Collimating with a video camera tutorial with photos.

[TopHouse]

Hello Dion,

I think using videocameras would be a very obvious next step to overcome the

obstacle of watching what's happening at the focal plane while adjusting

collimation bolts at the opposite end of a long tube. (This or remote

control of the collimation bolts!). It can be done, I have.

These are the steps as suggested in the thread:

1. Fitted a crosshair reticle into a C Mount adapter.

2. Fitted this into the Sony Handycam.

3. Inserted handycan + Nosepiece into the focuser of the scope.

4. Pluged the Firewire lead into the laptop and the Handycam

5. Opened up WxAstrocapture software

6. Your live view instanly appears on your laptop.

7. Rotate camera until crosshairs are central.

8. By looking at image you can see if secondary mirror is centralised on

primary.

9. You can now align the crosshairs right into the middle of your donut

marking on your primary

10. Eventually everything will be exactly aligned. You can zoom in and make

very small adjustments to get it spot on.

11. No need to worry about offset as this is automatically taken care off.

>>>>

There are 3 basic requirements to collimation, in ascending order of

precision required:

A) centering the secondary on the light path (to center the fully

illuminated FOV)

aiming the focuser axis on the center of the primary (adjusting the tilt

of the secondary)

C) aiming the primary's axis on the center of the focal plane (Cheshire,

Barlowed laser).

If you have done and C), you can at least detect a misalignment of the

secondary by noting whether the edge of the secondary is concentric with the

edge of the primary inside it, and then shift the secondary, and repeat ,

C) and A) until satisfied. However, if what is done is adjusting the

secondary to center the primary's reflection in it, this does not achieve

to a meaningful precision. One should keep in mind that an error in does

NOT affect the image in the center of the field to any serious degree - the

difference is in the outer parts of the field.

1. This crosshairs reticle - can you focus directly on the crosshairs? Or

instead, can you image the distant reflection of it in the primary? Or, as

it seems but is not quite clearly described, both? See 9. From the latest

pictures, I guess the faint, fuzzy cross in the last image of message #14,

slightly offset from the sharp image of the spider, is the crosshairs placed

far inside focus. If so, and the crosshairs are actually centered in the

camera adapter, then the alignment is nowhere near accurate enough in ,

see below.

7. What exactly does this mean/how is it done?

9. Does this refer to the distant reflection of the crosshairs (are they

illuminated), or to a direct view?

So, in 8, what do you adjust if it isn't?

And in 9, what is adjusted to align? The primary or the secondary? The

primary, possibly - in the 2 next to last images in #14 one has the

impression of a slightly brighter circle with crosshairs, and a smaller

circle representing the primary's center marking. If so, bringing them in

alignment, this step will set the tilt of the primary C) correctly and

accurately, in the same way a Cheshire is used.

However, if the secondary is not accurately aligned first in , and I

suspect it is not, this is of limited value - aligning the secondary

afterwards will undo the alignment of the primary.

Thus, the procedure used is at least to me not clear enough to really

udge - the steps A-C must be taken accurately enough, whatever method you

choose, but if they are here, and by what steps above, I cannot determine.

What I think could work is aligning the tilt of the secondary with a laser

(as it seems people have - but unless it is a Glatter, always check the

alignment ;-), then use the handycam to align the primary, then check the

centering of the secondary and adjust if necessary.

Nils Olof

[Doc]

Nils is correct in what he says quote:

However, if the secondary is not accurately aligned first in , and I suspect it is not, this is of limited value - aligning the secondary

afterwards will undo the alignment of the primary.

This is exactly what I found when trying to align the secondary by just placing as near as central in the primary allowing me to see the three mirror clips and getting the secondary to look round as it can be.

I found that doing this way always disagreed with the Hotech laser collimator, and the best way was to do the following.

1. Insert collicap to centre secondary so all three mirror clips are visible.

2.Then insert laser collimator to align the tilt of the secondary and recheck with the collicap.

3. Insert the handycam and adjust the primary until donut is on the crosshairs.

4. Check all observations again making sure secondary is showing completely round and mirror clips all visible and donut is exactly on crosshairs.

