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Equipment Discussions >> Binoculars

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Mr. Bill
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BT-70s on way....
      #5890567 - 05/29/13 11:36 AM

After reading Phil H review I decided to get these for future Australia trip (as well as now Nevada trips.)

Will get in time for next new moon cycle. 19mm Pans= 20x and 3.5mm exit pupil and 3+ degree fov.

http://bigbinoculars.com/images/64-65.pdf



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Jarrod
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5890666 - 05/29/13 12:33 PM



I look forward to hearing your impressions.


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Jawaid I. Abbasi
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Re: BT-70s on way.... new [Re: Jarrod]
      #5890703 - 05/29/13 01:06 PM

Mr Bill,
Is not "Garrett 90 degree 70mm" has the same quality plus 90 degree, twist lock eyepieces holder as an extra feature much better ?


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Mr. Bill
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Re: BT-70s on way.... new [Re: Jawaid I. Abbasi]
      #5890763 - 05/29/13 01:55 PM

Quote:

Mr Bill,
Is not "Garrett 90 degree 70mm" has the same quality plus 90 degree, twist lock eyepieces holder as an extra feature much better ?




No. Frankly, I have not been impressed with Garrett products and find 45 degree oculars to be just fine. If Phil H. is impressed with the BT70 45s, I'm sure I will be too (although I think I tend to be a bit more critical in my product evaluations.)

I prefer doing business with Kevin B...at least I can talk on the phone with him; try that with Garrett

Edited by Mr. Bill (05/29/13 02:17 PM)


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Mr. Bill
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Re: BT-70s on way.... new [Re: Jarrod]
      #5890873 - 05/29/13 03:24 PM

Quote:



I look forward to hearing your impressions.




These were bought to compare directly to my Fuji 16x70s....if they pass the "smell test" I'll probably put the Fujis up for sale. I'm a user, not a collector and don't need two that do the same job.



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Jawaid I. Abbasi
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5890886 - 05/29/13 03:31 PM

I do like Oberweck too. As a matter of fact; I have Deluxe 100mm Center focus and that thing is very good to excellent in every aspect.

The twist lock feature if available in Oberweck; then it will be even better and perhaps will also be a selling point.
The twist lock feature almost eliminate the "collimination" problem and changing eyepieces in a snap.

Anyways, Let us know you liking and first report when you receive your instrument.

Thank you,


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chuck56
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Re: BT-70s on way.... new [Re: Jawaid I. Abbasi]
      #5890925 - 05/29/13 03:52 PM

Ditto on the report!

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curiosidad
sage


Reged: 06/09/11

Re: BT-70s on way.... new [Re: chuck56]
      #5890967 - 05/29/13 04:26 PM

Hello,
It would be possible to use with this binoculars two ep. zoom?
Thanks


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Mr. Bill
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Re: BT-70s on way.... new [Re: curiosidad]
      #5891068 - 05/29/13 05:43 PM

Quote:

Hello,
It would be possible to use with this binoculars two ep. zoom?
Thanks




Don't know...send me a pair and we'll find out.



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daniel_h
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5891188 - 05/29/13 07:19 PM

i think Rony the sketching guru has a pair of these, teleskop-express sell them

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curiosidad
sage


Reged: 06/09/11

Re: BT-70s on way.... new [Re: daniel_h]
      #5892111 - 05/30/13 10:38 AM

Hello,
Thanks for the reply.
I will ask to TS in Europe.
Best


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Mr. Bill
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Re: BT-70s on way.... new [Re: curiosidad]
      #5893941 - 05/31/13 10:17 AM

BT70s in Fed Ex system....expected delivery next Wed.

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Rich V.
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5894000 - 05/31/13 10:43 AM

It will be interesting to see how these BT70s compare to your 16x70 FMTs at 16x, Bill.

The 45 viewing angle will certainly be a plus but I'm wondering about contrast and edge of field correction. Looking forward to your impressions...

Rich


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Goodchild
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Re: BT-70s on way.... new [Re: Rich V.]
      #5896056 - 06/01/13 01:28 PM

I just received my edition of Astronomy magazine with Phil's review of these binos. Can I say that he "raved" about them? A very promising report. No chromatic abberation, that's encouraging. The only thing missing in his report is whether or not these objectives lived up to their stated 70mm aperture. Bill, looking forward to your evaluation to compare to Phil's. If you concur, I can see a pair of these in my future.

