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BIG problems with EQ8

VilleM

By VilleM
in Discussions - Mounts

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VilleM

VilleM

Posted
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So, we bought brand new EQ8 from UK to be shipped here in Finland. Mount arrived, everything seems normal during installation but now as Ive polar aligned it goto is way off!

Ive tried 3 star and 1 star align. Handset settings are correct (Ive checked this god knows how many times). Mount is well balanced, leveled and PA is good enough for visual wich is 99% of things we do on this observatory. Its mounted on solid steel pier and there is little to none image shift due to optics (primary is locked and we use external focuser system).
I cant think of anything else wich might be wrong. Gotos are atleast degree off, in the first try even 15 degrees! However as goto seems to be now a bit more "precice" park position is weird as you can see from photos below. When I disabled encoders gotos seem to be bit better. If I enable them and choose auto home gotos are again million miles off.

So, what would you do? This mount is used in a public observatory for visual observations and educational purposes every week if weather is good so sending it back for months is not option. Ive spoken to SkyWatcher + dealer aswell, they didnt figure it out yet.

meade (1).jpg

meade (2).jpg

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VilleM

VilleM

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46 minutes ago, ChrisLX200 said:

You sure you don't have Daylight Savings enabled?

ChrisH

I stumbled on this on my own HEQ5 and learned my lesson few years back. Its disabled, also this would affect RA only - declination is also affected on our mount.

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ronin

ronin

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Presently can only suggest you power it up and read what the handset says in regards the data you entered, sure there has been cases of the data getting changed by the system. Better you write it dwn and get someone else to read and check it. However having said that the goto should correct for a reasonable innacuracy in position, that is what it is there for afterall.

Also sort of implies the question what is the software version you have , is there a more up to date version and what does (if newer) it fix, or add.

Another is when you received it did you clear everything by a reset or add your data assuming it was already clear. Just for some reason and from posts in general I get the impression that some data sort of hangs round and you end up with your setup and somewhere something is maintained incorrectly. May sound strange but worked in software for so many years you just get the feeling for what is happening.

Just read the mount spec and slightly surprised that it does not appear to have GPS as standard for a mount of that specification. Odd Skywatcher site says it comes with GPS. Which is it on yours.

I guess you are around the Helsinki area not sort of Oulu level or more, just the mount says up to 65 degrees North.

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jambouk

jambouk

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If you can do a sucessful three star alignment then the location (coordinates) and the day light saving stuff is not important for the actual GOTO this time; if you subsequently park and then try to GOTO then the time may be an issue. The time and location are used to help identify stars for the alignment process and to build up a picture of the likely horizon and when targets are below the horizon.

how accurately / closely are you centring the stars during the alignment process? Are you certain you are centring on the correct stars during the alignment process?

Do you have much cone error with the scope you are using? If unsure, try a two star alignment using two stars on the same side of the meridian and then test the GOTO out on that same side of the meridian - then try the GOTO out on the other side of the meridian.

Do you need the encoders on? If the GOTO is better without them does it pose an issue to turn them off?

good luck.

james

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VilleM

VilleM

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On 24.12.2016 at 22:26, Toxophilus said:

Have you got the observatory location correct? not something daft like entering the longitude for the latitude and vise versa.

Yes, Im familiar with Synscan handset settings. I dont think its problem with the settings, Ive checked them so many times and also showed them to other people. They dont find anything wrong in them. Also tried with EQMOD with same results.

Mount parks (without encoders) in the position in the photos. If I use encoders it parks normally but doesnt find anything. When I do 3 star aligment Im using cross eyepiece to avoid anything being off center. Ill try to put another time in it when there is more clear skies to see how it works.

-V

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Zakalwe

Zakalwe

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Have you Have you tried resync ing the encoders? If the mount is moved when powered off the it will think that it's pointing in the wrong part of the sky. Park it's and then issue a resync command in EQMOD, unpark and then try a 3 star alignment.

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jambouk

jambouk

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Given the update, I'm putting my money on either the incorrect stars being centred during the alignment, or there is a shed load of cone error. Yes a three star alignment helps to compensate for cone error, but only helps and if the three stars aren't well picked from the suggestions the cone error compensation isn't great. 

What is the focal length of the scope?

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VilleM

VilleM

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On 27.12.2016 at 00:07, jambouk said:

Given the update, I'm putting my money on either the incorrect stars being centred during the alignment, or there is a shed load of cone error. Yes a three star alignment helps to compensate for cone error, but only helps and if the three stars aren't well picked from the suggestions the cone error compensation isn't great. 

What is the focal length of the scope?

Im putting in the corrects stars, handset suggests only bright ones so there is no real chance of getting it wrong. There is little to none cone error involved, I base this on previous mount we had (EQ6) wich worked just fine. Scope has focal lenght of 3048mm.

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jambouk

jambouk

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It is easy to centre on the wrong star; i've done it when there is partial cloud, getting Deneb and Vega mixed up - anything is possible :) And what is surprising is that the tolerance in the handset is such that I got the other two stars correct but Vega wrong, and it still said "alignment sucessful" but the GOTO accuracy was unsurprisingly awful.

I'm at work so can't type out about cone error but there is loads of stuff about it on the internet. As I though, you are using a long focal length scope and this always challenges even the tightest of star alignments, add in some cone error and it will make GOTO less reliable.

What I do if I am doing a star alignment with a long focal length scope is to centre the alignment star with a low power eye piece, then drop in a reticle one on a barlow, so the 12mm reticle effecticely becomes a 6mm or 4mm EP and centre again. Another important thing I think is to end the centring always with the same manouver of motors; my last actions to centre the star are to use the right and up arrows ALWAYS, to minimise the impact of backlash on my alignment - again people with a 600mm focal length will poo-poo this, but at nearly 4m it makes the difference as to whether your subsequent targets are in the FoV or not when GOTOing. 

Read up on cone error and I think it would be worth trying to work how hw much you have. You probably have cone error correcting screws on the dovetail - if it is possible i'd aim to reduce your cone error as much as possible. It's relatively easy to do in day light if you've got a very distant horizon object, else use Polaris at night.

James

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