Nexstar 4SE GOTO inaccurate

[Roy@Aldermaston]

Hi everyone,

I've had this (my first scope) for a few weeks now, but owing to the poor weather I've not had a lot of practice time. However, I've carefully followed all the GOTO setting up advice - avoiding batteries, adjusting backlash and balance, levelling the tripod and carefully centring stars - but the alignment accuracy seems poor. I'm still very much a beginner and I can never be confident which of the stars in the FOV is the star selected in the list of named stars catalogue. Its rare for a selected star to appear anywhere near the centre of the eyepiece, even if I get the scope to go back to one of my alignment stars its way off centre. If I GOTO a planet -say Jupiter its well outside the FOV. Is this likely to be lack of practice - there seem to be so many reports of how simple it is - or do I have a faulty scope?

Thanks,

Roy

[rowan46]

hello roy it may be there is some fault with your scope but its probably as well to recheck your alignment routine its amazing how easy it is to do sonething wrong till you get the hang of them. I also find that the 2 star align works best i don't know what i do wrong but 3 star never seems to work right. check the scope is level with the horizon. I have marked this whilst on a level surface and then just align the marks . this site may help http://www.nexstarsite.com/ when aligning get the target as central in the highest power eyepiece you have. and hopefully this will work for you

[Roy@Aldermaston]

Thanks Rowan,

Like you I have found the three star alignment difficult and I follow the method given on the nexstar site for the two star alignment. I do wonder if the problem is my inability to centre the alignment stars precisely in the centre of the FOV - I'm thinking of getting a cross-hair eyepiece to see if that will help. Truth is its been so cold recently that the eyepiece fogs up making it difficult to be sure of the centre! I'm just hoping it isn't a problem with the scope itself. I read posts on another site about some of the 4SE/5SE tube assembles being miss-aligned with the base - although most posts were dated to 2007-2008 and none referred to recently bought scopes.

Roy

[rowan46]

if you defocus the star slightly whilst aligning it may help in centering I find it easier to centralise a ring than a spot (perhaps thats just me)

[Bigwings]

I always use 3 star align. Check in your setup which way the scope approaches its GOTO mine is set moving to the right and up as seen in the EP. Its important that you use the same approach when centering your 3 stars. Make sure that the time set is accurate and the scope is level. My scope still seems to be off to the right a bit as seen in EP but this is consistent so I know where to look if the object does not appear after a goto.

Even with a fairly good GOTO it helps if you use a finding EP (40mm) which gives good wide views and when the object is located change .

Its a good system when you get the hang of it.

I use a 12mm lighted reticule EP for centering.

[valleyman]

Have been having the same problems with my 5SE. it just would not align properly.

outside the view of my 40mm.

With a 3 star align it would be of to the left of Jupitor, and with a 1 star align it would be of to the right, very frustrating . So I went to the Celestron web site and checked the Knowledge base for info.

I found a article about Flashing the handset and motor drivers and followed the instuctions(This is basiclly ensuring the handset is up to date with the latest information). After flashing the handset and motor drivers I went out and did a few test alignments and now have 3 star alignment (using a 12mm EP ) bringing Jupitor within my 25mm EP . not in the center but near enough.

here is the link

How do I program my flash upgradeable hand control? What about motor control upgrades?

Hope this helps you

[Earl]

Is your time and location set correctly?

[dmahon]

From personal experience - this goes for Skywatcher scopes, but Celestron ones should be similar (unless you have it in Alt-Az mode, in which case the park position is probably level and north rather than pointing at Polaris):

Start with a wide angle EP.

At the end of each session, PARK the scope. First time round turn it on, align on something, then park it, and turn off. Manually move the scope to the park position - pointing pretty much directly at Polaris in the centre of your EP. Each time you set up and polar align, point the scope at Polaris before you turn it on to begin the alignment - it will be fairly close on the first named star.

Named stars in alignment routines should be really obvious - they are much brighter than any of the other stars in the viewfinder. Centre it in your wide angle EP, then move to a narrow angle EP and do the same. An illuminated crosshair EP will get it bang in the middle.

I can align like this, then I am spot on in the centre of my camera chip for the rest of the evening.

[brantuk]

Ensure the tripod is level and on firm ground. Learn where the winter triangle is and use those as your three alignment stars (or any triangle of stars you are familiar with). I suggest the winter triangle because they are the first stars you see as dusk turns to night. At least be sure you can identify your triangle and slew to each star without goto. Make sure your tube and finder are accurately aligned. Use an object 2-3 miles away for this (e.g. top of a pylon or church spire). Make sure you have your exact location and time keyed in (switch off daylight saving).

