Megawatt

Morpheus is excellent, once you get used to the eye placement. 

I find I do the bulk of my observing in the 7-9mm range with my f/5 reflector. Having a tracking mount certainly helps.

On 29/05/2024 at 10:22, Albir phil said:

Hi I have the same scope, I do however use the W O adjustable flattener/reducer, and never had any problem.So I agree best to use the dedicated F/R for the scope 

I'm using the dedicated reducer/flattener. If you are using the adjustable version, chances are you have the newer version of the GT81. Mine is first generation, I believe, which came out before adjustable flatteners were even available. 

On 29/05/2024 at 05:42, kirkster501 said:

Flattener spacings are absolutely critical and the faster the scope the more critical it becomes.  Even a fraction of a millimeter is all it takes to ruin the star shapes.  Are you sure the flattener is at the exact distance recommended?  Are you using the WO flattener?  Does it do this at all temperatures?  Does it do it pointing at the Zenith?  Have you overtightened the scope mounting?  Are you over tightening the flattener?

On another note, tools such as Blur Xterminator make a superb job of correcting star shapes.

Yeah, I've been playing with the back spacing for years. I think whatever issue I'm having has made it harder to determine if my spacing is correct, because the stars are never round no matter what spacing I use. I'm using the exact recommended spacing now, but there is some debate on how "exact" that recommendation truly is. It astounds me how hard it is to find accurate information. You'd think there would be a published spec and that would be the end of it., but instead we have page after page of threads discussing what the published specs even mean. 

As for your other questions, these are all things I'm attempting to answer. So far, I haven't been able to say for sure that it has anything to do with the altitude angle or temperature. Focuser is centred and doesn't seem to sag at all. However, I'm beginning to suspect that my scope mounting is indeed overtightened, because when I loosened it I saw some immediate improvement (see my previous comment). More testing is required, but I appreciate your input. 

And you're absolutely correct that BlurX works miracles on star shapes, but I don't use Pixinsight and I haven't found any other program which can make any difference on my star shapes.

On 29/05/2024 at 04:38, Stuart1971 said:

I would not take much notice of results with a “Universal” flattener, you need to be using the dedicated one to get best results, the only real way to test whether the flattener is the issue, is to buy another and if the problem is still there, then return it, you have 30 days to do this with FLO..😉

Well, if two different flatteners are giving the same poor result, it seems unlikely that a third flattener will provide a solution. 

One thing I did try it loosening the tube rings, and I don't want to get my hopes up but I do see an improvement. These were shot with the original William Optics 0.8x reducer/flattener. The first image is completely uncropped. There is still some distortion in the stars, particularly in the second image, but they look better than in 90% of my other images.

Quick update for those who have been assisting me with this issue:

I borrowed an Orion universal field flattener from a friend. The recommended 55mm back spacing was clearly not enough, but that aside, it didn't help much at all. Star shapes are still garbage. The first pic shows a recent sub with the replacement flattener and my newly-repaired ASI2600MC Pro. 

The second picture is just for comparison. This was shot last year and shows much better, though still far from perfect, star shapes. I'm really not sure what to make of all this. All I can think to do is loosen off my tube rings a bit, and maybe call around to some local places about repair.

9 hours ago, Backyardscope said:

Triplets are much more prone to curvature then doublets, I agree with @Stuart1971 if the stars are not round in the centre of the image it minuses the issue of spacing regarding the flattener.

Did you need to have a dew band on while using the scope while imaging? what was the temperature outside?

It does look like a case of pinched optics. Another thing to check which is often ignored, is the retaining ring in the flattener , the one which rests on the optics. Is it screwed on ok, not loose or anything? 

You could just try imaging without the flattener to see how the centre stars look.

First I just want to say thanks to you guys for helping me out with this issue. Makes me feel a little less crazy when people actually attempt to understand the problem before tossing out solutions.

It seems like there is a consensus that some pinching is happening somewhere. I always use the dew heater since 9 out of 10 nights, dew or frost will form at some point. Though last time, I forgot to bring it and I didn't have issues with condensation, but the stars looked horrible as usual. 

The very best I've been able to manage with this setup is "ok-ish" stars, as you put it. And for what I paid, it is not acceptable. But I bought it secondhand so there's no dealer I can appeal to. I'll start saving for a new scope if I have to, but better if I can get this one working properly. Incidentally, it works wonderfully for visual use, which also makes me wonder about the flattener...

I see the retaining ring you mentioned but I haven't figured out how to loosen/tighten it without risking scratches on the lens. Likewise, I have no idea how to address pinching if it the telescope objective. I've seen others loosen the grub screws on the lens cell of their William Optic doublets, but I'm pretty hesitant to start messing with my triplet until I know exactly what I'm doing. 

I'll do more testing without the flattener and see if I can get consistent results. 

