ASKAR FMA180 40mm aperture apochromatic telescope.

[Quetzalcoatl72]

3 minutes ago, Space Oddities said:

I think you're using the wrong spacers between the camera and the flattener. The one with 3 screws is designed for an eyepiece, not a camera. I'm pretty sure this is causing the coma.

This is what you need to reach 55mm of back focus:

Tip: you might want to place the 21mm before the 16.5mm spacer, unlike the diagram above. It will work better with the Askar's rear T2 mount!

Some documentation:

http://www.askarlens.com/index.php/class3/186.html

https://astronomy-imaging-camera.com/tutorials/best-back-focus-length-solutions-55mm.html

Thanks, I used the 1.25" because i could put a filter on there and it was easier to take out instead of screwing it in. But i now put a filter on the front of the scope so i'll try that out before i waste any more imaging tonight. I'll let you know thanks!

[900SL]

Askar service is pretty good. I dropped the objective assembly and chipped the lens quite badly. Dropped them an email and they have provided a link to buy and ship a new objective (the front tube with the lens) for a very reasonable price.

Thanks Bonnie at Askar, appreciated!

 

[Adam J]

36 minutes ago, 900SL said:

Askar service is pretty good. I dropped the objective assembly and chipped the lens quite badly. Dropped them an email and they have provided a link to buy and ship a new objective (the front tube with the lens) for a very reasonable price.

Thanks Bonnie at Askar, appreciated!

 

Yes FLO where able to get hold of some tube rings for me for the FMA180 that I misplaced. 

Adam

Edited March 7, 2022 by Adam J

[alcol620]

Hi

I have obtained a ZWO294 MC camera and fitted it to my ASKAR180, unfortunately I reach focus. I have the correct spacers etc 55mm including the camera back focus as per other posts on this string.  I wind the focuser round and as I movr towards focus I run out of turns. I am at the focuser stop.

Probably doing something stupid, any ideas on what is wrong? Thanks for looking

[Adam J]

58 minutes ago, alcol620 said:

Hi

I have obtained a ZWO294 MC camera and fitted it to my ASKAR180, unfortunately I reach focus. I have the correct spacers etc 55mm including the camera back focus as per other posts on this string.  I wind the focuser round and as I movr towards focus I run out of turns. I am at the focuser stop.

Probably doing something stupid, any ideas on what is wrong? Thanks for looking

It's not 55 from the flattener it's 55 from the spacer designed to sit after the flattener. Just incase you have that wrong. 

[alcol620]

19 hours ago, Adam J said:

It's not 55 from the flattener it's 55 from the spacer designed to sit after the flattener. Just incase you have that wrong. 

Thanks for getting back to me. I am a little confused. I thought it required 55mm from the face of the sensor to the face of the flattener  ie where the flattener tube screws into the spacers before the camera? Can you clarify for me. Currently the set up is as shown. Do I need to add the 28mm spacer next to the flattener? Thanks Adam

[Adam J]

57 minutes ago, alcol620 said:

Thanks for getting back to me. I am a little confused. I thought it required 55mm from the face of the sensor to the face of the flattener  ie where the flattener tube screws into the spacers before the camera? Can you clarify for me. Currently the set up is as shown. Do I need to add the 28mm spacer next to the flattener? Thanks Adam

Yeah that is wrong. There is a short extension that fits after the flattener and it's 55mm from that extension. I don't remember the length off hand be 28 sounds about correct. 

So just keep it as is and add that extension between the camera extensions and the flattener. 

Adam 

[alcol620]

1 hour ago, Adam J said:

Yeah that is wrong. There is a short extension that fits after the flattener and it's 55mm from that extension. I don't remember the length off hand be 28 sounds about correct. 

So just keep it as is and add that extension between the camera extensions and the flattener. 

Adam 

That's great Adam, changed that and all is functioning as it should. It got me totally confused with statements like "needs to be 55mm between reducer and sensor face". Thanks again for your very helpful feedback. Best regards  Alec

[Gonzo]

On 25/03/2021 at 12:57, Space Oddities said:

Hello, may I ask if you could please measure the overall length of this setup? From the back of the camera to the front of the FMA180.

thanks

[alcol620]

Since Adam kindly sorted me in terms of spacing to achieve focus, I have successfully run the set up and completed images. however, I am still plagued by distorted stars towards the corner of images. I have adjusted the spacing but can't get rid of the distortion. I have used the Pixinsight script FWHMEccentricity and got the attached outputs. Anyone like to clarify what these mean. The image tested had distorted stars in the lower left hand corner. My understanding is that the contours for Eccentricity should indicate higher values for eccentricity in the lower left hand corner rather than lower values.

As adjusting spacing has not solved the distortion, I assume the problem must be caused by tilt somewhere. However, I have tried 3 different Canon cameras and the ZWO294MC I have now and the problem on distorted stars towards 1 corner still persists.

Comments welcome

[Adam J]

15 hours ago, alcol620 said:

Since Adam kindly sorted me in terms of spacing to achieve focus, I have successfully run the set up and completed images. however, I am still plagued by distorted stars towards the corner of images. I have adjusted the spacing but can't get rid of the distortion. I have used the Pixinsight script FWHMEccentricity and got the attached outputs. Anyone like to clarify what these mean. The image tested had distorted stars in the lower left hand corner. My understanding is that the contours for Eccentricity should indicate higher values for eccentricity in the lower left hand corner rather than lower values.

As adjusting spacing has not solved the distortion, I assume the problem must be caused by tilt somewhere. However, I have tried 3 different Canon cameras and the ZWO294MC I have now and the problem on distorted stars towards 1 corner still persists.

