Farpoint auto collimator

[Jason D]

I'm tempted to prefer the cats eye from FLO and compare the two and do a write up on them both

Dan, if you ever decide to go down that route, you can reference the criteria I posted here http://stargazerslou...r/#entry1675198

I will be happy to explain any of the items on the list.

Jason

[Daniel-K]

which one would you recommend ?

[Jason D]

I have not evaluated the Farpoint autocollimator; therefore, I can't comment on its quality and value.

On the other hand, I have evaluated several Catseye autocollimators and I have nothing but praise for their quality and accuracy.

I also know Jim Fly -- Catseye owner. Unlike the other 3 autocollimator vendors, Jim is quite knowledgeable about autocollimators and he is the only one who provides a complete set of correct instructions.

Jason

[Daniel-K]

i have just done a star test and can confirm it works very well its the closet i have been to near perfect, im still interested in the cats eye version though

[Jason D]

Dan, after you collimate with the cheshire/sight-tube and insert the autocollimator, do you stack reflections by only adjusting the secondary mirror without touching the primary mirror? Do you check again using the cheshire/sight-tube?

Back to the rotation test, it is unclear to me if you conducted the test on a slightly miscollimated scope with all 4 reflections showing. Can you clarify?

[Tim]

If you are anywhere near Coventry Dan then perhaps you might like to borrow my Cats Eye Kit and compare?

The quality of the engineering is obvious, the comprehensive instructions, the acetate with mirror centring function, the adjustable for f-ratio sight tube, I got the whole caboodle, and yes it is on the pricey side, but as they say, you get what you pay for, and given the quality of the equipment supplied, the Cats Eye system is actually good value for money.

I also have a copy of Vic Menards reference work on Newtonian collimation which makes interesting reading, explaining in depth the methods of achieving best possible collimation, including using the Cats Eye system, well worth a read, if a little heavy in places, but the formulas and explanations help to bring home the tiny tolerances we are working with, especially with the current trend for fast short focal length newtonians.

http://www.firstlightoptics.com/books/new-perspectives-on-newtonian-collimation-vic-menard.html

Having tools you can have absolute confidence in is very reassuring

[Daniel-K]

Dan, after you collimate with the cheshire/sight-tube and insert the autocollimator, do you stack reflections by only adjusting the secondary mirror without touching the primary mirror? Do you check again using the cheshire/sight-tube?

Back to the rotation test, it is unclear to me if you conducted the test on a slightly miscollimated scope with all 4 reflections showing. Can you clarify?

i collimate with the cheshire then insert the AC. stack the reflections with the secondary, theres 1 big reflection i see that i can get with he secondary so i use the primary to stack that then check the cheshire and repeat. the scope was not collimated before

[Jason D]

i collimate with the cheshire then insert the AC. stack the reflections with the secondary, theres 1 big reflection i see that i can get with he secondary so i use the primary to stack that then check the cheshire and repeat. the scope was not collimated before

Which "big" reflection were you referring to? All 4 center spot reflections should be about the same size -- unless your autocollimator mirror is away from the focal plane.

The proper method to use an autocollimator is:

1- Collimate the scope using any tool of your choice. This step does not have to be accurate. It is intended to bring the scope close to collimation so you can see all 4 center spot reflections in the autocollimator.

2- Use CDP method to align the focuser axis. This requires decollimating the primary mirror then stacking reflections P+3 via secondary mirro adjustment.

3- Finally re-stack all reflections via primary mirror, mainly reflections P+1

All above steps are outlined in details at the Catseye website.

Ending collimation with stacking center spot reflections via the secondary mirror is improper. Check attachment. Both photos show stacked reflections and darkened background but it is obvious that the left photo is way off. I exaggerated the error purposely to convey the point. The error could be much subtle to the point you can’t discern it. The proper procedure I outline above will avoid this type of error.

Jason

[Daniel-K]

yup thats the pretty much the way i done it. Farpoint really need to send out instructions with this thing. i have no idea what CDP is though

[Daniel-K]

If you are anywhere near Coventry Dan then perhaps you might like to borrow my Cats Eye Kit and compare?

The quality of the engineering is obvious, the comprehensive instructions, the acetate with mirror centring function, the adjustable for f-ratio sight tube, I got the whole caboodle, and yes it is on the pricey side, but as they say, you get what you pay for, and given the quality of the equipment supplied, the Cats Eye system is actually good value for money.

I also have a copy of Vic Menards reference work on Newtonian collimation which makes interesting reading, explaining in depth the methods of achieving best possible collimation, including using the Cats Eye system, well worth a read, if a little heavy in places, but the formulas and explanations help to bring home the tiny tolerances we are working with, especially with the current trend for fast short focal length newtonians.

http://www.firstligh...vic-menard.html

Having tools you can have absolute confidence in is very reassuring

your fair trek away from TIM im in Halewood on the edge of LIverpool but thanks anyway

[Jason D]

yup thats the pretty much the way i done it. Farpoint really need to send out instructions with this thing. i have no idea what CDP is though

CDP procedure is explained in the following link from Catseye

http://www.catseyeco...om/vicsCDP.html

Also it is covered in the following Catseye video between 4:25 and 5:28

Aligning P+3 as part of CDP looks like the attachment

[Jason D]

More photos with the "Hotspot". I prefer the "Hotspot" center spot shape when using an autocollimator. It makes aligning reflections easier and accurate. The photos I included in previous posts in this thread is off my old triangle center spot. That does not mean the autocollimator can't be used with a ring (or donut) shape center spot.

