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Jerry_K

Optimum height of S-C OTA for alignment

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Last week was 1st time I had a chance to take my Celestron AVX mount and C6 out since last November. The joy was short lived when I have tried to do all star and then Polar alignments. The eyepiece was so low to the ground that I would had to be Indian yoga master to be able to contort my body so that I could have just a glimpse through the reticle eyepiece. Only after ruined night have I realised that the tripod was set at the height that was perfect for me to sit at the table with laptop and reach the main focusing knob for solar and moon imaging. The eyepiece in focuser was at 45" in a starting position when both markers (Dec and RA) were aligned and OTA was pointing at Polaris. When I looked at it, it is also the highest position that EP will ever be. At 1st alignment star in west the EP dropped down to 38"!!! There is no way that with my crappy back I can do any alignment at all. Question is: Is it practical or good idea to have EP at the eye level, in my case 65", when aiming at Polaris? Or are there any situations where I would regret to have tripod that high? Once the scope is aligned I never look through it again or even come within feet of the scope. Any ideas or remarks are welcome. What do you say?

Jerry

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Jerry

 

I feel your pain.

 

I use BYE in frame & focus mode with my camera instead of a eyepiece to do my alignment. I also make sure that my finder scope with 90 degree diagonal is aligned with my camera that way I only have to look through the finder then use the camera for final centering of all alignment stars.

 

after the first few alignment stars they usually come in to the field of view of the frame & focus screen on the first go.

 

another benefit of this is that your camera is aligned so you don't have to do much adjusting after a goto slew.  

 

 

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Thanks Jim, I'll give it another try. I did last year but I had to jack up the StarHD to the max and than it was hard to see the guide star. I will try to raise the tripod so that EP will be at my eye level when both marks are aligned on the mount. When it comes to finder scope I was out of luck as well. The Celestron star finder is in such a weird location that with 1st east alignments star the finder was completely under the already very low OTA. There was absolutely no way to look through regardless of how flexible you are. I have base for Telrad installed so I will use that next time out. It can be on either side but never under.

BTW, the 1st alignment star was nowhere near where it was expected to be, about full hand with thumb away when arm fully extended! Second star got better and it kept improving. Since I have bought the mount last October I had only 2 opportunities tor try to align it so I am a total newbie. Thanks for the help, maybe tonight I'll have another chance. Is it normal to have 1st star so far out? Original alignment was done with polar scope and was very, very close, only 8 arc minutes out after 2 star alignment.

Jerry

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The AVX Mount has really decent and solid 2in steel tube legs, which remain rather steady even when extended rather far.  With the rather light load of the C6, your tripod should be steady enough for decent AP Imaging even if the legs are fully extended, although it will likely vibrate noticeably during slewing and when knocked slightly.  You can increase the steadiness of the tripod by hanging a weighty object (gallon jug of water or battery powerpack)from the bolt under the tripod Spreader (just be sure to tether it to one of the legs as sell to keep it from swinging).

 

But, that being said, the "Optimium Height" is always with the Tripod Legs as short as can be yet still allow you to perform the necessary operations such as Alignment.

 

Using LiveView in Frame&Focus Mode is convenient for performing the Star Alignments.  BUT you need to be aware that all this LiveView Usage will be soaking your DSLR Electronics in Heat which will then impact the amount of Noise captured in your Images until the Sensor cools down.  So, it is best to use LiveView sparingly.

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Jerry,

 

I'm glad you finally got a chance to exercise your new mount, but sorry for you pain!

 

I know that Polaris is higher for you than it is in the US, but if you get your mount set up so the polar axis is close to Polaris, you should be within a degree or two of having a good alignment.  I ignore the altitude scale on the side of my mount and instead I use a digital level on my saddle to set the altitude.  That allows me to adjust only the azimuth to bring Polaris to its correct position.

 

For azimuth adjustment I have a polar alignment finderscope in my mount to assist with a rough polar alignment.  Use of the PA finder requires me to get down on one knee to look into it.  This will be tougher for you at a higher latitude. Then I use a low power eyepiece with an illuminated reticle to do a 2+4 star alignment.  This is good enough to hit targets all night long. However, if I will be doing photography I then do an All Star Polar Alignment and then redo the 2+4 alignment.

 

Also, I use a Rigel Quick Finder as a naked eye finder.  It attaches to a small base that is stuck to my OTA with double-sided tape.  The finder body unsnaps from the base for easy storage of both the OTA and the finder. The finder does not need to be re-adjusted for subsequent sessions as long as it was not used on another scope. It is easily aligned to the OTA with 3 adjustment knobs and when I center a bright star in the Quick Finder it is always visible in images (both DSLR and CCD).  Oh, and the Quick Finder comes with 2 bases so I can move it between scopes.