Comments welcome

i cant interperate that image, really need to see a star feild to give you an answer. What i will say is the colimation was not perfect on my scope and i had to tweak it. Tilt is possible also but really cant tell the difference without an image.

Adam

Edited June 19, 2022 by Adam J

[alcol620]

Thanks Adam, silly question, but what do you mean by collimation in terms of the askar180? I will post an image.

 

[Adam J]

16 minutes ago, alcol620 said:

Thanks Adam, silly question, but what do you mean by collimation in terms of the askar180? I will post an image.

 

Basically it comes down to if the objective lens is optically aligned correctly such that the centre of the optical axis passes though the centre of the corrector and intersects the centre of the imaging chip. 

This can be micro adjusted by placing a foil spacer on the red ring between the front objective assembly and the helical focuser. Ill provide a picture of mine if your image proves it relevant. 

Adam 

Edited June 20, 2022 by Adam J

[alcol620]

Thanks Adam, I have attached 3 images with the Pixinsight FWHMEccentricty script analyses images. My initial set up was the ZWO294MC camera and the ASKAR180 with an L-Extreme filter held in a filter drawer, which made up part of the 55mm back focus between the sensor and the reducer connection extension. This is Image A.  I then added a 1.2mm spacer ring between the filter draw and the reducer connection extension, thus giving a back spacing of 56.2mm.  This being Image B. Another spacing ring amounting to 2.4mm was then added, thus giving a back focus of 57.4mm, shown as Image C. I did also run this with a 0.6mm spacer, but this info seems to have vanished! It did, however, also have distorted stars

Before taking each image I rougly aligned the camera with the same ara of the sky. The star Sadr glows brightly in the images. This meant (I think) that the reducer connection extension, the reducer and the focuser wre rotated in relation to the Camera sensor?

I'm hoping that you will be able to deduce something from this information. Thanks for your help.

[alcol620]

Apologies, images not labeled. A at the top and C at the bottom.

[Adam J]

1 hour ago, alcol620 said:

Thanks Adam, I have attached 3 images with the Pixinsight FWHMEccentricty script analyses images. My initial set up was the ZWO294MC camera and the ASKAR180 with an L-Extreme filter held in a filter drawer, which made up part of the 55mm back focus between the sensor and the reducer connection extension. This is Image A.  I then added a 1.2mm spacer ring between the filter draw and the reducer connection extension, thus giving a back spacing of 56.2mm.  This being Image B. Another spacing ring amounting to 2.4mm was then added, thus giving a back focus of 57.4mm, shown as Image C. I did also run this with a 0.6mm spacer, but this info seems to have vanished! It did, however, also have distorted stars

Before taking each image I rougly aligned the camera with the same ara of the sky. The star Sadr glows brightly in the images. This meant (I think) that the reducer connection extension, the reducer and the focuser wre rotated in relation to the Camera sensor?

I'm hoping that you will be able to deduce something from this information. Thanks for your help.

So to me it looks like a combination of some tilt and a little colimation error too, but not ideal images tp judge from as they look like they have not been bedayered?

I would purchase an artificial star from FLO and have a play, its an invaluable tool when investigating colimation. Defocus (outside) until you have about 3 - 4 rings and then make sure the bright spot (caused by undercorrection in a fast apo) is in the center of the rings .

https://www.firstlightoptics.com/other-collimation-tools/hubble-optics-5-star-artificial-star.html

I can say its not entiarly a spacing issue. If it was the star shape would be out by the same amount in each corner.

How old is it?

Adam

 

Edited June 20, 2022 by Adam J

[alcol620]

Thanks Adam, bought the ASKAR with very minimal use in Jan 2021 so not old. From new it had only been used to test and review it for a journal.

Before embarking on the use of an artificial star. I will produce some better images to show the star field for the examples above.  In the meantime is it possible that you could illustrate where/how you placed a foil spacer on the red ring between the front objective assembly and the helical focuser?

As I have run the set up with three different Canon cameras and now the ZWO294MC and always had poor stars it seems unlikely that tilt has nothing to do with the sensor end of the set up?  Thanks again for your patience and feedback

[Adam J]

10 minutes ago, alcol620 said:

Thanks Adam, bought the ASKAR with very minimal use in Jan 2021 so not old. From new it had only been used to test and review it for a journal.

Before embarking on the use of an artificial star. I will produce some better images to show the star field for the examples above.  In the meantime is it possible that you could illustrate where/how you placed a foil spacer on the red ring between the front objective assembly and the helical focuser?

As I have run the set up with three different Canon cameras and now the ZWO294MC and always had poor stars it seems unlikely that tilt has nothing to do with the sensor end of the set up?  Thanks again for your patience and feedback

Its in the garage so ill have to take some pictures tomorrow after work. What journal was it for?

Adam

Edited June 20, 2022 by Adam J

[alcol620]

Thanks Adam, Astronomy Now

[900SL]

Did you try it without the L extreme? 

[alcol620]

I have had similar misshapen stars without the filter.

[Adam J]

On 20/06/2022 at 22:53, alcol620 said:

Thanks Adam, Astronomy Now

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. 

Edited June 25, 2022 by Adam J

[Gonzo]

An alternative to the autofocuser with belt.

source: https://www.cloudynights.com/topic/718608-askar-fma180-d40mm-f55-triplet-ed-super-apo/?p=10849882

[Gonzo]

I asked that person, and here are the printed files https://www.thingiverse.com/thing:5422376 for it.

[Adam J]

16 hours ago, Gonzo said:

An alternative to the autofocuser with belt.

source: https://www.cloudynights.com/topic/718608-askar-fma180-d40mm-f55-triplet-ed-super-apo/?p=10849882

I think that the reason that i have a preference for a pulley system is the lack of backlash, which is already low on a helical focuser. 

Adam