Attachments:

1- Misaligned CDP. P+3 reflections are unstacked.

2- Aligned CDP (stacked P+3)

3- Misaligned final step. Reflections are unstacked

4- Aligned (stacked) reflections for the final step

5 & 6 are off XLK with white Hotspot. After trying many center spots I settled for the white Hotspot.

Jason

[Daniel-K]

thanks for the pics jason, the hot spot will probaly be another upgrade from your method it looks like i have done it correctly, it is a tad hard to get the doughnuts aligned because of there shape i can see how a triangle or the catseye center spot will be better and i get the gray background as well

[Jason D]

from your method it looks like i have done it correctly

I believe there is some misunderstanding. I do not believe you have executed the CDP procedure. That would require decollimating the primary mirror then aligning reflections P and 3. You need to be able to identify the 4 center spot reflections as "P,1,2,3". The details are in the links I have provided.

Jason

[Tim]

If that Crab Nebula picture is anything to go by Dan, there is some way to go here :s

Even if you have terrible coma in your images, when the scope is properly collimated the coma will be centred on the image, with stars stretching out towards each corner by the same amount.

With fast newtonians the depth of focus is tiny, and a tilted mirror will mean that one side of the image could be in sharp focus, but the other side would be unfocused, being further away or closer to the focal point. Coma notwithstanding, you should be able to achieve sharp focus across the whole image with good collimation.

Cheers

Tim

[Daniel-K]

I believe there is some misunderstanding. I do not believe you have executed the CDP procedure. That would require decollimating the primary mirror then aligning reflections P and 3. You need to be able to identify the 4 center spot reflections as "P,1,2,3". The details are in the links I have provided.

Jason

ok jason i will have to have another go tomorrow, could you give me some advice on how to get the secondary right postion

Dan

[Jason D]

Collimation consists of three fundamental alignments:

Positioning the secondary mirror under the focuser for optimal illumination. This is the step we typically refer to as centering/rounding the secondary mirror under the focuser. A sight-tube is the best tool for this task. A collimation cap or an autocollimator can be used but these are not the best tools for this task.

Aligning the focuser axis to eliminate focal plane tilt. This is the step that involves fine tuning the secondary mirror to redirect the laser beam to the primary center spot or to coincide the cross hairs of the sight-tube with the center spot.

Aligning the primary axis to eliminate coma. This is the step that involves adjusting the primary mirror.

The autocollimator is mainly for the last two alignments which are referred to as “axial alignment”.

Following CDP procedure to align P+3 reflections will take care of the focuser axial alignment (2^nd from above).

Aligning P+1 reflections after successful CDP will take care of the primary axial alignment (3^rd from above)

Identifying the 4 center spot reflections (P,1,2,3) is important -- Refer to the video link I provided earlier.

Back to positioning the secondary mirror (1^st from above), you can refer to only the first few pages of the following thread

http://www.cloudynig...7/o/all/fpart/1

Here is a good post the describes the 3 alignment I mentioned above

http://www.cloudynig...sb/5/o/all/vc/1

Jason

[Daniel-K]

whats the best tool to align the secondary ?

Dan

[Jason D]

whats the best tool to align the secondary ?

Dan

As I explained earlier, there are two distinct alignments for the secondary mirror. This tends to be a source of confusion.

The first alignment has to do with centering/rounding the secondary mirror under the focuser. A sigh-tube is the best tool for this task.

The second alignment has to do with fine tuning the secondary mirror alignment to eliminate focal plane tilt. An autocollimator, a sigh-tube with cross-hairs, and a quality laser collimator can all handle this alignment. A quality autocollimator is the most accurate.

Jason

[Daniel-K]

ok after the stress over the primary last night got that washed this morning and back in the scope, follwed the CDP as best as i could as i have a doughnut not a triangle (next upgrade) so i could'nt do davids star but after going through the steps and then looking through the cheshire i am pleased, thank for the help jason

Dan

[Daniel-K]

after doing the CDP the collimation looks even better so when i get my recenerting spot kit it will be even better

[Mike73]

when i get my recenerting spot kit it will be even better

Where have you ordered this Dan?

[Kai]

Where have you ordered this Dan?

FLO can supply the Catseye ones http://www.firstligh...g-template.html

[Black Knight]

That page at FLO must be new - I'm sure that Catseye template wasn't there yesterday! Either that, or I sailed straight past it . I'm mulling over ordering the Catseye Combo kit myself at the moment. It's just difficult at this time of year ....

[Daniel-K]

thats the kit i ordered