Barlow problem or scope limit...

[Unicronicus]

With our 130p scope, having eyepieces like a decent 8mm, 6mm looking at Jupiter produces really nice crisp images. But as soon as we put on our ts optics 2x barlow to either if them the image is hard to focus and blurry around the edges. The colour at the top left of Jupiter is also quite red, and the bottom right edge has a blue tinge to it... It just doesn't seem right.

The useable magnification of our scope is apparently 260x so with a focal length of 650mm, an eyepiece of 2.5mm is our absolute limit, so why would a 2x barlowed 8mm eyepiece (essentialy 4mm) struggle to focus? We're just wondering whether it's our relatively cheap barlow at fault (as opposed to our £70 8mm ep) or something else...

[brantuk]

The useful magnification quoted by scope manufacturers is often exaggerated or dependent on top of the range optics and perfect collimation. So it's not always reliable and I find observing around 150x to 200x is more realistic in most commercially produced scopes (nearer 150x for the 130P).

Plus when you magnify the object you also magnify the atmosphere - so high mag is very dependent on the seeing and weather conditions. Also - as you correctly noticed - the cheaper eye pieces do tend to tail off towards the edges and can introduce a degree of CA to the views - adding a cheap barlow limits it further. Often - a smaller but clearer, sharper, view is better than a fuzzy over magnified view. Hope that helps.

[ronin]

The limit of 260x is a 0,5mm exit pupil that is the limit of the eye.

So if the scope can deliver 260x then the eye is the limiting factor.

If however the scope cannot deliver 260x then the scope is the limiting factor.

Just because someone says 260x it doesn't really mean anything.

One scope running round says just over 3x dia.

Have you not seen these scopes of 50mm that claim 565x ???

Not that long ago the max mag from a scope was said to be 1.5x.

That really is a more realistic value and then it relies on a good scope.

For a 130P I would suggest a max of 180x, even that could be a bit of a problem, 150x would be much happier.

You will start to see coma, a short fast scope is not the scope for high magnification.

The barlow sounds poor, if you are getting colour from planets on a reflector then that means glass problems and the barlow is the most likely. Could be the focuser is not orthogonal - so the eyepieces are not correctly aligned. Sorry but Synta put these together quickly, they are not assembled as precision equipment.

To get 162x you need a 4mm eyepiece and about the only one I know of (before prices go up) is the Vixen SLV (?)

It is quite normal that a collection of eyepieces amount to more then the scope cost.

[andyb505]

On my scope I had problems focusing using the stock 10mm EP with a 2x Barlow. I found the way around it was not too extend the scope all the way but leave it an inch or two short of being fully extended. That allowed me to focus properly.

Not sure it that would apply to your scope as it is not clear if you have the same Heritage 130p flextube.

Andrew

[Unicronicus]

Thanks for the replies, just for this topic though, the image we got of Jupiter through the Barlow is similar (but not as bad as) this...

I also understand how a manufacturers maximum magnification is grossly exaggerated but I think an 8mm and a 2x barlow would look better than the image we were getting.  What Barlow would you guys recommend then for use with decent Eyepieces (the likes of our Vixen NPL, NED8 etc...)? 

[rwilkey]

I find the sweet spot for Jupiter is 150x or a bit higher.  Jupiter does not take any more really.  Saturn, however, can take quite a bit of magnification, around 250x I think is best.  I don't think it's your Barlow at fault, although there are better ones out there, such as the Orion Shorty Plus and so on.  No, I should stick with your standard eyepieces that give you good views at lower magnification.

[Schorhr]

The main problem are the cheap barlows, usually.

I have a no-name 2x achromatic that is identical to the typical 12-30£ achromatic barlows.

And a 3x Bresser.

The color fringe on the 3x is about what your image shows, the 2x for 12£ is a tad better.

Even IF the telescope mirror can not provide 260x, a achromatic barlow will add color fringe, reducing contrast even further.

Seeing, air turbulences, either atmospheric or windows/balcony/neighbor's roof also make focusing impossible at high magnification, a good observing location is important.

Inexpensive eyepieces under 10mm such as Plössl have short eye relief, so 40£ HR Planetary, Bst explorer or TS NED is a solution.

Or the cheaper 27£ gold line / 66 degree UWA for 27£. Nice 6mm wide angle eyepiece, performance is okey at f/5, and still a LOT better then any eyepiece with a cheap barlow.

http://www.ebay.co.uk/itm/wide-angle-eyepiece-1-25inches-66-degree-F-6mm-/140717462903?pt=UK_Telescope_Eyepieces&hash=item20c36a1577 (or check your local tax free values, www.ebay.co.uk/itm/Wide-Multi-Coated-Eyepiece-Lens-6mm-Eye-Relief-Ultra-Wide-for-photo-telescope-/370914950572?pt=UK_Telescope_Eyepieces&hash=item565c40fdac http://www.aliexpress.com/item/Ultra-Wide-Multi-Coated-6mm-ocular-Eyepiece-Lens-for-astronomical-telescope-free-shipping/897540280.html)

by extending the tube you can even increase magnification to an equivalent of 4 or 3mm.

http://blog.pixelgiraffe.com/wp-content/uploads/2014/05/WIN_20140527_223113.jpg

http://blog.pixelgiraffe.com/wp-content/uploads/2014/05/WIN_20140527_223136.jpg

http://blog.pixelgiraffe.com/wp-content/uploads/2014/05/WIN_20140527_223234-1024x576.jpg

(coating inner tube and securing with tape advised)

Good barlows (ed/apochromatic) cost as much as a good eyepiece, easily.

