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

Where Does Your Refractor Max Out?

  • Please log in to reply
26 replies to this topic

#1 briansalomon1

briansalomon1

    Viking 1

  • *****
  • topic starter
  • Posts: 518
  • Joined: 21 Jul 2018
  • Loc: Oxnard CA

Posted 24 September 2021 - 09:28 PM

I've been observing for over 40 years, almost all of it with refractors. The lions share has been with a TV102 and now I've had an NP101 for several years.

 

I've read Ed Ting reviews of really good refractors similar to the TV102 and NP101 getting up to really high magnifications and after some pretty good seeing earlier this week I've decided I can get ~300X with my NP101 but the view in my opinion breaks down above that and I'm not certain it was the scope but I'm wondering what others have experienced. The eyepieces were Nagler 5mm and 3.5mm, both with the same 2X power mate.

 

I have an Obsession 15UC coming pretty soon but until I get that, I have to judge the seeing by how much the overhead stars twinkle. Seeing wasn't "best ever" but definitely "very good".

 


  • Bomber Bob likes this

#2 vtornado

vtornado

    Skylab

  • *****
  • Posts: 4,247
  • Joined: 22 Jan 2016
  • Loc: 42N 88W

Posted 24 September 2021 - 09:33 PM

Unless I am trying to split a double star, or turn neptune into a disk,

I only use .5mm exit pupil (200x) for a 100mm frac.

My atmosphere caps out around there too, no matter how big the scope is.


  • stevew, ewave, Bomber Bob and 1 other like this

#3 teashea

teashea

    Gemini

  • *****
  • Posts: 3,047
  • Joined: 20 Dec 2020
  • Loc: Lincoln, Nebraska, USA

Posted 24 September 2021 - 09:51 PM

I've been observing for over 40 years, almost all of it with refractors. The lions share has been with a TV102 and now I've had an NP101 for several years.

 

I've read Ed Ting reviews of really good refractors similar to the TV102 and NP101 getting up to really high magnifications and after some pretty good seeing earlier this week I've decided I can get ~300X with my NP101 but the view in my opinion breaks down above that and I'm not certain it was the scope but I'm wondering what others have experienced. The eyepieces were Nagler 5mm and 3.5mm, both with the same 2X power mate.

 

I have an Obsession 15UC coming pretty soon but until I get that, I have to judge the seeing by how much the overhead stars twinkle. Seeing wasn't "best ever" but definitely "very good".

I do not find it important to push the magnification limits of my refractors.  


  • Jon Isaacs and jena100 like this

#4 sanbai

sanbai

    Apollo

  • *****
  • Posts: 1,331
  • Joined: 18 May 2019
  • Loc: Baton Rouge, LA

Posted 24 September 2021 - 10:43 PM

My SW 80mmED f/7.5 can take a 0.5 exit pupil without major problem. There will be a bit of chromatism but not annoying at all. Moon views with the Ethos 3.7 are astonishing. I can go further than 3.5 mm eyepiece (yet...), but I guess that would start to be to challenging.

I can go 0.5 mm exit pupil with the C8edge if seeing allows, but the contrast is noticeable lower compared to the refractor. I see why some people really like refractors. Despite that, I'm going the dob way. My retractor is mostly for wide fields (exit pupils 2 to 7 mm). IMHO, just for high magnifications is more reasonable getting a larger reflector.

#5 PKDfan

PKDfan

    Messenger

  • -----
  • Posts: 471
  • Joined: 03 May 2019
  • Loc: Edmonton

Posted 24 September 2021 - 11:52 PM

Seeing maxes out at way less than 200× for me usually so on only a few glorious nights got my Sky-Watcher 4" F/9 scope to very high powers above that.
I got to a .37mm exit pupil(270×) on the last Mars opposition.
The image was very bright and essentially perfect, when perfect seeing materialized, so I imagine if I could have doubled that power then that would have been the upper limit.

This scope has a superlative figure!

It has been so addicting a view that I will setup in very marginal conditions just to look through the thing!



Clear skies & Good seeing

Edited by PKDfan, 25 September 2021 - 12:01 AM.

  • Astrojensen and therealdmt like this

#6 Astro-Master

Astro-Master

    Apollo

  • *****
  • Posts: 1,342
  • Joined: 09 May 2016
  • Loc: San Diego County,Ca.

