Barlow advice (again)

[Alfian]

I'd come to thinking that  I'd prefer not to use a Barlow  but given that I can't quite find what I think I need  I'm back to thinking that  a Barlow  makes some kind of sense. I'm looking for something that is as optically invisible as possible, well engineered, but under £100 a fair bit under if poss' so that rules out TV optics.  Given that I have 10mm BCO a Baader Q turret 2.25x with 1.3x nosepiece would give me the most options, although I would prefer a barlow with a compression ring which I dont think the Baader has.

The next choice would be to push the boat out a little for an ES 2x focal extender. These look good and I know I've  just missed one on ABS!

Starguider do a 2x ED barlow but this seems to be an unknown quantity. I have also come across an Antares x2 Twist Lock Barlow. I know good things are said of the 2" 1.6x but can find nothing about these. Does anybody know anything about these or have any other ideas?

http://www.rothervalleyoptics.co.uk/antares-x2-twist-lock-barlow-lens-125.html

Alternatively if  a 2nd hand 7mm UWAN/Nirvana comes up, I might just be tempted.

[triton1]

I use a 2 inch ed barlow by revelation which I think is the same as the sw one,both have 1 1/4 adapters with them with compression fittings and too be honest I don't pay them any attention when using it.Tele house prices have over doubled in the last two years but should go for about £40 s/hand so why not buy and try.If your not happy you will get your money back on resale then maybe go for a more expensive one.

[Alfian]

I had looked at the 2" option given that I'd be using it with the ED100. Worth a thought.

[John]

Of the ones you mention (which I have used at one time or another) I'd say that the ES 2x Focal extender is the one to look out for. The one I tried was very, very similar to TV Powermate standards (ie: more or less invisible apart from the power boost) but significantly less expensive.

Optically the Baader Q-Turret is really good but if you wan't a compression ring then it's not what you are after.

The Celestron Ultima 2x barlows (or the identical Orion Shorty Plus 2x barlow) are another that is optically excellent but again, no compression ring fitting.

If this is going to be a regularly used item it's worth getting something that has the performance to compliment your excellent scopes rather than impact the image in any negative way.

 

[Pete Presland]

There is Televue X2 Barlow on AB&S FOR £70 right now, not mine I hasten to add.  http://www.astrobuysell.com/uk/propview.php?view=127804

[Alfian]

1 hour ago, John said:

If this is going to be a regularly used item it's worth getting something that has the performance to compliment your excellent scopes rather than impact the image in any negative way.

Thanks John - I think this is the crux of it , and it is partly for this reason that I've resisted the "be sensible" temptation to go back to using a barlow. The other reason is that I don't particularly like a a lot of hardware hanging out of the focuser, which is why I would prefer something with a compression ring.  In this light the ES focal extender is probably the best I'm going to get under £100 although the 2nd hand  TV is not to be sniffed at I guess. Thinking out loud here but I have a SLV and a couple of LVs with good eye relief so I think the ES would be better in that respect too. The 10mm BCO is a short on ER but surprisingly manageable. Think I'm talking myself into something here.

[YKSE]

Just to create a bit more confusion there's another way to use the QT barlow:

buy a 2" to 1.25" twist lock reducer, then a M48(2" filter thread) to M28(1.25" filter thread adapter like this one

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p4985_TS-Optics-Adaption-von-1-25--Filtern-an-2--Filtergewinde.html

you can thread QT barlow's lens piece into the adapter, then into the wist lock.

When not using the barlow, you have a twist lock reducer.

[Alfian]

Just to give a conclusion to this thread, I said in my OP "I'd prefer to not use a barlow" and  "Alternatively if  a 2nd hand 7mm UWAN/Nirvana comes up, I might just be tempted", well I've eventually heeded my own inclinations. A 7mm Nirvana came up for sale and that was that, see:

 

[davyludo]

Hi Ian,

I bought the BST Starguider 2x Barlow last week. Had my first session with it last night and personally I really liked it. Had tried it during the day and image was totally washed out but I think that was down to the ST102 because other Barlow (Skywatcher) was the same.

In my short refractor I'd say it coped pretty well. Used it on the moon with a 25mm x-cel (so 40x mag) and the clarity of the image was unreal, good colour, lots of detail. Actually preferred the view to the unbarlowed 9mm x-cel (55.5x)! 

Stars were pin sharp across most of the fov (started to become a little distorted towards the edge) maybe 80-90% was sharp though. Tested this on Vega - however with fainter starts I really didn't notice it. If I tilted my head slightly when Vega was at the edge of fov then it would go pin sharp again.

Used it on M57 as well (I think I used 9mm and then barlowed for comparison) I expected M57 to vanish or become a lot fainter with barlow.... nope, it was still there and it was still just as clear (as far as I was concerned).

All in all, as an inexperienced newbie, I was really happy and I'm pretty sure I'll just stick with this for the foreseeable future  never been sold on Skywatcher or Celestron free ones. The BST definitely feels like a higher quality item, both in the hand and at the eyepiece. I have no desire to look/research other barlows now....which is how I know I'm truly happy!

