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9mm ES parfocalization and 2" barrel extension fix

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#1 Scanning4Comets



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Posted 24 June 2013 - 07:20 PM

I just wanted to pass along some information related to what I have done to my 9mm ES 100° eyepiece. In order for it to reach focus in my 10" dob, my focuser has to be racked all of the way out and the eyepiece needs to be outwards by 12mm or close to 1/2". I could use an extension tube, but I use an extension tube with my 2" filters and I don't want to have to remove the extention tube plus the eyepiece in order to use my filter already on another extension tube I have in my eyepiece case.

So, what I have done to parfocalize my eyepiece, is add 12mm of a few rounds of electrical tape to the 2" eyepiece barrel. Now my 9mm and 14mm ES 100's are both parfocal with each other.

The only thing about that on the 9mm is that the 2" barrel is somewhat shorter and doesn't feel as secure in the focuser, so in this instance, I have added two 2" empty filter cells to add length to the 2" barrel and now it sits in the focuser deeper and is more of a snug fit. You could also use a 14mm Baader fine tuning ring which would be just as good, if not better. For those of you who want to do this there are some added bonuses:

1. The eyepiece no longer has a tapered part sitting in the focuser, so when you loosen your focuser with the compression ring, your eyepiece barrel will no longer "snag" on the way out on the compression ring.

2. The 2" empty filter cells are threaded for your 2" filters, so you can still use filters on your eyepieces if you add the empty filter cells to lengthen the barrel of your eyepiece.

3. The added 2" empty filter cells makes the 2" barrel longer and you will no longer need to worry about your soft field lens caps making smudges on the field lens of your eyepiece.

*NOTE* You'll have to add something inside of your 2" eyepiece cap because the filter cells are slightly smaller than the 2" barrel for a snug fit. I added a soft piece of craft store stuff with double sided tape for a snug fit on mine.

Just wanted to pass this along. Pics added.

9mm ES 100 with 2 empty cells attached to EP barrel
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9mm ES with 12mm of electrical tape parfocalization showing tapered barrel no longer in use. EP barrel is now all straight. No more "snags" on compression ring.
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9mm ES with soft rubber field lens cap
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Soft field lens cap with piece added inside to make a snug fit over the 2 empty 2" filter cells.
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#2 Jarrod



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Posted 25 June 2013 - 03:13 PM

Clever, but honestly I would be concerned about the electrical tape putting its adhesive goo onto my focuser over time, and having that transfer to my other eps. Keep an eye on that, especially when using your kit in hot weather.

#3 Scanning4Comets



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Posted 25 June 2013 - 03:57 PM

I don't observe in hot, hazy weather ever. I've used electrical tape for parfocalizing my eyepieces before and never had a problem with "goo". The only thing I find with the adhesive from electrical tape is from leaving it on something for years.....and I mean a LOT of years.....the goo then is a mess to get off.

I could also just use a bunch of rubber gaskets I have if I really needed to...but I am not concerned about it now.


#4 Starman1


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Posted 25 June 2013 - 05:05 PM

Other possible solutions to extend the barrel (in addition to filter housings):
--add 14mm Baader Fine Tuning ring to bottom of eyepiece.
--add 28mm Baader Fine Tuning ring to bottom of eyepiece
--Add 30.5mm TeleVue barrel extender to eyepiece.
Any of those would allow you to pull the eyepiece out of the focuser and have enough in the focuser for safety.

In the place of tape around the eyepiece, to create a "pull-back" spacer, add:
--2" parfocalizing ring from ScopeStuff.com or others
--add a couple large o-rings around the eyepiece for the eyepiece to rest on when in the focuser
--make a "snap-ring" out of a piece of 2" plastic pipe to go onto the eyepiece barrel. Cut this ring exactly the right thickness and you could result in the eyepiece becoming parfocal with many other eyepieces.
--get a roll of metal tape and build up the appropriate thickness with that.

Why an extension tube is a bad idea:
--pulls the eyepiece back the full length of the 2" barrel. This will require substantial inward focuser travel to get to focus (probably 2" or so), then, and there may not be enough in-focus to accommodate that.
--pulls the heavy eyepiece even farther out of the focuser, which might result in more sag in the focuser.

#5 Scanning4Comets



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Posted 25 June 2013 - 05:08 PM

Great suggestions Don! :waytogo: I think I'm going to go with some of the large "O-Rings" as I do have a few in my eyepiece case. I have used these in the past on quite a few eyepieces. The electrical tape is really just a quick fix for now.

See my pic attached with three O-Rings used on a 14mm ES 82.


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