squared and shortened by 3mm.
The focuser holes were not aligned as the aluminium tube was not cut square at the focuser end and the focuser was only being held loosely by 2 screws when I received it.
2. While star testing I discovered the doublet was over corrected so the lens spacing was changed and while the telescope was apart the lens edges blackened.
Afterwards I took it to a friend in Czech Republic and we spent some time checking the lens for center, orientation and tilt.
3. The tube interior was repainted in ultra flat black as the factory grey was blotchy and very thin in some places allowing the metal to show through.
4. The factory baffles were removed and replaced with 5 new ones.
The center factory baffle had been placed to far forward so after drawing out the light cone to find the proper position, the factory baffles were removed and replaced with new ones placed so the shadow of the front baffle falls onto the face of the one behind.
5. The standard single speed R&P was replaced with a Moonlite CF 2 speed 50.8mm Crayford. The drawtube interior and front edge were also painted ultra flat black to reduce reflections off of the gloss black anodizing.
6. I had a 3.5kg brass internal counterweight built into the focuser tube adapter.
This allowed me to remove the ankle weights from the telescope tube and gives the telescope its normal nice clean look.
This substantially moves the balance point towards the rear of the telescope tube.
7. A brass 50.8mm- 31.75mm eyepiece adapter was made.
It weighs 0.49kg and has a brass compression ring as well as threading for standard filters. (A copy of the Mercury Systems adapter)
8. All factory chromed screws were replaced with stainless steel.
9. A lightweight 380mm long flocked plastic dewshield was fabricated.
I am considering making a baffled aluminium one at the moment.
10. The factory finderscope was replaced with an Antares 8×50RACI model.
11. The 200mm extruded aluminium dovetail was replaced with a 280mm aircraft grade solid aluminium Vixen style dovetail.
This helped remove some vibration that was present when using higher magnifications.
12. Teleskop-Service CNC HD tube clamps.
The last two modifications I still wish to do is change the Vixen dovetail to a Losmandy plate and have the tube and dewshield painted.
There is also a 152mmf/ 8 ED doublet conversion designed by APM Telescope that I have been looking at occasionally, but as the telescope is now, I am very happy with its performance and after almost 14 years of use it is still one of my favourite telescopes.
The short tube version seems to be getting popular of late so some thoughts on my refractor.
The Synta yard cannon, sold by Celestron, Skywatcher, Omegon, Saxon, Kson and various other retailers since it first became available in 2000.
If you have not seen one of these in the field, the first impression from people is usually “That is a really big telescope!”
They are an impressive looking piece of kit when set up and always seem to gather a crowd at outreach nights.
Showing new people views of the planets or lunar surface are memorable moments.
The C6-R is a mid focal length 150mm
It comes packaged with the standard Synta rack & pinion focuser, cast aluminium tube clamps, 200mm extruded Vixen style dovetail plate, a 9×50 straight through finderscope, plastic bodied 31.75mm mirror diagonal, a 20mm Plossl eyepiece and collimation eyepiece finish the accessories package.
The C6-R when first released seemed to have a noticeable lack of consistency in lens quality and spacing with them arriving under-corrected, neutral or over-corrected.
It was akin to a lottery at times and some people reported having to return 2-3 telescopes before finally receiving a good one.
Consistency progressively became better over time at least, the chances of getting a poor one are quite minimal now.
The Advanced Series Go To mount with slightly re-designed
The tripod/ mount and telescope are packaged in three very large boxes with moulded styrofoam and accessory boxes holding everything in place.
The instruction manual was written reasonably well and the mount had the ability to do a one or two star alignment, quick align, or last alignment.
What was in the boxes with some weights:
C6-R: 8.6 kg
ASGT mount: 5.44 kg
Counterweight Shaft: 0.932 kg
Counterweight(s): 5.244 kg (the
Tripod: 7.455 kg
Spreader Bar: 0.340 kg
Hand Controller: 0.228 kg
Power Cord: 0.225 kg
Total weight of the C6-R/ ASGT: 33.708 kg
The C6-R performs better than one would first expect, chromatic aberration is present of course but less than what would normally be expected with a larger mid focal length refractor, spherical aberration is also well controlled, and contrast and sharpness are very good. Chromatic blur is approximately 6.9
Strictly on a view per cost basis it is an excellent option for a large
Using this refractor I was able to have my first views of Scorpii B.
It works extremely well for splitting close double stars or viewing globular clusters, and puts up great lunar and planetary views.
