33 replies to this topic

[jmoore]

i'm probably gonna sell my Televue 2x Barlow (I don't use it much, and need the $$), but if I find myself wishing for a 2x Barlow again, I may soon pick up the less expensive Shorty Plus or Ultima barlow instead.

I've heard somewhere that the Shorty Plus is more like a 2.5x Barlow though (rather than 2x). Is this true? If so, is the same true of the Celestron Ultima Barlow?

Finally, how do these compare to the 2.8x Klee Barlow? This question is mainly relevant if the others mentioned give similar magnification, e.g., around 2.5x instead of 2x.

thanks
jeff

[Catapoman]

Jeff,

I don't know about the Shorty Plus, but the Celestron Ultima's do average out to between 2.2x and 2.3x. I have owned a couple and found this to be true on both. This has also been confirmed to me by others when I was doing my calculations.

I can't answer your question about the Klee comparo.

Pernel

[EdZ]

This link will provide you with an understanding of why a barlow can be a different magnification with various eyepieces. The stated magnification is nominal for all barlows. I've measured the Celestron Ultima barlow to range from 2.15 to 2.52. It varies all over the place depending on the eyepiece. However, when used with most eyepieces below 20mm, it did fall within a narrow range around 2.2x and most eyepieces above 25mm within a range around 2.4x. When used with a few eyepieces less than 10mm, magnification measured 2.15x.

All of these measurements were based on drift times with and without the barlow. I assumed no vignetting of the eyepiece field of view. It's possible there is some vignetting involved in the longer focal length eyepieces. That might account for why I got readings of 2.66x with my two differnt 40mm plossls.

Barlow Formula

edz

[Rushwind]

The Orion Shorty Plus and the Celestron Ultima are reportedly the exact same object.

Jimbo

[jmoore]

thanks, ed. So I can probably assume the same results with any Barlow (including TV 2x), yes (at least in terms of there being some variability across diff't EPs used)?

cheers,
jeff

[EdZ]

Yes, I think so, because magnification varies according to the distance between the focal point of the eyepiece and the barlow lens elements, and that is different for every eyepiece.

edz

[SAL]

Hi Jeff. I agree the Orion Shorty Plus appears to have a bit more than 2x magnification. When I upgraded to Televue EPs, I was going to upgrade to a Televue Barlow, but for the life of me, I can't bring myself to part with the Shorty Plus. I think you'll enjoy it or the Ultima very much... (Scott)

[erik]

having had the shorty plus, standard shorty, and ultrascopic 2x barlows, in addition to viewing through countless others, the shorty plus is by far my favorite. while i agree that it seems to be *slightly* more than 2x, i'm pretty sure that it's not 2.5X. while i haven't done any drift testing, i have compared it many times to an ep by itself of the same magnification (25mm ep w/barlow vs. 12.5mm ep, etc.) and the views are very similar. i also think you'll enjoy the shorty plus, jeff!!

[Oldfield]

Buying and selling has overhead, think twice, since you've already got the best.

[Mike Hosea]

thanks, ed. So I can probably assume the same results with any Barlow (including TV 2x), yes (at least in terms of there being some variability across diff't EPs used)?

Yes, but the Tele Vue varies less because it has a longer focal length (the same variation in field stop position produces a smaller magnification difference with a longer focal length Barlow). It's also unclear which eyepiece the Ultima/Shorty Plus was supposed to yield 2x with. At least with the Tele Vue you know that any Tele Vue eyepiece with field stop 0.25" below the flange (including all TV Plossls 32mm and shorter, Radians, 16mm Nagler Type 5, 24mm Panoptic, type 6 Naglers, Nagler zooms, and probably some others) will produce a 2x result and also be approximately parfocal when the Barlow is inserted all the way to its flange, as it would be in a Newt and probably a 2" star diagonal.

Check the going rates for 1.25" 2x Tele Vue Barlows. I don't think you can really extract a lot of capital here by downgrading.

[erik]

yes, but won't the TV barlows (or any long barlow) have more of a problem with tunnel vision? one of the things i like about shorty barlows is that they don't have that problem at all. they also come to focus in every scope, unlike many long barlows. maybe the magnification isn't exact in all ep's, but i can live with that for the ease of use and it fitting in my overstuffed ep case....

[jmoore]

thanks for the tips all...but just to clarify...I'm not intending to 'downgrade' at this time. I'm simply selling the TV 2x, and that may very well be the end of it. I probably won't need a 2x Barlow at all.

