Stars with tails - tilt issue? *help*

Thank you for the quick response.

I thought of this too and that was the first thing I "eliminated" - no heat on the second and third night. However - the problem remained. Below is one capture of NGC4565 at midnight - even the heat from the day should have dissapated by then. Plus I have 3 fans behind my primary mirror, pulling cold air in from the front, which helps keeping everything inside at ambient temperature.

Hi Buyman,

the issue with the first image you posted seems kind of familiar to me. I've seen similar issues before, when there is an obstruction in the optical train, that's causing diffraction. Could be the head of a screw, or something similar.

But the second and third image puzzle me a lot. To me, it seems like the main mirror and the focuser are not aligned, causing 'shading'. On a big reflector like yours, I'd recommend using a tilt adapter between scope and focuser.

Leaving the 'smear' in the bottom left corner of the stars aside, your stars are all elongated across the Y-axis of the image. This could also be due to tilt between focuser and scope. Without a tilt adapter, collimating the scope with a laser will cause you to adjust the telescope to a tilted laser beam.

Next time you are outside, also try plate solving the image, and check if the calculated focal length is not too far off the actual focal length. If it is, you should probably check with customer support.

Clear Skies,
Tim

Thank you all for your answers. To respond to some of your questions:

Oskari Nikkinen:
Strange, looks exactly like thermal issues but given that you run mirror fans it is a bit puzzling.

I would suggest trying without the secondary heater, it could well be the cause of your problems. Have never used one, nor needed one, in my typical conditions which are usually above 80% humidity and often closer to 95%.

I did that on the second night already, but on the next clear night, I will keep ALL the dew heaters off - including the camera one. Just to exclude "plume". And they're not just for condensation - I had the mirrors "ice over" before. Takes a while to defrost with a hair blower and leaves streaks - keeping the dew heater on, helps.

Tim Richter:
Hi Buyman,

the issue with the first image you posted seems kind of familiar to me. I've seen similar issues before, when there is an obstruction in the optical train, that's causing diffraction. Could be the head of a screw, or something similar.

But the second and third image puzzle me a lot. To me, it seems like the main mirror and the focuser are not aligned, causing 'shading'. On a big reflector like yours, I'd recommend using a tilt adapter between scope and focuser.

Leaving the 'smear' in the bottom left corner of the stars aside, your stars are all elongated across the Y-axis of the image. This could also be due to tilt between focuser and scope. Without a tilt adapter, collimating the scope with a laser will cause you to adjust the telescope to a tilted laser beam.

Next time you are outside, also try plate solving the image, and check if the calculated focal length is not too far off the actual focal length. If it is, you should probably check with customer support.

Clear Skies,
Tim

The obstruction was/is a good idea, but wouldn't that also show on the defocused star? And I just checked - I don't see anything looking down the tube.

I believe the tilt adapter might be the solution I need. But I want to exclude everything else first, to avoid spending extra money. 

Good point on the elongation - I put that under the "not focusing" thought, but think you may have a point. But then again - wouldn't that show on the defocused star as well? I mean it actually is not perfectly centered, so maybe you are right.

I always plate solve from "0". Every time I setup my rig, or uncover it, I zero the focal length of the camera. I had to learn it the hard way, when switching to a NB filter, and couldn't figure out why I can't plate solve...  *duh*

Uebrigens - klasse YouTube Kanal. Hab' viel von Dir gelernt! Mach bitte weiter so - bin ein grosser Fan!!! Gruss aus Pennsylvania...

andrea tasselli:
The only other similar issue I can think of is that one of your mirror clips is somehow too tight. This can easily be seen at high magnification with an EP and it would definitely clear what the source is (I still think that the first picture is an heat plume). By any chance where is the scope stored when not in use?

See an example of too tight mirror clip(s) and I'm sure you notice the similarities:

Thanks again for your fast feedback - much obliged. You don't live here, do you?  

The Orion Optics tube doesn't have any clips to hold the mirror in place - none that I can see. And you can see that on the defocused star pictures. But I'd have to lie, if you'd ask me how it's being held in place. I might have to take a look in the rear of the tube, to see how they managed to fix its position.

As for the storage: All parts are being stored outside in a poolshed with its doors open year around. Therefore there is not much time needed to adjust the scope to the ambient temperature.

Dave Rust:
I doubt my experience is relevant, but I get misshapen stars like this on some night and not others. The only correlation seems to be when the jet stream is overhead or overlapping fronts causing high altitude turbulence. I tried so many “solutions,” only to find the stars perfectly round 2 days later.

Interesting take. I have to keep an eye on this. The nights I was working on this issue did have some cloud coverage coming and going - maybe there were some unseen turbulences involved as well. Interesting idea - thx for the feedback!

Buyman3375:
Thanks again for your fast feedback - much obliged. You don't live here, do you?

The Orion Optics tube doesn't have any clips to hold the mirror in place - none that I can see. And you can see that on the defocused star pictures. But I'd have to lie, if you'd ask me how it's being held in place. I might have to take a look in the rear of the tube, to see how they managed to fix its position.

