Hyperstar wizards?

[8324689]

Hello there

Are there any people here that are HyperStar aficionados please? 

This is my second year (!) of trying to get it working and failing. Ive spent so many hours attempting to get it right. Im guessing its either or collimation and backfocus. 

 

I have a Tri B mask but still failing miserably 

If anyone could spare me a few mins on Zoom or similar I would so grateful for my and my families sanity!

 

Thanks all 

 

 

 

 

 

[AKB]

Hi there.  I have a C9.25 with a Hyperstar that I use all the time (for EEVA.)  In fact, this evening I was out there collimating it for the start of a new season (not having touched it since April!)

What seems to be the problem?

 

[8324689]

17 minutes ago, AKB said:

Hi there.  I have a C9.25 with a Hyperstar that I use all the time (for EEVA.)  In fact, this evening I was out there collimating it for the start of a new season (not having touched it since April!)

What seems to be the problem?

 

Hi there and thanks so much for the reply. 

I believe I have the corrrect spacing but when I was trying to collimate I was getting nowhere. There was no difference in turning the short screws really. I took one screengrab but this was a star that was off dea center in the FOV. I was trying with the Tri Baht mask Do you use the mask?

 

Im just constantly (when there are clear nights) chasing my tail in circles 

 

My stars have massive fan looking things coming off them 

Thanks - I have a C8 by the way 

 

 

 

 

 

 

 

 

Edited November 12, 2022 by 8324689

[AKB]

Several things to note:

• Collimation is most easily accomplished by pointing the scope to the zenith.  This way, gravity helps to keep the hyperstar actually resting correctly on the (long) collimation screws.
• The short screws should be loosened and the collimation achieved with the long ones... then tighten up the short ones.
• For focus I have used a Bahtinov mask in the past, but now rely on an autofocus routine which usually nails it.

If we have a good night tomorow or soon after, I will try to capture an image with a mask for you, if that's any help, so that you can see what it should look like.  When collimating I simply use a rich star field with defocused image which gives a lot of points to check the alignment on all over the field of view.  I'll get an image of that too.

If you want a comprehensive discussion of tuning the hyperstar, then have you seen this:

https://www.cloudynights.com/articles/cat/articles/the-amazing-hyperstar-a-guide-to-optimize-perf-r3013

It's an interesting read, but I wouldn't suggest that you even consider much of this until you have the basics sorted out.

Tony

[8324689]

Thanks Tony But what do you mean by autofocus routine please? Do you mean just defocusing?

 

 Thanks 

[ollypenrice]

 

The B-mask is a focusing tool, not a collimation tool. I'm not sure from your wording whether or not you have this clear, but perhaps you do.

There are four things to get right with fast systems. I'm familiar with the RASA, not the Hyperstar, but there will be lots of common ground.

1) Check that whatever camera you are using for collimation is tilt-free. If it isn't, you're doomed! Have a look at the video at the end. 

2) Collimate looking at the zenith, as  Tony says, and with the star dead central. Out of focus circles must be concentric. I'm not sure exactly how the pairs of antagonistic collimating screws work but you need to be sure that they are not at their limits of travel. The lens system must be 'suspended' between them and able to move both ways. It sounds as if this might not be the case for you.

3) the spacing must be right.

4) The focus must be nailed. A mulit-star autofocus routine is best for this. On the RASA we use Celestron's own autofocus motor and find it very good.

Olly

 

Edited November 13, 2022 by ollypenrice
typo

[Elp]

How you route your cables in front of the corrector plate will make a massive difference to the sort of diffraction spikes you get around stars, how are you doing it currently?

Starizona recommend with the HS that you set the adjustment screws so that there's no gap in the base of the HS to start with (so the long screws will be fully retracted).

I tried John Hayes method of shimming provided in the link above, I used a cut up bank card as it's close to 1mm thickness, but I found this method more exasperating as by setting the gap you're introducing another variable.

Collimation is done by defocusing when looking at a star field so every star is a doughnut shape, concentrate on a star in the centre of the field and make tiny like 1/8 clockwise turns or less to the long screws (the short ones will have to be loose at this point otherwise pushing the long screws in will not have an effect), you will see the shadow of the central obstruction move slightly depending on which set of screws you've adjusted. Once you've adjusted what you need slightly tighten all the adjustment screws and focus back to sharp focus and take an image. Repeat where required.

It's not easy though, I tried it yesterday thinking it was right and the stars top left were tilted with bad coma in the bottom right. I set it back to how Starizona recommend and it was much better again. Think it requires practice.

Edited November 13, 2022 by Elp

[AKB]

I use one of these for cable routing

https://www.firstlightoptics.com/adapters/buckeyestargazer-cable-router-for-front-mounted-cameras.html

clips nicely onto the rim of the scope

[AKB]

1 hour ago, ollypenrice said:

The lens system must be 'suspended' between them and able to move both ways. It sounds as if this might not be the case for you.

Not quite the technique I’ve used.  For me, with the scope pointing to zenith, the short locking screws can be relaxed and then the Hyperstar lens just sits on the three long adjustment screws.  Then it’s just the same as for adjusting a Newtonian. A rich star field will mean that it doesn’t matter that adjusting the collimation moves the image, since there are always stars near enough to the centre.  You also get a feel for how things vary off centre.  For me, again, with a relatively small chip, it’s pretty good across the field.

