Lowest magnification barlow? (1 Viewer)

[dothedr3w]

I'll try to keep this as to the point as possible. What is the lowest magnification barlow lens available with a 1.25" barrel?

I'm using a Kowa 883 with a Nagler 3-6mm zoom eyepiece. With the Kowa 1.6x extender attached to the scope, the 3-6mm zoom can focus to infinity; without the extender the eyepiece will only focus between 13ft-150ft. The reason for this is the extender allows the eyepiece to be seated one millimeter deeper (it bottoms out regardless of extender or no extender). Who'd have thought that a single millimeter would make the difference.

I want the barlow for reason beyond it's intended purpose; the eyepiece can't achieve focus without the extender, so I want to use the barlow to cheat. The 3-6mm zoom has a longer than standard barrel, so if I can plug the Nagler zoom into a low power barlow (which should be able to correctly seat into the scope), I can potentially circumvent the focusing issue. So to be clear, I don't want a higher power barlow to try and squeeze out even more magnification, I want the lowest power available just to be able to seat the eyepiece properly.

 

[GeorgeL]

If you’re trying to get much magnification from a spotting scope an astronomical refractor will be much more practical with that zoom eyepiece.

 

[henry link]

You're essentially using a low power Barlow now in the form of the 1.6x extender. Since the distance between the eyepiece focal plane and a Barlow element determines the true magnification factor of the Barlow the extender's magnification factor could already be lower than 1.6x when combined with the Televue zoom. I'd suggest measuring the true magnification difference when the Televue is combined with the extender before you do anything else.

 

[Binastro]

As Henry says, distance matters.

There are 2x to 3x teleconverters for camera lenses that just add an extra tube.

The Minolta AF to MD lens converter uses a lens to achieve focus. This magnifies about 1.2x.
This is common with other makes also that incorporate lenses, maybe doublets or singlets. The older doublets may have fungus between the elements if old and poorly stored.
These are generally 1.2x to 1.3x.

I use a good old Nikon 500mm f/8 mirror lens with various converters that ends up at about 1300mm on a Sony Alpha camera.

Also an as new Sigma lens 300mm f/2.8 with fully functioning manual controls.
It is for Canon FD and was £100 as the shop thought it useless. I use Canon FD to Minolta AF/Sony 1.25x approx converter.

I have several 1.4x camera lens converters that I value highly. Some are well corrected, maybe triplets or more.

There are dedicated optimised teleconverters called matched converters for, say, Vivitar lenses that fit individual lenses. These have strange curves on the elements.

I have a Televue eyepiece as yours, I'll see if the tube can be unscrewed without lenses dropping out.

Machining a tube or cutting a tube may achieve what you want.

SRB Griturn specialise in odd converters.

Regards,
B.

 

[jring]

Hi,

before we look into barlows, maybe check if there might still be a way to get your Nagler zoom to focus w/o one... two questions:

- does the Nagler zoom 1.25" barrel hit the protective glass in front of the prism?

- if not, which astro adapter do you have - the one with the grub screw or the other one?

The one with the grub screw:

Teleskop-Express: Kowa Astro-Adapter für 1,25"-Okulare - für Kowa TSN Spektive-TSN-AS1.25G

Der Adapter ermöglicht die Verwendung von 1,25"-Okularen an den KOWA Spektiven.

www.teleskop-express.de

The other one:

Teleskop-Express: Kowa Astro-Adapter für 1,25"-Okulare - für Kowa TSN Spektive-TSN-AS1.25K

Der Adapter ermöglicht die Verwendung von 1,25"-Okularen an den KOWA Spektiven.

www.teleskop-express.de

The reason why I'm asking is that the adapter with the grub screws offers a bit more backfocus... might be your missing millimeter...

Joachim

 

[Binastro]

Astroboot 1.5x Barlow £8.30.

I have an AE Engineering 1.5x barlow in 1.25 inch barrel.

There are also 1.5x Barlows in 0.965 inch or 24.5mm barrel.

Regards,
B.

 

[jring]

Hi,

if using a different adapter will not help, one could also try so called glass-path correctors... basically very low magnification barlows used to get more backfocus w/o cutting the tube for use with binoviewers mainly...

Teleskop-Express: Baader Glasspathcorrector 1:1.25 for Baader Binoviewers with T2 Connection-GWK1,25x

The # 2456314 shortens the optical path of the binoviewer by 18 mm and is suitable for the Baader Maxbright Binoviewers.

www.teleskop-express.de

Problem with this example is that it has T2 threads designed to fit the Baader maxbright binoviewer - no so great if you want to use it with sth else...
In general these are also designed to correct the spherocromatism introduced by the glass path in the binoviewer and if you use the w/o this might actually introduce it...

