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ASKAR FMA180 40mm aperture apochromatic telescope.


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I've seen the design from DeepSkyDad and it's quite clever and complex at the same time with the belt system and actual stepper motor moving as you focus. I agree that with a belt system it removes quite a lot of backlash, but maybe something with little backlash can be achieved in the above design, maybe different gears teeth tolerances?

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  • 3 weeks later...
On 25/06/2022 at 13:42, Adam J said:

This is the foil spacer I use. To be exact I used aluminium tape from B&Q, rapped around the ring one and a half times. 

It wedges the primary cell just enough to bring it into perfect alignment. 

IMG_20220625_133651731_HDR.thumb.jpg.7ae06a3c13afe7bfea2e885c1f9769a0.jpg

Thanks Adam, only just spotted your image. I have now put a ZWO tilt adjuster in the optical chain with the spacing still at 55mm. Star field image attached. Comments on the misshapen stars welcome253481391_distortedstarimage.thumb.jpg.007f6c1c1fcd3194132ab1dadd890c02.jpg

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Posted (edited)
1 hour ago, alcol620 said:

Thanks Adam, only just spotted your image. I have now put a ZWO tilt adjuster in the optical chain with the spacing still at 55mm. Star field image attached. Comments on the misshapen stars welcome253481391_distortedstarimage.thumb.jpg.007f6c1c1fcd3194132ab1dadd890c02.jpg

could be tilt but also could be colimation, the only way I would be able to tell is with a star test. The fact that your RGB channels look out of alignment pushes me towards it being colimation though.

259333074_FInalM45askar180-4small_clarity.thumb.jpg.09d55a2242fda6f158e28c9b392ae554.jpg

This is how its performing for me with a ASI1600mm pro and a L3 filter to cut down the blue. But I did need to tune the colimation as described to get to this result. I show you this so as you dont feel its just the scope design itself.

Another possibility with latteral CA is that of a de-centered lens element on the objective and thats not something that can be cured yourself.  The issue with amature scopes and amature astronomy equiptment in general accross the board is that of smaple to sample variation. Its unfrotunate, but not all of it is even the responsibility of the manufacturer with fast apos as all it takes is a jolt in transportation.

All I can say is get a artificial star, they are useful things to own in anycase.

Adam

Edited by Adam J
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22 hours ago, Adam J said:

could be tilt but also could be colimation, the only way I would be able to tell is with a star test. The fact that your RGB channels look out of alignment pushes me towards it being colimation though.

259333074_FInalM45askar180-4small_clarity.thumb.jpg.09d55a2242fda6f158e28c9b392ae554.jpg

This is how its performing for me with a ASI1600mm pro and a L3 filter to cut down the blue. But I did need to tune the colimation as described to get to this result. I show you this so as you dont feel its just the scope design itself.

Another possibility with latteral CA is that of a de-centered lens element on the objective and thats not something that can be cured yourself.  The issue with amature scopes and amature astronomy equiptment in general accross the board is that of smaple to sample variation. Its unfrotunate, but not all of it is even the responsibility of the manufacturer with fast apos as all it takes is a jolt in transportation.

All I can say is get a artificial star, they are useful things to own in anycase.

Adam

Thanks Adam, appreciated. When it was tested for Astronomy Now, the out of shape stars did not appear, so somewhere down the line things have changed. I am now fiddling with the tilt adjuster, but it is all getting too much - doing my head in!!! last questions how far away does the artificial star have to be and did you simply fiddle with the spacer added to the red ring until the stars became more circular? Thanks again

 

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Posted (edited)
20 minutes ago, alcol620 said:

Thanks Adam, appreciated. When it was tested for Astronomy Now, the out of shape stars did not appear, so somewhere down the line things have changed. I am now fiddling with the tilt adjuster, but it is all getting too much - doing my head in!!! last questions how far away does the artificial star have to be and did you simply fiddle with the spacer added to the red ring until the stars became more circular? Thanks again

 

No not quite, its not how circular the stars are that you are looking for. You want to defocus the star so that you get a ring with a bright centre just on the outside of focus, this is undercorrection in a bright APO. It best to do this with a mono sensor but you can do it with a OSC its just harder. Once you have that then you need to make sure that the brighter central dot is in the centre of the outer rings. This must be done with the star dead centre in the FOV.

With such a short focal length you can have it very close (relatively speaking) 20 x focal length is the minimum. So I would think 5 metres is a safe bet.

