newt collimating - ocal collimator and my baader mk3 coma corrector

[powerlord]

So I hate collimating, and I'm rubbish at it.

So I bought one of these Ocal Collimators. I collimated my ts-photon 150 tonight with it, and though I have not star tested yet - I was waaay out before with secondary rotation, position, and welll everything.

then I read (btw the manual is attrocious chinglish) that i should use my coma corrector for a more accurate result.

that made sense to me - I'm always using it, so it should be collimated through it... after fitting I was surprised to find it was massively out again. I checked everything was bedded properly, and yup - it's just waay out with coma corrector.

So I started again, collimated with coma corrector in, and got it spot on.

Now, I hate the idea of start tests as I'm an imager, and that means faffing about with eyepeices, then losing target after a twiddle, hunting for ages to find star again, rinse and repeat.

So frankly the chance of me looking for airy disks is zero. I'll be happy if my subs have reasonably round stars.

So, I will update when I've had a chance to actually test it. I will now be using it for my other 5 (!!!) reflectors.

A few early review comments:

1. it is at the heart just a simple camera, and a basic program which overlays circles. it's not AI magic. However that alone made the whole process soooo much easier for me. And for larger scopes if will be a godsend (300 PDS coming saturday!!). Whether this is worth 160 squid is up to you. To me, so far.. providing the resultant symetrical goodness results in roundish stars.. the answer is a resounding YES.

2. the manual is atrocious chinglish. I'm tempted to rewrite it for them, and charge em a free ocal for the trouble. Going by the number of returns to FLO (4 resales have appeared in last few days) I reckon that is not helping.

But here is my dumb question:

Is this normal ? To find collimation is totally different with coma corrector ? I'd have thought not, and maybe mine is just off somehow, but it does explain I think why my stars were still a bit rubbish last time I imaged - a: it wasn't collimated very well anyway, b)add the coma corrector and it was even further off.

stu

Edited March 2, 2022 by powerlord

[teoria_del_big_bang]

10 minutes ago, powerlord said:

Is this normal ? To find collimation is totally different with coma corrector ? I'd have thought not, and maybe mine is just off somehow, but it does explain I think why my stars were still a bit rubbish last time I imaged - a: it wasn't collimated very well anyway, b)add the coma corrector and it was even further off.

As collimation is the aligning of primary and secondary mirrors I would not think the coma corrector should affect the collimation when it is collimated.
Perhaps if out of collimation then the introduction of the corrector could make it look different (i,e either more out of alignment or less out of alignment) but when in alignment should stay aligned.

That is how I see it but I am not saying this with 100% confidence I am right.

I got one of those returns from FLO to use on a Ritchey-Chrétien, and can't even get the offset adjustment to work, it works but the maximum both horizontal and vertical is only about half what I need to centre the circles.
I think it is the scope that is at fault though and the focusser (which is attached to primary mirror, is not straight.

Steve

[Same old newbie alert]

2 hours ago, powerlord said:

2. the manual is atrocious chinglish. I'm tempted to rewrite it for them, and charge em a free ocal for the trouble. Going by the number of returns to FLO (4 resales have appeared in last few days) I reckon that is not helping.

The manual?? What manual?? I bought mine for use with my SCT and was planning to take the reducer off and use it natively with the camera.. presume a coma corrector is the same as a flatener part of the reducer, correcting the field

[Same old newbie alert]

2 hours ago, teoria_del_big_bang said:

 

I got one of those returns from FLO to use on a Ritchey-Chrétien, and can't even get the offset adjustment to work, it works but the maximum both horizontal and vertical is only about half what I need to centre the circles.
I think it is the scope that is at fault though and the focusser (which is attached to primary mirror, is not straight.

Steve

I was seriously looking at getting a RC but on my searches I find like the fact that the focuser is attached to the mirror plate, it's only separated  on the 10 inch  and upwards truss designs

[powerlord]

9 hours ago, Same old newbie alert said:

The manual?? What manual?? I bought mine for use with my SCT and was planning to take the reducer off and use it natively with the camera.. presume a coma corrector is the same as a flatener part of the reducer, correcting the field

 

9 hours ago, Same old newbie alert said:

The manual?? What manual?? I bought mine for use with my SCT and was planning to take the reducer off and use it natively with the camera.. presume a coma corrector is the same as a flatener part of the reducer, correcting the field

videos and link to manual on FLO:

https://www.firstlightoptics.com/other-collimation-tools/ocal-electronic-collimator.html

"We denfine the distrance from secordary mirror to OCAL as "Eye Point Distance." The OCAL view of
A and B have little difference bewteen red and greed circles."

