Disappointing Collimation with Catseye Infinity XLKP

[richyrich_one]

Hi

Still trying to get my 130P-DS sorted.

According to the instructions with the catseye system I need to get the XLKP at or as near to the focal plane so as to get all the reflections of the hotspot the same size.

This does not seem to be possible if only using the focuser. With it all the way out I still have to add a 2" extension to do this. To me this adds a whole load of possible squew issues and really defeats the object of the exercise.

Without the extension, trying to stack the all the reflections via the central pupil is impossible as there is always ghosting due to each reflection getting progressively larger. The best I can do is stack P+ and the somewhat larger reflection 2 via the offset pupil and check the primary with the telecat. Not as precise as it should be.

Do I need to return this as it doesn't seem fit for purpose on PD-S scopes? I'm pretty sure I am not doing anything wrong but I'll be glad to be be corrected.

Any help much appreciated.

[faulksy]

i wish i could help. i have the full kit as well and can't get my head around it. @jetstream is the man. he should chime in

[Martin Meredith]

Hi Rich

I must admit I always use an extension and haven't considered the consequences, but I make sure it is well in and tightened.

At the start of each session I use only the autocollimator (unless I have reason to suspect the secondary is twisted or otherwise off).

I follow these two steps:

(1) via the central hole, adjust the primary to get the reflections as stacked as I can

(2) via the offset hole, adjusting the secondary to get the right hand pair of symbols stacked (the left hand pair move in concert anyway as far as I understand it, and the right hand pair are brighter)

Repeat (1,2) as needed (usually 2 or 3 times is sufficient).

I have tried the 'carefully decollimated primary' procedure but can't get on with it.

I'd be interested to hear what everyone else does!

Martin

 

[richyrich_one]

I'm pretty sure I get the mechanics of it all it just seems that to use it for supreme accuracy, which is the point, you have to add some variables into the mix. At least with the 130P-DS I'm using it on.

I am mounting my DSLR centrally in the focuser via a threaded connection so I need to try and collimate centrally. The XLKP is a nice snug fit in the focuser without any clamping required so it should work fine. But if I have to add an extension I have to clamp that in the focuser and it's then all off centre.

[jetstream]

42 minutes ago, faulksy said:

i wish i could help. i have the full kit as well and can't get my head around it. @jetstream is the man. he should chime in

Thanks for the vote of confidence Mike I am no expert however, but Jason D is and hopefully he will chime in I can AC my reflectors no problem though...

[jetstream]

8 minutes ago, richyrich_one said:

I'm pretty sure I get the mechanics of it all it just seems that to use it for supreme accuracy, which is the point, you have to add some variables into the mix. At least with the 130P-DS I'm using it on.

I am mounting my DSLR centrally in the focuser via a threaded connection so I need to try and collimate centrally. The XLKP is a nice snug fit in the focuser without any clamping required so it should work fine. But if I have to add an extension I have to clamp that in the focuser and it's then all off centre.

To back up a bit, is the scope collimated with the sight tube and cheshire first? In the end all the tools must agree.

[richyrich_one]

7 minutes ago, jetstream said:

To back up a bit, is the scope collimated with the sight tube and cheshire first? In the end all the tools must agree.

Yes, using a telecat, nice and snug no clamping required.

[faulksy]

14 minutes ago, jetstream said:

Thanks for the vote of confidence Mike I am no expert however, but Jason D is and hopefully he will chime in I can AC my reflectors no problem though...

lets hope @Jason D helps out . cheers gerry

[ronin]

Owing to the mechanics of it all and what you describe then you will need an extension tube in order to place the Catseye at the correct position. Guess the Catseye is designed for a visual scope and the different focuser needed for attaching a camera at the correct location for the prime image plane will mean that for an AP set up the image plane will be outside the end of the focuser tube (especially with a DSLR) So for a DSLR the image plane will be about 25mm outside the end of the focuser tube whereas for an eyepiece it will be about 25mm inside it.

The Catseye fits inside like an eyepiece, so about 50mm difference and I guess the focuser cannot take care of that much difference.

[richyrich_one]

And yet ironically an AP setup is surely the time you need the precision.

