Skywatcher AZ GOTO alignment and accuracy

[DrRobin]

Hi,

Nothing wrong with a bit of veroboard and the bluetac is an interesting idea, I would have tacked them down with glue, but the end result would just be the same.

I started as a hobbiest, wanted to get into short wave radio and couldn't afford a set so bought a kit and my Dad taught me to solder. I now design electronics and systems for a living, concentrating on rf, circuit and system design, but know a bit about processors and some low level programming, mostly the stuff at the hardware level.

If you ever need any help with a circuit, values or simple just some ideas give me a call. I would say that over half my job used to be interfaces between systems (test, measurement and control) and processor or micro-computers, so have lots of experience with RS232, RS485, TTL and parallel interfaces, together with some of the more obscure industry buses.

I will try and finish my USB focuser in Jan and post some pics.

[mindburner]

HI

I appreciate the offer on the electronics help. I will probably have to take you up on that at some point as I am just about to try a USB relay to operate a Nikon remote shutter cable. I could just use the cable but like the idea of remote controlling it through the PC.

That's a pretty good range of electronic and control knowledge you have. I am from an AV background but big into analogue synthesizers. That is where I learned a bit about circuits. My brother was also a tinkerer and showed me how to solder. It's a skill that should be taught in school:)

[Clayton]

I just had a go at my backlash on the 14"

It took me a while to realize what it was doing, and after that not long to adjust it.

In the end it was a simple matter of using cross hairs on a distant object and taking a stab at a number for both Alt and Az. I began with 30" each and doubled or split the difference each time.

Alt after a few iterations ended up at 50" and Az at 2' 25"

You can tell if the value is too low by the delay in response, and if it is too high then the scope moves too rapidly for a short time before slowing to the slew speed (1 in my case)

Still to trial it in the real world but I am happy that it is much more responsive.

[DrRobin]

Hi Clayton,

Sorry for the late reply, it's been a busy old time since I came back from holiday. The idea of splitting the difference is the fastest way of finding an unknown value and is called a Fibonnaci search after the 12 century mathematician who invented it. I know this as I used it in a computer program in the early 1990s which eventual gained a patent, but that's another universe away.

Still pleased that you have managed to get your mount and scope working a bit better.

I have an admission to make, as you will see from my signature I have bought an EQ6 and 8" Quattro and ordered a C1100 Edge, so the the 10" dob has to go, my missus has orderd. This is a move away from visual and the planets to DSO long exposure imaging and I can't keep too many scopes.

Chris, did you get your mount back and is it okay? Did they fix your problem?

I want to thank everyone on here for their input, all posts have been useful to build up a picture of how these mounts work and how to improve them. I will keep looking from time to time but without a mount it might be hard for me to try and advise.

Good luck everyone.

[SeedyF]

Hi Robin. I got the base back on Friday but not the old one its a complete replacement. The delivery mote just apologised for the fault.

I tested the accuracy of the slew away and return in the daylight and it was spot on. I looked at the sun through my home made filter then left it tracking the sun for about an hour and it hardly moved in the 25mm eyepiece. All seems well so far but no decent clear sky to try allignment and goto as yet. Forecast later in the week looks good though.

[DrRobin]

Hi,

Hey that is great, fingers crossed your new base will be okay, just a shame it took so long for them to get a new one. It sounds like it is tracking really well now.

We have reasonably clear skies here, there is some high cloud showing on the satellite picture (Met Office: British Isles: Infrared satellite imagery) but outside it looks pretty clear.

I am still at work, trying to get finished off and then I want to try and finish my USB auto-focus (the focus knob from my scope is here) and try and get home and have a go.

I have a new mount now (EQ6) and a new scope (8" Quattro) and I am finding the polar alignment harder than I had imagined.

[SeedyF]

Robin

As it turned out it was clear all evening yesterday down my way too so I went through the full set up and star alignment and used the goto to select objects and it was perfect. Even using a 10mm eyepiece I had objects appearing in the centre of the field of view. So after 4 months I was finally able to appreciate the extra aperture, I have to say I am really pleased with the power of this scope. I was able to see a number of open clusters that I would have little chance of finding in the light polution over my house but the Goto gives me access to them. And the huge number of individual stars the scope is able to resolve with a 25mm eyepiece is incredible.

Maybe Thursday/Friday I can start with some simple imaging if the forecast holds up - at last! That will really test the tracking.