"Now, we skip notice primary mirror. Adjust B
and C screw of secondary mirror holder to
make the outter shape of secondary mirror fit
to "green circle"."

and so it continues.

however, you can work it out if you've collimated before. If you havn't - fair play to you if you work out what yer supposed to do from the manual!

I was surprised the camera at electric focus - that makes things a lot easier too than manual - get a nice sharp edge where you need it.

[teoria_del_big_bang]

10 hours ago, Same old newbie alert said:

I was seriously looking at getting a RC but on my searches I find like the fact that the focuser is attached to the mirror plate, it's only separated  on the 10 inch  and upwards truss designs

This is my first RC and I think most make some sort of separation by adding a tilt plate.
Not a perfect solution I know, as movements of the primary still move the focusser which then has to be re-aligned but it is a way round it.

One question about tilt plates I have is that once some adjustment is made there is a gap between the plates, do you then hove to cover this gap up with tape or something ??

Steve

[teoria_del_big_bang]

56 minutes ago, powerlord said:

 

videos and link to manual on FLO:

https://www.firstlightoptics.com/other-collimation-tools/ocal-electronic-collimator.html

"We denfine the distrance from secordary mirror to OCAL as "Eye Point Distance." The OCAL view of
A and B have little difference bewteen red and greed circles."

"Now, we skip notice primary mirror. Adjust B
and C screw of secondary mirror holder to
make the outter shape of secondary mirror fit
to "green circle"."

and so it continues.

however, you can work it out if you've collimated before. If you havn't - fair play to you if you work out what yer supposed to do from the manual!

I was surprised the camera at electric focus - that makes things a lot easier too than manual - get a nice sharp edge where you need it.

Yes this is where I am now, I have collimated a Newt once or so a few years ago, I now in my head the principle of what I am trying to do but as you say the manual makes very little sense to me at all.
when I bought this OCAL I thought it actual did the same job as a Howie Glatter laser which seems to be the choice tool for collimating RC's looking at tutorials, but they are even more expensive (as looks like you need the targets as well and a new switch so you can dim them), so looking at around £500 for one (if you can get hold of one in UK). But I don't think they do.

Steve

[alacant]

15 hours ago, powerlord said:

To find collimation is totally different with coma corrector

Hi
 

With the mpcc III and Baader's t2 adapter, I'm not at all surprised.  

Go with the m48 threads instead. Don't forget that you'll now need around 58mm shoulder of m48 thread to camera sensor.

The other main issue with the mpcc is the undercut. The compression ring on the focuser will force it to tilt no matter how carefully you tighten around it. So lose the brass ring and have the screws bear directly against it. Or arrange that the imaging train clamps against a matt (or shiny type which has been sanded) m48 extension tube.

You might also check the seating of the focuser. I think the GSO models are free of distort-under-load rubber, but it could be that the tension screw may need a 1/4 turn clockwise. then leave it. Use only the locking screw in the field.

So that collimation holds at all angles, seal the main mirror to its cell, fit uprated springs, spread the tube rings on a Losmandy dovetail and tie the top of the rings with rigid aluminium profile.

You may want to consider a Cheshire sight tube with crosshairs for collimation.

Cheers and HTH

**EDIT: forgot. Loosen the retaining rings for each of the cc elements in turn and on a flat surface, shake/nudge to seat them. Tighten until the ring just touches the glass; no more rattle can be heard.

And of course, be sure to read both seronik and telia's collimation myths;)

Edited March 3, 2022 by alacant

[powerlord]

Sorry - few questions - i might be getting wrong end of stick here so bear with the stupid questions:

- why would m42 vs m48 be any different ? the baader is 50 on OTA side. so that just slides in to focuser. on the camera side the camera is m42 thread, so surely no point in goinf m48 to m42 as the adapter on the mk3 does that anyway ?

undercut - you mean the slight increase in diameter half way down focus side of mk3 from 49.8 or so to 50.7 or so ? the 49.8 bit is wider than the brass ring on the 150 so not followin that bit ? Seemed a good idea to me, as when brass ring tightening it stops the thing slipping out whatever load is on it ?

the focuser on the tsp 150 is just bolted directly onto the side if the tube as far as I can tell.

distance to CC wise didn't see how it mattered that much as all Im doing is centring things, but i will set it right (to 55 as above - not following why id want to use a different m48-m42 adapter.

