8mm Ethos --Question

[Timebandit]

45 minutes ago, faulksy said:

to the one with the biggest bank account i mean heart

 

That's sweet Mike . Wine and dine and then back to yours to show her your 20"dob under the stars, that's sure to impress and win her over? 

[faulksy]

5 minutes ago, Timebandit said:

 

That's sweet Mike . Wine and dine and then back to yours to show her your 20"dob under the stars, that's sure to impress and win her over? 

i think so simon

[alanjgreen]

Just pinging this old thread.

i was looking for a 30mm barrel extender (m48 thread 2" eyepiece) for 8mm ethos as i try to make it parfical with the 10&13 ethos (in the paracorr2)

anyway, I purchased a 30mm Revelation from Telescope House only to discover it won't screw onto any ethos eyepiece.

https://www.telescopehouse.com/accessories/eyepiece-adaptors-and-extension-tubes/revelation-m48-2-spacer-extension-ring-30mm.html

I called TH and they tried several others from their stock and could not get any to fit to the ethos eyepieces!! ( they did fit some other branded eyepieces they said)

I am returning it for a full refund.

the folks above in this thread tried the 20mm version of the Revelation so that may work and the 30mm not?? But I need 30mm to make it parfocal.

i have now ordered the overpriced Televue 30mm barrel extension! 

I should also say that I have a 14mm Baader Finetuning ring and this fits easily on to any of my Ethos 2" eyepiece threads

https://www.firstlightoptics.com/baader-planetarium/baader-hyperion-finetuning-ring.html

shame they don't do a 30mm. The baader also comes with an end cap included which the Revelation did not FYI.

Alan

[DRT]

2 hours ago, alanjgreen said:

i have now ordered the overpriced Televue 30mm barrel extension! 

I wish you had posted this story before pulling the trigger, Alan - I've got a spare TV extension that I haven't used since selling my Ethos 6mm

 

[John]

I use the 28mm Baader FT rings on my 6mm, 8mm and 13mm Ethos. They allow me to fit 2" filters onto these eyepieces. They don't make the 6 & 8 par-focal with the 13 though. I just put up with that "quirk" 

[alanjgreen]

John,

i have purchased a parfocalising ring, I just need to make the 8mm sit half an inch out of the focuser/paracorr2 and it should be parfocal with the 10&13mm eyepieces. And therefore use the H position as well.

with the extra 30mm on the eyepiece barrel, backing it out 12mm should be doable.

Alan

[Pig]

Guys, not having parfocal eyepieces has never really bothered me, I am not criticising I am just wondering why people get so hung up on it ? It will not prevent a quality eyepiece being a quality eyepiece. Does it show that the designers have gone that extra mile ?

[alanjgreen]

Shaun,

Parfocality is of no interest to me at all.

I am only bothered about ensuring that I can use the ethos 8mm in the paracorr2 in 2" mode. The default is that I must use 1.25" mode to achieve focus with the 8mm in a paracorr2.

I just don't want to use the 1.25" adapter on the paracorr in the dark (when the dark returns  ) and want to minimise the number of paracorr positions that I need to remember.

Alan

[DRT]

The extension on the 6mm and 8mm Ethos also has the benefit of ensuring you can reach focus with the same focuser set-up as their siblings. Having to add an extension tube when switching EPs is a pain. Putting these tubes on the EPs at the start of a session means you don't need to faff around in the dark.

[Louis D]

3 hours ago, Pig said:

Guys, not having parfocal eyepieces has never really bothered me, I am not criticising I just wondering why people get so hung up on it ? It will not prevent a quality eyepiece being a quality eyepiece. Does it show that the designers have gone that extra mile ?

If they're within 1/4" of most of my other eyepieces, it doesn't bother me.  However, with the extreme example of the 12mm Nagler T4, it requires 3/4" of out focus relative to its shoulder where my Pentax XL/XW, Morpheus, AT AF70, and most ES eyepieces focus.  This is annoying to say the least.  I added 30mm of extension and five 4mm rubber O-rings to get it close to 3/4".  Now it's well within the 1/4" toleration zone.  I was going to use a parfocalizing ring until I found out that it would need to sit over one of the two barrel tapers for the undercut.  That, and the screw points would have left serious marks in the chromed barrel.

Another important reason is that I am using a GSO coma corrector with a fixed separation distance in my F/6 dob.  If focus is within 1/4" on either side of where it is set, I don't notice the correction being any worse than if it is spot on.  Being 3/4" out, the 12mm T4 has noticeably poorer correction without parfocalization.  Same with my field flattener on my AT72ED.  I need focus to be within a 10mm sweet spot for it to work well.

[Pig]

Ok guys very enlightening and it seems the CC is the common factor, I guess the only way around it is to sell your dobsonians and buy refractors ?

[niallk]

... or SIPS, as I should have done, tbh!!

[John]

One of the attractions of my F/5.3 OO 12" OTA was that I'd not need to bother with a CC. It's one (not the only one by some way though) of the factors that puts me off going for a larger aperture - F/4.5 and I'm sure that I'd not enjoy my Ethos quite as much 

[DRT]

1 hour ago, John said:

One of the attractions of my F/5.3 OO 12" OTA was that I'd not need to bother with a CC. It's one (not the only one by some way though) of the factors that puts me off going for a larger aperture - F/4.5 and I'm sure that I'd not enjoy my Ethos quite as much 

Are you trying to say that long focal length, small aperture dobs is the way to go, John? 

If I were you I would lock all your windows and doors tonight - the Mob will be gathering outside in their vans   

 

[Louis D]

22 hours ago, Pig said:

Ok guys very enlightening and it seems the CC is the common factor, I guess the only way around it is to sell your dobsonians and buy refractors ?

Except if you notice I had to buy a field flattener to make my AT72ED bearable in the outer field.  I'm used to the essentially flat field of 1000mm+ FL dobs and couldn't stand the outer field being out of focus.  I don't know if it is just because it is a short focal length refractor or what, but it has a massively curved field clearly visible in wide field eyepieces.  Do you use long focal length refractors that have a relatively flat field or field flattened (Petzval?) designs to avoid field curvature?

[Pig]

1 hour ago, Louis D said:

Except if you notice I had to buy a field flattener to make my AT72ED bearable in the outer field.  I'm used to the essentially flat field of 1000mm+ FL dobs and couldn't stand the outer field being out of focus.  I don't know if it is just because it is a short focal length refractor or what, but it has a massively curved field clearly visible in wide field eyepieces.  Do you use long focal length refractors that have a relatively flat field or field flattened (Petzval?) designs to avoid field curvature?

It must be your scope, I do not notice any ?

[faulksy]

10 hours ago, DRT said:

Are you trying to say that long focal length, small aperture dobs is the way to go, John? 

If I were you I would lock all your windows and doors tonight - the Mob will be gathering outside in their vans   

 

we are already there derek

[John]

9 hours ago, faulksy said:

we are already there derek

Ha, ha - I'm on holiday in France - you missed me guys !

Trouble is ...... can't come home now ........

[estwing]

1 hour ago, John said:

Ha, ha - I'm on holiday in France - you missed me guys

we know....your fridge isn't very well stocked...!!