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Old 21-01-2021, 10:45 AM
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Tak FSQ106 - Advice Please

This is a repost of a topic that I have posted in the Cloudy Nights forum.

I'm looking for the opinion of others on the performance of my recently acquired Tak FSQ106 EDXIII. Scope has been purchased on the second hand market and would be a few years old. I am seeing what I believe is coma and field curvature leading me to conclude that the only option would be to send the OTA to Takahashi for service. I am posting here to report on my testing and have my conclusions reviewed by others that have more experience with this OTA so please feel free to pull apart my analysis and provide your thoughts.

To save space here I have written a report on my testing and uploaded the report and some test files to my drop box. Here is a link to the drop box folder.

I have tested the scope with two cameras; a ZWO ASI6200 and a QSI683. Both gave me the same results.

Attached are a 3:1 zoomed image taken of the Rosette Nebula taken with the ASI6200 and an image of the aberration inspector from the Pixinsight application. The zoomed in image shows what appears to be elongation or coma in the stars in the centre of the image. The aberration inspector image shows classic field curvature. I conducted a rotation test by rotating the CAA on the OTA by approximately 90 degrees. The coma elongation in the centre of the image rotated with the rotation in the image train. From this I conclude that the issue lies in the OTA and not in the image train.

There are no reducers in the image train and the image train is configured to bring the image into focus at the requisite 178mm backfocus for this OTA. SGP Pro was used for image acquisition and I took great care to make sure that the auto focus routine was giving the best focus possible.

The extent of these aberrations is sufficient to mean that I cannot use the OTA for imaging so it seems to me that the only option is to get a quote from Takahashi to service the OTA.

I would appreciate that thoughts and ideas of others on this forum that may have more experience with the FSQ106.

Thanks for looking,
Rodney
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  #2  
Old 21-01-2021, 11:42 AM
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Good day Rodney, had a good look at all your files and TBH I can't see much wrong with the scope. That's what I would expect for that type of refractor with that level of scrutiny

Having said that how do you focus? Are you absolutely sure you are in focus when you get outer field aberrations?

Re:CAA it's very easy to fix. Pull it apart. You'll see there is no bearing or bush. It's only two parts extremely tight fitted. You need to pull them apart, degrease and clean them, then put just one drop of very thin oil and slide them back together then adjust the ring for tension. You'll then see you'll have no sag or play and it will rotate very smoothly.
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Old 21-01-2021, 11:55 AM
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Rodney, to me the spacing looks like it needs attention.

When one has "warp speed" in the corners, it means the sensor is too close (ie: more spacing is required), the Goldfish bowl look is the opposite.

Your corners are showing the warp speed pattern, and a hint of tilt.

Cheers

Andy
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Old 21-01-2021, 12:05 PM
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Quote:
Originally Posted by multiweb View Post
Good day Rodney, had a good look at all your files and TBH I can't see much wrong with the scope. That's what I would expect for that type of refractor with that level of scrutiny

Having said that how do you focus? Are you absolutely sure you are in focus when you get outer field aberrations?

Re:CAA it's very easy to fix. Pull it apart. You'll see there is no bearing or bush. It's only two parts extremely tight fitted. You need to pull them apart, degrease and clean them, then put just one drop of very thin oil and slide them back together then adjust the ring for tension. You'll then see you'll have no sag or play and it will rotate very smoothly.
Thanks Marc. I can certainly look at some maintenance with the CAA to take up any play. At this stage though I'm not convinced that this will solve the issue but it is still worth doing.

Being aware of the importance of getting the focus correct I took care to make sure that the focus was as spot on as I could get it. I checked the SGP Pro auto focus routine carefully and in addition stepped the focuser through the focus range as a reference.

