Quality Barlow?

[Aenima]

Hello astro-ppl,

I'm currently finding issues with my ep's and barlows regarding a colour aberration - namely white light showing coloured edges, redish one side, kind of through a spectrum, to greeny blue the other side (of a star, or Venus etc) of the usual whiteish object. I have a reflector, so narrowed the problem down to cheap lenses in ep's and barlows.

Now really my best option is to buy a quality barlow - I need it for imaging, otherwise would just get a decent eyepiece. But as my aim is both visual and imaging with webcams, I need to find a good quality barlow with minimum CA - Can anyone recommend such a barlow? My approx budget £50 so its a trade-off - economic yet well made lenses - doesn't have to be powerful, just decent quality. If possible.

Any suggestions would be greatly appreciated.

Regards

Aenima

[Naemeth]

TAL x2 Barlow is a great Barlow, although others' will be more knowledgeable than me as to whether or not it's AP friendly. The fact that it is almost always sold out should tell you something .

[FarSide]

I use a celestron X-cel barlow. It's a pretty good barlow if you can ignore some kidney beaning; personally i don't notice it. The Celestron Ultima i've heard is excellent also.

[John]

I've been trying a Revelation 2.5x three element barlow which costs very little. I did not have high expectations for visual use (I bought it for use in barlowed laser collimation) but it actually performs pretty well.

[JamesF]

I'll second John's opinion. I have both the Revelation 2x and 2.5x barlows and use both for planetary imaging.

You will still get some CA of course, because there's one lens you've not yet accounted for: the Earth's atmosphere. Where planetary imaging is concerned that's usually fairly easy to fix in processing though.

James

[alan potts]

I have a powermate x2 which is excellent, but then TV is amoung the very best. I am told these are the tools of choice for imaging. I have to say for the times I use it was a waste of money, still it was second hand so I maybe could sell it for the same as I paided. But the Revelation that John talks about. I was chatting on the phone with someone at Telescope House and they were well impressed with a great deal of the Revelation gear, they spoke very high of the APO scopes.

Alan.

[sologuitarist61]

I'm not sure, but aren't Revelation a GSO rebrand?

[alan potts]

I'm not sure, but aren't Revelation a GSO rebrand?

I wish they re-beanded Teele-Vue's

It strikes me there is a great deal of eyepiece on the markets that are the same glass made in the samre factory in China with different clothes on and in a different box, most likely with a different price. I mean look a Meade they just moved a good deal of the 5000 range and beranded it Bresser.

Alan.

[JamesF]

It strikes me there is a great deal of eyepiece on the markets that are the same glass made in the samre factory in China with different clothes on and in a different box, most likely with a different price.

I think that's very true. There appear to be far more astronomy "brands" than there are manufacturers, some just rebadging the complete kit whilst others just use the optics, and some sourcing from one manufacturer whilst others source from several.

Revelation eyepieces are to the best of my knowledge just rebranded GSOs. I don't know about the Revelation telescopes though.

James

[John]

I'm not sure, but aren't Revelation a GSO rebrand?

Yes they are. GSO re-brands are all over the place, and generally pretty good pieces of kit for their cost. Re-branding is extremely common with Astro equipment and can cause confusion !

[alan potts]

Re-branding is all over the place, When I worked I set up production of UK models all over the world, The same model, different name, different colour, twice the price, and that is only bathroom suites. With eyepieces it is going on in the same factory. When I got my 40mm Aero which in the states was called Astro Professional, I think. I was real pleased with it coming back on the plane. Took it to Sofia to show my friend the Meade dealer and he said ,'nice I got one of them, its a sky watcher Aero". There was me thinking I had something special.

Alan.

[John]

A while back TMB Optical marketed a 2" eyepiece range called the Paragon. Although these looked different from the Aero ED and clones, the general consensus seems to be that the optics are the same. The Paragon's were well thought of:

http://ejamison.net/...t_reviews6.html

One area that it's much harder to pin down is the exact specification that each brand has commissioned from the manufacturer. Aspects such as the quality of coatings, where they are applied, interior light baffling and lens edge blackening can all be varied to "fine tune" the performance of the eyepiece, sometimes quite noticeably. So what externally looks the same eyepiece can actually perform rather differently.

There are also rumours that the manufacturers quality control systems throw up graded products, say "A", "B" and "C" for the sake of argument. I seems to me that a brand that commissions high volumes could expect (and demand) to be assigned the "A" graded products with the others going to "lesser" brands and unbranded sales.

One of the attractions of the Tele Vue range is that each eyepiece is tested by Tele Vue to work well down to F/4 before being released for sale.

[Aenima]

Well, first off Thanks for the many responses, its clear the issue is not quite straightforward. Although I know little about the actual brands and who might have made them, I did notice that under a certain price level your pretty much looking at very similar optics with a mixture of 'names' on the boxes, I have tried a 'Revelation Astro 5x' and although it seemed top quality and had Revelation in its name, when used it was bog-standard in performance and glass/coatings appeared little different than the SW stock x2 barlow supplied with my scope.

I definitely agree with the lottery as to branding and 'more names than product' theory, but end o' the day I need a reliable but not overpriced barlow, i saw a few promising suggestions above (thank you) and some great advice/guidance i'm just hoping to find an item generally agreed to be of decent quality for the price.

Thanks again,

Regards

Aenima

[alan potts]

Excellent piece John and I agree.