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rdandrea
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5896087 - 06/01/13 01:48 PM

Quote:

BT70s in Fed Ex system....expected delivery next Wed.




Great. That means rain for the full new Moon week.


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Mr. Bill
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Re: BT-70s on way.... new [Re: rdandrea]
      #5896096 - 06/01/13 01:52 PM

Quote:

Quote:

BT70s in Fed Ex system....expected delivery next Wed.




Great. That means rain for the full new Moon week.




Only over my house...


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Goodchild
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Reged: 12/31/08

Re: BT-70s on way.... new [Re: Mr. Bill]
      #5896475 - 06/01/13 05:32 PM

Would a TV Telepod mount handle this bino? If I get one I'd like to get a fork mount for it.

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John F
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5900865 - 06/03/13 11:59 PM

Congratulations on your purchase. I look forward to hearing what you think of them after using them. I called BigBinoculars.com this morning to ask a few questions concerning them and decided to order a pair.

When I read Phil Harrington's review in Astronomy magazine the other day they looked very interesting and I was amazed by four things. First, their feature set. Second, their apparent quality. Third, their very low price. Fourth, that you can use standard astronomical eyepieces with them. I also like the fact that they're not too large or heavy.

With the TV binoviewing eyepieces that I already have I should be able to use this new BT-70-45 at 16x-20x-24x-28x-34x & 42x so that enables a lot of potential uses for it both astronomically and terrestrially. After I receive it and get to try it out for a while I post my impressions of it.

John Finnan


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Vondragonnoggin
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Re: BT-70s on way.... new [Re: John F]
      #5901293 - 06/04/13 08:40 AM

As far as Garret vs Oberwerk, from Kevin's reputation, I would rather deal with Kevin.

Buying the Garret's is a crapshoot on issues as Glenn can attest by seeing the issues in mine. I would rather have Kevin's inspection and QC.

Rather have 90 over 45, but rather have a 45 that has better quality than a 90 with one barrel having unfixable astigmatism.

Maybe you get a great pair from Garret, maybe not, but I'll never chance tht one again. Still nice for lower powers (up to about 40x).

The twist lock oculars aren't that great. Depending on your eyepieces used I suppose. If using less expensive eyepieces, I found it better not to lock them because you have to leave them loose to turn sometimes to get precise merging at higher powers. Leaving them loose in a 90 degree is pretty safe. Don't think a 45 at high positions would be good to leave loose as they might slip out.

Good luck with yours. I'm sure you'll get a decent pair from Oberwerk.


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Mr. Bill
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Re: BT-70s on way.... new [Re: John F]
      #5901400 - 06/04/13 10:04 AM

I'll start a new thread comparing the Fuji 16x70 to the BT70 which is also 16x70 with the supplied eps...also have pairs of 24mm and 19mm Pans and 14mm Denks.



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Mr. Bill
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5906948 - 06/06/13 09:53 PM Attachment (83 downloads)

Arrived...

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Mr. Bill
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5906951 - 06/06/13 09:54 PM Attachment (77 downloads)

More....

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Mr. Bill
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5906957 - 06/06/13 09:56 PM Attachment (62 downloads)

Some more...

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Mr. Bill
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5906960 - 06/06/13 09:57 PM Attachment (81 downloads)

And still more...

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Jarrod
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Loc: SE USA
Re: BT-70s on way.... new [Re: Mr. Bill]
      #5907110 - 06/06/13 11:18 PM



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hallelujah
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5907116 - 06/06/13 11:23 PM

Mr. Bill,

Did you find any fingernails, or any other stray light, internally?

Stan


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Mr. Bill
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Re: BT-70s on way.... new [Re: hallelujah]
      #5907154 - 06/06/13 11:45 PM

All will be revealed in the next few days...



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plyscope
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Loc: Perth, West Australia
Re: BT-70s on way.... new [Re: Mr. Bill]
      #5907162 - 06/06/13 11:52 PM

Thanks for the update Mr Bill, looks like a nice compact binocular telescope.

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mercedes_sl1970
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Loc: Canberra, Oz
Re: BT-70s on way.... new [Re: plyscope]
      #5907238 - 06/07/13 12:47 AM

Looks like a rather nice, relatively compact setup. Look forward to reading about how it goes.

