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Re: Considering buying a G11 mount for astrophotography.
Hi Nicholas
Great idea to ask here
I think Losmandy used to be more DIY, and it attracted a more DIY audience. The currently shipping units are pretty much out-of-the-box ready to go.?
I would ask what year is the gemini, and what?upgrades are included on it. the more you know about it, the better you can judge. Newer models with the latest upgrades tend to perform better out of the box.?
i personally would go for any unit with a Gemini II mini, i can't speak for Onstep, i think there are a few users of that here on the boards
Hope that helps, i'm sure others will chime in?
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Re: Considering buying a G11 mount for astrophotography.
Hi Nicholas,
I went from a IEQ 45 Pro to the G11 with a Gemini 2 controller. There is nothing more difficult about the Gemini 2 than the IEQ 45 control system,?it is just different. Once you learn it is much easier and logical than the IEQ work flow. the G11 is a much higher quality mount than the iOptron. I?loved the IEQ 45 after I adjusted the worm gear. I probably read the same reviews you did about the Losmandy mounts. Now that I own one I suspect those reviews were referring?the Gemini?2`s ability to do much more than other systems. So, if you want you can set the controller to do much more than other systems.?
Purchasing a used G11 you may need to make sure all the settings?are correct and the battery inside the Gemini 2 is still good. Other than that you should be good. One thing I loved about the mount after I purchased it, the polemaster adapter from the IEQ fits the G11, and the adapter that Losmandy sells for the mount fits right on the Tri Peer.?
There are also good tutorials and many people who will help you through the initial set up and other deeper aspects of the system.?
Take care,
James
Hello, I am interested in a G11, (there is one in the classifieds with a Onstep, or I would get a gemini version but it is more expensive. However I have been told that these mounts are very complicated to use and require a lot of tinkering. Can you tell me if that is true?? ?I have a IEQ45 Pro and these types of mounts I am very familiar with. I could buy like a CEM70 and use it out of the box. But from what I read, well. again the G11 is hard to use at first.?
Would appreciate your comments to the above. and anything about the Onstep version.
THANK YOU!
Nicholas A. DiSabatino
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Hi Jeff
welcome!
that's great to hear.?
Sounds like you figured out how to adjust the RA height by loosening the big bolt to move it, and also you can adjust the bolt into one of the other holes for additional height?
if not, let me know. i dropped a response back to you on your open ticket
Brian
Hi everybody. I received my new G11T mount this week from Losmandy. I had it out to one of my favorite dark sites a few days ago but the many fires in California and in my own state
made finding stars really difficult. I have gone through a few too many mount issues in the last year and I am hoping I have found a reliable mount for the next decade or so. I have always
been undermounted, but I now have a mount that should be good enough, even for my C14. The price tag for the G11T was almost the max I could afford, but I would have taken out a
loan to get a new Titan, if there were still being made. With my C14 the G11T seems pretty stable, and it should be really good for imaging with my smaller SCT¡¯s. A very kind guy in the
Cloudy Nights forum helped me out with some setup issues and I should be good to go. His name is Jeff also, so thanks, Jeff.
Jeff Marston
-- Brian?
Brian Valente portfolio
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Hi everybody. I received my new G11T mount this week from Losmandy. I had it out to one of my favorite dark sites a few days ago but the many fires in California and in my own state
made finding stars really difficult. I have gone through a few too many mount issues in the last year and I am hoping I have found a reliable mount for the next decade or so. I have always
been undermounted, but I now have a mount that should be good enough, even for my C14. The price tag for the G11T was almost the max I could afford, but I would have taken out a
loan to get a new Titan, if there were still being made. With my C14 the G11T seems pretty stable, and it should be really good for imaging with my smaller SCT¡¯s. A very kind guy in the
Cloudy Nights forum helped me out with some setup issues and I should be good to go. His name is Jeff also, so thanks, Jeff.
Jeff Marston
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Considering buying a G11 mount for astrophotography.
Hello, I am interested in a G11, (there is one in the classifieds with a Onstep, or I would get a gemini version but it is more expensive. However I have been told that these mounts are very complicated to use and require a lot of tinkering. Can you tell me if that is true?? ?I have a IEQ45 Pro and these types of mounts I am very familiar with. I could buy like a CEM70 and use it out of the box. But from what I read, well. again the G11 is hard to use at first.?