A 25mm ep should be ok to do the initial alignment (assuming the above). As you find each star - swop a higher power ep into the focuser (eg 12mm or 10mm) and center it before hitting the "Align" button. Allways use the same "approach" with each star aligned (I use up and right).

If the goto isn't accurate after those steps - recheck the levelling. Try a bigger triangle of stars. Program the approach. Ensure all the setup is put together firmly without undue lateral movement in any joints. Check the leg extensions are locked firmly. Ensure you remembered to lock the clutches.

If I think of anything else I'll post it here

(if you're outside for a long session then the alignment may drift slightly after 2-3 hours. You can redo the alignment or replace alignment stars as you notice stuff going off center - allways keep a well spread triangle)

[Questions]

When 1st alinging the finder scope to your viewing scope, start with the 40 to get it centered then use a high power to recentre, this helps a lot.

And also (as the other poster said), defocus so the stars turn into a ring make the ring fat and you can get a sense of how centered it is.

[Capricorn]

You don't give a great deal of information, is the alignment star not in view because you have picked a 10, 15 even 20mm eyepiece. As the field of view is the EP FoV/Mag on a 4SE the actual FoV will be small.

A 20mm EP will have a 0.75-0.8 FoV. You will have to be very close to due north for the scope to get the first alignmet star in. Even a 32mm EP would only give 1.25deg FoV.

Note that if you centered Polaris and used that as due North then it is I think 1.2deg off of due North so if 100% accurate the first alignment star would be out of the field of view with a 20mm.

I Have a Meade 105 and have the same hassle. Bought a 40mm EP to help. Still needs a very accurate set up. Now have several WA EP's as well.

No mention of a finder in he post, These help, I have an RDF.

[brantuk]

The 4SE comes with a "Star Finder" RDF unless it's been changed.

[Ags]

I don't think getting the star in the exact center of the field when aligning makes any practical difference. The difference between nearly in the middle and exactly in the middle is a tenth or less of a degree, these being the endpoints of an arc stretching 90 or more degrees across the sky. So I don't really bother with being fussy on the initial alignment.

Secondly, three-star alignment is not more accurate than two-star methods. The three star method uses the three points to identify the points and then uses the best two points for alignment.

Many of the objects that can be GOTOed with the 4SE are not visible in the scope even under ideal circumstances - they are just too faint. Perhaps sometimes your goto is accurate but the objects cannot be seen?

I find the goto function inaccurate with planets and other solar system objects (although I have not tried flashing my handset). But once I have given it some manual correction, it tracks OK.

Good luck!

PS: I think if you did a two star alignment, you could try going back to your aligment stars. If the mount is operating correctly it should find its way back to the aligment stars. You can't rely on that with a 3-star alignment as it does not use all the stars for alignment.

[Demonperformer]

My first guess at this time of year would be the date has been entered DD/MM/YY instead of MM/DD/YY which it requires (it becomes easier after 12th of the month!)

[Roy@Aldermaston]

Thanks to you all for the many replies,

I thought that it might help if I listed my set-up and alignment steps and the things that I have tried to improve the accuracy.

Tripod - legs, accessory tray all fitting tightly and levelled

Date and time - mm/dd/yy, 24 hr universal time

Location - lat/lon from hand held GPS

Alignment - auto 2 star, as far as I understand it skyalign only uses the third star to confirm the first two. I use Vega and Capella, which are the most clearly visible from my location. They are located in the 25 mm eyepiece and then defocussed and centred in a 10 mm Possl. The handset always reports a success, but if I re-insert the 25 mm and ask the scope to return to Vega (my first star) it is in the eyepiece, but only just in the FOV.

I forgot to mention that I'm using the red dot finder that came with the scope. Its very poor - a huge red dot that sometimes cuts out (I've tightened the on-off screw) and even at the lowest setting is so bright that it obscures the star that its aimed at. I've aligned the finder using the reticule projected on my laptop by SharpCap ccd software.

To try to improve the GOTO I've flashed the HC and MC firmware to the latest versions and played with the backlash settings, GOTO calibration and OTA balancing. As far as I can tell balancing the tube and adjusting the backlash appear to make no difference whatsoever, although these are frequently cited as critical adjustments. Balancing the tube is an interesting exercise; using the recommended technique, ie, all the usual kit added, tube set astride a pencil and resting on the dovetail there is something like a 2 to 3 cm difference between the point where the tube falls to the rear or falls to the front. Given this, I'm not quite sure how the precise balance point is achieved - I usually mark the two points and then mount the tube so that the index arrows on the mount arm align half way between the two. But then some people suggest re-adjusting the balance point to make the tube back-heavy, others to make it front heavy!

