21 replies to this topic

[gregory93]

Hello folks!I just ordered an ES x2 barlow(behaves more like a powermate as i have read) from astronomics!I should give me all the desired focal lengths; 6mm when used with my 12T4,and 4-12mm when used with my Baader zoom mk3.My scope is an 8" f/5.9
Looking forward to get it!
Clear skies and merry christmas to all of you!

[russell23]

Excellent choice! I really like mine and the 3x for deep sky observations. Performance is very similar to a Powermate.

Dave

[karstenkoch]

Ditto! I got the 2x and 3x and use them liberally without any hesitation.

[Vondragonnoggin]

I bought a 5x for christmas. I like my long eye relief, low power eyepieces at high power and i sold my 5x powermate to a friend and missed it.

[gunfighter48]

I've got the 2X 1.25" and it's excellent. Does a great job in my F/10 scopes!!

[EuropaWill]

What is the clear aperture of the 4 element 2" ES 2x? Will using a widest FOV 2" eyepiece like a 36mm 70* cause vignetting? How about UWA 24mm?

[JustaBoy]

Hi Will,

The ES 2x "Focal Extender" (not a Barlow) is telecentric, like a Powermate, so the clear aperture will be quite small, as it is with the Powermates.

This should be of no consequence because the upper 2 elements correct for the divergent rays from the lower Barlow elements.

I dunno because I have never seen one, but I would find it hard to believe that they would sell a 1.25" or a 2" device that wouldn't handle Any of their eyepieces of whatever size. - At least not without a warning?

Merry Christmas to ALL!

[Vondragonnoggin]

I have the 2" Meade 5000 series Telecentric. Same as ES version. It will handle any eyepiece you throw at it and remain transparent. The main problem for most is stack weight. When my 34mm SWA eyepiece is in the 2" 2x, the views are fantastic, but the weight is very heavy. Make sure you can balance things or you'll hate stacking like that. Fortunately on my dob I used big magnets on the bottom of the tube to balance and on my MCT, there is plenty of rail to slide into balance as long as I have its heavy dew shield on. The MCT on a twilight II with dew shield and stacked combo of 34mm in 2" Telecentric still balances perfect where I don't have to engage clutches in normal movement. Only when changing out eyepieces in which case I lock it good because it will tip fast if I don't.

All the comfortable eye relief and big flat eyecup of the 34mm in a 17mm equivalent once it's in the barlow. Some really hate stacks like that, but I've been utilizing low power 2" eyepieces in the TeleXtender for several years now.

I like it. 23mm Axiom LX too. Even just tried my new 30mm ES 82 in it.

Telecentrics are great.

If you hate the weight of some of these 2" models like the Luminos, ES, or Powermate, you can get that performance but half the weight with a 2" Siebert Telecentric.

[Starman1]

What is the clear aperture of the 4 element 2" ES 2x? Will using a widest FOV 2" eyepiece like a 36mm 70* cause vignetting? How about UWA 24mm?

1) Clear aperture doesn't matter if the focal length of the barlow lens results in its being placed the correct distance from the eyepiece.
2) the four-element design used results in the rays hitting the bottom of the eyepiece nearly parallel, so vignetting is not an issue with large field stop eyepieces.
3) Many eyepieces with 46mm field stops are not designed to fully-illuminate the edge of the 46mm field anyway. Try looking at the sky through the eyepiece. Many times you can see vignetting when just looking through the eyepiece.
4) Most of the time, a well-thought out eyepiece collection will not require the barlowing of the lowest-power eyepiece anyway. If you're choosing eyepieces based on magnification, the longest focal length is for widest field and lowest power. You probably already have a medium-power eyepiece anyway that duplicates the low power when doubled, so, from the standpoint of usage, the lowest power eyepiece is seldom barlowed in a scope.
5) I wouldn't expect additional vignetting from either of your examples.

[EuropaWill]

Thanks all for the quick and informative feedback!

I see vignetting when using the GSO ED 2" 2x with my QX36. The QX36 doesn't vignette itself natively and to Don's point: I'm expecting the EP to barlow spacing to be correct when the eyepiece is fully seated into the barlow so what is causing the vignetting? I can't physically get the EP closer to the unit when fully seated, and if I increase the distance, It wont be at 2x any longer...

Don, I certainly agree with your 4th point. This is mostly academic in my case because there is little utility in 2x barlowing my QX36 at this point since I recently acquired an ES68 20mm, atleast from a magnification standpoint. The benefits of getting a vignette free 2x barlow of the QX36 would be higher comfort due to much better eyerelief and slightly better FL spacing from my 24mm UWA. I can use my glasses with the QX36 and can't with my ES68 20. (FWIW, I also have a 14mm UWA)

The Telecentric/powermate designs intrigue me. Does the "flatter" nature of these designs become a liability when trying to remove native curvature found in fast refractors? I've found the curvature of some barlows (GSO ED 2" 2x) seems to help cancel out some of the curvature of the scope which is defintely a beneficial thing.

I didn't even know Meade had a sister version of the ES 4-element telecentric. I just did a search and can't seem to find the Meade version for sale, perhaps it has since been discontinued.

