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Tuning a classic Meade model 2080 8" SCT

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#1 wcoastsands

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Posted 21 July 2021 - 01:03 AM

Back in January I was given a Meade model 2080 8" SCT. The previous owner had passed away, and his wife had reached out to our local astronomy club to find it a new home. This is my first SCT, and my first experience with this type of scope. My understanding is this scope is about 40yrs old. Which is also about as old as I am, a fact that I really get a kick out of, especially being a long time fan of Meade. The scope was a little dirty, but overall it was well taken care of and still in great shape. Mirrors were spotless. This LX3 classic didn't come with a tripod, though. So I decided to de-fork it and install an ADM DM8 D Series dovetail bar to fit the ADM dual saddle of my Celestron AVX. Cleaned it up, and took it for a spin. Got to see Mars, Uranus, and the Moon with more clarity and detail than ever before. Incredible.
 
It's been a few months now, but I finally worked up the courage over the weekend to clean the corrector plate. Not sure if or when the corrector had last been cleaned. It wasn't super filthy, but it did have some deposits on it that I was concerned might eventually eat away, or already be eating away, at the coating. It's clean as a whistle now. Clean enough to see that it also has a film and some more spots on the rear surface of the corrector. Would have to remove it to clean further. Fresh out of courage, I decided to leave that for another day.
 
E6nfBM0UcAUVAEF.jpg
 
Last night was a big success for me. Sky was clear. Got to see Venus and Mars before the dipped below the horizon. My goal for the night was to figure out how to evaluate and correct the scope's collimation. I've spent a lot of time collimating Newtonians, but had never attempted to collimate an SCT before. From all the research I'd done, it seemed super complicated. My plan was to use MetaGuide to assist with the collimation, but I hadn't really used before. I struggled a bit with it at first. Realized that I needed to install the ZWO DirectShow drivers before I could use my ASI290MM Mini with the software. Once connected, it still wasn't getting anywhere. Seemed like the scope needed to be roughly collimated first before using the tools available through MetaGuide.
 
Using SharpCap, I attempted to adjust collimation with the scope slightly out of focus on a mag 4 star close to the zenith. From the screenshot, you can see how this started out:
 
E6wx404UUAYLugA.jpg
 
Figuring out which screw to adjust was easy enough: just extended a finger into the light path over each screw in turn to see which needed adjustment. I adjusted the secondary collimation screws until the diffraction rings were all centered up around each other. Everything looked good except the star seemed to take on a triangular shape as it approached focus.
 
E6w0T-JUcAEm8ZQ.jpg
 
I believe the triangular star shape is due to astigmatism caused by the secondary collimation screws applying too much pressure to back of the secondary mirror, deforming its shape. I was able to correct for it somewhat by backing each of the screws out a bit.
 
Using MetaGuide, I can confirm collimation is now pretty darn close to spot on, but can also more clearly see the result of astigmatism, especially with the first airy ring.
 
E6w1aVoUcAMMwRj.jpg
 
Had a chance to run some test captures on the moon just before the marine layer moved in around 1AM. The moon was pretty low by then. So seeing wasn’t great, but I think I got one of my best captures of the moon so far.
 
E6xNounVcAUTZkh.jpg
 
For this image, I used an Astronomik ProPlanet 642 BP IR-pass filter threaded onto the ASI290MM Mini. This is about 1000/2000 exposures stacked using AutoStakkert 3 with wavelets applied using RegiStax 6. Gain was set to 90 for minimal read noise while maintaining high dynamic range. Color space used was MONO16, since there was no visible noise using MONO8, and was stored in .ser file format. Stacked image was stored as a FITS file.
 
I made a few captures before the clouds moved in. This is just the first I’ve had time to process. I'm hoping to focus more on planetary imaging over the coming weeks, especially with Saturn reaching opposition on August 2, and Jupiter at opposition on August 19.
 
Here’s a pic with my setup from the night before. Didn’t have much luck with the clouds, but it sure was pretty out.
 
E6o4m9FVEAA73N2.jpg
 
If you got this far, thanks for taking the time to read.
 
