Chromatic Aberration on OEM 2x Barlow?

[Guest]

I've noticed a couple of times recently whilst using an OEM 2x Barlow lens, some chromatic aberration.  It's not there when just using the EP alone.  As it's a cheap plastic 2x Barlow, would this be considered normal? Would upgrading to a better 2x Barlow remove the chromatic aberration?

Edited March 5, 2020 by Guest

[Ruud]

You are probably right.

There's also the possibility for a good Barlow to reveal the CA of a refractor (do you use a refractor?) but the way you describe your Barlow, I suppose it's the Barlow that is to blame.

[joe aguiar]

Ya I agree change Barlow to good one.

When I first got into hobby I was sure I could tell the smallest difference when I had a very good Barlow and ep compared to just Barlow.

So I started using ep only if I can.

If u have st scopes this may not work u may need a Barlow. 

So in a cheap Barlow I'm sure the quality of the image is much worse

Joejaguar 

[Guest]

54 minutes ago, Ruud said:

You are probably right.

There's also the possibility for a good Barlow to reveal the CA of a refractor (do you use a refractor?) but the way you describe your Barlow, I suppose it's the Barlow that is to blame.

It's a reflector, a Meade 114-900 circa 2000 vintage...

[Guest]

42 minutes ago, joe aguiar said:

Ya I agree change Barlow to good one.

When I first got into hobby I was sure I could tell the smallest difference when I had a very good Barlow and ep compared to just Barlow.

So I started using ep only if I can.

If u have st scopes this may not work u may need a Barlow. 

So in a cheap Barlow I'm sure the quality of the image is much worse

Joejaguar 

It's a f8, so I guess that's considered slow....  I was more used to f numbers back in the 35mm SLR days...

[mikeDnight]

I find the Skywatcher 2X Delux barlow to be excellent. I've used one in my Takahashi apochromat for years and the views are totally colour free. 

[Louis D]

Personally, I find the TV 2x Barlow, Meade 140 APO 2x Barlow, and Orion Deluxe Japan 2x Fully Baffled Barlow are all color free and super sharp.  They are all medium to long Barlows and only the TV is available new.  I have a cheap, generic 2x shorty Barlow that is so bad, a friend returned it to me after I gave it to him to get him started in astronomy.  He literally didn't want to keep it because it was so bad.  It wasn't exactly cheap at $30 20 years ago.

[Waldemar]

Reflectors do not have chromatic aberration normally, so your problem is the Barlow. The used lenses inside the Barlow may be plastic like the outside...
 

[Guest]

5 hours ago, Waldemar said:

Reflectors do not have chromatic aberration normally, so your problem is the Barlow. The used lenses inside the Barlow may be plastic like the outside...
 

They do feel like plastic. Testing with and without the Barlow confirmed it was the culprit. 

[Alan64]

I got this rogue's gallery with my Meade "Polaris" 114/900, and a current model...

Indeed, the plastic 2x barlow, and probably with a plastic lens(es) even, introduced considerable false-colour, and with Newtonians being 100% apochromatic, colour-free, in the first place.

In addition, the images through the eyepieces exhibited graininess.  The telescope, however, is excellent, as I had tested it with my better eyepieces. 

Did your Meade 114/900  come with a .965" visual-back, eyepieces and barlow?

[Guest]

8 hours ago, Alan64 said:

Indeed, the plastic 2x barlow, and probably with a plastic lens(es) even, introduced considerable false-colour, and with Newtonians being 100% apochromatic, colour-free, in the first place.

In addition, the images through the eyepieces exhibited graininess.  The telescope, however, is excellent, as I had tested it with my better eyepieces. 

Did your Meade 114/900  come with a .965" visual-back, eyepieces and barlow?

Here's the original EP's, all 1.25 inch. The 2x Barlow looks cheap and nasty... Time for an upgrade, in the near future... 

[joe aguiar]

Yep Barlow needs upgrade look on the used market 

UK astro buy and sell

U may also upgrade the eps too if u can afford it even to plossls or super plossls will be much better

joejaguar 

[Guest]

2 hours ago, joe aguiar said:

Yep Barlow needs upgrade look on the used market 

UK astro buy and sell

U may also upgrade the eps too if u can afford it even to plossls or super plossls will be much better

joejaguar 

You mean like this? 🤔😉

[joe aguiar]

yes those are much better then the oringinals

some may even say even better eps but I think these here are decend and can last many years unless you just want a wider fov

joejaguar

[Alan64]

A 2x-barlow serves two purposes, in so far as visual-use...  

1. The economical aspect,  in combining a barlow with 2 or 3 eyepieces resulting in 4 to 6 differing powers.  In carefully selecting the eyepieces to combine with the barlow, the goal is to avoid duplications.  For example, if you barlowed a 20mm, and for a simulated 10mm, you would not need a dedicated 10mm; and so on.  You might then choose an 8mm, 12mm, or 15mm instead.

2. The ergonomic aspect, in avoiding a 4mm eyepiece for example, and with its tiny eye-lens and tight eye-relief.  Instead, you would barlow an 8mm or 9mm, and with their larger eye-lenses and greater eye-relief.  Now, that's when dealing with orthoscopics and Plossls.  There are eyepieces that have barlowing lens-elements built in; for example...

Note the generous eye-lens, and for a 4mm eyepiece.  Then, compare it to this 4mm symmetrical-Ramsden...

Such enhanced eyepieces also offer slightly wider fields-of-view over Plossls.  Plossls are the current, minimum standard in performance-eyepieces, and they have come down in price considerably within the last several decades.  "MA" stands for modified-achromat, like the ones that came with our Meade kits.  Eyepieces that are less complex than Plossls, and even cheaper to produce -- modified-achromats, Huygenians, Ramsdens -- do work well with telescopes with longer focal-lengths, like our own.  Since they do in fact, the manufacturers tend to include them with all entry-level telescope kits, albeit regardless of a given telescope's focal-length.  In that enterprise, the rubbing of two copper coins together makes four or more.

Although, that 4mm Ramsden illustrated there, from a kit, has astounded me, albeit when paired with its 127/1000 telescope.

Don't hesitate to acquire quality eyepieces, barlows and other accessories for your telescope, for unlike telescopes those items can be used with other telescopes that may be had in future.  They're wonderfully interchangeable; and like luggage, they are with us for a lifetime.

Plossls... https://www.365astronomy.com/GSO-Super-Plossl-Eyepieces/

An example of a quality barlow, and one that I have myself... https://www.rothervalleyoptics.co.uk/antares-x2-achromat-fmc-barlow-lens-125.html

Enhanced eyepieces... https://www.firstlightoptics.com/bst-starguider-eyepieces.html

Of those, the 8mm and 12mm have been reviewed most favourably.

That's another nice thing about telescopes with longer focal-lengths, in that you can get quality performance with all of those eyepieces, including the simpler ones, and for relatively little outlay.

[John]

The image is only as good as the weakest link in the optical chain. In this case I think it's clearly the cheap barlow lens. There are pretty good ones available at reasonable cost as mentioned in the posts above.