As for the storage: All parts are being stored outside in a poolshed with its doors open year around. Therefore there is not much time needed to adjust the scope to the ambient temperature.

So thermal plume can be excluded unless it was unseasonally warm out there in Germany. Remains the clipping. You might not see them if they are shielded by an aperture ring. By the way, what OOUK scope do you have; VX, CT or the new one I forget the name of?

andrea tasselli:

Buyman3375:
Thanks again for your fast feedback - much obliged. You don't live here, do you?

The Orion Optics tube doesn't have any clips to hold the mirror in place - none that I can see. And you can see that on the defocused star pictures. But I'd have to lie, if you'd ask me how it's being held in place. I might have to take a look in the rear of the tube, to see how they managed to fix its position.

As for the storage: All parts are being stored outside in a poolshed with its doors open year around. Therefore there is not much time needed to adjust the scope to the ambient temperature.

So thermal plume can be excluded unless it was unseasonally warm out there in Germany. Remains the clipping. You might not see them if they are shielded by an aperture ring. By the way, what OOUK scope do you have; VX, CT or the new one I forget the name of?

Thanks for sticking with me and my issue(s). To answer your questions, the OOUK scope is a CT, but the secondary mirror - even though bought from them - is not from this line. It possibly could be, but I bought it as a replacement from OOUK, because the first one got damaged (still worked), but needed to be replaced. Maybe the mirror is the issue? Sorry I forgot to mention the replacement before!

Btw - I don't live in Germany, I moved to the US in 2011 and live in PA. It was unusually warm out here for March, but not enough to consider heat plumes from that.

As for the extra-focal and intra-focal imgages - I am too close to my minimum limit to create the intra-focal image. The image wouldn't be to good to compare - unless I go the same maximum distance on the other side. I can try that...

If the CT mirror cell is the same as the VX one, which looks like the same in images i have seen, then the mirror is glued to the cell with silicone sealant. At least my VX cell is, manufactured in 2020.

I will say that my OOUK secondary mirror coatings have started to deteriorate only after 3 years of use, so i have no trouble imagining there are some quality issues with their secondaries. Might be a decent idea to buy an affordable GSO secondary mirror to test.

Hello again.

So I am still fighting tooth and nail to get this resolved. So far I had no luck. The most recent images haven't changed much, but I noticed an inconsistency with the spider vanes and was wondering if that could be the cause of my issues? The screenshot below is from a short exposure of Polaris. And when I noticed the weird spider vanes, I checked with the earlier pictures in this thread and noticed the same thing. It appears that's the only variable that doesn't change and is consistent with my unfocusable images

Any advice on how to resolve this? I measured the center of the secondary, then tightened/screwed the vanes. I have done this several times, but it doesn't change the "look". Is there a proper or safe way to set the vanes right and tighten the screws in a certain order?

andrea tasselli:
It ain't the vanes for sure, that is a double diffraction from one set of vanes which means they aren't co-linear, but otherwise not a major issue. To cut the chase can you make a cardboard offset aperture mask such as shown below:

The important bit is to mask both spider and secondary. Test again with intra-focal or extra-focal images if possible. In-focus images are not much help to diagnose the matter at hand.

 To my knowledge the CTs are closed behind the rear of the mirror, that is another area to investigate. I'm still convinced something is wrong with either mirror.

Hi Andrea. Thanks for the response and not giving up on me. (yet) 

Maybe it's my lack of vocabulary or I'm simply to dumb to understand what you're asking of me, in regards to the "cardboard offset aperture mask". Would you please be so kind to explain?

I attached two pictures of the intra- and extra focus pictures. Sorry for the quality, but I'm too close to zero, to create a nice intra focus picture. And to keep them equal, I could one go "1800" steps in each direction. Both are terribly copped and resized - I hope these will be of any help...!

I personally believe it has to do with the secondary mirror, since I never changed anything on the primary. The secondary was glued to the stalk by myself and offset, like the previous was. I'd like to say I was as precise as I could, but I'm not sure if I clued it exacly on the same position as before - in regrads to nm, or even mm. I would like to think i did...

Intra Focus
 

Extra Focus

Incidentally, you said you "glued" the secondary on the support. That's a bad idea which can lead to astigmatic images unless the "glue" is more like sealant rubber and spacing provided by rubber grommets.

andrea tasselli:
Incidentally, you said you "glued" the secondary on the support. That's a bad idea which can lead to astigmatic images unless the "glue" is more like sealant rubber and spacing provided by rubber grommets.

Well...

This is where I fear I am going to lose you. Because of my incompentence. The first mirror was only glued to the stalk with a silicone from the inside of the of the stalk, not underneath where it touches the mirror, nor on the outside.

When I wanted to fix it in place, I played with a glue gun on an example first and realized that the dew heater would soften the glue and I feared that it might loosen during the heating outside and fall into the tube. Out of fear, I had the "great" idea to glue it with 3 different silicones. I used one for the direct contact to the mirror, one for the inside of the stalk to the mirror and one on the outside of the stalk. It doesn't look terrible and I did a good job at keeping it at a minimum. But I am slowly having this creeping feeling, that this might have caused my dilemma... Please tell me it can't be...