Clear skies,
 
Nikko


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#2 quilty

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Posted 21 July 2021 - 04:06 AM

nice report. I got the very similar 2080 which dates, regarding its serial No. from 1982 or 1983. And I' ll also try to losen a bit the three screws for that triangular asti might be seen as well. But there' s already very little torque necessary to turn the screws, and I don't want to have the secondary too lose. Do the three beams move and flatter? Through my scope they do and the Airy spot is hard to see and no diffraction ring regardless to star magnitude. It's just the question what performance we can expect from such a scope. Your moon shot looks great, I am sorry that I'm not able to do imaging.

I consider to drill six new bores through the blue tube into the black cast aluminium front and buttpiece and fix the tube by the new screws in order to have easy access to the mirror and Schmidt-plate.

 

 

Stephan



#3 macdonjh

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Posted 21 July 2021 - 02:54 PM

Removing the corrector plate is not difficult.  When you summon your courage, remember to mark the orientation of the corrector and put it back in the same orientation.  They typical, and easiest, way to mark orientation is to put a piece of tape across the seams between the corrector and that plastic retaining ring, and the ring and the aluminum front piece.  Then slit the tape with a sharp knife.  When you put the scope back together, just line all the pieces of tape up.

 

The figure of the corrector plate may not be symmetrical, so reassembling it with an orientation different than the original may result in soft images that are tedious to correct (lots of trial and error needed).

 

Good luck.


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#4 quilty

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Posted 22 July 2021 - 06:59 AM

nevertheless. With the new screws the 2080 disassembly would be as easy as it is at the GSO Cassegrains.

The moon picture reveals craters in Clavius in the size of about 2.2 km which is a definition of 1.3 arcsecs. Not too bad!



#5 rmollise

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Posted 22 July 2021 - 09:22 AM

Back in January I was given a Meade model 2080 8" SCT. The previous owner had passed away, and his wife had reached out to our local astronomy club to find it a new home. This is my first SCT, and my first experience with this type of scope. My understanding is this scope is about 40yrs old. Which is also about as old as I am, a fact that I really get a kick out of, especially being a long time fan of Meade. The scope was a little dirty, but overall it was well taken care of and still in great shape. Mirrors were spotless. This LX3 classic didn't come with a tripod, though. So I decided to de-fork it and install an ADM DM8 D Series dovetail bar to fit the ADM dual saddle of my Celestron AVX. Cleaned it up, and took it for a spin. Got to see Mars, Uranus, and the Moon with more clarity and detail than ever before. Incredible.
 
It's been a few months now, but I finally worked up the courage over the weekend to clean the corrector plate. Not sure if or when the corrector had last been cleaned. It wasn't super filthy, but it did have some deposits on it that I was concerned might eventually eat away, or already be eating away, at the coating. It's clean as a whistle now. Clean enough to see that it also has a film and some more spots on the rear surface of the corrector. Would have to remove it to clean further. Fresh out of courage, I decided to leave that for another day.
 
E6nfBM0UcAUVAEF.jpg
 
Last night was a big success for me. Sky was clear. Got to see Venus and Mars before the dipped below the horizon. My goal for the night was to figure out how to evaluate and correct the scope's collimation. I've spent a lot of time collimating Newtonians, but had never attempted to collimate an SCT before. From all the research I'd done, it seemed super complicated. My plan was to use MetaGuide to assist with the collimation, but I hadn't really used before. I struggled a bit with it at first. Realized that I needed to install the ZWO DirectShow drivers before I could use my ASI290MM Mini with the software. Once connected, it still wasn't getting anywhere. Seemed like the scope needed to be roughly collimated first before using the tools available through MetaGuide.
 
Using SharpCap, I attempted to adjust collimation with the scope slightly out of focus on a mag 4 star close to the zenith. From the screenshot, you can see how this started out:
 
E6wx404UUAYLugA.jpg
 
Figuring out which screw to adjust was easy enough: just extended a finger into the light path over each screw in turn to see which needed adjustment. I adjusted the secondary collimation screws until the diffraction rings were all centered up around each other. Everything looked good except the star seemed to take on a triangular shape as it approached focus.
 