Would appreciate your comments to the above. and anything about the Onstep version.
THANK YOU!
Nicholas A. DiSabatino
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Now, I'm happy with my mount because I know more about it . Here are the results :
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Re: technique for selectively assessing and removing 7 microns from non-concentric SS shaft bearing area
Thanks for the warm note and complement.? Bearings are a science but I thought of the technique and wanted to share it.? I should have indicated 7 microns is at the lower end of what I can reasonably measure, I am quite sure the declination shaft uneven diameter was in excess of this, but less than 0.0006 as a shaft "high point".? The 4,000 silicon carbide with a bit of WD-40 works great.? I also used 3000 then 4000 to polish the face of the thrust bearings, using a new sheet taped to granite surface plate for improving the condition of the received bearing surface into a "polished flat mirror".? Total material removed from the race face was ~0.0003+/-.? Overall, over the years multiple elements of the mount had been receiving successive upgrades by the prior owner, it does have a "precision" ground worm, and a "black anodized" worm gears, revolving around a brass sleeve into which the roller bearing was tightly inserted.? It is interesting that the right ascension axis has a shaft that measures about 0.0021 to 0.0299 less in diameter.? It revolves good and has no detectable play, but I am holding final judgement when I mount my home-brew 5" refractor and run the magnification up to several hundred to assess if any excess shaft to bearing play exists on this axis.? If this exists, another set of solutions will be needed, but that is another story...? I am impressed with the overall design and machining of the entire package.?? I have added some small 0.010 and 0.030 brass washers to fit onto the 6-32 screws to help optimize the precise mounting of drive reduction gear hardware to obtain a precise offset for two new oldham couplers.? Also, upon arrival one of the rear plastic cases of one of the gear drives was loose so after considering the options, I drilled out the remaining 2 metal rivets and drilled and tapped using three 3-48 screws to secure the plastic case to the aluminum base plate with a spot of 5 minute epoxy on the screw heads to prevent them from getting loose. Big next steps include completing integration of adapter for mounting /aligning optical center of the scope to mount, and becoming fluent in operating the Gemini version 3.? Thanks again for your response.
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Re: technique for selectively assessing and removing 7 microns from non-concentric SS shaft bearing area
Nice work, John!
Yours is the first report I've read about such a small shaft diameter variance causing a pinch problem.? Another member did report the screw behavior on his GM8 that he attributed to a misalignment of the 2 parts of the outer shaft enclosure...which he saw a slight difference in the gap between those parts.? ?He resolved his issue by realigning the outer parts so the gap was uniform.??
The DEC shaft is not rotated very much, except for GoTos then just autoguided.? Binding would be a problem. I think your point is that one could suspect either shaft is getting pinched, if binding is observed.
In your case, the binding was found to be from an oversized shaft diameter in one region.? Your mount is the oldest variety Celestron G11 (aka CG11).? I have one too.??
Would slightly undersizing a shaft cause a different operational problem?? What about the tolerance on the needle bearings themselves?? I could see how their variance would cause a pinch on some shafts and looseness on other shafts.? The design has to allow for some variation in the bearing and the shaft manufacture.??
Anyway, thanks for your report, and the clever way you used a marker wear to determine where the wear was occuring.??
Enjoy your (renewed) mount.
Oh...look also for this: the CG11 used steel worms.? Far better works are now available from Losmandy...the precision brass worm.? You should replace at least the one on the RA, if not both.??
All the best, Michael
Losmandy G11 colleagues,
I recently acquired a "vintage Celestron by Losmandy G11 mount with the Gemini System computer".? Mechanically, the mount needed some TLC.? I decided for a complete end to end take apart and rebuild to fully understand how it was built.? This email is to highlight and share how I solved an interesting problem.? This was that the unloaded motion of the Declination shaft when rotated liked to slowly cork-screw either up or down depending upon clockwise or counter-clockwise shaft rotation.? Additionally the level of hand applied torque was also somewhat uneven when rotated, fully free at times and then "binding", then free again, this was even when the end clutch was removed and the shaft flipped 180 for general checkout, something was just not OK with the behavior of the shaft and bearings.? Eliminating possible causes included a close visual inspection of the shaft and bearings for dings, nicks, dents, etc.? Then I verified the shaft was acceptably straight using a granite surface plate and two Starrett # 278B V-Blocks and and a ~0.00005 resolution dial indicator.? I rotated and measured shaft at bearing point areas and in the center (either side of the shaft hole) and satisfied myself the shaft mechanical run-out was OK.? I then checked the overall state of the shaft diameter using a 1 to 2 inch carbide tipped micrometer with vernier (good for no better than 0.00005 (visual interpolation)), multiple locations of the bearing tracks, in general this shaft measured 1.2500 +/-, did not pick up any signal requiring intervention.??
