HEQ5 Pro mount problems.

[Detec]

Hi Guys, I am new here this is my first post. I have a problem that is driving me mad and I cant seem to correct it no matter what, so I need more information from people that know.

I polar align my HEQ5 pro mount, then I star align it ok. I focus the scope , then start doing 1 minute subs. The first image is clear with pinpoint stars, then the second slightly moves diagonally and the stars are not round, then the third image is worse. By about the fourth image the stars are pinpoint again.

Then its starts going diagonally back the oposite way, slightly oval stars then worse stars, then pinpoint perfect again. The the cycle begins again. So I get 2 good images in about six or seven subs. If the polar alignment was out I wouldnt get any good stars.

I have belt modded the mount but this makes no difference. There was a very slight movement in the one axis which I thought might be causing it so I followed the instructions on line which showed me how to fix this. But this also did not change anything.

The scope I am using is a celestron C8. I thought this might be causing it due to such a large focal length so I purchased a focal reducer hoping the new focal length of the scope would make smaller problems for me. But still the same.

Sorry for such a long post, I have one final thing to say. If I use my zenithstar 61 from FLO, this movement problem still remains but is greatly reduced, so I get more good subs.

Is my mount just faulty? Or is this normal?.Or am I doing something wrong? I dont do guiding because I dont have a guide scope or laptop. And the light polution is so bad in my area I dont think longer subs would be any good. Any ideas?

 

 

 

[vlaiv]

Hi and welcome to SGL.

Yes, that is quite "normal" (although we all wish it was not the case). What you are seeing is periodic error of the mount.

Worm turns every 638 seconds and in those 638 seconds - pattern will roughly repeat itself. This happens because gears in the mount are not perfectly round. Yes, you have made a belt mod and that removed some of the gears - but main reduction remains - worm and worm gear and these are not round enough.

There are two things that you can do to fix this to some extent:

1. Guide - this is what most people do. Guiding will sort out mechanical defects in the mount (to a degree - even it is not all powerful, your mount still needs to be decent to guide well - heq5 guides well in 99% of the cases).

2. Do Periodic error correction, or PEC. PEC is process in which you record average "wobble" of the gears over said period of time - and let software play it back in sync to counter act actual error (software plays back reverse movement or correction).

HEQ5 does not have PPEC - permanent periodic error correction like newer mounts, but if you use EQMOD - you can use VSPEC which is nice feature of EQMOD (VS stands for variable speed) - driver itself will slow down and speed up the mount to counter periodic error.

In the end, this is recording from my HEQ5:

Left to right movement is due to polar alignment error - it is uniform drift over time and not as bad as PE. Vertical oscillatory movement is Periodic Error - sometimes it is slow and smooth - and at moments it is fast changing.

You want slow changing periodic error - fast moving is harder to guide out (although here it looks like fast moving - it is really not - each of these frames is one minute long in reality - so my mount guides really well).

[Space Oddities]

As vlaiv said, I'd recommend investing in a guide scope and camera. I've been in your situation, and guiding really helped eliminate the periodic error from my pictures, and drastically increased the # of keepers in your images. Other factors like a passing cloud, a plane or a satellite, wind... are nuisances that we already have to deal with, so it's comforting to know that at least the nuisance of PE can be corrected.

Since I started guiding, I keep 90-100% of my subs, and they all have pinpoint stars. When I didn't guide, this is what I had on some of my images:

 

 

 

A guide scope & camera is an investment, I'd say £200 minimum if you buy new. It also complicates the logistics, since you need to learn a new software, that's one more thing to setup in the field, and you need a computer of some sort. However, that's a worthy investment every astrophotographers makes at some point. Not necessarily to increase the exposure time, but at the very least to increase the % of keepers and thus make your time outside really worth it. Especially in cold winter nights.

With the Z61, a small 30mm guide scope like this one or this one will work just fine. Perhaps with the C8 you would be better off with a 50-60mm guide scope, since the C8 has more focal length and will be more demanding for the HEQ5. I never owned a C8, so I'll let more experienced users share their thoughts.