Andrew


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Man in a Tub
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Re: BT-70s on way.... new [Re: hallelujah]
      #5907352 - 06/07/13 06:09 AM

Quote:

Mr. Bill,

Did you find any fingernails, or any other stray light, internally?

Stan




I see a fingernail at about 2 o'clock in the objective lens picture. ;-)


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Mark9473
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Re: BT-70s on way.... new [Re: Man in a Tub]
      #5907419 - 06/07/13 07:46 AM

Hahaha, you had me fooled there for a second, Todd!

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Mr. Bill
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Re: BT-70s on way.... new [Re: Mark9473]
      #5907744 - 06/07/13 11:19 AM

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



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Mr. Bill
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5907760 - 06/07/13 11:26 AM

I didn't do the effective aperture until this morning.

I got a feeling something was not right when I compared views of M24 between binoculars and the Fujis were much brighter. That was the tipoff.

Also exit pupil was smaller than it should have been...another tipoff.

Edited by Mr. Bill (06/07/13 01:15 PM)


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Rich V.
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5907772 - 06/07/13 11:33 AM

Bummer, dude.

Being how simple this test is, I wonder if Kevin is aware of this? Better call it a BT-60, huh?

Hasn't the Garrett offering been aperture tested at ~70mm?

Rich


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Mr. Bill
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Re: BT-70s on way.... new [Re: Rich V.]
      #5907939 - 06/07/13 01:18 PM

Surprised Phil H didn't catch this...

I bought these on the strength of his review.



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John Miele
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5908040 - 06/07/13 02:13 PM

Man...that's too bad. I had this model on my short list as well. I thought that the 45 deg. models typically did not have effective aperture reduction issues like the 90 deg. models often seem to have...?...John

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Mr. Bill
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Re: BT-70s on way.... new [Re: John Miele]
      #5908055 - 06/07/13 02:19 PM

Yeah, me too.

I guess I'll have to "limp along" with the Fujis...they're looking pretty good now. I was hoping for BT70 45s so I didn't have to use a p-mount for overhead viewing.


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Rich V.
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5908087 - 06/07/13 02:42 PM

Quote:

Surprised Phil H didn't catch this...

I bought these on the strength of his review.






Mr. Harrington may be an accomplished observer but I thought his review was pretty similar to the many other gushy astro magazine "reviews". I'm supposing brevity was needed in this instance...

Now, if EdZ did a review of this BT, we would be reading about effective aperture, percent illumination and the more objective aspects we like to read about and discuss on this forum.

Rich


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Jarrod
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Re: BT-70s on way.... new [Re: Rich V.]
      #5908111 - 06/07/13 02:57 PM

Wow, that is really too bad. Thanks for the report, short and disappointing as it is...

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Mr. Bill
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Re: BT-70s on way.... new [Re: Rich V.]
      #5908121 - 06/07/13 03:05 PM

Quote:


Mr. Harrington may be an accomplished observer but I thought his review was pretty similar to the many other gushy astro magazine "reviews". I'm supposing brevity was needed in this instance...

Now, if EdZ did a review of this BT, we would be reading about effective aperture, percent illumination and the more objective aspects we like to read about and discuss on this forum.

Rich




Maybe Garrett and Big Binocular would like me to review their next product....not.



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SpaceNetworks
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5908137 - 06/07/13 03:13 PM

I'm fairly new to binocular astronomy and this forum-- mostly lurking actually as part of my due diligence research. I passed on the BT-70s merely because I couldn't see how to effectively use an optical finder mounted on the center dovetail shoe where the handle is located. The Astronomy mag review suggested using a finder for higher magnifications, but I couldn't visualize how using the center shoe would work with the 45 degree focusers. Now that I see Mr. Bill's profile photo, I think that's a valid concern. Well, I opted for the Zhumell 25x100, BP red dot finder and UA mounting bracket. First light-- probably tonight. I'm planning on taking this setup to Barstow for dark skies when I tour the Goldstone DSN site this summer. I'll also be able to borrow a Celestron NexStar 8i for the summer, so I'm looking forward to that, too.

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Rich V.
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5908206 - 06/07/13 03:50 PM

Quote:

Maybe Garrett and Big Binocular would like me to review their next product....not.






If I were them, I'd welcome the beta testing you could provide. Why not let someone wring out the bino to see if it's everything it can be at that price point. Sloppy engineering shouldn't be one of the compromises, IMO. You'd think that before a run of binos is produced would be the time to make any tweaks. That is, of course, if these aren't just picked out of existing inventory in China and painted/decorated with logos and shipped to the USA.