Posted 25 September 2021 - 01:39 AM

I have a Stellarvue 105mm f/7 triplet with a Feather-touch focuser, and live 13 miles from the Pacific Ocean on a 450 foot hilltop.  The seeing gets good, to very good quite often, and when the marine layer comes in slowly, the seeing can get excellent.

 

On a good night, Jupiter, and Saturn at 250x to 300x is possible, on an average night 185x to 210x is the norm.  I use a TV 3-6 Zoom and my Celestron Ultima SV barlow with the zoom on double stars and the Moon on the better nights.

 

I've split close doubles at 375x to 420x with beautiful star images, and close up views of the craters and mountains on the Moon are amazing on the better nights.

 

On the average nights, 185x to 250x is about it on double stars, and the Moon.  The 105mm has been my first refractor, so far, and is such a joy to set up and use, I just love the perfect star images, and it has never needed collimation, its a keeper for life for sure.


  • Ballyhoo and Bomber Bob like this

#7 Ballyhoo

Ballyhoo

    Fly Me to the Moon

  • *****
  • Posts: 6,818
  • Joined: 22 Jul 2011
  • Loc: San Diego

Posted 25 September 2021 - 03:03 AM

My 6" Explore Scientific CF is a new member to my family and does  hold up well @ 300 power which is what one might expect.  An absolutely amazing planetary and lunar instrument.   Just dabbling in some lunar imaging with the moon low in the sky.

Attached Thumbnails

  • red moon.jpg

  • paul hart, niteskystargazer and Bomber Bob like this

#8 RadioAstronomer

RadioAstronomer

    Ranger 4

  • *****
  • Posts: 358
  • Joined: 13 Jun 2018
  • Loc: Tucson, AZ

Posted 25 September 2021 - 03:15 AM

For me any telescope with diffraction limited optics maxes out around the 1mm exit pupil range. I find that I don't see additional planetary detail if I go under 1mm EP. Double stars is a different story. Sirius comes to mind. I can get a better view of Sirius B if I go under 1mm exit pupil. 

 


  • Rutilus likes this

#9 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 95,040
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 25 September 2021 - 06:29 AM

I've been observing for over 40 years, almost all of it with refractors. The lions share has been with a TV102 and now I've had an NP101 for several years.

 

I've read Ed Ting reviews of really good refractors similar to the TV102 and NP101 getting up to really high magnifications and after some pretty good seeing earlier this week I've decided I can get ~300X with my NP101 but the view in my opinion breaks down above that and I'm not certain it was the scope but I'm wondering what others have experienced. The eyepieces were Nagler 5mm and 3.5mm, both with the same 2X power mate.

 

I have an Obsession 15UC coming pretty soon but until I get that, I have to judge the seeing by how much the overhead stars twinkle. Seeing wasn't "best ever" but definitely "very good".

 

I also have an NP-101 and use it with the 5mm and 3.5 mm Naglers with a 2X TV Barlow.  The 3.5 mm with the 2x Barlow provides a 0.32 mm exit pupil, that's about the maximum I use, mostly for Dawes and Rayleigh criterion Doubles.  A 0.32 mm exit pupil is very small.  Higher magnifications can be used but with little purpose.

 

Jon


  • doctordub likes this

#10 sportsmed

sportsmed

    Viking 1

  • *****
  • Posts: 516
  • Joined: 01 Aug 2012
  • Loc: Hot Springs, AR

Posted 25 September 2021 - 07:38 AM

With my 80mm ED and 120ST the most I have tried is around 230x which is with a Meade 5000 UWA 5.5mm and a 2.5 barlow. But I guess with double star viewing I could get more, I just dont have the eyepiece or barlow to get it.



#11 CHASLX200

CHASLX200

    ISS

  • *****
  • Posts: 24,274
  • Joined: 29 Sep 2007
  • Loc: Tampa area Florida

Posted 25 September 2021 - 07:46 AM

On my better fracts 100x per inch is the norm for some objects.