[SeedyF]

PS - the USB focusser sounds interesting! Going back to a manual focus with this scope is a nightmare compared to my old electronic one on the previous scope so I'll follow your progress with interest

[DrRobin]

Hi Chris,

That sounds like you have cracked the tracking issue. The other thing I think is critical to these dobs is to make sure that the base is as level as you can manage. I don't think the star alignment makes any compensation for levelling errors.

I put a concrete block in the ground on to which I sat a table that was as level as I could possibly get it.

The last time I had a go at Jupiter with a 250mm dob, DFK camera and 5x Televue converter, I could keep Jupiter in the frame for 3 - 4 minutes with only minor adjustments. I couldn't even manage that with a 3x converter a couple of months ago.

I tried long exposure with my dob, I could get 60 seconds before star trails started showing, throwing away about a half of the images and could get 90 seconds, but throwing away most of the images. Ultimately, I decided I couldn't guide with the dob, hence the move to an eq6 mount.

I had a great night last night, didn't finish my USB focuser, so took the manual focus bits home and fitted it back on my scope. After another long session polar aligning and star aligning my eq mount I had about an hour of imaging on M42 and just as my battery went flat M31. I was very pleased with the results of M42.

The USB focuser has been under construction for the last 3 months, it is a design from a chap on UKAI (Sharpsky) who is in the UK and very helpfull. I have nearly finished mine, all of the elctronics are done and I just need to complete the bracket to hold it to the focus knob on my newt.

[DrRobin]

Hi Chris,

By the way I upgraded the focus on my 250 dob to a 10:1 dual speed using a [low?] cost kit from Modern Astronomy. It replaces one of the knobs, works really well and cost 50 quid. Don't know if you hav done this but it is well worth it.

[SeedyF]

Robin

I had read about the levelling issue before I got the scope. My first project was to build a low platform with adjustable feet so I could get it really level. I then marked the patio where each foot should go so I can get the platform rock solid every time. I still keep a bullseye level on the base to check though One day the platform will serve its purpose better when I take it somewhere else and have to adjust it!

I had been looking at getting the skywatcher electronic focusser - £50 on FLO, it's what I had on the old 150 Explorer. I definitely need something that does fine focus.

[DrRobin]

Hi Chris,

I had a look for some adjustable feet, without too much success, so cut a hole in my decking and sunk a big block of concrete, on to which I sat a very strong, highly modified table from Ikea. My bullseye says its level, probably to within a couple of degrees and my spirit level reckons its level as well.

Interesting, now I have an EQ6, getting the tripod level doesn't actually matter, it's sorted out when you polar align. I also think that the EQ mounts correct for all errors when they are aligned with a 3 star alignment. Pity Skywatcher didn't do some thing similar with the AZ mounts as well. A two star alignment on EQ mount doesnt correct for all errors and that is the only option on Alt/AZ. That said, if your base is level or near too it, I think the errors are small.

I would recommend the 10:1 focuser from Modern Astronomy, it's 50 quid, but well worth the money and then fit your electric focuser, or make a Sharpsky or similar. I have never fitted an electric focuser to mine (didnt get it finished in time) but the 10:1 has never let me down. Under high magnification the scope wobbles for bit after touching the focuser, but every scope I have owned does that.

When I fitted an electric focuser to my 127 Mak it was a revelation, so I understand where you are coming from.

[mindburner]

hi robin

this is slightly off topic on this thread but I have just got the lignmaster program to help with polar alignment. It seems very good although I have not had a chance to ty it out properly yet. I have had good results with EQmod. It's well worth a look although some folk do not like having to get the laptop out and such, but most will be imaging and using a laptop anyway.

regards

[DrRobin]

Hi Chris,

I will have to look at that, thanks.

[peter_w82]

Hi guys, just thought I would post a comment on here. I've been following this thread for a while and it's been really interesting and useful to read when deciding whether to get the GOTO Dob or not!

At present I am planning on getting the SkyWatcher 250px Flextube GOTO Dob. I was considering a 200 on an EQ mount but I am not really that bothered about the photography side of things and I think I would prefer the extra aperture as I mainly want a scope for visual use.

My only worry is that it seems that the tracking / goto can be a bit temperamental and I don't want to spend £1000 on a scope that can't track very well. I know a very level surface seems to help but my patio is uneven sandstone on one side of the house and a gravel drive on the other!

SeedyF I am guessing I would need to make an platform with adjustable legs like yours. Can you give me any advice on this? like where you brought the adjustable legs from?

I am thinking of buying a laser collimator at the same time as the scope as lots of people recommend these for saving time, is this true? Also is there any other essential items I should I buy with the scope for first use?

