Tilt with new imaging train.

[FiveByEagle]

Hello all!

Got my GT81IV-Flat6AIII+OAG-L-EFW 2"-2600MC rig going, and so far it has been a nightmare.

Installing the OAG-L and moving the M48 tilt plate from the camera to the OAG, I have been almost completely unable to fix the tilt I am experiencing. Using ASTAP and Hocus Focus to try and diagnose the issues but with little to no progress.

Step one was to place the flattener as close to the "recommended spec" as possible - knowing that it could be way off.

When it was attached the stars in about 1/3rds of the image were OK (fairly round, within my own margin of "screw it") but 2/3rds were in lines pointing outward. Using my backfocus chart, I see this typically means I am too close to the flattener. Move it back 1.5mm and now only half of the stars were bad! Closer...

Realized the bad half was coma shaped so I assumed tilt from the OAG. Frankly everything else is hard bolted together so I can not imagine tilt from the EFW region. The 3 tilt adjustment screws are in odd places imo to adjust the 4 corners of the sensor. I tried my very best but it is still wildly out. In fact, now all my stars are kinda wonky so I obviously made it worse. However there is zero documentation for this gear, so what am I supposed to do? Not wing it?

I usually average about 3 clear nights a month, and so far have spent 6 trying to solve this and have not captured an image since last December. Really losing my patience trial and erroring without any sense of progress.

Question 1 - Are there any great resources online on fixing tilt with the OAG-L's tilt plate? Or adjusting tilt in general? Not sure how my changes are making no difference. I am not buying anything else to make this work. Zero AP purchases until 2023, so we are making it work with the gear I own. (which is all the correct stuff anyway, its just misaligned)

Question 2 - I am located in Indiana. I am willing to pay someone to come and fix it, perfect it, lock it down and guarantee it. If anyone has a lead here, let me know. Sadly our local astronomy group in Fort Wayne is worse than useless for anything of a modern or technically oriented nature.

Question 3: Is there anything that can be done for this issue during the day? Wasting clear sky time is seriously heartbreaking.

There have been a total of 9 clear nights in Fort Wayne since Jan 1 2022. 8 of them have produced zero images due to this ONE issue, and that one was a 2 hour SHO trial (that worked and came out gorgeous) but it is still not worthwhile until I get back to a 50% K/D here.

[iantaylor2uk]

I have the same telescope but don't use an OAG - have you tried guiding through a simple guidescope attached to the telescope?

In my view you don't really need an OAG for a telescope of this focal length.

[FiveByEagle]

29 minutes ago, iantaylor2uk said:

I have the same telescope but don't use an OAG - have you tried guiding through a simple guidescope attached to the telescope?

In my view you don't really need an OAG for a telescope of this focal length.

No plans of going back to a guide-scope or adding/removing any components.

[Same old newbie alert]

Personally I don't see any gain from using a oag with a 80mm frac

Check your focuser, presuming it's the original, mine had some sag and the focuser bearing finally quit being useful

[FiveByEagle]

OAG remains. Guidescopes are not my speed. 

 

What else? Has anyone use the tilt adjust on these?

[michael8554]

21 hours ago, FiveByEagle said:

Realized the bad half was coma shaped so I assumed tilt from the OAG.

Is it the OAG ?

IIRC there are posts here and on other Forums to the effect that 2600's often have tilted sensors ?

Michael

[FiveByEagle]

4 hours ago, michael8554 said:

Is it the OAG ?

IIRC there are posts here and on other Forums to the effect that 2600's often have tilted sensors ?

Michael

It could be either. You have to remove the tilt plate from the 2600 and mount it to the OAG-L. 

[symmetal]

The easiest way to adjust tilt is to make a wooden test jig and get a cheap laser pen as shown in this thread. I wasted many nights trying to adjust tilt by analysing star shapes but got nowhere. 5 mins on the wooden jig and it was easily fixed. Keep the camera, filter wheel and OAG screwed together and place the whole assembly on the test jig. Adjust which ever tilt adjuster is easiest to access. Cost is minimal. 🙂

Alan

[Starflyer]

As Alan says, don't try and do this under the stars it'll drive you crazy, the wooden / aluminium jig and a laser pointer is the way to do it, inside with warm fingers and a clear head.

