FaDG

Yes, you're right. But considering that I fully solved that issue in less than half an hour, I'm now 129 pounds richer! 🙂 Seriously though: this was a friend's scope and it was a catastrophe, as the secondary was totally uncollimated and almost stuck to the point that one of the spider vanes bent when I tried to get it free, the primary strongly tensioned (almost triangular), the focuser was squinted, so the flare was really only the minor issue! Actually I told him to sell the bloody thing for cheap, but then I tried messing with it and the Ugly Duckling became a wonderful Swan, as it had really great optics, just assembled by the wrong guy! Yet, when it finally was perfect my friend decided that a Newt was too complicated for him (a newbie) and asked me to keep it: I struggled to convince him even to accept some money (what I consider a low price for that value: I've been lucky on that). Hence, you see, there was really no sense in investing on it at the time. Fabio

If you were really happy with the optics, you could have tried a 4cm extension tube between focuser and camera. This way you could have kept the focuser retracted, yet enjoy the optic performance. But now, all the best with your triplet! Fabio

I have a Photoline 72 f5.5 linked above, and I just love it! It's so compact and lightweight that the Star Adventurer perfectly supports it, and using FPL53 it's virtually free from chromatic aberration, even better than my ED80, which is f7.5. I have found enthusiastic reviews of the WO ZS61, yet my view is that, while for photo the aperture difference is negligible (shorter focal length), for visual already 72mm is quite small. I don't want to start the FPL53 vs whatever quarrel, but I think that the SW 72ED is slightly less corrected than the others. Fabio A field flattener is in order for all of them, for astro photo...

Yes, you're fully right. After chopping it off I did not have the hideous flare anymore. And this is what the reworked focuser looked like. Actually, the design is not flawed per se: you REALLY need the extra length in order to use the scope visually, just, when rectracting it all the way in, the end of it enters the light path. It's just another trade-off: to avoid it, Skywatcher should have used a MUCH larger tube for the 6". Hardly a better design choice. Even so, 90% of the users never complain and are super happy of their results. Not me! But now I find it to be a great budget scope. Yet, if you find the root cause of the weird spike, I'll be happy to deal with it too. Fabio

Here you are. It's the only image affected by this artifact, luckily. It's on Electra.

No, not strange at all, actually! If you needed a confirmation that it was a reflection, now you have it. The fan like flare is a reflection of the light cone off the focuser drawtube. To solve it I took a hacksaw and cut about 3 cm off it. Issue solved, but it won't focus with eyepieces anymore: I don't care as i never use it visually. The single stray spike is a reflection off something depending on the specific position of the point light source (star). It seems to be a characteristic of the Skywatcher newts design, as I have the same in my 150 f5

The point there is to clearly separate the sky background from the read noise, as it will improve your SNR We didn't stay long in Adeje, but El Duque was really fun due to the huge waves, and we also loved Medano, my son started surfing there. And my best Milky Way so far was shot from the southern shore of La Gomera: pitch black sky, the closest light in the south being Dakar (Senegal), 1500 km away! 🤣

I have used a Y mask and, while letting more light trhrough, this stays in the stars Instead of migrating into the spikes. So, my experience with it wasn't positive and I reverted back to a bathinov. I post a picture of the comparison: the Y mask is the leftmost one, the others are two slightly different bathinovs. Fabio

Your tracker periodic error and RA rate, your polar alignment and balance and light pollution will be the limits, alongside thermal noise for very long exposures in hot climate. This being said, the habit is to avoid very long exposures because you lose a lot due to a plane or a gremlin, and shorter exposures set lower constraint on the mount. Also, few great lenses are really crisp and with flat field when used wide open, so you'll probably want to stop it down a bit to increase image quality. I imagine that with all the above, my suggestioni would be: don't get too analytic, find the best ISO value for your camera and expose in order to have the sky background about 1/4th to 1/3rd of the histogram. And enjoy your time in Tenerife! My family is longing to go back there... Fabio

I'm pretty sure that the additional small spike is due to reflection. I found it in only ONE of my images, namely M45, I acquired with my 150pds. It was on ALL subs in that sessione and NO other. Neither different targets, nor the same target taken with a different FOV. And I'm sure that in my newt the focuser doesn't protrude in the light path, so it must have had a different root cause. Could you try to take a longer exposure of a rich star field, in order to cause spikes around multiple stars around the image? It could help debugging... Fabio

Ciao Luca, benvenuto! Fabio

Great post! I'm using APT and All Sky but I plate solve separately. I'll try to integrate them now. Thanks, Fabio

Let's say that misalignment is the cause, drift the measurable effect.