One of the key issues I noted is that because of the elongation in the stars in the centre of the image, I am having trouble trying to register the pre and post meridian sub frames. As well as that I don't believe that the OTA is performing to what an FSQ106 should.
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Old 21-01-2021, 12:09 PM
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Hi Rodney,

Couple of thoughts from me

1. I believe, you mentioned that SGP was used for focusing. Doesn't SGP focus based on field of view? If yes would it be possible for you to focus some other way on a star in the center to check the curvature/tilt?

2. Yet to compare the fits, but from document images QSI image appears to be tighter in the corners compared to ZWO ASI images. Is that the case?

Regards
Raki
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Old 21-01-2021, 12:10 PM
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Quote:
Originally Posted by Andy01 View Post
Rodney, to me the spacing looks like it needs attention.

When one has "warp speed" in the corners, it means the sensor is too close (ie: more spacing is required), the Goldfish bowl look is the opposite.

Your corners are showing the warp speed pattern, and a hint of tilt.

Cheers

Andy
That is where the 'gotcha' is with this OTA Andy. The Tak FSQ106 EDX range are supposed to have a flat field out of the box with an image circle of 88mm. There is no reducer in the image train so as long as you reach focus at the back focus distance of 178mm then all should be sweet. There is no option to play with the spacing because that is effectively what is being done with the focusing of the telescope. Or - to put it another way - if the image plane of the camera is in focus then the field should be flat.

Admittedly, full fame sensors with small pixels are somewhat demanding but I still thing there may be an issue with the OTA.
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Old 21-01-2021, 12:14 PM
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I looked at the Rosette Luminance. That's tilt. You don't have coma in all 4 corners but rather only 2 left and right top and bottom.

My advise is to get rid of the CAA. That's what the difference is between the EDX111 and the EDXiv. It was replaced with a solid casting. The CAA is not good enough.

An alternative is to replace the whole FSQ focuser with a Feathertouch 3515. They make a specific focuser replacement for the FSQ.

Tak brought out EDX1-4 in an attempt to fix these sorts of problems. If you send it back to Tak they are likely to tell you the scope is within design parameters.

Having a tilt adapter is not going to help if the flex is coming from the CAA in front of it.

Another point. The lock focus lever on the EDX scopes is defective. If you engage it you will get a shift of focus. You either don't use it at all or have it half engaged, focus then fully engage and it won't shift focus.

I have had an EDX111 myself I bought new and also an FSQ106N which had a much sturdier focuser and a simple but problem free focus lock.

Tak may be great for optics but they are no AP or Feathertouch for focusers.


Greg.
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Old 21-01-2021, 12:16 PM
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Quote:
Originally Posted by niharika View Post
Hi Rodney,

Couple of thoughts from me

1. I believe, you mentioned that SGP was used for focusing. Doesn't SGP focus based on field of view? If yes would it be possible for you to focus some other way on a star in the center to check the curvature/tilt?

2. Yet to compare the fits, but from document images QSI image appears to be tighter in the corners compared to ZWO ASI images. Is that the case?

Regards
Raki
Good points Raki. SGP does use or can use the entire field of view for focusing. It does also have the option of using a cropped portion of the field as well to allow for any distortion in the corners of the image. For this reason I configured the auto focus routine to crop the outer 30% of the image to remove this risk. Having said that, it would be worthwhile me having another test run and maybe tighten this up a bit.

On the issue of the QSI image being tighter in the corner. Yes this is the case. Zooming on on the QSI image does show the star elongation in the centre though. I was expecting the QSI camera to produce a better outcome due to the small sensor size which when compared to the ASI6200.
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Old 21-01-2021, 12:20 PM
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The QSI sensor (KAF683) micro 4/3rds size is less than half the size of the ASI6200 -full frame 36 x 24.

So you the centre stars are always sharper than the outer stars. Star sizes get larger the further out from the centre you go.

Its not a focusing issue its a tilt/flex issue.

By the way Rodney the 178mm is the backfocus. FSQ is a flat field scope meaning there is no optimum spacing for the imaging components so long as its less than 178mm.

