130 replies to this topic

[Richard Whalen]

Also if anything, maybe your sampling is a bit off for seeing conditions? Was this binned?

[buckeyestargazer]

Joel, stars look good to me in the corners, how was the seeing and transparency the night the image was taken?

Without a dark frame looks good, probably a "soft" night. I think you now have a real winner! 

Seeing was really bad when this image was taken.  So yeah, it was definitely a soft night.  

 

Since posting the image of M33 I also took some flats, and the flats show a dark area along the top and middle, brightening as you move from top to bottom.  I'm not sure what to make of that.  

Attached Thumbnails

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[buckeyestargazer]

Also if anything, maybe your sampling is a bit off for seeing conditions? Was this binned?

This was not binned.  The image scale is 0.61 arcs/px.  My intention is to use a reducer in regular use which will put the scale around 0.82.

[dpastern]

well congrats on the new mirrors arriving and things starting to work out for you!  

 

Might I suggest trying test images with the camera directly attached to the focuser with no extensions etc and see if the gradient looks the same.  Then add an extension at a time and test at each point to establish where the problem (or potential problem) is entering the equation at.

[Stephen Kennedy]

buckeyestargazer, on 20 Nov 2017 - 6:14 PM, said:

 

Richard Whalen, on 20 Nov 2017 - 5:47 PM, said:

Joel, stars look good to me in the corners, how was the seeing and transparency the night the image was taken?

Without a dark frame looks good, probably a "soft" night. I think you now have a real winner! 

Seeing was really bad when this image was taken.  So yeah, it was definitely a soft night.  

 

Since posting the image of M33 I also took some flats, and the flats show a dark area along the top and middle, brightening as you move from top to bottom.  I'm not sure what to make of that.  

 

On my computer monitor, It looks like you have a dark rectangular shaped area with fairly well defined borders in the middle of the top of your flat.   In the middle there seems to be a large dark ring right below the rectangle with smaller dark rings on both sides of it.  I have no idea what would cause this.

[Richard Whalen]

Joel, after talking with a buddy about what I see in your images he thinks it's collimation. He thinks you have the primary and secondary very close, but not square to the focuser. He thinks problem is in the secondary, a bit of tilt. Since you have had the primary out that can open up a can of worms.

 

You need a starting point, an anchor so to speak. He says start with the focuser, make sure it is square to the back of the scope, make sure the secondary is in exact center mechanically. Then go from there, make sure secondary is hitting center of focuser. If you use a laser, make sure the laser is accurate. He puts his in a lathe and bounces the beam with mirrors around 100' adjusts it till when rotated in lathe point does not move. Then adjust primary if needed.

 

It can be a time consuming process, and frustrating if you are not an expert collimating RCs. When you get it right you will see a difference. He said you can also start with a sight tube to see that everything is centered mechanically. 

[buckeyestargazer]

Thanks everyone for the replies and advice.  

 

 

Joel, after talking with a buddy about what I see in your images he thinks it's collimation. He thinks you have the primary and secondary very close, but not square to the focuser. He thinks problem is in the secondary, a bit of tilt. Since you have had the primary out that can open up a can of worms.

 

You need a starting point, an anchor so to speak. He says start with the focuser, make sure it is square to the back of the scope, make sure the secondary is in exact center mechanically. Then go from there, make sure secondary is hitting center of focuser. If you use a laser, make sure the laser is accurate. He puts his in a lathe and bounces the beam with mirrors around 100' adjusts it till when rotated in lathe point does not move. Then adjust primary if needed.

 

It can be a time consuming process, and frustrating if you are not an expert collimating RCs. When you get it right you will see a difference. He said you can also start with a sight tube to see that everything is centered mechanically. 

I have a Howie Glatter 2" laser and I have tested it by putting it in a V channel and rotating it while observing the beam at a point about 20' away.  The point didn't appear to move while rotating the laser so hopefully that is good enough.

 

One thing I forgot to do at the start is to make sure the secondary is centered in the spider vanes/front of the scope.  I'll double check that but I have no reason to think that changed from before.

 

Part of what is throwing me off is the focuser.  I believe that the Feathertouch focuser, which I bought as a cosmetic second from Starlight, has some tilt in the focuser itself.  With the laser in the focuser, if I rotate either the laser or the whole focuser, the laser traces a small circle on the secondary, rather than stay at a point.  I've talked with Starlight about this and they are sending me another focuser to try out.  Here's a video of what I'm talking about.