Next for a more sensitive diagnostic test, I realized I needed to see what was going on between the shaft bearings and the shaft interface while the shaft was rotated.? For this I cleaned all the residual grease off the shaft, and used a black indelible marker (Sharpie) and made a continuous thin uniform band of ink around the perimeter of the shaft, slightly in excess of the track of each of the two shaft bearings.? I then inserted the shaft back into the bearings, and rotated it by hand about 50 turns, pulled out the shaft and visually inspected the wear pattern results.?
One end of the shaft was tracking reasonably perfectly with the bearing surface, evenly, continuously around the full diameter of the shaft, ink was uniformly removed. The other end (clutch end) had three "high" visual wear points on the shaft where the ink was worn away, one wear area was about 1/4 inch diameter, the other two wear areas were about 3/8 inch ellipse with long axis of ellipse parallel to the length of the shaft.? The wear points shown by Black Sharpie ink worn away and surrounding shaft remained black.? Using the micrometer I checked the overall diameter at these locations.? The diameter was about 0.00027 larger than adjacent shaft area, this was the source of the shaft binding.? I used 4,000 silicon wet and dry cut paper into a 1/2 inch strip, about 10 inch long with a slight amount of WD-40 oil on the surface and lapped the shaft at these high points.? This was initially done as a spot polish application about 10 strokes (measured after 5) using a very flat piece of highly polish tool steel ~0.4 x 3 inch as a backing to the paper, this was followed with a total of about 20 lapping strokes (measured after 10) holding the strip tight with thumb and forefinger of each hand and moving back and forth keeping the polishing paper tight.? I cleaned up the residue and placed the shaft back into the bearings.? I have had success, the shaft now tracks very smoothly and uniformly now with even application of torque.? I hope that this helps others who may be experiencing this type of defective behavior.? It also shows that 4,000 grit silicon carbide paper (3-M) is helpful to the level of precision needed.? Time to enjoy the G-11? Cheers John
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technique for selectively assessing and removing 7 microns from non-concentric SS shaft bearing area
Losmandy G11 colleagues,
I recently acquired a "vintage Celestron by Losmandy G11 mount with the Gemini System computer".? Mechanically, the mount needed some TLC.? I decided for a complete end to end take apart and rebuild to fully understand how it was built.? This email is to highlight and share how I solved an interesting problem.? This was that the unloaded motion of the Declination shaft when rotated liked to slowly cork-screw either up or down depending upon clockwise or counter-clockwise shaft rotation.? Additionally the level of hand applied torque was also somewhat uneven when rotated, fully free at times and then "binding", then free again, this was even when the end clutch was removed and the shaft flipped 180 for general checkout, something was just not OK with the behavior of the shaft and bearings.? Eliminating possible causes included a close visual inspection of the shaft and bearings for dings, nicks, dents, etc.? Then I verified the shaft was acceptably straight using a granite surface plate and two Starrett # 278B V-Blocks and and a ~0.00005 resolution dial indicator.? I rotated and measured shaft at bearing point areas and in the center (either side of the shaft hole) and satisfied myself the shaft mechanical run-out was OK.? I then checked the overall state of the shaft diameter using a 1 to 2 inch carbide tipped micrometer with vernier (good for no better than 0.00005 (visual interpolation)), multiple locations of the bearing tracks, in general this shaft measured 1.2500 +/-, did not pick up any signal requiring intervention.??
