Takahashi E-130D Double Diffraction Spikes - trying to identify the cause - Forums

Hi there,

So, I received my Takahashi e-130d several weeks ago. As is custom to receiving new equipment, I had cloudy skies for a couple of weeks. I ended up taking it out for first light on 04/06/24 (april 6) and noticed the diffraction spikes on the blue star were doubled on one axis. I know the focus is a bit off, but I'm trying to identify the cause of the double spikes. I did rotate the focuser 180 degrees and installed an MEF-3 + Optec ThirdLynx QuickSync TKX motor. I noticed that the focuser tube has some wiggle (1mm max) when I don't lock it down.

I can safely say that when I used the AM3, guiding wasn't great and it was extremely windy.

My imaging train includes an M54 to M54 adapter (2mm), a ZWO m54 filter drawer (20mm) (no filter installed during this sequence), and an Askar M54 backfocus adjuster (set to add 16.70mm of backfocus to get me to 56.2), and my ASI2600MC Duo)

So, I'm trying to identify the cause for 3 things:

1. Quite a bit of vignetting even though I'm using an APS-C sensor (2600MC Duo) and no filters (my guess is some tilt)
2. Oblong stars on the outside (I think this is a backfocus issue or just guiding problems - they seem to all go in the same direction)
3. Double diffraction spikes on the blue star (right side and bottom right)

I posted the image here with the details: https://www.astrobin.com/gc7aj8/

And directly below.
The fact that the top left is darker and the bottom right is brighter makes me think I need to adjust the backfocus out a little to see if that's the issue with the double diffraction spikes (of course, I need to fix the tilt as well).

Any ideas as to the cause? I hope it's not collimation (I have the Tak Tools but lack the experience...)

Thanks in advance!

andrea tasselli:
Tilt.

SWEET, Pretty sure that's easier to fix than collimation
Thank you

Hi Gustavo,

the E130D is a great telescope - once you have tilt under control. In contrast to collimation, tilt is not easy to fix. You need to have a good (i.e. user friendly) camera tilt adjuster unit (CTU) . It may be that its better to replace your Askar M54 backfocus adjuster with a CTU. I am using the big one by Astronomik with good results, but there may be other good products on the market.

BTW, are you aware that you need to redo the collimation when you rotate the focuser ? If not, you should first readjust the collimation and hope that this solves your double cross as well. Collimation is very easy with the TAK tool. With some practice it can be done in under 20min. Only there collimation manual is difficult to understand.

Regards

Götz

Götz Golla:
Hi Gustavo,

the E130D is a great telescope - once you have tilt under control. In contrast to collimation, tilt is not easy to fix. You need to have a good (i.e. user friendly) camera tilt adjuster unit (CTU) . It may be that its better to replace your Askar M54 backfocus adjuster with a CTU. I am using the big one by Astronomik with good results, but there may be other good products on the market.

BTW, are you aware that you need to redo the collimation when you rotate the focuser ? If not, you should first readjust the collimation and hope that this solves your double cross as well. Collimation is very easy with the TAK tool. With some practice it can be done in under 20min. Only there collimation manual is difficult to understand.

Regards

Götz

Thank you for the detailed information!
I am aware about the collimation after rotation step (just need to do it).

I also ordered a Photon Cage to help with tilt and back focus. I’ll swap out the Askar BF adjuster and figure out what spacers I need to get to 56.2 / 57 (with filter).

if you’ve already done the math, what did you use to get back focus?

would you be able to share your imaging train so I can compare?

thank you, again!

Just a few comments on this:

1) Agree it is tilt
2) Agree tilt is harder to deal with than collimation
3) Agree that the Tak collimation tools work well. Here is a diagram that explains it better than the Tak instructions. I would provide a link to the OP for the diagram but can't find where it was posted.

The trick is to note dark and light rings from the middle - ignore the rings way to the outside.....

Epsilon Collimation Diagram.pdf

4) I have an add on you can print for the collimation tool: Collimation Cap
5) Tip-tilt is sometimes tricky. Best tools are the NINA plugin tool combined with hardware like the Photon cage or Octopi. Trying to adjust tilt on an Epsilon with a three axis device is gonna drive you nutty!

6) Stock focuser, like all Tak focusers, is less than ideal. The go to device is the Optec LEO.

Gustavo Tandeciarz:
Götz Golla:
Hi Gustavo,

the E130D is a great telescope - once you have tilt under control. In contrast to collimation, tilt is not easy to fix. You need to have a good (i.e. user friendly) camera tilt adjuster unit (CTU) . It may be that its better to replace your Askar M54 backfocus adjuster with a CTU. I am using the big one by Astronomik with good results, but there may be other good products on the market.

