Is a cheshire good enough?

[Harpage]

I'm thinking of getting a 6" f/4 scope for astrophotography and wondering if a cheshire would suffice? While I'd love to get some fancy Hotech laser or whatever, I simply don't have the funds for one, and I'm not really scared of a cheshire as I've already used a collimation cap for my dob that I use for visual. Just wondering if a cheshire is accurate enough for f/4.

[sunslayr]

I think most purists will tell you only a star test is accurate enough. For me I find I can correct the axial tilt and get it close with a cheshire then I finish with a laser collimator in a barlow. You might need to collimate the laser collimator if you buy one of the cheaper ones, but that's easy enough.

[glend]

Well this will likely get a lot of posts, because most people have a view (haha). Yes a Cheshire can be good enough, provided you know what your doing and what your seeing. Everyone should have one and know how to use it.
Personally I prefer a good laser for precise collimation of any Newt or dob. The issue you will find with an f4 is the secondary offset, and I suggest you read Astro Baby's excellent article on collimation, which shows photos of the differences in offset between and f4 and f5.
And as always, a star test is the final arbiter, but again you need to be able to read what your seeing, inside, at, and outside focus.

[Harpage]

Thanks guys, looks like a cheshire will work fine for me. Now, just gotta wait for the scope to come in stock! :D

[Camelopardalis]

Just to chime in with my (limited) experience with my f/4 scope...

From my research and experimentation, a simple cheshire is not sufficiently accurate to get you in the ballpark for imaging. At best your stars will be slightly off, and you'll notice it in small and large stars in the FOV.

A Barlowed laser is an "accepted" means of checking/collimating the primary, but a sight tube, and autocollimator are the tools you'll need for bringing the secondary into alignment. It's quite a chore if the mechanics of the scope have any flex, slack or play whatsoever, and in such a case won't give you consistent results as it tracks an object across the sky.

By "accepted", I refer to the methods/techniques discussed at length at that site over the big pond. That doesn't mean it's right, or the only way, just that's what you'll see when digging a little deeper. High-precision collimation of fast newtonians doesn't seem to come up very often here...or I'm completely missing it :shrug:

[Startrek]

Danh,


I only use Newtonians ( f4.9 to f6 ) to image and observe



I use an Orion Cheshire to align the secondary mirror first then the primary and a laser to finish and double check both. 9 times out of 10 the Cheshire ends up being more accurate than the laser especially for imaging



Here's a good tutorial I found 3 years ago from Starizona on how to collimate a newtonian



It may help you



Cheers
Martin


PS: Ive used Astro Baby as well

[Harpage]

Thanks for the guide Martin!