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Downsizing OTA C-11 to C-8

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#26 Rustler46

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Posted 09 January 2021 - 05:42 PM

Is the Celestron Super C8 plus OTA weight 28 pounds?

The current C-8 OTA tips the scales at around 13 lbs. with lower dovetail. I just weighed my Super C8 Plus (1985 version) as shown below. With accessories (DewBuster controller, upper dovetail, 2 X dovetail clamps, refractor tube rings, telephoto camera lens tune rings, Telrad, 1-1/4" prism diagonal, etc......), it is around 21 lbs. All the accessories nearly doubles the weight. Adding my piggybacked AT115EDT refractor and telephoto/camera adds another 15 lbs. So in all the mount is carrying over 35 lbs. It is a substantial load for my Losmandy G11/G-1 mount. 

 

Best Regards,

Russ

 

C-8 OTA.jpg



#27 pweiler

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Posted 09 January 2021 - 06:05 PM

Thanks, I am close to setting up a similar setup with 6.2 pound 72mm refractor on top of an 18 pound 8” classic cass with other visual stuff bringing the total weight to just under 30 pounds. I am hoping that a G811g can handle it. But, when I see your setup on a G11, I am starting to wonder???

#28 Rustler46

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Posted 09 January 2021 - 06:51 PM

Thanks, I am close to setting up a similar setup with 6.2 pound 72mm refractor on top of an 18 pound 8” classic cass with other visual stuff bringing the total weight to just under 30 pounds. I am hoping that a G811g can handle it. But, when I see your setup on a G11, I am starting to wonder???

I'm not familiar with the capacity of the G811g. But your intended use will figure into it. I have used my C-8 and C-11 on the G11 mount for long exposure astrophotography. For that it worked OK as long as there wasn't much wind. For visual use the C-11/AT115EDT combo works great for visual use, even though the total load is pushing the mount's capacity.  

 

Added thoughts:

While there are other high quality mounts available, I have found everything about Losmandy products is of highest quality. With that in mind their mounts are more likely to perform well when pushed toward the weight capacity limit. So for visual use, that is something to consider. For photographic uses your mount's utility will depend on which OTA will be used and what is the length of exposure. For EAA (electronically assisted astronomy) with shorter exposures, even a challenged mount could perform quite well. The image scale will also figure in. The cassegrain will be much more demanding in that regard versus your nice refractor.

 

While I have gone away from long exposure astrophotography, the C-8 is capable of some fine results at f/7 on the G11. For my uses, EAA is the best of visual and photographic observations. Here's an example of long exposure astrophotography:

 

NGC 7293 Whew.jpg

 

Helix Nebula, NGC 7293, C-8 f/7.0, 1420 mm, 4-1/3 hours exposure, Sony NEX-7, ISO 800 - Processed with PixInsight: 8 X 15-minute & 7 X 20-minute lights, 7 darks, 10 flats, 20 bias, Post processing in PixInsight by Chris Rock

 

Here are some examples of EAA. These I was able to see build up on the computer screen as the image was live stacked.

 

EAA M42.jpg

Orion Nebula, M42, Pentax 200mm f/4 @ f/5.6, 36mm aperture, ZWO ASI290MC video camera, 200 frames live-stacked with SharpCap, dark frame applied, hot pixels not removed

 

EAA M1.jpg

Crab Nebula, M1, Stack of 24 frames, 10-seconds each using SharpCap, C-11 F/6.3

 

EAA NGC 2438.jpg

Planetary Nebula NGC 2438 in O.C. M46, C-11, f/6.3, ZWO ASI290MC camera, live stack of 49 6-second frames with SharpCap

 

 

Let us know what you come up with.

 

 

Warm Regards,

Russ


Edited by Rustler46, 09 January 2021 - 09:19 PM.

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#29 Rustler46

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Posted 13 January 2021 - 06:13 PM

Progress report C-11 to C-8:

 

Astronomics has my order for Losmandy DC8, dovetail plate for C-8, on back order. When that comes back in stock, I'll replace the orange upper dovetail with the better design.

 

The orange Celestron dovetail is a low cost, low weight solution. But being an extrusion has its drawbacks - it has the same cross section for its entire length. So to reduce overall dovetail cost & weight, there is a gap underneath where the three attachment screws penetrate, leaving the under side unsupported. This can be a source of flexure and places unnecessary stress on the screws and threaded holes. To deal with that potential problem I have placed suitable thickness washers (shown below) in the gap, to make a more solid connection.

 

C-8 Upper Dovetail-02434.jpg

The above image shows a front view, where the single screw attaches the dovetail to the front corrector casting. There are similar washers surrounding the two attachment screws on the rear casting. To the left of the dovetail can be seen the Telrad finder, with dew heater power connection.

 

C-8 Dovetail SIde View-02436.jpg

The view above shows the upper and lower dovetails, along with DewBuster controller, dew heater strip and temperature sensors for OTA (clipped under dew heater) and ambient air (on curved wire above dew heater). Also visible are tube rings for AT115EDT refractor and camera lens for EAA photography.

