Old 20-07-2013, 05:10 AM
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Skyhawk (Justin)
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Location: Cape Town, South Africa
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Cutting my OTA

I have an 8" f/5 Skywatcher Newtonian. Obviously with a T-adaptor I cannot get focused. Removing the T-adaptor and connecting the T-Ring dirctly to the focuser, which the Skywatcher can do allows me to focus. However I cannot use any filters doing this as there is no T-Adaptor in the train.

I'm going to have to cut the tube, the question is by how much for a DSLR?
I've looked around IIS forums and have come up with anything from 25mm to 55mm, also if I cut the tube by say 35mm do I just need a 35mm extender to do normal observations with my eyepieces?

Also thinking about getting the F5 Coma Corrector, so not sure how this is all going to affect how I cut my tube.

Any advice?

Many thanks
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Old 20-07-2013, 08:55 AM
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rmuhlack (Richard)
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Why not just use longer bolts and springs for your main mirror. I did this on my old newtonian - cost was just a few dollars at the local hardware store
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Old 20-07-2013, 09:01 AM
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Do it.... it's a quick/simple process.
I documented my go at it in 2006 - here.
Funny enough not long after that I bought a CCD, and hardly ever used the newt with the DSLR (apart from some moon shots occasionally...), but have used it visually with no problems.
Moving the mirror will obviously adjust the balance of the OTA in whatever mount you use....

Your EPs will then come to focus with an extender.
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Old 20-07-2013, 09:51 AM
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kinetic (Steve)
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Lee's and Clive's (Alchemy) articles are a good resource.
Best to read up and understand the consequences and benefits
before the cut.
I'd advise against mounting the mirror on longer springs btw,
although for a smaller 8" mirror, mirror flex might be minimal.
I did the cut on my 12" OTA, never looked back.
I can still do visual with a low profile Crayford focuser and an
extension tube/ tubes.

Clive's article is here:

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Old 20-07-2013, 11:30 AM
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RobF (Rob)
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On the consequences side remember you will also be decreasing the distance between primary and secondary in your lightpath.

This might another option to consider: http://www.iceinspace.com.au/forum/s...an+adaptor+m54
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