Quote:
Originally Posted by drrockso
Hey Folk!
Thanks for building up such an informative community. It has been very helpful so far.
I recently bought a used 150EQ. It was nice and cheap and meant that if we (the family) lost interest, our buy in was low. The mount is a bit wobbly (even wind) and the finder scope is utter rubbish(plastic with so much play that adjusting it using the knobs moves the FS in its mount completely moving alignment). But the scope works :-)
But as it seems, I need more. Last night we managed to see Saturn through the 10mm EP and that was great but man it was small. So i'm looking to buy new Barlow I think, to double or triple the existing 10&20mm EPs we have.
Now I dont particularly want to buy more cheap ... stuff so what would be recommended and while i'm asking questions. Does the Barlow affect the FoV at all?
I understand I will be spending more then I did on the scope on any EPs and Barlow's and I guess that's ok.
Cheers all
John |
Welcome to the universe. While your first scope may not be the top of the line it is certainly good enough to get you started.
With a 150 mm aperture the scope should be capable of going up to 300X. Unfortunately the atmosphere will often prevent you from working that high.
Transparency and Seeing - Note that atmospheric conditions, rather than your telescope, will often be the limiting factor on practical magnification for any given observing session. When the atmosphere is turbulent, poor “seeing” conditions, you may find that the image breaks down too much above a certain magnification regardless of the size of your telescope. Transparency is also a factor that can be affected by humidity, air pollution and thin clouds that you may not be able to see. My 8”/203 mm often tops out around 180X due to “seeing” and transparency issues. However, under exceptional conditions I have been able to go 300X or higher.
As for field of view. Some simple formula will help you.
Focal Length scope / Focal length eyepiece = magnification
Apparent field of view, AFOV, is a specification provided with most eyepieces.
AFOV/ magnification = field of view.
So, as you go up in magnification you go down in field of view. This is a matter of physics.
The only way to address this is to buy eyepieces that have wider AFOV specs. This usually raises the price.
Selecting an eyepiece - Orion telescope
This is a very general discussion of eyepieces and why there are a variety of designs. Ignore that it is done by Orion as everything he says applies to virtually all eyepieces from all manufacturers.
https://www.youtube.com/watch?v=m7u9Q5hV7yc
Barlow
Considering the 150 mm aperture of your scope and your current eyepieces I would suggest a 3X barlow. That would take you to 37X, 75X, 111X, 225X using your current eyepieces. Under reasonably good skies 225 shoudl be a useful magnification.
I am in the USA so you will have to check local suppliers. Here is a sample.
http://agenaastro.com/catalogsearch/...?q=3X%20barlow
GSO and Antares have very good reputations at moderate prices.
Eyepieces
I am very partial to zoom eyepieces. I have two. The Celestron and the Baader Hyperion 8-24.
http://agenaastro.com/eyepieces/zoom...anetarium.html
Eyepiece Strategy
For each of my scopes I have one or two low power wide view eyepieces. For your scope that might be a 32mm Plossl Plus your 20 mm.
Then I have a zoom which I use for 8-24 mm but frankly I use it mostly in the 8-18 mm range.
Then, for high power I put the zoom in a barlow appropriate to the scope I am using. In your case I have recommended a 3X barlow.
In your scope that would give you 31.5X to 93.75X. Drop it in a 3X barlow and you have 94X to 281.5X You would have every magnification between 31.5X and 281.5X.
- I never expected the zoom eyepiece to become my primary eyepiece, but it has.
- The Celestron 8-24 zoom is good and comparable to my Plossl eyepieces ($65)
- The Baader Hyperion is great and comparable to my Explore Scientific eyepieces ( $289)
- Watching doubles split as I rotate the barrel is wonderful
- One filter serves over a wide range of magnifications, no screwing and unscrewing to try other eyepieces
- Moving smoothly from and between small changes in magnification helps when seeing is not the best
- I am always working at the optimum magnification for this target.
- Sharing the view with others is easier, especially in my manual tracking Dob - I hand it over at low mag so it stays in the view longer. They zoom back in to whatever magnification works best for them.
- My eyepiece case has been greatly simplified
- Kids love the zoom