 

Below is the Telrad finder, taken from the Celestron-11.

Telrad-02437.jpg

Underneath the Telrad window can be seen the 3 resistors for dew prevention. These are powered by the Dewbuster system through the RCA phono plugs and speaker wire cable. This keeps the Telrad window free of dew under the very wettest conditions. The commercial Telrad dewshield accessories are worthless in my experience. Directions for making the Telrad dew heater are found on the DewBuster website.

 

Kind Regards,

Russ


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#30 Stevegeo

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Posted 13 January 2021 - 06:27 PM

Great idea about the telrad... and I agree, the so called dew shield  , worthless...

 This gives me ideas... thank you..

Stevegeo 



#31 Rustler46

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Posted 13 January 2021 - 09:20 PM

Hi Stevegeo,

 

I'm glad the progress report was helpful. For the Celestron dovetails, I recommend the washer reinforcement, especially between OTA and mount. This is the area of greatest load. Yet, I have used un-reinforced dovetails on both C-8 and C-11 for over 10 years. And there have been no problems with the weaker connection. But with ever increasing loads, I feel better about using more solid connections. Those Celestron dovetails will eventually be replaced with the better designed Losmandy units.

 

Russ

 

Losmandy Dovetail - 2430-2.jpg

These dovetails cost 3 times that of the Celestron units. If your finances can handle that, I think they are worth the cost.



#32 Rustler46

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Posted 14 January 2021 - 03:41 PM

Progress report:

 

"Aperture-Fever" has broken, or at least is in temporary remission. winky.gif I'm looking forward to pushing the limits on my reduced aperture.

 

Warm Regards,

Russ



#33 Rustler46

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Posted 16 January 2021 - 04:13 PM

So tonight looks to be at least minimally clear (i.e. not raining). So I'm foregoing the 10-inch grab-n-go telescope for my old Celestron Super C8 Plus on the Losmandy G11 go-to mount. It is a bit more to the setup versus the dob/DSC mount. But it's much more comfortable viewing. Eyepiece height is more fixed, along with ability to change eyepiece orientation to work well with a seated position. 

 

The first goal for the night will be getting the Telrad finder aligned with SCT OTA. The finder came off my C-11, so is not tweaked to fit the C-8. Now that I think of it, it might be best to align finder in daylight on a distant treetop. A bright moon is good to use for finder alignment. But Moon is a thin crescent, likely below my local horizon when it is dark.

 

Edit:

Telrad aligned on a tree top across the road. The crescent Moon was high in a blue twilight sky. Good seeing with great view of Mare Criscium.

 

Back out after dark. Even though it was a bit on the murky side, I opted to power up the G11 for some quick, easy go-to finding. But to no avail. There must be a bit of grit on the RA worm-gear. It tried to slew to the first alignment star, but it kept stalling. Since it was not the most transparent of skies, I opted to forego star-atlas and finder object location. So I removed the C8 OTA to inside storage and covered the mount with a heavy Telegizmo cover to keep the dew at bay. With that large cover I was able to keep the counterweight and shaft attached for tomorrow. During the daylight hours I'll have a look at the RA & Dec worm-gears, clean and re-lube.

 

Best Regards to All,

Russ


Edited by Rustler46, 16 January 2021 - 11:35 PM.


#34 Rustler46

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Posted 18 January 2021 - 10:15 PM

So tonight looks to be at least minimally clear (i.e. not raining). So I'm foregoing the 10-inch grab-n-go telescope for my old Celestron Super C8 Plus on the Losmandy G11 go-to mount. It is a bit more to the setup versus the dob/DSC mount. But it's much more comfortable viewing. Eyepiece height is more fixed, along with ability to change eyepiece orientation to work well with a seated position. 

 

The first goal for the night will be getting the Telrad finder aligned with SCT OTA. The finder came off my C-11, so is not tweaked to fit the C-8. Now that I think of it, it might be best to align finder in daylight on a distant treetop. A bright moon is good to use for finder alignment. But Moon is a thin crescent, likely below my local horizon when it is dark.

 

Edit:

Telrad aligned on a tree top across the road. The crescent Moon was high in a blue twilight sky. Good seeing with great view of Mare Criscium.

 

Back out after dark. Even though it was a bit on the murky side, I opted to power up the G11 for some quick, easy go-to finding. But to no avail. There must be a bit of grit on the RA worm-gear. It tried to slew to the first alignment star, but it kept stalling. Since it was not the most transparent of skies, I opted to forego star-atlas and finder object location. So I removed the C8 OTA to inside storage and covered the mount with a heavy Telegizmo cover to keep the dew at bay. With that large cover I was able to keep the counterweight and shaft attached for tomorrow. During the daylight hours I'll have a look at the RA & Dec worm-gears, clean and re-lube.

Problem solved - I got the worm-gear cleaned, so the mount functions as designed. I'm headed out to explore some of the "Treasures in Taurus" from the January 2021 Sky and Telescope magazine (pg. 54-56). Clear nights in the winter are too rare here on the Oregon coast to pass up, even with a bright Moon in the sky. My old C-8 will not let me down.