Joachim

 

[Tringa45]

As you have noticed, the barrel on the 3-6 mm Nagler zoom is too long. According to the Televue specifications it is 1.6". All their Plössls are less than an inch and even the barrel on a 3.5 mm Nagler, which will reach infinity focus with the thumb screw adapter on my 883 is only 1.2".

AFAIK the first birding scopes that were adapted to astronomical eyepieces were Swarovskis and Zeiss Diascopes. Swarovski even sold a rebadged 6 mm Vixen LV for 77x magnification. I have a licensed copy of the original Swarovski adapter. Zeiss offered a grub-screw adapter for the Diascopes, which was rather awkward to use as it had to be fixed with a female-threaded retaining ring. One dealer here offered 5 mm Vixen LVWs with shortened barrels and a customer used one on a Diascope at 100x to check the blades of wind machines for cracks. A birder I know also uses one on his ATM80 (92x) to read rings.

John

 

[Binastro]

Adriano Lolli seems to make anything optical, at least the mechanical side.

He has a 1.4x semi apo Barlow listed as well as a 1.5x apo Barlow.

He seems to do intricate binocular repairs.
The videos are in Italian but spoken slowly and clearly.

I don't know if anyone here has had anything made by him.

Regards,
B.

 

[dothedr3w]

Hey thanks everyone for the thoughtful replies. I'll try to clear a couple things up as I don't think I gave enough info:

- I have the Baader eyepiece adapter with grub screws and brass compression ring;

- I also have the Kowa astro adapter with knurled thumbscrews;

- The eyepiece, with it's longer-than-standard barrel bottoms out in both the scope, and the scope with the 1.6x extender (which I acknowledge is basically a proprietary barlow);

- the eyepiece adapter I use is inconsequential with this particular eyepiece as it bottoms out regardless. Neither variant affects the eyepiece's ability to fully seat as with most other eyepieces.

I realize a dedicated telescope over a spotting scope is the obvious choice for astronomical uses, however, I'm not made of money. For that very reason I purchased a 3-6mm zoom to avoid purchasing multiple eyepieces. Plus, looking at wildlife is just as much, if not more fun than looking at bright dots, so spotter > tele for my uses.

The 1.6x extender gives more magnification than I'll ever need with this scope. 1.5x barlow is so close to the 1.6x extender it's redundant and a waste of money. 2.0x barlow is simply too much with the 3-6mm zoom, and would necessitate the purchase of further eyepiece's. $$$

With my current setup I'm covered from 25x-96x, and 133x-267x. The intent of the low power barlow is to fill the gap between between 97x-132x. IF the Nagler zoom worked in the scope without the extender it would cover 83x-167x, which would be perfect.

The low power barlow is ideally 1.1x/1.2x/1.3x to make the investment worthwhile and not redundant.

Joachim, what is this glass path corrector you speak of? You might be into something!

 

[GeorgeL]

You’ll probably not like this but my suggestion, frankly, is to sell your TV zoom eyepiece and replace it with a couple of very short, wide field EP’s. TV eyepieces have high resale values so you wouldn’t be losing much. I know it’s inconvenient swapping out EP’s but you’ll appreciate the AFOV these fixed focal length EP’s offer.

 

[dothedr3w]

You’ll probably not like this but my suggestion, frankly, is to sell your TV zoom eyepiece and replace it with a couple of very short, wide field EP’s. TV eyepieces have high resale values so you wouldn’t be losing much. I know it’s inconvenient swapping out EP’s but you’ll appreciate the AFOV these fixed focal length EP’s offer.

Hey man I appreciate the suggestion. I've already grown pretty attached to the zoom and the convenience is tough to argue against. If I can't find a barlow or similar solution, and can't live with the gap in zoom range, I'll likely just get a 4.5mm fixed.

 

[jring]

Hi,

the Baader 1.25x glass path corrector can be found here... it will give 18mm of backfocus but I'm not sure how to adapt it in your case and whether the adaption will eat up the offered backfocus or not. Also Baader states expressly that the device is designed mainly to correct the spherochromatism introduced by the glass path of the prisms inside a binoviewer, so results with your Kowa (which also has prisms but is already corrected for it) might be non-optimal.

Glasspathcorrector 1:1,25 for Baader-Binoviewer with T-2 thread (MaxBright® II and MaxBright®)

Glasspathcorrector Factor 1,25. Optical path length: ≥ -30 mmInsert diameter: ∅ 38 mmSuitable to insert into the Baader MaxBright (Classic and MaxBright® II)A Baader Glaspathcorrector is not a Barlow lens! The reason for this name (in Germany the name Gla

www.baader-planetarium.com

Siebert Optics also makes correctors for binoviewers including two versions with 1.25x. He has a waitlist now due to Covid (not him being sick but people having plenty of time and money for astro stuff as pubcrawls and traveling are not recommend or allowed). Since his products are basically made to order it is probable that his corrector can be made so it fits your EP directly - for a fee...

