First light VX8L Newt - M42

[rocketandroll]

Hi all

So, finally managed to get first light on my new imaging Newt tonight... I'm not 100% happy with the result but it's not bad.

I pointed it at a known target I had 'benchmarks' for in terms of optical quality to see how it did.

The scope (before I forget) is a customised Orion Optics (UK) VX8L Newtonian at f6 and 1.2m focal length.

I knew guiding on something this big at that focal length on a HEQ5 was pushing it... and I did loose about 30% of the subs to odd shaped stars... but the guiding otherwise worked pretty well.

The scope was collimated immediately before the imaging run and focus was allegedly bang on according to the Bahtinov mask, yet the finished image is still a bit 'fuzzy'... I was also (both visually and in the images) getting a strange effect where the stars seemed to spread their spectrums top left to bottom right so they were all a bit oval with the top left edge blueish and the bottom right edge reddish.... any suggestions on what that is and how to fix it?

Anyway, enough waffle, this is just 40 minutes or so of useable 4 minute subs with a core of 30 sec subs (glad to see all the trap stars are at least visible, but they should be at 18mp and 1.2m fl!)

I'm fairly happy... but the seeing was awful, hazy cloud everywhere and horrible levels of LP... I am hoping, if I can work out what that last little optical gremlin is, and shoot on a better night, this scope will really give some great results.

Cheers all

Ben

Full image:

And just the core:

[Darth Takahashi]

That a pretty good first light with a new scope especially if the weather is hazy as you say it is. Too much thin cloud up there for me tonight..! Still it appears to be getting better, the weather that is!!!

[Coco]

Looks like your off to a good start, new scopes take time to get used to, 1,200mm... your a very brave man on an HEQ5

I bet the visual views through is are fabulous , you have the best of both worlds... very nice indeed.

[slim80]

Breathtaking pics

[Tim]

Looks like its going to be a very capable scope Ben. Nice focal length for imaging that.

As regards the blue/red stars, is there any glass in the imaging train? Coma corrector etc? You have likely (correctly) focused on the green channel, but something is bringing the blue and red to focus at a different point, usually glass will do that. You can test if it is this by taking a pic with bahtinov mask in place, and then splitting the channels and comparing them. There will likely be differences, with red and blue being the most different to each other.

Usually with newts there is very little chromatism, but correctors can introduce a bit of it. If you do have a corrector in place, try imaging without it to see what gives.

Sort the collimation out though, the rounder you can get the stars, the less visible the chromatism will be, and the easier to deal with in post processing.

At any rate, very nice first light, you must be very encouraged

Tim

[Zul]

Beautiful image!

[rocketandroll]

Cheers all for the comments...

Firstly.... nope, there isn't any glass in the imaging train... well, apart from the LP clip filter in my camera, that's it... and I know that's flat and ok from previous use with other scopes.

I've now noticed the red/blue shift is in line with the optical tube... ie: the edge of the image facing the front of the tube is where the blue is shifted and the primary (back) end is exactly the direction the red is shifted?

I can only assume that points at it being an issue with the secondary?

I do really want to work out what it is that's up with it... it's not a cheap scope and having paid extra for the 1/10th PV optics, my expectations are (perhaps a little too) high.

One other wierd thing... with the Bahtinov mask... rather than with my frac where the central bar moves up as you aproach focus, is in the center in focus and then continues up as you go past focus in the other direction... with the Newt, it goes up, closer to the center... then goes back the way it came as you go through focus?

Is that right? I wasn't expecting it and wasted 10 minutes wondering why I was continually chasing focus and never getting close.

I also still can't explain why the stars are all a bit blobby and fuzzy despite the Bahtinov mask showing (eventually) just about perfect focus? I guess the poor seeing could acount for some of it... but i was expecting somewhat closer to 'pinpoint' stars out of a relatively high-end Newt?

Oh, and as I said... it was collimated perfectly about an hour or so before the imaging run... I am wondering if it needed to be done again after it had cooled? being a steel tubed scope?

Thoughts?

Ben

[steelfixer]

Hi Ben.

I think you have a perfection disorder.

I would just about give anything to get a photo like that.

I have just run the full image up to 200 times magnifacation and it still looks brilliant.

The spikes on the stars are all dead straight and even.

I was wondering if your little mishap has slightly bent the focus tube.

It might be an idea if we collimated it again but with the focus tube set out to where it is when you have the camera in.

Graham

[rocketandroll]

Hi Graham....