If, down the road, I decide that I do need a 2x Barlow, it would mainly be for photographic purposes (e.g., if I need more magnification than a 25mm Plossl and 3x camera zoom can get me). In this case, a little variation from precise 2x (e.g., 2.2-2.5x) will not be a problem, nor will any slight reduction in quality. Considering that I'm getting $85 for my Barlow, and could probably get a used Ultima or Shorty Plus for $55 or so (if I need one), I think I'll feel that the price difference is significant enough to justify the 'downgrade'.

cheers,
jeff

[Starman1]

I've owned several Barlows through the years, and the Klee was my first excellent one. It has a small clear aperture, though, so it might vignette some very wide field 1-1/4" eyepieces.
However, to increase the power on 10-22mm Plossls, it is one of the best.
And, as for vignetting, even the Orion Shorty Plus vignettes a 1-1/4" eyepiece with a diameter-limited FOV, but not as severely.
By the way, eyepiece types not particularly good at handling the light cone of a short FL scope may be fine if barlowed. My 24.5mm Meade SWA eyepiece does poorly with edge-of-field star images at f/5.5, but at f/11 (the ratio with the barlow), it does much better, and it is a wonderful 12.3mm eyepiece. When I do the same thing in the f/12 MCT, the Orion Shorty Plus Barlow does NOT improve the star images, so I would guess the SWA eyepiece isn't noticeably improved by going from f/12 to f/24.
Don

[Mike Hosea]

yes, but won't the TV barlows (or any long barlow) have more of a problem with tunnel vision?

I don't know what you mean by "tunnel vision", but then I don't have much experience with traditionally long Barlows (the Tele Vue 2x is definitely not "long" like an Orion Ultrascopic or UO 2x), nor have I spent much time with either Tele Vue 2x or 3x Barlow in a star diagonal. I have used the older 2.5x in a star diagonal, though. Certainly shorty Barlows are more prone to cause vignetting, i.e. to reduce the apparent field of view, than a Barlow with a longer focal length. In that sense the 2x Tele Vue is superior to the Ultima, causing less vignetting whenever either one causes any, and the Tele Vue models are approximately parfocal in Newts or in any scope where it can be inserted all the way, whereas the Ultima always seems to require in-travel when being swapped in (behind the diagonal). In fact, when I had my Teleport set up "aggressively" in terms of the strut length, I used a Tele Vue 2x, but I could not use a 2x Ultima because of the in-travel required.

I suppose there is a greater possibility of reflections off the walls of a longer Barlow. Is that what you mean? However, the Tele Vue Barlows that I have owned have all had excellent baffling. The design has changed over the years, but the last Tele Vue 2x I owned had fine-cut threads in the barrel that was astonishingly effective--there was no benefit to flocking the tube with Protostar flocked paper.

[Mike Hosea]

I'm simply selling the TV 2x, and that may very well be the end of it. I probably won't need a 2x Barlow at all.

Makes sense to me. How do you think I ever got to the point of owning a total of about 4 Tele Vue 2x Barlows and 2 Celestron Ultimas at different times, not to mention so many others? Come to think of it, you might want to take that into consideration the other way.

[jmoore]

good point, Mike! I'm trying to not fall into those kinds of cycles *quite* as badly has you have.

So Mike, what kind of barlow/s do you use now, if any? Have you "settled" on one yet?

jeff

[Tom L]

Good question to Mike. Didn't you also get the GSO 2" 2x barlow? What was your final opinion of that barlow?

[Mike Hosea]

I've apparently settled on a 2-4mm Nagler Zoom and 5mm and 7mm Nagler Type 6's. The only thing I could really use a Barlow for anymore would be the 24mm Panoptic, but I have the adapter from the GSO Barlow mounted on it with the thumbscrew replaced by a set screw in order to convert the Pan to a 2" eyepiece for convenience in my current scopes. However, for a long time I used a Tele Vue 2x with the Type 6 Naglers to service my highest magnification needs. It's conceivable that I might go back to that someday if I ever decide that the Nagler Zoom is too much capital tied up in one eyepiece. But for the moment, anyway, I use the zoom quite a bit (percentage wise -- with the rain there hasn't been a lot of observing going on here lately).

I thought the GSO Barlow was okay. I didn't have any problems with it, other than the fact that I felt it was gratuitously heavy and that the lens cell on mine needed to be loosened a little in order to fit in my focusers easily. I didn't really have any other Barlows to compare it to, though. I sold the Barlow (without the adapter) and the 30mm GSO (short version) last week. I might be moving within the next few months, and everything is getting a close look from the basis of is it worth its weight and space to me.

[jmoore]

hey Mike...I'm taking a similar tactic, as evidenced by my post here. Trying to put together a collection that eliminates the need for Barlows altogether. My 3-6 Nagler zoom (a recent purchase) went toward that goal. Kind of a pricey approach, but then again, I'm selling off my 2x Barlow and 2.5x Powermate, along with a couple other EPs that I previously only used with a Barlow...so I'm actually coming out a little ahead.