  • doctordub and Bomber Bob like this

#12 russell23

russell23

    Voyager 1

  • *****
  • Posts: 12,138
  • Joined: 31 May 2009
  • Loc: Upstate NY

Posted 25 September 2021 - 10:08 AM

Seeing conditions have not allowed me to max out my 102mm f/11 ED doublets.  But for deep sky I generally find the max due to image brightness is around 160x.  For Moon and planets that is where I max out due to floaters.   Last night I was at 280x with the scope and it was sharp when seeing allowed, but the floaters in my eyes were pretty bad at that magnification. The scope can certainly handle more magnification.  My eyes can’t.


  • sportsmed and Bomber Bob like this

#13 vdog

vdog

    Vanguard

  • *****
  • Posts: 2,086
  • Joined: 30 Aug 2018
  • Loc: California Central Valley, U.S.A.

Posted 25 September 2021 - 11:03 AM

With the 76, I generally don't go past 90x as this is my dark site / low power scope and I almost never use it for planets. When I want to go deeper, I haul out the 16" dob.

 

With the 120, I'll do 327x with the Meade 5.5 and an Orion Shorty Plus 2x Barlow.   When seeing allows, this provides an awesome view of Saturn and also allows me to see the disks of Jupiter's moons.



#14 gwlee

gwlee

    Gemini

  • *****
  • Posts: 3,038
  • Joined: 06 Sep 2015
  • Loc: 38N 120W

Posted 25 September 2021 - 11:32 AM

Unknown because my tolerance for small exit pupils maxes out at 25x/inch. 



#15 Bomber Bob

Bomber Bob

    ISS

  • *****
  • Posts: 20,237
  • Joined: 09 Jul 2013
  • Loc: The Swamp, LA (Lower Alabama)

Posted 25 September 2021 - 12:30 PM

I've been observing for over 40 years, almost all of it with refractors. The lions share has been with a TV102 and now I've had an NP101 for several years.

 

I've read Ed Ting reviews of really good refractors similar to the TV102 and NP101 getting up to really high magnifications and after some pretty good seeing earlier this week I've decided I can get ~300X with my NP101 but the view in my opinion breaks down above that and I'm not certain it was the scope but I'm wondering what others have experienced. The eyepieces were Nagler 5mm and 3.5mm, both with the same 2X power mate.

 

I have an Obsession 15UC coming pretty soon but until I get that, I have to judge the seeing by how much the overhead stars twinkle. Seeing wasn't "best ever" but definitely "very good".

You got a usable 75x per inch.  In my system, that's an Outstanding Refractor, if the seeing was 7/10 or better.  Thursday night, my planetary seeing was a solid 8/10, and I got my 1988 Tak FC-100 up to 100x per inch (400x) on Saturn & Jupiter.  I could focus the limb of each planetary disk to a sharp edge.  I don't stay at that power -- cruised at 250x most of the time -- but top-tier refractors can deliver at that extreme magnification -- When the Seeing, Object, & Observer can use / support it.

 

To get 400x in my FC-100, I used a 1.25" newish Tak 2x Barlow + older TV Radian 4mm...

 

Same Night, I had a high-quality 1983 Mizar Comet (100mm F8 Newt) as a comparison scope.  The Newt maxed-out at 50x / inch (200x) -- very soft / chasing focus at 250x.  But IMO, Outstanding performance for a small Vintage Reflector.


Edited by Bomber Bob, 25 September 2021 - 12:37 PM.

  • doctordub likes this

#16 StarAlert

StarAlert

    Surveyor 1

  • *****
  • Posts: 1,649
  • Joined: 11 Aug 2019
  • Loc: SoCal

Posted 25 September 2021 - 12:33 PM

Unknown because my tolerance for small exit pupils maxes out at 25x/inch.


1mm exit pupils are heaven.

I first saw the E and F stars in the Trapezium using a 9mm Morpheus in my f/9 Tak DL. Increasing the power beyond that didn’t make them easier to see for me.

That was my first lesson in exit pupils and image brightness vs. empty magnification.
  • John Huntley and Rutilus like this

#17 Bomber Bob

Bomber Bob

    ISS

  • *****
  • Posts: 20,237
  • Joined: 09 Jul 2013
  • Loc: The Swamp, LA (Lower Alabama)

Posted 25 September 2021 - 01:03 PM

Seeing conditions have not allowed me to max out my 102mm f/11 ED doublets.  But for deep sky I generally find the max due to image brightness is around 160x.  For Moon and planets that is where I max out due to floaters.   Last night I was at 280x with the scope and it was sharp when seeing allowed, but the floaters in my eyes were pretty bad at that magnification. The scope can certainly handle more magnification.  My eyes can’t.

