Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Magnification Sequence...

  • Please log in to reply
42 replies to this topic

#1 Dave Bush

Dave Bush

    Vanguard

  • *****
  • topic starter
  • Posts: 2354
  • Joined: 28 Jul 2004

Posted 14 November 2019 - 10:07 PM

Looking at a couple different eyepiece configurations.  

 

One would give me this sequence...

 

31mm Nagler  69x

21mm Ethos   106x

17mm Ethos   125x

13mm Ethos   163x

10mm Ethos   193x

 

The other one is this...

 

31mm Nager  69x

20mm Nagler 101x

16mm Nagler 133x

13mm Nagler 163x

11mm Nagler 213x

 

If you had an EdgeHD 8 like me, which might you prefer?

 

Oh and I'm thinking in either case the 125x/133x might be unnecessary.    

 

What do you think?

 

 

 



#2 TOMDEY

TOMDEY

    Fly Me to the Moon

  • *****
  • Posts: 5081
  • Joined: 10 Feb 2014
  • Loc: Springwater, NY

Posted 14 November 2019 - 10:45 PM

Well... they will certainly all perform well, and cover the range equally well, especially with an F/10 feed. Your quoted magnifications seem 7% more than the nominal 2000mm of the scope, unless I'm missing something? I'm guessing the 31mm Nagler would get vignetted, especially with the Star Diagonal involved... but that's minor, in favor of ergo comfort. I take it the presence of the Star Diagonal is what is shifting the focal length above nominal?   Tom



#3 ButterFly

ButterFly

    Ranger 4

  • *****
  • Posts: 300
  • Joined: 07 Sep 2018

Posted 14 November 2019 - 10:47 PM

Fied of view is more relevant at low magnifications for star fields and nebulae.  You get 0.18 degrees more with the 31Nagler than you do with the 21Ethos.  Do one or the other, or pair the 21E with a 41 Panoptic.  You really only need one though - 21E.

 

Magnification step closeness is more important at the high end where you are trying to beat seeing.

 

31N, 17E, 10E and 21E, 13E, 8E are very common sets.  A 13E field is just bigger than the moon on that scope.



#4 Dave Bush

Dave Bush

    Vanguard

  • *****
  • topic starter
  • Posts: 2354
  • Joined: 28 Jul 2004

Posted 14 November 2019 - 10:57 PM

Well... they will certainly all perform well, and cover the range equally well, especially with an F/10 feed. Your quoted magnifications seem 7% more than the nominal 2000mm of the scope, unless I'm missing something? I'm guessing the 31mm Nagler would get vignetted, especially with the Star Diagonal involved... but that's minor, in favor of ergo comfort. I take it the presence of the Star Diagonal is what is shifting the focal length above nominal?   Tom

Focal length of the 8” EdgeHD is 2125mm 



#5 Redbetter

Redbetter

    Cosmos

  • *****
  • Posts: 8236
  • Joined: 16 Feb 2016
  • Loc: Central Valley, CA

Posted 15 November 2019 - 12:49 AM

Focal length of the 8” EdgeHD is 2125mm 

Do you have a link for that?  All I have found is 2032mm.    Like Tom I was assuming you were accounting for a 2" diagonal's impact on focal length.

 

My most used eyepiece with the 8" f/10 SCT has been a 9mm Nagler.  However, that was primarily in an area with good seeing...because when I moved out here I added the 11 and 13 to fill the gap for poor seeing in the backyard and the 9mm could not be employed as often.  A 7mm Nagler (T1) has been my high power planetary eyepiece on the nights of best seeing.  Of course this sort of thing varies with one's eyes and sample of scope, not just seeing.

 

I like having the 16mm as an intermediate power eyepiece because it is about as wide as I can go in that range in 1.25" without dropping down in magnification to a 24 Pan or similar.  That limits how often I feel the need to swap to 2"--although admittedly I think of this more with my large Dob than I did with the SCT.  Nothing wrong with a 20mm and 31mm Nagler combo either.  I do not actually see the vignetting in my old non-edge SCT even with 46mm field stops, although it has to be there. 