A light yellow filter or one of the various Minus Violet filters does a reasonable job of curbing the chromatic aberration the telescope produces on bright objects and with the telescope capable of a 2.3° field of view it shows good views of various deep sky objects.
Having a mid focal length of
When seeing the images of these on various websites you will see the tube rings centered or slightly to the rear of the tube.
These images are strictly marketing images.
The telescope is very lens heavy and the actual balance point places the rings almost directly behind the lens cell.
This places the eyepiece low to the ground and can make viewing in some positions a bit uncomfortable.
There are a few things to do to get the eyepiece into a more convenient position such as:
1. Add weight to the focuser end of the tube. 2.3-3.5 kg of ankle weights are usually sufficient to get the telescope more centered.
2. Remove and replace the factory dewshield with a lightweight one.
The factory dewshield is made of steel and weights 1 kg.
3. Use a heavy CNC 50.8mm diagonal.
4. Replace the factory focuser with a stronger model.
Besides adding needed weight to to the back of the telescope, I consider this upgrade a bit of a necessary one as the factory focuser is not very good.
5. Replace the straight through finderscope with a heavier
6. Use a heavy eyepiece adapter for 31.75mm eyepieces.
TeleVue still makes a heavy adapter called the “Equalizer”, but taking a regular aluminium adapter to a mill shop and having a copy made from brass is usually not an expensive option and is slightly heavier than the TeleVue.
It will also most likely cost less than the normal 72,00 € that TeleVue charges as well.
7. Metal focuser knobs. There were various places you could buy 24.5mm, 38.1mm or 50.8mm Brass or Steel knobs for this purpose.
A mill shop can also make them for a reasonable cost.
8. This is a tripod mount modification but helps place the eyepiece in a more accessible location.
Orion Telescopes in USA sells a 405mm half pier that fits any standard
This also adds a bit of weight and stability to the tripod since the legs do not have to be extended much.
Comfortable observing should never involve gymnastics!
In all the C6-R is an excellent telescope to have and use though some things should be considered.
As I stated already the package is large and heavy so can take 4-5 trips to get set up.
The included ASGT mount is just adequate for visual use with the large refractor on it, a Hypertune of the mount does help get rid of most mechanical slop but many recommend a
There are some modifications as stated above and improved accessories that will enhance the telescopes use considerably so budgeting 1/3 of the overall original cost for this would not be out of line.
So best done over time instead of at once.
I have had my C6-R since 2005 when I purchased it at an estate sale and have made numerous changes to it over the years, some due to necessity as our relationship did not start out well.
This is how it currently is:
1. The aluminium tube was squared and shortened by 3mm.
The focuser holes were not aligned as the aluminium tube was not cut square at the focuser end and the focuser was only being held loosely by 2 screws when I received it.
2. While star testing I discovered the doublet was over corrected so the lens spacing was changed and while the telescope was apart the lens edges blackened.
Afterwards I took it to a friend in Czech Republic and we spent some time checking the lens for center, orientation and tilt.
3. The tube interior was repainted in ultra flat black as the factory grey was blotchy and very thin in some places allowing the metal to show through.
4. The factory baffles were removed and replaced with 5 new ones.
The center factory baffle had been placed to far forward so after drawing out the light cone to find the proper position, the factory baffles were removed and replaced with new ones placed so the shadow of the front baffle falls onto the face of the one behind.
5. The standard single speed R&P was replaced with a Moonlite CF 2 speed 50.8mm Crayford. The drawtube interior and front edge were also painted ultra flat black to reduce reflections off of the gloss black anodizing.
6. I had a 3.5kg brass internal counterweight built into the focuser tube adapter.
This allowed me to remove the ankle weights from the telescope tube and gives the telescope its normal nice clean look.
This substantially moves the balance point towards the rear of the telescope tube.
7. A brass 50.8mm- 31.75mm eyepiece adapter was made.
It weighs 0.49kg and has a brass compression ring as well as threading for standard filters. (A copy of the Mercury Systems adapter)
8. All factory chromed screws were replaced with stainless steel.
9. A lightweight 380mm long flocked plastic dewshield was fabricated.
I am considering making a baffled aluminium one at the moment.
10. The factory finderscope was replaced with an Antares 8×50
11. The 200mm extruded aluminium dovetail was replaced with a 280mm aircraft grade solid aluminium Vixen style dovetail.
This helped remove some vibration that was present when using higher magnifications.
12. Teleskop-Service CNC HD tube clamps.
The last two modifications I still wish to do is change the Vixen dovetail to a Losmandy plate and have the tube and dewshield painted.
There is also a 152mm