BTW, are you aware that you need to redo the collimation when you rotate the focuser ? If not, you should first readjust the collimation and hope that this solves your double cross as well. Collimation is very easy with the TAK tool. With some practice it can be done in under 20min. Only there collimation manual is difficult to understand.

Regards

Götz

Thank you for the detailed information!
I am aware about the collimation after rotation step (just need to do it).

I also ordered a Photon Cage to help with tilt and back focus. I’ll swap out the Askar BF adjuster and figure out what spacers I need to get to 56.2 / 57 (with filter).

if you’ve already done the math, what did you use to get back focus?

would you be able to share your imaging train so I can compare?

thank you, again!

The Photon Cage looks like a very interesting product.

I am using a backfocus of 56.3-56.4mm. My image train looks like this

ASI 7x filter wheel : 20mm
ASI camera: 12.5mm
Astronomik CTU XT 68mm: 17.3mm
2x adapter 68-54: 4mm
Spacer : 1mm + 1mm + 0.5mm = 2.5mm

Bill McLaughlin:
Just a few comments on this:

1) Agree it is tilt
2) Agree tilt is harder to deal with than collimation
3) Agree that the Tak collimation tools work well. Here is a diagram that explains it better than the Tak instructions. I would provide a link to the OP for the diagram but can't find where it was posted. The trick is to note dark and light rings from the middle - ignore the rings way to the outside.....

Epsilon Collimation Diagram.pdf

4) I have an add on you can print for the collimation tool: Collimation Cap
5) Tip-tilt is sometimes tricky. Best tools are the NINA plugin tool combined with hardware like the Photon cage or Octopi. Trying to adjust tilt on an Epsilon with a three axis device is gonna drive you nutty!
6) Stock focuser, like all Tak focusers, is less than ideal. The go to device is the Optec LEO.

incredibly helpful! I’m going to give this a try tonight. I guess I need to invest in a 3D printer given the plethora of attachments and things I could print that could make my life easier.
the photon cage arrives next Saturday

and yeah, trying to manage tilt with that 3 point system using the included tilt adapter on the ASI2600 Duo was … less than ideal.

Götz Golla:
Gustavo Tandeciarz:
Götz Golla:
Hi Gustavo,

the E130D is a great telescope - once you have tilt under control. In contrast to collimation, tilt is not easy to fix. You need to have a good (i.e. user friendly) camera tilt adjuster unit (CTU) . It may be that its better to replace your Askar M54 backfocus adjuster with a CTU. I am using the big one by Astronomik with good results, but there may be other good products on the market.

BTW, are you aware that you need to redo the collimation when you rotate the focuser ? If not, you should first readjust the collimation and hope that this solves your double cross as well. Collimation is very easy with the TAK tool. With some practice it can be done in under 20min. Only there collimation manual is difficult to understand.

Regards

Götz

Thank you for the detailed information!
I am aware about the collimation after rotation step (just need to do it).

I also ordered a Photon Cage to help with tilt and back focus. I’ll swap out the Askar BF adjuster and figure out what spacers I need to get to 56.2 / 57 (with filter).

if you’ve already done the math, what did you use to get back focus?

would you be able to share your imaging train so I can compare?

thank you, again!

The Photon Cage looks like a very interesting product.

I am using a backfocus of 56.3-56.4mm. My image train looks like this
ASI 7x filter wheel : 20mm
ASI camera: 12.5mm
Astronomik CTU XT 68mm: 17.3mm
2x adapter 68-54: 4mm
Spacer : 1mm + 1mm + 0.5mm = 2.5mm

No issue with the added glass of the filters? I think native clear path back focus is 56.2, but with a 3mm filter it would be 57.2. My filters are all 1.85 mm so I’m guessing around .65mm more (so 56.8-ish).

thank you for taking the time to list this out!

Gustavo Tandeciarz:
I guess I need to invest in a 3D printer

LOL! I bought a Bambu X1C around Christmas and have used it for so much stuff (astro and non-astro) that I have lost count. As long as you don't mind learning something like Fusion 360, it really makes creating custom parts almost fun! In fact I am printing the final version of a guider focuser for the Indigo guider right now.

So, you know what sucks? It looks like my collimation screws on the secondary are glued to the actual secondary. I doubt this is normal, but if it is (maybe to hold collimation during shipping), can someone weigh in?

I'm emailing Agena Astro to identify next steps.

Here are photos of the screws using my macro lens.
https://adobe.ly/3Q1yeDa

Gustavo Tandeciarz:
So, you know what sucks? It looks like my collimation screws on the secondary are glued to the actual secondary. I doubt this is normal, but if it is (maybe to hold collimation during shipping), can someone weigh in?

