Go Back   IceInSpace > Equipment > Equipment Discussions

Reply
 
Thread Tools Rate Thread
  #1  
Old 24-01-2012, 06:01 PM
04Stefan07 (Stefan)
Make it so! - Capt.Picard

04Stefan07 is offline
 
Join Date: Jan 2012
Location: Melbourne
Posts: 1,982
Maximum Mag for a telescope, your thoughts

I just wanted to get everyones opinion on powerful EP's.

For my scope (in my sig) what would be the maximum you would go for an EP?

My guess I am thinking between 5mm-7mm?
Reply With Quote
  #2  
Old 24-01-2012, 06:24 PM
AndyK's Avatar
AndyK (Andy)
VK2AAK

AndyK is offline
 
Join Date: Aug 2011
Location: Darawank NSW 2428 Australia
Posts: 84
I think the rule of thumb for maximum practical magnification is 50 times the aperture in inches.
So, for a Celestron 130 that would be 50 x 5 (130mm = 5.1") giving you a maximum practical magnification of 250.
The magnification of a telescope can be found by dividing the focal length of the scope by the focal length of the eyepiece.
I believe your scope has a focal length of 650mm and by juggling the formula and dividing this by the practical maximum magnification, we can arrive at the corresponding eyepiece focal length.
In this case this would be 650 divided by 250 which comes out at around 2.6mm

A 5mm focal length eyepiece on your scope would give you a magnification of 650/5 or 130, which should be well within the capability of the scope.
Reply With Quote
  #3  
Old 24-01-2012, 07:43 PM
Rodstar's Avatar
Rodstar (Rod)
The Glenfallus

Rodstar is offline
 
Join Date: Jan 2005
Location: Central Coast, NSW
Posts: 2,702
Hi Stefan, the 50x per inch rule Andy refers to would only apply in almost perfect conditions. I have a 20 inch scope, and I have NEVER, in almost 5 years, gone higher than about 500x. Under average conditions, I tend to stay at about 200x, which would translate to about 10x per inch.

Andy's suggestion that you only go to about halfway on the 50x per inch rule is no doubt much closer to reality, and even then, in very still conditions only. If you are looking to invest in a good EP, you will use high power eyepieces the least, and midpower eyepieces the most. I expect something around the 10mm mark would be close to your sweet spot.
Reply With Quote
  #4  
Old 24-01-2012, 08:06 PM
AndyK's Avatar
AndyK (Andy)
VK2AAK

AndyK is offline
 
Join Date: Aug 2011
Location: Darawank NSW 2428 Australia
Posts: 84
Thanks Rod. Yes, I should have explained that the figures I gave were only really applicable to almost perfect seeing conditions.
Even though 2.6mm gives the maximum practical magnification, that's unlikely to be usable.
Even half that magnification ... a 5mm eyepiece ... could be stretching things much of the time.
Perhaps a suggestion would be to invest in a good 10mm eyepiece as Rod suggests and complement that with a decent 2X Barlow ... then if conditions are excellent you can use the Barlow and the 10mm to give you 5mm.
Remember that investing in good eyepieces is just that ... an investment. A nice Barlow and a good 10mm eyepiece are likely to stay with you even if your telescope changes in the future.
Reply With Quote
  #5  
Old 24-01-2012, 08:14 PM
astroron's Avatar
astroron (Ron)
Supernova Searcher

astroron is offline
 
Join Date: Mar 2005
Location: Cambroon Queensland Australia
Posts: 9,313
Quote:
Originally Posted by Rodstar View Post
Hi Stefan, the 50x per inch rule Andy refers to would only apply in almost perfect conditions. I have a 20 inch scope, and I have NEVER, in almost 5 years, gone higher than about 500x. Under average conditions, I tend to stay at about 200x, which would translate to about 10x per inch.

Andy's suggestion that you only go to about halfway on the 50x per inch rule is no doubt much closer to reality, and even then, in very still conditions only. If you are looking to invest in a good EP, you will use high power eyepieces the least, and midpower eyepieces the most. I expect something around the 10mm mark would be close to your sweet spot.
Thanks Rod you said it for me
I was just about to post something similar when I read your post.
I could never see a 5" scope using that sort of magnification
Cheers
Reply With Quote
  #6  
Old 24-01-2012, 08:34 PM
04Stefan07 (Stefan)
Make it so! - Capt.Picard

04Stefan07 is offline
 
Join Date: Jan 2012
Location: Melbourne
Posts: 1,982
Thanks for the help!!
Reply With Quote
  #7  
Old 24-01-2012, 10:48 PM
g__day's Avatar
g__day (Matthew)
Tech Guru

g__day is offline
 
Join Date: Dec 2005
Location: Sydney
Posts: 2,807
My most used eyepieces were the two longest focal length (lowest magnification) ones. Agree with the above - in average seeing I use 30x as a maxium rule.

Lower magnification is kinder for seeing issues.

I'll add another rule - high quality apo's - from their design work better at maxium magnification than SCTs, the central obstruction gives you another factor to compensate.

The other consideration is only a handful of objects love magnification - the Moon, Jupiter, Mars, Saturn, Omega Centurai - a lot look great at lower magnifcation if you have sufficent light grasp.

Finally eye pieces have vastly different wow factor based on design and price. A plossl variant costing around $60 - $90 isn't going to remotely compare with a $250 - $300 Vixen LVW eye piece, which is behind a $500 - $600 Nagler which is far behind the Ethos maxing out at around $850 - $900. I'd prefer to have a smaller set of really satisfying eye pieces that a great swarm of un-impressive ones.

Look at the second hand sales - you can find some good bargins!
Reply With Quote
  #8  
Old 25-01-2012, 05:07 AM
Rodstar's Avatar
Rodstar (Rod)
The Glenfallus

Rodstar is offline
 
Join Date: Jan 2005
Location: Central Coast, NSW
Posts: 2,702
Quote:
Originally Posted by g__day View Post
The other consideration is only a handful of objects love magnification - the Moon, Jupiter, Mars, Saturn, Omega Centurai - a lot look great at lower magnifcation if you have sufficent light grasp.
I am surprised that that is your experience. For me, under steady conditions pretty much any object will eat up magnification. I have seen incredible detail in the full range of objects under high power. I guess I have the benefit of 20 inches light grasp.

Even under average conditions, I find that galaxies will hold up to magnification pretty well. That ends up being my dilemma when observing from the backyard (surburban) in average seeing conditions; do I go for the faint fuzzies at high power, which may be a bit washed out due to light pollution, or do I go for the local stuff, where seeing is compromised.
Reply With Quote
Reply

Bookmarks

Tags
ep's, magnification, scope

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 07:07 PM.

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