Pretty disappointed with this. It really should be made clear that this will be an issue with imaging scopes.

Looks like I might be having a word with FLO and see if I can return it.

[richyrich_one]

Raised the issue with FLO and suggested there should be mention of this issue on the product page.

[richyrich_one]

A detailed discussion of the problem is here is anyone is interested.

http://www.cloudynights.com/topic/247920-questions-re-the-use-of-the-infinity-xlk-ac/

[Jason D]

 

Without getting deeply into technical details, let me try to shed some light on the autocollimator performance vs focal plane.

Part 1: When the autocollimator (AC) mirror is approximately located at the focal plane:

First, let me emphasize the word "approximately". The AC mirror does not have to be "precisely" located at the focal plane. As long as reflections P and 2 appear to have the same size then the AC mirror is close enough to the focal plane. Typically, both P & 2 reflections will appear to have the same size when the AC mirror is within several millimeters from the focal plane. Actually this range is a percentage of the primary mirror focal length. The longer the focal length the wider the range from the focal plane.

When the AC mirror is close enough to the focal plane, both reflections P & 2 are located at the same distance from the AC; therefore, there is no parallax when viewing them from the central or offset pupils. When both are stacked via the offset pupil and only reflection P is visible from the central pupil, your scope is "axially" collimated.

It is important to note that when the AC mirror is located close to the focal plane only and only up to four reflections will be visible: P, 1, 2, 3. 

 

Part 2: When the autocollimator mirror is substantially below the focal plane:

Reflection 2 will move closer to the autocollimator mirror in relation to reflection P; hence, it will appear larger and some parallax will be noticed between both pupils. In addition, reflection 2 might not disappear as observed from the central pupil when axial collimation is achieved, though it might get dimmer. Reflections 1 and 3 will appear smaller. Additional reflections might appear beyond the typical four -- all with different sizes. The ones with reversed orientation compared to P will progressively get larger and the ones with the same orientation as P will progressive get smaller. But what does all this mean in terms of accuracy? Well,  very little. The sensitivity of reflections movement will increase when the AC mirror is below the focal plane. Wiggle the AC when it is at the focal plane then again when it is below the focal plane. You will clearly notice that reflection 2 will swing much wider (more sensitive) when the AC is below the focal plane. The AC performs ideally when its mirror is located close to the focal plane. When the AC mirror is substantially away from the focal plane, a small (I mean a small) AC error will be introduced which will be magnified as a noticeable discrepancy between both pupils. That is, reflections P and 2 might appear stacked from the offset pupil but not from the central pupil.

Here is my recommendation on using the XLK or XLKP when the AC mirror is substantially below the focal plane:

1- Follow Catseye procedure which comes down to:

A-  Stack reflections P and 2 via the offset pupil by adjusting the secondary mirror -- Note that reflection 2 will appear larger than reflection P.

B- Stack reflections P and 1 via the central pupil by adjusting the primary mirror -- Note that reflection 1 will appear smaller than reflection P.

C- Re-iterate between A and B until relevant stacks are achieved from each pupil.

2- After the above procedure is followed, if reflection 2 is visible from the central pupil (it shouldn't be visible when the AC is close to the focal plane) and if it appears unstacked against P -- though it is stacked against P via the offset pupil, optionally you can do the following: At this point, you can ignore the offset pupil and only use the central pupil. You can continue stacking reflections 2 and P by adjusting the secondary mirror and stacking reflections P and 1 by adjusting the primary mirror. What you might notice is that a minute adjustment will be needed to stack reflection 2 and P via the central pupil by secondary mirror and no adjustments will be needed for the primary. That is, this step will have very little impact on the excellent collimation that was already achieved by following the Catseye AC steps.

I do realize this post is long and might sound confusing to many. To summarize, AC performance is ideal when the AC mirror is located close to the focal plane. When the AC mirror is substantially below the focal plane, AC performance will not be as ideal; however, the degradation is too small to impact the overall collimation accuracy.

Jason 

 

 

[richyrich_one]

34 minutes ago, Jason D said:

 

Without getting deeply into technical details, let me try to shed some light on the autocollimator performance vs focal plane.