Thanks :-) Might be worth a look... the 'accident' certainly did something to the focuser... it did occur to me, I wonder if the focuser not being straight any more would have a strange effect, I'd have though the effect would be it not being in perfect focus across the whole image... as the distance from the chip to the secondary would be very slightly altered from one edge to the other? That said, the tube looks straight so the difference in distance would be measured in hundredths of a millimeter at most?

Anyway... yes, might be an idea to try collimating it at the focus point, see if that makes a difference?

Ben

[steelfixer]

Well Ben my steel delivery has not turned up so I guess I have the afternoon off if your not busy.

[ollypenrice]

Hi Graham....

Thanks :-) Might be worth a look... the 'accident' certainly did something to the focuser... it did occur to me, I wonder if the focuser not being straight any more would have a strange effect, I'd have though the effect would be it not being in perfect focus across the whole image... as the distance from the chip to the secondary would be very slightly altered from one edge to the other? That said, the tube looks straight so the difference in distance would be measured in hundredths of a millimeter at most?

Anyway... yes, might be an idea to try collimating it at the focus point, see if that makes a difference?

Ben

I think a slight tilt of the chip is very likely to be the cause of the issue. The faster the system the more you need to be orthogonal and, since a Newt has coma unless corrected, the mis-focus of the R and B channels might well be exaggerated via the coma.

Tim's tri-colour Bahtinov idea is brilliant. I must remember that one.

Olly

[rocketandroll]

I think a slight tilt of the chip is very likely to be the cause of the issue. The faster the system the more you need to be orthogonal and, since a Newt has coma unless corrected, the mis-focus of the R and B channels might well be exaggerated via the coma.

Tim's tri-colour Bahtinov idea is brilliant. I must remember that one.

Olly

Cheers Olly... do you think I might need a coma-corrector? I was told (by Brian at Orion)because the scope is slow at f6 it didn't need it?

I will definitely have a play with the focuser then, see what we can do about the possible 'angle' issue... I am hoping it can be corrected relatively easily.

Ben

[rocketandroll]

...in the mean time...

I added in a couple of luminance layers from my meg72 data from December, seeing as that had the whole nebula with all the feint whispy bits...

It's actually added a lot to it... here's a new version...

you can't see the fuzzy looking stars with a 1024 pixel wide reduced version, the full size is 5 X larger.

Anyway... gonna have a play over the weekend... sorry Graham, thanks for the offer but got to be clearing the house and doing some work this afternoon... might have to be over the weekend or early next week?

Cheers all!

Ben

[ollypenrice]

Cheers Olly... do you think I might need a coma-corrector? I was told (by Brian at Orion)because the scope is slow at f6 it didn't need it?

I will definitely have a play with the focuser then, see what we can do about the possible 'angle' issue... I am hoping it can be corrected relatively easily.

Ben

I'm afraid I just don't know. On a large chip I'd be surprized if an uncorrected F6 gave a sensibly flat field but I don't image with Newts. I have just corrected a very small tilt arising from a cheap temporary extension tube on Yves' 14 inch ODK. (I used a superior Altair Astro one with 2 lockscrews instead of one). The improvement is star shape is dramatic and this instrument is F6.8.

I would get onto that tilt, myself. It's a classic bugbear in imaging.

Olly

[rocketandroll]

I'm afraid I just don't know. On a large chip I'd be surprized if an uncorrected F6 gave a sensibly flat field but I don't image with Newts. I have just corrected a very small tilt arising from a cheap temporary extension tube on Yves' 14 inch ODK. (I used a superior Altair Astro one with 2 lockscrews instead of one). The improvement is star shape is dramatic and this instrument is F6.8.

I would get onto that tilt, myself. It's a classic bugbear in imaging.

Olly

If the tilt is the result of the focuser being damaged or knocked out of true by the 'accident' (if no one read the thread, the OTA broke off the mount and fell 5ft on to my head, then primary first onto the tarmac just before I managed first light back in Dec, the focuser was at full extension with an extender and a pound of Panaview 32mm EP in the end when it hit, and it definitely did something to the focuser as it almost fell out when I picked the OTA up, I tightened it back but it's been very strange ever since).

Is it going to be a 'send it back to the factory' job? Or is there a way of straightening it back up or introducing some way to nudge the camera straight?

I am guessing that's the most likely cause of the odd shaped stars.

Ben

[rocketandroll]

...and tweaked a bit more...

gonna have a play with the Newt tomorrow, see if here's anything that can be done with the bent/out of alignment focusser... no ideas yet though.

Ben

[Quatermass]

Im loving that really nice colours