Rich


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Goodchild
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Re: BT-70s on way.... new [Re: Rich V.]
      #5908829 - 06/07/13 09:39 PM

Me thinks that this bino is made like so many of the others, i.e. to cater to the general public and not we astronomers. Most non-astronomers are probably not aware of "effective aperture, or if they are, not concerned with it.

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Mr. Bill
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Re: BT-70s on way.... new [Re: Goodchild]
      #5908850 - 06/07/13 09:49 PM

Quote:

Me thinks that this bino is made like so many of the others, i.e. to cater to the general public and not we astronomers. Most non-astronomers are probably not aware of "effective aperture, or if they are, not concerned with it.




At $850....I think the target group is probably not the WalMart crowd. Oh BTW, its "us astronomers"... My wife's an English teacher.



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Goodchild
scholastic sledgehammer
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Reged: 12/31/08

Re: BT-70s on way.... new [Re: Mr. Bill]
      #5908879 - 06/07/13 10:07 PM

Quote:

Quote:

Me thinks that this bino is made like so many of the others, i.e. to cater to the general public and not we astronomers. Most non-astronomers are probably not aware of "effective aperture, or if they are, not concerned with it.






At $850....I think the target group is probably not the WalMart crowd. Oh BTW, its "us astronomers"... My wife's an English teacher.







Okay, but then Kevin, who frequents this forum and knows the issue with effective aperture, should have made this a criterion with the manufacturer. It appears that he didn't, which then begs the question "why".

Edited by Goodchild (06/07/13 10:16 PM)


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Jarrod
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5908882 - 06/07/13 10:11 PM

Quote:

Oh BTW, its "us astronomers"... My wife's an English teacher.




We wouldn't want you to have to sleep on the couch, so we won't tell her that you used its instead of it's.


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Mr. Bill
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Re: BT-70s on way.... new [Re: Jarrod]
      #5909052 - 06/08/13 12:10 AM

Quote:

Quote:

Oh BTW, its "us astronomers"... My wife's an English teacher.




We wouldn't want you to have to sleep on the couch, so we won't tell her that you used its instead of it's.




right you are


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Jawaid I. Abbasi
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Loc: LEVITTOWN, PA
Re: BT-70s on way.... new [Re: Mr. Bill]
      #5909080 - 06/08/13 12:47 AM

Mr Bill,
Despite what you got the expectation; I have the new newer version of 100D which is SUBERB in every aspect. The only thing was missing the 45 or 90 degree oculers. Otherwise; Oberweck product is good to excellent.

I have a chance using both Oberweck and Garrett and I can say that thay have the same quality. The BT-70 90degree that I suggested was based on some credible reviews as well as it has couple of unique features.

Anyways, I am sorry that it did not come to your expectation. I would suggest that you would do a mini review for those that do not have concern about effective aperture.
Thank you,


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GlennLeDrew
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Re: BT-70s on way.... new [Re: Jawaid I. Abbasi]
      #5909123 - 06/08/13 02:05 AM

Perhaps insufficient time has passed for even the general astro community outside us geeks here on CN to have become aware of effective aperture concerns.

The 70mm Mk II, 90 degree job does work at 69mm+ clear aperture, but the one example I've examined exhibits significant astigmatism in one barrel, and about 1/2 that in the other barrel. I suspect it arises from the pentaprisms; the orientation on both sides is suspiciously similar. I wonder if a rush was put on to make larger pentaprisms for the Mk II, and one or both reflective surfaces was not finished sufficiently flat??? Those elements which just fully accommodate the light cone (as do the pentas, being positioned far up the light cone) have more stringent tolerances on error of figure.

It seems difficult to find *both* full aperture performance and not-significant aberrations. The original 70mm 90 degree, which was restricted to 60mm, had a rather better image, with less astigmatism, spherical aberration and chromatic aberration. However the lesser aperture resulted in poorer efficiency.

But how much can one expect for the price?...


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KennyJ
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Re: BT-70s on way.... new [Re: GlennLeDrew]
      #5909133 - 06/08/13 02:20 AM

I can understand the disappointment of discovering the effective aperture being only 60mm.rather than the advertised and expected 70mm.

If all other aspects of build and optical quality are satisfactory, I personally don't think the price of $850 is necessarily too much to pay.

