RASA 11 progress and a long exposure setback

[symmetal]

Having fitted the Baader UFC tilter unit to the UFC filter assembly I've got the tilt corrected pretty well for the full frame ASI6200. The UFC system was causing terrible flares from modest brightness stars significantly outside the FOV as shown on my previous post with the ASI2600MC. This is a common problem with the RASA 11 and UFC system.

I seem to have fixed this by 3D printing a funnel/barrel shaped piece  to fit from the rear lens element and down inside the UFC assembly to the filter. I was going to fit flocking to the inside but the funnel portion made cutting pieces a bit awkward so i thought of trying 'super' black paint and bought 100ml of Musou Black which is rather expensive.  I sprayed it over the end and inside with a cheap airbrush kit and it looked good. It seems to have solved the flaring too, even on full frame which is a relief. Here it is next to un unpainted one. Even at shallow angles with a bright light there is little reflection visible.

Here's a test 30s Lum exposure with a quick arcsinh stretch showing pretty good stars over full frame and not much vignetting either. Very pleased. 😊

Now for some NB OIII as a long exposure test. The Flying Bat was at 30 degrees in the Eastand rising. so tried a 10min exposure. Oh no. Horrible stars. Polar alignment is pretty much spot on with the odd small dec guiding adjustment required every 1 or 2 mins. The guiding trace was no different in excursions for the 10 min compared to a 1 min exposure. Oddly top right shows trailing in a different direction. Guide scope is well aligned with the main scope.

5 subsequent 10 min exposures were just the same. The weights were vertical, so I tried a target in the South where they were horizontal and East heavy and got this after 10 mins.

The long image axis is parallel to RA all the time. Guiding in all cases showed no large excursions which would cause this.

I found exposures up to 5 mins showed no trailing, while those over 5 mins did to increasing amounts depending on their duration.

It can only be differential flexure, but it's very consistant, while I would have thought flexure or mirror movement would be rather random in its effects. Anyone have any ideas?

Here's the scope on the mount. Note the 3D printed rings to allow the scope to lie firmly on its side when attaching to the mount via the adjustable table. They also give a good plug fixing points for the flocking lined dew shield I also 3D printed.

I hope I'm not limited to 5 min exposures maximum with this setup which kind of defeats the money spent on the fast NB filters. What's your longest exposure with your NBZ filter @gorann?

Long exposure imaging East causes trailing in Dec while to the South causes trailing in RA should be a clue, but if the guiding shows no problems it can't just be a balance/backlash issue as that would show continuous corrections in one direction  which doesn't happen.

Alan

[gorann]

For NB imaging I use 5 min exposures and see no reason for longer ones. Strange that you are getting trailing with such a short focal length which is usually forgiving. I got my dual RASA8 rig on a Mesu 200 so a different beast than the EQ8, but then I have a 40 kg 14" SCT with 3.5 m focal length on an EQ8 in a second obsy and that one does not show trailing. Something is wrong somewhere in your rig.

[Elp]

Check the musou, I've read it works at stopping reflections due to it being uneven and textured, so it's quite flaky. I wouldn't want it anywhere near any optical surfaces if this is the case.

[symmetal]

37 minutes ago, gorann said:

For NB imaging I use 5 min exposures and see no reason for longer ones. Strange that you are getting trailing with such a short focal length which is usually forgiving. I got my dual RASA8 rig on a Mesu 200 so a different beast than the EQ8, but then I have a 40 kg 14" SCT with 3.5 m focal length on an EQ8 in a second obsy and that one does not show trailing. Something is wrong somewhere in your rig.

Thanks Göran, Do you have an OAG on your SCT rig as they are usually preferred with a SCT I can only think it's mirror movement in my case, or it would show on the guiding. But the mirror moving would generally give two distinct stars side by side, while this seems like a continuous movement only occuring after 5 mins which is odd. The shift from 5 to 10 mins is much more than any shift from 0 to 5 mins. 🤔

47 minutes ago, Elp said:

Check the musou, I've read it works at stopping reflections due to it being uneven and textured, so it's quite flaky. I wouldn't want it anywhere near any optical surfaces if this is the case.

The manufacturer does say that the paint has a low surface strength and any surface abrasion may cause it to detatch. As nothing rubs it when in place and it doesn't touch the glass I hope it will be OK. Rubbing a test piece with the finger surface seems OK, though using your nail will scratch bits off and what's left will not appear so black.

Alan

[gorann]

1 hour ago, symmetal said:

Thanks Göran, Do you have an OAG on your SCT rig as they are usually preferred with a SCT I can only think it's mirror movement in my case, or it would show on the guiding. But the mirror moving would generally give two distinct stars side by side, while this seems like a continuous movement only occuring after 5 mins which is odd. The shift from 5 to 10 mins is much more than any shift from 0 to 5 mins. 🤔

The manufacturer does say that the paint has a low surface strength and any surface abrasion may cause it to detatch. As nothing rubs it when in place and it doesn't touch the glass I hope it will be OK. Rubbing a test piece with the finger surface seems OK, though using your nail will scratch bits off and what's left will not appear so black.