 

So if the focuser is square against the back plate of the scope, the laser dot is about 3mm off from center.  If I adjust the focuser flange to center the laser dot on the center of the secondary, as soon as I rotate the focuser it moves out of center.  I'm not sure if any of this is normal or not.

 

I get the focuser aligned with the secondary as close as I can get it.  Then I use a Takahashi collimating scope to align the secondary, followed by the primary.  

 

Now here's something else I don't understand.  The image above of M33 where the stars appear to be pretty well round shows that the scope appears to be collimated well, but when I look at the secondary it looks noticeably tilted in relationship to the rest of the scope.  

[dpastern]

Joel, I don't think the laser dot should be moving at all during rotation.  Not at least, if the secondary is perfectly square to the focuser.  

 

I'd wait and see what happens with the new Feathertouch unit on its way to you before any further testing. 

[Stephen Kennedy]

I did a quick experiment with a laser pointer.  When the laser pointer is held exactly perpendicular to a wall on the other side of the room and rotated, there is absolutely no movement of the dot of light on the wall.  I was able to produce movement of the light dot in a small circle on the wall by rotating the laser pointer when it was tilted so that it was no longer pointing perpendicular to the wall.  This could indicate your focuser is not square to the optical axis of the telescope.

[buckeyestargazer]

I did a quick experiment with a laser pointer.  When the laser pointer is held exactly perpendicular to a wall on the other side of the room and rotated, there is absolutely no movement of the dot of light on the wall.  I was able to produce movement of the light dot in a small circle on the wall by rotating the laser pointer when it was tilted so that it was no longer pointing perpendicular to the wall.  This could indicate your focuser is not square to the optical axis of the telescope.

Thanks for doing that experiment.  The focuser is flush against the back plate of the scope, so theoretically that should make it square to the optical axis.  With the laser pointed at the secondary center spot, the laser is then reflected back onto the face of the laser in the center of the laser.  That would indicate to me that the focuser is square with the optical path.  But again, if I rotate the focuser (or the laser in the focuser) a small circle is traced.  

[buckeyestargazer]

The new focuser should come next week. I sure am tired of waiting on stuff to use this scope.

[dpastern]

The new focuser should come next week. I sure am tired of waiting on stuff to use this scope.

patience. It'll all be worth it.  The scope is showing really nice promise with that latest image.  I'm rather envious of you and your gear (in a good way)!  I wish I could afford a CFF   

[AtmosFearIC]

One thing to remember is that less than perfect seeing conditions hide miscollimation. If you think of miscollimation causing less than perfect star shapes, if those star shapes are smaller than the local seeing then you’ll have perfect looking stars as their “fuzz” is larger than their imperfection.

[Jared]

The new focuser should come next week. I sure am tired of waiting on stuff to use this scope.

A couple of quick observations...

 

1) I wouldn't worry too much about the unevenness in the flat at this point.  The dust donuts are obviously exactly what a flat is intended to correct for, so no issue there.  As far as the remainder of the non-uniformity, it could easily be something as simple as slight variations in transmission for the filter.  As long as your correct lights look good, don't stress on it.  You could try rotating the filter and see if the pattern changes, if you like.  Again, though, as long as the flat does its job I wouldn't think there is anything you need to correct.  Remember that when you look at a flat like this you are really seeing quite tiny variations in illumination--it's heavily stretched.  You still care about these tiny illuminations since your light frames will likewise be heavily stretched, but there is no reason to think it is affecting image quality in any appreciable way as long as the flat does its job.

 

