OAG and Extension Tubes

[Shano592]

Hi All,

I would like to invoke the brains trust for a moment, if I may.

I have the LX200 10-inch scope, and for imaging I have been taking short frames through an EOS50D unmodded or EOS20D modded, setup on a T-ring. No problems there, aside from PEBTAG* issues.

However, I also have an Off-Axis Guider that has been sitting idle in my kit for several years.

Also, a couple of years ago I bought an appropriate webcam and had the LX-upgrade done to it. This has pretty much sat next to the OAG since then.

The LX has a wedge, which doesn't get used a lot, but I am wanting to change that, and try to get some guiding going. Software and hardware are covered, mostly. My big issue at the moment seems to be spacers for Off-Axis Guiding.

Do I space the webcam, or do I space the EOS? The reason I ask is because finding 1.25-inch extension tubes is pretty hard. I can find a lot of 2-inch sets. Bintel has a Televue set, and there are several on Aliexpress and eBay.

For those who have walked this path with similar setups, how did you proceed?

FWIW, I haven't set this up as a whole yet, but I am planning to this weekend if the weather holds, just to have a rough idea of where things are.

Also, at this stage I wish to pursue OAG rather than a separate guide scope. I value Don@Bintel's advice, and this was his recommendation with such a long focal length (2.5m).

Thanks all. Parking will be validated on the way out.







* Problem Exists Between Telescope And Ground.

[Merlin66]

Shane,
You don't say which OAG you're using.
I had an effective OAG on the Lx200 10" and 12".....
The process is to focus the imaging camera first and then find the guide focus, best done during the day on a distant object.
The chances are you will need some spacers for the guide camera.
(edit) the attached images (not mine) show the typical OAG set-up and the FOV overlap.

[Shano592]

Thanks Ken, I thought that might be the process.

I am using a Meade OAG.

The primary imager (DSLR) bolts on to the 2-inch T-Ring connection. The LX Webcam would hook in to the 1.25", off-axis section.

This is the problem though. 1.25" extension tubes seem to be hard to find.

[Merlin66]

http://www.ebay.com.au/itm/like/253024988037?chn=ps&dispItem=1

This may do the job.....

[Shano592]

Oh of course!

I was looking for a set of rings, 5,10,15,20mm.

I did see a heap of these, but discounted them as potentially too long.

OK, I will have a look in this direction, and see what comes out of it.

Thanks for the back'n'forth.

[Shano592]

I ordered the one in Ken's last post. I shall endeavour to set it up and test it all out, when this last part arrives.

There are a few good landmarks, several kilometres away from the house, which is elevated, on the top of a long hill.

Results will be posted once I have them.

In the meantime, I guess I should order a replacement motherboard for that old torched laptop that is doing nothing. 2TB of drives just going to waste, for the sake of $100...

[Merlin66]

Shane,
In the meantime you could "practice" setting up and using the guide camera on the distant object....
You can then refocus the imaging camera on the same object to verify the overlapping FOV.
In the end it may mean adding spacers between the OAG body and the imaging camera.......

[Shano592]

It is a sound plan, Ken, with exception of this East Coast weather.

One thing I miss about living in Perth, is that the weather takes it's sweet time to change. You can see some clouds, and have a couple of hours to think about moving stuff.

Here, you turn your back on a sunny day and there is a thunderstorm on your shoulder!

It reminds me of Sir Launcelot, in Monty Python and the Holy Grail, when he attacks the castle, thinking he is saving a damsel in distress...

https://www.youtube.com/watch?v=GJoM7V54T-c --- From about 40 seconds.


One thing I don't miss about Perth... It is the City of Lights. Sodium vapour, for as far as you can see, and often even further! That, and the wind.

[Shano592]

OK, the extension tube arrived, along with an electronic protractor / inclinometer that I picked up for about $10 on eBay (accurate to 1/10 of a degree). Both very quick from China, impressed.

I'll see if I can have a play with the setup tomorrow or Sunday. I hear the moon is somewhat visible right now, and an easy target to hit...

[Astrofriend]

Hi Shane,
To get field flattener, OAG, DSLR working together stable and with correct distances could be very tricky. Hard to find the correct parts.

I have written down how I did it on my refractor, part of it will be the same for you:
http://astrofriend.eu/astronomy/projects/project-mechanical-construction-adapters-for-apo-refractor/project-mechanical-construction-adapters-for-apo-refractor.html

Biggest problem was to control the vignetting to not be too big.

/Lars

[Shano592]

Hi Lars,

Thanks for your post.

No need for a field flattener, as the LX200 has the ACF optics. Flat to the edge. I will keep the x0.63 reducer (which is not a flattener) away from things while I am learning.

It really just comes down to hitting that happy spot with the DSLR focus, and the OAG camera focus.

If I can do that, then that will hit a happy spot with me.

I never got around to trying this out over the weekend. My scope is on a pallet, 3 levels up a pallet rack. A couple of weeks ago, I managed to fill the floor space in front of the rack with other stock, so my scope is locked in until I can clear the floor. Hopefully that will be this week.

[Astrofriend]

Hi Shane,
With that telescope you then have one less problem to worry about. How much backfocus does it have, any data on that? I think it must be much more than the standard 55 mm and then easier to get it to work.

Maybe the driver to your camera will be the biggest problem then.

/Lars

[Shano592]

With the backfocus numbers, I am completely unsure! It is generous, and can be setup to work, though.

I know that visually, I can achieve focus with the reducer, and have imaged with the EOS with the reducer as well. If I put too many items in the image train, then it fails.

If I do something like Reducer => 2-inch Adaptor => T-Ring with Camera, then it is fine. Anything else such as the 90-degree prism makes it too long for it to reach focus.

The driver for the webcam is a WDM driver, but for Windows 10 I am unsure how it will go. It was ok in testing a couple of years ago, under Windows 8.1. The EOS Drivers are fine but won't necessarily be used, as I will probably use an intervalometer with it instead, initially.

I'm excited to try it. Maybe this weekend, as the moon wanes.

[Astrofriend]

Hi,
I'm not used with that telescope, maybe it's the reducer that make the problem with the 90 degree prism. Is it possiblie to mount the reducer after the prism? Normally you don't do that.

The camera:
When you run the camera program, do a right click on the icon. See the compabilty modes, try some older operation system from the menu. Maybe that helps.

Lars

[Shano592]

Hi Lars,

It is definitely the reducer. Without it, using the prism with the camera is no problem.

Yes, if the driver has an issue, I will try compatibility mode. That should solve things. Hopefully.