 

Ian

[mrflib]

+1 for bench test. You can make sure that your *imaging train* is completely aligned to your sensor, regardless of whether your sensor is actually aligned itself.

Once this is done, if you still have tilt it's most likely in your focuser.

I had this issue and it's impossible to diagnose assembled. You need to break it down.

[ollypenrice]

I have to join the chorus singing that the OAG is asking for trouble... but your call.

I wonder if this thread might be of any use to you?

It deals with camera sensor tilt adjustment but, off the top of my head, this simple jig might also be made to work for testing other parts of the train for tilt. It's a daytime test.

The other way to do daytime/cloudy night testing is to make an artificial star by gluing a ballbearing onto a black card and lighting it up with a flashlight. You then observe or image this from a good distance. It really does make a decent 'test star.'

Olly

 

[FiveByEagle]

On 09/04/2022 at 07:56, mrflib said:

+1 for bench test. You can make sure that your *imaging train* is completely aligned to your sensor, regardless of whether your sensor is actually aligned itself.

Once this is done, if you still have tilt it's most likely in your focuser.

I had this issue and it's impossible to diagnose assembled. You need to break it down.

I am seeing these, however not sure how to jig up the entire setup for this.

It would have to be the entire OAG,EFW,2600 on this platform and getting it correctly built. 

 

[FiveByEagle]

On 09/04/2022 at 12:42, ollypenrice said:

I have to join the chorus singing that the OAG is asking for trouble... but your call.

I wonder if this thread might be of any use to you?

It deals with camera sensor tilt adjustment but, off the top of my head, this simple jig might also be made to work for testing other parts of the train for tilt. It's a daytime test.

The other way to do daytime/cloudy night testing is to make an artificial star by gluing a ballbearing onto a black card and lighting it up with a flashlight. You then observe or image this from a good distance. It really does make a decent 'test star.'

Olly

 

OAG's are what I use. I do not prefer On-Axis, and its been 26 months since losing a sub to a guiding error. It works without flaw, and will never be removed.

Also. 2" EFW bolts directly to the 2600, which the OAG-L bolts directly to it.. there is no "removing" it that would not result in exactly where I am at now. The tilt plate would need to be re-located again... thus putting me right back to where I am now. This issue started with me relocating it once, and being unable to get it back to square. This would just be me doing that, with the added benefit of downgrading my guiding. No can do.

 

 

[FiveByEagle]

On 09/04/2022 at 12:42, ollypenrice said:

I have to join the chorus singing that the OAG is asking for trouble... but your call.

I wonder if this thread might be of any use to you?

It deals with camera sensor tilt adjustment but, off the top of my head, this simple jig might also be made to work for testing other parts of the train for tilt. It's a daytime test.

The other way to do daytime/cloudy night testing is to make an artificial star by gluing a ballbearing onto a black card and lighting it up with a flashlight. You then observe or image this from a good distance. It really does make a decent 'test star.'

Olly

 

I do have an AstroZap false star, but the issue is distance.

Its been heavy rain so there is not even the option of rolling the scopes outside, and I live in the city so I can MAYBE 30 feet of travel to use it. 

[ollypenrice]

1 minute ago, FiveByEagle said:

I do have an AstroZap false star, but the issue is distance.

Its been heavy rain so there is not even the option of rolling the scopes outside, and I live in the city so I can MAYBE 30 feet of travel to use it. 

That's a bit close. Don't you know anyone with a longer interior space?  I used to have a friend with a... well... condom warehouse... who let me use it for star testing. I'm sure other warehouses would also do! 

I don't know how well an artificial star would work for collimating the RASA but it would be worth a try. Firstly, though, you really do need a jig such as the one in the thread earlier.

Olly