If you find the defocused star is concentric in the centre of the FOV then you can be reasonably sure that it is tilt and not colimation. In this case you can move the star to each corner and focus on it. If you have an auto focuser you can read off the movement relative to the centre focus position, that way you know which direction you are out in.

Post images of what you see here and ill help if I can.

Adam

Edited by Adam J
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23 hours ago, Adam J said:

No not quite, its not how circular the stars are that you are looking for. You want to defocus the star so that you get a ring with a bright centre just on the outside of focus, this is undercorrection in a bright APO. It best to do this with a mono sensor but you can do it with a OSC its just harder. Once you have that then you need to make sure that the brighter central dot is in the centre of the outer rings. This must be done with the star dead centre in the FOV.

With such a short focal length you can have it very close (relatively speaking) 20 x focal length is the minimum. So I would think 5 metres is a safe bet.

If you find the defocused star is concentric in the centre of the FOV then you can be reasonably sure that it is tilt and not colimation. In this case you can move the star to each corner and focus on it. If you have an auto focuser you can read off the movement relative to the centre focus position, that way you know which direction you are out in.

Post images of what you see here and ill help if I can.

Adam

Thanks Adam, appreciated. Much to my surprise I found an artificial star amongst my bits and pieces that I must have bought a few years ago (and didn't know I had). I currently have a fixed set up and I may need to break this down to enable the artificial star to be aimed at the ASKAR set up. As soon as I have an image I will take up your offer of further help.

Regards Alec

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On 17/07/2022 at 22:49, alcol620 said:

Thanks Adam, appreciated. Much to my surprise I found an artificial star amongst my bits and pieces that I must have bought a few years ago (and didn't know I had). I currently have a fixed set up and I may need to break this down to enable the artificial star to be aimed at the ASKAR set up. As soon as I have an image I will take up your offer of further help.

Regards Alec

Hi Adam it is the old duffer again. Last night I tried to check out collimation with the set up I have without an artificial star. Method: I ran my normal set up with the ASKAr riding piggyback on the ED120 scope and the AZEQ6 mount. I found Polaris and put this in the centre of the image. With accurate guiding running, I defocused Polaris  in and out. The 2 images obtained (attached) were debayered and stretched in Pixinsight. I am not sure what the results indicate, apart from the fack that the stars are round!! Your input is appreciated.

Alec

collimation test focus in  zwo294 extreme filter_10sec.jpg

collimation test focus out  zwo294 extreme filter_3sec.jpg

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Posted (edited)
44 minutes ago, alcol620 said:

Hi Adam it is the old duffer again. Last night I tried to check out collimation with the set up I have without an artificial star. Method: I ran my normal set up with the ASKAr riding piggyback on the ED120 scope and the AZEQ6 mount. I found Polaris and put this in the centre of the image. With accurate guiding running, I defocused Polaris  in and out. The 2 images obtained (attached) were debayered and stretched in Pixinsight. I am not sure what the results indicate, apart from the fack that the stars are round!! Your input is appreciated.

Alec

collimation test focus in  zwo294 extreme filter_10sec.jpg

collimation test focus out  zwo294 extreme filter_3sec.jpg

Hi you are too far out of focus, you should have only about 5 rings visible. If you get too far outside focus the test becomes less sensitive as the errors blend into each other.

Not sure what your using but you dont want to auto stretch the image as it will ruin the detail. You want to set exposure so that you can see the rings correctly with autostretch turned off in something like NINA.

I tend to do this with a mono camera so not sure how well it works with OSC, the problem being that the different wavelengths may blure the result, I tended to use a green filter for best results.

This is an example star test from a friends scope, I did not have any of my own saved.

Green filter on a mono camera three rings seen. What you are looking for is that little dot in the middle to be dead in the centre of the outermost ring.

As you have less rings the effects of seeing on the star test will be increased and in these temperatures I really doubt you will get good seeing, so defo use an artificial star, 5 meters of atmosphere is much more stable than 10km.

140537491_WhatsAppImage2022-03-07at22_57_46.thumb.jpeg.1120114de15c43586b6b4bf6635f0d61.jpeg

Edited by Adam J
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IMG_20220722_115000.thumb.jpg.c373e72bd159cb7c47ff29234a971ffa.jpg

 

My replacement objective finally arrived, big thanks to Flo for going above and beyond to order a replacement after I chipped the original. 

