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OCAL collimators


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Hello would appreciate  so wisdom please

I have a OCAL collimator for the 8"SCT. I use a 2x barlow to image Saturn for example. So when you collimate would you leave this in the imaging train? They doesn't seem to be clear instructions about this. It does say though not to collimate with reducers or flatteners. 

Would it seriously affect collimation by taking in/out barlows or ADUs? The reason I ask is that  each time items added or taken out would it affect collimation?

 

Thanks Dean

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Thanks Stu much appreciated, was getting myself into a muddle the other day. 

Especially where to place green circle. Some where doing around the draw tube and others around the primary mirror

 

Dean

 

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For planetary imaging, collimate with the complete imaging train, eg ADC, barlow etc on a star. When you get the hand of it collimate on Saturn's or Jupiter's moons.

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I always collimate with just the scope and a short focal length eyepiece or camera. If you do this then you know that the scope is capturing high quality collimated images. Collimating with the image train in place means that you can make adjustments to see a collimated image but if you remove the train then the collimation of the scope itself will be off. If you are capturing uncollimated that's what counts in my reckoning 

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I always do primary collimation through the imaging train when I’m setting up for planetary imaging.  And always on an in-focus star near to the target planet, by looking at how evenly illuminated the first diffraction ring is. It can be a very tricky to do it on a star especially if seeing isn’t great, but well worth it. You can also do it with a Cheshire this way if you remove the barlow lens from the barlow body, but again best to do a final check on a star after putting the lens back on the body. 

Personally I’ve only found the Ocal any use for collimating the secondary and useless for primary collimation as the lens on the Ocal is too wide angle and there is not really a defined “peephole” on it, but that’s only been on the newts that I have, not sure what they’re like for SCTs. 

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not sure i get you there ? you can zoom in on the view and get adjust till the exact centre of the camera lens is centred. I use it for my newts 150,200 and 300 and have perfect results as far as I can see.

The op is asking about OCAL calibration, so there is no 'collimating in a star' - that is the whole benefit of the ocal at the end of the day.

Of course, there is nothing to stop you fine tuning on a star if you wish, but in my experience anyway, it's unecessary - once practiced you can collimate the primary and secodary accurately with the OCAL

Now, I grant you, if you then fit a camera or barlow that is hanging off it like a pun of mince... it's all for nothing, but I'd suggest that the thing to do there is fix that, not collimate to the pun of mince.

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Thankyou all for your wisdom. I did a initial collimation on the C8 with the Ocal camera. Took a while to figure out which was edge of focus tube. Then in  evening tweeked using a star with full imaging train.  Saturn was much better  then before, although no good enough to post just yet 😁 Will keep practicing

 

Cheers

Dean

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