2) If I understood you correctly, when you rotate the laser pointer inscribes a small circle on the secondary.  But also, when you rotate the laser by itself in the focuser you also get a small circle.  Do I have that correct?  It also sounds like the laser itself is collimated--that you have confirmed it is fine.  Is that also correct?  If so, there is something strange going on, and it's not simply a defect in the focuser.  If the focuser by itself had some wedge, rotating the focuser would create the circle you are describing, but rotating the laser would not.  If the laser were out of collimation, your test with the block wouldn't have passed.  I think the laser may not be perfectly seated when you use the compression ring to clamp it down.  That's the only way I can think of that you would get circles both from rotating the laser and from rotating the focuser.  The laser isn't being held by the focuser in a consistent manner.  This problem--if it's the only area of tilt--is not going to be replicated with your camera since presumably your camera is using a threaded adapter of some kind to attach to the focuser, not the 2" or 1.25" compression ring.  When the new focuser comes, I would recommend just swapping out the compression ring 2"/1.25" adapter and see if that makes a difference before actually changing the focuser itself.  If you get the same behavior, try a different laser.  It is possible, for example, that the 2" tube for the laser is coaxial with the laser itself (which is why it would pass the test in the block), but that there is tilt in the machining of the back flange, so when the laser is inserted fully into the visual back the laser itself is introducing tilt.  That is, it seems the laser itself is not sitting straight in the visual back, either because the back flange of the laser is not machined right or because the flange in the visual back is not machined right.  You may want to borrow a second laser from someone else to see if you get the same results.

 

Good luck!

[buckeyestargazer]

 

The new focuser should come next week. I sure am tired of waiting on stuff to use this scope.

A couple of quick observations...

 

1) I wouldn't worry too much about the unevenness in the flat at this point.  The dust donuts are obviously exactly what a flat is intended to correct for, so no issue there.  As far as the remainder of the non-uniformity, it could easily be something as simple as slight variations in transmission for the filter.  As long as your correct lights look good, don't stress on it.  You could try rotating the filter and see if the pattern changes, if you like.  Again, though, as long as the flat does its job I wouldn't think there is anything you need to correct.  Remember that when you look at a flat like this you are really seeing quite tiny variations in illumination--it's heavily stretched.  You still care about these tiny illuminations since your light frames will likewise be heavily stretched, but there is no reason to think it is affecting image quality in any appreciable way as long as the flat does its job.

 

I've calibrated a few subs with these flats and I wasn't very impressed.  The gradient is so strong that it was over/under correcting and even some dust spots remained.  But you are right...if the flats corrected well I wouldn't be worrying too much about how the flats look.  That's what flats do, is correct the ugliness.  I'm much more concerned with eliminating the tilt I see.

 

2) If I understood you correctly, when you rotate the laser pointer inscribes a small circle on the secondary.  But also, when you rotate the laser by itself in the focuser you also get a small circle.  Do I have that correct?  It also sounds like the laser itself is collimated--that you have confirmed it is fine.  Is that also correct?  If so, there is something strange going on, and it's not simply a defect in the focuser.  If the focuser by itself had some wedge, rotating the focuser would create the circle you are describing, but rotating the laser would not.  If the laser were out of collimation, your test with the block wouldn't have passed.  I think the laser may not be perfectly seated when you use the compression ring to clamp it down.  That's the only way I can think of that you would get circles both from rotating the laser and from rotating the focuser.  The laser isn't being held by the focuser in a consistent manner.  This problem--if it's the only area of tilt--is not going to be replicated with your camera since presumably your camera is using a threaded adapter of some kind to attach to the focuser, not the 2" or 1.25" compression ring.  When the new focuser comes, I would recommend just swapping out the compression ring 2"/1.25" adapter and see if that makes a difference before actually changing the focuser itself.  If you get the same behavior, try a different laser.  It is possible, for example, that the 2" tube for the laser is coaxial with the laser itself (which is why it would pass the test in the block), but that there is tilt in the machining of the back flange, so when the laser is inserted fully into the visual back the laser itself is introducing tilt.  That is, it seems the laser itself is not sitting straight in the visual back, either because the back flange of the laser is not machined right or because the flange in the visual back is not machined right.  You may want to borrow a second laser from someone else to see if you get the same results.

 

Yes, you are correct in your assumptions.  As far as I can tell the laser is collimated, but I hadn't thought of the possibility of the back flange of the laser being out.  I would always push the laser in with some force and then clamp it down.  Perhaps I should back out the laser a little and clamp it down and see what happens.

 

Regarding the compression ring being the culprit, I thought of that too and in fact is a strong possibility for the laser tracing a circle as well.  

 

Good luck!

 

Thanks for the tips!

[rpineau]

I have the exact same telescope and a Feather Touch focuser and the exact same Howie Glatter 2" laser .. and I see the exact same thing with mine (small circle when rotating the laser).

 

I came to the same conclusion as Jared.. compression ring and potentially a non perpendicular surface of the flange.

