Encoders...
- WilliamPaolini
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Encoders...
U.S.A.F. Veteran - Visual Amateur Astronomer since 1966 - Fully Retired since 2019
8" f/5 Newt - Lunt 152 f/7.9 - TSA 102 f/8 - Vixen 81S f/7.7 - P.S.T. - Pentax 65ED II - Nikon 12x50 AE
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- OzEclipse
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Re: Encoders...
There is no consensus nor any one answer. It really depends what you want to do with the mount. For example, if you just want to have an object in the 1 degree field of a low power eyepiece, then 1/2 degree(720 steps) should always have it in field, 1/4 degree(1440 steps) definitely. Most encoders are much better than this. It gets more difficult if for example you want to place a particular body near the centre of field of a small 5x3mm sensor at the 5 metre focus of an
From your signature, it looks like your longest
Cheers
Joe
Amateur astronomer since 1978...................Web site : http://joe-cali.com/
Scopes: ATM 18" Dob, Vixen VC200L, ATM 6"f7, Stellarvue 102ED, Saxon ED80, WO M70 ED, Orion 102 Maksutov, ST80.
Mounts: Takahashi EM-200, iOptron iEQ45, Push dobsonian with Nexus DSC, three homemade EQ's.
Eyepieces: TV Naglers 31, 17, 12, 7; Denkmeier D21 & D14; Pentax XW10, XW5, Unitron 40mm Kellner, Meade Or 25,12
Cameras : Pentax K1, K5, K01, K10D / VIDEO CAMS : TacosBD, Lihmsec.
Cam/guider/controllers: Lacerta MGEN 3, SW Synguider, Simulation Curriculum SkyFi 3+Sky safari
Memberships Astronomical Association of Queensland; RASNZ Occultations Section; Single Exposure Milky Way Facebook Group (Moderator) (12k members), The Sky Searchers (moderator)
- SkyHiker
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Re: Encoders...
- Piet Le Roux
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Re: Encoders...
- WilliamPaolini
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Re: Encoders...
U.S.A.F. Veteran - Visual Amateur Astronomer since 1966 - Fully Retired since 2019
8" f/5 Newt - Lunt 152 f/7.9 - TSA 102 f/8 - Vixen 81S f/7.7 - P.S.T. - Pentax 65ED II - Nikon 12x50 AE
Pentax XWs - Baader Morpheus - Takahashi LEs - Edmund RKEs - BST Starguiders - 6ZAO-II/5XO/4Abbe
PM and Email communications always welcomed
- OzEclipse
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Re: Encoders...
Hi Bill,WilliamPaolini wrote: ↑Sat Oct 09, 2021 4:00 pm Thanks for the feedback. Thinking about it, I guess the resolution can all be for naught if the mount has a lot of slop in its movement. So accuracy is really going to be a function of the encoders and mount working together. Weakest link of the two (plus the alignment accuracy by the user) will determine final outcomes.
PS - my question was related to visual only...sorry I forgot that critical point :twitch:
Yes backlash can come into it.
A friend who has an uncooperative mount chooses a bright star in the vicinity of the object he is looking for. he slews to that first, using the finder and scope he centres the bright star, synchronises the
Visual and at those focal lengths, you should not need to worry about resolution.
Joe
Amateur astronomer since 1978...................Web site : http://joe-cali.com/
Scopes: ATM 18" Dob, Vixen VC200L, ATM 6"f7, Stellarvue 102ED, Saxon ED80, WO M70 ED, Orion 102 Maksutov, ST80.
Mounts: Takahashi EM-200, iOptron iEQ45, Push dobsonian with Nexus DSC, three homemade EQ's.
Eyepieces: TV Naglers 31, 17, 12, 7; Denkmeier D21 & D14; Pentax XW10, XW5, Unitron 40mm Kellner, Meade Or 25,12
Cameras : Pentax K1, K5, K01, K10D / VIDEO CAMS : TacosBD, Lihmsec.
Cam/guider/controllers: Lacerta MGEN 3, SW Synguider, Simulation Curriculum SkyFi 3+Sky safari
Memberships Astronomical Association of Queensland; RASNZ Occultations Section; Single Exposure Milky Way Facebook Group (Moderator) (12k members), The Sky Searchers (moderator)
- Piet Le Roux
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Re: Encoders...
