Collimating a triplet Refractor

[diegocolonnello]

I have got an explore scientific ED80 refractor, this thing is a beauty, triplet apo that promises good views and photos.......... but....

I found this second hand on a really good condition........... after testing it, i noticed weird looking stars:

https://3.bp.blogspot.com/-Lotg5LMLejM/WGc7CaqBvfI/AAAAAAAAGFU/Gvk-8FXHMm4q1X__DCum12AtCF4LcjP7gCLcB/s1600/apotest.jpg

I don't know anything about refractors but this doesn't look right for an APO...

so i decided to take it apart and find what is going on....
Checked that everything was in place and that the focuser is properly alligned to the Lens cell...... so, what happens?

I found a manual from Explore Scientific where they instruct the user on how to collimate their telescope, it happens that the second and third objectives have radial centering screws..... easy, use a high power eyepiece and look for the shape of the airy discs and done, adjust and ready to go....
:sadeyes:
it doesn't work that way, looking at the airy discs its hard, it moves and its too small, i can't tell if the center is ok or off.......

Tried to look for info on google and NADA........ people collimates Newts and checks focuser alingment on refractors but nothing on triplet lens centering.......

I came up with the idea of installing my ZWO 034MC camera to the scope and use an artificial star ..... after trying to get an image centered on my scope, it worked......... and saw this on SharpCap...

https://1.bp.blogspot.com/-Pn-SKVujG2g/WGc4RjVjnCI/AAAAAAAAGE0/kEaYp37SB3o_-_nuPvkULnM0Yd4f7IC9ACLcB/s1600/20161228_235648.jpg

Clearly i can see the discs are not centered and maybe this is the cause of my problem....... RADIAL CENTERING

Started to try and adjust the screws and at last i found out i could see what i was doing, but it was too late to continue....

Maybe i am bananas trying to collimate a triplet, but i am getting close...:rofl:

Episode 2...

Again, lets try.....

Installed the little beauty on my eq5 mount, started the mount and installed the artificial star across the house, all the way to the kitchen, after 10 minutes i had the star on my FOV and started tweaking the image for gain, contrast and exposures to get the best i could....

After trying and moving the objectives i learned what moves where and the effect it has on the image,,,,,,,

got it all the way to this...

https://2.bp.blogspot.com/-r6n7EhnIZZc/WGc4Tg7v09I/AAAAAAAAGFE/NAr4LWVJIF8a-AF_JqCgx2wOlr9r_IStACLcB/s1600/20161231_010001.jpg

Looks better live on my screen, i think it has to be really close to be good..... thing is every time you move the second lens, it moves the star across the FOV, then you have to center it again using the mount keypad and keep going................ untill it looks fine...

This is what pinched optics looks like...

https://1.bp.blogspot.com/-DPV2kFJ3ikI/WGc4UFAycZI/AAAAAAAAGFI/DeS5P6JY8d4ErgyNJLVjKWaRXMwOKCODgCL cB/s1600/20161231_013137.jpg

those 3 hills on the circle are the result of over tight setting screws....

This is a part of SHARPCAP that i consider interesting, it lets you separate LIVE the color channels....

https://2.bp.blogspot.com/-pxc0TLnQsEw/WGc4Tk_Gt9I/AAAAAAAAGFA/IBFsqedST88mE8vi_sz8K_GI6d4TXnztACL cB/s1600/20161231_011710.jpg

This lets you set up an offset on each channel and that way you know if one or two channels are in need of more adjustment......

I hope this helps someone, i will be posting my resulting images from this scope.............. WEATHER..... PLEASE, LET ME PLAY WITH IT>>>>

:screwy:

[brian nordstrom]

Forget what the images show for now as its probably in the allignment/spacing of the CCD to scope .

What I would do is take it outside and let it settle ( cool ) for an hour then put a high power 200x min eyepiece in and look at a mag 2 star close the the zenith and focus to the hardest point you can , it will ( should ) look like a small tight ball , the aeiry disc .

Then move focus in about 8 light and dark rings ( looking like a record , with rings ) and study the image with your eyes , then move back to focus and move focus out 8 rings and look at that image .

If the images are similar , round , concentric and central the optics are good , this test is very , very sensitive just be careful to keep the star central in the FOV of the eyepiece when doing this .