E6w0T-JUcAEm8ZQ.jpg
 
I believe the triangular star shape is due to astigmatism caused by the secondary collimation screws applying too much pressure to back of the secondary mirror, deforming its shape. I was able to correct for it somewhat by backing each of the screws out a bit.
 
Using MetaGuide, I can confirm collimation is now pretty darn close to spot on, but can also more clearly see the result of astigmatism, especially with the first airy ring.
 
E6w1aVoUcAMMwRj.jpg
 
Had a chance to run some test captures on the moon just before the marine layer moved in around 1AM. The moon was pretty low by then. So seeing wasn’t great, but I think I got one of my best captures of the moon so far.
 
E6xNounVcAUTZkh.jpg
 
For this image, I used an Astronomik ProPlanet 642 BP IR-pass filter threaded onto the ASI290MM Mini. This is about 1000/2000 exposures stacked using AutoStakkert 3 with wavelets applied using RegiStax 6. Gain was set to 90 for minimal read noise while maintaining high dynamic range. Color space used was MONO16, since there was no visible noise using MONO8, and was stored in .ser file format. Stacked image was stored as a FITS file.
 
I made a few captures before the clouds moved in. This is just the first I’ve had time to process. I'm hoping to focus more on planetary imaging over the coming weeks, especially with Saturn reaching opposition on August 2, and Jupiter at opposition on August 19.
 
Here’s a pic with my setup from the night before. Didn’t have much luck with the clouds, but it sure was pretty out.
 
E6o4m9FVEAA73N2.jpg
 
If you got this far, thanks for taking the time to read.
 
Clear skies,
 
Nikko

 

Good work! Hope you have a lot of fun with this old girl! :)


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#6 wcoastsands

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Posted 22 July 2021 - 05:28 PM

Good work! Hope you have a lot of fun with this old girl! smile.gif

Thank you! I'm looking forward to it grin.gif

 

Removing the corrector plate is not difficult.  When you summon your courage, remember to mark the orientation of the corrector and put it back in the same orientation.  They typical, and easiest, way to mark orientation is to put a piece of tape across the seams between the corrector and that plastic retaining ring, and the ring and the aluminum front piece.  Then slit the tape with a sharp knife.  When you put the scope back together, just line all the pieces of tape up.

 

The figure of the corrector plate may not be symmetrical, so reassembling it with an orientation different than the original may result in soft images that are tedious to correct (lots of trial and error needed).

 

Good luck.

Thanks for the tips! These are all really good suggestions. Will definitely keep them in mind.

 

nice report. I got the very similar 2080 which dates, regarding its serial No. from 1982 or 1983. And I' ll also try to losen a bit the three screws for that triangular asti might be seen as well. But there' s already very little torque necessary to turn the screws, and I don't want to have the secondary too lose. Do the three beams move and flatter? Through my scope they do and the Airy spot is hard to see and no diffraction ring regardless to star magnitude. It's just the question what performance we can expect from such a scope. Your moon shot looks great, I am sorry that I'm not able to do imaging.

I consider to drill six new bores through the blue tube into the black cast aluminium front and buttpiece and fix the tube by the new screws in order to have easy access to the mirror and Schmidt-plate.

 

 

Stephan

Thank you! I appreciate the kind words. I started out imaging with a modified Logitech webcam a few years ago. I've gradually improved with time. Actually, I made a mosaic of the moon using that camera with my 8" Newt back in December, and at the time thought that was my best so far. When comparing the two, I was surprised to see just how much better this latest image is. Leaps and bounds better. Still, not bad for a 14yr old webcam, but I think the newer purpose-built ASI290MM Mini is just a bit better at the task. Also think the longer focal length and IR-pass filter helped make up the difference as well.

 

I suspect this scope was made around the same time as yours. It really is in good condition. Was kept in it's original footlocker when not in use.

 

I think I can do better in correcting the astigmatism caused by the secondary. I wasn't sure how the secondary assembly worked until someone in my local astrophotography group sent me a graphic that shows how the secondary assembly is structured. It has a central pivot, and the three collimation screws pull on the mirror to hold it in place. The screws were all overly tight before I got started in on them. I think I can still loosen them some more. I'm also considering adding a small o-ring under the head of each screw to alleviate some of the tension while making sure the mirror remains secure.