I started with a cheshire. I didn't like it, hence the ocal

the loosen/tighten rings on CC is an interesting tip - will try that.

stu

[alacant]

20 minutes ago, powerlord said:

why would m42 vs m48 be any different

The Baader m42 adapter is known to cause tilt, in exactly the way you describe when you insert the cc into the optical train The m48 connection is directly to the corrector. Are you on zwo? Don't they include a proper m42-m48 in the box?

20 minutes ago, powerlord said:

you mean the slight increase in diameter half way down

Yes. If the compression ring fits entirely into the channel, then no problem. The issue is only when the compression ring is tightened part way between the channel and the full diameter.

20 minutes ago, powerlord said:

why id want to use a different m48-m42 adapter

To eliminate tilt. I'll attach the Baader spacing recommendation. It has helped many a Baader cc user who has passed by here. 

20 minutes ago, powerlord said:

focuser on the tsp 150 is just bolted directly onto the side if the tube

I can't remember whether is has flexible rubber within. The skywatcher focuser e.g. does. Again, tilt inducing.

HTH

 

 

Edited March 3, 2022 by alacant

[teoria_del_big_bang]

1 hour ago, alacant said:

With the mpcc III and Baader's t2 adapter, I'm not at all surprised.  

So is my thinking right then that all things being perfect the collimation should not change by introducing a cc or flattener,  that it is the fact the focusser is ending up with tilt that would make it appear to need re-collimating after adding the cc ?
From what I think needs to happen for perfect collimation is that the focusser needs to be central and aligned to the OTA, which in itself is one of the complications to collimating RC scopes as the focusser moves with the primary mirror adjustment so it ends up with a process of back and forth aligning the focusser (with the added tilt mechanism) then adjusting the collimation, which in turn moves the focusser a little, so there is a need to go back and repeat the process after re-aligning the focusser so each attempt gets is closer and closer to perfect alignment needing smaller and smaller adjustments.
Forgive my ignorance as all this is new to me so trying to get my head around it all and I may well just not have grasped this yet.

Steve

[alacant]

7 minutes ago, teoria_del_big_bang said:

the focusser is ending up with tilt that would make it appear to need re-collimating after adding the cc ?

It could be. At this stage, we don't know. 

17 minutes ago, teoria_del_big_bang said:

for perfect collimation is that the focusser needs to be central and aligned to the OTA

Not necessarily. Please see the links I posted. 

9 minutes ago, teoria_del_big_bang said:

to collimating RC scopes

The OP has a Newtonian. The advantage you have with the rc is that you don't need to introduce any more glass in the form of a cc. The adjustments on a rc are tiny in comparison to the equivalents on a Newtonian and yes, more iterations are required.

For your rc, maybe start a new thread? The differences are significant enough to cause confusion. 

Cheers

[bottletopburly]

@powerlord check your focuser is square to the ota first I found this out fitting  a steeltrack to my 200pds no amount of collimating will fix this until it’s squared up .

[alacant]

14 minutes ago, bottletopburly said:

focuser is square to the ota

Mmm...  have a look at seronik and telia's collimation myths.

 

[powerlord]

mine wise - i used my own 48 to 42 as suggested and made sure backfocus was correct. and it's still collimated fine. And I took CC off, and it's also fine. All I can assume is that I screwed up doing it the first time without the CC.

I've now done 4 telescopes! 2 to go!!

stu

[bottletopburly]

2 hours ago, alacant said:

Mmm...  have a look at seronik and telia's collimation myths.

 

Can only go on my experience  Steve until I squared focuser up only then could I get collimation  right using the concentre mind it was way off being square.

[alacant]

3 hours ago, bottletopburly said:

go on my experience

Absolutely.

We've probably never had one that far misaligned; the tilt on the secondary has taken care of any non orthogonality.

Cheers