Imaging with the 130pds

[poogle]

Hi all

So I finally got around to shifting my trusty qhy8l over to the 130pds last week  I took a load of subs the other day and at first glance they seemed ok. However, on closer inspection there was some obvious tilt present - tut! It's painful to have to throw subs away...  I tried to correct the tilt earlier but I think there might still be a hint present. I'm using the qhy tilt ring as well as the focuser screws. I'm wondering if there's an easy, foolproof way of getting the adjustment spot on? Is CCD Inspector the way to go or is there another magic technique I can use? I don't want to waste more subs!

Grateful for any input/advice/suggestions.

Thanks

Louise

(have also posted this on the Cameras forum)

To get the camera "tilt free" you might try this method: http://www.sxccd.com/maintenance_info/Aligning_CCD.pdf

Hopefully your focuser is square, otherwise you'll have to align that as well

/Patrik

[Thalestris24]

To get the camera "tilt free" you might try this method: http://www.sxccd.com/maintenance_info/Aligning_CCD.pdf

Hopefully your focuser is square, otherwise you'll have to align that as well

/Patrik

Hi

Thanks but that was essentially what I was doing but it was a PIA plus it relies on my judgement... They also mention ccd inspector so maybe that would be better.

Cheers

Louise

[JimFR]

Anyone want to enlighten me on what tilting is?

Sent from my GT-I9195 using Tapatalk

[Thalestris24]

Anyone want to enlighten me on what tilting is?

Sent from my GT-I9195 using Tapatalk

Hi

It's when the sensor/camera isn't square to the incoming image light . This results in one side or part of it having elongated stars.

Louise

[JimFR]

Hi

It's when the sensor/camera isn't square to the incoming image light . This results in one side or part of it having elongated stars.

Louise

Cool, ta!

So an issue of collimation with the (assume already collimated) optics then...

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[Thalestris24]

Cool, ta!

So an issue of collimation with the (assume already collimated) optics then...

Sent from my GT-I9195 using Tapatalk

Hi

Well it boils down to how the camera / coma corrector sit in the focuser tube.

Louise

[Uranium235]

Hi all

So I finally got around to shifting my trusty qhy8l over to the 130pds last week  I took a load of subs the other day and at first glance they seemed ok. However, on closer inspection there was some obvious tilt present - tut! It's painful to have to throw subs away...  I tried to correct the tilt earlier but I think there might still be a hint present. I'm using the qhy tilt ring as well as the focuser screws. I'm wondering if there's an easy, foolproof way of getting the adjustment spot on? Is CCD Inspector the way to go or is there another magic technique I can use? I don't want to waste more subs!

Grateful for any input/advice/suggestions.

Thanks

Louise

(have also posted this on the Cameras forum)

There are any number of causes regarding tilted fields.

#1 of these is collimation, collimation and collimation. Yes, I know thats three times - but thats how important it is when trying to get good corners on a larger than average chip

#2 Have you upgraded your 2" pushfit adaptor to 3 screws? If you havent, then the coma corrector will be sitting crooked in the drawtube.

#3 Are all your adaptors fitting flushly together?

#4 If you have done/checked all of the above, then you need to square your focuser (mine was a long way out).

You need to get to the point where you dont need to use the tilt adaptor (or only very minor adjustments), but having an image to look at would make things easier for us to work out. If you can reduce it to a minimal level - you can further eliminate it by focusing in the bad part of the field, that helps balance it out a bit better.

To help you visualise whats going on, Ive put together this diagram so you can see whats happening in regard to your coma/field correction: (slightly exaggerated for illustration)

The red line is what your camera sees, point A is within the tolerance of correction and focus but if you have a tilted field the other side (or one corner) - point B of your image will be either above or below the two white lines. Above the tolerance gives radial distortion, and below giving coma. If the corrector is skew-iff, then your depth of tolerance will be too (ie: the red line might be straight, but the white lines would be the ones that are tilted). I just need to add, that the faster the f ratio - the shallower that tolerance becomes.

The best way to get points A and B within that tolerance is by adjustment of the secondary mirror and ensuring everything is fairly stiff so it doesnt sag the focuser. Adjusting camera side (after the corrector) is ok, but if you think about it - the more you adjust, the further out of collimation your telescope going to get (because you collimated it without the imaging train in place).

[Thalestris24]

Hi Rob

Here is a before adjustment image:

And one I did last night after adjusting:

Some improvement, I think but I didn't have the imaging time to try again. That's really why I was asking about any techniques to help me - preferably in daylight...

I just (last week) moved the qhy8l over from my 150pds. I didn't have a problem previously with the 1100d + gso coma corrector on the 130pds so it looks like I've introduced it. I didn't have a problem previously with the qhy8l on the 150pds and I just moved the qhy8l+spacer+mpcc en bloc from the 150pds to the 130pds.

Unfortunately, I don't think I have the skills or wherewithal to add a third screw to the focuser tube though I can see there'd by a distinct advantage to it! I've downloaded CCDInspector so will have a look with that tomorrow.