Also check out astrozoom.de, basically doing the same thing as my film can hack, but with neat mechanical adapter. This way you can set your eyepiece to the best magnification the current seeing conditions allow, easily replacing 2 or 3 eyepieces. Can be a bit difficult to attach the 1.25" element under the 2" Astrozoom to a 1.25" focuser, at least with my old version, but works. Compared to other zooms this adapter does not change the apparent field of view's size.

[Unicronicus]

Thanks for the tips, and it's interesting to know about maximum zooms for certain observations. Jupiter through the 8mm NED was the best I had ever seen it! The rings were really prominent, excellent colours, all moons on show easily etc... I just wanted more zoom but obviously that comes at a price... But yes, Saturn seems to love a lot of zoom with a 6mm ultra wide fov and long eye relief ep with a 11/2 x Barlow. It's just when we attach the 2x to anything below, say, 15mm that things start to become hard to focus...

[John]

Zoom = magnification - we tend to use the latter term for it

It's to avoid confusion with zoom eyepieces, which really do zoom !   

[Unicronicus]

Sorry my bad, I would usually refer to it as magnification... :-)

[great_bear]

I've had surprisingly good results and a nice crisp view of the moon from the 130p using a 2.5x PowerMate and 9mm Series 5000 Plossl - that's 180x - although admittedly the PowerMate is a premium item, and results from cheaper combinations have been disappointing.

[AndyWB]

Thanks for the replies, just for this topic though, the image we got of Jupiter through the Barlow is similar (but not as bad as) this..

.

Just saw this thread - how high was Jupiter at the time? That looks a lot like atmospheric dispersion to me - that's the sort of thing I see looking at Venus or Mercury when they're low in the sky. I saw the same thing with Antares a couple of nights ago, too, but it's always low...

Edit: And FWIW, I rarely use more than 5mm on planets in my 130mm. I've had a couple of times where it was worth using a 4mm with the 130p, but to be honest, they were rare. Mostly, it does make things very soft and blurry - though not normally with the rainbow colour scheme....

[Unicronicus]

Cheers for the replies. We bought a better Barlow in the end and it had made viewing more sharper though all eyepieces. Obviously we can't try it on Jupiter now because it's cleared off...

[Merlin]

Now you've lost those lovely rainbow colours .. .

[Don Pensack]

First, is the telescope cooled completely?  Even a scope of that size should be sitting outside cooling for at least an hour or hour and a half before trying high power observations.

Second, is the telescope collimated?  What tool do you use?  Hopefully not an inexpensive laser (which always seems to be miscollimated itself).  You might have better luck with a simple combination sight tube + cheshire tool.  Exact collimation is critical for high power use.

Third, are you maximizing conditions?

--don't look at a planet directly over a roof.  Roofs emit heat at night and this distorts the atmosphere.

--don't look at any planet (except Venus and Mercury) below 30 degrees off the horizon.  You're looking through too much air and the atmosphere will blur the planet chromatically (separating blue and red--and it gets worse as it goes lower in the atmosphere)

--if the jet stream is overhead, it will not be a night for high powers due to blurring caused by scintillation and poor seeing.

--avoid setting up a scope on concrete, where heat escapes nearly all night from the material.  Set up on grass or dirt if you can and heat will not constantly be rising from the ground around you.

--if your scope has a cover over the back of the mirror, remove it.  It will help the scope cool.

And last, if the scope look bad at 1x/millimeter of aperture (130X in your scope), then the optics may have quality issues.  2x/mm is a VERY stringent standard, and any optic capable of delivering a sharp image at that magnification is a truly excellent optic.

Oh, and observe often.  Atmospheric issues vary from night to night and even hour to hour.  If you look often, you'll find that there will be nights when the image is sharper at high powers.  THESE are the nights to attempt the higher powers.

[great_bear]

Don's post above ought to be a 'sticky' somewhere.

Comprehensive yet concise; and the "observe often" tip is particularly valuable - only through this have I learned the capabilities of all my scopes. Now I know, I no longer blame the scope or eyepiece when the view is bad.

[glynnlondon]

+1 for Dons post very informative

[John]

I think Don's post makes a lot of sense but if I tried to follow the guidelines I'd have to give up observing from my back garden where 99% of my observing is done 

[AndyWB]

I think Don's post makes a lot of sense but if I tried to follow the guidelines I'd have to give up observing from my back garden where 99% of my observing is done 

Me too, and I'm not sure I'd ever see Saturn...

Though this bit: 

--don't look at any planet (except Venus and Mercury) below 30 degrees off the horizon.  You're looking through too much air and the atmosphere will blur the planet chromatically (separating blue and red--and it gets worse as it goes lower in the atmosphere)

… is what I meant. I've only ever see Venus and Mercury through a scope a few times, but they've always had that rainbow thing going on. First time I thought it might be a problem with the scope. Later I learnt that it's called Atmospheric Dispersion. Apparently you can get correctors for it, but they're expensive...

[northernstar]

Excellent advice from everyone. Thanks, I have picked up soom good tips that I never knew before.

[Moonshane]

Everything is a compromise. Just make the best of what you have and can see. It is better to have observed and seen (no matter what the quality of the view) thn to have never seen at all. Now where have I heard that before :0)