This is basically What Nils has said and it does work.

It took me a while to think of this as I could never understand why my Hotech didn't agree but after a while the penny dropped.

[TopHouse]

TopHouse, with all due respect, you are approaching collimation the wrong way. You are putting too much emphasis on mechanical alignment when collimation is all about optical alignment. Collimation consists of three main alignments:

1- Centering the secondary under the focuser – impacts field illumination

2- Aligning the focuser axis to strike the center of the primary mirror – impacts focal plane tilt at the eyepiece

3- Aligning the primary axis to coincide the focal point with the focuser axis – impacts focal plane shift at the eyepiece

Interestingly, the first two are not as critical for visual observation. Only the third alignment is the most critical. Image sharpness has little to do with the first two alignments but is significantly impacted by the third.

Jason

"With respect", people always put that before something when they're going to be either insulting or patronising thinking that it excuses it.

The fact is that firstly, centering of focuser in the tube is important, to what degree of accuracy it is centered has what affect on collimation is unimportant, ie being 'more' accurately centered can certainly not be any worse than, 'roughly centered'

Centering the secondary within the focuser, as done with a collicap or cheshire or camera, no difference except that with a camera it can actually be measured and henceforth IS more accurate.

Adjustment of 'slight' amount of tilt using a laser, recognised method.

Adjustment of secondary using barlowed laser, arguably recognised as THE best method of aligning primary and verified and invented by Nils Olof.

It dismays me Jason that, after all the research and experimentation that was put into this thread and it's results, that despite claiming to know it all, you chose not to provide ANY constructive input whatsoever! Not only that, but any user choosing to look at your 13 posts on this forum will undersatandably think, as i do that almost your entire presence on here consists of following me round and being patronising, condescending and/or dismissing comments or theories I offer, and I happily invite anyone to check that.

If you have a problem with me Jason, then take it up with me in private. If not then I respectfully request that you stay away from me!

[Jason D]

TopHouse, I am absolutely dumbfounded by your response. My criticism is constructive by clarifying what is important and what is not for collimation.

I assure you I have nothing against you personally. Some of your collimation related conclusions and claims are incorrect. I was trying to provide some balance.

Honestly, I have no interest in personalizing any post exchanges. Certainly, I do not want my presence in this forum to be disruptive. I will respect your wish by staying off this thread.

Jason

[Doc]

Bringing this thread back on topic.....

It looks like a clear night tonight so I've just collimated my scope by doing the following....

1. Collicap to centre secondary

2. Hotech to tilt secondary

3. Handycam to position donut ontop off crosshairs.

Looks pretty good to me so I'll let you know how I get on.

[TopHouse]

Looking forward to it, it's actually a bit cloudy here but just called my wife out, the sunset was amazing! shades of blue going into orange and reaching almost directly overhead with orange glowing clouds. I want to have a go at a moon mosaic if weather permits with my totally unsuitable camera screwed to a hyperion.

[TopHouse]

Ooo it's cleared, the moon is out, venus is shining, a few stars showing, going to get my baby out! I feel like a labrador when someones about to throw a ball!

[Doc]

Collimation was very good indeed. Pin point stars, 5 Saturian moons and a few bands seen on Saturn.

[njs]

Mick, thank you for this idea.

I'm new to astronomy and I bought an 8" skywatcher second hand with an EQ4 mount last September, came with a 25mm eyepiece and was amazed with it. I later bought a 2mm eyepiece and a variable 7mm-20mm eyepiece with barlow. Since then I have been made redundant and dropped the telescope. Luckly nothing was smashed, just the tube dented and spider vane buckled. However my viewing was now so fuzzy I was distraught. It seemed after researching I needed a collimator, which I could no longer afford. Thanks to this thread I have managed to use my Fuji Finepix DSLR which fits snugly into the 2" focuser to collimate my scope and the results are now better than when I bought it.

Thank you so much.

Neil

[dobserver]

Oh what a downer for you Neil!

How fantastic that you were able to sort it out for free though, great stuff.