That is the rub!  I was floater-free for a few years, but they've returned, and that limits Me more than my Taks.  Throw in Seeing, and the Object, and the equation gets very complicated.

 

In my years of USAF travel, I lived in places where 30x per inch was a rarity.  Much as I fuss about The Swamp, my Planetary Seeing can rival what CHAS has at the coast.  How do I know this?  I now own his old Meade 826, and I can get similar results -- it's a known factor.  Different Location, and Different Observer, but we're not doing research for JPL...  Can't control for every variable.

 

IF you live under Canadian Clippers... get a Big Dob, and look for Fuzzies.  If you live (& put up with) hot stagnant air, you may have much better than average planetary seeing.

 

Sorry OP!  IMO, you have an outstanding 4" refractor; and, it sounds like you have better than average seeing.  Enjoy!!


Edited by Bomber Bob, 25 September 2021 - 01:04 PM.


#18 Rutilus

Rutilus

    Gemini

  • *****
  • Posts: 3,051
  • Joined: 17 Dec 2010

Posted 25 September 2021 - 01:22 PM

In the past I had 4 inch Takahashi scopes and now achromat scopes. They all 

(apo /achromat) would and do 100x per inch on objects like double-stars.

With the planets, things were different, here I noticed that 200x (0.5 exit pupil) is the

point where my 4 inch scopes started to run out of light. 


  • Bomber Bob likes this

#19 Bomber Bob

Bomber Bob

    ISS

  • *****
  • Posts: 20,237
  • Joined: 09 Jul 2013
  • Loc: The Swamp, LA (Lower Alabama)

Posted 25 September 2021 - 01:55 PM

In the past I had 4 inch Takahashi scopes and now achromat scopes. They all 

(apo /achromat) would and do 100x per inch on objects like double-stars.

With the planets, things were different, here I noticed that 200x (0.5 exit pupil) is the

point where my 4 inch scopes started to run out of light. 

Both my eyes are photosensitive.  To see the fine / low-contrast details on Jupiter (and Mars, to some extent), I have to lower the overall disk brightness -- with magnification or filters -- or those details are washed-out.  

 

Again, I don't stay at 100x / inch on the planets.  When conditions allow, I'll Zoom-Up, verify some tiny something that I potentially ID'ed at 75x / inch or lower, then Zoom-Down.  IIRC, I got my FC-100 up to 625x before the Jupiter's disk got too dim & soft -- but that night was near-perfect (9/10).  A very rare night.

 

My 1970s Dakin 4" F10 achromatic can also deliver at 100x / inch, but is reliably Outstanding at 200x (Nagler 5mm); whereas, my FC-100 best views are at 250x (AT Paradigm 3.2mm) -- the Tak fluorite is a better instrument.


Edited by Bomber Bob, 25 September 2021 - 02:00 PM.

  • scooke likes this

#20 John Huntley

John Huntley

    Gemini

  • *****
  • Posts: 3,192
  • Joined: 16 Jul 2006
  • Loc: SW England

Posted 25 September 2021 - 04:34 PM

1mm exit pupils are heaven.

I first saw the E and F stars in the Trapezium using a 9mm Morpheus in my f/9 Tak DL. Increasing the power beyond that didn’t make them easier to see for me.

That was my first lesson in exit pupils and image brightness vs. empty magnification.

E & F Trapezium seem to have a "goldilocks" zone of magnification. Straying much outside of that (either above or below) tends to make them harder to discern I've found.

 

One the specific topic of this thread, I've found that I can (seeing conditions and target allowing) usefully use up to around 230x with my Vixen ED, up to around 350x with my Tak FC100-DL, up to 350x with my Skywatcher ED120 and somewhere around 450x with my TMB/LZOS 130mm F/9.2 triplet.

 

Sometimes with the latter scope I've used 600x on tight double stars or, as I did a couple of nights back, to tease out Neptune's moon Triton which is pretty much on the magnitude limit for the 130mm aperture.

