Nexstar 4se

[Roy@Aldermaston]

Hoping for some help, the GOTO on my scope is very inaccurate. Although with skyalign it confirms the alignment, even a large object such as the moon is outside the FOV. I've carefully followed all the setting up advice, including levelling the tripod, but with little improvement. I'm beginning to wonder if the OTA arm is misaligned with its mount, I've noticed that when I slew at a slow speed in a verical direction an object in the FOV moves at a slight diagonal rather than vertically. It's also noticeable that my ccd pics of Jupiter show the bands at a diagonal -tilted down to the left. Does this sound like a misaligned OTA, or is there something that I'm missing?

Thanks,

Roy

[Astro_Baby]

Forgive shabby typing I am mobile.......

Ok there are a few things it might be........

Is the mount level ?

The scope likes to be set up with the arm on the left and the scope on the right looking from the rear.

When using sky align use the Ed dot only for star alignment and pick the stars that are far apart ie one low down in the east, one halfway up in the west and one half way up in the south as an example.

Next when you steer the scope to it's ,target stars with sky align always approach the target in the same way ie from below and to the left. Use the same approach with each alignment star that should remove backlash from the process.

Make sure the stars are well centrex in the scope......a c Ross hair reticule may help.

Those things should improve alignment, the scope you say moves in a diagonal rather than a straight line.......that ma suggest the scope is not well balanced. Make sure the scope is balanced properly front to back and that it is secure.

The diagonal movement could be an indication of something more serious like a gear problem but I haven't ever seen anyone post with a broken down nexstar so I would think that's unlikely.

Hope tphats of some help

[Roy@Aldermaston]

Thanks for the quick response. I've gone through all the usually alignment methods, the tripod levelled, same final GOTO approach to reduce backlash etc, but no improvement. Struck me as a bit odd that the bands on Jupiter are not horizontal as they are on all them other pics that I've seen. I'll try rebalancing the OTA, but I heard read on another forum that some 4 and 5SE mounting arms are out of alignment.

Roy

[Ags]

The angle of jupiter's bands changes throughout the course of the night. No particular orientation is right.

I find the 4SE goto is fairly accurate for DSOs - it finds most objects within the 25mm EPs field of view, if the objects are not too far from the alignment stars. But solar system objects are not found very well - I always have to slew to these manually. The moon is the fastest moving object in the sky, so it is the hardest object for the mount to find, not the easiest!

Once I've got something in the field of view, the tracking is fairly accurate, but you have to make sure you don't suffer from backlash. To fix backlash: for example if the object is drifting to the left, pull the object back past the centre, then reverse direction to bring it to the center. If you don't do this doubling-back trick, the backlash will just make the object drift off again. Maybe that is just my mount.

[cgarry]

Hi Roy,

Are you powering the mount with AA batteries or with an external power supply/power tank?

There have been many reports of accuracy problems when AA batteries are used.

Chris

[Nexus 6]

Roy,

try using the 2 star align to see if that helps. You just have to know a handfull of the prominent stars that are visible to you. As has been mentioned, if you are low on power that will cause the align system to track inaccurately.

Alan

[Roy@Aldermaston]

Thanks for the helpful replies. As for power, I'm using a 12 volt mains adaptor. The scope tracking is fine one I have centred an object after the GOTO has missed it. What worries me is the curious angular offset from the vertical of an objects movement when slewing in altitude. I've noticed that even with moon pictures, using lunar tracking, my view is tilted by several degrees to the north-west when compared to a moon map. The tripod has been levelled using a builders level, the only thing that I'm uncertain of is the OTA balance. Following advice from another forum, I've set the OTA to be back-heavy and though I'm not sure it seems to me that the accuracy has been worse since then.

Thanks,

Roy

[rowan46]

get yourself a level like this NEW! 360° TRIPOD / TELESCOPE ALIGNMENT BUBBLE LEVEL on eBay (end time 08-Dec-10 22:09:50 GMT) attatch it to the base of your mount and level the whole thing together get the tube properly balanced when you put eyepieces camera etc on it that will make it slightly back heavy which is what you want. you may find this site useful http://www.nexstarsite.com/index.html and the book is very useful it tells you about marking the mount etc i hope this helps somewhat and do try 2 star align its much simpler and seems to be more reliable. my nexstar takes about 3mins to get set up using 2 star align i dont know many stars but its easy to learn enough to to do 2 star align no gps co ordinates to input its much quicker

[Roy@Aldermaston]

I've taken your advice and ordered the bubble level and I will try a two star alignment. Having said that, I'm confident that the tripod was level and still puzzled why the up and down keys move an eyepiece object at an angle from the vertical instead of precisely vertical, and why my pics of the moon are not vertical.

Thanks,

Roy

[rowan46]

i am not sure what you mean by a vertical moon, but you are right that the up down buttons should take it in a vertical direction. is it possible that your tripod and mount isnt as level as it should be if its down on one side that may be whats taking it diagonally the mount should only move on 2 axis so a diagonal movement shouldnt be possible unless both drives are engaged.

[tinvek]

if you mean the scopes up and down is not directly up and down the face of the moon and that the moon appears to move left or right as you go up or down, then probably your mount isn't level, if you just mean the features of the moon, then just like jupiter, their orientation alters depending on where in the sky the moon is

[rowan46]

i think ive clicked about what you mean by a vertical moon i dont think thats anything to worry about my guess is that a moon map is orientated north to help with navigating it. i would guess that the earths tilt is responsible for for the moon appearing non vertical but mo doubt somebody who knows what they are talking about will put me straight.

[rowan46]

thanks tinvek beat me to it and explained it better

[Roy@Aldermaston]

Thanks for those answers. You've obviously guessed by now that I'm new to this, and it sounds as though I'm creating a problem where one doesn't exist! I had imagined that the vertical axis of the moon would always be aligned north-south when viewed from the earth - obviously not. I spend a lot of time working with maps, and I suspect my error comes from being used to viewing things in two dimensions with a fixed terrestrial grid.

I take care to ensure that the tripod is level, and as soon as the skies clear I'll try a two star alignment rather than the sky align method.

Roy

[sixela]

Well, "North" is in these charts (roughly, for planets and the moon) facing the North celestial pole, while West is in the direction of natural movement in the sky.

It takes some time to adapt to the nomenclature (these concepts have something to do with your N, E, S ,W azimuth directions but aren't identical).

Just to give one example, when facing North and looking at the meridian (the line connecting your North azimuth on the horizon and your South azimuth on the horizon and passing overhead), North is "up" for everything under the celestial pole and "down" for all objects above. If you then face South, North is always "up" (which is actually the direction that corresponded to "down" when you were facing North).

That the N-E-S-W star is mirrored on star charts with respect to what you see on land maps is because on land maps you're looking from outside inwards, whereas when you look at the sky, you're looking from the inside of the celestial sphere outwards.

[cgarry]

If do not have your telescope's star diagonal pointing straight up, something you might do to make the EP easier to look through from a chair, then the up/down buttons can make objects in the EP move at angles or even move left/right. The whole image appears to be rotated but it is actually because your eye is rotated with respect to the EP.

Just thought I would throw that in to confuse things!

Chris