I'm emailing Agena Astro to identify next steps.

Here are photos of the screws using my macro lens.
https://adobe.ly/3Q1yeDa

No this isn't normal. Did you try to use a screwdriver vs your fingers? Like you say it may just be for shipping and breaks off easily? The screws are quite tight (I use a screwdriver when collimating).

Also a couple of other add-ons to above:

1. You do need an Optec Leo. The stock focuser is shockingly bad.
2. Do you have an aperture mask on your primary mirror (I had one installed at-purchase)? That may help with your star shapes ever-so slightly.

Good luck - the 130 is a fantastic scope!

D.

Gustavo Tandeciarz:
So, you know what sucks? It looks like my collimation screws on the secondary are glued to the actual secondary. I doubt this is normal, but if it is (maybe to hold collimation during shipping), can someone weigh in?

I'm emailing Agena Astro to identify next steps.

Here are photos of the screws using my macro lens.
https://adobe.ly/3Q1yeDa

No need to be too skeptical. There is some glue involved, but only so that the screws dont come loose too fast. You can apply quite some torque to turn these screws and its OK. Its one of the reasons why collimation is so stable. There is a reason why people say that the Epsilons are build like a tank

Also, I do not think you absolutely need a different focuser. There may be two problems with the focuser:

When you rotate the focuser more than 1/8 rotation you may need to adjust your collimation. Thats why some people collimate there Epsilons when the focuser is halfway between portrait and landscape mode, so that both positions can be reached with 1/8 rotation. You can test this easily and you may also find that if collimation is not absolutely perfect the image quality is not necessarily affected. Other factors like seeing and even a slight tilt will have a larger impact.
When you change the direction of the focusing motor, stars may shift a few acrsec. This may or may not play a role when you want to focus automatically and your software gets confused. But I didnt have any problems with N.I.N.A and ASIAIR.

The amount of the problems depends on your individual focuser. I didnt change mine and I am happy with it. I personally would only do it if you have real problems in your practical imaging work.

I got a response from Takahashi America and they mentioned the glue was normal to protect collimation during shipping!
Phew!

That is perfectly normal. The Epsilons come from the factory this way since it helps to prevent the screws from loosening during shipping. One can still turn them with a thin bladed screwdriver. However, be careful and slightly loosen the center nut before adjusting the three screws. Don't loosen the center nut completely, however, as it will allow the secondary to rotate. Also, the collimation will change slightly as the focuser is rotated. This is normal. I generally recommend collimating the scope to the camera position one prefers to use most often.

Götz Golla:
There may be two problems with the focuser:

Mine was completely broken: it was not sitting correctly inside the focuser tube and would actually rock side-to-side as I racked it in and out.

If you have a look here in the forums there is another (very large) thread which goes into a lot of detail regarding focuser issues with the Epsilon:

https://www.astrobin.com/forum/c/equipment-forums/takahashi-epsilon-160ed/setting-up-the-e160-ed-for-full-frame-imaging/

On the other hand, the Optec Leo is very expensive, and if you are blessed to have a working focuser then of course there's no need to replace ;-)

Gustavo,
I'm not sure that I agree with the consensus here. First, let me address the easy one. The double spider pattern on the blue star is mostly likely due to a double star. You can tell that simply because none of the other stars show a similar pattern AND those double spikes are parallel. On a well aligned telescope with a spider, double parallel spikes are an indication of a double star.

Second, I can see that you've got an unbalanced field with respect to astigmatism and coma so you'll need to do some optical alignment to clean up the field. You may have some sensor tilt but from what I can see, that's not your biggest problem. Start by fixing the field aberrations before you start fooling with sensor tilt.

Finally, before you start tearing into your system. Do a simple test to confirm that your sensor is tilted. Put a B-mask on the scope, take an exposure of a dense star field and then carefully examine the patterns to see if the sensor is really tilted. The B-mask pattern gives both magnitude and direction for the tilt. You can use the B-mask pattern to dial out the tilt (as I recently did on my 24") or once you confirm that your sensor is tilted you can move to a software based measurement method.

Just remember that a non-uniform illumination pattern in the focal plane does not indicate sensor tilt! Stars with either different diameters or different ellipticity that vary throughout the field are an indication of tilt. In fact, you can also use the FWHMEllipticity tool in PI to measure tilt by looking at the support images. The problem with that approach is that although it shows the problem it doesn't show magnitude or direction so there's some guessing involved to make that work. Illumination non-uniformity may be due to your filters, baffling, or other causes. It is not normally a show stopper and in most cases, it's not worth a lot of effort to fix.