Mike...I also sold my 30mm GSO...but kept my 42mm (so far). You bought a 42mm, too, didn't you. Did you keep that one?

jeff

[Mike Hosea]

Still have the 42mm--same reason as you. Doesn't get much use, but it doesn't tie up much capital, either.

[Tom L]

That's how I felt about the 30mm...I found I just don't like the 40mm+ sizes so I didn't even bother getting the 42mm GSO...the 30mm is a great finder though.

I guess I should sell my barlows as well...I don't use them...I have the eyepieces I want a the mags I want. I'll keep the 3x TV for sure, but the other 2 may have to find new homes...

[erik]

yes, but won't the TV barlows (or any long barlow) have more of a problem with tunnel vision?

I don't know what you mean by "tunnel vision", but then I don't have much experience with traditionally long Barlows (the Tele Vue 2x is definitely not "long" like an Orion Ultrascopic or UO 2x), nor have I spent much time with either Tele Vue 2x or 3x Barlow in a star diagonal. I have used the older 2.5x in a star diagonal, though. Certainly shorty Barlows are more prone to cause vignetting, i.e. to reduce the apparent field of view, than a Barlow with a longer focal length. In that sense the 2x Tele Vue is superior to the Ultima, causing less vignetting whenever either one causes any, and the Tele Vue models are approximately parfocal in Newts or in any scope where it can be inserted all the way, whereas the Ultima always seems to require in-travel when being swapped in (behind the diagonal). In fact, when I had my Teleport set up "aggressively" in terms of the strut length, I used a Tele Vue 2x, but I could not use a 2x Ultima because of the in-travel required.

I suppose there is a greater possibility of reflections off the walls of a longer Barlow. Is that what you mean? However, the Tele Vue Barlows that I have owned have all had excellent baffling. The design has changed over the years, but the last Tele Vue 2x I owned had fine-cut threads in the barrel that was astonishingly effective--there was no benefit to flocking the tube with Protostar flocked paper.

mike, i mean the blacking out effect that occurs when long barlows are used with long ep's. my ultrascopic barlow did it very badly, and even my tri-mag barlow does it. it's also even worse if you ever stack barlows, which i do to obtain the magnification i need for taking pictures without vignetting. using two shorty type barlows works best for that. as for the "threaded" baffling inside of the barlow tube, my tri-mag has that as well. it still had a glare problem until i flocked the tube and blackened the lens edges. don't know which one got rid of the glare, but i'm sure the flocking didn't hurt!

[Mike Hosea]

Oh, you mean problems holding the exit pupil because of increased eye relief?

I always assumed that the shorter the Barlow focal length the greater the increase in eye relief (aka pupil throwout), which would suggest that the problem should be worse with a shorter Barlow, all other things being equal, but I don't really know. At least, I can't think why the pupil throwout would be greater with a longer focal length. Maybe it's just something to do with the particular combinations you're using.

[erik]

thanks mike, that's interesting. i should've better explained what i meant. i've only noticed it with longer barlows though, mainly when using long ep's (combinations that i don't usually use visually, no reason to barlow a 32mm except for astrophotography through the ep). never seen any evidence of it when using shorty barlows, even the standard shorty which has a reduced aperture..

[jmoore]

That's how I felt about the 30mm...I found I just don't like the 40mm+ sizes so I didn't even bother getting the 42mm GSO...the 30mm is a great finder though.

I guess I should sell my barlows as well...I don't use them...I have the eyepieces I want a the mags I want. I'll keep the 3x TV for sure, but the other 2 may have to find new homes...

Yeah Tom...for me, I quickly found that I just don't like messing with 2" EPs period. I suppose this would change if I got a 2000mm focal length scope, but the only scope I have that accepts 2" EPs is only 1000mm long. So, I use 1.25" EPs (24mm-32mm) for my finder, and increase mag from there. I decided the only reason for ME to have a 2" EP is for those rare occasions when I need the widest true field possible (e.g., when two interesting objects are about 2 degs away, or for a comet, etc). To this end, the 42mm is more useful to me than the 30mm, because it gives a wider (and flatter) field. I'll probably rarely use it, but it does fill a small speciality niche at least. By contrast, I don't think I'd EVER use the 30mm because it's not my finder (prefer 1.25" EPs for that...like a 24 Pan), nor does it give me the widest FOV I can get (will use the 42mm for that), nor do I enjoy the edge performance in it.

So, Tom, what are the other 2 Barlows you have that you're thinking of selling?

jeff