With the Meade Autostar/Audiostar controller this is referred to as "high precision" mode and can easily be de-selected in the menu. I personally don't use it because it is very time consuming to first go to a bright star every time you do a
- Don Pensack
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Re: Encoders...
Depends. To achieve high accuracy with the accuracy of a poor quality mount may be beyond the capabilities of 1.3 million tick encoders, while a perfectly accurate mountWilliamPaolini wrote: ↑Sat Oct 09, 2021 1:01 am What is the consensus for what the accuracy should be for "good" encoders for a mount? +/- what fraction of a degree?
might put every target in the center of the field with 2000 tick encoders.
1' resolution requires 21600 tick encoders, so I put that at the base considering the average mount accuracy and average telescope true field size.
You won't need that with a 4.5° true field on a short focal length refractor.
I find that 32K tick encoders work adequately in most dobs.
Most DSC screens have GUIs yielding 0.1° resolution, or 6' resolution. If the mount is perfect, that is achievable with 2160 tick encoders, In practice, however, mount inaccuracies often achieve poorer resolution
with 10K tick encoders.
Of course, you can make nearly every mount more accurate, even with low resolution encoders, by simply moving to a named star near the object and synchronizing the scope on that star.
When I was hunting very faint and small galaxies in Corona Borealis, I first did a search for Alpha Coronae Borealis (Gemma, or Alphecca) with my DSC, centered and synched on the star, and every other object in the constellation
was dead center. Meade used to call this "High Precision Pointing" in their older LX200s, and it worked very well, placing every object dead center. With DSCs, you have to pick a star in the DSC database
to sync on, but it essentially works the same way.
Optical encoders seem to max out around 80K resolution. Just about everything above 10K will require constant reading from the encoders, which doesn't happen in Tangent DSCs or Sky Commander DSCs, so they are not usable with
truly high resolution encoders. Magnetic encoders use much less power and have resolutions of 192K to 1300K ticks. As far as I know, only the Nexus DSC boxes are compatible with such high resolution encoders.
The advantages of the magnetic encoders are they are waterproof, and don't have to be placed at the center of the axes to work (though most are on most mounts).
Currently using a 12.5" dob and a 4" apo refractor
- OzEclipse
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Re: Encoders...
It's an 18" f5.5, 2500mm focal length.
1 degree field in a Nagler 31,
38 mins in a Nagler 17,
26 mins in a Denkmeier 14.
The Nexus DSC is connected to an 8K alt az encoder pair.
I do a two star + zenith alignment at the start of the night just eyeballing the stars to the centre of field in the 31mm Nagler. I can usually put any object in the field but not centre of the 14mm for the rest of the night. 17mm & 31mm are easy. If I took the trouble to use a crosshair eyepiece I could probably get it more accurate. The Nexus has ALT AZ guidance readouts to 0.1 deg. Sometimes it drifts a little by the small hours of the morning. I could re-align, takes a couple of minutes. But I usually just memorise the two offsets in my head and keep going.
Joe
Amateur astronomer since 1978...................Web site : http://joe-cali.com/
Scopes: ATM 18" Dob, Vixen VC200L, ATM 6"f7, Stellarvue 102ED, Saxon ED80, WO M70 ED, Orion 102 Maksutov, ST80.
Mounts: Takahashi EM-200, iOptron iEQ45, Push dobsonian with Nexus DSC, three homemade EQ's.
Eyepieces: TV Naglers 31, 17, 12, 7; Denkmeier D21 & D14; Pentax XW10, XW5, Unitron 40mm Kellner, Meade Or 25,12
Cameras : Pentax K1, K5, K01, K10D / VIDEO CAMS : TacosBD, Lihmsec.
Cam/guider/controllers: Lacerta MGEN 3, SW Synguider, Simulation Curriculum SkyFi 3+Sky safari
Memberships Astronomical Association of Queensland; RASNZ Occultations Section; Single Exposure Milky Way Facebook Group (Moderator) (12k members), The Sky Searchers (moderator)
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Re: Encoders...
For
- Don Pensack
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Re: Encoders...
