11 replies to this topic

[Astro_Nic]

Hi everyone

 

Hopefully this is in the correct forum....so many to choose from!

 

So I have a 14 inch OO UK dobsonian on a TEPP equatorial platform.  I need a better way of getting great polar alignment for astrophotography.  Now I have a large aperture dob on an EQ platform, so I'm not expecting 300s exposures or anything and would be happy with 10s TBH.

 

I also have an OAG with ZWO ASI174MM mini, the platform has the ST4 guiding port, and I will be using a ZWO ASI2600MC with Antlia 5nm dual band filter with a view to using it for some DSOs.  Oh and also a Nexus Coma/ 0.75x reducer.

 

So far I have been playing around with placing a laser in a TEPP laser holder that I attach to the RA axis at one of the ends.  I just kinda guess using Stellarium etc where the actual celestial North is versus the North star.  I've been using a ZWO ASI678MC and 2.5x powermate for some moon and planetary action.  Realistically I'm getting about a minute at that mag before the image slowly moves enough that I re-centre and start again.  Probably fine for planetary/moon but not DSO I expect.  For visual on the moon I can have an Ethos 13mm in the eyepiece, wander off and 10 mins later there doesn't appear to be much movement.

 

I want the next level of polar alignment.

 

I was thinking of either the iOptron ipolar electronic polar scope or the QHY Pole Master.  Both have a flat base that I can attach to my RA axis like I do my laser.  I have no real idea how these devices work though and as mentioned, I'm not looking for massively long exposures as with 14 inches of F3.5 I don't think I need it.  I've seen reviews where long exposures with the iOptron is problematic, but hat probably wouldn't be an issue.

 

Will my idea work?  One better than the other?  Any other options?  I'm leaning towards the iOptron becase the setup of the polemaster talks about moving the mount 30 degrees then another 30 degrees to calibrate and I'm not sure this will be compatible with an EQ platform.

 

So my question (after all the waffle above), is will the iOptron ipolar work on an EQ platform?

 

Thanks you very much for your help.  Polar alignment is such a pain!

 

Nic 

Edited by Astro_Nic, 24 March 2023 - 03:48 PM.

[CowTipton]

You should be able to roughly polar align visually and then use your imaging software to get it precise.

No?

[ngc7319_20]

I use an old-school Celestron "Polaris" 8x50 finder scope.  I attach it to the platform on a quick-release bracket for alignment, and then remove it.

[Dynan]

Polar alignment is such a pain!

 

Nic 

Not with SharpCap Pro it isn't.

 

At ≈ 4¢/day, it's one of the best investments I ever made in astronomy equipment.

[wtd1114]

I have used Polemaster and Sharpcap for polar alignment.  I have not used iPolar, but have looked at the instruction manual.  All three work kind of the same way.  All three needs to rotate around the RA axis.  The reason is to find the center of rotation of the image.  As far as I can tell you need to have a clear view of Polaris ( I am assuming you are in the Northern Hemisphere) and pointed in that direction.  You will need to have a laptop or some computer at the mount to take the picture and run the software.  The software takes one picture.  The RA axis is rotated and another picture is taken. With some math the center of rotation is determined by the two pictures.  The software does some platesolving of the polar region to find where the location of the Central Polar point is.  The software will then indicate 2 points on the computer screen.  Typical they are crosses.  You then move your Altitude and Azimuth bolts on your mount to superimpose the 2 crosses over each other and you should have a very accurate polar alignment.

 

Sharpcap is a subsciption program and it uses any astrocamera and a guidescope to take the pictures.  Polemaster and iPolar have a camera device that is included and USB connected to your computer.  Polemaster has different mounting attachments you can buy for different mounts, or you can get a universal mount and then mount it in your finderscope dovetail mount.  I do not know what mounting is for iPolar.  Basically, you need to mount the camera device to your mount or scope and have it point to the polar region.  It just needs to rotate with the mount when you rotate the RA axis to take the pictures to find the center of rotation.

 

So to answer your question- Polemaster and iPolar should be able to help you achieve a very accurate polar alignment.

 

Regards,

 

Willis

[Astro_Nic]

The issue is that this is an EQ platform, not a GEM.  So using SHarpcap or other program isn't an option - It'sa real struggle to get the dob on the mount - limit of my strength, so I don't want to have to lift off the scope, move the platform 5mm, put it back, find out it should have been moved more/less etc and do that a hundred times.  I cannot move the platform with the scope on it - far too heavy.

 

So need something that attaches to the platform base before I add the scope and base.

 

Just need to know if an iPolar attached to the RA plate at the front will work, as these devices are designed to attach to a GEM in a specific way.

 

Thanks

[Astro_Nic]

The platform is a dual axis equatorial photographic platform.  The manufacturers show some great images using 180s subs for the full 110 minutes of each rotation.  So I think it is up to the job, although there are some DEC limitations as mentioned.

 

I attach two photos of how they suggest you polar align.  I was thinking that something like the iPolar would be significantly more accurate, but don't know if it would work.  They suggest it should.

 

 

[Dynan]

The issue is that this is an EQ platform, not a GEM. 

I actually did not realize that. Only using GEMs and CEMs has led me down a dark path. Sorry for the misinformation.

[Astro_Nic]

Trying to understand this!

 

Looking at the pics above, the ipolar will be attached to the RA axis, but in my example, I would have to rotate the camera only in situ - that way it is rotating around the RA axis.  I was thinking I would then move the mount in RA - but that would move the whole camera to a different position.  Is that right or have I got it wrong?

 

Thanks!

[beatlejuice]

You could try this no tool method

 

Eric

[RTLR 12]

Not really familiar with a Dobsonian telescope on an equatorial mount, but in the old days (and many people still use it) we used the “Drift” method for polar alignment. I still use it from time to time.

Stan

https://skyandtelesc...olar-alignment/

[smiller]

Hi Astro_Nic,

 

Another CN member named "Odyssey" does Dobsonian Deep sky with the TEPP EQ platform and gets some outstanding results.   This is his list of equipment:

 

SW Stargate 500P 20"
Meade LightBridge 16"
Triangulum Equatorial Photographic Platform
AsiAir, AsiAir Pro
50/180 GuideScope
60/240 GuideScope
Asi120mmMini guidercamera
Secondary mirror heating

 

I suggest you reach out to Odyssey and I bet you can learn from each other.

 

Cheers,

 

Steven

Edited by smiller, 26 March 2023 - 02:03 PM.