Most favoured barlow?

[woodchop146]

Hey, I have been researching what barlow to purchase for astrophotography primarily and visual observations secondly. I suspect a 3x barlow is the best bet, after finding 5x too powerful to be used with a less than premium dobsonian mount, but I have no idea which one would be the best purchase.
I currently use a Skyliner 250PX dobsonian with a ASI120MM-S, with a budget of around £100.

I'm currently looking at the Orion Tri-Mag, Televue 3x Barlow and the Meade 3x Telextender, but I'm frankly unable to differentiate their ability through the images I've seen with these in use.

Any help would be greatly appreciated.
 

[SnakeyJ]

I can recommend the Baader Q barlow (2.25x). I tried the Revelation EDs a celestron xcel and various others, but the Baader produced the best image results. Until I brought my TV x3 barlow and 5x Powermate, but the Baader was excellent price/performance.

[woodchop146]

Interesting, would you recommend the Baader Q over even the Revelation 2.5x? (not sure if you implied this barlow with the reference to Revelation EDs)

Would you expect there to be a quality difference between the Televue 3x and the Baader Q 2.25x such that would truly justify the extra cost?

[paul mc c]

I have never used a TV barlow,or similar high end ones,but i use a Ultima 2x Japan barlow and it is excellent,to my eyes there is no degrading of views with any eyepiece.

They can be had for around £50 used.

[John]

I've owned and used lots of barlows but for visual use rather than imaging. I tend to prefer the TeleXtender / Powermate / Focal Extender designs over the plain barlows because they seem to have little or no negative impact on image quality, just adding the magnification boost. The Tele Vue Powermate 2.5x is excellent but they are very expensive. I found the Explore Scientific Focal Extender performed pretty much the same for quite a lot less as was the Meade TeleXtender which also performed well. Because they work in a slightly different way to a barlow lens the focal point of the eyepiece they are used with is unaffected which can help ensure that focus can still be reached with focusers that have relatively short travel. They also do not extend the eye relief of the eyepiece as barlows do, which can be an advantage if the eyepiece being used already has generous eye relief. Sometimes though it had to be said that the extension of the eye relief that the barlow design gives can help viewing comfort when used with eyepieces with short eye relief. It's a case of "swings and roundabouts" as they say !

Thinking of the barlows I've used I agree that the Celestron Ultima 2x is pretty good although it's closer to 2.2x I believe in reality. If used with eyepieces with large field stops (eg: ultrawide angles and longer focal lengths) the edges of the field of view can be vignetted (cut off) with the Ultima barlow but it's a nice optic. For what it's worth the Orion Shorty Plus barlow is the same as the Celestron Ultima as is the Parks Gold Series barlow and I think there was an Antares badged version too.

The Tele Vue barlows are very nice as well - about equal to the Ultima I felt. The long format of the Tele Vue barlows is fine with newtonian scopes but the shorty design of the Ultima fits better when used with scopes that use diagonals. As with all Tele Vue products they are priced high when bought new. On the used market the price of Tele Vue and Ultima barlows seems around the same though.

The Baader Q-Barlow is optically very nice - probably the best for that retail price point that I've used. I've also owned and used the TAL 3x and 2x barlows which are good optically if a little rough in their construction and also the Revelation 2.5x 3 element barlow which is not at all bad for it's very low cost.

I've used a few that I'd not recommend which include the Celestron Omni barlow and the Meade 126 shorty barlow.

It is a bit of a maze of choices I agree !

[Ruud]

Hi OP,

of the barlows you mention, the TeleVue 3x is the best, at least if you follow this source: http://www.cloudynights.com/topic/487812-praise-for-the-3x-tv-barlow/

[SnakeyJ]

Interesting, would you recommend the Baader Q over even the Revelation 2.5x? (not sure if you implied this barlow with the reference to Revelation EDs)

Would you expect there to be a quality difference between the Televue 3x and the Baader Q 2.25x such that would truly justify the extra cost?

I've owned and used both the Revelation 2.5x and 5x ED barlows, which I brought new from Teleskop Service.    I believe the 5x was a bad example, either being incorrectly assembled or a Friday afternoon special - this has always given a bad ghost or reflection.   The 2.5x was better and useable, but never performed as well as the Baader Q - I've also found that this needs more infocus than any of the other barlow combinations that I've tried.    There are quite good reviews around for the Revelations, so perhaps just bad luck in my case.

IMO my Baader Q was head and shoulders above my Revelation 2.5x!    

The TV 3x is slightly better than the Q, but the differences start to become much finer here.   I can say without doubt that the image train is more solid with the TV, despite being at least a good inch longer.

Ideally with this sensor you will probably be imaging between F15 and F20, which would be approx 3-4x and is easily achieved with the barlow and a little extension.     On occasions I have pushed this a little further to F25 (F30 on Mars), but there have been very few occassions when the seeing has been stable enough to offer improved results!

[jetstream]

The Baader VIP works well.

[woodchop146]

Thanks John, very informative comment , good thing you mentioned the Meade #126, I was low-key considering to purchase it! 

 http://www.cloudynights.com/topic/487812-praise-for-the-3x-tv-barlow/

Great find, thanks for sharing that.
One user in that thread mentioned his success being greater with an Orion Tri-Mag than the TV 3x Barlow, in terms of sharpness on axis, that's unexpected.

[Charic]

Does your Dobsonian have a tracking system ( ........ less than premium dobsonian mount......[sic] )? High powered astrophotography on a Dob is not easy, even without a Barlow, I'm sure you have tracking, or have I misread something?