After all, one could easily pay up to twice as much as that for the body alone of a spotting scope of similar aperture, the optical qualities of which would likely be ripped to shreds by some of the more demanding critics who have contributed to this forum, past and present.

At least the built-in aperture restriction saves one having to make one themselves!


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charen
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Re: BT-70s on way.... new [Re: GlennLeDrew]
      #5909145 - 06/08/13 02:31 AM

They should call them BT-60's. My old Oberwerk 45/100 BT's measured 91 mm. The front baffle reduced the aperture. I presume it's the same with the BT-70's, a front baffle is to 'blame'. A positive outcome is that it does reduce CA.


Chris


Edited by charen (06/08/13 02:38 AM)


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JKoelman
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Re: BT-70s on way.... new [Re: charen]
      #5909194 - 06/08/13 04:24 AM

Overstating the light gathering capability of an astronomy binocular by as much as 36% is inexcusable. <deletes Oberwerk BT-70-45 from wish list>

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mercedes_sl1970
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Re: BT-70s on way.... new [Re: JKoelman]
      #5909221 - 06/08/13 05:45 AM

A very frustrating outcome.

Just out of curiosity, how was the view?

Andrew


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Mr. Bill
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Re: BT-70s on way.... new [Re: mercedes_sl1970]
      #5909400 - 06/08/13 09:19 AM

Using the supplied 23.9mm ep, on axis very sharp out to about 50%, good out to 80% where image degraded rapidly to fieldstop. Pretty typical of binocular fields.

Substituting 24mm and 19mm Pans produced images that were sharp out to 90%. This shows that the use of high quality eps improves the views dramatically.

Same with my Oberwerk BT100 45....Pans turned it into an entirely different binocular.

Of course, the Pans cost at least three times as much as the BT eps would cost if bought separately....which if supplied with the BTs would have made the price point well over a $1000.

Edited by Mr. Bill (06/08/13 09:38 AM)


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Mr. Bill
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Re: BT-70s on way.... new [Re: KennyJ]
      #5909415 - 06/08/13 09:29 AM

Quote:

I can understand the disappointment of discovering the effective aperture being only 60mm.rather than the advertised and expected 70mm.

If all other aspects of build and optical quality are satisfactory, I personally don't think the price of $850 is necessarily too much to pay.

After all, one could easily pay up to twice as much as that for the body alone of a spotting scope of similar aperture, the optical qualities of which would likely be ripped to shreds by some of the more demanding critics who have contributed to this forum, past and present.

At least the built-in aperture restriction saves one having to make one themselves!




Kenny

If your intended use is primarily non astronomy, ie daytime use, birding etc I would agree. They were quite impressive with my daytime evaluations.

For my purposes, examining Milky Way structure which is extremely low contrast fields, light gathering and edge of field illumination and contrast are all important.

It was quite obvious to me when looking at MW fields through both the BT70s at 16x (24mm Pans) and Fuji 16x70s that there was a problem with the BTs. The images were much dimmer and much subtle detail was lost as a result. Comparing exit pupils (which should have been identical) showed what was going on immediately...vignetting in the BTs.

For my use, they are not satisfactory...I paid for a 70mm aperture, not 60mm.

Edited by Mr. Bill (06/08/13 09:33 AM)


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Mr. Bill
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Re: BT-70s on way.... new [Re: charen]
      #5909460 - 06/08/13 09:58 AM

I don't believe that a baffle is the problem with the BT70s.

I estimate that the distance from the focal plane (fieldstop of ep) to the rear prism face to be more than 2 inches, way more than necessary. The prism could have been pushed back at least an inch which would have improved the effective aperture considerably.

This was probably done to accomodate various eps with different fieldstop locations.

The fieldstops of most 1 1/4 eps are within plus/minus 0.25 inch of ep shoulder, so range of focus and therefore minimum distance to prism could have been much closer.

Design decision error, IMO. Aperture sacrificed to accomodate focus any ep.


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GlennLeDrew
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5909654 - 06/08/13 12:15 PM

Bill,
A rear prism-to-focus distance of about 2" (50mm), as you report, is indeed a factor limiting effective aperture. The older, proprietary eyepiece BTs had this distance down to not much larger than zero, although the then-smaller frontmost prism (penta, in the 90 degree config) would still cause a restriction.

