Ethos and Powermate

[guillaume320]

Hello

I have a question for the TV experts

I want to get the Ethos8 and Ethos6... I plan to use them in 2” mode in a Dob. Now it seems those two are not parfocal with the rest of the family, so I’m planning to install a parfocal ring.

Now the question is: would that parfocal ring prevent the E8 end E6 to be used with a Powermate?  My intuition says yes... Does anyone know for sure?

Kindest regards,

Guillaume

[alanjgreen]

44 minutes ago, guillaume320 said:

Hello

I have a question for the TV experts

I want to get the Ethos8 and Ethos6... I plan to use them in 2” mode in a Dob. Now it seems those two are not parfocal with the rest of the family, so I’m planning to install a parfocal ring.

Now the question is: would that parfocal ring prevent the E8 end E6 to be used with a Powermate?  My intuition says yes... Does anyone know for sure?

Kindest regards,

Guillaume

Yes, you are correct.

What you need to do is add a Televue 2" eyepiece barrel extension on the bottom, like this...

(Both of these EPs are parfocal with the Ethos 13mm after I made the changes you can see in the pic. They work in the Paracorr2 just fine)

This is the part you need:

https://www.firstlightoptics.com/adapters/tele-vue-2-eyepiece-barrel-extender.html

A Baader 28mm Hyperion finetuning ring will also work

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

(Dont be tempted by the cheaper Revelation Barrel Extension from Telescope House, the threads don't match and you will have to return it, both of the above will screw onto the EP with no problems )

Alan

[John]

Hi Guillaume,

The 8mm and 6mm Ethos are parfocal with each other but not the rest of the Ethos line, thats correct. I don't use a Parfocal ring with them but I do use a Baader 2" fine tuning ring on the end of the barrel of my 6mm and 8mm Ethos which means that they don't fully insert into the Powermate 2 inch 2x, sticking out around 8mm. The Powermate still works just fine with them.

My feeling, based on the above, is that using a par-focal ring with the 6mm and 8mm Ethos would not prevent a Powermate from working.

Here is a pic of my 8mm Ethos inserted into the Powermate 2x with the Baader FT ring (28mm) fitted to the barrel of the 8mm Ethos. The Powermate works fine in this mode:

 

 

 

[alanjgreen]

11 minutes ago, John said:

My feeling, based on the above, is that using a par-focal ring with the 6mm and 8mm Ethos would not prevent a Powermate from working.

Here is a pic of my 8mm Ethos inserted into the Powermate 2x with the Baader FT ring (28mm) fitted to the barrel of the 8mm Ethos. The Powermate works fine in this mode:

 

Seems a contradiction. You dont need a barrel extension but I am using one.

With £600 of EP hanging out the end, I would defo get a barrel extension if I were you (but its not a competition )

[John]

I use the barrel extensions because I want to use 2" filters with the Ethos eyepieces that have a hybrid barrel.

Sorry if that jibe in that other thread needled you Alan - not intentional of course

 

[guillaume320]

I was actually not too worried about the extension ring being an obstacle, but the parfocal ring preventing the eyepiece from sliding far enough into the power mate...

[John]

19 minutes ago, guillaume320 said:

I was actually not too worried about the extension ring being an obstacle, but the parfocal ring preventing the eyepiece from sliding far enough into the power mate...

As you can see from the photo of my 8mm Ethos and the Powermate, even if not fully inserted, the Powermate will work. As Alan says though, you do want enough of the Ethos barrel inserted into the Powermate for the compression ring to get a good grip on it. I would not want my Ethos hanging a long way out of the Powermate

[guillaume320]

Thanks for the detailed feedback gents...

[Louis D]

7 hours ago, guillaume320 said:

Hello

I have a question for the TV experts

I want to get the Ethos8 and Ethos6... I plan to use them in 2” mode in a Dob. Now it seems those two are not parfocal with the rest of the family, so I’m planning to install a parfocal ring.

Kindest regards,

Guillaume

There are at least three distinct focus points relative to the shoulder for Ethos as shown in the TV eyepiece specs below:

ETH-21.0	21	Ethos	2"	/	100		15	36.2	4.3		1.62	2.95		-0.38	2.25 / 36.0		Y	Y
ETH-17.0	17	Ethos	2"	/	100		15	29.6	4.5		1.4	2.4		-0.39	1.55 / 24.8		Y	Y
ETH-13.0	13	Ethos	2" & 1¼"	/	100		15	22.3	4	1.6	1.1	2.5	1.1	0.27	1.30 / 20.8	Y	Y	Y
ETH-10.0	10	Ethos	2" & 1¼"	/	100		15	17.7	3.8	1.6	1.1	2.3	1.1	0.27	1.10 / 17.6	Y	Y	Y
ETH-08.0	8	Ethos	2" & 1¼"	/	100		15	13.9	3.3	1.7	0.94	2.1	1.2	0.7	0.95 / 15.2	Y	Y	Y
ETH-06.0	6	Ethos	2" & 1¼"	/	100		15	10.4	3.5	1.5	0.94	2.1	1.1	0.7	0.97 / 15.5	Y	Y	Y
ETH-04.7	4.7	Ethos SX	2" & 1¼"	/	110		15	8.94	5.4	0.9		2.2		0.25	1.30 / 20.8	Y	Y	Y
ETH-03.7	3.7	Ethos SX	2" & 1¼"	/	110		15	7.04	5	1.1		2.2		0.25	1.10 / 17.6	Y	Y	Y

They are -0.38mm/-.39mm for the 21mm/17mm, 0.27mm/0.25mm for the 13mm/10mm/4.7mm/3.7mm and 0.7mm for the 8mm/6mm.  I don't understand your comment implying there are just two distinct focal points.

[guillaume320]

32 minutes ago, Louis D said:

There are at least three distinct focus points relative to the shoulder for Ethos as shown in the TV eyepiece specs below:

ETH-21.0	21	Ethos	2"	/	100		15	36.2	4.3		1.62	2.95		-0.38	2.25 / 36.0		Y	Y
ETH-17.0	17	Ethos	2"	/	100		15	29.6	4.5		1.4	2.4		-0.39	1.55 / 24.8		Y	Y
ETH-13.0	13	Ethos	2" & 1¼"	/	100		15	22.3	4	1.6	1.1	2.5	1.1	0.27	1.30 / 20.8	Y	Y	Y
ETH-10.0	10	Ethos	2" & 1¼"	/	100		15	17.7	3.8	1.6	1.1	2.3	1.1	0.27	1.10 / 17.6	Y	Y	Y
ETH-08.0	8	Ethos	2" & 1¼"	/	100		15	13.9	3.3	1.7	0.94	2.1	1.2	0.7	0.95 / 15.2	Y	Y	Y
ETH-06.0	6	Ethos	2" & 1¼"	/	100		15	10.4	3.5	1.5	0.94	2.1	1.1	0.7	0.97 / 15.5	Y	Y	Y
ETH-04.7	4.7	Ethos SX	2" & 1¼"	/	110		15	8.94	5.4	0.9		2.2		0.25	1.30 / 20.8	Y	Y	Y
ETH-03.7	3.7	Ethos SX	2" & 1¼"	/	110		15	7.04	5	1.1		2.2		0.25	1.10 / 17.6	Y	Y	Y

They are -0.38mm/-.39mm for the 21mm/17mm, 0.27mm/0.25mm for the 13mm/10mm/4.7mm/3.7mm and 0.7mm for the 8mm/6mm.  I don't understand your comment implying there are just two distinct focal points.

Hi,

Sorry I thought they were all parfocal with the exception of the 6 and 8... Thanks for putting that straight.

G