Louise

[Uranium235]

From looking at your images its most likely one of three things. Firstly, your corrector is skew-iff, Secondly (depending on angle you have your camera attached) you may have secondary rotation, or the secondary tilt is wrong. My camera is mounted so the bottom edge of the camera is in line with the dovetail bar (not in-line with the focuser lock). That way, if I see any coma on the left or right sides - I know its rotation.

A way to check if the corrector + camera is mounted crooked is to first secure is, with one hand grab the dovetail bar and hold the telescope vertically (ie: move it around like it would on a mount). Then, get a bright torch and hold it behind one side of the pushfit connection - now look from the other side... where the corrector meets the 2" pushfit adaptor, do you see any gaps where the light is getting through? (it should be flush... no gaps). If you have a gap, then its time for that third screw, if you have a friend with a bench drill and M4 tap its only a little job - shouldnt take long.

[Thalestris24]

From looking at your images its most likely one of three things. Firstly, your corrector is skew-iff, Secondly (depending on angle you have your camera attached) you may have secondary rotation, or the secondary tilt is wrong. My camera is mounted so the bottom edge of the camera is in line with the dovetail bar (not in-line with the focuser lock). That way, if I see any coma on the left or right sides - I know its rotation.

A way to check if the corrector + camera is mounted crooked is to first secure is, with one hand grab the dovetail bar and hold the telescope vertically (ie: move it around like it would on a mount). Then, get a bright torch and hold it behind one side of the pushfit connection - now look from the other side... where the corrector meets the 2" pushfit adaptor, do you see any gaps where the light is getting through? (it should be flush... no gaps). If you have a gap, then its time for that third screw, if you have a friend with a bench drill and M4 tap its only a little job - shouldnt take long.

Hi Rob

I'm not sure I understand what you mean by shining a torch... The cc is all the way in the focus tube. All you can see is the variable spacer - plus the qhy8l, of course.

Here is a pic of the setup:

I can't have the camera in line with the dovetail as I have a 70mm guide scope on the other side so have to balance the two. It's been like that for a while now and didn't cause a problem with the 1100d.

Sadly, I don't have any friends - let alone one with a bench drill and tap... I could try doing it with a hand drill but would likely make a hash of it...

I might get an imaging window between 2-4am so will maybe have another go at trying to adjust. It can only need a small amount but I obviously need to get it just right.

Thanks

Louise

[Uranium235]

What I mean by using a torch is shining it on one side of the pushfit connection, while looking at the other to see if any light makes it through (around the edges):

[Thalestris24]

What I mean by using a torch is shining it on one side of the pushfit connection, while looking at the other to see if any light makes it through (around the edges):

Hi Rob

Oh ok, no gap there! It was unexpectedly clear last night so did some more adjusting. I managed to improve things a bit more but it still needs a tweak. I'll post another image a bit later.

Thanks

Louise

[Thalestris24]

From Last night:

Maybe not any better after all

Louise

[Uranium235]

Then its a process of elimination.

If your CC isnt crooked, then your next step is to look at secondary rotation or tilt.

But before you try that, just pop your DSLR on with the CC to see if the problem persists (ie: dodgy stars on one side of the field, getting increasingly worse). If it goes away, then it cant be the telescope.

[Thalestris24]

Then its a process of elimination.

If your CC isnt crooked, then your next step is to look at secondary rotation or tilt.

But before you try that, just pop your DSLR on with the CC to see if the problem persists (ie: dodgy stars on one side of the field, getting increasingly worse). If it goes away, then it cant be the telescope.

Hi Rob

As I mentioned before, it was ok with the 1100d and gso cc up until I swapped over to the qhy8l and mpcc last week so I suspect it's tilt. However, Perhaps it's showing up with the mpcc which has a tighter spacing. The difficulty is really in making the tilt adjustment. I could be at it forever! Um, there's an allen key screw on the base of the focus tube - might that be relevant?

Anyway, it's cloudy at the moment but there's a chance of a clear spell later.

Thanks

Louise

[Uranium235]

Um, there's an allen key screw on the base of the focus tube - might that be relevant?

If youre talking about the ones under each side of the focuser controls, and the one at the top. Those are for adjusting the tilt of the whole focuser, you shouldnt mess with those unless you are in the process of squaring the focuser (ie: with secondary removed + spider).

Watch this, its for a quattro - but the principle is exactly the same:

[Thalestris24]

Hi Rob

Yeah, I've watched that video of Dion's and decided I will have a go! I've ordered some accessories  and when I've got them I'll start from scratch as per Dion's instructions. If that doesn't work maybe I'll just go back to the 150pds which has always been perfect. The 130pds has been troublesome since I first got it  http://stargazerslounge.com/topic/238240-my-brand-new-130pds-hmm/

Louise

Edited September 17, 2015 by Thalestris24

[Uranium235]

Meanwhile.... the 130 kicks out another image:

[Pally86]

Hi all, I'm looking to got into astronomy and after spending some time browsing the forums I think I've settled on the 130PDS as the scope for me to get started with.

What I'm looking for is some guidance as to what else I should buy at the same time. Ultimately I want to take some images, hopefully similar to what some of you have shared in this thread but I realise that may be some way off.