 

SCTSecondary.jpg



#7 quilty

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Posted 23 July 2021 - 12:25 AM

guess a soft silicone tube around the central pivot might do. It could provide a permanent slight tension without excessive stress. Alternatively a small spring around each screw


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#8 jgraham

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Posted 23 July 2021 - 01:10 AM

One of my 2080s had a problem with the little pivot stand-off. I placed a tiny silicone o-ring around it to provide a little spacing and cushion. It worked like a charm! I like to keep my adjustment screws just a tad snug.

Enjoy your scope!
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#9 wcoastsands

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Posted 23 July 2021 - 01:03 PM

Looking at o-rings on Amazon. Trying to decide between two options:

Smaller ID would have a snug fit. I haven't backed out the screws far enough to measure the shaft diameter, though. Screw heads are about 5mm in diameter, so these should fit under them, and in the recesses of the cap.



#10 jgraham

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Posted 23 July 2021 - 02:12 PM

Hmmm, I would suggest using silicone or fluorosilicone o-rings. Nitrile rubber usually contains about 15% oil as a plasticizer. This will evaporate over time and the o-ring will harden. Nitrile rubber also reacts with atmospheric ozone and degrades. Silicone and fluorosilicone does not have a plasticizer and is ozone resistant. You can often find silicone o-rings in the plumbing section at a hardware store. Hobby shops may also carry the small ones.

Food for thought.
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#11 wcoastsands

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Posted 23 July 2021 - 02:43 PM

I removed one of the secondary collimation screws to measure dimensions:

  • 2.0mm hex button head
  • 6.5mm head diameter
  • 3.5mm thread OD
  • 8mm length

Recess dimensions:

  • 7.0mm diameter
  • 1.5mm depth

Based on these measures, I'm now considering 6.5mm x 3.5mm x 1.5mm o-rings:

Think I'm leaning toward silicone, because I'm not confident that nitrile won't react with the plastic of the secondary assembly. Although the nitrile is a harder material, and may provide better support.



#12 wcoastsands

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Posted 23 July 2021 - 02:45 PM

Hmmm, I would suggest using silicone or fluorosilicone o-rings. Nitrile rubber usually contains about 15% oil as a plasticizer. This will evaporate over time and the o-ring will harden. Nitrile rubber also reacts with atmospheric ozone and degrades. Silicone and fluorosilicone does not have a plasticizer and is ozone resistant. You can often find silicone o-rings in the plumbing section at a hardware store. Hobby shops may also carry the small ones.

Food for thought.

Thank you! This is what I was concerned about. So I think I'll try the silicone ones.



#13 wcoastsands

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Posted 23 July 2021 - 03:01 PM

Now that I've taken one of the screws out, it seems like the screws only thread into the secondary by a few millimeters. I'm concerned the screws might not be long enough to add the o-rings.

 

I might not even need the o-rings. The plastic of the secondary seems pliable enough to get a similar effect. I think the screws may have just started out overly tight. Now that I'm more familiar with this setup, I'm going to try collimating again and see if I can avoid the astigmatism this time. Leaving the screws loosened until then to allow some time for the mirror to relax.



#14 jgraham

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Posted 23 July 2021 - 03:43 PM

I only placed an o-ring around the pivot. I was concerned that they would be too stiff if I installed them around the screws.

 

Just for yucks… I have 2 early production 2080s; one from LX3 production and one is from the _original_ LX production. There are a few interesting differences between them, but both are fine telescopes.


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#15 wcoastsands

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Posted 23 July 2021 - 04:28 PM

This is the one I have:

 

EsIvtSNVQAExnP1.jpg

 

This might be that original LX model you mention. Although I was reading on Bob's Knobs website that there were some early model 2080s that shipped with just 2 collimation screws instead of 3. So maybe there's an earlier version as well?