 

Some of this comes down to your observing habits/sky darkness and targets.  I like to be able to cover the full range of capability of my scopes, so I have the 41 Pan and 55 Plossl for use with nebula filters.  However, when I was using the 8" SCT the most I did not have that 41 Pan (or 31 Nagler) and was using the 35 Pan or 55 Plossl for low power.  The big Plossl was reserved for larger diffuse nebula and a few other larger targets while the 35 Pan was my basic low power finder eyepiece. 


  • Jon Isaacs likes this

#6 Traveler

Traveler

    Gemini

  • *****
  • Posts: 3264
  • Joined: 19 Aug 2007
  • Loc: The Netherlands

Posted 15 November 2019 - 12:59 AM

I would add an ep with longer focal length (40mm) and i might consider a Baader Hyperion Zoom ep if i had a C8 instead of the Nagler/Ethos ep's. 


  • Jon Isaacs and Bob4BVM like this

#7 Bob4BVM

Bob4BVM

    Vanguard

  • *****
  • Posts: 2009
  • Joined: 23 Mar 2015
  • Loc: W. Oregon

Posted 15 November 2019 - 02:20 AM

I would add an ep with longer focal length (40mm) and i might consider a Baader Hyperion Zoom ep if i had a C8 instead of the Nagler/Ethos ep's. 

I'll second that, I love the shear viewing efficiency of my BHZ in my SCT !

While you are agonizing over what EP will give you the best view of the object at the moment of best seeing, I am just dialing it in and soaking up the view before that moment slips away.

 

Coupled with my 2" ED barlow, the BHZ gives me a FL range of 4mm - 24mm, all without leaving the chair (or spending a fortune ! )

 

CS

Bob


  • aeajr likes this

#8 stevenrjanssens

stevenrjanssens

    Explorer 1

  • -----
  • Posts: 69
  • Joined: 24 May 2018

Posted 15 November 2019 - 03:32 AM

Does a parfocal set matter at all? My current thinking is to slowly build up a parfocal 1.25" set beginning with a 24 Pan, 16T5 and then T6's.


  • Jon Isaacs likes this

#9 Redbetter

Redbetter

    Cosmos

  • *****
  • Posts: 8236
  • Joined: 16 Feb 2016
  • Loc: Central Valley, CA

Posted 15 November 2019 - 03:54 AM

Does a parfocal set matter at all? My current thinking is to slowly build up a parfocal 1.25" set beginning with a 24 Pan, 16T5 and then T6's.

It is convenient, but I wouldn't say it is necessary.  I have the set you speak of:  24 Pan (used mostly in the ST80 as a finder eyepiece, although I have a 25mm Meade HD60 that I could use instead...it got bumped from the ST80 by the Pan), 16T5, all of the T6's other than the 7 which I have as a T1.  With the 20" f/5 I typically use the 16 as the first increment after the finder ST80 for galaxy hops, followed by the 11 if the seeing is poor, 9 otherwise, and then by the 7 for greater mag if the seeing is good, and sometimes the 5 if the seeing is particularly good and the target is very dim and/or very small.  The 13 only gets used in particularly poor seeing with this scope.  My working eyepiece case on the ladder shelf is typically:  31T5, 16T5, 11T6, 9T6, 7T1.  Other eyepieces get subbed depending on conditions and as needed.

 

For other scopes the sequence is somewhat different depending on seeing.  I have already described how I used the 8" f/10 SCT.  With my son's 10" f/5 I tend to jump from an 18mm ES82 down to a 9mm Nagler (or his 8.8 ES82) to a 7mm (or his 6.7mm ES82) or to 5mm (or his 4.7mm ES82).  If the seeing is particularly good I will either use 2x Barlow on the 7 or 6.7, or I will put in the 3.5 T6.   

 

With the f/15 ES 127 Mak I typically use the 24 Pan for "low" power, along with the 16T5, and the 11 and 9T6--often the seeing won't support the 9 and sometimes I end up using the 13 because that is what the seeing will allow in the backyard.


  • Jon Isaacs likes this

#10 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 79927
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 15 November 2019 - 05:21 AM

Fied of view is more relevant at low magnifications for star fields and nebulae.  You get 0.18 degrees more with the 31Nagler than you do with the 21Ethos.  Do one or the other, or pair the 21E with a 41 Panoptic.  You really only need one though - 21E.

