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Celestron 8SE newbie questions


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Hi all

So, I have been thinking what to get for some months, I know what I should have got but I also know what I was going to get away with 😞

Last Tuesday my wife bought me the 8SE and I had already bought the wedge for it, although having now read a thread on here that says the 8SE mount just isn't good enough to work with the wedge I may have stuffed this all up. However......

Could someone tell me what sort of accuracy I can expect from the 8SE goto system?

I had stupidly assumed once aligned with two or three stars any object chosen would be in the centre of the lens. This does not seem to be the case.

Again, if correctly aligned, what sort of tracking accuracy can I expect to get whilst viewing a star?

 

regards

Trevor

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11 hours ago, Trevor Matthews said:

Hi all

So, I have been thinking what to get for some months, I know what I should have got but I also know what I was going to get away with 😞

Last Tuesday my wife bought me the 8SE and I had already bought the wedge for it, although having now read a thread on here that says the 8SE mount just isn't good enough to work with the wedge I may have stuffed this all up. However......

Could someone tell me what sort of accuracy I can expect from the 8SE goto system?

I had stupidly assumed once aligned with two or three stars any object chosen would be in the centre of the lens. This does not seem to be the case.

Again, if correctly aligned, what sort of tracking accuracy can I expect to get whilst viewing a star?

 

regards

Trevor

I wouldn't worry too much about the wedge at the moment - you'll only need that for long exposure photography not visual - and there will be plenty who will advise you to start with a shorter focal length telescope for that.

Some easy 'gotchas' to check that can affect alignment:

  • Ensure you have entered date/time correctly - especially be aware input might be US rather than UK format (month-day rather than day-month)
  • Ensure you have your location correct -the nearest large town can be close enough but you can enter the co-ordinates for your exact location if you want
  • Ensure you have allowed for British Summer Time

The goto accuracy will depend in part on how well you get your home position set and how well centered you get the alignment stars in the eyepiece. After alignment you should always have the target within the eyepiece view if not exactly centered. Swapping to a higher power eyepiece when aligning can help getting the target centred, as can a reticle eyepiece (something like this would do - or this in stock item at FLO). I was surprised when I first used a reticle eyepiece how far out I was for a star I thought I had centred in a a lower power eyepiece.

If you have a bit more money to spend you could consider something like Starsense which will automate the alignment process for you. IF you search the forum you will find some mixed opinions on its effectiveness - I have one and it works fine for me - it also helps if you have a relatively high level of light pollution which can make it difficult to pick out some of the stars with the naked eye.

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When I had my SE mount I found that the more accurate I was when levelling the mount the better the goto accuracy was. However, I used to use a wider field EP (32mm) first to get the items in view in the EP. This meant that even when any object wasn’t near the centre of field of view I could still see it near the edge. I would then centre the target, then switch to a different EP if required. I always did a 3 star align which always worked the best, but don’t expect all objects to be bang in the centre of view as they won’t always be.

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12 hours ago, Trevor Matthews said:

Could someone tell me what sort of accuracy I can expect from the 8SE goto system?

I had stupidly assumed once aligned with two or three stars any object chosen would be in the centre of the lens. This does not seem to be the case.

Again, if correctly aligned, what sort of tracking accuracy can I expect to get whilst viewing a star?

The sought object should appear somewhere within the field of the 25mm eyepiece.

The tracking accuracy will be good enough to keep the object within the eyepiece field.  You may see some movement initially as the drive takes up the slack in the gears.

I would stress that the 6/8 SE mount is intended for visual use and is not good enough for astrophotography.  The sole exception is that you can try it for planetary imaging, as the 'lucky imaging' scheme is tolerant of mount movement.

It is difficult to align a wedge mount with the accuracy required for deep space imaging (and you don't need a wedge at all for anything else).  The wedge is only really satisfactory in a permanent observatory (e.g under a 16" SCT).   I don't think I need to underline how useless the SE/wedge combination is, even though some opinions may differ.

The bubble level may cause some puzzlement. My kit was second -hand, but the bubble level is stored on the eyepiece tray and placed for use on the machined top of the tripod.   A complication is that this requires you to separate the tripod and mount/OTA, which you may not want to do at all if you prefer to carry the OTA/mount/tripod outside as one lump.  If you have a traditional (long) spirit level, you could try placing it across the eyepiece tray.

Edited by Cosmic Geoff
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I find the best alignment procedure is two star alignment and using "up" and "right" motions to centre them.  Accurate high power centering is very beneficial, tripod levelling, within reason, should have no affect on accuracy.    🙂

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3 minutes ago, Peter Drew said:

tripod levelling, within reason, should have no affect on accuracy.

Except on the 8SE mount that I had I did find (even though people told me it shouldn’t matter too much) that the more accurate I was in levelling the mount the more targets I managed to get successfully in my fov in the EP. :) 

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2 minutes ago, Knighty2112 said:

Except on the 8SE mount that I had I did find (even though people told me it shouldn’t matter too much) that the more accurate I was in levelling the mount the more targets I managed to get successfully in my fov in the EP. :) 

This is often reported and hence the dilemma.  In Michael Covington's "The Nexstar Users Handbook" he explains the levelling "myth".  I've never levelled mine and have had no alignment problems provided that the other procedures are followed.  However, levelling doesn't take long so why not, just don't obsess over it.    🙂

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Peter's comment about always using "up" and "right" as the last movements when centering a star is easily overlooked. The reason is that it takes up the slack in the gears in the same way that normal tracking will. My 9.25 evo mount has a suprising amount of backlash in the gears and failing to do this definitely does affect accuracy.