Here's my lightweight set up with a D5600 (my ZWO 533 is permanently mounted on a GT71 with EAF these days)

Couple of useful add ons:

Extended hood using a TS reducer collar which is two piece and holds an L3 filter

Askar M48 rear spacer to M48 F mount 

Now to get back focus dialled in again🔭

 

IMG_20220722_103250.jpg

 

Edited by 900SL
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On 19/07/2022 at 23:21, Adam J said:

Hi you are too far out of focus, you should have only about 5 rings visible. If you get too far outside focus the test becomes less sensitive as the errors blend into each other.

Not sure what your using but you dont want to auto stretch the image as it will ruin the detail. You want to set exposure so that you can see the rings correctly with autostretch turned off in something like NINA.

I tend to do this with a mono camera so not sure how well it works with OSC, the problem being that the different wavelengths may blure the result, I tended to use a green filter for best results.

This is an example star test from a friends scope, I did not have any of my own saved.

Green filter on a mono camera three rings seen. What you are looking for is that little dot in the middle to be dead in the centre of the outermost ring.

As you have less rings the effects of seeing on the star test will be increased and in these temperatures I really doubt you will get good seeing, so defo use an artificial star, 5 meters of atmosphere is much more stable than 10km.

140537491_WhatsAppImage2022-03-07at22_57_46.thumb.jpeg.1120114de15c43586b6b4bf6635f0d61.jpeg

Hi Adam, thanks for getting back. I am using a ZWO294MC camera so I have no option but to use a colour camera for testing. At present I am reluctant to break down my rig to use the artificial star. With my set up I can't position the star to point at the scope.

On the issue of: is it tilt or some other factor in producing the misshapen stars, I have stumbled on some free software that stacks subs and measures tilt and off-axix aberration. (ASTAP) and subject to clear skies I am going to retrace my steps and use ASTAP to produce tilt values for various adjustments, rather than currently visually assess images for improvements.

One other thing I noticed with my set up is a small amount of play when holding the objective lens tube and the flattener tube. A small amount of play can be felt. Is this normal? Thanks again for your help in this ongoing saga.

Alec

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Posted (edited)
21 hours ago, alcol620 said:

Hi Adam, thanks for getting back. I am using a ZWO294MC camera so I have no option but to use a colour camera for testing. At present I am reluctant to break down my rig to use the artificial star. With my set up I can't position the star to point at the scope.

On the issue of: is it tilt or some other factor in producing the misshapen stars, I have stumbled on some free software that stacks subs and measures tilt and off-axix aberration. (ASTAP) and subject to clear skies I am going to retrace my steps and use ASTAP to produce tilt values for various adjustments, rather than currently visually assess images for improvements.

One other thing I noticed with my set up is a small amount of play when holding the objective lens tube and the flattener tube. A small amount of play can be felt. Is this normal? Thanks again for your help in this ongoing saga.

Alec

yes that is normal for this scope, what you will find is that if you move focus in and out then it will centre itself. But if you then move it with your hand you will see some wiggle across the helical focuser. In that situation you have caused an issue by wiggling it and if you then imaged with it colimation would be a long way out. Just move the focus back and forth and it will recenter itself. Maybe something to do before you use it if you have transported it. It will wiggle more the further the focus is pushed outwards.

So basically mine does the exact same and if I don't mess with it then it seems to work fine regardless of this "feature". 

However, having said all this I cant see how bad your wiggle is so one thing to check is this. If you remove the objective you will see three small screws on the focuser ring that hold the thread for the objective onto the focuser. Make sure that they are not loose. They are only small so dont strip them, they just need to not be loose, they should not need to be super tight. 

Honestly I know the type of program you mean and I have never gotten along with them. My recommendation is that you bit the bullet and do a proper start test its the only thing I have ever found to help me really diagnose these type of issues. 

 

Adam

Edited by Adam J
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I’m with AdamJ on this one. An artificial star test is the best way. It can be done  indoors any evening and repeated at will to confirm any mods. Waiting for stars in the Uk is going to take a lot of your time.  Really is worth breaking up your rig and letting AdamJ cast his eye. 

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37 minutes ago, PadrePeace said:

I’m with AdamJ on this one. An artificial star test is the best way. It can be done  indoors any evening and repeated at will to confirm any mods. Waiting for stars in the Uk is going to take a lot of your time.  Really is worth breaking up your rig and letting AdamJ cast his eye. 