Part 1: When the autocollimator (AC) mirror is approximately located at the focal plane:

First, let me emphasize the word "approximately". The AC mirror does not have to be "precisely" located at the focal plane. As long as reflections P and 2 appear to have the same size then the AC mirror is close enough to the focal plane. Typically, both P & 2 reflections will appear to have the same size when the AC mirror is within several millimeters from the focal plane. Actually this range is a percentage of the primary mirror focal length. The longer the focal length the wider the range from the focal plane.

When the AC mirror is close enough to the focal plane, both reflections P & 2 are located at the same distance from the AC; therefore, there is no parallax when viewing them from the central or offset pupils. When both are stacked via the offset pupil and only reflection P is visible from the central pupil, your scope is "axially" collimated.

It is important to note that when the AC mirror is located close to the focal plane only and only up to four reflections will be visible: P, 1, 2, 3. 

 

Part 2: When the autocollimator mirror is substantially below the focal plane:

Reflection 2 will move closer to the autocollimator mirror in relation to reflection P; hence, it will appear larger and some parallax will be noticed between both pupils. In addition, reflection 2 might not disappear as observed from the central pupil when axial collimation is achieved, though it might get dimmer. Reflections 1 and 3 will appear smaller. Additional reflections might appear beyond the typical four -- all with different sizes. The ones with reversed orientation compared to P will progressively get larger and the ones with the same orientation as P will progressive get smaller. But what does all this mean in terms of accuracy? Well,  very little. The sensitivity of reflections movement will increase when the AC mirror is below the focal plane. Wiggle the AC when it is at the focal plane then again when it is below the focal plane. You will clearly notice that reflection 2 will swing much wider (more sensitive) when the AC is below the focal plane. The AC performs ideally when its mirror is located close to the focal plane. When the AC mirror is substantially away from the focal plane, a small (I mean a small) AC error will be introduced which will be magnified as a noticeable discrepancy between both pupils. That is, reflections P and 2 might appear stacked from the offset pupil but not from the central pupil.

Here is my recommendation on using the XLK or XLKP when the AC mirror is substantially below the focal plane:

1- Follow Catseye procedure which comes down to:

A-  Stack reflections P and 2 via the offset pupil by adjusting the secondary mirror -- Note that reflection 2 will appear larger than reflection P.

B- Stack reflections P and 1 via the central pupil by adjusting the primary mirror -- Note that reflection 1 will appear smaller than reflection P.

C- Re-iterate between A and B until relevant stacks are achieved from each pupil.

2- After the above procedure is followed, if reflection 2 is visible from the central pupil (it shouldn't be visible when the AC is close to the focal plane) and if it appears unstacked against P -- though it is stacked against P via the offset pupil, optionally you can do the following: At this point, you can ignore the offset pupil and only use the central pupil. You can continue stacking reflections 2 and P by adjusting the secondary mirror and stacking reflections P and 1 by adjusting the primary mirror. What you might notice is that a minute adjustment will be needed to stack reflection 2 and P via the central pupil by secondary mirror and no adjustments will be needed for the primary. That is, this step will have very little impact on the excellent collimation that was already achieved by following the Catseye AC steps.

I do realize this post is long and might sound confusing to many. To summarize, AC performance is ideal when the AC mirror is located close to the focal plane. When the AC mirror is substantially below the focal plane, AC performance will not be as ideal; however, the degradation is too small to impact the overall collimation accuracy.

Jason 

 

 

Jason, thanks for your extremely detailed response. I know you know your stuff here!

I will attempt to follow this procedure and see what results I can get. Unfortunately it looks unlikely that I will get any suitable weather to test them.

I will say that since this "issue" has been known about for some years, and the popularity of imaging newtonians can only have increased since it was highlighted, I wonder why this has not been addressed with a mechanical solution. The obvious solution is a properly machined extension. According to the CN thread above it was proposed but then seems to have been ignored. Personally I find this hard to understand. I am certainly no expert so perhaps there is a good reason for this. Is there a suitable off the shelf solution available?