Thanks Pete.

[mindburner]

Hi to be honest after buying the 300p dob with tracking, I think it's great but the eq mount is better. Even if you are just doing visual, you might want to try some Planetary web cam images. The eq is far better for this. Better for general visual use as images stay in the eyepiece for much longer. My advice would be get an eq. my 127 refractor is Nearly as bright as the dob and sharper plus with rock solid tracking

[DrRobin]

Hi,

I agree with Mindburner, an EQ mount is always going to track better than a dob, but there are a few things to consider:

Your eq6 pro costs close to £1,000 and you will need an eq6 for a scope of 250mm. You might get away with an HEQ5 (£750) but a 250mm scope will be too heavy for imaging, so doesn't that defeat the object?

A decent 250mm scope is going to cost upwards of £500.

I am finding EQ mounts take much longer to set up and align than my old dob.

Lifting the weight of a 250mm on to an eq mount is much harder than lifting it on to a dob.

My eq6 weighs 23kg, plus 10kg for the two weights, which I remove before moving the scope. A 250 dob base weighs about 14kg.

So an eq mount is going to perform better, but there is a trade off. Reducing scope size is fine for visual but you do loose a lot of light gathering capability and exposure times, even for the planets, increase with a reduction in aperture.

I have just swapped from a 250 dob to a 200 newt and noticed straight away an increase in exposure times on Jupiter.

Once I had set the clutch nut on my dob and balanced the scope it will hold Jupiter in a webcam and 5x Barlow for around 2 minutes. I never tried it just in an eyepiece, but after aligning and before imaging Jupiter hadn't moved at all and it often takes me 10 minutes after alignment and before getting going with the camera and Barlow.

So a difficult decision £1,000 on a 250 dob, Synscan or you could get the Skywatcher 200p on HEQ5 also with Synscan. The HEQ5 is at least on a tripod, so easier to level on uneven surfaces. The 200p is probably just too heavy for an HEQ5 for long exposure astrophotography but would be great for the planets.

So my advice, if you want to get the biggest aperture for your money and you want to use it for visual and photos of the planets I would go for the dob.

If however, you want to use it for visual, photographs of the planets with the option of getting into long exposure photography of galaxies then the 200P on a HEQ5 would be the way to go.

Finally regarding you question about a laser collimator, yes they are much quicker and more accurate. Even with a flex tube dob I found that I didn't have to collimate more than every couples of months, but I would still go for a laser.

[peter_w82]

Hi Guys,

Thanks very much for your replies, your comments are very helpful!

Unfortunately like with most things, this one is going to come down to money and what I can afford. My maximum budget is definitely no more than £1000, which basically means the 250 Dob or as you say the 200p on an HEQ5!

I am suprised by your comment about long exposure on the HEQ5 as I thought the maximum load for that tripod was almost twice the OTA weight of the 200p, which I just assumed (maybe foolishly) would be enough?

I was also wondering about the difference in the visual image between the 200 and 250 scopes as this is probably the most important thing to me! Someone in another thread said that the extra 50mm gives 5x more light gathering ability, does this make a big difference to visual observations or is it more of a benefit for astrophotos?

I also appreciate what you said about the extra weight of the EQ mount and taking longer to setup, this seems to be a winner for the Dob. Could you also tell me about the operation of both scopes, e.g. which gives the most hassle free viewing experience in terms of looking into the eye piece etc?

Thanks again for your help, your comments are very much appreciated!

[DrRobin]

Hi Pete,

An HEQ5 will take 18kg. *A 200p weighs about 10kg, but you need to add a little bit for the finderscope and eyepiece, so nearer to 60% of the capacity, but probably still okay.

Dobs have another advantage, the eyepiece position remains in the same place. *It goes up and down and round but it always stays in the same place and in a comfortable viewing position.

*A newt on an EQ mount rotates around the polar axis so at any time the eyepiece might be at any angle, even upside down. *You can rotate the tube in the rings (see Astro Baby's website) or just decide on what you want to look and make sure the eyepiece is in a comfortable position before aligning the mount.

EQ mounts do have one other advantage, they are versatile. You could mount any scope on the HEQ5 (up to the weight limit and provided it had rings). *With the Dob, you are limited to what will fit.

