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Altair 10" RC


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Hi

Has anyone got any experience with this scope, in particular the carbon fibre deluxe model.

If so would it be an upgrade from the SCT (apart from mirror flop); and are there issues when it comes to cleaning the optics and of coarse collimation?

hypnotoad.....................

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I have one. It's a f/8 system and I reduced it with an Astro-Physics CCDT67 reducer, to make it a bit quicker at f/5.5 (1380mm @ 85mm backfocus). The focuser is connected to the primary mirror, so if you adjust the primary, you're going to introduce tilt in the focuser (so that the focuser isn't pointing at the centermark on the secondary). So you need to detach the focuser from the primary with this ring. After that collimation is simple. It's an astrophotography telescope and I would not advice it for visual use. Cleaning is not an issue, even dirty mirrors will perform almost as good as clean optics.

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I have an 8" version and am also considering the 10". I wouldn't bother with CF unless weight is an issue. Two aluminium Losmandy bars are bolted to the tube and they will expand/contract with temperature anyways and excert some kind of force to the tube. What this force actually does to the tube I have no idea...

/Jesper

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Hi jjongmans, can you still achieve focus with that ring with the three extension tubes provided with the scope? Also, how do you adjust the ring? Do you have to keep taking of the focuser or can you make the adjustments with the focuser on?

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The focuspoint is quite far outside the OTA, that's why the extension tubes are included. I'm using a reducer, so in that case the focuspoint comes a lot closer to the OTA, but I'm still able to achieve focus. With a focal reducer you probably don't need the extension tubes.

The ring has three collimation allen screws, just like would collimate a mirror. And there's no need to take of the focuser. This is how I get my collimation spot on:

1) Correct tilt in focuser, I use a Howie Glatter laser collimator. This laser needs to point at the center mark of the secondary.

2) Correct secondary, I use a Howie Glatter with holographic attachment so it projects concentric rings. These rings need to be projected concentric at the primary when looking in the OTA.

3) Correct primary, I center a defocused star on the CCD and adjust the primary until the 'donut' is concentric.

When you're doing adjustments to focuser, secondary or primary, keep in mind that you have to recheck everything again. Repeat this until no adjustments are necessary and you're done.

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Hi Folks

Cheers for that ! I heard that Rc`s scopes were a nightmare when it comes to collimation. Evidently, this may be relevant on much older RC scopes? What attracts me is the flat field, particulary in regards to photometry etc regarding variable star fields and hunting for some of the brighter asteroids. Mind you I do like imaging the not so well known nebulae`s in mono with my ccd.

regards

Hypnotoad..............

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RC's do suffer from field curvature causing astigmatism in the corners. The good news is that RC's don't have severe coma, like newtonians, that's more problematic.

Collimation can become a nightmare without the proper tools and without some knowledge of what you're doing.

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hi jjongmans

I had a look at your web site, very nice equipment, I noticed you have a QSI 683; that is a ccd I may be buying in the near future.

I agree about the field flattener; I think the 8300 chip would about right the 10" RC. You would need a flattener for a DSLR.

Thanks folks for all your comments.

Hypnotoad..........................

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jjomgmans,

Regarding point 2. Do you mean you look straight into the front of the OTA? So the concentric circles projected by the Howie Glatter (in the focuser) reflect off the secondary and back onto the primary and you are checking the "concentricness" of the circles on the primary looking in from the front? By adjusting the secondary it changes the pattern of the circles on the primary? I have never seen that method before sounds ingenious....

Is that what you mean?

If that's the case why do you need to do step 3?

Regards, Steve

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That's correct, you must look into the OTA and check the projected rings. There's also a central beam, which should point directly back into the focuser on the laser itself.

Point 3 can also be done with the concentric rings projected onto a wall. Where the shadow of the secondary is concentric in the projected rings. But I think a defocused star test is much more sensitive and is done with the camera. That way you'll see what the starshape will be in final images.

The workflow in post #5 gives me repeatable and good collimation with a difficult to collimate RC.

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That's most ingenious indeed. Where did you learn this method? I shall have to look at doing this. I suppose an ordinary laser collimator, as long as its collimated itself, could perform steps 1 and 2 since

1. adjusting the focuser with the tipping device will aim the laser at the center spot - could be done with any collimator

2. adjusting the secondary will adjust where the laser gets reflected to back to the 45 degree spot on the collimator.

That makes sense?

I must say though, I like the idea of the holographic method. I need to check into getting one of the collimators you have.