John

John Hayes:
The double spider pattern on the blue star is mostly likely due to a double star.

I don't think so, as ALL the stars on the right hand side end have double spikes, it so happens that the OB star is the brightest there so most easily seen. Otherwise I'd agree with your other points.

I agree with `John above, this is not all tilt at all, and the scope itself does come with the adjustment screws glued up as the collimation is only supposed to be done back at the factory, and not by the end user, they don’t make it easy at all for use users to do any adjustments.
I had a tak FSQ85 with very similar issues only worse, and it was a very poor scope, and in the end went back for a full refund, the astigmatism was awful, and yous is not great either, this is a combo of bad collimation and tilt, the dark edges are nothing at all to do with the tild of collimation and is pretty normal with your camera and filters. Flats will sort those out.
im afraid no amount of expensive tilt adjusters is going to sort that issue out.
the stars in the bottom left look pretty good, the bottom right are bad the top right are not good either, but are elongating in a slightly different direction to the bottom right, so nothing to do with the guiding either, the top left stars again are not great.
now the diffraction spikes i am unsure about, but does not look right at all….

AstroShed:
I agree with `John above, this is not all tilt at all, and the scope itself does come with the adjustment screws glued up as the collimation is only supposed to be done back at the factory, and not by the end user, they don’t make it easy at all for use users to do any adjustments.

Not sure I agree with this. Collimation will most definitely need to be done (at some point) by the end user. Yes, it does come collimated from the factory (actually from Takahashi America in Texas if bought in the US) but you are in for an unpleasant surprise if you think you won't need to collimate it. I had one a couple years ago that, after fighting with it for four months, ultimately returned. A scope with a lot of promise, but takes a lot of work to get right. The graveyards of Astrobin are littered with the shriveled corpses of those that tried to get their Epsilons to work.

Arun H:
AstroShed:
I agree with `John above, this is not all tilt at all, and the scope itself does come with the adjustment screws glued up as the collimation is only supposed to be done back at the factory, and not by the end user, they don’t make it easy at all for use users to do any adjustments.

Not sure I agree with this. Collimation will most definitely need to be done (at some point) by the end user. Yes, it does come collimated from the factory (actually from Takahashi America in Texas if bought in the US) but you are in for an unpleasant surprise if you think you won't need to collimate it. I had one a couple years ago that, after fighting with it for four months, ultimately returned. A scope with a lot of promise, but takes a lot of work to get right.

I won’t be suprised at all if I didn’t have to collimate, as I had one but as it was a quad and it was the built in flattener that was out of collimation, it was impossible for the end user to collimate, maybe the standard doublet and triplets are different, but I would not touch another with a barge pole…not worth the money at all….and certainly not worth all the trouble and issues that potentially come with them, for a high price premium scope I don’t rate them at all.

AstroShed:
Arun H:
AstroShed:
I agree with `John above, this is not all tilt at all, and the scope itself does come with the adjustment screws glued up as the collimation is only supposed to be done back at the factory, and not by the end user, they don’t make it easy at all for use users to do any adjustments.

Not sure I agree with this. Collimation will most definitely need to be done (at some point) by the end user. Yes, it does come collimated from the factory (actually from Takahashi America in Texas if bought in the US) but you are in for an unpleasant surprise if you think you won't need to collimate it. I had one a couple years ago that, after fighting with it for four months, ultimately returned. A scope with a lot of promise, but takes a lot of work to get right.

I won’t be suprised at all if I didn’t have to collimate, as I had one but as it was a quad and it was the built in flattener that was out of collimation, it was impossible for the end user to collimate, maybe the standard doublet and triplets are different, but I would not touch another with a barge pole…not worth the money at all….and certainly not worth all the trouble and issues that potentially come with them, for a high price premium scope I don’t rate them at all.

The Epsilon series of scopes are newtonians which require the end user to collimate. This isn't like a refractor which is extremely difficult for the end user to collimate.

AstroShed:
I won’t be suprised at all if I didn’t have to collimate

Takahashi America responded with how to collimate and that the screws were glued only to protect collimation during shipping. If they didn't expect owners to collimate, I would imagine they would say so in their response, no?

So, as hard as I try to realign the secondary, I can’t get the crosshairs of the tak tools centered… is this a primary mirror alignment thing?

Ok, I think I’m pretty close… just sliiiightly to the left.

Can you adjust the football position by adjusting the primary or do I need to continue with the secondary?

my fingers hurt (literally bleeding fingertips).

I'd stop right here! ;-)