Altair has some nice bundles, like this one. FLO also offers some guide cam/scope bundles, but most are out of stock right now.

Of course, as you said, you'd need a computer of some sort to handle the autoguiding... You have a few options, with different levels of complexity & cost:

• Use a laptop. If you don't have one, you don't need an expensive or a recent one. Autoguiding isn't very ressource intensive, so any cheap laptop should work just fine. That's the cheapest option, and if you're on a budget, buying it used and dedicating it for astro is a route many people take, and used laptops are very easy to find.
• Use a standalone guider. They're like a guide camera and computer combo, therefore they can be very pricey, but they work autonomously and without any computer. The MGEN version 3 from Lacerta is one, the version 2 is cheaper I think and can be found used. The drawback of these, apart from the steep price, is that you can only do guiding with them. With a normal computer, you can also have other functions, like imaging sequences, plate solving, polar alignment help, etc. So the features per £ ratio is the lowest.
• Use a mini computer that you control wirelessly via a phone, a tablet or another computer. There are different options out there:
  • The ASIAIR from ZWO is one option (I'm using it since a few years, and love it), you just need your phone or an Android/iOS device to control it. It is very simple to use, very smooth, really makes setting up your mount and guiding a breeze. You can guide, focus, polar align and control your mount and camera. However it only works with Canon/Nikon DSLRs and ZWO cameras. And that's £290 to invest on top of a guide scope & camera. The 1st version of the ASIAIR (non PRO) can sometimes be found in the classifieds for about £100. It still has great value IMO!
  • Similar options include Stellarmate ( and Astroberry (a little Raspberry Pi computer, controlled via network by another computer/tablet), they're cheaper than the ASIAIR (Astroberry is even free, you just need to buy a Raspberry Pi computer, which costs around £50) and non bound to a specific brand of cameras, but they don't have a dedicated iOS/Android app like the ASIAIR. Also you need to install the OS and in the case of Astroberry, buy and assemble all the hardware yourself. Still, nice options if you're not afraid of the technical part.
  • Mini computers, like the NUC series from Intel. Older models are quite cheap, you can also find them used very easily. They're great, because you can run Windows on them and install any software, so that's the most flexible option. But like other options, you'll need a tablet or another computer 

So, I'm afraid this is the true cost of having nice, round stars on most of your pictures  Astrophotography is a world of compromises, and definitely not a cheap hobby.

On the positive side, investing in a guide camera also brings 2 extras:

• With autoguiding, you gain access to narrowband imaging, with long exposures. This is a great way to ignore your light polluted sky or image during a full moon. This gives you access to some dim emission nebulae, that would be difficult to image otherwise.
• Guiding cameras are also the perfect tool to do planetary imaging, especially if you already own a C8. This would give you access to the other half of astrophotography, without any additional investment to make. And imaging planets is really fun!

Hope that helps!  

[Detec]

HI, Thanks for that thorough explanation. That makes sense to me. I dont really fancy guiding because my garden is very open to the public, and if I left a laptop outside and I go inside like I normally do, there would be no laptop. So I will look into this PEC that you are talking about.

Thanks for your help.

[Detec]

From what you both say, it seems I have a lot of learning to do If I want better images. Trouble is im nearly seventy and anything I seem to learn nowadays only stays in there for about two days. Chemo brain I think.😁

But thank you both for the extremely thorough replies. Very helpful.

[Space Oddities]

Glad I could help   Yes that's definitely an additional learning curve, in a hobby that already has many. Which might not be what you're after.

If some day you still want to go this route though, then of all options above, and given your constraints, I'd recommend looking into the ASIAIR. It's by far the simplest to setup and to use, and is very beginner friendly. 

Also, this little computer has the size of a pack of cigarettes, and doesn't look like a computer at all, so very inconspicuous. You can control the it with just your phone when you're setting it up, but after that, it's doing its thing and doesn't need you or your phone nearby at all   

[Detec]

I will have a look  at that Pierre, Thank you.