 

 

At F/10 (or F/10.5) the 21mm Ethos provides a 2 mm exit pupil. For me, that is way too dim for a lowest magnification eyepiece.  I'd want the 41mm Panoptic and some sort of ~55mm Plossl. 

 

Other than that, I like Red's advice and Steven's suggestion.  With an SCT, parfocal is nice because it makes swapping eyepieces much less painful.. No endless turning of the focuser knob.  

 

I have the 22mm Panoptic, the 16 mm T-5 and all the T-6's except the 2.5mm. I like the eyepieces all being focal or nearly so and of a reasonable weight.  (I am using the 22mm Panoptic as 1.25 inch only eyepiecie, I removed the 2 inch barrel, the only TV eyepiece that one can do that with.)

 

I also have the 31mm-21mm-13mm-8mm Nagler-Ethos combination with the 13mm and 8mm fitted with 2 inch barrel extensions, they're parfocal except the 8mm, at least in a Paracorr.

 

Jon


  • TOMDEY likes this

#11 TOMDEY

TOMDEY

    Fly Me to the Moon

  • *****
  • Posts: 5081
  • Joined: 10 Feb 2014
  • Loc: Springwater, NY

Posted 15 November 2019 - 07:32 AM

At F/10 (or F/10.5) the 21mm Ethos provides a 2 mm exit pupil. For me, that is way too dim for a lowest magnification eyepiece.  I'd want the 41mm Panoptic and some sort of ~55mm Plossl. 

 

Other than that, I like Red's advice and Steven's suggestion.  With an SCT, parfocal is nice because it makes swapping eyepieces much less painful.. No endless turning of the focuser knob.  

 

I have the 22mm Panoptic, the 16 mm T-5 and all the T-6's except the 2.5mm. I like the eyepieces all being focal or nearly so and of a reasonable weight.  (I am using the 22mm Panoptic as 1.25 inch only eyepiecie, I removed the 2 inch barrel, the only TV eyepiece that one can do that with.)

 

I also have the 31mm-21mm-13mm-8mm Nagler-Ethos combination with the 13mm and 8mm fitted with 2 inch barrel extensions, they're parfocal except the 8mm, at least in a Paracorr.

 

Jon

Jon's is a great point. Even the 31mm Nagler provides a fairly constricted 3mm pupil... so nebulae and galaxies will be inexorably dimmed. The 41mm Panoptic yields 4mm and the 55mm Plossl gives over 5... which are low mags but greatly improved surface brightness. It also keeps you with your "All TeleVue" tradition. Those two would surely vignette some, but at least you would have the brighter renditions there. That's about as close to ~Rich Field~ as one can get with the slower commercial SCTs.    Tom



#12 Dave Bush

Dave Bush

    Vanguard

  • *****
  • topic starter
  • Posts: 2354
  • Joined: 28 Jul 2004

Posted 15 November 2019 - 09:24 AM

Do you have a link for that?  All I have found is 2032mm.  

https://s3.amazonaws...paper_final.pdf

 

Page 13



#13 Dave Bush

Dave Bush

    Vanguard

  • *****
  • topic starter
  • Posts: 2354
  • Joined: 28 Jul 2004

Posted 15 November 2019 - 09:27 AM

Jon's is a great point. Even the 31mm Nagler provides a fairly constricted 3mm pupil... so nebulae and galaxies will be inexorably dimmed. The 41mm Panoptic yields 4mm and the 55mm Plossl gives over 5... which are low mags but greatly improved surface brightness. It also keeps you with your "All TeleVue" tradition. Those two would surely vignette some, but at least you would have the brighter renditions there. That's about as close to ~Rich Field~ as one can get with the slower commercial SCTs.    Tom

I might mention that my astigmatism kicks in at about 3mm so the 31mm Nagler is about a low as I can go.

 

Unless I wanted to use the Dioptrix on a 35 or 41 Pan.  A possibility.



#14 Dave Bush

Dave Bush

    Vanguard

  • *****
  • topic starter
  • Posts: 2354
  • Joined: 28 Jul 2004

Posted 15 November 2019 - 10:10 AM

Well I just had a great conversation with Al Nagler.  First of all, I have to say, it's pretty cool to call a manufacture and get to speak with not only the founder but the designer of so many of their products.  

 

Anyway, he was very interested in my situation and very helpful.  I'm pretty sure now that I have a good handle on what I need and what decisions I need to make.