Rgds, Steve

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Don't assume that if you point the laser back into the focuser with a single beam laser, that the secondary is also pointing 100% to your primary. That's only the case in a perfect world, and I can assure you we don't live in a perfect world... ;)

It's also a lot more difficult to point a single laser beam at a precise point, than pointing concentric ring onto another ring shape. Exactly the reason this method also doesn't work with newtonians, in that case it's advised to use a barlowed laser and use the centermark shadow instead of the beam itself.

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I have a 2", I don't want to use a 1,25" to 2" adapter when my CCD is 2", that will introduce inaccurate results.

The holographic attachment is the only extra thing you'll need for an RC. Choose the extra bright laser to see the rings more clearer.

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Thanks very much. I am very grateful for your help and am sure others who stumble on this thread searching for RC collimation will do as well.

I am buying a large dobsonian soon as well so the money spent on an accurate collimator will be well spent.

Ross, Steve

Sent from my iPhone using Tapatalk

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  • 2 months later...

I have now bought a Howie Glatter and a holographic attachment :) A thing of beauty !!! Used it to collimate my Newt to perfection! Next up is my RC scope. Not got the tipping device yet. Will check it out tomorrow to see if my focuser is OK without the tipping/tilting device. I might be lucky?

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In fact, since my rig is set up outside now I just checked it out. Looks spot on!

Step 1. Difficult to see the laser on the center spot - how do you do that? But the laser seems to be firing back at itself down the tube.

Step 2. By stepping some distance away from the OTA - 3m or so - and looking directly down the tube and bobbing myself about to get into position I see the rings from the holographic attachment are perfectly concentric in the primary mirror proving the secondary must be correct. Following you method jjongmans if I were to adjust the secondary it would ruin this perfect concentric circles?

Step 3: Rings projected onto wall are almost concentric with the shadow of the secondary perfectly central. Maybe a fraction out. I projected it onto the house wall 10 feet away and measured with a ruler.

What can be a bit tricky is that whilst the 2" Howie Glatter is very tight in the focuser, if I flex it in the tube a fraction it slightly changes the pattern of the reflections on the wall. So how do I know what *is* the perfect position of the collimator in the focuser? Maybe if the laser is reflected back to itself - as in step 1- ten that proves the focuser is central and I should leave it alone and assume that is OK.

Thanks, Steve

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I have now bought a Howie Glatter and a holographic attachment :) A thing of beauty !!! Used it to collimate my Newt to perfection! Next up is my RC scope. Not got the tipping device yet. Will check it out tomorrow to see if my focuser is OK without the tipping/tilting device. I might be lucky?

Please let us know how you get on with using the Glatter to collimate your RC - it's currently on my wish list :smile:

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I have now bought a Howie Glatter and a holographic attachment :) A thing of beauty !!! Used it to collimate my Newt to perfection! Next up is my RC scope. Not got the tipping device yet. Will check it out tomorrow to see if my focuser is OK without the tipping/tilting device. I might be lucky?

Please let us know how you get on with using the Glatter to collimate your RC - it's currently on my wish list :smile:

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See my post number 20 for where I am at this point. Not had chance to look further as of yet. jjongmans system looks good and makes absolute sense.

Thanks Steve, must have missed your posting while I was doing my post #21 which somehow got doubled up :smile:

Understand what you mean about nudging the laser and the resultant effect. I currently have a Baader Laser Colli and that does the same but as you said if you don't touch it and get it to reflect back on itself that should be okay? The Baader is fine for adjusting the focuser tilt but I'm attracted to the Glatter for the concentric circles attachment to check the secondary and primary alignments. I'd like to know how the Glatter compares with what can be achieved using a Cheshire eyepiece.

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Thanks Steve, must have missed your posting while I was doing my post #21 which somehow got doubled up :smile:

Understand what you mean about nudging the laser and the resultant effect. I currently have a Baader Laser Colli and that does the same but as you said if you don't touch it and get it to reflect back on itself that should be okay? The Baader is fine for adjusting the focuser tilt but I'm attracted to the Glatter for the concentric circles attachment to check the secondary and primary alignments. I'd like to know how the Glatter compares with what can be achieved using a Cheshire eyepiece.

Mike, when I have got it sorted I will do a video and put it onto Youtube over the weekend. Not enough help and advice on this scope at all. Maybe me and you ought to start?

That said. Don't knock the cheshire. I am a great fan of that on the Newt. But with a RC the two surfaces are a bit trickier and i am not convinced a Cheshire cuts it. But I am convinced jjongmans is onto a sound method. I am very pleased with the RC scope. Once collimation is bang on - hopefully with the jjongman method - it will purr, I am sure of it :)

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