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Using 100 degree eyepieces with an 8" f/10 SCT

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#1 BPoletti

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Posted 15 September 2020 - 11:18 AM

I've owned a Nexstar 8SE for a few months and have enjoyed the views as I've gained experience.  I have acquired a few eyepieces that are used for specific purposes.  I'm generally satisfied.  Mostly.

 

I am curious / interested in 100 degree eyepieces.  TeleVue Ethos are out of my price range, but maybe APM or used ES might fit.  I am concerned about the weight of the ES 100 series.  The TV 20mm NagT2 is a burden when used with the 8SE and a dewshield.  An ES 100 would probably be as bad, but might be worth it if the view are a big improvement over what I have now.

 

But all that aside, what differences or improvements can I expect with a 100 over the 82 degree eyepieces I currently have?  Is the view limited by the physical limitations of the OTA?  

 

What if I was using a Meade 8" LX90 instead of the 8SE?  Would that better handle heavy eyepieces?



#2 Beeham

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Posted 15 September 2020 - 11:24 AM

I have one of the 5mm Meade mega-wide 100-degree eyepieces, I've used it in my C8 a couple times.  It's typically too much magnification for all but the best seeing conditions.  That being said, it doesn't seem to vignette or anything.

 

I hope that's helpful.  Cheers!


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#3 ButterFly

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Posted 15 September 2020 - 11:51 AM

But all that aside, what differences or improvements can I expect with a 100 over the 82 degree eyepieces I currently have?  Is the view limited by the physical limitations of the OTA? 

50% more true field in the eyepiece (at the same focal length).  100 degree eyepieces are a try before you buy size.  Some people just don't like them, others do.  Look for a good return policy, or just buy used.

 

As long as the field stop of the eyepiece is smaller than the SCT baffle (~37mm for a C8), there is no vignetting to worry about.  Above that, you lose some magnitude at the edges of the field.  Coincidentally(!?), the 21 Ethos has a field stop of 36.2mm and weighs as much as your Nagler.  Smaller focal lengths are lighter.


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#4 petert913

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Posted 15 September 2020 - 12:28 PM

My experience is that the eye relief is very short on anything over an 82 deg eyepiece.  You have to really smoosh your eyeball in there to get the whole field.


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#5 swsantos

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Posted 15 September 2020 - 01:51 PM

I use all 100 degree eyepieces, Ethos in my case, with my 8" Edge F10 SCT. I use an undriven mount most of the time so much of my reason for 100 degree eyepieces is not having to move the scope as much as I would otherwise have to with a narrower field of view. It help a lot especially on planets with high magnification to have a 10mm 100 degree eyepiece because it gives longer time to study an object before it moves away.

 

Not sure if you are using the Nexstar SE mount with that OTA but if you are it is a driven mount so that benefit might not apply to you.

 

I also really like the 17mm Ethos for general viewing of objects that do not need as much mag and it is the 17mm that is in my focuser most of the time as the exit pupil works for me and I can take in more object context with it than would be possible through a narrower field eyepiece.

 

Even on a driven mount I would recommend a 2mm-ish exit pupil 100 degree eyepiece (20mm or thereabouts) for the first one into the focuser on other-that-planetary viewing nights.


Edited by swsantos, 15 September 2020 - 01:52 PM.

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#6 junomike

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Posted 15 September 2020 - 05:03 PM

Loved my ES 14 & 20mm 100's when I had my C8.  They worked great in the C11 also.


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#7 Eddgie

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Posted 15 September 2020 - 05:54 PM

I would say that it depends a great deal on the observer and their tolerance to field curvature and coma.

 

The standard C8 has about as much coma as an f/5 reflector, but that comatic blur is defocused out at the edge of the field, and this leads to bloated and misshapen stars.  The thing is, a lot of people don't mind that and are primarily concerned with what is at the center of the field, but of course if that is all they are concerned about, why bother with a 100 degree eyepiece?

 

Anyway, for some observers, the aberrations will be to extreme for them to tolerate. For others, they will be perfectly acceptable. 

 

As the focal lenght gets shorter, this is less of an issue, but with a 20mm/100, I did not find the view to be particularly enjoyable but the same eyepiece in the EdgeHD provided quite an excellent view.

 

So, as the saying goes, your mileage might vary.  If you don't think you are particularly sensitive to off axis aberations, then a 20mm or 21mm could be fine, but if you don't like to see bloated stars at the edge of the field (how much is too much??? That is the question) then it is harder to give assurance that you would love it as much as the view you would get by using a 35mm Panoptic or 41mm Panoptic, both of which are excellent in the standard C8. 


