ICEINSPACE
Most Read Articles
Moon Phase
CURRENT MOON Waxing Crescent
11.2%
The Sun Now
Time Zones
Sydney*
5:50 am
Perth
2:50 am
Auckland*
7:50 am
New York
1:50 pm
Paris
7:50 pm
GMT
6:50 pm




  #1  
Old 19-09-2018, 10:55 AM
Mooned (Ed)
Registered User

Mooned is offline
 
Join Date: Aug 2018
Location: Sorrento, Australia
Posts: 2
Barlow fuzzy

I recently bought the National Geographic 76/700 EQ for my kids to look at the moon and planets. I'm not expecting much!
But have hit one major issue when it comes to the Barlow lens and I hope that someone can help.
When I look at the moon for example, it is sharp and clear with all the eyepieces. But when I try to add in the 2x Barlow that came with the telescope I find that I wind the focus in and the image gets sharper, but it doesn't fully sharpen before I hit the limit of travel.
Looking at other threads I can see that the actual Barlow is probably not great quality so may not be perfect, but the fact that it seems to be continuing to get sharper until I run out of travel makes me wonder if there is another issue at work here?

Can anyone help? Thanks in advance!
Reply With Quote
  #2  
Old 19-09-2018, 11:28 AM
bojan's Avatar
bojan
amateur

bojan is offline
 
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 5,417
Most likely the main mirror is not at right distance, try to move it a bit by adjusting colimation screws (of course, you will have to colimate the scope after this, pages 14 & 15 of user manual, attached).
You did not indicate in which direction you are moving focuser... knowing that will tell you in which direction the main mirror should be moved.

BYW, this barlow is most likely really bad, I think it is single negative lens (and probably made of plastic), so perhaps you should just forget about it.
Attached Files
File Type: pdf All About Telescopes from Skywatcher.pdf (490.5 KB, 3 views)

Last edited by bojan; 19-09-2018 at 11:45 AM.
Reply With Quote
  #3  
Old 21-09-2018, 02:13 PM
Mooned (Ed)
Registered User

Mooned is offline
 
Join Date: Aug 2018
Location: Sorrento, Australia
Posts: 2
Thank you Bojan, very useful. Would you have a recommendation for a Barlow that would be a good choice - in the budget range but good enough to allow a little detail in planetary viewing?
Reply With Quote
  #4  
Old 21-09-2018, 04:30 PM
bojan's Avatar
bojan
amateur

bojan is offline
 
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 5,417
I have Meade 2x Telenegative (doublet), it is not bad, I bought it on ebay (from China) for ~$30 10 years ago... Recently I tried to use it on Mars with my 10"and Canon 60D, results were quite good.

I can see that that model is now selling on ebay for 2x as much....


Don't spend too much for new Barlow, the performance of your scope doesn't warrant expensive accessories. Sort the focus first, because you will most likely have the same issue with another barlow anyway.

Perhaps the better option is to buy a short eyepiece (Ortho?) (4~5mm FL)
Reply With Quote
  #5  
Old 24-09-2018, 09:02 AM
sil's Avatar
sil
Registered User

sil is offline
 
Join Date: Jun 2012
Location: Canberra
Posts: 1,119
That model scope package comes with a 3x barlow of hideously cheap design and build using plastic optics. a 2x barlow may work to focus better, if you're winding the focuser out and hitting limit before getting focus you need to get a small extension tube to bring the barlow out a bit further to the focal point. This is a bottom of the range scope , you are paying for Nat geo to put their logo on a generic unbranded product, so what it comes with is not necessarily what it is capable of using. Mostly likely someone somewhere said "chuck in a few extras, we need to shift more of these scopes". The scope tube should be ok, but everything else is made down to a budget only, tripod, eyepieces, finderscope, barlow, etc. I dont recommend buying a small eyepiece eg below 6mm, as you get blurring anyway from the atmosphere. A barlow magnifies this blurring anyway and people blame the blur on the wrong thing.

Yours certainly seems to be an issue of not reaching focus with the barlow. As Bojan suggests it could be a colimation issue which means the optical path is a tad longer or shorter than it should be meaning when you add the barlow you're now out of the focal point range. the build accuracy of cheap scopes is not great and if you've bought this second hand someone else may have messed with things without understanding. It does seem a distance problem wherby the focal point of the scope is not in the small range it was constructed to have, which can only really be done by poorly collimating the scope.
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 04:50 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Advertisement
Atik Horizon
Advertisement
SkyWatcher WiFi Adaptor
Advertisement
Lunatico Astronomical
Advertisement
OzScopes Authorised Dealer
Advertisement
NexDome Observatories
Advertisement
Interest Free Finance
Advertisement
FLI Cameras and Imaging Accessories
Advertisement
SkyWatcher 2018 Catalogue
Advertisement
Bintel
Advertisement
Astronomy and Electronics Centre
Advertisement