 

When doing inside collimation with the TAK collimator, I put the laser in the focuser, not lock it so that its own weight put it flat on the inside of the focuser.

I then squared the focuser to the optical axis as best as I could. I then put back my imaging train on it (all screwed , no 2" clamp or anything like that), then put the TAK collimator where my camera would be ... on the back of my FLI filter wheel (yep.. that means another adapter from precise part..) and then finished the inside collimation like that.

Bad weather and camera issue (was sent back for servicing and should be back today) did not allow me to test my collimation under the star to do the fine tuning that will certainly be required.

 

I too have been frustrated with this telescope.. but this is probably 90% user error as it's well known that collimation RC is not the easiest thing in the world.

I took a few images a while ago.. all blurry and star that looks like flying bird... hopefully with all the changes I've made and with collimation done with all the equipment as it will be I can get something good soon

 

So don't give up ! (I haven't ).

Regards,

Rodolphe

[buckeyestargazer]

I have the exact same telescope and a Feather Touch focuser and the exact same Howie Glatter 2" laser .. and I see the exact same thing with mine (small circle when rotating the laser).

 

I came to the same conclusion as Jared.. compression ring and potentially a non perpendicular surface of the flange.

 

When doing inside collimation with the TAK collimator, I put the laser in the focuser, not lock it so that its own weight put it flat on the inside of the focuser.

I then squared the focuser to the optical axis as best as I could. I then put back my imaging train on it (all screwed , no 2" clamp or anything like that), then put the TAK collimator where my camera would be ... on the back of my FLI filter wheel (yep.. that means another adapter from precise part..) and then finished the inside collimation like that.

Bad weather and camera issue (was sent back for servicing and should be back today) did not allow me to test my collimation under the star to do the fine tuning that will certainly be required.

 

I too have been frustrated with this telescope.. but this is probably 90% user error as it's well known that collimation RC is not the easiest thing in the world.

I took a few images a while ago.. all blurry and star that looks like flying bird... hopefully with all the changes I've made and with collimation done with all the equipment as it will be I can get something good soon

 

So don't give up ! (I haven't ).

Regards,

Rodolphe

Please post back here when you have a chance to collimate with a star test and tell me what you find.  I'm hoping to try again tomorrow night when it's clear. I have an idea for addressing the tilt issue and if that works then I will have a finely tuned telescope.  Collimation was super easy a few nights ago and once I get the tilt taken care of I'm good to go!  I was quite pleased with the above image of M33 after collimating, and all the stars looked good.  That was taken on a very bad seeing night.  

[akulapanam]

I have the exact same telescope and a Feather Touch focuser and the exact same Howie Glatter 2" laser .. and I see the exact same thing with mine (small circle when rotating the laser).

I came to the same conclusion as Jared.. compression ring and potentially a non perpendicular surface of the flange.

When doing inside collimation with the TAK collimator, I put the laser in the focuser, not lock it so that its own weight put it flat on the inside of the focuser.
I then squared the focuser to the optical axis as best as I could. I then put back my imaging train on it (all screwed , no 2" clamp or anything like that), then put the TAK collimator where my camera would be ... on the back of my FLI filter wheel (yep.. that means another adapter from precise part..) and then finished the inside collimation like that.
Bad weather and camera issue (was sent back for servicing and should be back today) did not allow me to test my collimation under the star to do the fine tuning that will certainly be required.

I too have been frustrated with this telescope.. but this is probably 90% user error as it's well known that collimation RC is not the easiest thing in the world.
I took a few images a while ago.. all blurry and star that looks like flying bird... hopefully with all the changes I've made and with collimation done with all the equipment as it will be I can get something good soon

So don't give up ! (I haven't ).
Regards,
Rodolphe

Please post back here when you have a chance to collimate with a star test and tell me what you find. I'm hoping to try again tomorrow night when it's clear. I have an idea for addressing the tilt issue and if that works then I will have a finely tuned telescope. Collimation was super easy a few nights ago and once I get the tilt taken care of I'm good to go! I was quite pleased with the above image of M33 after collimating, and all the stars looked good. That was taken on a very bad seeing night.

I have not had a problem with the glatter 2” drawing a circle in either my feathertouch and OS or moonlite and GSO RC. One key is getting the compression ring equally applied so that it is truly centered and can rotate but only barely. That said I did ask feathertouch about making a m48 adapter which would speed up the process but they weren’t particularly interested.

