Spacehead

2 hours ago, michael8554 said:

In that case Spacehead has come up with the next-best method of displaying the sinusoidal shape of PE. 

Sorry I can't think of a way to I prove his mount. 

Michael 

It isnt a PE error - that occurs periodically and measurably - this is all over the shop and pretty much constant no matter the position of the gears.

Hi All,

I have an EQ5 motorized on RA with a 200p.

For 2 years I did fine with tracking, gradually it got so the stars started trailing a bit so I decided to look into it.

I'm fine with the PA and focus.

I have replaced the motor, the thrust bearing on the main shaft, the main bearing on the main shaft, swapped the RA worm with the hardly ever used DEC worm, re-greased, I can see no wear at all even on close inspection.
I have experimented with different tensions on the Worm drive to main ring and the motor cog to the worm cog.  Nothing makes a blind bit of difference to the outcome no matter what I try.

The following first two pics show my mount tracking with the mount rotated off PA by about 20 degrees clockwise - but in essence - I am deliberately trailing the stars whilst off-tracking so I can see if there is a pattern.
So the first pic is an 11 min sub - a green line through a star trail shows the straight path the star SHOULD take.  The second image is a zoomed in image of an approx 1 minute section of that long trail.  The third image shows what the stars look like when tracked using this mount with strong PA, basically egg shaped (kind of) in the direction of the "bumps" on the trail - as we would expect.

There is no "drift" over time - (well - about 7 pixels per hour) - what is happening here is the telescope is falling behind so the star moves "forward", then the scope catches up again and the star moves back into position creating a wavy line (mainly) but you'll see on the long line image that even this is not consistent.

I am close to trying guiding now - but having replaced pretty much everything on the mount which moves - I am really confused as to what caused this - and more importantly, will this mount even work with guiding.

Any advice/thoughts appreciated.

Cheers


 

The thing is that I write websites for a living - and nobody pays me - the most i get is £150 for two weeks solid work.
In other words im skint as - so guiding is out of the question.
 

I've stripped it all down now today and am changing all the bearings - will have to wait on delivery.  PE on the RA worms are intermingled with this error on the images - I have seen the extreme errors occasionally and am fairly happy with that.
Yes I am only tracking because I have no money.
This problem has been progressively getting worse (I was browsing my old images).
There is about 1mm or even less play on the main bearing (shown hanging on the shaft) - so I am replacing both bearings - see what happens.  Took me two damn hours to get that sealed ring off the shaft - what a bind!!!

3 minutes ago, pete_l said:

The repetition rate of deviations often provides insight into their origin. Do you have the option of producing longer exposures - say 20 minutes? But not with a 90° offset from the pole, but just a few degrees. That way the position of a star won't move it out of frame during the exposure.
The goal would be to see whether these deviations occur at regular times (and therefore are associated with the drive) or are random and therefore have an external source.

Yes I had thought about doing EXACTLY that tonight!!! Because I thought "if only the star would stay in view longer I could get a repeat pattern!!" - I tried joining multiple exposures to achieve the same thing but it didnt work out very well.

The "error" direction (the angle of the star blips within a frame) - when polar aligned - is equal to the direction of the tracking - so I have to find a nice angle for the North leg which allows trails in long exposures, but also shows the error clearly, as it will - if the angle is too small, overwrite itself if you see what I mean!!
 

(I have even tested the ground stability!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!)

8 hours ago, JamesF said:

My initial guess would be that this is just down to the accuracy of the gearing and the amount of backlash in the gear chain.  The gearbox on the motor contains quite a few gears and there can be a fair bit of movement between them all.

If there's any breeze at all the 200P can be a bit of a sail, too.

What you could try is making the east side of the mount slightly heavier than the west, so it's slightly out of balance and the gears are always fully engaged.  Whether that's the counterweights that need to be heavier or the OTA depends on which side of the meridian they're on.

James

Hi James - I have replaced the motor and its gearbox with new, there is no backlash on the worm at all now - during experiments, I have - if anything - very slightly over tightened everything just to eliminate.  To no avail.
No - there is no breeze - during my testing I ensure dead calm only - if there is even the slightest breeze I do no testing.  Breezes tend to give a more random wobble too in my experience - but this error is consistent over many nights - always the same.
I have overloading the east side to varying amounts over various nights - no effect - the error still occurs.

I am thinking its the large main bearing in the RA head now - that is the only thing I have not managed to gain access to yet.

Hi All - I track with an eq5, RA motor I added, SW 200p, PA = perfect, balance perfect and tried different things.

I get stars deviating over time and then re-locating themselves in the correct position.

So lets say I do a 1 min sub - I will get this when tracking (see small pic with stretchy stars zoomed in).

If I point the north leg of the mount to east, then switch on the RA - I am tracking offset to the actual motion of the planet.  Thus, I can now see the deviation of the stars on the mirror over time.

But not all the stars show the same deviation / bumps!!!!! 

It is important to know that this is NOT drift.  My alignment is perfect and the end of a 1 hour shoot results in only 6 pixels of drift.  Whereas each shot can be 20 pixels out - but over time the stars come back into position - within a minute normally.

I've got two examples below with star trails and ive coloured in a straight line to show how the stars deviate to give the stretched / jumpy appearance in the actual tracked properly image.

