Televue Powermates Vs Barlows

[dc509]

Can anyone tell me the key differences between the Televue Powermates and Barlows (Televue or other). The cost difference seems huge - do Powermates justify the extra cost?

I've been using a cheap Barlow and it's clearly not any good! I'd like to work out how long I'm going to have to save up for to upgrade!

Many thanks

Duncan

[brantuk]

I've not used the powermate but I did just get a regular TV barlow - it's better than others I've tried (Celestron, Skywatcher etc). As with all TV products I expect the powermate will be that much crisper, clearer and wider fov than the regular one - hope so at the price lol

[John]

I've owned good barlows (Tele Vue and Celestron Ultima) and a Tele Vue 2.5x Powermate. The Powermate was superb, retained par-focaliality and did not extend eye relief, all of which made it a joy to use. Not cheap I agree but really excellent nonetheless. I also tried a Meade 5000 TeleXtender 2" 2x (similar optical design to a Powermate) and that had similar qualities.

Not to knock the TV and Ultima barlows though - they are very nice as well. Don't ask the impossible question on whether the extra cost is justified - it's really so difficult to answer that one because the answer varies for everyone !.

[Moonshane]

I have a 2.5x powermate and can honestly say it knocks the socks off any other barlow I have ever used.

the main differences are better explained by Televue than me :

Tele Vue Optics Article Page

but I can say that it basically seems like you don't have one in.

I also have a Cape Instruments barlow which I use for collimation only these days but I was told when I bought it by someone that knows, that he compared it with a TV barlow and it's as good as far as the eye can tell anyway. I'll try and compare the two objectively and maybe do a mini review if the sky ever clears.

the Powermates are about 3x the cost of a decent barlow (well maybe 2x) but I always buy used and got one for £100. this means I paid maybe £30 more. if you do buy used, make sure you get the compression ring one.

[Merlin66]

The Powermates are not Barlows!!

They have the ability of acting as a Barlow but don't change the magnification with varying back focus distance.

Google the TV site and see the performance curves.....

Ken

[Moonshane]

Ken is quite right of course and I understand they don't change the focal length of the scope (which I think Barlows effectively do) and this is an important issue for imagers I think?

[pvaz]

I have the TV big barlow which is perfect opticly, however I'm looking to sell it and get a powermate 2" 2x to replace it.

The reason is the barlow increases the Eye relief of my nagler 31T5 too much and the eye position becomes critical to avoid blackouts, making it a bit uncomfortable to use. I understand I'll also have the advantage of not having to refocus when I switch from the Nagler to the barlow + Nagler combination, although that doesn't bother me much, it will be a bonus.

If you plan to use it frequently on wide field EPs (25mm++) then it's a good idea to get a powermate. Short FL EPs don't suffer from this extended eye relief and blackout problems (at least I couldn't see it in my other EPs).

[dc509]

Great advice but I'm not sure I understand the comment about focal length. I thought the point was that they did increase magnification...

The Powermates are not Barlows!!

They have the ability of acting as a Barlow but don't change the magnification with varying back focus distance.

Google the TV site and see the performance curves.....

Ken

Still new to this, so trying to get my head round the implications. Having said that, it sounds like the Powermates will be of great assistance in planetary imaging, which is something I've just started on.

d

[Merlin66]

A conventional Barlow is designed to give a magnification at a nominated distance behind the lens. For instance if you have a x2 Barlow and double the distance by adding an extension then the magnification will rise to around x3. So basically if you used a Barlow in front of your camera to increase the focal length and hence image size, the final outcome will vary and depend on the length of the various adaptors and camera type ie DSLR v's CCD etc.

This doesn't happen with a Powermate....

The camera can be 20mm or 120mm behind the lens and you still get the quoted magnification..... it doesn't change.

Tele Vue Optics Article Page

Ken

[dc509]

thanks- think I'm beginning to understand!

d