The big benefit of the Tak scope is the screwed connection and magnification. It is important to get as far forward in the assembly is possible so it should go directly into the focuser or even the back of the scope itself.

Edited by akulapanam, 23 November 2017 - 01:28 PM.

[rpineau]

 

It is important to get as far forward in the assembly is possible so it should go directly into the focuser or even the back of the scope itself.

Interesting. I would have though that getting as far away as possible would give me a "better" alignement as any deviation would be amplified. This is why I got an adapter to put mine when the camera would be in my imaging train.

So was I wrong in doing so ?

 

Rodolphe

[akulapanam]

It is important to get as far forward in the assembly is possible so it should go directly into the focuser or even the back of the scope itself.

Interesting. I would have though that getting as far away as possible would give me a "better" alignement as any deviation would be amplified. This is why I got an adapter to put mine when the camera would be in my imaging train.
So was I wrong in doing so ?

Rodolphe

You don’t want to mess up the collimation of the mirrors because of tilt or misalignment of your focuser/imaging train. That is what the laser is for. Extending out a little can be helpful though to better see the primary.

There are two really helpful sources for collimating an RC the Alina optics manual on their website and the Officina Stellare manual on their google groups.

Edited by akulapanam, 23 November 2017 - 02:48 PM.

[rpineau]

I see your point and it seems I've been doing it wrong ... using the laser to square the focuser and then puting the TAK collimator where my camera is to collimate ... where I should be doing the opposite.. remove the focuser, put the TAK there, collimate, then put the focuser back with all the imaging train and the laser where the camera should be to square the while imaging train the to telescope..

Well.. now I have some homework to do.. and I need more adapters

Thanks

Rodolphe

[akulapanam]

I see your point and it seems I've been doing it wrong ... using the laser to square the focuser and then puting the TAK collimator where my camera is to collimate ... where I should be doing the opposite.. remove the focuser, put the TAK there, collimate, then put the focuser back with all the imaging train and the laser where the camera should be to square the while imaging train the to telescope..
Well.. now I have some homework to do.. and I need more adapters
Thanks
Rodolphe

I start with making sure my focuser is square, then the Tak scope, and then add the FW/ OAG/ camera and do final collimation on a star only slightly defocused.

Edited by akulapanam, 23 November 2017 - 05:07 PM.

[Richard Whalen]

Start with your focuser, you need an anchor point to collimate the optics to.

[buckeyestargazer]

SUCCESS!!!

As some of you know from another post, I had a lot of tilt in my system and as far as I could tell it appeared to be a problem in the focuser. Last night was a very clear, steady night with above average seeing conditions.

 

Here are my collimation/tilt adjusting steps:
1. I squared the focuser flange with the back plate of the scope. The flange was tight up against the back plate.
2. Collimated indoors with the Tak TCS (easy!)
3. Star collimation using the DSI method - a tiny adjustment to the primary and a tiny adjustment to the secondary was needed.
4. At this point the stars across the whole field of view looked great, round to the edges.
5. I took a series of test images on a star field and loaded them into CCDInspector. CCDI showed a large tilt, as expected.
6. I began to adjust the focuser FLANGE to correct the tilt. I realize this is backwards...
7. After making tiny adjustments to the focuser flange, I ended up with a 3% tilt. Not too bad!

I realize that in the above way of doing this, if I rotate the focuser I may introduce a little more tilt, since it is possible that the focuser is not truly aligned with the optical axis. Actually, I removed tilt with the camera angled at 90deg relative to the sky. But I image at 0deg relative to the sky, so I rotated the focuser so the camera was oriented at 0deg and repeated the tilt adjustments on the focuser flange. I was glad to see that rotating the focuser resulted in only a slight increase in tilt, which I then removed by further flange adjustments.

I'm pretty happy right now. I think the system is finally coming together.

Attached are my CCDI results and a single image of NGC891. Here is a link to download the raw fit if anyone wants to take a look:

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[dpastern]

Nice stuff Joel - very glad it's all coming together for you.  I look forward to seeing many images from this scope.

 

edit: I just checked your website out and gobsmacked by the images!

Edited by dpastern, 24 November 2017 - 09:51 AM.