Alan

Yes, with my SCTs and refractors I use OAG and I always use that when possible (so not on my RASAs). Do you have version 1 or 2 of the RASA11? I remember reading that version 1 had terrible problems with mirror movements which prompted version 2.

Edited March 27, 2023 by gorann

[symmetal]

15 minutes ago, gorann said:

Yes, with my SCTs and refractors I use OAG and I always use that when possible (so not on my RASAs). Do you have version 1 or 2 of the RASA11? I remember reading that version 1 had terrible problems with mirror movements which prompted version 2.

Mine's the version 2. The version 1 has three visible mirror locks mounted on the rear panel. They're blanked off on mine. I've rechecked focus after doing flips and there is no change in focus or any noticeable change in tilt effects, (apparently very evident on the v1), which makes me think the mirror is stable enough not to move during an exposure.

Alan

 

[gorann]

12 hours ago, symmetal said:

Mine's the version 2. The version 1 has three visible mirror locks mounted on the rear panel. They're blanked off on mine. I've rechecked focus after doing flips and there is no change in focus or any noticeable change in tilt effects, (apparently very evident on the v1), which makes me think the mirror is stable enough not to move during an exposure.

Alan

 

That is a relief. I doubt the EQ8 would wobble this much so could it be that the guide scope is moving?

Edited March 28, 2023 by gorann

[symmetal]

2 hours ago, gorann said:

That is a relief. I doubt the EQ8 would wobble this much so could it be that the guide scope is moving?

Hopefully it's something as simple as that. I'll give it a thorough check over when it stops raining. As the trailing direction changes by 90 degrees between East and South it must be gravity related.

Alan

[DaveS]

At least you got rid of the reflections quicky. I didn't from my ODK 12 and assumed that the poor calibration was my fault (A bad workman etc). Turned out (Thanks to Oddsocks for the tip off) to be reflections from the tapered M82 - M68 adaptor. Cured by painting with Black 3.0. I only lost just over 2 years worth of images   

[symmetal]

1 hour ago, DaveS said:

At least you got rid of the reflections quicky. I didn't from my ODK 12 and assumed that the poor calibration was my fault (A bad workman etc). Turned out (Thanks to Oddsocks for the tip off) to be reflections from the tapered M82 - M68 adaptor. Cured by painting with Black 3.0. I only lost just over 2 years worth of images   

That's a real pain that you had it for two years Dave, before finding a fix. There are a couple of topics on CN concerning issues with the Baader UFC system on the RASA 11 causing rainbow flare effects (with a colour camera of course) on many images, with masking and flocking tried with varying amounts of success. I thought the 3D printed shaped tube was easier to try. I was going to get Black 3.0 but the UK was out of stock and Semple's ebay site seemed the only source, with no indication that they shipped to Europe, so I thought I'd try Musou Black which was available next day from Amazon, though more expensive. They seem very similar in their blackness.

How robust is the Black 3.0 to abrasion? Not that that really matters inside the scope, but would be handy to know for the future. I did use a brush for the first try but the finish was not so great at shallow reflection angles. Musou do recommend spraying it in many thin coats, and that did produce a much better, uniform finish.

Alan

[DaveS]

I had bought some RAL 9005 matt black auto paint but it wasn't very black, but found it was good as a primer undercoat on the anodising. I tried rubbing my finger over a test piece and although the surface became slightly smoother nothing appeared to rub off.

I was able to get the Black 3.0 pretty quickly as they had it in stock at the time.

[DaveS]

I used a brush and applied two coats.

[michael8554]

Hi Alan

The guidescope mounting is much better than the commonly used soft-tippped screws in rings.

Maybe good enough to discount diff flex from that source.

In each 10 minute guided runs, were the RA and Dec guide figures similar to each other ?

That suggests guiding was good enough to give round stars,

Leaving only gravity related movement elsewhere.

Michael

[symmetal]

9 hours ago, michael8554 said:

Hi Alan

The guidescope mounting is much better than the commonly used soft-tippped screws in rings.

Maybe good enough to discount diff flex from that source.

In each 10 minute guided runs, were the RA and Dec guide figures similar to each other ?

That suggests guiding was good enough to give round stars,

Leaving only gravity related movement elsewhere.

Michael

Hi Michael,

I thought I'd better analyse the guide logs and they indicate poorer results than were evident looking at the live trace, but not bad enough to give the trailing visible. Image scale is 1.5"/pixel. The south facing trails are around 6 pixels long which implies 9" total movement and equally bright over most of their width. The periodic error suggests 2" spread over like 98% of the imaging run. The odd spikes in RA looking South need looking at. Maybe a bit less East heavy needed as the East imaging shows less RA spikes when the weights were near vertical. Seems I need to increase RA agression a bit more too as the PE is too evident as well.