Looking at the Rosette ASI image in CCD Inspector it says 11% tilt and 54% curvature which is very high. Not sure why its saying that.
But fix the tilt first. Coma would be all 4 corners not just 2.

Greg.
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Old 21-01-2021, 12:32 PM
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Quote:
Originally Posted by gregbradley View Post
I looked at the Rosette Luminance. That's tilt. You don't have coma in all 4 corners but rather only 2 left and right top and bottom.

My advise is to get rid of the CAA. That's what the difference is between the EDX111 and the EDXiv. It was replaced with a solid casting. The CAA is not good enough.

An alternative is to replace the whole FSQ focuser with a Feathertouch 3515. They make a specific focuser replacement for the FSQ.

Tak brought out EDX1-4 in an attempt to fix these sorts of problems. If you send it back to Tak they are likely to tell you the scope is within design parameters.

Having a tilt adapter is not going to help if the flex is coming from the CAA in front of it.

Another point. The lock focus lever on the EDX scopes is defective. If you engage it you will get a shift of focus. You either don't use it at all or have it half engaged, focus then fully engage and it won't shift focus.

I have had an EDX111 myself I bought new and also an FSQ106N which had a much sturdier focuser and a simple but problem free focus lock.

Tak may be great for optics but they are no AP or Feathertouch for focusers.


Greg.
Quote:
Originally Posted by gregbradley View Post
The QSI sensor (KAF683) micro 4/3rds size is less than half the size of the ASI6200 -full frame 36 x 24.

So you the centre stars are always sharper than the outer stars. Star sizes get larger the further out from the centre you go.

Its not a focusing issue its a tilt/flex issue.

By the way Rodney the 178mm is the backfocus. FSQ is a flat field scope meaning there is no optimum spacing for the imaging components so long as its less than 178mm.

Greg.
Thanks Greg, yep - I'm fine with the fact that the OTA should have a flat field at 178mm backfocus which is consistent with my observations thus far. This is why I was a surprised to see such an obvious radial pattern in the field.

From my review of the images, the radial pattern to me looks to be too consistent in the corners to blame tilt at this point. I am happy to be proved wrong of course. I even used the Dynamic PSF tool in Pixinsight to measure the ratio of x/y coordinates of the stars in the corners and they all looked to be the same to me.

Having said that, when I bought this scope I had in the back of my mind that I wouldn't be surprised if I finished up changing the stock focuser as I have been down this path with my TSA120. I fought with that scope for 18 months before finally buying a Feather Touch focuser for it and I have never looked back. I would really want to be sure that the optics are up to scratch first though before spending that sort of money on this one.

I do have a spare Moonlight focuser sitting around that I might try. I would just have to buy the adapter from them to match the FSQ. Would be a cheaper option to check it before taking the plunge.
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Old 21-01-2021, 12:41 PM
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Swapping out the focuser if you already have one and getting rid of the CAA would be a definite first step. Then the optics can be analysed more
accurately.

There is another thread on CN where a guy had an FSQ with some chromatic aberrations in the corners and sent it back only to be told the scope was per spec by Tak.

If you look at the spot sizes graph for the FSQ stars do get a fair bit larger further out.

But as images from Mike Sidonio have shown the FSQ can do great all the way out to the corners.

The FSQ106EDX111 I had gave round stars to the corners of a 9 micron 16803 sensor which is several times the size of your 683 and 50% larger than the ASI6200 but with larger pixels.

Greg.




Quote:
Originally Posted by Ryderscope View Post
Thanks Greg, yep - I'm fine with the fact that the OTA should have a flat field at 178mm backfocus which is consistent with my observations thus far. This is why I was a surprised to see such an obvious radial pattern in the field.

From my review of the images, the radial pattern to me looks to be too consistent in the corners to blame tilt at this point. I am happy to be proved wrong of course. I even used the Dynamic PSF tool in Pixinsight to measure the ratio of x/y coordinates of the stars in the corners and they all looked to be the same to me.