Is the Luminos 4 element 2.5x "barlow" also a telecentric design or really a barlow? Its a bit less expensive than the ES 2" 2x version. I once called Celestron to ask them this exact question and they couldn't seem to give me a straight answer. I even had to explain the difference to the tech support person.

[Starman1]

A telecentric design should have a negative lens for magnification, followed by a positive lens to make the rays parallel again. One of the advantages to that is that magnification will be the same regardless of distance between the eyepiece and barlow. That means that vignetting will not increase as the eyepiece gets farther from the barlow. Also, the eye relief of the eyepiece will not change from its parent eye relief.
In your standard barlow, the rays diverge so it's always possible the outer rays might miss the edge of the lens and yield vignetting. The shorter the focal length of the barlow (the shorter the tube), the worse the problem gets. It's one of the reasons barlows were so long back in the day. Compare the length of the TeleVue Big barlow, or the older Parks 2" barlow with the GSO ED and you get the picture.
This is unlikely in a telecentric barlow because the parallel rays will be smaller than the inside of the barrel, and an eyepiece with a large field lens will automatically field the entire ray package from the barlow.

Meade's telecentric Series 5000 barlows were made by JOC, which, with a slight package redesign, became the ES focal extenders.

Adding additional lenses to a barlow can shorten the focal length of the barlow without having to make really "deep" lenses, so i can't tell you if the Luminos barlow is telecentric or not. It seems suspiciously light, though.

As to field flattening, this occurs because of the extension of the focal length, and this occurs in all barlows, telenegative or telecentric. If it didn't, the magnification wouldn't change.

[Vondragonnoggin]

I don't think most of those wanting to Barlow a 2" lowest power piece are doing it out of necessity. I think most do it because they like the view through the 2" enough to make it a higher power piece. Even though they already have a single to cover that mag.

At least I have read quite a few that do that, and my own experience is the same. I already have incrementing powers enough that I never need to use a barlow, but I still do it out of preference for a particular eyepiece.

[faackanders2]

I don't think most of those wanting to Barlow a 2" lowest power piece are doing it out of necessity. I think most do it because they like the view through the 2" enough to make it a higher power piece. Even though they already have a single to cover that mag.

At least I have read quite a few that do that, and my own experience is the same. I already have incrementing powers enough that I never need to use a barlow, but I still do it out of preference for a particular eyepiece.

Maybe it is an eye relief observing with glasses kind of thing.

[pga7602]

Has anyone done a side by side between ES Focal extender and a Powermate? Were you able to do the "pepsi" challenge and notice any slight differences?

[Starman1]

I did just that with the Meade 5000 ones (the ES ones may be updated more than simply the barrels) and found:
--the JOC ones required in-travel of the focuser (the TV ones did not)
--the JOC ones had a little more scattered light when using them on the Moon
Other than that, remarkable for the price.
Note: I did not look for vignetting with low-power eyepieces since i did not use them that way.
Are they better than some normal high-quality barlows? Can't really say, because seeing always limits high power sharpness anyway. But, since these are close to the same price as conventional barlows, they represent a high-quality alternative.

[russell23]

Has anyone done a side by side between ES Focal extender and a Powermate? Were you able to do the "pepsi" challenge and notice any slight differences?

Yes, I compared the 2.5x Powermate with the 2x and 3x ES Focal Extenders. For deep sky I like the ES better as I think they preserve contrast and sharpness a tiny bit better than the Powermate. For Lunar the Powermate is better because the ES introduce a brown glare. However the 2" 2.4x Dakin is significantly sharper than the Powermate for lunar observations so I sold the Powermate.

I did find there was some eyepiece dependence in the comparisons. For example the 20mm XW was improved with the ES Extenders whereas with the Powermate the EOFB was enhanced which was not a good thing. With some eyepieces the Powermate was just as good as the ES for deep sky.

Dave

[gregory93]

Well i am still waiting for the shipping quota from astronomics,since it is an international order,but i have not received anything yet(have already emailed them/paid the price of the FE)

[pga7602]

[quote name="JustaBoy"]Hi Will,

The ES 2x "Focal Extender" (not a Barlow) is telecentric, like a Powermate, so the clear aperture will be quite small, as it is with the Powermates.

This should be of no consequence because the upper 2 elements correct for the divergent rays from the lower Barlow elements.

I dunno because I have never seen one, but I would find it hard to believe that they would sell a 1.25" or a 2" device that wouldn't handle Any of their eyepieces of whatever size. - At least not without a warning?

Merry Christmas to ALL! [/quote

Chuck, isn't this the case with televue 2x and it working properly with TV Plossls?

[JustaBoy]

Yes - The TV Plossls vignette with their own Barlow:-(

This would be sad had Uncle Al not graciously provided a way around it - The P:money:owermate.

[gregory93]

Post deleted by gregory93

[Vondragonnoggin]

Maybe check your spam filter. They might have replied and it got whisked away mistakenly as spam.

[youngamateur42]

That's happened to me a couple of times responding to ads in the CN classifieds. Astronomics is awesome, I've bought a few things from them and never had a problem.