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Old 08-06-2020, 08:13 PM
Scarey67 (Brian)
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Can't focus 2" Diagonal

Dropped my 1.25" diagonal so thought I would upgrade to a 2". Have only tried it on the moon, but I cannot achieve focus with it. Is there a quick fix out of this?
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Old 08-06-2020, 08:20 PM
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Outcast (Carlton)
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What scope are you using it on?
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Old 08-06-2020, 08:24 PM
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And, is it a prism diagonal or dielectric?

Which direction are you running out of focus travel?

As you rack the focuser in or out?
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Old 10-06-2020, 05:12 AM
Scarey67 (Brian)
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Hi Outcast,
It is an Orion dielectric on a Svbony 90mm refractor.
I run out of focus travelling in.
Cheers
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Old 10-06-2020, 09:27 AM
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Merlin66 (Ken)
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The 2 diagonal has a much longer path length than the 1.25, about 20mm longer.
Sounds like your OTA was designed for the smaller diagonal.....not much you can do.
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Old 10-06-2020, 10:24 AM
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As Ken has stated, a 2" diagonal adds a significant amount to the light path & there isn't much you can do.

However, depending on how much inwards travel you need to get to focus you may have one option. If you are extremely close to the focus point when your focuser is racked all the way in then you might look at the Televue in-travel adapter.

This is essentially a 2" adapter you put on the eyepiece which has a 5mm well at the top. This will move your eyepiece a further 5mm inwards with respect to the light path which, depending on how close to focus you are, may allow your eyepiece to come to focus.

If you require more than 5mm more in-travel then, I'm afraid there are no other options that I'm aware of.

Hope this helps

Cheers
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Old 10-06-2020, 10:32 AM
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Merlin66 (Ken)
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A bit drastic, but you could remove the focuser, reduce the length of the OTA by 25mm and remount the focuser.
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Old 10-06-2020, 11:53 AM
Scarey67 (Brian)
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Thank you very much for your time and input. I've had a quick look at my hacksaw but I think it will come down to a 1.25".
Cheers Brian
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