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#8 Astrojedi

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Posted 15 September 2020 - 06:03 PM

I use APM 100 deg EPs 20mm and 13mm with my EdgeHD 8. View is superb. I do prefer smaller exit pupils especially from my LP backyard as it improves contrast and also because of the ambient light my pupils do not dilate as much as when I am at a dark site. A side benefit of smaller exit pupils is that it takes aberrations in my eyes out of play. In fact most of us have these and they become apparent when the eyes are much more dilated.


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#9 SeattleScott

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Posted 15 September 2020 - 06:19 PM

Let’s see:

8mm Ethos $590
9mm ES 100 $550
APM 9mm XWA $240

If Ethos are too expensive, ES probably are too.

For some reason people still think ES eyepieces are a bargain compared to TV but that isn’t really the case. They might be worth considering every other month when they are on sale though.

APM XWA are also lighter than ES.

Scott
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#10 audioengr

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Posted 15 September 2020 - 06:34 PM

I have the same size scope, but the Evolution EdgeHD, so I don't have to worry about coma.

 

Here is a great 30mm German-made APM eyepiece that is around 80 degrees actual, and affordable.  It got a lot of great reviews, so I got one.  Very flat field.

 

You might consider a used 22mm Tele Vue Nagler.  This is just a great eyepiece all-around.  Just feels right.

 

I have the Tele Vue Ethos, 13mm, 6mm and 4.7mm.  They are great, but you do have to get your eye close.  No mascara for the wife.  You might look at used ones.  They are usually carefully cared-for and mint.  Used, they will still cost you $480 each though, particularly with the demand that COVID has created.

 

Tele Vue Delos is $350 new and $275-285 used.  72 degrees FOV is pretty nice too.

 

The less expensive option is APM, with the 70 degree ultra-flat 30mm, the 110 degree 9mm, 100 degree 13mm and the 110 degree 4.7mm.  All good choices and excellent quality.  Better than ES.  Add the 22mm Nagler and you have a nice collection.


Edited by audioengr, 15 September 2020 - 06:38 PM.

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#11 Beeham

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Posted 15 September 2020 - 06:51 PM

I would say that it depends a great deal on the observer and their tolerance to field curvature and coma.

 

The standard C8 has about as much coma as an f/5 reflector, but that comatic blur is defocused out at the edge of the field, and this leads to bloated and misshapen stars.  The thing is, a lot of people don't mind that and are primarily concerned with what is at the center of the field, but of course if that is all they are concerned about, why bother with a 100 degree eyepiece?

 

Just speaking for my own preferences, I don't use any goto mounts, so having the wider field makes locating targets easier.  I'm not overly concerned with a little distortion on periphery after I've located the target, but the 100-degree eyepiece still adds value in my application.

 

Just me $0.02.  Cheers!


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#12 Echolight

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Posted 15 September 2020 - 07:20 PM

Let’s see:

8mm Ethos $590
9mm ES 100 $550
APM 9mm XWA $240

If Ethos are too expensive, ES probably are too.

For some reason people still think ES eyepieces are a bargain compared to TV but that isn’t really the case. They might be worth considering every other month when they are on sale though.

APM XWA are also lighter than ES.

Scott

There's a few TV eyepieces I'd like to have based on reputation and maybe nothing else out there compares. 3-6 zoom, 22T4 Nagler, 35 Panoptic. Usually beyond my weight limit, but you could add the 31 Nagler and I guess the 41 Pan.

 

ES? The 12-92 I'd take if someone was giving, in spite of it's weight.

 

Problem is, I don't want to pay for any of them. Although I feel I'm getting dangerously close. I might be tempted by a short focal length Nagler as the gap closes with these.

 

But with the APM XWA's available, for now..., the desire for an Ethos is quelled.


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#13 Tfer

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Posted 15 September 2020 - 09:49 PM

Checking out your equipment list.

I think the first thing you should look at to widen your FOV, is a 6.3 reducer.  


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#14 BPoletti

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Posted 15 September 2020 - 10:29 PM

Checking out your equipment list.

I think the first thing you should look at to widen your FOV, is a 6.3 reducer.  

I've got one.  Just didn't list it and haven't used it.  I will try it later this week if the smoke clears.  


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#15 SeattleScott

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Posted 16 September 2020 - 12:29 AM

I've got one. Just didn't list it and haven't used it. I will try it later this week if the smoke clears.

Oh well that changes everything. Now you want to be looking at more like 12-13mm to get 100x and 2mm exit pupil, not 20mm. Now you don’t need 2” eyepieces.