Id like to stick to a max budget of £500, so with this in mind, can anyone reccomend a mount, I'm thinking a motorised one would be more up my street.

Thanks in advance for any and all help.

Cheers, Dave

[Uranium235]

An EQ5 or CG5 may be good enough if youre wllling to work at it, but their hit rate is quite low (60% useable subs on avarage), but if you want reliability (ie: 100% hit rate, all night, every night) then the HEQ5 is the one to go for if you can grab one 2nd hand. You might end up spending a bit more than £500, especially when you factor in guiding, adaptors and a coma corrector (the CC can wait, but adaptors are mandatory items).

If you get a good mount in place right from the start it will save you a lot of bother. If you have no spare $$ left after buying the mount, just mount your DSLR + lens on the HEQ5 and it should take some smashing widefield photos until youve saved enough for the telescope + other bits.

The mount is the heart of it all...

I just need to add: It took me about 6 months of constant tinkering to get mine sorted out, so be prepared. I think I collimated mine about 120 times (yes) before I got to the stage where I was happy with it. Post-squaring of the focuser, collimation got a lot better.

[JimFR]

An EQ5 or CG5 may be good enough if youre wllling to work at it, but their hit rate is quite low (60% useable subs on avarage), but if you want reliability (ie: 100% hit rate, all night, every night) then the HEQ5 is the one to go for if you can grab one 2nd hand. You might end up spending a bit more than £500, especially when you factor in guiding, adaptors and a coma corrector (the CC can wait, but adaptors are mandatory items).

If you get a good mount in place right from the start it will save you a lot of bother. If you have no spare $$ left after buying the mount, just mount your DSLR + lens on the HEQ5 and it should take some smashing widefield photos until youve saved enough for the telescope + other bits.

I've got the EQ5 under my 130PdS, both RA and Dec axes are driven.

My beginners efforts aren't too bad - not ventured longer than 30s DSLR exposures, but quite pleased!

Can be heavy to shift outside as a unit, but sturdy once levelled and aligned - can get a bit of play on the dec axis, but not bad for just a smidge over the stated budget for a whole system!

Edited September 17, 2015 by JimFR

[Uranium235]

Hi Rob

Yeah, I've watched that video of Dion's and decided I will have a go! I've ordered some accessories  and when I've got them I'll start from scratch as per Dion's instructions. If that doesn't work maybe I'll just go back to the 150pds which has always been perfect. The 130pds has been troublesome since I first got it  http://stargazerslounge.com/topic/238240-my-brand-new-130pds-hmm/

Louise

And youve not touched that wonky focuser since you took those photos?

Errrmm... I think we have found your problem then! You have no choice, bite the bullet and square the focuser - only then can you be sure. One item you must have to do that job is the digital calipers, worth their weight in gold. Even if you find that your focuser is already squared enough (unlikely), at least youve checked.

Something to remember, then measuring the inner diameter of the tube - you must take into account the seam along the inner edge, its raised by roughly 1.5mm so it has the potential to throw your measurement out in one direction by up to 3mm (which is a lot). 

[Thalestris24]

And youve not touched that wonky focuser since you took those photos?

Errrmm... I think we have found your problem then! You have no choice, bite the bullet and square the focuser - only then can you be sure. One item you must have to do that job is the digital calipers, worth their weight in gold. Even if you find that your focuser is already squared enough (unlikely), at least youve checked.

Something to remember, then measuring the inner diameter of the tube - you must take into account the seam along the inner edge, its raised by roughly 1.5mm so it has the potential to throw your measurement out in one direction by up to 3mm (which is a lot). 

Hi Rob

Well I fiddled with it at the time and adjusted the mirror collimation as best as I could. The modded1100d images I got on the 130pds were acceptable - no tilt! I just decided to put it (the modded 1100d) on the heq5 for widefield with a lens, and put the qhy8l on the AVX/130pds because the qhy8l was being wasted and just gathering dust since the spring!

I have digital callipers Thanks for the measuring tip!

Cheers

Louise.

[Uranium235]

I've got the EQ5 under my 130PdS, both RA and Dec axes are driven.

My beginners efforts aren't too bad - not ventured longer than 30s DSLR exposures, but quite pleased!

Can be heavy to shift outside as a unit, but sturdy once levelled and aligned - can get a bit of play on the dec axis, but not bad for just a smidge over the stated budget for a whole system!

Depends on how hard youre trying to push it mate. My old CG5 would throw up the odd perfect session (ie: 600s-900s subs all night), but that was the exception rather than the rule. Eventually however, DEC backlash was the killer most of the time - so I settled on a more sensible sub lengh of 450s in order to get the hit rate up.

I took this on a CG5 four years ago, so it can certainly do the business on a good night:

[JimFR]

Depends on how hard youre trying to push it mate. My old CG5 would throw up the odd perfect session (ie: 600s-900s subs all night), but that was the exception rather than the rule. Eventually however, DEC backlash was the killer most of the time - so I settled on a more sensible sub lengh of 450s in order to get the hit rate up.

I took this on a CG5 four years ago, so it can certainly do the business on a good night:

There's hope for me yet then!

My current obstacles are light pollution, Rubbish weather, work!