Having said that, when I bought this scope I had in the back of my mind that I wouldn't be surprised if I finished up changing the stock focuser as I have been down this path with my TSA120. I fought with that scope for 18 months before finally buying a Feather Touch focuser for it and I have never looked back. I would really want to be sure that the optics are up to scratch first though before spending that sort of money on this one.

I do have a spare Moonlight focuser sitting around that I might try. I would just have to buy the adapter from them to match the FSQ. Would be a cheaper option to check it before taking the plunge.
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Old 21-01-2021, 12:50 PM
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Quote:
Originally Posted by Ryderscope View Post
Thanks Marc. I can certainly look at some maintenance with the CAA to take up any play. At this stage though I'm not convinced that this will solve the issue but it is still worth doing.
Well you have tilt in your field so sort that one out first, tick that box and move to the next item.

Quote:
Originally Posted by Ryderscope View Post
Being aware of the importance of getting the focus correct I took care to make sure that the focus was as spot on as I could get it. I checked the SGP Pro auto focus routine carefully and in addition stepped the focuser through the focus range as a reference.
Yeah but nah... do it visually with a Bath mask and make sure you're spot on zoomed at 400%. Then insulate your tube so you keep focus. I assume you have a MEF or other (micro focuser) on that scope right?

Quote:
Originally Posted by Ryderscope View Post
One of the key issues I noted is that because of the elongation in the stars in the centre of the image, I am having trouble trying to register the pre and post meridian sub frames. As well as that I don't believe that the OTA is performing to what an FSQ106 should.
As I said I had a look at your raw files and I can't see much wrong with them. My feeling is that you're not 100% in focus. If you are then there's something else.

PS: get rid of that tilt adaptor as well for testing.
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Old 21-01-2021, 01:44 PM
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Quote:
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Well you have tilt in your field so sort that one out first, tick that box and move to the next item.


Yeah but nah... do it visually with a Bath mask and make sure you're spot on zoomed at 400%. Then insulate your tube so you keep focus. I assume you have a MEF or other (micro focuser) on that scope right?



As I said I had a look at your raw files and I can't see much wrong with them. My feeling is that you're not 100% in focus. If you are then there's something else.

PS: get rid of that tilt adaptor as well for testing.
1. I'm still not convinced that it is tilt as the radial pattern looks fairly even in the corners to me. (Once again, I'm happy to be proved wrong on this. I'm just not seeing any convincing arguments here).

2. I wouldn't have thought that focusing with the Bath mask would be more accurate than using the auto focuser, no worries though I can give this a shot. I have one that should fit the FSQ. It does beg the question though which is that if this was an issue, what is wrong with the auto focusing? Note that I also tried 'manually' focusing by moving the stepper motor through the focus zone in small increments until the best focus was achieved.

3. I have the Feather Touch posi drive focuser on this OTA. I has a step size of 2.3 microns which equates to 26 steps per critical focus zone for this OTA.

4. We will have to disagree on the quality of the raw files. To me they are not up to the quality I would expect to the extent that I would not bother attempting to process the data.

5. There is also an issue with registering images from this OTA which have been taken pre and post meridian resulting from the elongation of the stars in the image. This will take longer to explain so I will post a separate reply on that one.

6. The Gerd Numen M68 tilt adapter is a solid unit which comes with good recommendations from others that have used them. I specifically purchased this one as the ZWO tilt adapters have a very poor reputation. The general advice is that small pixel full frame sensors are always going to show up any foibles in the image train, particularly tilt, which I why I included one in the image train.

Thanks Marc, I hope you don't mind me challenging some of your responses. I appreciate the input and am just trying to nut my way through this

Best,
Rodney
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Old 21-01-2021, 02:06 PM
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Quote:
Originally Posted by Ryderscope View Post
1. I'm still not convinced that it is tilt as the radial pattern looks fairly even in the corners to me. (Once again, I'm happy to be proved wrong on this. I'm just not seeing any convincing arguments here).