Next for a more sensitive diagnostic test, I realized I needed to see what was going on between the shaft bearings and the shaft interface while the shaft was rotated.? For this I cleaned all the residual grease off the shaft, and used a black indelible marker (Sharpie) and made a continuous thin uniform band of ink around the perimeter of the shaft, slightly in excess of the track of each of the two shaft bearings.? I then inserted the shaft back into the bearings, and rotated it by hand about 50 turns, pulled out the shaft and visually inspected the wear pattern results.?
One end of the shaft was tracking reasonably perfectly with the bearing surface, evenly, continuously around the full diameter of the shaft, ink was uniformly removed. The other end (clutch end) had three "high" visual wear points on the shaft where the ink was worn away, one wear area was about 1/4 inch diameter, the other two wear areas were about 3/8 inch ellipse with long axis of ellipse parallel to the length of the shaft.? The wear points shown by Black Sharpie ink worn away and surrounding shaft remained black.? Using the micrometer I checked the overall diameter at these locations.? The diameter was about 0.00027 larger than adjacent shaft area, this was the source of the shaft binding.? I used 4,000 silicon wet and dry cut paper into a 1/2 inch strip, about 10 inch long with a slight amount of WD-40 oil on the surface and lapped the shaft at these high points.? This was initially done as a spot polish application about 10 strokes (measured after 5) using a very flat piece of highly polish tool steel ~0.4 x 3 inch as a backing to the paper, this was followed with a total of about 20 lapping strokes (measured after 10) holding the strip tight with thumb and forefinger of each hand and moving back and forth keeping the polishing paper tight.? I cleaned up the residue and placed the shaft back into the bearings.? I have had success, the shaft now tracks very smoothly and uniformly now with even application of torque.? I hope that this helps others who may be experiencing this type of defective behavior.? It also shows that 4,000 grit silicon carbide paper (3-M) is helpful to the level of precision needed.? Time to enjoy the G-11? Cheers John
?
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Re: G11 Mount Not Tracking Correctly
Hi Doug!
Did you ever resolve your original issue?
If yes, what things worked?
If not, please contact me!
Best of luck, Michael
On Sat, Aug 22, 2020, 11:27 AM Mark de Regt < deregt@...> wrote: When my G11 has had either bad goto or bad tracking, here are the problems I have found:
1. Bad polar alignment.? This is by far the most likely culprit, IMO.? Unless you¡¯ve done a good drift alignment, or correctly used an electronic aid like PoleMaster, that would be top of the list of things to check.? Aside from the physical hassles of dealing with the polar scope, a polar scope gives ?a rough alignment even if you did it perfectly, and if you made a mistake, it¡¯s not polar alignment at all, just a recipe for frustration . ? 2. Poorly balanced axes.? This can cause slipping in the clutches, which will throw your goto off, and kill your tracking. ? I am sure there are other possible causes, but these are the simple ones. ? Mark ? ? Hey everyone, first post here.
I have used the G11 mount before and had success with it, but this past weekend, it seems like no matter what I tried, I could not get the alignment correct.? I purchased the GPS attachment thinking that would make things more accurate and simple, but that didn't seem to help.? After setting up my mount, I aligned it due north with a compass and waited for sunset to align with Polaris using the polar scope.? The app I have on my phone to match the reticle never seems to be in the same position when looking through the reticle of the polar scope, but I've never had difficulty aligning before.? So after aligning Polaris between the correct lines in the reticle, I fired up the mount and used quick start.? I verified the GPS data with another source and verified the time zone UTC -5, or Central Daylight Time, and ensured the time was also correct, and it was.? However when using the two bright stars to perfect the alignment, (typically I use Vega and Deneb), the GoTo was way off.? It would slew but point in totally different directions for either star.? After using the buttons to slew to the correct position, it still would not go back to the correct spot and then trying to slew back to Polaris did not even work.? I put everything back in the correct position with CWD and all that, all my cameras pointing at Polaris and tried again using Vega and Arcturus, and then Arcturus and Dubhe and never got good results.? All my images ended up with trailing and I was using short focal lengths with relatively short shutter times of 3-4 minutes.? I have previously done 8 minute exposures and had no trailing whatsoever at 24mm focal length on a 35mm full frame.? For this past weekend I had three cameras mounted and balanced, with an 85mm lens, a 24mm lens, and a medium format camera with 23mm lens (18mm full frame equivalent).