It's also disappointing that the AC is marketed implying a simplicity of operation, when used in the correct focal range, but absolutely no mention of any difficulties that might arise (and how to deal with them) when it is not. And athough the collimation accuracy might not be greatly impacted the usability (the interpretation and stacking of the reflections and attaining that accuracy in the first place) certainly is.

Again, I thank you for taking the time to assist.

[richyrich_one]

2 hours ago, Jason D said:

Here is my recommendation on using the XLK or XLKP when the AC mirror is substantially below the focal plane:

1- Follow Catseye procedure which comes down to:

A-  Stack reflections P and 2 via the offset pupil by adjusting the secondary mirror -- Note that reflection 2 will appear larger than reflection P.

B- Stack reflections P and 1 via the central pupil by adjusting the primary mirror -- Note that reflection 1 will appear smaller than reflection P.

C- Re-iterate between A and B until relevant stacks are achieved from each pupil.

2- After the above procedure is followed, if reflection 2 is visible from the central pupil (it shouldn't be visible when the AC is close to the focal plane) and if it appears unstacked against P -- though it is stacked against P via the offset pupil, optionally you can do the following: At this point, you can ignore the offset pupil and only use the central pupil. You can continue stacking reflections 2 and P by adjusting the secondary mirror and stacking reflections P and 1 by adjusting the primary mirror. What you might notice is that a minute adjustment will be needed to stack reflection 2 and P via the central pupil by secondary mirror and no adjustments will be needed for the primary. That is, this step will have very little impact on the excellent collimation that was already achieved by following the Catseye AC steps.

 

Well I feel I've given this a fair try and to be honest the reflections are far too ambiguous to achieve any kind of alignment.

Such a shame, I so wanted this to work.

FLO have offered to take it back for a refund and I will be taking them up on their offer.

 

[Jason D]

Hello Rich,

I do understand your frustration. I need to clarify that I am not affiliated in any way with either Catseye or FLO but I am interested to learn more from your experience. I would appreciate it if you could answer the following questions:

1- Your scope has a focal length of 130mm (correct me if I am wrong). Can you estimate how far is the AC mirror located below the focal plane? Just an estimate -- no need to get out of your way to measure.

2- How many reversed reflections (compared to reflection P) do you see? These are the sharp reflections that will progressively get larger

3- Can you estimate (again just a rough estimate) the size of reflection 2 compared to reflection P?

4- Was stacking reflections 2 and P via the offset pupil hard? If yes, was it due to reflection cluttering? Was it due to stacking two different reflection sizes (P & 2)? Was it due to the mechanics of adjusting the secondary mirror to get both reflections 2 and P to stack?

5- How difficult was it to stack reflections P and 1 via the central pupil by adjusting the primary mirror? Was the difficulty due to the inability to discern reflection 1 in the clutter of other visible reflections?

It would be helpful if you could take photos using your cell phones from each AC pupil then upload the photos. 

Jason

[Martin Meredith]

Until Rich brought up this issue I'd been happily collimating my Newt with the extender in place (to get P and 2 the same size). My use case is EAA with a small sensor, so not as critical as for AP, and I've been happy with my results. But just now I tried collimating without the extender. I started with the extender in place, collimated, then checked collimation without the extender and it was quite different (P & 2 clearly misaligned by perhaps as much as half of their diameters). So I suppose this means I've been mis-collimated for the last couple of years. I have regularly seen slightly eggy stars in just one corner and wondered where they came from, but as a hit-and-run EAA observer it has never bothered me.

So now I've re-collimated with the focuser draw tube as far out as possible. The reflections are not quite the same size (2 is perhaps 20% larger), but I followed my normal procedure, which is precisely what Jason recommends above, and *hope* I've managed to get a well-collimated scope. I found myself trying to align the circular holes in the hotspot reflections while keeping an eye on the outer circumference.

Let's see what the night brings!

Martin

 

[richyrich_one]

I've not had a chance to get out and get that info, should be able to tomorrow.

I've had a thought, it shouldn't be too difficult to make up an inexpensive adaptor from 2 pieces of alluminium tube from here:

https://www.forwardmetals.co.uk/

A piece 50.8mm OD with wall of 4.8mm slid inside another piece 63.5mm OD with wall of 6.4mm making an ID of 50.7mm, might have to cool one and heat the other to fit them?