Thanks Adam and PP for further encouragement and feedback

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  • 2 weeks later...
On 25/06/2022 at 13:42, Adam J said:

This is the foil spacer I use. To be exact I used aluminium tape from B&Q, rapped around the ring one and a half times. 

It wedges the primary cell just enough to bring it into perfect alignment. 

IMG_20220625_133651731_HDR.thumb.jpg.7ae06a3c13afe7bfea2e885c1f9769a0.jpg

Hi Adam, I didn't get to try the artificial star test, but continued to adjust the ZWO tilter without moving to any improvement. I reset the scope so it had no tilt adjustment to it and tried your suggesttion of the foil spacer to adjust the primary cell. To my great relief it had an immediate effect and once I found the best position of the red spacer, the tilt reading on the software ASTAP was significantly reduced, see attachments, and the image visually showed the improvement. Although not perfect, I am happy to accept this degree of improvement. Many thanks for your patience and help. I assume the cause was the Primary cell being slightly out of line, caused by what I do not know. Thanks again

no tilt.JPG

tilt before.JPG

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Posted (edited)
1 hour ago, alcol620 said:

Hi Adam, I didn't get to try the artificial star test, but continued to adjust the ZWO tilter without moving to any improvement. I reset the scope so it had no tilt adjustment to it and tried your suggesttion of the foil spacer to adjust the primary cell. To my great relief it had an immediate effect and once I found the best position of the red spacer, the tilt reading on the software ASTAP was significantly reduced, see attachments, and the image visually showed the improvement. Although not perfect, I am happy to accept this degree of improvement. Many thanks for your patience and help. I assume the cause was the Primary cell being slightly out of line, caused by what I do not know. Thanks again

no tilt.JPG

tilt before.JPG

Happy for you that you are now happy with it. It would be really hard to get that perfect without star testing but its great you got it close enough. I would now get some tape / mark the position of the red ring incase it shifts in future. 

For the record tilt is actually much less common in imaging than collimation issues. What most think is tilt will actually be collimation 90% of the time.  Thinking about it one reason for this is likely that telescope makers and stores have a vested interest in convincing users that their issues are between the scope and the camera (tilt) and not the scope itself. 

As for what caused it, a slight knock is all it can take. 

Adam 

Edited by Adam J
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On 03/08/2022 at 20:00, Adam J said:

Happy for you that you are now happy with it. It would be really hard to get that perfect without star testing but its great you got it close enough. I would now get some tape / mark the position of the red ring incase it shifts in future. 

For the record tilt is actually much less common in imaging than collimation issues. What most think is tilt will actually be collimation 90% of the time.  Thinking about it one reason for this is likely that telescope makers and stores have a vested interest in convincing users that their issues are between the scope and the camera (tilt) and not the scope itself. 

As for what caused it, a slight knock is all it can take. 

Adam 

Thanks Adam, your help is much appreciated. Take care, Alec

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Is there a possibility to fit a filter between the camera and the Askar instead of placing one at the front? I can't see if if it's possible.

This is without using a filter wheel or drawer, so a permanent filter setup.

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9 hours ago, Gonzo said:

Is there a possibility to fit a filter between the camera and the Askar instead of placing one at the front? I can't see if if it's possible.

This is without using a filter wheel or drawer, so a permanent filter setup.

That would largely depend on your choice of camera, some ASI cameras will suit having a 1.25 inch filter infront of the camera via an included adaptor. Also Astronomik actually make a M42 filter type designed to be inserted as you would insert an extender into the imaging train. So its no more or less possible to do this with the FMA180 than it is with any other telescope.

 

Adam

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  • 4 weeks later...

Little bit of Ha from the FMA180, only 1.5hours infact.

Question_mark_test_with_darks-Ha-session_1-St.thumb.jpg.5993e2f0796a33c788108c0e4775a176.jpg

Added 3.5h of OIII,

question_mark_full_test-HSO_1--90degCCW-1.0x-LZ3-NS-crop-St_processing.thumb.jpg.5d9649e55622a145480e2dabb8704adc.jpg

Messing about with starless processing.

548931164_starlessRGBfull.thumb.jpg.1158be7959127b5886f5a7b4577d1aa1.jpg

 

Clearly still loads of work left to do on this one.

Adam

Edited by Adam J
add oiii
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