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Old 11-08-2021, 01:45 PM
Emuhead (Andrew)
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Paracorr 1 : Focuser travel 0

Hi guys,

So first time using a Televue Paracorr Type 2 with my 8" Quattro. Focuser is at max travel and even with a Baader clicklock collar that extends the focuser a bit i still can't reach focus when the Paracorr is all the way in.. i have to leave it out by 20mm.

Back focus is fine, I managed to get some data with it like this so i could leave it, but the OCD side says that's not going to fly. Question, I've had a look for M54 extension tubes but they're not easy to find, any ideas?

Thanks
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Old 11-08-2021, 02:15 PM
RyanJones
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Hi Emuhead,

I think I read somewhere when I was looking at the parcorr that they extended the focal length by 20mm to allow for filter wheels etc. I have a similar issue with mine but I created my issue by redesigning my primary mirror holder. You can put cork spacers under your primary to lift it closer to the focuser but that will cause some extra vignetting because of the reduced distance to your secondary. You can also put extensions on your focuser but that will cause more focuser flex. I’m making a new OTA and my issues will be fixed with that but I agree it’s not a great situation to have to deal with.

Cheers

Ryan

Last edited by RyanJones; 11-08-2021 at 02:29 PM.
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Old 11-08-2021, 02:31 PM
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AstroJunk (Jonathan)
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I think it looks fine as it is. The Paracorr has a pretty long tube so should still have plenty inside the focuser for it be true and stable.

BTW the space between your camera chip and the glass element should be as close to 55mm as possible for the best results. You may well be able to better attach your filter wheel to reduce the distance - ah the wonderful world of spacers, can never have enough!!!
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Old 11-08-2021, 07:49 PM
Emuhead (Andrew)
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Thanks all, i think this might help, assuming the compression ring doesn't add tilt to my imaging train. Link here.

Agree, i could just leave it as is, as it's a long barrel. The data collected with it left like this is very usable. Yes its 55mm backfocus (+1mm for a filter) and the filter wheel is down the end next to the camera as one might expect.
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Old 11-08-2021, 08:00 PM
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AstroJunk (Jonathan)
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Unfortunately, you won't be able to slide the paracorr more that 35mm into it before it stops. That will see you run out of in-focus. Any extender will have to be between the focuser draw tube and the Baader click lock. It can be done, but you may need to find a friendly machinist...
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Old 11-08-2021, 08:04 PM
Emuhead (Andrew)
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Indeed, you're right there.. back on the hunt for a M54 extension tube.. or machinist, or settle for the Skywatcher Aplanatic Coma Corrector (which is very good also).
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