I've used them before, they do 2 free cuts so just need to calculate a rough length to bring the AC within the focal plane. They should cut them nice and square. At £13 delivered it might be worth a try. They would be a much better fit than the usual extension tubes and pretty substantial.

Oh I wish I had a lathe!

 

[Jason D]

21 hours ago, Martin Meredith said:

I started with the extender in place, collimated, then checked collimation without the extender and it was quite different (P & 2 clearly misaligned by perhaps as much as half of their diameters)

 

1- Complete a perfect collimation when the AC was located at the focal plane. Rotate the AC 360 degrees and both reflections P & 2 should remain stacked. Perfect!!!! (I have something more to say about this at the end of the post)

2-  Lower the AC below the focal plane by a noticeable distance. You will see that reflections P & 2 are still stacked from the central pupil though reflection 2 is larger. You might also notice additional fainter stacked reflections appearing with different sizes. If you observe from the offset pupil, you will see the same reflections spreading radially with larger/fainter reflections spreading away from the center (including reflection 2) and the smaller/blurrier reflections spreading towards the center. If you rotate the AC, reflections will also rotate maintaining their relative distances from the center. 

To explain what is going on, refer to attachment. Consider an autocollimator with three offset pupils.  When the AC is at the focal plane, reflections P & 2 are located at the same distance from the AC and are stacked with collimation is achieved. There is no parallax. They will appear stacked regardless which pupil is used -- including the central pupil. 

When the AC mirror is below the focal plane, reflection 2 moves up and will appear larger. Since reflections P & 2 are no longer at the same distance (reflection 2 is closer), there will be a noticeable parallax and reflection 2 will appear to have shifted outward. However, reflection 2 movement sensitivity will also increase compared to when the AC was located at the focal plane. Stacking reflections P and 2 from one of the three offset pupils will take a minute amount of adjustment. That is, you will hardly deviate from the perfect collimation that was original achieved.

Back to what I mentioned in # 1, I strongly discourage anyone from stacking P & 2 then do the rotation test. Unless the AC mirror is precisely positioned at the focal plane, the stack will not be perfectly maintained. At 180 degree, collimation error is magnified by 8X. As long as reflections P & 2 appear to have similar sizes then your collimation will be superb. Make sure to place the autocollimator with the same orientation to re-check collimation. Do not place it in random orientation unless you know the AC mirror is located precisely at the focal plane. The hassle of placing the AC mirror precisely at the focal plane is NOT worth the effort and frustration.

Jason

[richyrich_one]

On 25/02/2017 at 07:48, Jason D said:

Hello Rich,

I do understand your frustration. I need to clarify that I am not affiliated in any way with either Catseye or FLO but I am interested to learn more from your experience. I would appreciate it if you could answer the following questions:

1- Your scope has a focal length of 130mm (correct me if I am wrong). Can you estimate how far is the AC mirror located below the focal plane? Just an estimate -- no need to get out of your way to measure.

2- How many reversed reflections (compared to reflection P) do you see? These are the sharp reflections that will progressively get larger

3- Can you estimate (again just a rough estimate) the size of reflection 2 compared to reflection P?

4- Was stacking reflections 2 and P via the offset pupil hard? If yes, was it due to reflection cluttering? Was it due to stacking two different reflection sizes (P & 2)? Was it due to the mechanics of adjusting the secondary mirror to get both reflections 2 and P to stack?

5- How difficult was it to stack reflections P and 1 via the central pupil by adjusting the primary mirror? Was the difficulty due to the inability to discern reflection 1 in the clutter of other visible reflections?

It would be helpful if you could take photos using your cell phones from each AC pupil then upload the photos. 

Jason

Hi Jason

I'll do my best with these.

1- Focal length is 650mm and I estimate with the focuser fully out the AC is 30mm below the focal plane.

2- Really hard to tell, perhaps you can make it out from the photos but they aren't very good.

3- See photo.

4- Difficult due to the relative sizes

5- Very difficult, too much clutter

 

[Jason D]

Thanks for the photos and info.