I wanted to also do a series of Andromeda with my 600mm lens, but that would have been out of the question since I was getting trails at short focal lengths.
Any recommendations for how to fix this?? Honestly, even if the GoTo doesn't take me to the exact position, I'm fine with using the buttons to slew to where I want to go, but I at least need it to track properly.
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Re: Valid Guide Rates for PEC on Gemini Level 4
This is a followup to using PEMPro and PEC guide rate. I have just restored the full PEC guide rate range 0.2x - 0.8x to the latest build of PEMPro, which I just uploaded. Here is the direct download link to V3.00.32 (or use check for updates in PEMPro's help menu): ?
? Here is also an example screenshot showing where to adjust the guide rate. Note that the East and West move distances are not the same. For example, the East moves are 0.241 arc-secs, and West moves are 0.130 arc-sec in the screenshot below. The move distance values can differ based on the number of cells used, the number of worm cycles that the PEC cells contain, the number of teeth in the worm wheel, and the guide-rate. ?
? ? -Ray Gralak Author of APCC (Astro-Physics Command Center): https://www.astro-physics.com/apcc-pro Author of PEMPro V3:? https://www.ccdware.com Author of Astro-Physics V2 ASCOM Driver: https://www.siriusimaging.com/apdriver ?
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> -----Original Message----- > From: [email protected] [mailto:[email protected]] On Behalf Of sbasprez via groups.io > Sent: Monday, August 17, 2020 11:11 AM > To: [email protected] > Subject: [Losmandy_users_io] Valid Guide Rates for PEC on Gemini Level 4 > > I have always used 0.8x as the guide rate when training PEC on my G11 with Gemini 1 Level 4.? I was just > looking at the Gemini instructions in PEMPro V3 and it has this warning:? The Gemini firmware only supports > 0.3x and 0.5x guide rates - 0.5x is recommended.? This conflicts with the description of command ID 502, > Guide Speed used for training PEC, in the Gemini Level 4 Users Manual.? That seems to indicate the full 0.2x, > 0.5x, and 0.8x range is valid.? Which is it?
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Re: G11 Mount Not Tracking Correctly
When my G11 has had either bad goto or bad tracking, here are the problems I have found:
1. Bad polar alignment.? This is by far the most likely culprit, IMO.? Unless you¡¯ve done a good drift alignment, or correctly used an electronic aid like PoleMaster, that would be top of the list of things to check.? Aside from the physical hassles of dealing with the polar scope, a polar scope gives ?a rough alignment even if you did it perfectly, and if you made a mistake, it¡¯s not polar alignment at all, just a recipe for frustration . ? 2. Poorly balanced axes.? This can cause slipping in the clutches, which will throw your goto off, and kill your tracking. ? I am sure there are other possible causes, but these are the simple ones. ? Mark ?
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From: [email protected] < [email protected]> On Behalf Of dougwheeler90@... Sent: Monday, August 17, 2020 8:06 PM To: [email protected]Subject: [Losmandy_users_io] G11 Mount Not Tracking Correctly ? Hey everyone, first post here.
I have used the G11 mount before and had success with it, but this past weekend, it seems like no matter what I tried, I could not get the alignment correct. ?I purchased the GPS attachment thinking that would make things more accurate and simple, but that didn't seem to help. ?After setting up my mount, I aligned it due north with a compass and waited for sunset to align with Polaris using the polar scope. ?The app I have on my phone to match the reticle never seems to be in the same position when looking through the reticle of the polar scope, but I've never had difficulty aligning before. ?So after aligning Polaris between the correct lines in the reticle, I fired up the mount and used quick start. ?I verified the GPS data with another source and verified the time zone UTC -5, or Central Daylight Time, and ensured the time was also correct, and it was. ?However when using the two bright stars to perfect the alignment, (typically I use Vega and Deneb), the GoTo was way off. ?It would slew but point in totally different directions for either star. ?After using the buttons to slew to the correct position, it still would not go back to the correct spot and then trying to slew back to Polaris did not even work. ?I put everything back in the correct position with CWD and all that, all my cameras pointing at Polaris and tried again using Vega and Arcturus, and then Arcturus and Dubhe and never got good results. ?All my images ended up with trailing and I was using short focal lengths with relatively short shutter times of 3-4 minutes. ?I have previously done 8 minute exposures and had no trailing whatsoever at 24mm focal length on a 35mm full frame. ?For this past weekend I had three cameras mounted and balanced, with an 85mm lens, a 24mm lens, and a medium format camera with 23mm lens (18mm full frame equivalent).
