Is a 2 lens barlow decent for planetary viewing?

[Ahgii]

Hello, i am a relatively new astronomer, got my telescope just a few weeks ago, along with a barlow, that came later. At first i thought my barlow had just 1 lens because it was only 1 piece, didnt know they were sticked together, than i saw a barlow review video on yt and realised how to find out how many lens my barlow had. I realised it actually had 2 lens, for a fair price. And my question is, is a 2 lens barlow at least decent for planetary viewing. I imagine it is since i saw good quality expensive barlows, also good brands, who had 3 lens in the barlow. Clear skies!

[Ben the Ignorant]

Yes, a barlow with two lenses made of ordinary glass is good enough for high resolution, but barlows with special "ED" glass are better, and three-lens or four-lens barlows are further improvement, but not at the very center of the image, which is already excellent starting from two-lens ED units.

The advantage of three-lens and four-lens focal multipliers (that's what barlows do) is the image quality is maintained over a larger section of the field, sometimes the whole field, but that also depends on the telescope and eyepiece. If you use a tracking telescope, the planet stays in the center of the field all the time, so a double-lens ED barlow is enough.

But if your scope doesn't track, like a dob, the target does not remain centered, thus you need a larger corrected field. Then extra lenses make financial and practical sense.

[mikeDnight]

Hi Ahgii,

Modern two element Barlows are very good value and are excellent for viewing the Moon and planets.They allow you to use longer focal length eyepieces which are more comfortable to use than short ones with less eye relief. I use a cheap SkyWatcher delux Barlow regularly for observing the Moon and planets with my 100mm apochromat. There is no noticeable false colour introduced by the Barlow, and on occasion I even double stack Barlows to get very high power. Views are sharp to the edge and contrast is not reduced by barlowing an eyepiece.

Mike

[Dave In Vermont]

An inexpensive Barlow of 2X - photo below - is good not only for planets and the Moon. If you unscrew the 2-lens element - shown in the lower photo - this can be screwed into an eyepiece and will give you between 1.5X and 1.6X. It simply screws in the same way as you would screw in a filter.

So one of these can do double-duty! Getting one of these is a win-win situation.

Enjoy -

Dave

 

 

 

[Louis D]

I would stay away from the cheapest 2 element 2x shorty barlows.  I have a no-name one I picked up years ago for $25 that noticeably blurs the image compared to my 2 element TV 2x barlow which is more of a mid-length barlow.  That no-name is so bad I gave it to friend who then disliked it so much he regifted it back to me in 6 months time. 

I also have a 3 element Meade 140 barlow from the 90s that yields basically the same views, so the extra element doesn't make much difference when compared to an excellent 2 element barlow.  Vintage long barlows such as the Japanese made Orion Deluxe from the same era are also excellent.

The most important thing to keep in mind when choosing a barlow besides optical quality is whether or not you can reach focus with it.  Vintage long barlows often require too much back focus for refractors when using a diagonal, but are fine in Newtonians because you can just insert them way down into the focuser.  SCTs and Maks can accommodate pretty much anything in the focuser, so no worries there.