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#16 quilty

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Posted 23 July 2021 - 05:04 PM

I removed one of the secondary collimation screws to measure dimensions:

  • 2.0mm hex button head
  • 6.5mm head diameter
  • 3.5mm thread OD
  • 8mm length

Recess dimensions:

  • 7.0mm diameter
  • 1.5mm depth

Based on these measures, I'm now considering 6.5mm x 3.5mm x 1.5mm o-rings:

Think I'm leaning toward silicone, because I'm not confident that nitrile won't react with the plastic of the secondary assembly. Although the nitrile is a harder material, and may provide better support.

Thanks for the data. Another possibility is to find longer screws maybe as Bob's knobs and consider the softest silicone available


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#17 Rick-T137

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Posted 23 July 2021 - 05:10 PM

This is the one I have:

 

EsIvtSNVQAExnP1.jpg

 

This might be that original LX model you mention. Although I was reading on Bob's Knobs website that there were some early model 2080s that shipped with just 2 collimation screws instead of 3. So maybe there's an earlier version as well?

That is an LX3.

 

Clear skies!

 

Rick


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#18 wcoastsands

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Posted 23 July 2021 - 05:37 PM

That is an LX3.

 

Clear skies!

 

Rick

Yep! You're right.

 

Went searching for the history behind these scopes. Just found Uncle Rod's Used SCT Buyer's Guide. That's a really good read.

 

Thanks!


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#19 jgraham

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Posted 24 July 2021 - 06:37 AM

Yep, an LX3. The base of the LX has no ports of any kind, not even a power switch. Just plug it in, and it goes! The other distinguishing visible difference is that there are only 2 adjustment screws on the secondary; left/right, up/down. It's a little wonky, but actually works quite well.
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#20 quilty

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Posted 25 July 2021 - 07:02 AM

"Actually, I made a mosaic of the moon using that camera with my 8" Newt back in December, and at the time thought that was my best so far." 

 

Sorry, I can't open it. Is there a trick?

 

I'm using http://www.arcturus....Mappa Luna .htm instead. Haven't yet succeeded in finding visually a detail wich isn't displayed better on the map



#21 macdonjh

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Posted 25 July 2021 - 12:51 PM

Now that I've taken one of the screws out, it seems like the screws only thread into the secondary by a few millimeters. I'm concerned the screws might not be long enough to add the o-rings.

 

I might not even need the o-rings. The plastic of the secondary seems pliable enough to get a similar effect. I think the screws may have just started out overly tight. Now that I'm more familiar with this setup, I'm going to try collimating again and see if I can avoid the astigmatism this time. Leaving the screws loosened until then to allow some time for the mirror to relax.

When a fellow club member taught me how to collimate my C11, we found the collimation screws to be quite tight as well.  Tighter is better, right?  So we started by backing off all three screws until the secondary was just "floating", completely messing up collimation.  Not to worry, there were two of us and with one of us looking through the eye piece and keeping our collimation star centered (using the mount controls) and the other making adjustments to the secondary mirror, it only took about ten minutes to get back into collimation.  Another couple of minutes and we'd tweaked collimation as well as seeing that night would allow.  In the end, my scope's collimation screws were snug, but not tight. 


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#22 wcoastsands

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Posted 25 July 2021 - 03:34 PM

When a fellow club member taught me how to collimate my C11, we found the collimation screws to be quite tight as well.  Tighter is better, right?  So we started by backing off all three screws until the secondary was just "floating", completely messing up collimation.  Not to worry, there were two of us and with one of us looking through the eye piece and keeping our collimation star centered (using the mount controls) and the other making adjustments to the secondary mirror, it only took about ten minutes to get back into collimation.  Another couple of minutes and we'd tweaked collimation as well as seeing that night would allow.  In the end, my scope's collimation screws were snug, but not tight. 

I managed to get it roughly collimated again before the marine layer rolled in. It was really far out of collimation. Took me the better part of an hour, because I kept loosing the star and having to hunt for a new one. The Spiral Search button in SharpCap Scope Controls is a real godsend.

 

The silicone o-rings just arrived in the mail. Would like to give those a try, but might be a few days before I see clear skies again.

 

"Actually, I made a mosaic of the moon using that camera with my 8" Newt back in December, and at the time thought that was my best so far." 

 

Sorry, I can't open it. Is there a trick?