I wanted to also do a series of Andromeda with my 600mm lens, but that would have been out of the question since I was getting trails at short focal lengths.
Any recommendations for how to fix this? ?Honestly, even if the GoTo doesn't take me to the exact position, I'm fine with using the buttons to slew to where I want to go, but I at least need it to track properly.
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Re: Side by side saddle or piggy back scope alignment
The linked document is very nice though.
You can use it to prove to yourself that the angle between the guide camera and main scope is largely irrelevant at least from a polar alignment standpoint as in my example below.?
Assume that the max tolerance for field rotation is 3.76 microns (typical pixel size), target declination is 85 degrees (close to the worst case scenario), polar alignment is within 3 arc minutes (we can easily do better than that), guide exposure is 4 seconds, and focal length is 3000 mm (most of us image considerably shorter focal lengths, and anyone imaging at this long of a focal length is likely using an off axis guider).?
Then the maximum angle between the guide scope and main OTA is 25 degrees to prevent visible field rotation in 4 seconds. You would easily detect this mismatch just visually looking at your setup. No optical alignment needed.
For more typical cases (eg. 600mm f/l, smaller declinations), the permissible deviations are even higher.?
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Re: Side by side saddle or piggy back scope alignment
Good point. I was using total image exposure time and even there, field rotation wasn¡¯t a problem I had to worry about.?
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On Aug 21, 2020, at 12:16 PM, Arun Hegde <arun.k.hegde@...> wrote:
?In reading the article linked (authored by Frank Barrett), I am not so sure that those calculations apply to the type of guided imaging we do. In fact, you could use his calculations to prove that with reasonable care, field rotation is unlikely to be a problem at all with today's methods of polar alignment.?
Hook's equations in Frank's article are for unguided imaging and Frank appears to have extended it to guided imaging. Which is fine, but then the relevant exposure time is not the exposure time of your sub, but the exposure time of your guide camera. This is normally on the order of a few seconds, and much shorter than the exposure time of your sub.? As Frank notes, in autoguiding, the motion of the centroid of the guide star is tracked with reference to a reference pixel. Motion beyond a certain tolerance results in a correction. And that correction is applied in both RA and DEC. And as long as that correction is applied before appreciable field rotation occurs, you should be fine. As noted by Frank himself in his example:
"In other words, if our alignment error is less than about 11.25 arc minutes we should see no field rotation greater than 9 microns during a 15-minute exposure at 35 degrees declination and the given setup."
11.25 arc minutes is an absolutely horrendous standard for polar alignment! We can easily get under 2 arc minutes, and with some care, under 1 arc minute in a matter of minutes using things like SharpCap. And guide exposures are much, much smaller than 15 minutes usually 2-4 seconds.
To the point then about the mismatch between the guide scope and the OTA. With reasonable polar alignment, the issue isn't field rotation, but atmospheric refraction. If the guide cam is pointing at a vastly different area of the sky refraction will cause differences in the motion of your subject versus guide star (eg. see discussion of King Rate versus Sidereal Rate). You should be able to avoid this very easily by even visually assuring that the guide cam and OTA are atleast somewhat aligned.?
?
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Re: Side by side saddle or piggy back scope alignment
In reading the article linked (authored by Frank Barrett), I am not so sure that those calculations apply to the type of guided imaging we do. In fact, you could use his calculations to prove that with reasonable care, field rotation is unlikely to be a problem at all with today's methods of polar alignment.?
Hook's equations in Frank's article are for unguided imaging and Frank appears to have extended it to guided imaging. Which is fine, but then the relevant exposure time is not the exposure time of your sub, but the exposure time of your guide camera. This is normally on the order of a few seconds, and much shorter than the exposure time of your sub.? As Frank notes, in autoguiding, the motion of the centroid of the guide star is tracked with reference to a reference pixel. Motion beyond a certain tolerance results in a correction. And that correction is applied in both RA and DEC. And as long as that correction is applied before appreciable field rotation occurs, you should be fine. As noted by Frank himself in his example:
"In other words, if our alignment error is less than about 11.25 arc minutes we should see no field rotation greater than 9 microns during a 15-minute exposure at 35 degrees declination and the given setup."