I am in Seattle so I feel your pain. Maybe we can pool our money and build a high altitude balloon and get up above this crap? But seriously you need to figure out the reducer before you do anything else. If you prefer using the reducer, it changes your scope. It changes your useful focal lengths. It eliminates most of the point of 2” eyepieces. I suppose you could always get something around 13-17mm which would be useful with or without a reducer. Basically something in the middle. Probably won’t be your most used eyepiece either way, but will be usable either way.

Scott

Edited by SeattleScott, 16 September 2020 - 12:34 AM.

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#16 Voyager 3

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Posted 16 September 2020 - 07:23 AM

Let’s see:

8mm Ethos $590
9mm ES 100 $550
APM 9mm XWA $240

If Ethos are too expensive, ES probably are too.

For some reason people still think ES eyepieces are a bargain compared to TV but that isn’t really the case. They might be worth considering every other month when they are on sale though.

APM XWA are also lighter than ES.

Scott

I always bang my head whenever people go to ES 100s against ethos especially in the above mentioned FL . You can get an ETHOS with extra 50$ 🤨 ... If you could shell out 525-550$ why not save and get the Ethos for 50$ more ? Ok the longer ethos are 627$ but still why not save a bit for a month or two ? The ES is good AS APM , maybe at some FLs it can beat the APMs but still it's nearly HALF the price ! And I've heard that the 20ES goes to kneels when comparing it to the APM but the cost difference is a bit more than half !!!
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#17 BPoletti

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Posted 16 September 2020 - 08:30 AM

Oh well that changes everything. Now you want to be looking at more like 12-13mm to get 100x and 2mm exit pupil, not 20mm. Now you don’t need 2” eyepieces.


Scott

 

I have been under the assumption (maybe misunderstanding) that using the f/6.3 reducer would shrink the potential TFoV.  The 8SE has a field stop of 39mm.  Eyepieces with a field stop of greater than 39mm would be limited to that 39mm field stop.  Does using an f/6.3 reduce  reducer actually cause vignetting in an eyepiece with a, say, 36mm field stop.  Would the 39mm field stop become ~ 24.5mm when using an f/6/3 reducer in an f/10 SCT (39mm x (6.3/10)?

 

I guess my REAL question is: Would there be physical obstruction / vignetting when using the f6.3 reducer because the relative TFoV is compressed into a smaller area?

 

Am I stating my concerns logically?  Does this question make sense?



#18 jmillsbss

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Posted 16 September 2020 - 09:01 AM

I have the same size scope, but the Evolution EdgeHD, so I don't have to worry about coma.

 

Here is a great 30mm German-made APM eyepiece that is around 80 degrees actual, and affordable.  It got a lot of great reviews, so I got one.  Very flat field.

 

You might consider a used 22mm Tele Vue Nagler.  This is just a great eyepiece all-around.  Just feels right.

 

I have the Tele Vue Ethos, 13mm, 6mm and 4.7mm.  They are great, but you do have to get your eye close.  No mascara for the wife.  You might look at used ones.  They are usually carefully cared-for and mint.  Used, they will still cost you $480 each though, particularly with the demand that COVID has created.

 

Tele Vue Delos is $350 new and $275-285 used.  72 degrees FOV is pretty nice too.

 

The less expensive option is APM, with the 70 degree ultra-flat 30mm, the 110 degree 9mm, 100 degree 13mm and the 110 degree 4.7mm.  All good choices and excellent quality.  Better than ES.  Add the 22mm Nagler and you have a nice collection.

And VERY well corrected.  I have a mass-produced Orion 10" f/4.7.  I KNOW what coma looks like!  The HRCC in the dob solves that. And some say the C8 won't be corrected to the edge.  Let me tell you, my older black C8 with Delos is VERY sharp to the field stop.  I can set an object just OUTSIDE the field and watch it track in and transit the FOV and there's no visible abberation of any ilk.  For the money, the Delos are a bangin' good deal.  And long eye relief to boot.  You fix where you're comfortable and sit back and enjoy.

 

As far as the 22 Nagler.  I say "YES!"  Another very good choice.  Buy this one used.  It shouldn't show abuse or mishandling, as any EP that costs $500 new is gonna be very well cared for.

 

There are many very good options out there, but the 22N and all the Delos are mine!



#19 SeattleScott

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Posted 16 September 2020 - 09:10 AM

I have been under the assumption (maybe misunderstanding) that using the f/6.3 reducer would shrink the potential TFoV. The 8SE has a field stop of 39mm. Eyepieces with a field stop of greater than 39mm would be limited to that 39mm field stop. Does using an f/6.3 reduce reducer actually cause vignetting in an eyepiece with a, say, 36mm field stop. Would the 39mm field stop become ~ 24.5mm when using an f/6/3 reducer in an f/10 SCT (39mm x (6.3/10)?

