Go Back   IceInSpace > Equipment > Eyepieces, Barlows and Filters

Reply
 
Thread Tools Rate Thread
  #1  
Old 22-07-2013, 03:41 PM
mental4astro's Avatar
mental4astro (Alexander)
kids+wife+scopes=happyman

mental4astro is offline
 
Join Date: Jun 2008
Location: sydney, australia
Posts: 4,979
Low power EP for fast refractor?

Hi all,

I'm looking for a good EP match for an f/5 achro. 2" format, focal length between 34 & 40mm, AFOV preferably between 68* & 82*. Edge performance doesn't need to be 100% (not overly important to me. But astigmatism, pincushion & as far as possible field curvature controlled pretty well.

Any suggestions for a ripper rich field EP?

Mental.
Reply With Quote
  #2  
Old 22-07-2013, 08:22 PM
Wavytone
Registered User

Wavytone is offline
 
Join Date: Jul 2008
Location: Killara, Sydney
Posts: 4,147
is there a type you haven't tried ? How about that nice Masuyama ?

Ive culled my surplus ones, though I still have a Skywatcher 2" 28mm LET lying around... That would do pretty well.
Reply With Quote
  #3  
Old 22-07-2013, 09:45 PM
anj026's Avatar
anj026
Plyscope

anj026 is offline
 
Join Date: Oct 2006
Location: Perth
Posts: 518
I'm happy with a 21mm Ethos in my Jaegers 6" f5 achro. The next best choice (especially away from the city) is the 31mm Nagler for the slightly wider field and 6mm exit pupil. Haven't tried a 26mm Nagler but would expect it to be a good compromise.

If I couldn't have those I would look at a 35mm Panoptic or 27mm if viewing mostly from the suburbs.

The f5 ratio is demanding on eyepieces and focusing. When your focal length is 760mm or less then field curvature is hard to avoid for visual.
Reply With Quote
  #4  
Old 23-07-2013, 02:40 PM
MattT's Avatar
MattT
Reflecting on Refracting

MattT is offline
 
Join Date: Jul 2011
Posts: 1,215
This is a hard one Alex.
When I had my 4" f5 achro I couldn't find any eyepiece to do what you want and ended up using a 30mm plossl that gave 3º FOV from memory. It was the only one that had a fairly flat field. Tried ES 28mm 68º and was pretty bad half way out and was only 3.8º... RKE 28??? looks bigger than it is, also not 2" as you know.
Reply With Quote
  #5  
Old 23-07-2013, 03:49 PM
omegacrux's Avatar
omegacrux (David)
Registered User

omegacrux is offline
 
Join Date: Jan 2012
Location: Ulverstone Tas
Posts: 733
Hi Alex
I just have a 2in 30mm gso
Does me fine but when you move it you can notice its not flat !
There cheap as though

David
Reply With Quote
  #6  
Old 23-07-2013, 05:06 PM
mental4astro's Avatar
mental4astro (Alexander)
kids+wife+scopes=happyman

mental4astro is offline
 
Join Date: Jun 2008
Location: sydney, australia
Posts: 4,979
Thanks for the replies, gentlemen.

Wavy, I think there's just a couple of EPs I'm still to try,

David, the Superviews are Erfle designs, which is the most common EP design in binos. Certainly worth a try as I too have the 30mm Superview. I do know some bino EPs have small field stops put into them to control abberations, so the view with the 30mm should be interesting. I tend to forget my old workhorse these days. I'm glad I still have it. I'll report what I see with it in the next few days.

Matt, I too am not too keen on my 28mm Meade SWA in the 4" achro. BUT the 34mm is pretty good I have to say. I'm just getting greedy with wanting even more than the 4.5deg TFOV it gives me. Not that I can get too much more, but a 5deg TFOV sounds mighty goooood!