OzEclipse wrote: ↑Wed Oct 13, 2021 2:12 am As a practical guide, I purchased an ATM dob built by another member on this site.
It's an 18" f5.5, 2500mm focal length.
1 degree field in a Nagler 31,
38 mins in a Nagler 17,
26 mins in a Denkmeier 14.
The Nexus DSC is connected to an 8K alt az encoder pair.
I do a two star + zenith alignment at the start of the night just eyeballing the stars to the centre of field in the 31mm Nagler. I can usually put any object in the field but not centre of the 14mm for the rest of the night. 17mm & 31mm are easy. If I took the trouble to use a crosshair eyepiece I could probably get it more accurate. The Nexus has ALT AZ guidance readouts to 0.1 deg. Sometimes it drifts a little by the small hours of the morning. I could re-align, takes a couple of minutes. But I usually just memorise the two offsets in my head and keep going.
Joe
The Nexus DSC has a guidance readout that can be selected for 0.1, 0.01, and 0.001 degree. I prefer the 0.1 degree choice myself as then the numbers aren't continually changing and because it is possible to achieve 0.0/0.0 pointing, but impossible to achieve 0.00/0.00 pointing.
But if the scope tracks, the higher level readout might help attain a higher level of accuracy. Not with 8K encoders, though, which have 2.7' resolution. You're better sticking to 0.1 degree readout guidance. Perhaps with the 1.3 million tick encoders that are also compatible with the Nexus DSC.
Currently using a 12.5" dob and a 4" apo refractor
- OzEclipse
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Re: Encoders...
Thanks Don,Don Pensack wrote: ↑Sat Oct 23, 2021 4:45 pmOzEclipse wrote: ↑Wed Oct 13, 2021 2:12 am As a practical guide, I purchased an ATM dob built by another member on this site.
It's an 18" f5.5, 2500mm focal length.
1 degree field in a Nagler 31,
38 mins in a Nagler 17,
26 mins in a Denkmeier 14.
The Nexus DSC is connected to an 8K alt az encoder pair.
I do a two star + zenith alignment at the start of the night just eyeballing the stars to the centre of field in the 31mm Nagler. I can usually put any object in the field but not centre of the 14mm for the rest of the night. 17mm & 31mm are easy. If I took the trouble to use a crosshair eyepiece I could probably get it more accurate. The Nexus has ALT AZ guidance readouts to 0.1 deg. Sometimes it drifts a little by the small hours of the morning. I could re-align, takes a couple of minutes. But I usually just memorise the two offsets in my head and keep going.
Joe
The Nexus DSC has a guidance readout that can be selected for 0.1, 0.01, and 0.001 degree. I prefer the 0.1 degree choice myself as then the numbers aren't continually changing and because it is possible to achieve 0.0/0.0 pointing, but impossible to achieve 0.00/0.00 pointing.
But if the scope tracks, the higher level readout might help attain a higher level of accuracy. Not with 8K encoders, though, which have 2.7' resolution. You're better sticking to 0.1 degree readout guidance. Perhaps with the 1.3 million tick encoders that are also compatible with the Nexus DSC.
I have it set for 0.1. It’s a push to
Cheers
Joe
Amateur astronomer since 1978...................Web site : http://joe-cali.com/
Scopes: ATM 18" Dob, Vixen VC200L, ATM 6"f7, Stellarvue 102ED, Saxon ED80, WO M70 ED, Orion 102 Maksutov, ST80.
Mounts: Takahashi EM-200, iOptron iEQ45, Push dobsonian with Nexus DSC, three homemade EQ's.
Eyepieces: TV Naglers 31, 17, 12, 7; Denkmeier D21 & D14; Pentax XW10, XW5, Unitron 40mm Kellner, Meade Or 25,12
Cameras : Pentax K1, K5, K01, K10D / VIDEO CAMS : TacosBD, Lihmsec.
Cam/guider/controllers: Lacerta MGEN 3, SW Synguider, Simulation Curriculum SkyFi 3+Sky safari
Memberships Astronomical Association of Queensland; RASNZ Occultations Section; Single Exposure Milky Way Facebook Group (Moderator) (12k members), The Sky Searchers (moderator)
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