 

Thanks to every one here for all your input.


  • Jon Isaacs, rowdy388 and bbqediguana like this

#15 Miranda2525

Miranda2525

    Surveyor 1

  • *****
  • Posts: 1920
  • Joined: 12 Jul 2016

Posted 15 November 2019 - 10:52 AM

Looking at a couple different eyepiece configurations.  

 

One would give me this sequence...

 

31mm Nagler  69x

21mm Ethos   106x

17mm Ethos   125x

13mm Ethos   163x

10mm Ethos   193x

 

The other one is this...

 

31mm Nager  69x

20mm Nagler 101x

16mm Nagler 133x

13mm Nagler 163x

11mm Nagler 213x

 

If you had an EdgeHD 8 like me, which might you prefer?

 

Oh and I'm thinking in either case the 125x/133x might be unnecessary.    

 

What do you think?

There's hardly much of a difference in magnification for there to be of a concern between the two scenarios...

 

Here are better mag jumps: (they don't have to be exact to this, but close anyways).

 

50x

100x

150x

200x

250x

300x


Edited by Miranda2525, 15 November 2019 - 10:54 AM.

  • Asbytec likes this

#16 Riccardo_italy

Riccardo_italy

    Viking 1

  • -----
  • Posts: 716
  • Joined: 29 Sep 2014
  • Loc: Italy

Posted 15 November 2019 - 11:38 AM

AFAIK the maximum field stop in a C8 is about 37-38mm.

 

The Ethos 21mm almost maximizes it (no need for the Nagler 31mm with a 42mm field stop) BUT it gives you a 2.1mm e.p.  which is optimal for many, but not for all DSOs.

 

Why not:

35mm Panoptic + Dioptrix

17mm Ethos

10mm Ethos

And something very sharp for maximum magnification: 7 or 5mm Delite or 6mm Delos (depending on your seeing).


Edited by Riccardo_italy, 15 November 2019 - 11:40 AM.


#17 AstroVPK

AstroVPK

    Explorer 1

  • -----
  • Posts: 72
  • Joined: 12 May 2019
  • Loc: Sunnyvale, CA

Posted 15 November 2019 - 12:03 PM

Well I just had a great conversation with Al Nagler.  First of all, I have to say, it's pretty cool to call a manufacture and get to speak with not only the founder but the designer of so many of their products.  

 

Anyway, he was very interested in my situation and very helpful.  I'm pretty sure now that I have a good handle on what I need and what decisions I need to make.

 

Thanks to every one here for all your input.

 

What did he recommend?



#18 Dave Bush

Dave Bush

    Vanguard

  • *****
  • topic starter
  • Posts: 2354
  • Joined: 28 Jul 2004

Posted 15 November 2019 - 12:11 PM

What did he recommend?

All TV eyepieces of course.  :-)

 

Basically his recommendation was for a couple possibilities..

 

31mm T5 Nagler

13mm Ethos 

 

He called this his dyslexic set.  He said that for most nights I could be happy with just these two.  Alternately I could through in the 17mm Ethos for a middle magnification.

 

His other possibility was to use all Ethos...

 

21mm 

13mm

10mm 



#19 MitchAlsup

MitchAlsup

    Skylab

  • -----
  • Posts: 4052
  • Joined: 31 Aug 2009

Posted 15 November 2019 - 12:13 PM

Looking at a couple different eyepiece configurations.  

 

One would give me this sequence...

 

31mm Nagler  69x

21mm Ethos   106x

17mm Ethos   125x

13mm Ethos   163x

10mm Ethos   193x

 

The other one is this...

 

31mm Nager  69x

20mm Nagler 101x

16mm Nagler 133x

13mm Nagler 163x

11mm Nagler 213x

 

If you had an EdgeHD 8 like me, which might you prefer?

 

Oh and I'm thinking in either case the 125x/133x might be unnecessary.    

 

What do you think?

When I had a C11, I used::

 

31NT5 later on, 30mm Zeiss 86º FoV earlier on

21E later on, 20 NT2 earlier

13E later, 13 NT1 earlier

9ES120 later, 9NT1 earlier

7NT1

 

I never needed anything shorter than 7mm and the 31NT5 has almost a big a FoV as 41 PAN



#20 Eddgie

Eddgie

    ISS

  • *****
  • Posts: 24975
  • Joined: 01 Feb 2006

Posted 15 November 2019 - 12:41 PM

You know best what is best for you, but your magnifications seem far to granular to me.  I bet you spend a lot of time swapping eyepieces.