Haven't tried a 31mm Nagler yet. I'll see what I can do. See Wavy, one I haven't tried yet...
Reply With Quote
  #7  
Old 23-07-2013, 05:50 PM
AG Hybrid's Avatar
AG Hybrid (Adrian)
A Friendly Nyctophiliac

AG Hybrid is offline
 
Join Date: Nov 2009
Location: Toongabbie, NSW
Posts: 1,581
Well in a 4" my 30mm ES 82 gives 3.5 degrees. In yours it will give you 4.5 degrees TF. Reviews indicate the view is nearly identical to a nagler 31. You can have a loan of it next time we meet.
Isn't 4.5 degrees about 9 Moon diameters? Do you really need the 10th?
Reply With Quote
  #8  
Old 24-07-2013, 10:55 AM
brian nordstrom (As avatar)
Registered User

brian nordstrom is offline
 
Join Date: Apr 2007
Location: Perth WA
Posts: 4,374
Hi Alex , H grabbed a SW 100mm f5 , it was cheep and I wanted to see how it performs , anyway , I have found my AT Titan 40mm 2 inch is a great match for this scope , about 13x and its good out to about 75-80 % to the edge , great for deep sky scanning .
Brian.
Reply With Quote
  #9  
Old 24-07-2013, 11:13 AM
Satchmo's Avatar
Satchmo
Registered User

Satchmo is offline
 
Join Date: Dec 2005
Location: Sydney
Posts: 1,875
You're probably enjoying about 70mm of aperture there but they can't take the wide field away from you ...
Reply With Quote
  #10  
Old 24-07-2013, 02:13 PM
mental4astro's Avatar
mental4astro (Alexander)
kids+wife+scopes=happyman

mental4astro is offline
 
Join Date: Jun 2008
Location: sydney, australia
Posts: 4,979
Quote:
Originally Posted by AG Hybrid View Post
Isn't 4.5 degrees about 9 Moon diameters? Do you really need the 10th?
In the words of the Great Austin Powers "YEAH! Baby!"

Can never have enough wide field,

Mark, there in lies a dilemah- stick to exit pupil & lose TFOV. Grab as wide a field as barrel size allows & reduce effective aperture. For my "thing", I'm happy to go a bit big in exit pupil.
Reply With Quote
  #11  
Old 25-07-2013, 10:26 AM
brian nordstrom (As avatar)
Registered User

brian nordstrom is offline
 
Join Date: Apr 2007
Location: Perth WA
Posts: 4,374
Right , but if the last 1/3rd is un-usable is it worth it ?

Brian.
Quote:
Originally Posted by Satchmo View Post
You're probably enjoying about 70mm of aperture there but they can't take the wide field away from you ...

Last edited by brian nordstrom; 25-07-2013 at 10:29 AM. Reason: wrong
Reply With Quote
  #12  
Old 25-07-2013, 02:01 PM
Camelopardalis's Avatar
Camelopardalis (Dunk)
Drifting from the pole

Camelopardalis is offline
 
Join Date: Feb 2013
Location: Brisbane
Posts: 5,425
Have you tried a Paragon? Weren't they supposed to be orthoscopic?
Reply With Quote
  #13  
Old 25-07-2013, 02:05 PM
Satchmo's Avatar
Satchmo
Registered User

Satchmo is offline
 
Join Date: Dec 2005
Location: Sydney
Posts: 1,875
Quote:
Originally Posted by brian nordstrom View Post
Right , but if the last 1/3rd is un-usable is it worth it ?

Brian.
Why would the outer third of your aperture be unusable .
Reply With Quote
  #14  
Old 26-07-2013, 10:48 AM
brian nordstrom (As avatar)
Registered User

brian nordstrom is offline
 
Join Date: Apr 2007
Location: Perth WA
Posts: 4,374
Coma , my friend , Horrendous COMA .. .
Brian.
Quote:
Originally Posted by Satchmo View Post
Why would the outer third of your aperture be unusable .
Reply With Quote
  #15  
Old 26-07-2013, 11:00 AM
Satchmo's Avatar
Satchmo
Registered User