2. I wouldn't have thought that focusing with the Bath mask would be more accurate than using the auto focuser, no worries though I can give this a shot. I have one that should fit the FSQ. It does beg the question though which is that if this was an issue, what is wrong with the auto focusing? Note that I also tried 'manually' focusing by moving the stepper motor through the focus zone in small increments until the best focus was achieved.

3. I have the Feather Touch posi drive focuser on this OTA. I has a step size of 2.3 microns which equates to 26 steps per critical focus zone for this OTA.

4. We will have to disagree on the quality of the raw files. To me they are not up to the quality I would expect to the extent that I would not bother attempting to process the data.

5. There is also an issue with registering images from this OTA which have been taken pre and post meridian resulting from the elongation of the stars in the image. This will take longer to explain so I will post a separate reply on that one.

6. The Gerd Numen M68 tilt adapter is a solid unit which comes with good recommendations from others that have used them. I specifically purchased this one as the ZWO tilt adapters have a very poor reputation. The general advice is that small pixel full frame sensors are always going to show up any foibles in the image train, particularly tilt, which I why I included one in the image train.

Thanks Marc, I hope you don't mind me challenging some of your responses. I appreciate the input and am just trying to nut my way through this

Best,
Rodney
That's cool. As emailed if you want to rule out the refractor fix the CAA potential tilt, get rid of all attachments but for the camera and reshoot at different angles. If there's a problem you'll pick it up straight away. If not add components and reshoot until you figure out where the issue lies.
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Old 21-01-2021, 02:32 PM
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That's cool. As emailed if you want to rule out the refractor fix the CAA potential tilt, get rid of all attachments but for the camera and reshoot at different angles. If there's a problem you'll pick it up straight away. If not add components and reshoot until you figure out where the issue lies.
Thanks Marc.
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Old 22-01-2021, 07:49 PM
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What Marc said.

There is clearly tilt in the Rosette image. 2 corners show elongation the other 2 aren't bad. That's tilt. Fixing something else will be a dead end.

The CAA isn't helping so I would get rid of that and get that adapter for the Moonlight and replace the Tak focuser which is a known weak link.

Greg.
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Old 22-01-2021, 09:37 PM
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Quote:
Originally Posted by gregbradley View Post
What Marc said.

There is clearly tilt in the Rosette image. 2 corners show elongation the other 2 aren't bad. That's tilt. Fixing something else will be a dead end.

The CAA isn't helping so I would get rid of that and get that adapter for the Moonlight and replace the Tak focuser which is a known weak link.

Greg.
Thanks Greg, I've checked out the spare Moonlite focuser that I have and unfortunately it isn't going to work. It is one that I had on the TSA120 and won't suit the FSQ as it has the integrated long draw tube. The Nitecrawler focuser that Moonlite make for the FSQ106 has a recess that the rear lens element from the FSQ can slip into. If I'm going to replace the focuser then I will lash out and get the Feather Touch one. I would like to make that pesky CAA go away but I don't know how I can do this without replacing the whole focuser any way.

I have a few more things which I am going to try tonight whilst it is clear (albeit with some moon about). I'm interested to spend a little extra time making sure that the focus is correct by zooming in on the stars in the centre of the image. I want to be sure that the radial stars in the corners were not affecting the focusing.

Attached images:
* My spare Moonlite focuser
* A screen shot from a video showing the Moonlite night crawler being installed on an FSQ106


Cheers,
Rodney
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Old 23-01-2021, 06:22 AM
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That's a shame it doesn't fit.

Try focusing a star in one of the better corners and then noting the position and then focusing on a star near the centre and see if there is much difference.

Greg.