11.25 arc minutes is an absolutely horrendous standard for polar alignment! We can easily get under 2 arc minutes, and with some care, under 1 arc minute in a matter of minutes using things like SharpCap. And guide exposures are much, much smaller than 15 minutes usually 2-4 seconds.
To the point then about the mismatch between the guide scope and the OTA. With reasonable polar alignment, the issue isn't field rotation, but atmospheric refraction. If the guide cam is pointing at a vastly different area of the sky refraction will cause differences in the motion of your subject versus guide star (eg. see discussion of King Rate versus Sidereal Rate). You should be able to avoid this very easily by even visually assuring that the guide cam and OTA are atleast somewhat aligned.?
?
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Morning Joe,
I am looking for help understanding?CCDOPS software in relationship to my Sti Camera and G11/G2. ?Specifically, what the issues with X&Y axis telling me showing me there is either drift in each axis and how to correct the errors I am seeing as the drift only gets worse and no apparent correction going on. ?
I am just getting back into astro?photography after a couple of years away from it due to health issues, so I have?forgotten how to use this?software the STi or my ST5c. ?By the way, I am using a?modified Cannon Xsi?camera, so am able to take images via Images Plus and @ 5 minutes that do not show any visual movement, but in the 10 minutes there is?slight visual drift. ?In essence how ?do you turn on corrections of the mount if possible?
Any reply & suggestions most appreciated,
Doug Askew?
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Re: Side by side saddle or piggy back scope alignment
Chuck -- If you are wondering about the effect of misalignment of the guidescope on astrophotography, it can cause star trailing.? This is due to ¡°field rotation¡± and it could occur if the polar alignment isn¡¯t perfect, and the guidescope and OTA don¡¯t point to the same spot in the sky. There is a good calculator available for this () and an article that explains it in some detail.? For exposures of a few minutes or less and decent polar alignment (as with Polemaster, Sharpcap Pro, or drift alignment), and reasonably close alignment of the OTA with the guidescope, it¡¯s not likely to be a problem.? I aligned my OTA and guidescope on a tower about 3 miles away and I haven¡¯t seen a problem in my images, but YMMV.? ? Joe ?
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From: [email protected] < [email protected]> On Behalf Of E. Brett Waller Sent: Friday, August 21, 2020 2:30 AM To: [email protected]Subject: Re: [Losmandy_users_io] Side by side saddle or piggy back scope alignment ? Chuck, Two scopes with the centerline of their optical axes exactly parallel will point to the same location on the sky. So if you shim them to be parallel. their fields of view will be concentric. ? Brett Thanks for your reply. Yes, by concentric I meant having the same view in the sky. Since I put a losmandy dovetail on the top and bottom of my c11 (it has hyperstar capability) and put an 80 mm refractor f5 on top of that it was apparetly their view in the sky was close but not totally concentric and the refractor doesn't have adjustable rings. So i was wondering do I shim the dovetail using a laser to get the two perfectly parallel or not. I understood in general their view of the sky would be nearly the same but would that matter and in what circumstances.? But I found they were slightly off of each other.? Since I don't do AP yet but have been playing with a camera and I am a complete babe in the woods with AP I was looking for input.?
Chuck
-----Original Message-----
From: E. Brett Waller <cedargreenobservatory@...>
To: Losmandy_users <[email protected]>
Sent: Tue, Aug 11, 2020 01:25 PM
Subject: Re: [Losmandy_users_io] Side by side saddle or piggy back scope alignment
Chuck, If I am reading your post correctly, you are wondering whether the scopes?should be parallel?or should point to the same place in the sky (I assume that is what you mean by having the views concentric). If they are parallel, they will point to the same place in the sky, despite the fact they are separated by several inches. This would NOT be true for a terrestrial object where the distance between two parallel scopes would offset the field of view by the same spacing as between the two optical axes.? For an astronomical object such as the moon, your best case resolution is going to be on the order of a kilometer or so, and you would never notice such a small offset. In similar fashion, you would be hard pressed to see the difference in the fields of view on a terrestrial object at a distance?of several miles. In those cases, the lines of sight for the two telescopes?are effectively parallel. Thus, two telescopes which are parallel will point to the same location on?the sky. I hope I haven't misread your original question, if so I apologize. At any rate, I hope you find my reply useful. ? On Tue, Aug 11, 2020 at 12:02 AM crocco1250 via <crocco1250=[email protected]> wrote: This may not be the right place for this question but a recent post talked about side by side saddles and it raised a question. If you had a side by side or piggy back, say a c11 and 80 mm refractor, do you want them perfectly parallel or have the views more or less concentric? What are the pros and cons? If someone has a site I would appreciate more info.