So in summary the pros of each mount,

250 Flextube Dob

Larger aperture, 50% more light than a 200

Quicker to set up

Lighter, easier to move and store

Eyepiece always in a comfortable position

200p on HEQ5

Superior tracking

Versatile

Best for astrophotography*

It's a really tough decision, but I think for you the 200p might just have two advantages which would make it more suitable, it's ability to be set up on any ground ( the tripod can easily level the scope) and its versatility/better tracking.

I would offer the final advice, find a nearby shop that has both set up and go and have a look at the size and weight. *And/or get 5 more opinions from people who have owned the scopes, or preferable both as anyone who owns one will always prefer it to the other.

I hope this helps

[DrRobin]

Hi Pete,

When I wrote the last post, I meant to ask you what you currently use, it might help if you look at what you like and dislike about your current set up.

Sorry I didn't really answer your specific questions.

Is having a larger aperture only useful for photography? No, it's always a benefit unless the object you are viewing is really bright (like the moon and possible Venus/Jupiter) then you might have to use a filter to reduce the glare.

Which gives the most hassle free viewing experience? The eyepiece stays in the same place with a dob, but in an EQ setup it does rotate round the polar axis. You can move the tube round in the rings but it's a bit more hassle.

I still think you have a tough decision and suggest visiting a local shop where they have both. I considered buying a 250 or 300mm dob until I went to a shop (there aren't any around here, so had to have a look when I was away for work). The shop had a 300mm dob and boy was it large. It made my mind up to go for the 250mm.

Are you close enough to any of the shops?

Both are good scopes and both will serve you well. Like most things they just need a bit of time to set up and maintain.

[peter_w82]

Hi Robin,

Thanks again for your comments. I am pretty much new to the astronomy scene so I don't own any equipment at present except for a very cheap refractor that I have had for years.

I definitely agree with you about seeing the scopes in real life as I am finding it difficult to decide based on pictures / descriptions alone! Unfortunately I live in deepest darkest Dorset, which although has great viewing conditions also lacks telescope shops. I am considering a trip to FLO as I believe they are based in Exeter, which isn't too far away but I am not sure if they have a proper shop there?

At the moment I am leaning more towards the Dob as the easy setup / storage / operation definitely does appeal to me. I also like the thought of getting as much aperture for my money as possible. I know the tracking probably won't be perfect but as I mainly want it for visual use I suppose that isn't a deal breaker if it's reasonable?

My main concern at present is being able to find a level surface for a dob as I mentioned earlier I have a gravel drive, which is level in places or a level patio but with annoying uneven slightly raised sandstone slabs to choose from. However I don't know how important it is to have a 100% perfectly level surface with these GOTO dobs?

Thanks for all your comments so far! This forum has proved to be invaluable.

Pete.

[DrRobin]

Hi Pete,

It hadn't really occurred to me that they might not have a shop, but I just checked their website and they might not have one? I bought a scope from FLO recently and they were very helpful, they also sponsor this site so my best advice is give them a ring and see what they can arrange.

Once I got the clutch nut set on my dob and the tube near balance it tracked very well. Perfectly adequate to capture Jupiter with a webcam and 5x Barlow for up to 2minutes without adjustment.

Mind, touch anything on the scope and I had to wait around 30 seconds for it to settle down.

Visual usually uses a lot less magnification and I think that even in a high powered eyepiece you would keep targets in view for 5 to 10 minutes without too much problem.

There doesn't appear to be any adjustment in the alignment procedure to level the base, but most people reckon if it is within 5 degrees it will be okay. Again for fine tracking under high magnification it is more important but for visual use you wouldn't need to be quite as accurate.

I bought a butchers block table from Ikea (about £35), chopped the legs down and it made a great platform to sit the dob on. Have a look on this thread, it might give you a few ideas for making something for your gravel.

http://stargazerslounge.com/discussions-scopes-whole-setups/160082-compact-observatory-even-wife-approves.html

I would prefer to sit a cheap (but solid) table on uneven ground than my new shiny scope.

[tteedd]

Hi All

Used to have a goto Mak 127 and I sorted out the problems with that but when the 10" goto Dob came up second had at virtually half price I had to go for the increased aperture.

I have had all the problems itemised in this thread.

Balance - I used magnetic blocks designed to hold signs on taxie roofs.

However it has spent most of the time I have had it with Astronomia due to sticking Az and jerky tracking.

Luckily it was with me not Astronomia when they recently stopped trading, but now I am on my own.

The current situation is that it tracks smoothly but:

When you use the handset to change position in AZ it moves a little stops but eventually moves on if you keep pressing.

Goto is rubbish (although it was reasonable before Astronomia cured a jerky tracking problem).

Where do I go from here?