Quattro 8" first light

[Black Knight]

This is a test run from my Quattro last week. Could do with much longer subs obviously, but my laptop was running out of power so I just ran through a bunch of 60 second subs before I totally lost power.

12 x 60 seconds at 1600 IS0

10 x flats, 5 x darks, 5 x bias

No post processing done at all.

There are obviously problems with the image, but TBH I was pretty staggered that I could get that much data from just 12 minutes!

[blinky]

Looking good, can you show a 100% crop of the bright star?

[Black Knight]

Here you go. So what's causing those double diffraction spikes? Is that a focus thing?

[blinky]

Not sure, probablly that the spider vanes are not 100% square - each spider vane actually gives 2 spikes, 1 either side of the star. If the vanes are perfectly aligned then you will only see 4 and not 8 spikes but if they are a tiny bit off you will get 8, I think!

Good collimation though, thats what I wanted a look at!

[Black Knight]

Not sure, probablly that the spider vanes are not 100% square - each spider vane actually gives 2 spikes, 1 either side of the star. If the vanes are perfectly aligned then you will only see 4 and not 8 spikes but if they are a tiny bit off you will get 8, I think!

Good collimation though, thats what I wanted a look at!

I'm glad you think the collimation is OK, because I had a devil of a job getting it. When you say the vanes may not be perfectly perfectly aligned, do you mean that the secondary housing is absolutely central? TBH, this has me really confused, because I had just taken a quick run of Vega only minutes before this M27 run that didn't show double diffraction spikes. But did show some other tasty donut-shaped artifact.

[barkis]

Usually, spider vanes, if there are four of them, are not exactly opposite each other. If you imagine yourself looking into the mouth of the scope at the secondary holder, The left horizontal arm, will be lower than the right Horizontal arm. In some cases, as much as half an inch. The same applies to the vertical pair. The effect of this is, due to refraction, each of the four arms will appear to be double in an Image, giving eight in all especially on the brighter stars. The effect is most pronounced when these brighter stars are towards the edge of the field of view, and less so in the central regions of the image

The offset arms have a purpose, which is to make the secondary holder less prone to movement, and or vibration. Diametrically opposed arms would not be as effective .

If a Newtonian had only three arms, 120 degrees apart, you could see six diffraction spikes in an Image.

Ron.

[Beyond_Vision]

It could be a double star

[FLO]

As others have said, it might be the spider-vanes (secondary mirror supports). Have they become twisted during collimation? Check thet are straight and in-line with thier opposite partner. A screwdriver and some and some gentle tweaking should fix it.

It could be a double star

That too is possible, particularly as your second image shows perfect diffraction spikes.

HTH

[blinky]

Could be a double star, as FLO said, the Vega image shows perfect spikes.

[Black Knight]

I shall try and find out if this is actually a double star. Would twisted vanes cause this then? They are a bit twisted actually, although they were already like that before I started collimating the secondary, I hasten to add!

[MikeWilson]

Nice first light. In my limited experience twisted vanes cause brighter/wider spikes but not double spikes. I had the double spikes too when out of focus so it's possible it could be collimation or focus as when I had the Quattro I could get perfect focus in the center but slightly out of focus with double diffraction spikes towards the edges. (Do a star test in the center and also at the edges of the frame to check).

[Black Knight]

Thanks Mike. Yeah, someone suggested it could be focus. I've checked the collimation again. It's fine. Tricksy, but fine .

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[Starblazer]

I'd say stacking error?

Looking at the stars in the cropped image shows a ghost star at about 5 o'clock on every star. Try restacking the subs, check the focus on them for shift also.

I'd have expected twisted spider to show on all stars, although the one of vega does show a thicker in the other image, if it was twisting, it's not that extreme surely? Unless it's due to the placement and reflection of the star at the edge of field as someone has already mentioned.

[Black Knight]

No, it's not a stacking error - I've already checked. Those double spikes appear in each individual sub.

[Black Knight]

You're right about the ghost stars though. I'd assumed that was my guiding or bad PA causing that.

[Deneb]

How about vibrations...

[Black Knight]

Hmmm... Hadn't considered that.

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[Deneb]

Another thing it could also be a tad out of focus, can we have some shots of the corners please & some more of the central area.... cheers

Edit: But saying that It could be a double star, what region was you imaging to get those double spikes.

[Black Knight]

OK here you are. They are in order: top left, top right, bottom left, bottom right, and mid-left edge showing another brightish star with double diffraction spikes.

[Black Knight]

And around the centre .....

[Black Knight]

No, I'm pretty sure it's not a double star. When you look closely at other reasonably bright stars I've got the same double diffraction spikes. Too much of a coincidence .

[Deneb]

mmmm, look at the 1st top left image, those smaller stars do look a tad out of focus, im still just thinking about vibrations, even from a small amount of wind, newts are like a sail in the wind.

But hey ! dont worry about it ! im sure your next session will be even better.

[Black Knight]

mmmm, look at the 1st top left image, those smaller stars do look a tad out of focus, im still just thinking about vibrations, even from a small amount of wind, newts are like a sail in the wind.

But hey ! dont worry about it ! im sure your next session will be even better.

You're very kind . TBH, I do struggle with focusing, even with Live View and a Bhatinov mask. I'll just have to try even harder ....

[Deneb]

You're very kind . TBH, I do struggle with focusing, even with Live View and a Bhatinov mask. I'll just have to try even harder ....

i must admit it does take a bit to get used to a new scope when focusing, little bit like trying to find the biting point in a cars clutch.

[Black Knight]

i must admit it does take a bit to get used to a new scope when focusing, little bit like trying to find the biting point in a cars clutch.

You're right there. In my experience so far the Quattro is a lot more difficult to focus than my 200p ever was. Still ... onwards and upwards eh?