[8324689]

OK so I removed the Atair filter drawer and I think its a bit better but still need to collimate. Will check once I get kids to bed! Its misty here though.  Thanks all 

[ollypenrice]

1 hour ago, AKB said:

Not quite the technique I’ve used.  For me, with the scope pointing to zenith, the short locking screws can be relaxed and then the Hyperstar lens just sits on the three long adjustment screws.  Then it’s just the same as for adjusting a Newtonian. A rich star field will mean that it doesn’t matter that adjusting the collimation moves the image, since there are always stars near enough to the centre.  You also get a feel for how things vary off centre.  For me, again, with a relatively small chip, it’s pretty good across the field.

So the system works by having the lens drop onto three upward pointing 'bottom-position' screws and is then pinned to them by screws pointing down? In that case it wouldn't matter if one of the 'bottom position' screws were bottomed out, but if more than one were bottomed out you'd lose a dimension of adjustment? I'm not the engineer! 

Olly

[AKB]

56 minutes ago, ollypenrice said:

In that case it wouldn't matter if one of the 'bottom position' screws were bottomed out, but if more than one were bottomed out you'd lose a dimension of adjustment? I'm not the engineer! 

This only works, IMHO, if the screw you chose was aligned with lowest point of the optical ‘tilt’? From a practical point of view, a little leeway for all three of them helps. 
 

From what I’ve read here, your practical expertise exceeds many who might be happy to call themselves ‘engineers’ (which, BTW, seem barely to be technicians these days.  Although, I give you, that the term engineer has a much higher standing in Europe than in the UK.)

[8324689]

 

Is this ok??

 

 

 

 

 

I

[8324689]

maybe I should look at a varaible spacer now? 

To get the 3d effect out?

However this is a 3 min light with no guiding !

 

 

Edited November 13, 2022 by 8324689

[8324689]

Another 3 min

[8324689]

Versus 1 min 

So I dont think its the tracking that is the problem

 

[AKB]

Well, this looks like progress!

For the defocussed image, I’m a little concerned about the strongly ellipsoidal nature of the off-centre stars.  I’ve not noticed that so strongly on mine before.  Wondering if that might be a spacing inaccuracy?  Or perhaps it’s normal for a C8?

Beats me how you found any stars at all this evening!  All cloudy here.

[8324689]

1 minute ago, AKB said:

Well, this looks like progress!

For the defocussed image, I’m a little concerned about the strongly ellipsoidal nature of the off-centre stars.  I’ve not noticed that so strongly on mine before.  Wondering if that might be a spacing inaccuracy?  Or perhaps it’s normal for a C8?

Beats me how you found any stars at all this evening!  All cloudy here.

Hahah thanks! and thanks for your help.....

Yes next call is variable spacer to see what happens there I think

 

 

[ollypenrice]

While I wouldn't bet my life on this diagram (which is for chip distance on flatteners) your defocused image looks consistent with the chip being too close, perhaps? Your stellar elongations look radial from the centre to me.

Olly

Edited November 14, 2022 by ollypenrice
clarification

[8324689]

39 minutes ago, ollypenrice said:

While I wouldn't bet my life on this diagram (which is for chip distance on flatteners) your defocused image looks consistent with the chip being too close, perhaps? Your stellar elongations look radial from the centre to me.

Olly

Excellent stuff thanks !!!!

 

Yes I have the vari spacer so will try that next.

 

Getting there!!!! 

 

 

[Elp]

10 hours ago, AKB said:

I’m a little concerned about the strongly ellipsoidal nature of the off-centre stars.

I get this also with my C6, when I asked Starizona about it they said when collimating you should only concentrate on the centre star but in my mind all of them should be the same.

[Elp]

11 hours ago, 8324689 said:

varaible spacer now?

What backfocus distance are you using at the moment? The stars look more like they should across the field but the image has a soft focus across the frame a bit like a dewed over corrector plate or something. Did you also use a dew shield when taking those images?

[8324689]

30 minutes ago, Elp said:

What backfocus distance are you using at the moment? The stars look more like they should across the field but the image has a soft focus across the frame a bit like a dewed over corrector plate or something. Did you also use a dew shield when taking those images?

Im not sure what the measurement is to be honest. It was the spacer that the person I bought it from said was for the ZWO 2600 (i have the Touptek IMX571 - same thing)

I did use a Celestron dew heater ring but no shield. It was quite hazy last night ....Maybe I need a shield also....

Edited November 14, 2022 by 8324689

[Elp]

You can measure it. The start measurement is from the bottom of the thread of the hyperstar (where it reaches physical stop) where you attach the camera side and then any connecting equipment (filter drawer, extension tubes etc) and then finally your front of camera to sensor distance which is supplied by the manufacturer or if you tell us what camera you're using we can advise. You can measure all this whilst it's disassembled, a Vernier caliper will be more accurate if you have one at hand.

The tolerance of the HS backfocus distance is +/- 0.5mm.

The dew heater ring I find is excellent. A dew shield will help prevent dew formation in the first place, it also helps block out stray light entering the OTA which will also improve contrast slightly. If you look at the inside surfaces of the OTA when stray light is entering it, the reflected light off these surfaces is still quite bright so any reduction of this with a dew shield can help. The inside of OTAs should really be coated with vantablack or musou black paint/fabric really in this day and age but it's a more modern innovation so won't apply to previously made telescopes.

Edited November 14, 2022 by Elp

[ollypenrice]

We don't find any need for a dewheater with the RASA. We have a short dewshield as deep as the camera and the camera's heat and fan drafts do the rest.

Olly