I'm using the Sky-watcher 2x deluxe Barlow for the reasons depicted here..... http://www.absoluteastronomy.co.uk/2012/10/sky-watcher-2x-125-deluxe-barlow-lens.html

[SnakeyJ]

Does your Dobsonian have a tracking system? High powered astrophotography on a Dob is not easy, even without a Barlow, or have I misread something?

Well said, trying to find and keep any target centered on a tiny CMOS at 3.6m+ focal length is going to be tough with nudge to - The autodobs seem to cope with this quite well, with a little field rotation over a session, but these focal lengths are much simpler on a tracking eq mount.

[woodchop146]

I've owned and used both the Revelation 2.5x and 5x ED barlows, which I brought new from Teleskop Service.    I believe the 5x was a bad example, either being incorrectly assembled or a Friday afternoon special - this has always given a bad ghost or reflection.

I recently had to return a Revelation 5x for bad ghosting among other things, knowing it wasn't a one off might say something about Revelation 5x barlows.

Would you happen to know the extension roughly required with the Baader Q to achieve a 3-4x factor in magnification?

Charic, my dobsonian mount isn't motorized, but it does have quite bad 'stiction', top half sits atop 3 postage-stamp sized Teflon tabs. Pardon the ambiguity in the first post.

Luckily the ASI120MM-S can sustain about 70fps full frame, so it isn't as bad as it seems.

[damnut]

A 5* barlow,  WOW...You would be very limited in visual use.

I do not use barlows, I do have a revelation Ed 2" barlow, still in its box!.. The best I have seen through  is a colleague's TV Powermate, keeps eye relief constant and a consistently excellent image.

[ronin]

Luckily the ASI120MM-S can sustain about 70fps full frame, so it isn't as bad as it seems.

Might be OK for planetary imaging, but still not sure, but no use for DSO AP.

Also the camera appears to be mono.

Could also need a coma corrector.

[SnakeyJ]

I recently had to return a Revelation 5x for bad ghosting among other things, knowing it wasn't a one off might say something about Revelation 5x barlows.

Would you happen to know the extension roughly required with the Baader Q to achieve a 3-4x factor in magnification?

35-50mm? Not a precise art as the QHY5L-II are 1.25" cylinders and slides inside the barlow/extension tube combo - I usually adjust to conditions and rely on the Ephems data from Firecapture to report the capture focal length.    The rule of thumb seems to be around 1" extension for an extra 0.5x

[Charic]

I recently had to return a Revelation 5x for bad ghosting among other things, knowing it wasn't a one off might say something about Revelation 5x barlows.

Would you happen to know the extension roughly required with the Baader Q to achieve a 3-4x factor in magnification?

Charic, my dobsonian mount isn't motorized, but it does have quite bad 'stiction', top half sits atop 3 postage-stamp sized Teflon tabs. Pardon the ambiguity in the first post.

Luckily the ASI120MM-S can sustain about 70fps full frame, so it isn't as bad as it seems.

Interesting.....I hear the Philips TouCam was good in its day,  and easy to mod, but I feel drawn to the Philips SPC900NC. Fixing a webcam, then stacking may get me the images I desire. Ive seen something similar with a DSLR on an ALT-AZ mount?

[woodchop146]

Might be OK for planetary imaging, but still not sure, but no use for DSO AP.

Also the camera appears to be mono.

Could also need a coma corrector.

Rest assured, I don't intend on doing DSO imaging with this setup, other than the occasional bright double star system this setup is only for planetary/lunar imaging.

[ronin]

Rest assured, I don't intend on doing DSO imaging with this setup, other than the occasional bright double star system this setup is only for planetary/lunar imaging.

Good, but it is amazing how many have simialr equipment and then want/decide/expect to go DSO imaging.

Tends to go along the lines of:

1) I want a nice big scope to see as much as possible with = Get a dob.

2) I have the dob as suggested, can see lots, great.

3) How do I now attach a camera to the scope to take images like hubble ?

[Saganite]

Tried quite a few barlows before finding the 2.5x Powermate, and I recommend it.

[LukeSkywatcher]

The best barlow i ever used was the TAL 2X. I have a Revelation 1.5-2x now which never gets used. Ive no need for a barlow since i have just about every eyepiece i could possibly need or want.

[acey]

One of the first accessories I bought was a Meade apochromatic barlow. It works fine but I almost never use it - like Paul in the previous post I have enough eyepieces that do the job for me, and I don't want to put any more glass between my eye and what I'm looking at. Only time I ever use it is on the rare occasions when I need high power on my 80mm f5 refractor. I've also sometimes found the barlow tube handy, with the lens unscrewed. In fact I've probably used it more often as an extension tube than as a barlow. A pretty expensive bit of tube...

[LukeSkywatcher]

I should have also mentioned that on the very rare night when conditions are completely perfect that i may use an 8mm EP and a 2x barlow to give me a 4mm view. The reason for this is the eye relief/exit pupil  on a 4mm is pretty impossible to use so an 8mm will compensate and allow for this. Lunar craters when viewed in an 8mm+2x barlow...........goose pimples on the scalp.

[Pig]

I have just sold a Tal 1.25" x 2 Barlow and it was quite impressive. I have just purchased a Baader VIP Barlow but I haven't had chance to use it as yet, hopefully the weather will clear soon and I can give it a test drive

[woodchop146]

Thanks for the words of wisdom, I'll likely be ordering a TV 3x Barlow in the upcoming days.