Sorry if this sounds like a rant, but I went for a GOTO because I thought that it would help me through the first steps in familiarising myself with the night sky. It now seems that using GOTO, far from being the simple process that reviewers have suggested, is a sub-discipline in its own right. It was always my intention to use the scope as an introduction to astronomy before, budget permitting, moving on to a larger scope. I now think that the cautious approach was mistake and that it would have been better to have gone for a larger aperture without the GOTO facility. I realise that many objects will be too dim for this scope, but I had hoped that the GOTO would enable me to find a visible object and be confident that I had it correctly identified. As things stand I rely more on a star map than the GOTO, and and I think that a finder scope would be more useful than the red dot finder.

Time to stop ranting; in all other respects the SE 4 is a good scope for its size, the optics are brilliant and once I have manually centred an object it tracks well. I have taken some pleasing pics using Celestron's NexImage ccd camera. If anyone is interested in seeing what this little scope can do, I'll upload a pic of Jupiter taken last month.

I hope that I haven't gone over the top because I am really grateful for the feed-back.

Thanks again,

Roy

[Ags]

If the goto can find its way back to the alignment stars, it should at least be able to find targets near those stars...?

You seem to be following a very thorough alignment procedure. One thing I'm not sure about is whether you need to have daylight saving time switched on or off - I remember I had to change it recently but I can't remember which way... :-(

I've been quite conservative with the acccuracy of my goto. What I tend to do is pick alignment stars near to the objects I want to view. When I stray further from the alignment stars, I use the synch function in the new area I am looking at, or even go into the alignment menu to swap the alignment stars.

I've tried using the 'accurate goto' function, but it always asks me to center on an obscure named star, so I give up soon enough! With a little forward planning (learning the names of stars in a target constellation) I'm sure I could make better use of the accurate goto.

I bought a Hyperion 24mm to let me sweep a wider area of the sky when looking for objects, although with such a wide field of view it is not a very good alignment EP. When I'm feeling dilligent I align with a 15mm plossl.

PS: Ditto your point about the NexStar RDF - I'm on my second one now, and it is malfunctioning too, after maybe 3 hours of use.

I'd really like to see the pictures you have taken with the NexImage. You can see my attempts at sketching with a 4SE in the sketching section (don't get too excited!).

[rowan46]

hello roy like you i had problems at first with my nexstar. it turned out to be user error. mine is an older model so I am not sure how much the software has changed my 2 star align doesnt need long lat coordinates and I only need to put in date and time if I wish to find a planet the first time. also for the nexstar 4 it likes to use rt and down for centering this takes care of backlash. there is a book "the nexstar users guide" by michael swanson which I found useful

[Roy@Aldermaston]

Thanks Ags,

I always use a hand held GPS unit to set up the scope and that also gives me the date and time corrected for daylight saving or GMT. The weather has been so cold recently that I'm not able to endure long enough to get enough practice and I'm concious that I make a lot of mistakes. I suspect that this has a lot to do with my growing sense of frustration - patience was never one of my virtues.

Attached is the pic that I mentioned.

Roy

[Roy@Aldermaston]

That's interesting Rowan,

If you mean right and down in the eyepiece then I may have the wrong approach. I followed some advice on the Cloudy Nights forum which said that I should be using right and up, although it was suggested that the scope should be front heavy for those setting. As a matter of interest, what are your GOTO settings - mine are Alt negative and Azimuth positive, is that correct for the northern hemisphere?

Roy

[rowan46]

apparently the direction of travel changes depending on the model nexstar 4 along with some of the other small nexstars use use rt and down. as for the settings my old nexstar doesnt appear to have that although it may be the backlash was already set as i bought it 2nd hand but i am given to understand that every scopes backlash setting is custom. I guess the engineering tolerances are a little higher than on the more expensive mounts

[Roy@Aldermaston]

Hi Rowan,

Thanks for that - more practice needed I think. One point, I notice that you have a NexImage webcam, do you have any tips for focussing. Once I've inserted the camera into my X2 Barlow it takes ages to get a focussed image on the laptop screen - any tips would be appreciated.

Roy

[rowan46]

I use a homemade bahtinov mask to focus but i don't use it much as i'm waiting on an ir filter for the neximage at the moment. my images are not much better than yours a little more detail but much darker . your one is quite nice actually. the trouble with these go to thingys is there does seem to be a learning curve before it all clicks. to this day I still don't know what it was i was doing wrong but as soon as I switched to 2 star align it just worked.

[Roy@Aldermaston]

I hope the same is true for me, providing I don't die of exposure first!

Roy