Powermates and Barlows

[cyborg421]

Hi all,

I have a Sky-watcher 10" dob and a Revelation kit.I find the kit fine but have just bought a Hyperion 10mm lens which shows it's worth paying money for better EPs.

I find however that the Barlow that comes with the eyepiece kit I never use. Is this because it's basically poor quality?

I was thinking of buying the Televue 1.25" 2.5x Powermate while there is still 20% off. Will it be a good idea + suitable for my scope?

I am going to purchase a Skywatcher Panaview lens next + then 1 more quality EP.

Is there a difference between a Powermate and a Barlow?

Simon

[Pete Presland]

i am sure the televue will fine,they come very highly recommended!

but its the seeing condition that will dictate when its usable or not

[JAO]

I agree with Bunnygod1

I have used and own a number Barlows and Powermates. The first thing I would want to say is that the Powermates are in my opinion better than Barlows and I now tend to only use a

Televue 2.5x Powermate and on rare ocassions a Televue 2X Big Barlow, which I am replacing (at some point) with a 2" 2x Powermate.

The choice to use a barlow or Powermate with shorter focal length eyepieces is for me governed by seeing.

In my view you will find a difference in the quality of view between the Televue barlows and Powermates and the cheaper kit supplied barlow lenses.

Hope this helps

Adrian

[Stu]

There is a significant difference between a powermate and a barlow, and not just in optical quality. The powermate magnifies, but then sends the light on to the eyepiece in parallel rays so it maintains the original eye relief that the ep had, whereas a barlow reduces the eye relief so can make higher magnification viewing more difficult.

I have not been a fan of barlows generally because I have found that they reduce the image quality. I've just bought a 2x powermate and from the brief session I had with it the other night, the quality is fantastic, and it really does maintain eye relief well.

As mentioned by the other poster, you do need to check what magnification it will give because if it too high, it doesn't matter how good the tv is the views will be soft. Make sure the combination makes sense in your scope and that the exit pupil and magnification are within reason.

Cheers

[cyborg421]

Cheers for that guys.

My Skywatcher can take a 2" Powermate. Is there a reason I would choose it over a 1.25" one (obviously the 1.25" is cheaper?

Simon

[PARTY MARTY]

Televue's are great barlow's, if you can afford it, However the celestron ultima 2x is a excellent barlow. And at a price of £89 is so much cheaper than Televue. Even if Televue as got a 20% offer at the moment!

[brantuk]

2" ep's/barlows will give you wider fov's so you can fit larger dso's like galaxies and nebulae open clusters etc in the eye piece

[cyborg421]

Interesting thought Party Marty. Has anyone compared the two? Is it worth the £40 difference?

Simon

[cyborg421]

Thanks Brant.

S

[PARTY MARTY]

The difference between the quality on images of the Celestron Ultima barlow and the Televue 2x Barlow is exactly the same.

Both me and my mate can't tell the difference either.

The coatings are both multi coated and both are Apo lenses as well.

I feel that you are just paying more for the name, And the I prefer the Celestron cos it's got a shorter barrel than the Televue which is around 4.5 inches long, but the Celestron is only 2.75 inches long.

[Merlin66]

Guys...the TV Powermate is not a barlow! Its telecentric design means that the amplification doesn't vary (like the "normal" barlow) with backfocus distance.

For imaging you can remove the eyepiece section of the body and attach a T thread camera adaptor.

[cyborg421]

Which was part of my original question.

It seems to me 4.5" is a long object + lens on top. Does this cause any problems?

S

[PARTY MARTY]

Being quite long, could cause balancing problems, depends what scope you have?

For me personally I think long barlow's make my telescope's ugly and I don't like them being too long, Also when you fit large focal eyepieces and filters, the setup tends to sag down which I don't like at all, as it appears very unstable!

Some people might disagree here and say up rate your Focuser for a better one, Which I already have by putting a 10:1 Low profile SW focuser, but the problem is still there!!!

[swamp thing]

Hi All

As has been said a barlow does alter eye relief, but it moves the exit pupil further away from the eyepiece not towards it, so it increases eyerelief not shortens it.

This is where you can have problems with longer focal length eyepieces with lomg eye relief.

Sometimes eyepieces will require a Barlow interface to keep the eye relief where the manufacturer intended.

The powermate keeps the eye relief where it was originally.

i have the 2" x2 televue powermate and it is superb. well pleased with it. highly recommend it. Works wonderfully well regardless of whatever f length eyepiece.

Regards Steve

[Stu]

Thanks for correcting my ' deliberate mistake' Steve ;-). Got myself confused. Presumably, if the eye relief is too long, it can make things awkward too?

Just got the 2 x 2" PM myself and it is extremely good and, as you say, it works well with any ep focal length

[dmahon]

Why, specifically, do you want a Barlow/Powermate? If, for example, you would only be using it on your high quality 10mm eyepiece to get better magnification, you may be better off just spending the money on a high quality 4mm eye piece rather than a 2.5x Powermate. If, on the other hand, you were going to use it on multiple high quality EPs (40, 25, 10, 6) to increase the range (40, 25, 16, 10, 10, 6, 4, 2.5) of magnifications available to you, then that might financially make more sense - but pick your EPs well (a 2.5x Powermate on a 25mm EP will turn it into a 10mm EP - which you unfortunately already have).

I have a Powermate because I want to increase the magnification for my webcam to help with planetary imaging (it would be useless for DSO imaging, as it increases the focal ratio). My alternative would be to buy a smaller chipped webcam (not available, at least economically) or to buy a longer focal length telescope (more expensive and unwieldy).

I did have a 4x Barlow. I sold it and bought a 2.5x Powermate. The Powermate is much better, as you would expect given he difference in design.

[Chris H]

Televue's are great barlow's, if you can afford it, However the celestron ultima 2x is a excellent barlow. And at a price of £89 is so much cheaper than Televue. Even if Televue as got a 20% offer at the moment!

Currently the Televue x2 barlow (1.25") with the 20% discount is £68, so at £21 less than the Ultima it's no contest.

[riklaunim]

TV Barlows are 2-element Barlows (achro). Celestron Ultima (or the same lens in Orion Shorty Plus, Antares APO, Parks Gold APO Barlow...) are 3 element APO design. There is a difference between those two.

GSO/Revelation 1,25" 2x is 2-element achro, and other are APO 3-element. Powermate and Meade TeleXtender are 4-element telecentric design and shouldn't shift the focus point much. There are also 5-element Orion Barlows. They aren't telecentric.

I did some tests of few Barlows with a Bahtinow mask and parfocal RGB filters. The achro GSO 2x 1,25" did have some noticable focus shift (chromatic aberration) between colors, while 2.8x UO Klee and Shorty Plus Barlows did not. Here is an example for the Shorty Plus:

[cyborg421]

Thanks DMahon,

Perhaps I should get a 17mm and 5mm Hyperion for roughly the same cost as the Powermate and cut out the middleman.

Simon

[swamp thing]

A powermate is something you will keep in your eyepiece case for many years after you have "upgraded" your eyepieces.

If you stay in this hobby it is not something you will regret buying, although there most probably will be eyepieces that you will think " why oh why did I buy that?"

Regards Steve

[cyborg421]

Thanks

As usual food for thought and no easy answers!

Simon