Focus Problem Altair Starwave, 0.8x Reducer and Altair 1600m

[Astropedro]

Hi.

 

I finally got my observatory finished in mid February and I've been spending the last few weeks trying to sort out a myriad of problems.  The list is endless......

I've spent 3 weeks sat in there and haven't got a single image to show for it.

So one thing at a time.  I'm trying to get nina configured so I can plate solve as I really don't want to go back to using eyepieces and refocusing etc etc.  Gear is as follows.

Altair Astro Starwave 70 triplet, 0.8x reducer (bought with scope from Altair) zwo mini filter wheel(5) Altair 1600 mono tec Cooled camera.  Guidescope and guide camera seem to work OK but phd2 is hit and miss with them.  Heq5 Mount, 1 day old and bought new as I got fed up with my Exos2 Pmc8 connection problems( a whole other saga). I also bought the USB cable for the mount from the supplier which works and connects to eqmod ( eventually ).

My focus with the qhy5iii guide camera and guide scope seems OK and phd2 will guide.....sometimes.  My main problem seems to be getting good focus with the main imaging camera so Astap can platesolve within nina.  It solves sometimes then I slew elsewhere to solve again so I can sync and it usually fails with various error messages.  I've been using stellarium to slew with the heq5 connected to eqmod through stellarium.  

So is this more than likely bad focusing?   I have an eaf but I removed it as it gave me nothing but trouble and something else to battle.  Am I  missing something ?  The scope came with a reducer which I attached to the rotator, then the filter wheel, then the camera.  The focus seems terrible at the edges of the FOV and not great near centre if I'm honest.  This is ofcourse with the 1600 not an eyepiece.  My skies are bortle 5.   I can see polaris and several other of the brighter stars in Ursa Major, Cepheus etc but not much else.  I've got lrgb and narrowband filters and I've tried focusing through a variety of them but I don't think I'm quite getting as plate solving fails so often.

Anyone with experience with a similar setup?  Any advice would be well appreciated as I seem to be going round in circles.  I've got sharpcap Pro for polar align ent which I believe is accurate,  I don't  mind using something diferent than nina as I just want to get imaging of course.  I've tried APT.  The altair capture program seems a bit basic but I'm really open to options as I cant spend another night without any pay off.

Thanks in advance.

 

Pete

 

[scotty38]

You'll need focus for starters, if you have the reducer do you have the correct spacing to the camera sensor? If you get that then do you have the star databases installed in ASTAP, you'll need 17 or 18 in there which is done separately. I'd also configure NINA to use ASTAP as the primary and blind solver.

[Astropedro]

Thanks for the reply Scott.  Yes I've got the database installed and I've set nina to use astap and its file path etc.  Astap does attempt to solve and sometimes does.....but not often so I'm assuming it's a focus problem.

Spacing......I've got the filterwheel between the 1600 and the reducer and assume that's enough but I haven't measured. Along with the spacing on the camera itself I assumed(no doubt wrongly) that there's enough spacing.

 

Pete

[david_taurus83]

A picture of your setup would help.

[scotty38]

56 minutes ago, Astropedro said:

Spacing......I've got the filterwheel between the 1600 and the reducer and assume that's enough but I haven't measured. Along with the spacing on the camera itself I assumed(no doubt wrongly) that there's enough spacing.

 

Pete

As David says a picture could be good but you assumed correct based on what though? It has to be pretty accurate, even to fractions of a mm.....

[Chris-h]

If I remember correctly, you need 55mm from the flattener to the sensor. So 55mm-17.5mm (camera) = 37.5mm. The Filter wheel is 20mm I think? So that leaves you with 17.5mm. If your rotator is thicker than that, you will run into problems

Edited March 19, 2022 by Chris-h

[Astropedro]

Ok guys thanks.  Ill be measuring it to check shortly. The rotator on the scope is pretty beefy.......😊

[Astropedro]

Well I've tried all the spacers I've got and I tried removing the reducer too......can't achieve good focus.   The attached photo was the best I could get.

 

To clarify, the rotator I refer to came with the scope and is at the beginning of the train.  I'll attach a photo in another post of my imaging train which I'm guessing needs a spacer or something removing and changing as good focus is impossible.

[Astropedro]

[david_taurus83]

44 minutes ago, Astropedro said:

Well I've tried all the spacers I've got and I tried removing the reducer too......can't achieve good focus.   The attached photo was the best I could get.

 

To clarify, the rotator I refer to came with the scope and is at the beginning of the train.  I'll attach a photo in another post of my imaging train which I'm guessing needs a spacer or something removing and changing as good focus is impossible.

Is that with a bahtinov mask? What's it like when you remove it?

[SamAndrew]

Focus doesn't need to be that good for plate solve to work, I've forgotten to focus before doing the first plate solve several times, and it still works. So if it is plate solving some times, it might be the exposure length rather than focus, especially if plate solving with a narrowband filter. What exposure length are you using? would be worth taking a 30 second exposure and sharing the result here so we can at least see what you're getting.

[Astropedro]

1 hour ago, david_taurus83 said:

Is that with a bahtinov mask? What's it like when you remove it?

Was no better without it dave.  

 

Have just read that my camera has 17.5mm of backfocus.  The filter wheel is 20mm.  So at 55mm industry standard I would need a 17.5mm spacer with male m42 thread at filter wheel and female 48mm thread at reducer end.  I can only find a 16.5mm from zwo.  Would the 1mm short be that critical?

[SamAndrew]

It'll work, the corneres might not be perfect.

[Astropedro]

I've ordered spacers to get to the 55mm.  So tonight.......my Canon 1100d comes out of retirement for a few days.......