I guess my REAL question is: Would there be physical obstruction / vignetting when using the f6.3 reducer because the relative TFoV is compressed into a smaller area?

Am I stating my concerns logically? Does this question make sense?

You have the right general idea even if you didn’t state it the best. Yes the baffle tube is the limiting factor. Yes, if using the reducer that effectively shrinks the baffle tube. Consequently people almost always use either 2” eyepiece or reducer to get a wider view, not both. You can get to 1.2 degrees with a 40mm SWA or with a 32 Plossl and a reducer. Some people have tried combining reducer and 2” eyepiece but now you get vignetting and there are performance side effects; reduced effective aperture, reduced contrast, increased spherical abberations, etc. Basically the scope was not designed to be used as a wide field instrument. You can try and use it that way but most people don’t like the results.

Scott
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#20 Beeham

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Posted 16 September 2020 - 10:25 AM

You have the right general idea even if you didn’t state it the best. Yes the baffle tube is the limiting factor. Yes, if using the reducer that effectively shrinks the baffle tube. Consequently people almost always use either 2” eyepiece or reducer to get a wider view, not both. You can get to 1.2 degrees with a 40mm SWA or with a 32 Plossl and a reducer. Some people have tried combining reducer and 2” eyepiece but now you get vignetting and there are performance side effects; reduced effective aperture, reduced contrast, increased spherical abberations, etc. Basically the scope was not designed to be used as a wide field instrument. You can try and use it that way but most people don’t like the results.

Scott

Some added thoughts on the focal reducer, based on my experience using one with my C8 on a fork mount:

 

- Larger eyepieces and 2" diagonal no longer clear the bottom of the fork mount...Doh!

- Larger eyepieces and 2" diagonal no longer balance due to added weight and moment arm

- Threads on reducer are contemporary "loose tolerance" threads, don't go on to older C8 without some protesting...not cool

- Switching to high magnification requires taking off diagonal, taking off reducer, replacing diagonal, then switching eyepiece...that's a hassle

- most important: with longer optical path length of 2" diagonal...I couldn't achieve focus at infinity, so I need to bring that second 1.25" diagonal

 

These are the reasons I no longer own a 6.3 reducer.  I'm of the opinion that longer eyepieces are the way to go.

 

I hope that's useful.  Cheers!


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#21 SeattleScott

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Posted 16 September 2020 - 10:35 AM

Arguably the main issue with reducer is reduced contrast for planetary viewing, so then you are switching between reducer for DSO and no reducer for planets. Or live with reduced contrast for planets. A 2” diagonal and 2” eyepiece is more expensive, but more convenient.

That being said he already bought the reducer so he might as well give it a spin. He might like how it helps clean up the edge.

Scott

#22 BPoletti

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Posted 16 September 2020 - 10:42 AM

Thanks to all for the comments and feedback.  

 

Maybe using the 6.3 Reducer will depend on what objects I intend to view over the span of a given session.  The widest view with the lowest powers, big nebula, galaxies and the like, with the reducer.  Doubles, clusters, planets, without.  

 

I think there's a 22mm Nag T4 for sale in the classified.  How does that eyepiece compare to the 20mm Nag T2 I already own? 


Edited by BPoletti, 16 September 2020 - 10:43 AM.


#23 Magnetic Field

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Posted 16 September 2020 - 11:07 AM

Thanks to all for the comments and feedback.  

 

Maybe using the 6.3 Reducer will depend on what objects I intend to view over the span of a given session.  The widest view with the lowest powers, big nebula, galaxies and the like, with the reducer.  Doubles, clusters, planets, without.  

 

I think there's a 22mm Nag T4 for sale in the classified.  How does that eyepiece compare to the 20mm Nag T2 I already own? 

Has anyone posted that link (last Figure and text at the bottom): http://skymtn.com/ma...vignetting.html



#24 Echolight

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Posted 16 September 2020 - 11:14 AM

I believe the 22 has longer eye relief than the 20.

 

And a larger eye lens.

 

And it weighs more.


Edited by Echolight, 16 September 2020 - 11:15 AM.


#25 Rjettman

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Posted 16 September 2020 - 11:50 AM

I just got the TeleVue 17mm Ethos 100 degree and the 6mm as well, yesterday.  From my whopping one night of experience with it I find the views promising.  But viewing with the stock, "comes with the scope" eyepieces is all I have to compare it to.  The images are as clear as you can expect with all the smoke blanketing Colorado right now, and I saw no difference on the edges of the field.  You do have to move your eye around a bit to see the whole field, but I find that to be a good thing.  Taking the 8" scope up to the high country this week, so hopefully I will get better views then, and maybe a photo or two.


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