East guiding at 30 deg Dec

South guiding at 60 deg Dec

I've checked all the guide scope mounting bolts and got a fraction of a turn using the actual hex wrench compared to the screwdriver I normally use. The guide camera wasn't as tight in the rotolock as it could have been but didn't seem to move. No sign of any good weather for the next week so unable to do any more checks. 

Alan

[michael8554]

The guide figures for the east run were RA =  0.44 Dec =. 0.41 , and less than your image scale of 1.5"/pixel, so stars should be round.

But those Dec spikes you see too must have an impact.

RA has a noticeable sinusoidal wave in the graph,

The EQ8 has a 3.3 minute worm period, so looks to be PE,  maybe the belt drive ?

South guiding had RA =  0.53,  Dec = 0.22,  significantly different, and now RA spikes, again maybe the belt.

Michael

 

[symmetal]

@michael8554, thanks for your assessment. As you say it's not enough to account for the star trailing. There is Dec backlash but this doesn't affect imaging much, and is only apparent when a dither move has moved it to the other side and it takes a while to take up the backlash as shown at the end of the East run. When I first got the mount it sometimes didn't return fully to the home position in RA when parking so there was likely some binding but that doesn't happen now. I've monitored the current doing fast and slow slews from side to side with no significant changes.

Unfortunately it will be at least a week before the weather might improve and I can try again.

Alan  

[michael8554]

Hi Alan

So you're discounting the RA belt drive ?

Michael

[symmetal]

6 hours ago, michael8554 said:

So you're discounting the RA belt drive ?

Sorry I didn't refer to the belt drive. I assume you're implying that the belt tension may need adjustment. This webpage has some good pictures of the EQ8 and it looks like the block the stepper is attached to has a tension adjust mounting screw as shown.

I'll take the cover off and have a look. Not knowing what the correct tension feels like, it may be a case of trial and error, but worth checking if the problem persists.

Alan

[michael8554]

Tension yes but also misaligned pulleys, damage to belt.

Michael

[symmetal]

2 hours ago, michael8554 said:

Tension yes but also misaligned pulleys, damage to belt.

Michael

Ah! OK thanks. I'll check when the weather improves. 😉

Alan

[symmetal]

@michael8554 Mine is an EQ8-R which is different from the EQ8 arrangement with better tension adjustment. Belt condition and alignment looks good, though I'm wondering if the tension could be tighter. Only modest effort is needed to rotate the belt through 90 degrees or depress it as shown. The tension adjustment screws are tight so it hasn't slipped. On my AZ-EQ6 the belts were very tight with no real belt deflection available, which I thought could be too tight but it doesn't seem to cause problems. Do you think it should be tighter?

On car timing belts, 90 degree flex on the longest run is standard I believe, but that's over a much longer distance than this. 

Alan

[michael8554]

Track the mount with the covers off as in your images and observe the belt over one rev of the belt.

Is it running smoothly ?

Or bouncing, catching on a tooth, etc ?

And when slewing, to see behaviour when moving fast.

Michael

[AKB]

Loving the tube rings and dew shield on the RASA… what are they?

I’ve been struggling to find a decent dew shield – does it have an end cap too?

Tony

[symmetal]

On 02/11/2023 at 12:31, AKB said:

Loving the tube rings and dew shield on the RASA… what are they?

I’ve been struggling to find a decent dew shield – does it have an end cap too?

Tony

Sorry Tony, I missed your posting.

They are 3D printed tube rings in PLA+, which I designed in Blender, along with the dew shield. They allow the scope to sit upright or on its side on a table without risk of it toppling. They are 2cm thick and push against the ends of the dovetail bars with the aluminium rods holding them together. The inside rim is lined with 1mm thick neoprene sheet to grip the tube. An Ender 5 Plus printer is just big enough to print them. 🙂

I realised after, I could use the holes to attach the dew shield with suitable 3D printed plugs which works well, though I have since redesigned the dew shield to attach to the two lugs on either side of the tube front that the Celestron tube end cap fits onto, so it's just push the dew shield on and twist to latch it. It does have a 3D printed end cap too. 🙂 

I made a conical shaped front cover as well, attaching the same way, which fits over the camera when the scope's indoors. 

The black tape is just to protect the paint on the tube ends from being rubbed.

One of the mounting attachments with the cutout for the locating pin to ride in. The third attachment at the bottom (without the cutout), is just to stop the cover, or dewshield, from flopping forward in use, as all three attachments rest against the end of the tube. It took a lot of trial and error printings to get the attachment cutout location correct. 

Alan

[AKB]

3 hours ago, symmetal said:

They are 3D printed tube rings

Absolutely fantastic.  Functional and beautiful.  You should go into business.

 (Although, perhaps there aren’t that many customers for this particular scope!)

Tony