Quote:
Originally Posted by Ryderscope View Post
Thanks Greg, I've checked out the spare Moonlite focuser that I have and unfortunately it isn't going to work. It is one that I had on the TSA120 and won't suit the FSQ as it has the integrated long draw tube. The Nitecrawler focuser that Moonlite make for the FSQ106 has a recess that the rear lens element from the FSQ can slip into. If I'm going to replace the focuser then I will lash out and get the Feather Touch one. I would like to make that pesky CAA go away but I don't know how I can do this without replacing the whole focuser any way.

I have a few more things which I am going to try tonight whilst it is clear (albeit with some moon about). I'm interested to spend a little extra time making sure that the focus is correct by zooming in on the stars in the centre of the image. I want to be sure that the radial stars in the corners were not affecting the focusing.

Attached images:
* My spare Moonlite focuser
* A screen shot from a video showing the Moonlite night crawler being installed on an FSQ106


Cheers,
Rodney
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Old 23-01-2021, 01:26 PM
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Results of last nights testing:

Following up on the theory that I needed to make sure that I had the focus right, I changed the SGP pro setting to crop the auto focus image by 50%. I ran auto focus routine and then rechecked the focus by stepping the focus motor 13 steps at a time (half of the CFZ step count) whilst watching the HFR of a star in the centre of the image. This gave me the same result as the auto focus so I was happy with this.

I then:
Took an image (guided) 180s Lum with OTA on west side of pier
Found that I needed to do a meridian flip so did so before doing any more test shots
Took another image 180s Lum with OTA on east side of pier
Rotated the camera 90d clockwise
Took another 180s Lum image

When the camera was rotated I refocused and then recalibrated the guiding. All test images were guided. Guiding was performing well at around .5.

The following images taken with the PI aberration inspector have been attached to this post:
Test exposure with OTA on west side of pier
Test exposure with OTA on east side of pier
Test exposure with OTA rotated 90 d

Also attached are screen shots of a 3:1 zoom of the images taken before and after rotating the camera 90 degrees.

Observations from these exposures, particularly when compared to the previous test images taken a few days ago, are that the radial pattern is no longer evenly distributed around the frame. It is much more pronounced in the upper corners. In the rotated image the elongation in the centre does move with the camera rotation but the radial pattern in the upper corners appears to stay fixed. This supports the conclusion that the issue is tilt.

I also note that the pre and post meridian flip images changes noticeably in that the radial pattern shifted in a way that implies some movement in the focuser or image train. Given that the image train is all secured by screw connections it points to the focuser being the culprit. The only thing that I cannot quite see that fits into my theory is the elongation of the stars in the centre of the image.

My conclusion from this is that I must agree with the view that the aberrations that I am seeing are due to tilt and it also appears that there is some variable movement in the focuser as demonstrated by the changes taken in the image before and after the meridian. That plus the fact that the play in the CAA is really unacceptable for precise work, it would seem that the best option is to replace the focuser, preferably with a Feather Touch.

Comments on my analysis welcome.
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  #20  
Old 23-01-2021, 01:47 PM
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gregbradley
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gregbradley is online now
 
Join Date: Feb 2006
Location: Sydney
Posts: 16,704
Good testing. Nice to know before you go.

I am not seeing the elongation in the centre you mentioned except for one image which looks like guiding errors. The other last few images I assume are centre all look good. Just brighter stars.

FSQ106EDX111 was a bit hit or miss with sample scopes. I had one that had no issues (16803 corners were good). But there were a number of complaints on the Tak uncensored Yahoo Group.

Tak added a teflon pressure pad to reduce flex on one version (not sure it may've been the EDX111). A lot were fiddling with the pressure screws under the focuser to get rid of the flex with some good results.

The EDXiv removes the CAA and replaces it with a solid casting.

So you could try the tightening of the Tak focuser. I'd google for threads about this but basically its those small screws underneath the focuser.

Just out of interest did you know there was another version of the FSQ106EDX - its called the FSQ106EDP. Not sure what the differences are. I've seen it on a Japanese site - kyoei - Osaka:

Greg.
https://www.kyoei-osaka.jp/SHOP/taka...sq-106edp.html


Greg.
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