Satchmo is offline
 
Join Date: Dec 2005
Location: Sydney
Posts: 1,875
Quote:
Originally Posted by brian nordstrom View Post
Coma , my friend , Horrendous COMA .. .
Brian.
I think you are confusing the term `aperture' with `field of view' - when I say aperture I 'm talking about the usable diameter of the telescope whose light you are funneling in to your eye, not the the quality of the last 30% of your field of view.
Reply With Quote
  #16  
Old 27-07-2013, 01:29 AM
Wavytone
Registered User

Wavytone is offline
 
Join Date: Jul 2008
Location: Killara, Sydney
Posts: 4,147
Maybe, maybe not... With all lenses there comes a point off-axis where image quality deteriorates really badly, very suddenly. On a small refractor it's quite possible for that to occur within the field of a 2" eyepiece. Winged seagull shapes will be likely.

Alex, there's an LVW42 waiting...

Last edited by Wavytone; 27-07-2013 at 02:31 AM.
Reply With Quote
  #17  
Old 27-07-2013, 11:32 AM
brian nordstrom (As avatar)
Registered User

brian nordstrom is offline
 
Join Date: Apr 2007
Location: Perth WA
Posts: 4,374
WHAT ? , tell me one thing , what use is a full say , 4 degrees of sky if only 2 degrees is usable ? as Wavytone says , seagulls don't do it for me either .
That's where my 40mm AT Titan is OK , seagull city only the last 10-15 % , which is OK ,,, for me .
And every one is different .
Brian.
Quote:
Originally Posted by Satchmo View Post
I think you are confusing the term `aperture' with `field of view' - when I say aperture I'm talking about the usable diameter of the telescope whose light you are funneling in to your eye, not the the quality of the last 30% of your field of view.
Reply With Quote
  #18  
Old 27-07-2013, 05:46 PM
Fox's Avatar
Fox
Registered User

Fox is offline
 
Join Date: Jun 2006
Location: Camberwell, Vic
Posts: 319
Alex, I guess it boils down to field stop. The largest possible field stop for a 2 inch EP is 46mm. IMHO my first choice would be Televue, because Al Nagler obviously has his f/5 scopes in mind. My second choice would be Explore Scientific. If you stick as close as possible to the 46mm maximum field stop for greatest TFOV, a 100 deg vs 82 deg vs 68 deg FOV eyepiece will give you progressively smaller and smaller images for the same TFOV.

I agree with everyone above; I don't see much point in buying somewhat less expensive brands and designs if the outer edges of the field results in stars which look like seagulls and comets. And I would also add that the smaller the focal length of the eyepiece will give smaller images and less contrast - so the sky may look too washed out.

Another alternative - looks as though some manufactures are beginning to make 3-inch eyepieces. Awfully pricey I bet, and perhaps the size of your focuser will start becoming an issue.

Fox
Reply With Quote
  #19  
Old 28-07-2013, 10:05 AM
ausastronomer (John Bambury)
Registered User

ausastronomer is offline
 
Join Date: Mar 2005
Location: Shoalhaven Heads, NSW
Posts: 2,618
Quote:
Originally Posted by Satchmo View Post
I think you are confusing the term `aperture' with `field of view' - when I say aperture I 'm talking about the usable diameter of the telescope whose light you are funneling in to your eye, not the the quality of the last 30% of your field of view.
Hi Mark,

I think you're wasting your time, he hasn't got a clue what you're talking about

Cheers,
John B
Reply With Quote
  #20  
Old 28-07-2013, 11:38 AM
ausastronomer (John Bambury)
Registered User

ausastronomer is offline
 
Join Date: Mar 2005
Location: Shoalhaven Heads, NSW
Posts: 2,618
Quote:
Originally Posted by Satchmo View Post
You're probably enjoying about 70mm of aperture there but they can't take the wide field away from you ...
In fact running the numbers and making an assumption of 50 yrs of age and a 6mm maximum pupil dilation, the scope effectively becomes a 75mm/F6.67 scope. Plenty of wasted light going west there. Even with a 6.5mm maximum pupil dilation the scope becomes an 81mm/F6.1 scope

Cheers,
John B
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 07:03 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Advertisement
Bintel
Advertisement
Testar
Advertisement