 

I hope this helps.

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Thanks Shane,

yes, the AVX has quite solid tripod. I have made a spreader from plywood to replace the small aluminum cast spreader that came with the mount. I can place whole bunch of stuff on it to make it more solid but the weight itself is enough to stabilise it. As far as sensor heating up during Live View I have a rather unusual process: I align with my un-moded 500D that has crazy high ISO and than switch to full spectrum modified 450D that is direct contact cooled with 2 water cooled TECs for imaging. By the time I have done alignment the sensor will be at -3C or lower even at 26C ambient temperature. Air temperature has no impact at all on my design. My cold box works like magic. The reason for switching cameras is not the heat issue but rather tubing and cables swinging left to right and than back again during all the alignments. This way there is only one USB cable hanging from the mount. I'll post pictures of my setup later.

Thanks for your help,

Jerry

 

The AVX Mount has really decent and solid 2in steel tube legs, which remain rather steady even when extended rather far.  With the rather light load of the C6, your tripod should be steady enough for decent AP Imaging even if the legs are fully extended, although it will likely vibrate noticeably during slewing and when knocked slightly.  You can increase the steadiness of the tripod by hanging a weighty object (gallon jug of water or battery powerpack)from the bolt under the tripod Spreader (just be sure to tether it to one of the legs as sell to keep it from swinging).

 

But, that being said, the "Optimium Height" is always with the Tripod Legs as short as can be yet still allow you to perform the necessary operations such as Alignment.

 

Using LiveView in Frame&Focus Mode is convenient for performing the Star Alignments.  BUT you need to be aware that all this LiveView Usage will be soaking your DSLR Electronics in Heat which will then impact the amount of Noise captured in your Images until the Sensor cools down.  So, it is best to use LiveView sparingly.

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Thanks Rick, I knew I'll hear from you!

Not so fast with higher Polaris for me, I live just north of Lake Erie and we are at same latitude as North California. My is at 42.2N, but yes, it is higher but quite comfortable with the tripod a bit higher than I had that before. My Celestron Polaris finder is set perfectly, I can rotate it around axis and the center never moves. Last time I was 8 arc minutes out. As for star finder I have reinstalled my Telrad that is never on the bottom of OTA, the worst is on either side, not bad when tripod is 13" higher than before.

My reticle is 20mm (Orion) so it is not as wide as I would like but I'll get hang of it. Finally I can do some imaging!!! What a winter, you must be so happy to be out of Ohio, our next door neighbor.

Thanks Rick, I'll post results tomorrow, weather permitting.

Jerry

 

Jerry,

 

I'm glad you finally got a chance to exercise your new mount, but sorry for you pain!

 

I know that Polaris is higher for you than it is in the US, but if you get your mount set up so the polar axis is close to Polaris, you should be within a degree or two of having a good alignment.  I ignore the altitude scale on the side of my mount and instead I use a digital level on my saddle to set the altitude.  That allows me to adjust only the azimuth to bring Polaris to its correct position.

 

For azimuth adjustment I have a polar alignment finderscope in my mount to assist with a rough polar alignment.  Use of the PA finder requires me to get down on one knee to look into it.  This will be tougher for you at a higher latitude. Then I use a low power eyepiece with an illuminated reticle to do a 2+4 star alignment.  This is good enough to hit targets all night long. However, if I will be doing photography I then do an All Star Polar Alignment and then redo the 2+4 alignment.

 

Also, I use a Rigel Quick Finder as a naked eye finder.  It attaches to a small base that is stuck to my OTA with double-sided tape.  The finder body unsnaps from the base for easy storage of both the OTA and the finder. The finder does not need to be re-adjusted for subsequent sessions as long as it was not used on another scope. It is easily aligned to the OTA with 3 adjustment knobs and when I center a bright star in the Quick Finder it is always visible in images (both DSLR and CCD).  Oh, and the Quick Finder comes with 2 bases so I can move it between scopes.

 

I hope this helps.

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Well, I have raised the tripod by 12" and what a difference it made!!! 2 + 2 star alignment plus Polar alignment in under 15 minutes with error of 4 and 3 arc seconds! Happy, happy, happy and my back is just fine. Thanks guys for your help and encouragement, now the collimation is next. Will have to lower the tripod again so I can reach the screws <_<

Jerry 

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