I am analyzing the photos at this time. I will reply soon.

Jason

[Jason D]

By examining your photos, I can visualize the position of the autocollimator with respect to the primary mirror in 3D. See attachments. Left photo from the center pupil and right photo is from the offset pupil.

Please try to the following slightly modified steps:

1- Stack P1 and P2 via the offset pupil by adjusting the secondary mirror. You stated that this step was hard due to the larger P2 size. Do your best. Precise stacking is not needed. If stacking is difficult, at least make sure P2 is shifted little outward -- as opposed to inward. In your photo, P2 was shifted inward. Ignore the remaining reflections when executing this step.

2- The modified step: Align the AC center pupil reflection with P1 by adjusting the primary mirror. Typically, this step is difficult when the AC is close to the focal plane since the background will get darkened  which makes it hard to discern the pupil reflection. However, when the AC is substantially below the focal plane, the background will never be fully darkened and I presume it would be possible to discern the pupil.  Ignore all other reflections. Just focus on P1 and the pupil.

3- Re-iterate between steps 1 and 2

4- This is an optional step that might give you that last little precision. Stack P2 and P1 by adjusting the secondary mirror as seen from the central pupil (step 1 above was from the offset pupil). If discerning P2 is difficult in the clutter, ignore this step. 

Again, I want to remind you that the sensitivity of the AC increases when it is located below the focal plane. After completing the above steps, you might notice that some reflections might not stack perfectly. That is OK. Any stacking errors are highly magnified due to the extra sensitivity. 

Jason

 

[richyrich_one]

11 minutes ago, Jason D said:

By examining your photos, I can visualize the position of the autocollimator with respect to the primary mirror in 3D. See attachments. Left photo from the center pupil and right photo is from the offset pupil.

Please try to the following slightly modified steps:

1- Stack P1 and P2 via the offset pupil by adjusting the secondary mirror. You stated that this step was hard due to the larger P2 size. Do your best. Precise stacking is not needed. If stacking is difficult, at least make sure P2 is shifted little outward -- as opposed to inward. In your photo, P2 was shifted inward. Ignore the remaining reflections when executing this step.

2- The modified step: Align the AC center pupil reflection with P1 by adjusting the primary mirror. Typically, this step is difficult when the AC is close to the focal plane since the background will get darkened  which makes it hard to discern the pupil reflection. However, when the AC is substantially below the focal plane, the background will never be fully darkened and I presume it would be possible to discern the pupil.  Ignore all other reflections. Just focus on P1 and the pupil.

3- Re-iterate between steps 1 and 2

4- This is an optional step that might give you that last little precision. Stack P2 and P1 by adjusting the secondary mirror as seen from the central pupil (step 1 above was from the offset pupil). If discerning P2 is difficult in the clutter, ignore this step. 

Again, I want to remind you that the sensitivity of the AC increases when it is located below the focal plane. After completing the above steps, you might notice that some reflections might not stack perfectly. That is OK. Any stacking errors are highly magnified due to the extra sensitivity. 

Jason

 

Thanks Jason, I'll definitely give this a go.

It's quite obvious you have an insight and passion for this subject. You have gone to a lot of trouble and I appreaciate it.

The "reflections", at least in the instructions I have from Catseye, are refrerred to as P(actual hotspot), P1, P2 & P3. I just want to clarify the reflections you are referring to in the above instructions.

Could you just confirm please?

[Jason D]

I should have stuck to P,1,2,3 naming convention. So, replace P1 by P and replace P2 by 2.

Rich, I need to disclose that I am the one who came up with the autocollimator offset pupil idea and the radioactive center spot idea (the HotSpot). I am also the one who assisted Catseye with preparing the XLK instructions and the XLK video (the hands in the video are mine). However, I am not affiliated with Catseye business and I have never received any monetary payments from anyone pertaining to my autocollimator contributions.

I have always been fascinated by the physics behind the autocollimator reflections and how they relate to collimation. Your experience with using an autocollimator to collimate an imaging scope is interesting to me.

Jason

[richyrich_one]

Thanks Jason.