 

Apart from the faint planetary moons and occasionally faint supernovae, my observing at such high powers is invariably of binary stars.


Edited by John Huntley, 25 September 2021 - 04:35 PM.

  • doctordub and Bill Fischer like this

#21 sanbai

sanbai

    Apollo

  • *****
  • Posts: 1,331
  • Joined: 18 May 2019
  • Loc: Baton Rouge, LA

Posted 25 September 2021 - 07:42 PM

I have to update my post #4.

As of today I can max out my refractor (SW 80ED f/7.5) to a  0.33 mm exit pupil. A quick test with Jupiter showed that was tolerable and still useful. I can't tell you if there was more detail (there's some softening, no surprise), but the slightly bigger image size can help discern that detail.

There was something intolerable in this quick test: the mosquitoes. pfff.


  • doctordub, sportsmed and Bomber Bob like this

#22 SandyHouTex

SandyHouTex

    Fly Me to the Moon

  • *****
  • Posts: 6,173
  • Joined: 02 Jun 2009
  • Loc: Houston, Texas, USA

Posted 25 September 2021 - 08:26 PM

When I first took my (now) 3 month old Tak FC76-DCU-Q, I put a Tak TOE 4 mm in it to look at Jupiter for 240X.  The view was stunning.  I typically have excellent seeing where I live.  I’m 20 miles West of Galveston Bay, and 20 miles North of the Gulf of Mexico.  So that’s 80X per inch.


  • doctordub and Bomber Bob like this

#23 scooke

scooke

    Mariner 2

  • *****
  • Posts: 283
  • Joined: 14 Mar 2009

Posted 26 September 2021 - 10:23 AM

Both my eyes are photosensitive.  To see the fine / low-contrast details on Jupiter (and Mars, to some extent), I have to lower the overall disk brightness -- with magnification or filters -- or those details are washed-out.  

 

Again, I don't stay at 100x / inch on the planets.  When conditions allow, I'll Zoom-Up, verify some tiny something that I potentially ID'ed at 75x / inch or lower, then Zoom-Down.  IIRC, I got my FC-100 up to 625x before the Jupiter's disk got too dim & soft -- but that night was near-perfect (9/10).  A very rare night.

 

My 1970s Dakin 4" F10 achromatic can also deliver at 100x / inch, but is reliably Outstanding at 200x (Nagler 5mm); whereas, my FC-100 best views are at 250x (AT Paradigm 3.2mm) -- the Tak fluorite is a better instrument.

Same thing I do.  "Empty" magnification isn't always empty, it can serve a purpose.  It's fun to see the lowest magnification that details are detectable but then again, it's often more enjoyable to me to observe those details at a larger image scale.  Spending the time at the eyepiece to let some of those threshold details come into view is the key to me.


  • Bomber Bob and sanbai like this

#24 csrlice12

csrlice12

    ISS

  • *****
  • Posts: 28,998
  • Joined: 22 May 2012
  • Loc: Denver, CO

Posted 26 September 2021 - 10:38 AM

On the moon, I've used a 2.58XO in my ED81S with nice results.....except for all those floaters.



#25 russell23

russell23

    Voyager 1

  • *****
  • Posts: 12,138
  • Joined: 31 May 2009
  • Loc: Upstate NY

Posted 26 September 2021 - 11:20 AM

Same thing I do.  "Empty" magnification isn't always empty, it can serve a purpose.  It's fun to see the lowest magnification that details are detectable but then again, it's often more enjoyable to me to observe those details at a larger image scale.  Spending the time at the eyepiece to let some of those threshold details come into view is the key to me.

Exactly, with the Moon you can enjoy magnifications much higher than the theoretical maximum because the image scale at higher magnifications is a worthwhile experience.  One thing I've noticed about floaters is there seems to be a point where they are seriously problematic and if you keep going to smaller exit pupil (assuming seeing allows) they become less of a problem again.

 

A couple nights ago the floaters were a big problem between 225 and 280x and the seeing did not allow much higher, but I have gone to smaller exit pupils (~425 with the same aperture) where floaters did not seem as bad as at 240x.


  • Bomber Bob likes this


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