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Old 12-03-2009, 08:26 PM
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desler
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Help!

Can someone help me out please????



Ok, Canon Eos 1000D. Ed 80, and dobs 12 and 8 inch.

Here goes, have prime focus adapters and can achieve focus in the ed80 and am very happy. Cannot reach focus in either of the Dobs, I understand why.

Pop a x2 ed barlow (gso) in the ed80 at prime focus, won't reach focus????

Pop same barlow in 12 inch dob with camera at prime, focus (WHAT??????)

Sometimes I feel I've only peeped inside the door of a very long corridor.


I wonder if there's light at the end.


Darren
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Old 12-03-2009, 08:46 PM
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Darren,

My experience is you can't get enought inward focuser movement with the dob but the barlow moves the point of focus (out) so you don't need to rack the focuser in as far and can therefore achieve focus.

I suspect with the ED80 you have to rack the focuser out a lot to achieve focus without the barlow and when you use the barlow you don't have enough outward travel. I'm guessing if you put a spacer between the focuser and the barlow on the ED80 you will be able to achieve focus with the barlow as the spacer effectively gives you more outward focuser travel.

Peter
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Old 13-03-2009, 08:36 AM
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multiweb (Marc)
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Correct. You have to add at least another 80mm to the focuser barrel length to reach focus with a barlow x 2 on the ED80.
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Old 13-03-2009, 09:00 AM
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desler
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Thanks guys, Spent a fair bit of last night scratching my head!

Is there any other way of reaching focus on the dob, without a barlow?
Does a focal reducer have a similar effect?

Darren
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Old 13-03-2009, 05:57 PM
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I'm aware of a couple of options to achieve focus with the dob other than using a barlow:

1 - move the primary mirror forward either with longer collimation bolts or cut an inch or two off the tube.
2 - get a teleview universal parracor.
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