 

I'm using http://www.arcturus....Mappa Luna .htm instead. Haven't yet succeeded in finding visually a detail wich isn't displayed better on the map

I checked the link in that post. It should be working. It points to the following address: https://www.astrobin.com/xu940r/

 

Spent most of yesterday processing data captured this past week, mostly troubleshooting. Just posted a new image this morning:

 

E7IvrY8VgAEOpZT.jpg

 

This was captured using the new Player One Neptune-C II (IMX464) planetary camera: 1250/5000 frames stacked using Autostakkert!3, wavelets applied with RegiStax 6, additional processing in PhotoShop CC.



#23 wcoastsands

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Posted 26 July 2021 - 03:40 PM

I'm using http://www.arcturus....Mappa Luna .htm instead. Haven't yet succeeded in finding visually a detail wich isn't displayed better on the map

That lunar atlas is really cool. I really like the hand drawn aesthetic. They're really well done. Very readable. Thanks for sharing!

 

I processed another stack of data from the Player One Neptune-C II, this time in the area of Tycho. The detail isn't as sharp as the earlier capture made with the ASI290MM Mini. Seeing conditions were pretty poor in both cases, but I wasn't using an IR filter in this case. I was using an ADC, but I'm also still learning how to use it. So I'm not sure how much the image benefitted from its use.

 

E7MXZfxVgAMMczD.jpg

 

Once I get the collimation and astigmatism sorted out, I'd like to attempt another "mineral moon" image by combining RGB data with IR as a luminance. I have the option of using 642 BP or 807 BP filters. I suspect the 642 BP (having a narrower bandpass window of 200nm) may yield better results. However, the sensor isn't considered a mono sensor until above ~800nm. Anything lower may still produce checkered artifacts when applying wavelets. Will need to compare.

 

Another thing I'm noticing is that the image appears somewhat softer in the corners of the frame, most noticeable in the capture made with the ASI290MM Mini. I have a Meade f/6.3 reducer/flattener that I can try using to see if it makes a difference. Should also check to make sure the effect is uniform across the field, and adjust the tilt if needed.


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#24 jpengstrom

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Posted 27 July 2021 - 02:44 PM

I just finished cleaning the corrector plate (front and back) of my 2080LX!  If you decide to pull the corrector plate off it's a simple job.  The steps I followed are below:
 

1) Get two pieces of tape (I used blue painters tape) about an inch long and make a line down the middle of each piece of tape with a pen or fine black marker and put the pieces of tape nearby

2) Point the scope horizontally so if one of the 6 screws of the outer plastic ring gets dropped it won't land on the corrector plate

3) Pull 5 of the 6 screws holding the plastic ring in place leaving the screw on the bottom of the plastic ring in place

4) Point the scope slightly up - nothing will hold the corrector plate in place once the 6th screw of the plastic ring is pulled so you want gravity keeping the corrector plate in place

5) Remove the last screw holding the plastic ring in place

6) Remove the plastic outer ring

7) Place the two pieces of tape on the outside of the corrector plate and extending onto the black metal mounting ring

8) Be sure the tape is firmly attached to both the corrector plate and the black mounting ring

9) Carefully cut the tape with an exacto knife

10) Carefully pull the corrector plate out of the scope being careful not to disturb the cork spacers which should be glued onto the black metal mounting ring

11) There's also a rubber o-ring that sits between the corrector plate and the black metal mounting surface - it might stick to the back of the corrector plate but it's easy to remove and place on the mounting surface

12) Point the scope straight down while you clean the corrector plate to prevent dust from dropping in on the primary mirror

 

To reassemble just reverse the process, just remember not to tighten the 6 screws holding the plastic ring too much - you don't want to create any more pinched optics.  It's actually a VERY easy job and I would encourage you to do it.  Here's a picture of my scope right after I placed the tape and right before I cut the tape with the exacto and pulled the corrector plate.

51340338640_e53f5367d6_c.jpg


Edited by jpengstrom, 27 July 2021 - 02:45 PM.

  • Rick-T137 and wcoastsands like this

#25 jpengstrom

jpengstrom

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Posted 27 July 2021 - 02:47 PM

And those are really nice captures of the moon!


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