 

Russ



#35 Rustler46

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Posted 19 January 2021 - 03:28 PM

Problem solved - I got the worm-gear cleaned, so the mount functions as designed. I'm headed out to explore some of the "Treasures in Taurus" from the January 2021 Sky and Telescope magazine (pg. 54-56). Clear nights in the winter are too rare here on the Oregon coast to pass up, even with a bright Moon in the sky. My old C-8 will not let me down.

Last night was enjoyable with the downsized aperture. Among other things seen was M1, the Crab Nebula.  Best view was at 80X with Oxygen filter. Its oval glow was lumpy, showing a bit of "ropiness". This was influenced by what I remember seeing in photographs I've taken. Just knowing that one star of the close pair inside is a neutron star (pulsar) spinning 30 times per second - well it is awesome. While I could not see the neutron star pair, occasionally I could glimpse the bright star to its right on the periphery in the photo.

 

M1 - Crab Nebula.jpg

Stack of 24 frames, 10-seconds each using SharpCap, C-11 F/6.3, ZWO ASI290MC camera

 

Russ


Edited by Rustler46, 20 January 2021 - 02:32 AM.

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#36 Traveler

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Posted 20 January 2021 - 12:16 AM

Seems like you had  a great time Russ!

Enjoy!



#37 Echolight

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Posted 20 January 2021 - 12:28 AM

Thinkin about getting a goose down for my C8.



#38 Rustler46

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Posted 20 January 2021 - 04:07 PM

The second clear winter night in a row was last night. So despite being tired, I went out for another enjoyable evening. The Moon had not yet reached first quarter, so was not a huge source of extraneous light for deep sky observing. But DSOs did not end up in the view, since my go-to mount displayed another, malfunction. The declination motor stalled and would not allow for go-to star alignment. So I'll need to clean and lube that gear set to get back the go-to function.

 

But not to be deterred by that, I enjoyed viewing the Moon with the C-8. I needed to loosen the RA & Dec clutches for ease of manual tracking as the Moon drifted across the FOV of my TV Panoptic 24mm. At f/10 focal length (2000 mm) that eyepiece encompassed the entire Moon with 0.8° FOV and 85X. Using Sky and Telescope's  Mirror-image Moon Atlas I was able to identify many craters by name and located the Apollo-11 landing site. It's hard to believe 52 years has gone by since that milestone. The near future looks to be cloudy and rainy for a while. But I got my "fix" of under the sky astronomy, two nights in a row.

 

Here's another photo of the G11/C-8 combo in portable mode, April 2015. The occasion was photographing a lunar eclipse from 3600 feet elevation in the Oregon Coast Range Mountains. It was snowing when I got there, but soon cleared for a nice view of the eclipse. Behind the telescope can be seen the Moon nearing the end of partial phase.

 

 

Best Regards,
Russ

 

G-11-C-8-03470.jpg


Edited by Rustler46, 21 January 2021 - 12:17 AM.

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#39 Rustler46

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Posted Yesterday, 04:12 PM

The second clear winter night in a row was last night. So despite being tired, I went out for another enjoyable evening. The Moon had not yet reached first quarter, so was not a huge source of extraneous light for deep sky observing. But DSOs did not end up in the view, since my go-to mount displayed another, malfunction. The declination motor stalled and would not allow for go-to star alignment. So I'll need to clean and lube that gear set to get back the go-to function.

 

Yesterday during daylight hours, I had an opportunity to service the declination worm-gear set. I was able to tip the worm away from the worm-gear (ring-gear) without disconnecting from the drive motor. This allowed for cleaning the ring-gear of any debris that might be causing the motor to stall. An old toothbrush was used to clean each gear tooth and more uniformly distribute the lubricating grease. I see the need for a more thorough cleaning, to remove old grease and apply fresh lube. But for now I have done a quick service.

 

I used the opportunity to set the gear clearance for minimum free-play and backlash. Even though I could move the worm by hand with no resistance, upon tuning on the Losmandy G-11 electronics, I still got a "motor-stalled" warning. So I restarted and by passed go-to alignment. Then selecting the "Sidereal" drive rate, I was able to use the hand controller to move both RA and Dec without motor stall error. Then restarting the electronics allowed for normal go-to alignment, without motor-stall errors. This led me to believe the problem was not mechanical - that is detritus where the gears meshed causing the stall. It appeared the problem was electrical or software. Now I'm hoping the mount will function properly under nighttime conditions.

 

Edit:

I inquired on the Losmandy User's forum about the problem and got some useful advice.

 

Also I started a thread on the CN Mounts forum, where further discussion of the mount problem can continue. But for now, I'm waiting for the next clear night to continue enjoying my old Celestron Super C8 Plus. In addition to visual observing, I've gotten a camera/lens setup mounted piggyback for some EAA. I'll start a thread on that forum for progress in that avenue of observing.

 

Russ


Edited by Rustler46, Yesterday, 08:55 PM.



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