Barrel extenders

[Dantooine]

Ive just ordered 2 tv barrel extenders from widescreen centre and 2 parfocal rings from 365. I’m hoping to get my 6 & 8 ethos focal points near to my 13e. Have I done the right thing? Will it work?  Winding the focuser back and forth going to wear it out 😬

[John]

I'll be interested to hear how that works out for you.

I use Baader 28mm fine tuning rings with my Ethos 13, 8 and 6 but that is more about allowing a 2 inch filter to be used with them. It's not made them par-focal. The 8 and 6 are (extension or not) but the 13mm and 21mm are someway off (and different from each other as well). I've just kind of accepted that's the way that the Ethos range is. When I want to use par-focal eyepieces I switch to the Pentax XW's.

I've not yet worn out a focuser !

 

 

Edited November 8, 2020 by John

[Louis D]

I bought a couple of parfocalizing rings, but decided not to use them when I saw the sharp points on the set/grub screws.  I didn't want to ruin the resale value on my eyepieces by digging divots into the chrome on the lower barrels.  That, and they had to be secured into the lower taper of the safety undercut which wasn't going to be very secure.

Instead, I used rubber O-rings to bring my 12mm Nagler T4 into parfocalness with the rest of my eyepieces that focus at the shoulder.  I think I used a stack of five 4mm thick ones with a 50mm inner diameter.  It works well enough that I need only a small focuser adjustment now to bring it into focus relative to my ES, Baader, and Pentax eyepieces.

Edited November 9, 2020 by Louis D

[Dantooine]

8 hours ago, John said:

I'll be interested to hear how that works out for you.

I use Baader 28mm fine tuning rings with my Ethos 13, 8 and 6 but that is more about allowing a 2 inch filter to be used with them. It's not made them par-focal. The 8 and 6 are (extension or not) but the 13mm and 21mm are someway off (and different from each other as well). I've just kind of accepted that's the way that the Ethos range is. When I want to use par-focal eyepieces I switch to the Pentax XW's.

I've not yet worn out a focuser !

 

 

I know the focuser will be fine But sometimes I’m going back and forth between the 13 & 8 or the 6 & 4.7 as the magnification difference In ep’s is closer In my telescope. I still forget which way to wind in the excitement 😁

[Dantooine]

4 hours ago, Louis D said:

I bought a couple of parfocalizing rings, but decided not to use them when I saw the sharp points on the set/grub screws.  I didn't want to ruin the resale value on my eyepieces by digging divots into the chrome on the lower barrels.  That, and they had to be secured into the lower taper of the safety undercut which wasn't going to be very secure.

Instead, I used rubber O-rings to bring my 12mm Nagler T4 into parfocalness with the rest of my eyepieces that focus at the shoulder.  I think I used a stack of five 4mm thick ones with a 50mm inner diameter.  It works well enough that I need only a small focuser adjustment now to bring it into focus relative to my ES, Baader, and Pentax eyepieces.

Thanks for the information on the rings. I had thought about them clamping the barrels, also about the rings slipping up the barrel as the ring contacts the diagonal and making contact with my prism, a big worry as the baader has no stop ridge.  
 

if I don’t like what I see the rubber rings will go on instead. I do want the extension barrels though as they are only ever being used in 2 inch. Another reason is the bring the word weights up on these to so they are closer to the 13 & 4.7 for balance. 
 

I have also thoughts about putting the extenders on a lathe (Hence the tv instead of the baader rings) and making them exactly the same length as where the 1.25 barrels end. There seems to be no manufacturer that makes the perfect fitting extenders. 

[Louis D]

8 hours ago, Dantooine said:

I have also thoughts about putting the extenders on a lathe (Hence the tv instead of the baader rings) and making them exactly the same length as where the 1.25 barrels end. There seems to be no manufacturer that makes the perfect fitting extenders. 

If they were exactly the same length, would 2" filters safely clear the 1.25" barrel?  It would be mighty close.

[John]

8 hours ago, Dantooine said:

 

I have also thoughts about putting the extenders on a lathe (Hence the tv instead of the baader rings) and making them exactly the same length as where the 1.25 barrels end. There seems to be no manufacturer that makes the perfect fitting extenders. 

You will need to measure and lathe each eyepiece and extender separately. The 2 inch skirts and the 1.25" barrel sections of the Ethos 13, 8 and 6 are all slightly different lengths, just to make life interesting

 

[Dantooine]

2 hours ago, Louis D said:

If they were exactly the same length, would 2" filters safely clear the 1.25" barrel?  It would be mighty close.

I don’t use filters. Not a problem for me but I can see it could be for others.  

[John]

2 hours ago, Louis D said:

If they were exactly the same length, would 2" filters safely clear the 1.25" barrel?  It would be mighty close.

That was why I had to use the 28mm Baader FT rings. The 14mm gave insufficient clearance for a 2 inch filter. The ideal length would be 17mm-20mm I reckon, just clearing the end of the 1.25 inch barrel.

 

 

[Dantooine]

37 minutes ago, John said:

That was why I had to use the 28mm Baader FT rings. The 14mm gave insufficient clearance for a 2 inch filter. The ideal length would be 17mm-20mm I reckon, just clearing the end of the 1.25 inch barrel.

 

 

My main concern is keeping clear of my lovely prism. I think I will wait until I fit them and take some accurate measurements. For filters, a few mm longer than the 1.25 barrels would be better. I’m mainly looking at a better grip in the click lock and maybe the opportunity to get them closer focus point to my 13e.
Am I being too ocd? 🧐

Edited November 9, 2020 by Dantooine

[Louis D]

On 09/11/2020 at 10:59, John said:

That was why I had to use the 28mm Baader FT rings. The 14mm gave insufficient clearance for a 2 inch filter. The ideal length would be 17mm-20mm I reckon, just clearing the end of the 1.25 inch barrel.

I have a 20mm TPO spacer ring from OPT on my 12mm Nagler.  It doesn't thread on all the way, so it's more like 22mm or so of extension.  As a result, I've got 7mm of gap between the bottom of the 2" extension and the bottom of the 1.25" barrel.

I just found a snapshot of this eyepiece that I had forgotten about:

Edited November 16, 2020 by Louis D
Added eyepiece image

[Don Pensack]

On 08/11/2020 at 13:12, Dantooine said:

Ive just ordered 2 tv barrel extenders from widescreen centre and 2 parfocal rings from 365. I’m hoping to get my 6 & 8 ethos focal points near to my 13e. Have I done the right thing? Will it work?  Winding the focuser back and forth going to wear it out 😬

The 13E as a 2" focuses (with the shoulder of the 2" barrel as reference) 0.3" above the focal plane of the scope.

The 6mm and 8mm Ethos, used as 2", focus 0.7" above the focal plane.

Ergo, you will need parfocalizing rings installed so that the 6mm and 8mm are parfocal with the 13mm because they need to be an additional 0.4" farther out.

It can be done.  It also means all 3 would use the same setting in the Paracorr--setting H.

The parfocalizing rings will tighten down in the safety grooves on the 2" skirts, so you will need to use 3-screw parfocalizing rings to center the rings and keep them from moving.