Dec drift is caused by Polar misalignment. Dec guiding (on mounts which support it, that is) can compensate the drift, resulting in field rotation around the guide star. Fabio

From the height of my experience with this mount (hardly to be envied...) I'd say that you're looking at two different effects: A serious drift, in dec I'd say A mild Periodic Error (more on this in a moment). Let me assume that, in your second image, the RA axis is directed up/right, about 60degs up from horizontal, and your dec axis is down/right, about 30 degs down from horizontal. Let's start from drift: the long line should be caused by polar alignment. You say that you checked the star position in the polar scope, but is the PS correctly aligned? From my point of view, the Periodic Error is rather the small movement up/down, I see two cycles which, alas, make me think of a 160" period. My Star Adventurer mount has the same issue. So, I suggest that you spend some time clearly separating the two phenomena. Try to get a short image (15") with tracking off, and look at the direction of the drift. That's the RA. If I'm wrong, and the drift is actually in RA and not in Dec, then the tracking rate of your mount is wrong . Fabio

On my belt modded HEQ5 I use the ASI120MM with both a 50mm finder and a dedicated 60/224 guidescope: usually the finder goes with the 72ED or the ED80 and the guider with the newton. Both options are fine, and I get RMS anywhere between 0,4" and 1,8", depending on seeing : I live in the centre of Rome, and that's my limiting factor. So: Belt modding yields a main improvement; Bigger/longer scope helps a bit; Binning is not, in my Experience, changing much, IF you have a good guidestar (i.e. SNR > 45 on PHD2) : it effectively halves the guidescope Focal Length But, to fight the seeing, longer exposures really help, as well as SLIGHTLY defocusing: I assume the defocus improves thing because due to seeing the image doesn't pass THROUGH focus, and tends to be a tad steadier. Fabio

No, PA done with the stock polarscope which is perfect. I had zero (0!) dec drift in 10 minutes. Differently from yours, my wedge works great, no wobble at all, and is associated to a sturdy wooden tripod. The issue is in the head though: the total value of the PE isn't bad, but there is a high frequency harmonic preventing longer FL. it can track without limits below 100mm, but above it's a pain. The mount is out of warranty period, but anyway Skywatcher does not commit on a performance, so actually it works. With their QA Level and at this price tag, it's just a matter of luck in getting one that works BETTER! I'm happy for you.

Hi Steve, are you getting consistente 300" subs @ 135 MM unguided? The same for 150-180" @300mm, unguided too? If so I find that you have an exceptionally good sample. Mine, even with perfect Polar Alignment, doesn't even get close to that due to Periodic Error and high frequency harmonics... You lucky guy! Fabio

Mmmh, not sure I get the point : 31.8 is the size in mm of the 1.25" accessories. So I suspect you're referring to the same Product. Or am I missing anything?

Be informed that TS has actually TWO Photoline 72ED in their lineup: The f6 you referred above, And a 72 f5.5, also FPL53, which is even lighter and more compact, although more expensive. I have one of these and chromatic correction is astounding. Interestingly it is modular, so that the main tube can be unscrewed in two halves, and exhibits a huge backfocus (up to 16 cm!). I use mine reduced at f4.4 for astrophoto on the Star Adventurer. Field of view is very well corrected (but spent weeks to find the optimum spacing), with just a tiny bit of astigmatism visible in the corners. It is ultralight, well below 2 kgs. Actually, with my 600d and reducer, but a helical focuser, it weights 2040 grams, with only one section of the main tube. Obvioulsy, I have never compared it to a TV, yet the TV are normally great scope.

A lot of work. Was wondering whether it's really worth it? ?

Unguided is just with a camera looking through a scope or lens. Guided is with an additional camera taking short pics through a Guidescope to correct the error in order to get better (and longer) exposures through your imaging setup. In both cases the motor is turned on, but in the latter an additional cable (ST4) is plugged aside the mini USB socket.

You had a lot more patience than me. I just gave it a hand of Black Paint to cover the old one... ? ? ?

Disclaimer: I didn't find an indication for the thickness of the Y, so I used the same size of the bathinov spacing. But the principle seems clear: the grating of the bathinov uses constructive interference to sum up the light from various slots on only three spikes. This can't be reproduced with the Y.

I have (you can see it in the pic, 3D printed one for my 72ED) , and while the image is brighter, it fails to move the light from the star to the spikes. Please look at the comparison with a Bathinov. The Y is the leftmost image:all taken with the same setup and settings. So for me it was a failure and I continue using a bathinov for focusing.