Thanks
Chuck
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Re: Side by side saddle or piggy back scope alignment
Chuck,
Two scopes with the centerline of their optical axes exactly parallel will point to the same location on the sky. So if you shim them to be parallel. their fields of view will be concentric.
Brett?
Brett
Thanks for your reply. Yes, by concentric I meant having the same view in the sky. Since I put a losmandy dovetail on the top and bottom of my c11 (it has hyperstar capability) and put an 80 mm refractor f5 on top of that it was apparetly their view in the sky was close but not totally concentric and the refractor doesn't have adjustable rings. So i was wondering do I shim the dovetail using a laser to get the two perfectly parallel or not. I understood in general their view of the sky would be nearly the same but would that matter and in what circumstances.? But I found they were slightly off of each other.? Since I don't do AP yet but have been playing with a camera and I am a complete babe in the woods with AP I was looking for input.? Chuck -----Original Message----- From: E. Brett Waller < cedargreenobservatory@...> To: Losmandy_users < [email protected]> Sent: Tue, Aug 11, 2020 01:25 PM Subject: Re: [Losmandy_users_io] Side by side saddle or piggy back scope alignment Chuck,
If I am reading your post correctly, you are wondering whether the scopes?should be parallel?or should point to the same place in the sky (I assume that is what you mean by having the views concentric). If they are parallel, they will point to the same place in the sky, despite the fact they are separated by several inches. This would NOT be true for a terrestrial object where the distance between two parallel scopes would offset the field of view by the same spacing as between the two optical axes.? For an astronomical object such as the moon, your best case resolution is going to be on the order of a kilometer or so, and you would never notice such a small offset. In similar fashion, you would be hard pressed to see the difference in the fields of view on a terrestrial object at a distance?of several miles. In those cases, the lines of sight for the two telescopes?are effectively parallel. Thus, two telescopes which are parallel will point to the same location on?the sky.
I hope I haven't misread your original question, if so I apologize. At any rate, I hope you find my reply useful.
Best regards,
Brett On Tue, Aug 11, 2020 at 12:02 AM crocco1250 via <crocco1250= [email protected]> wrote: This may not be the right place for this question but a recent post talked about side by side saddles and it raised a question. If you had a side by side or piggy back, say a c11 and 80 mm refractor, do you want them perfectly parallel or have the views more or less concentric? What are the pros and cons? If someone has a site I would appreciate more info.
Thanks
Chuck
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Re: Counterweight down setup??
Never thought about "Upside Down".
But I did get the RA Extension to make my "chunks" more friendly to carry around. I have my GM811G configured into 1. Tripod; 2. RA/12" extension; 3. Dec/counterweight; and 4. My telescope/imaging rig.
The RAEXT allows me to separate the RA/Dec into lighter movable assemblies.
And interesting perk to the RA extension is to image through the meridian, do to the clearance advantage.
I've recently been doing that a few times. I use an Atik Infinity camera (OSC). And I can get on my object in the Eastern side of the Southern Meridian, and image deep into the Western side Non-Stop.
As in No Meridian Flip. And I've gotten files stacked 1300 images x 13,000 seconds long (10 second subs). And they almost take on a 3D depth.
Until now, with the RA extension, Meridian flips were always a PITA for me.
Now I can totally ignore them.
Like Michael, I've readjusted my limits to allow me to go further without crashing. (Different objects may require different settings. But they can be done on the fly while imaging, even)
--
SonnyE
(I suggest viewed in full screen)
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James B
jeff marston
Michael Herman
Doug Askew