17 hours ago, Stuart1971 said:

Looking again at the first 3 images you posted, I think it’s a bad flattener, as the last of the 3 images was without this flattener and the centre stars look very good, unlike the other images, yes the outside are elongated towards the middle but that would be expected, I would try another flattener iff possible 

You're right, the image without the flattener looks a lot more normal. Would be nice if the flattener is the culprit. The only thing which makes me question this theory is this shot taken the same night with the flattener in place, which also has mostly normal-looking stars (though the corners are still quite messy).

I don't often use filters, though I did in this case. I'll try to borrow a different flattener somewhere and see if it helps at all. 

15 hours ago, whipdry said:

You could try pointing close to the zenith focusing a star at the centre of the frame then do the same in all four corners. Assuming you have a remote stepper focuser make notes of the focuser position count for each, lets say it's 400 in the centre...

If all corners are the same higher or lower number it's backfocus...

With varying higher numbers in each corner it's a combination of backfocus & tilt, same applies to all lower numbers...

If when following the routine above you can't get round stars by adjusting focus in each corner it's likely you have an opitical issue!

I suffered a strange problem with a dual imaging setup, first exposure on a new target on one scope would sometimes have elongated stars... recently found the scopes threaded front lens cell was slightly loose!

 

Peter

I use a manual focuser. But interesting point. I don't doubt that I've got some back spacing and/or tilt issues, but I believe they are making the real problem harder to diagnose, and vice versa. 

I sometimes take pictures with my Dob and that can give bad stars, but it is perfectly explicable: poor focus, or bad tracking, or coma from the F/5 mirror. I have little doubt that if my Dob was mounted an an EQ8 or whatever, I would have no issues with the stars. 

With my refractor, the problem is inexplicable to me. Focus, tracking, and polar alignment are good, as far as I can tell. The star shapes aren't just elongated, as you would expect from coma or bad tracking. They are asymmetrical and slightly pointed, like flying saucers, and they stay consistent between different exposures but not necessarily night to night. 

How did you figure out your optical issue?

On 12/05/2024 at 12:44, Earl said:

is something overtightened somewhere?

I think so. Now it's just a matter of figuring which "something" and "somewhere". I think there are 6 sets of 3 screws around the lens cell, and I'm hesitant to start mucking about with them without guidance.

On 12/05/2024 at 12:26, david_taurus83 said:

Have you tried without the reducer? You will have coma around the edges but should all point towards the centre and stars should be round in centre. If they are anything but round then the issue is with the scope itself.

I did some testing without the reducer and it seemed to improve, but then my shots with the flattener were also not bad that night. The problem is inconsistent, which doesn't make things any easier. 

5 minutes ago, Elp said:

I think you can also defocus a very bright star so you can see the airy disk and take images either side of focus, this may help diagnose.

I'll try that on the next clear night.

51 minutes ago, Elp said:

The spacing needs a little tweak, from initial glance the sensor looks a little fraction too far away from the flattener.

Also, as it's a triplet do you allow it to cool sufficiently long enough, or if using dew heater bands are they near the triplet cell position as lenses not acclimatised can also cause pinched optics.

I assume your guide calibration, autoguiding and PA are all fine.

Thanks for the reply. I've lost track of how many times I've tweaked the back spacing. I think my inability to get round stars in the centre of the frame makes it much harder to tell where I'm at with the spacing. 

I think if I had issues with guiding or polar alignment, I would notice my issues getting worse over longer exposures but this is not the case. 

For comparison, below is one of the few images I took with my old ED100. Unguided with no flattener, and the stars are most round. With a flattener and good guiding, the stars would be perfect. This is what I expected from my triplet. I just feel like I'm going in circles with this scope. 

I also attached another recent image where the stars in the centre of the frame are spiky-looking. Again, makes me think pinched optics. I normally use a dew heater around the objective but in this case I forgot it. 

I wonder if the flattener might be the culprit. Maybe I can borrow a replacement somewhere and find out...

Hi all, first post here. 

I'm going to show you a couple of images with poor star shapes. I was going to write a long preamble but decided to just get opinions on the stars themselves without all the backstory.

These were taken with a William Optics GT81 (older model) and 0.8x reducer/flattener (non-adjustable). Cameras used are ASI2600MC Pro and Canon T5i. The stars are sort of almond-shaped but asymmetrical, with little spikes on two sides. 

The star shapes are not affected at all by exposure time. 3", 30", 300" yields about the same results, so it is not a tracking/guiding issue. Removing the flattener seemed to have a bigger impact, but I still see the little spikes. I suspect pinched optics but my stars don't look like other examples I've seen online. Maybe I'm not good at troubleshooting, but I've been struggling with this for years and feel about ready to give up on this thing. I don't believe decent-looking stars should be so hard to achieve. 

The first image is a recent sub with the 2600MC. Second is an old sub with the T5i. Third is with the 2600MC without the flattener. Mount is an HEQ5 Pro with a StarShoot autoguider and 50mm guidescope. 

Visually, the scope performs well and star tests look okay, but dodgy seeing makes it hard to get a really good look.

Any help would be appreciated!