I think a nice little task for you , if your willing, while the clouds and rain are preventing observing. Use your vaste knowledge to group together what you think are the same eyepieces that are available in the marketplace. I think it goes without saying to pass off the coating issue as you would never be able to tell.

What do you think,

Alan.

[LukeSkywatcher]

I have a Revelation 1.5-2X barlow and so far i have found it useless. I cant see anything with it. It must be a monday morning barlow.

[Aenima]

Thanks paul, its the experience of the people that have used these items that i'm hoping to hear from. So cheers 4 that.

Every input helps, and so far im narrowing my search down slowly but surely. My view so far has been of one or two excellent favourites that cost loads, and the vast array of cheap, vaguely named products that originate from similar manufacturers. As my budget is approx £50, I have been looking for that miraculous compromise of cost and quality.

As of now the Meade x2 'shorty' and celestron x2 (silver colour) omni or x-cel i think it's called, are looking good. Ebay, unsurprisingly, has many to offer but its a lottery.

Anyone else able to offer any of their personal experience of a suitable model that I can add to my checklist, I would be very grateful, many thanks.

Regards

Aenima

[John]

.....As of now the Meade x2 'shorty' and Celestron x2 (silver colour) omni or x-cel i think it's called, are looking good...

Obviously it's your call at the end of the day but the Meade Shorty and Celestron Omni 2x barlows are not of the same optical quality as the TAL 2x, in my opinion. The current Celestron X-Cel LX 2x barlows cost nearly £100 so I assume you mean the Omni here.

The TAL gets constant recommendations on here because it's optically really good for a < £50 barlow. I think you will struggle to equal it for that budget to be honest. There are others that look better finished though.

[Aenima]

Right, ok, good. Thats 2 ups for the Tal, and following the advice of the first post that recommended Tal, I looked online and yep, sold out everywhere - that does say a lot.

Thank you, John. This is the kind of thing that really helps, if I were to believe the blurb that the companies write to sell the items EVERY barlow would be the best choice and give excellent views etc. So thanks for the input, much apprciated!

Regards

Jay - Aenima

[LukeSkywatcher]

I'm sure my experience with the Revelation is not widespread. If i was to buy another barlow, i would go for the Tal without a seconds thought. Its simply brilliant for the price.

[miguel87]

rother valley optics online currently have TAL barlows in stock, got mine today.

[Aenima]

Wah, just checked....must have missed them.

Ta anyway.

Regards

Jay

[paul schofield]

+ 1 for the Tal x 2 if you can find one. Great for the £'s. Failing that I would look at Televue powermate if the budget stretches. Never tried a powermate but have a feeling I will be doing in the not too distant. And I have only heard really positive reviews of them.

[michael.h.f.wilkinson]

Incidentally, the effect you describe does not quite tally with chromatic aberration (CA) in the optics. CA produces red/yellow or blue/violet fringes, symmetrically around a stellar object in the centre of the FOV, with the colour very much sensitive to the exact focus. The "rainbow" effect you describe is due to some prismatic effect in the optical pathway. I get coloured fringes on Venus, red to one side, green/blue to the other, through a TV Radian 10mm in my C8, with or without a Meade TeleXtender 2x. This has nothing to do with the optics, but with atmospheric refraction (the atmosphere acting like a giant prism). I get the same effect on any planet or bright star at low altitude. In planetary AP you can (partially) correct for that in Registax (RGB-align tool). Be sure your current barlow is really the problem, otherwise, save up for a really good one, rather than getting something which might not be much better than your current one.

Furthermore, you might want to look at a more powerful barlow, as I find F/20 - F/30 is the best range for planetary AP with many webcams (including the SPC900 or the DMK/DBK/DFK21 series). A 2x barlow gets you F/10 in your scope, so a 4x barlow would be better.

[Naemeth]

Incidentally, the effect you describe does not quite tally with chromatic aberration (CA) in the optics. CA produces red/yellow or blue/violet fringes, symmetrically around a stellar object in the centre of the FOV, with the colour very much sensitive to the exact focus. The "rainbow" effect you describe is die to some prismatic effect in the optical pathway. I get coloured fringes on Venus, red to one side, green/blue to the other, through a TV Radian 10mm in my C8, with or without a Meade TeleXtender 2x. This has nothing to do with the optics, but with atmospheric refraction (the atmosphere acting like a giant prism). I get the same effect on any planet or bright star at low altitude. In planetary AP you can (partially) correct for that in Registax (RGB-align tool). Be sure your current barlow is really the problem, otherwise, save up for a really good one, rather than getting something which might not be much better than your current one.

Furthermore, you might want to look at a more powerful barlow, as I find F/20 - F/30 is the best range for planetary AP with many webcams (including the SPC900 or the DMK/DBK/DFK21 series). A 2x barlow gets you F/10 in your scope, so a 4x barlow would be better.

Since the Barlow alters the focal ratio of your scope, does it therefore require more exposure time to correct for it being effectively a slow scope?

[michael.h.f.wilkinson]

Since the Barlow alters the focal ratio of your scope, does it therefore require more exposure time to correct for it being effectively a slow scope?

The focal ratio in planetary photography must be matched to the pixel size of the CCD to capture all possible detail (technically, you want to sample the image at the Nyquist frequency). Planets have high surface brightness, so being slow is not really an issue.