 

And Nagler I think is giving good advice

 

I think it is far better to plan using field stop sizes, and while Nagler used to recommend a 50% difference in field stop size, I think this is also to granular, and I recommend step of 75% or even double/half. And in this case, it appears that Nagler has made a similar recommendation because the eyepieces he recommends, the 31mm Nagler (42mm field stop) and the 13mm Ethos (22mm field stop) is a 2:1 ratio.  Now I might go with the 31/17/ 10 if you think you need that kind of high power, but the 31mm and 13E will make for minimal fussing around with eyepieces, so I think Al has given the advice I am giving, which is that you can go overboard with granular magnication, and it is better to think in true field steps (field stop size) and 1.7x to 2x is typically a very good size true field step and keeps one from constantly searching for the correct field size.

If it does not fit in the wider field, then swapping to the next largest field stop will almost always ensure that it does.    Jumping magnifcation by 25% will almost never result in enough change in appearance to make it worth it.

Otherwise, you spend a lot of money on eyepieces and spend a lot of time swapping eyepieces, and frankly once you have framed the object, there is nothing to gain in the object itself for increasing the size of the field around it, and if the goal is to enjoy the object in it's background, then a bigger downward step lets you capture more of that background and in my experience, a 50% change in field size generally does not change things all that much. 



#21 Eddgie

Eddgie

    ISS

  • *****
  • Posts: 24975
  • Joined: 01 Feb 2006

Posted 15 November 2019 - 12:53 PM

And if you go the minimal eyepiece route, I recommend supplementing the minimalist set with a high quality zoom.  This will ensure that you always have exactly the right magnification for managing seeing when doing high resolution observing (Planets, lunar, and solar). 



#22 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 79927
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 15 November 2019 - 12:57 PM

I think it is far better to plan using field stop sizes, and while Nagler used to recommend a 50% difference in field stop size, I think this is also to granular, and I recommend step of 75% or even double/half.

 

 

I think in terms of field stop, exit pupil, magnification.. I also want to have the right eyepiece for the job.  If I have the 31mm, the 21mm, the 16mm and the 13mm, I can jump from the 31mm to the 13mm if I want to. If I want a smaller jump, I can choose that as well. 

 

Swapping from the 31mm to the 13mm, which I do quite frequently, is a difference in brightness of a factor of 5.7 that's big. 

 

For me, I keep my eyepieces where they're easy to swap and I find I am able to tease out fine details, particularly faint galaxies, with the fine steps in magnification. 

 

In Dave's situation, I would be thinking about the eyepieces for plantetary but maybe he has a different set in mind for that.

 

Jon


  • Asbytec likes this

#23 MartinPond

MartinPond

    Fly Me to the Moon

  • *****
  • Posts: 5080
  • Joined: 16 Sep 2014

Posted 15 November 2019 - 01:05 PM

My main hope is for ED refractors to keep creeping down.

Way too happy with most eyepieces.



#24 25585

25585

    Fly Me to the Moon

  • *****
  • Posts: 6223
  • Joined: 29 Aug 2017
  • Loc: In a valley, in the UK.

Posted 15 November 2019 - 01:38 PM

With a C8 though, the wider AFOV would be vignetted by the larger eyepieces while a C11 would be good for them all.



#25 Bob4BVM

Bob4BVM

    Vanguard

  • *****
  • Posts: 2009
  • Joined: 23 Mar 2015
  • Loc: W. Oregon

Posted 15 November 2019 - 08:32 PM

And if you go the minimal eyepiece route, I recommend supplementing the minimalist set with a high quality zoom.  This will ensure that you always have exactly the right magnification for managing seeing when doing high resolution observing (Planets, lunar, and solar). 

You best ignore this advice from Eddgie...

What you will find is that the zoom will be in the focuser 95% of the time,

your actual observing time will go way up,

and your time swapping EPs will go way down.

 

Good for you, but all those $$$ TV's in the case will be PO'd. You may have a rumble to deal with  in you EP case !  Not a good thing

;-)

Bob




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics