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Pulled the Trigger on Oberwerk BT-70-45 Binoculars

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#1 Eric63

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Posted 20 October 2013 - 11:24 AM

This fall I found myself using my 15x70 binoculars more and more and really loved the 2 eyed viewing experience, the ease of use and mostly the ability of taking in the big picture (which is how I started this hobby over a year and a half ago before I got a slight touch aperture fever :grin:). My problem however is that I get pretty bad neck strain above 45 degree viewing. I’m fine up to 40degrees or so but above 45 it’s really bothersome. So when my lovely wife offered me some astro equipment for my upcoming 50th Birthday, I immediately jumped on the BT70. I think I’m going to love these binos, especially at the cottage where I get Mag 6.5 skies. And the fact that I can increase magnification is just icing on the cake :) . Now, they are back ordered but I should have them by December at the latest (in time for my birthday :jump:).


I think these will also complement my 127Mak when I choose to use them in tandem. The BT-70 are good to a magnification of 47X and the Mak cannot really go below 48X. Also, the Binoculars will be a great grab and go instrument on cold winter nights when I don’t want to be out for too long.

Eric

#2 JustaBoy

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Posted 20 October 2013 - 11:51 AM

+1...!!!!!!!!!!!

#3 daniel_h

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Posted 20 October 2013 - 04:18 PM

70mm is a sweet spot in binos imo, almost a goldilocks

#4 GlennLeDrew

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Posted 20 October 2013 - 05:09 PM

Is this the newer MkII, which uses 1.25" eyepieces and utilizes the full aperture? (As opposed to the first iteration which employed proprietary eyepieces and worked at 60mm aperture?)

#5 JustaBoy

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Posted 20 October 2013 - 05:27 PM

http://www.bigbinocu....com/70bt45.htm

#6 Eric63

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Posted 20 October 2013 - 05:37 PM

This one does use 1.25" eyepieces and from what I have read it has the full 70mm aperture.

Eric

p.s. Happy Birthday :)

#7 Eric63

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Posted 20 October 2013 - 05:46 PM

I have to agree about the sweet spot. I am amazed with what I can see with my current 15x70, and they are not even working at full aperture. From what I understand these bt70's would be equivalent to an 80mm apo for both contrast and light gathering, which will be great under dark skies.

Eric

#8 JustaBoy

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Posted 20 October 2013 - 06:11 PM

There's nothing APO about them, so why do you say that?

#9 Eric63

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Posted 20 October 2013 - 06:21 PM

Well first of all they are a triplet and from reading previous post from EDz, a 70mm binocular is roughly equivalent to an 84mm scope (for light gathering and contrast but not for resolution). Now, I'm not buying these because I think they are an APO, I'm buying these because I prefer two eyed viewing and I love the wide field views that I will get. I was considering an 80ed at one point but I did not want to compete with my Mak at the high magnification end and I prefer two eyes at the lower end.

Eric

#10 JustaBoy

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Posted 20 October 2013 - 06:44 PM

Understood - Please understand that I am happy for you, and would love to have a pair for myself, but the fact that they are a triplet really doesn't count towards improved performance. They are still just an Achro.

-Chuck

#11 Eric63

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Posted 20 October 2013 - 06:49 PM

You may be right Chuck, but since I'm buying these for low power views it doesn't really matter. I guess that when I hear the word triplet I automatically think APO :grin:

Eric

#12 Jarrod

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Posted 20 October 2013 - 06:58 PM

Yes, it's a triplet, but it's an f/5 made of relatively inexpensive high-refractive-index glass. So while they are well-corrected for what they are, you aren't going to achieve true apo performance. The 20x80 deluxe III triplet is good, but does show a thin blue (or is it green?) line around the full moon. But the design produces good contrast. If the 70 triplet is like the 80, I think you'll be pleased.

#13 Eric63

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Posted 20 October 2013 - 07:05 PM

Thank you Jarrod, I was not aware of the type of glass. I never found the moon to be an issue when I had my 4"f5 achro, but Jupiter was another story altogether. Anyway, I have other instruments for those objects. I really like my 15X70 Skymasters and I think that these will be even better.

Eric

#14 JustaBoy

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Posted 20 October 2013 - 07:14 PM

I think you will Love them, Eric... Now start putting your coins aside for $Pairs$ of eyepieces:-)

It's great fun!
-Chuck

#15 Rich V.

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Posted 20 October 2013 - 07:20 PM

Is this the newer MkII, which uses 1.25" eyepieces and utilizes the full aperture? (As opposed to the first iteration which employed proprietary eyepieces and worked at 60mm aperture?)


Glenn, I think you're thinking of the 90° Garrett MKII; I believe Mr. Bill determined that these Obie 45° BTs were only 60mm effective. There is no MKII 45°. ;)

Rich

#16 Eric63

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Posted 20 October 2013 - 07:37 PM

Yes, my wife said that I get the binoculars for my birthday... but everything else is up to me :)

I'm really looking forward to them, thanks for the input.

Eric

#17 GlennLeDrew

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Posted 21 October 2013 - 01:41 AM

Rich,
Oops; I was indeed thinking of the 90 degree version! I must read thread titles more carefully. :grin: I wonder if the objective is different between the two?

Eric,
I have on hand for examination--and overdue for return--the 90 degree version of the Mk II 70mm BT. It has achromat-like chromatic aberration; it's certainly not APO-like.

I assume the prism rear aperture will be fairly similar. If so, a 19mm Panoptic is a wonderful eyepiece for it. Even a 24mm Pan is quite useable, albeit with a *very* small and not too objectionable edge darkening, which delivers the widest true field possible at a nice AFoV and with excellent correction across the great bulk of the field. I've tried both these eyepieces, as well as some of a friend's Naglers.

#18 Eric63

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Posted 21 October 2013 - 06:50 AM

I guess I am still learning about scope and binocular design :lol: But that all part of the fun!

Thanks for the info Glen. I'm really looking forward to getting these. Let me know if you are interested in taking a look at them when they come in.

Eric

#19 JustaBoy

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Posted 21 October 2013 - 08:49 AM

Eric,
Unless my eyeballs are failing me again, these are 60mm (effective), and you are still getting them?

-Chuck

#20 Eric63

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Posted 21 October 2013 - 09:08 AM

I'm going to have to look into this further. I had read that they were at full aperture. Thanks for the heads up.

Eric

#21 JustaBoy

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Posted 21 October 2013 - 09:13 AM

Yes,

Please check this out and let us all know.

If memory can be trusted, the 70mm-90° from Garrett are actually 70mm?

#22 planetmalc

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Posted 21 October 2013 - 09:16 AM

Eric,
I have on hand for examination--and overdue for return--the 90 degree version of the Mk II 70mm BT. I assume the prism rear aperture will be fairly similar. If so, a 19mm Panoptic is a wonderful eyepiece for it. Even a 24mm Pan is quite useable, albeit with a *very* small and not too objectionable edge darkening, which delivers the widest true field possible at a nice AFoV and with excellent correction across the great bulk of the field. I've tried both these eyepieces, as well as some of a friend's Naglers.


In the accessories list contained within Chuck's link, they're suggesting that their own 27mm 70degree AFOV eyepiece can be used at 14x. Seems unlikely to me, without vignetting (but who knows?).

What a shame that this instrument (like several others) has been designed to ride in a fork mount, but there IS no fork mount on offer. :bawling:

#23 Eric63

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Posted 21 October 2013 - 09:17 AM

BTW chuck, where did you get the 60mm figure from?

Eric

#24 Jon Isaacs

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Posted 21 October 2013 - 10:06 AM

Congratulations on your new Binos.. 70mm with angled 1.25 inch eyepieces... That's pretty darn nice.

It's my understanding that doublet-triplet doesn't really matter when it comes to achromats.. the correction is still the same 1 part in 2000.. but this is not a high power planetary double star instrument and it ought to be mighty sweet and any sort of reasonable magnification.

Jon

#25 JustaBoy

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Posted 21 October 2013 - 10:12 AM

Hi Eric,

It's in the link that Rich V. posted above:

http://www.cloudynig...5890567/page...

You have to read down apx 45% of the thread, and you will see Bill saying: "Well, on the positive side, build quality and coatings are first rate.

Unfortunately, they failed the effective aperture test....measured around 60mm.

Measured Fuji 16x70s and got 70mm.

Returning for refund"

There is an even longer thread about the Garretts somewhere on CN...

-Chuck






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