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A Really Cheeky Question


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(if in wrong thread please move)

I am having trouble with collimation of my scope, I have used every method I can without any proper tools and its still not right.

Even with Astro baby great guide....

I am looking for some really kind person to lone me a Ho-Tech laser collimator for the day as its the only tool I trust will get this done in 2 mins, I don't trust other lasers as they themselves need to be collimated and I just can't do it ( trust me, Spent hours doing mine and never could get it right )

Thanks

John:o

Edited by johnkirkpatrick
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Ultimately you're going to need a tool of your own since collimation is something you need to do regularly. A cheshire/sight-tube combo is sufficient but a laser may not be.

Telescope Reviews: Concise thread about autocollimators+improvements

Pay particular attention to the table at the bottom of the page.

Edited by umadog
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... a Ho-Tech laser collimator for the day as its the only tool I trust ...

Got a hotech and I'm pretty sure mine is off a bit so I wouldn't bet my money on it... well, actually you could say I already did and lost... :)

Edited by pvaz
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will a Cheshire collimate my secondary, as that's the bit I just cant get? I have a dust cap with a small hole in it and looking through it all seemed OK when focuser racked in, but racked out the secondary was not a circle. so I moved the secondary while racked out to show a circular mirror. so it looks OK to the unaided eye.. but when outside the scope just is not as sharp as it could be even with my TV ep. Funds are low at the moment which is why I have not bought anything yet ( twin girls due this month)

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It's the mirror inner circle that needs to be a perfect circle under the focuser. When it is, the dark area around it will naturally look oval in fast newtonians. That's just the reflection of the secondary's edge on to the primary so ignore it.

I was always trying to make this look like the perfect circles in some tutorials so my collimation was always a bit off.

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John, if the issue here is poor focuser to secondary alignment or the focuser itself is not square then a laser wont help you. Not even the Hotech and it might well create a false sense of well being as well.

The problem your havinmg might just be focus slop.

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Look at the link I sent: the cheshire/sight tube is sufficient to completely collimate your scope. It does both secondary alignment and axial alignment. It measures both primary and focuser axial alignment errors. There are 4 axial alignment errors and if two are minimised then your axial alignment is done. The barlowed laser and the cheshire measure exactly the same thing: primary axial alignment error. They're mutually redundant. An un-barlowed laser measures two different errors but it has to be collimated, which is a pain.

I check the collimation with a cheshire and autocollimator every single time I use my scope and usually more than once a night.

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...it might well create a false sense of well being as well.

Indeed. With the laser colli all seams well. Then when I star test it's a bit off. I get better star tests when I collimate using a simple colli cap.

To me the tricky part is to get the secondary just right. My main problem with it, is that I center it and when I'm tightening the screws it gets off a few mm. I need to hold it tight in place while locking the screws and need a few attempts to get it right.

Fortunately the last time I messed with the secondary I managed to get it just right. Since then I been very careful moving the scope so it's been that way for months now, I just tweak the primary if needed and star test on every session.

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Paulo, you probably know this but for the benefit of others: tweaking the primary alone usually isn't sufficient. Tweaking the primary is the last point of a multi-stage process which often requires one to go back and forth between primary and secondary adjustment

John Reed Home Page Collimation - Cheshire

Using an autocollimator and a cheshire, I find that whenever the collimation is off I usually need to adjust both the primary and the secondary.

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Yes you're right. First step I do is to make sure the secondary in perfectly centered under the focuser and all clips in the primary show in the secondary.

What I meant, is that my secondary has been holding in place for the last few months, so I just move on to the next steps after checking it.

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That's what I figured you meant, but not everyone will realise that. With my scope this hardly ever the case, even if I don't dissemble the OTA. Although probably this is because the autocollimator is so sensitive that I can pick up small errors.

EDIT:

Here is a thread on the HoTech

www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/4350415

Edited by umadog
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Orion has a product called lasermate deluxe - it provides both a laser and a target that you can see while twiddling the knobs that adjust the primary. I've found it to be simple and extremely easy to use by myself, either at home or in the field.

Cost is about $60 US, no idea in the UK, but I've had mine for years and I consider it to have paid for itself many times.

Dan

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I don't fully understand how the autocollimator works, frankly. Ultimately, however, you don't need to worry about that since all you need to do is stack the reflections and make sure that the view looks right through a cheshire. You don't need to understand how the reflections are generated or even what they mean (although that can help). A good autocollimator is expensive, however, and a cheshire/sight-tube will do the job for the moment.

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John, i have an old Astro Systems collimation plug, which is all i've ever needed.

You can make something similar with a 35mm film canister i believe by punching a small hole dead centre.

If getting it dead centre sounds too daunting, another ancient dodge is to look for a real cheap & nasty old high power eyepiece eg a"H6mm" the smaller the lenses the better, take the lenses out & hey presto a collimation plug with a small hole dead centre.

Finally,are you familiar with collimation using a star?

If not i'd recommend having a good read up about it, works a treat IMO ,once you've got things roughly right with your chosen collimation tool.This method does require reasonably steady seeing on the night in question however.

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