 

EDIT: oh and it has a compression ring which I really liked as well.

 

[Dave In Vermont]

Invisibility, thy name is TeleVue®. I know they're others that are said to be as good, but the TV is the one I'm familiar with (as well as lower-end options).

And they're really not that much more expensive.

My 2¢,

Dave

[alan potts]

Agreeing with John, commonsense as the man speaks from great expirence, I had the Meade copy of the Powermate made by Televue, the ExSc one is most likely identicle. I also had the Televue powermater, in honesty I couldn't pick them apart. I don't have either now as with the amount of eyepieces I have I found I didn't use them. The other night though I could of used one of them as I ran out of eyepieces, 3mm being my shortest, I was testing a fairly short scope at 780mm F6.

Alan

[triton1]

"As I ran out of eyepieces "?Chortle!

[triton1]

This is the crux of the matter barlows will give you extra focal lengths without buying extra eyepieces but with the focal length of my scope and the eps that I use I still struggle when wanting different focal lengths at higher powers depending on the seeing.I can do 125x,133x,200x,250x or 400x which for me leaves too much wiggle room and only one space left in my ep case however as you have more than one scope for you this maybe would eleviate the problem depending on what you are looking at.As I said before try a 2 inch revelation or sw s/hand and if it doesn't work out for you sell it and you shouldn't make a loss for not much outlay.If it does work out for you you can still sell it and go for one of the ones that have been recommended above.My tuppence worth.

[Piero]

I had a 1.25" Bresser SA barlow 2x and was very close to my 1.25" Televue Powermate 2.5x .  

It is not a barlow actually, but a tele-extender. In particular it is parfocal.

There is one on ABS right now for £65 : http://www.astrobuysell.com/uk/propview.php?view=128665  

[Ricochet]

11 hours ago, Piero said:

In particular it is parfocal.

What do you mean when you say a tele-extender is parfocal?

1. Eyepiece A is parfocal with Eyepiece A + tele-extender
2. Eyepiece A and eyepiece B are parfocal when used in a tele-extender even if not parfocal natively
3. Something else

 

[John]

8 minutes ago, Ricochet said:

What do you mean when you say a tele-extender is parfocal?

1. Eyepiece A is parfocal with Eyepiece A + tele-extender
2. Eyepiece A and eyepiece B are parfocal when used in a tele-extender even if not parfocal natively
3. Something else

 

When I've used telextenders (the ES, Meade and TV ones) I've found that they don't move the point of focus of an eyepiece (well, only a tiny bit) whereas barlows usually require inwards or outwards focuser movement when installed. Also Telextenders seem not to vignette low power wide field eyepieces, which barlows sometimes do, and the eye relief remains the same as the original eyepiece whereas barlows extend it. The latter point can be either an advantage or a disadvantage !

 

[Piero]

1 hour ago, Ricochet said:

What do you mean when you say a tele-extender is parfocal?

1. Eyepiece A is parfocal with Eyepiece A + tele-extender
2. Eyepiece A and eyepiece B are parfocal when used in a tele-extender even if not parfocal natively
3. Something else

What John said.  

[Ricochet]

53 minutes ago, John said:

When I've used telextenders (the ES, Meade and TV ones) I've found that they don't move the point of focus of an eyepiece (well, only a tiny bit) whereas barlows usually require inwards or outwards focuser movement when installed. Also Telextenders seem not to vignette low power wide field eyepieces, which barlows sometimes do, and the eye relief remains the same as the original eyepiece whereas barlows extend it. The latter point can be either an advantage or a disadvantage !

 

That's what I thought was meant but with my Meade 2x Telextender there is a definite need to move the focuser inwards. I'll have to try measuring the difference but it's got to be at least a few mm which is beyond what I would consider parfocal. 

[John]

6 minutes ago, Ricochet said:

That's what I thought was meant but with my Meade 2x Telextender there is a definite need to move the focuser inwards. I'll have to try measuring the difference but it's got to be at least a few mm which is beyond what I would consider parfocal. 

The TV Powermates require practically no movement. They do cost though !

[Ricochet]

1 hour ago, John said:

The TV Powermates require practically no movement. They do cost though !

Yeah they do. I think given how optically good the Meade is I can live with adjusting the focuser. Well unless someone wants to give me a Powermate that is, I wouldn't turn down a free one. 

[Piero]

With the Bresser SA and TV Powermate) on my TV diagonal I did require some inward travel adjustment, but that was not due to the optics of the telextender, but rather to the telextender barrel, which was longer of the diagonal eyepiece holder. That extra gap required a proportional inward travel adjustment. On my dobson it was essentially parfocal like a powermate (+/- 1mm). 

[Alfian]

Thought I'd just highlight that my original request for help/advice regarding barlows has been resolved with the a purchase of a 7mm EP, as per my post a few days ago. That doesn't preclude you guys from running with the ball but if there is ongoing interest it might be worth someone starting a new thread such as "barlow vs focal extender" or something. Just a thought.