If there is a major difference you are in trouble and it will need to be sent back to the manufacturer as triplets are NOT !!! I repeat NOT ! like doublets and reflectors , repeat DONT !!! touch it as you will only make it much worse .

You need top quality testing equpment to align a triplet sorry to say .

Good luck on the star test , you might be lucky .

Brian.

[diegocolonnello]

Brian, thanks for the advice, i will do as you say.
if this doesn't work i will have to keep the case and put the scope on the bin. i paid 450 for it and there is no way i will pay more than that sending it away for collimation. anyway i haven't found where to send it or who offers that service. i guess that maybe i am lucky and it will work. maybe it will be a good guidescope, Keychain, piece of art or part of the furniture.

[The Mekon]

Brian,

How about appreciating the effort Diego went to in collimating an inexpensive Apo? I reckon he has done a great job, and this post should in no way be in the beginners section.

well done Diego!

[theodog]

Couldn't agree more.:thumbsup:

[brian nordstrom]

:lol: Anything you say ,,,, I do apreciate what he has done , I am only stating that he got it right ( ish ) and most if trying would totally fudge it, especially me .
Lighten up man .
Brian.

[brian nordstrom]

:question: AS ABOVE ,,,
Brian.

[diegocolonnello]

It was already bad i only have 2 options, make it worse or a bit better........... and i am learning new stuff on my journey.....

If it gets better, and if it works fine, i am sure the article might help someone, believe me, i was looking for info like this... everywhere...

If i had the option of sending it to someone in AUS and not spend big $$$ i would do it, i like this telescope..... the focuser is really nice, the case is awesome and the thing looks perfect....... only need it to give me good images...

[Atmos]

It is something you picked up cheap and it is your little "project", make it work :) You've made a good start in getting nice concentric rings, as Brian suggests nothing beats a star test under stable skies at zenith.

One thing I have read on Cloudy Nights is the use of a 33% aperture mask and I believe a Cheshire Eyepiece but you'd be better off researching it. You have a perishable lens, you may as well make it your learning lens to see if you can bring it back from the grave. Worst comes to worst, throw the lens' and keep the tube :)

My collimating experience with telescopes is a newt and Glatter laser, focuser with a Glatter and star collimating a SCT than only needed very minor adjustments. Refractor lens', I'll leave that to you!

[doppler]

I always think that if someone else can do it so can I, it will just take me a lot longer. It does help a lot if you can get a guide from mr google though. Good on ya I say. :thumbsup:

[casstony]

Learning how to perform a task with cheaper gear is a good way to go, though with something this tricky 95% of your time needs to be spent reading and 5% doing. Final collimation adjustments need to be re-checked after a couple of days to see if there is any residual settling of the lenses.

[diegocolonnello]

First light with new Collimarion, Not happy but better than before, the curvature on ccd inspector looks way Crazy......... is it possible a field flattener will help?

i will continue my journey hahaha

5 x 60 seconds subs (between clouds) calibrated and processed... shot with canon 40Da...

I will get there,.,,,,,,,,, :screwy:

[Atmos]

The curvature would probably look pretty crazy even if the collimation was correct without a flattener. A visual star test will give more accurate results as you only work on the very centre of the field where there are not any other aberrations to contend with.

[Kunama]

Watching this 'journey' with keen interest. I am tempted buy a cheap triplet to play with its collimation... Well done Diego....

My guess it that you now know more about triplet collimation that most anyone on this forum...... :thumbsup::thumbsup:

[AstroJunk]

I thought all refractors (like cameras) had spherical optics and hence the need for exotic materials and designs to fix the inherent issues introduced by spherical and chromatic aberrations. (Very happy to be corrected on this point). You may be able to change the spacing little else. All I can see is the edges dropping off on a short FL refractor being used with a camera with too large a sensor.

I think you need to collimate your expectations of this telescope and buy a field flattener :rofl:

[multiweb]

You're imaging the wrong fov with CCDIS. You need to pick a uniform starfield with no bright stars and devoid of nebulae. Short exposures high gain to get a good reading. Also this refractor will still need a flattener so just look for odd star shapes on axis to start with and ignore the edges as long as the flaring is symmetrical and centered. A flat field will also help to check that the illumination is centered.