Siebert Optics - Barlow Lenses

But quite frankly, selling off the Nagler zoom and getting a used 8" dobs from the proceeds will be actually cheaper and get your astro views to another level... You can get an adapter made to use your Kowa wide zoom for it... and have a great mid to high mag EP.... https://www.cloudynights.com/topic/569030-kowa-te-11wz-the-plot-thickens/
You basically only need a low mag EP of 24-30mm in addition to the zoom...

Joachim

 

[dothedr3w]

I've emailed siebert about them making a barlow. Failing that, I'm going to just live with it. Thanks everyone!

 

[tenex]

With my current setup I'm covered from 25x-96x, and 133x-267x.

I'm just curious, thinking about a scope and eyepieces myself: how often do conditions actually allow you to use even 133x, and does your Kowa still perform well at 200x or more? Also, what are good eyepieces in the 3.5-4.5mm range with at least 60° field and 12mm ER? I've looked into DeLite, Nagler, Delos, Morpheus... and the last two seem quite big/heavy, esp. angled down on a 45° scope.

 

[DRodrigues]

I've emailed siebert about them making a barlow. Failing that, I'm going to just live with it...

I read that Harry Siebert is better contacted by phone and is slow replying to e-mails due to too much work...
Another solution is to use 1.25" GPC (that Joachim has mentioned on the different Baader format), if the nagler zoom has filter threads. The GPCs - Harry calls these OCAs - can have 1.25" filter threads and you should be aware that magnification mentioned and the gain in focus travel are for binoviewers that have >100mm light path. The 1.6x like 1.6x GPC should result on 1.2-1.3x when attached directly to an ep but the gain on focus will be reduced also - these are sold under several brands and you should look for one that doesn't have filter thread on the telescope side as the GPC 2.6x - these last versions result on a 1.6x increase - since would maximize the focus gain i.e. there would be no focus travel lost by the length of the filter thread on the telescope side - I have one that I removed the filter thread with a machine but even so the focus gain didn't result for what I wanted - I don't remembered how much was the gain in focus...

 

[dothedr3w]

I'm just curious, thinking about a scope and eyepieces myself: how often do conditions actually allow you to use even 133x, and does your Kowa still perform well at 200x or more? Also, what are good eyepieces in the 3.5-4.5mm range with at least 60° field and 12mm ER? I've looked into DeLite, Nagler, Delos, Morpheus... and the last two seem quite big/heavy, esp. angled down on a 45° scope.

Oh I'm definitely the wrong person to ask, I'm far too junior. I don't have the experience to differentiate between good and bad conditions; I've only had it out a few nights since I got it.

That said anytime the clouds broke enough for me to take the spotter out, I found 133x to be good everytime. Before I bought the Nagler zoom I was looking at the Pentax XW, Nikon NAV SW, and Takahashi TOE eyepieces. I think the Nikon's end at 5mm, but the other two go down to 3mm. Tak's will only be around 50 degrees, and the XW's will be around 70. I think anything 60 degrees or more they start to get pretty large.

 

[tenex]

There are 3, 4, 5mm DeLites with 62° that aren't too large... how do you like using the Nagler zoom? It sounds like a great idea but 50° is rather narrow, and the eye relief is listed as only 10mm. (We don't wear glasses but even so that seems tight.)

 

[GeorgeL]

I don’t own a zoom eyepiece, primary due to the lack of wide AFOV, but have several individual eyepieces ranging between 68 to 82 degrees of AFOV. On my 80mm spotter they cover magnifications of 20x 24x 34x 48x 54x 68x 96x 137x.
99% of the time I‘m using one of the four lower magnification EP’s for terrestrial use. And I usually just take one EP, 34x, for instance, when I go look at ducks and geese.

For quick, grab and go set up to view planets and the moon I use 96x & 137x. If I need better resolution or more magnification I use a telescope.
Once you get accustomed with viewing thru wide field EP’s anything less seems like tunnel vision, unless you’re into planets.

 

[dothedr3w]

There are 3, 4, 5mm DeLites with 62° that aren't too large... how do you like using the Nagler zoom? It sounds like a great idea but 50° is rather narrow, and the eye relief is listed as only 10mm. (We don't wear glasses but even so that seems tight.)

I don't find 50 to be prohibitive, and the zoom function and small size more than make up for this 'shortcoming'. At first I was worried about the eye relief, even as a non-glasses wearer, but the eyecup is very well positioned, and you get the full fov as soon as you put your eye to the cup, it's quite intuitive. Even though I can't use the eyepiece in the Kowa without the 1.6x extender installed (yet!), I would absolutely get it again because of the versatility of the zoom. I just leave the grub screw adapter installed on the eyepiece so it's just a matter of popping out the Kowa bayonet eyepiece, and threading this in.