I have stripped it (the mount) down - re-greased the worm gear and main ring, replaced the RA motor completely - but to no avail.



Totally at a loss.


 

Guys I cannot thank you enough!!!!!!!!!! THANKYOU - I would never have guessed "lens" spanner or "compass" spanner.

Hi All I am trying to dismantle my EQ5 - but need the tool as shown in the photo.  The thing is - not knowing what its called I cant find one online!!!
I've tried pin spanner - but that doesn't get me the right thing - anyone know by any chance?  Much appreciated.

Hi All.

Disaster has struck tonight.  I track using a fitted RA motor and its been great for about three years.  Then tonight, I noticed that the control knob on the mount for the RA was "thudding" very slightly with each motor pulse - ive never felt this before.
On looking at the photos, I have trails on stars at 1min exposure 

Can anyone advise me what may be wrong?  I changed the batteries but the result was the same.  When moving the RA manually with the control knob it seems ok - smooth etc.  But when the motor clutch is tightened, the thudding starts

2 hours ago, FaDG said:

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

Fabio, sounds like you got a deal as good as it can get.  What do you mean by these two things "the primary strongly tensioned (almost triangular), the focuser was squinted"?

11 hours ago, FaDG said:

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

Hi Fabio, cheers for all the tips.  I might look into shortening the tube myself - not sure yet - I will have to measure up the webcam and my camera focus to see how "little" I can get away with.
If I ever sort out the spike - I will let you know - but its not looking like I will be able to.

1 minute ago, harry page said:

Hi

agreed looks straight in line , then it means something else is in the light path- does your focuser stick out much ?

 

Harry

Yes - it does indeed - check out the post above from F in italy (an earlier one than the one with the star pics of his).
In his post he says that the wide flaring is caused by the protrusion of the focuser so he cut his right back for astro photography.  Which is why his stars above show round with no flaring - but note the one at the top - has the same artifact as mine (except mine is in more positions than his).  This means (at a glance) - that the focuser is not the cause of the extra spike (given he has chopped his back - so has no flaring - but DOES have the extra spike).

1 hour ago, harry page said:

Hi

extra star spikes you show going round in a circle are normally caused by a bright star bouncing off the edge off your secondary so black these up inc the small ground edge if you have one ( I suspect you have )

The extra spike is caused by the veins not being parallel to each other , do have to be straiht in line but parallel  so put a straight edge down each vein and check the opposite is completely parallel

with it .

this should remove your extra spike

Regards

Harry 

I'd be hard pressed to get the spiders more parallel than they are already without some kind of laser guided scientific device to be fair.  They are all but hidden behind the yellow lines.
 

6 hours ago, FaDG said:

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

It's on Electra. 

That is incredible the way cutting off the focal tube has got rid of the flaring - how utterly stupid a design is that????????  The mind boggles.
I can see your rogue diffraction spike too - if mine was in the outer region like yours rather than the middle of the image, I wouldnt bother with it.  But unfortunately mine is all over the place.

8 minutes ago, andrew s said:

You could try flocking the inside of the focused tube first.

Regards Andrew 

Will do that later today and test tonight if clear - yup.  The rest is flocked.

45 minutes ago, FaDG said:

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

Ok - regarding the general flaring - I am not too worried about that, as I see it all the time on photo samples from the 200p where there are many bright stars in one shot.  I admit - I don't like it - and may address it by cutting the focus tube down.

The single stray spike is my pet hate though - I mean its wrecking my life (lol) - are you saying that is also characteristic of sw newts?  Can you show me a pic displaying this problem from your 150?

This is a close up of the star (just lower iso) - in the center of the frame.  I think the flat left side of the circle is the intrusion from the focus tube maybe.
(just for info really)

Ive consolidated these into one image - pasting in the position of each shot.  Im pleased with the collimation - the flaring is center in the center - and "directionally" towards the center in those images with the star around the edges.
The green dots show the stars position when the extra spike does not show - the red dots are showing the spike.
Strange or what?
I will be honest - I dont know what this means or whether it helps at all?  Just hoping someone will know where next to look.  

Ive done some pics tonight - moving a star around the mirror - interestingly, the spurious spike is in some pics and not others.
 

4 hours ago, Ben the Ignorant said:

Try attaching a round disk of black paper or cardboard on the secondary, make it larger than any protrusion the secondary housing might have, and do a test shot.

Then remove it, and make an aperture mask, a ring smaller than the mirror so the mirror's retaining clips and the screws inside the tube are in its shadow. Do some test shots, you'll know where the spike is caused. 

I may have to give this a go.  Cheers.

3 hours ago, FaDG said:

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

This is in all images I have where a given star is bright enough to show the spikes.  There are very few constellations which have multiple stars bright enough - Pleiades is one - but its not there atm.  I will take a picture of a star in each corner instead.

If its nice tonight I will do some more testing - lost a lot of time on collimation yesterday.

1 hour ago, CraigT82 said:

Looking at the secondary from the front of the scope, is there anything at all protruding into the light path? I'm thinking screw heads or secondary heater or something like that? 

The focus tube does - but I cant test this as its out of focus on a star by the time its retracted far enough - so no spikes anyway.
There are 3 mirror clamps (black) holding the primary in place - these do show up in the secondary when looking through the collimation cap - I cant see it being these though - they have been there forever.