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I have the much smaller 4SE and have found this site to be a real help https://nexstarsite.com/

Specific parts on alignment here - https://nexstarsite.com/AlignmentFAQ.htm

Generally though, the two star alignment works well, providing you pick stars with some decent distance between them in the sky, time date and location settings are all critical if you want to get the object in the field of view

You can also "replace" the alignment stars if your goto's are being inaccurate (usually when you've moved to a different part of the sky, e.g. south to north) by tapping the align button and following the on screen prompts

In a wide eyepiece most of the time you will be in the field of view

 

One often overlooked thing is the power supply being used, the nexstars are known for being "fussy" when it comes to power so avoid the AA battery option entirely, mains power is best if possible via an adapter and apparently ideally a little over 12v as they are designed to run from a car lighter socket, which are usually more like 13.8v. My little 4SE isn't too power hungry so I use a salvaged 12v adapter from an old broadband router, but maybe something like this would suit you if you don't already have something? https://www.firstlightoptics.com/power-accessories/nevada-ps-08-6a-8a-regulated-linear-power-supply.html

 

Poor power = poor tracking

 

Feel free to ask if you have any more questions and enjoy the lovely 8 inches of aperture, it's a very nice scope! (Plus you can always pop it on an eq mount in future ;) ) 

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And get a dew shield. It should be standard equipment on a SCT, just as it is on almost all refractors.

I have found that levelling the mount is not critical, except for one-star or solar system align.  But you might be placing the mount on an uneven surface, and it's not hard to level, so why not check it?

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I really appreciate all the replies, I wasn't expecting that.

Perhaps one reply from someone taking pity on me........

 

I might try without the wedge fitted then as I won't be trying any imaging for some time.

And hopefully the moon will be making an appearance soon.

 

regards

Trevor

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Wedge removed.

Tripod in the garden and levelled. The most accurate level seems to be the one on my phone.

Exact coordinates entered.

Entered the time but will check again that I didn't mess up BST.

Hope it stays clear tonight but looking OK so far.

 

 

regards

Trevor

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I also ordered the Nextstar user guide II from Amazon, so thanks for mentioning that.

Don't quite understand why the Kindle version is only £1.50 less than the £21 paperback.

 

I have a power supply from Amazon https://amzn.to/3l99WGS

But will bear in mind the comments on voltage, without stripping the scope mount down to investigate the circuitry I am surprised this is an issue.

My to buy list is getting longer...

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1 minute ago, Trevor Matthews said:

My to buy list is getting longer...

Oh yes, this is the start of a long slippery slope here! ;) 

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9 hours ago, Trevor Matthews said:

And it clouded over before I could get the third star aligned.

Hopefully next time will be better.

 

regards

Trevor

Welcome to Astronomy in the UK! And just as you finished packing up, the skies probably cleared again - that's what normally happens for me.

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Looks like you are on the right track 👍

Weather has been particularly dire for astronomy for quite some time, fingers crossed for some clear skies for all of us 🤞

While I remember another handy Nexstar tip, keep a clothes peg handy when using the scope, clipped onto the focus knob it makes it much easier to fine focus! (I know it sounds daft, but it works)

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30 minutes ago, Trevor Matthews said:

I have some 3D printers and found some fine focus knobs for the SE so will be printing one off.

https://www.thingiverse.com/search?q=celestron+focus+knob&type=things&sort=relevant

Excellent news, they are handy for all sorts of bits 👍

May I also recommend to help with focus - https://www.thingiverse.com/search?q=Bahtinov+mask+8se&type=things&sort=relevant

Depending on the size of the printer you could possibly knock up a dew shield too, an essential extra always missed out by manufacturers, although easy enough to make out of a foam mat etc

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15 hours ago, Trevor Matthews said:

I also ordered the Nextstar user guide II from Amazon, so thanks for mentioning that.

Don't quite understand why the Kindle version is only £1.50 less than the £21 paperback.

I hope you find it useful. I got on fine with the Celestron instructions for their mounts (a multi-page A4 booklet). And the Nexstar system is easier to learn that the rival Sky-watcher.   Do you have time to cancel and save yourself some money?

The 2-star auto align is quicker and just as accurate, but you need to know your alignment stars.

Edited by Cosmic Geoff
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46 minutes ago, steviebee said:

Does anyone do the 3D printed fine focus knob for the Nexstar 6SE as l have just bought one as retirement pressie to myself. 

Would it be the same size as the 8SE?

I will be dusting the 3D printers off over the weekend, happy to print one off for you and post it out.

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26 minutes ago, Trevor Matthews said:

Would it be the same size as the 8SE?

I will be dusting the 3D printers off over the weekend, happy to print one off for you and post it out.

Yes, they are both the same diameter. I used to own  the OTA for a 4SE, and also had a C8 SCT, which is the same basically as the 8SE scope. I used an old ribbed roller that I had 2 of which made fine tuning work great on both scopes when put on the focus knob.

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