Is there much difference

[crush]

Hi all,

I have read a lot about Barlows, TeleXtenders and Powermates but can't seem to find a good comparison. It may be the way I am searching but the last one I found was from 2012 so not sure it is still relevant.

Is there a lot of difference between them or is it just preference?

If I have understood correctly they all increase the power of the EP and change FL of the scope. Happy to be corrected if I have misunderstood.

Is one better than the other? 

Is it a quality thing?

Thank for reading.

[Elp]

PM are generally the best of you want minimal CA showing up and less optical distortion, you'll notice it a lot more when imaging.

[John]

Powermates are simply superb. I've not used them for imaging but for observing they just get out of the way and you only see the boosted magnification. I have owned many barlows and a couple of ES and Meade Telextenders but, IMHO, the Powermates set the pace for others to try and follow. And you pay for that, of course.

The barlows that I've used that might compete with a Powermate in terms of optical quality are the Baader VIP barlow and I believe the Baader/Zeiss barlow is very, very good as well. But barlows do impact focal position and eye relief whereas Powermates (and Telextenders) either do not, or do so less. Ditto with vignetting when used with some longer / wider eyepieces.

 

 

Edited March 3 by John

[Ratlet]

I think barlows extend eye relief.  Don't remember by how much though.  Can be useful if you have a set with short eyerelief, though it can make a long eyerelief eyepiece awkward to use as it can get so long you need to hover to avoid blackouts.

[woldsman]

The main difference between a powermate & a standard Barlow is that the PM is a 4 element optical design whereas the Barlow is usually only 2. This leads to vignetting & other issues with the Barlow. A telextender is also a 4 element design. I only have a x2.5 PM (which is very good) but the performance difference over a telextender will be much less, I would think, than with other Barlows. 

[Stu]

As I understand it, the PowerMates and TeleExtenders maintain the eye relief of the eyepiece whereas Barlows extend it outwards. This can be useful for short focal length orthos for example, or annoying for long focal length plossls where the long eye relief can make eye positioning difficult.

I’ve used x2.5 PMs before and found them excellent. Barlows can be too though, I have a Zeiss Abbé Barlow and the quality is superb.

[crush]

Thanks for the replies, looks like I should save a bit more for a Powermate then.

[Second Time Around]

This is my understanding of the difference between Barlows and Powermates (Televue's name for focal extenders).

The reason focal extenders have 4 elements is that they have to first make the rays from the objective parallel.  Barlows don't do this so can be just 2 elements.

Therefore because of the extra elements focal extenders are more expensive, although not necessarily better.  Having said that Powermates are made to a very high standard.

However, as said, there are also some very good Barlow lenses on the market.  Apart from the ones already mentioned, the 2.7x APM is very highly regarded by experts.  Mine is excellent, although I've never used a Powermate so am not qualified to make a comparison.

As mentioned above, Barlow lenses increase the amount of eye relief, which may be good or bad.  Also on some long focal length eyepieces they may create vignetting.

One other point to bear in mind is that the amplification power of a Powermate is fixed or nearly so.

On the other hand, with many Barlows it can be changed to give a multitude of amplifications, so Barlows are more flexible.

[Stu]

2 hours ago, Second Time Around said:

On the other hand, with many Barlows it can be changed to give a multitude of amplifications, so Barlows are more flexible.

Ah yes! I knew there was another important difference! I use an AP Barcon element with my binoviewers and use extension tubes to vary the magnification rather than changing eyepieces, much quicker and the quality remains excellent.