Incorporating a wider variety of eyepieces results in the necessary evil of a larger working space behind the rear prism. This is in part because some eyepieces have longer lower barrels. But also because some do have their focus outside the +/-1/4"-of-the-shoulder zone.

But fundamentally, the long optical path length taken up by the total prism train is a significant limitation when the desire for faster objectives--and hence lighter, more compact instruments--is a prime driver in design. Such prism systems would benefit from f/7-8 objectives. For then both full aperture performance and good working distance at the back end would be achieved. But then maximal field diameter is reduced...


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RodgerHouTex
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Re: BT-70s on way.... new [Re: GlennLeDrew]
      #5909694 - 06/08/13 12:45 PM

One can expect for the price a brand new BT-70 that performs as described. If an item is defective I ALWAYS send it back. And if I have to, dispute the charge with my credit card company.

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Mr. Bill
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Re: BT-70s on way.... new [Re: RodgerHouTex]
      #5909711 - 06/08/13 12:55 PM

Quote:

One can expect for the price a brand new BT-70 that performs as described. If an item is defective I ALWAYS send it back. And if I have to, dispute the charge with my credit card company.




One of the reasons I like doing business with Big Binocular is that Kevin B. and I have a cordial relationship besides strictly business. I wouldn't say that the BTs were defective; just not as advertised. He was as suprised as I was about the restricted aperture.

He's paying return shipping....you can't ask for better than that.


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Mr. Bill
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5909727 - 06/08/13 01:08 PM

I guess I'll just have to "roll my own."

See if Kevin has a couple of those oversized prism assmbles used in my BT100 45s lying around.

Be fun to build a porro prism binocular...that way I know the job gets done right.


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Mr. Bill
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5909765 - 06/08/13 01:28 PM Attachment (38 downloads)

For those interested...this is from a PowerPoint presentation on raytracing I'm presenting this summer at Golden State Star Party.

Obviously, prism apertures lie inside on axis cone causing vignetting or loss of effective aperture.


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GlennLeDrew
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5909812 - 06/08/13 01:52 PM

I wouldn't call 'em defective, just improperly designed. But I suppose, from the standpoint of getting what's *advertised*, they could be considered 'defective.'

You haven't had the best of luck with commercial binos of late, eh Bill?

Most users will be blissfully unaware of the reduced aperture. Until recently, and perhaps to this very moment, the manufacturers have counted on ignorance. It's too bad reviewers didn't more universally highlight this aspect. Then there might be pressure to correct this deficiency. If one prized element is light weight, the extra mass involved in the unused aperture is unnecessary.

However, there *is* one potentially valid reason to design a bino with what is effectively an oversized objective. It's for the much the same reason Schmidt cameras, especially of wide field, are fitted with oversized primary mirrors. The off-axis illumination is improved. But the gain here is somewhat offset by the sheer length of the optical path length through the prism chain, plus the generally small-ish fields of view in these things anyway. And so the extra mass is overall a negative. Unless the lens making process tends to impart turned edges, which is more likely when speed of fabrication is paramount. *Then* the oversized objective can become necessary.

As an aside... It would be nice to completely disassemble a representative sample of one of these so as to test each optical element. I'd be curious to see accuracy of figure, amount of wedge, flatness of prism faces and angle accuracy on prisms. For example, I've seen bino Porro prisms with horrible non-flatness (especially turned edge), wicked angle error (departures from 45/90 degrees) and ghastly pyramidal error (the planes of the three surfaces make a section of a tall pyramid). The effects on image quality, and the potential for significant and necessary prism chain tilt hardly require elaboration.

I'd like to know if the larger-than-working aperture objectives might be for a reason other than merely providing the illusion of a bigger lens. My interest in prism quality stems from the pronounced astigmatism observed in a 70mm 90 degree Mk II BT, which I *suspect* is caused by the reflecting faces of the pentaprisms (it's definitely not caused by the Porro II groups, for it remains fixed when I rotate the prism cans.)


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Jeff Morgan
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Re: BT-70s on way.... new [Re: Rich V.]
      #5910512 - 06/08/13 10:19 PM

Quote:

Mr. Harrington may be an accomplished observer but I thought his review was pretty similar to the many other gushy astro magazine "reviews". I'm supposing brevity was needed in this instance...

Now, if EdZ did a review of this BT, we would be reading about effective aperture, percent illumination and the more objective aspects we like to read about and discuss on this forum.

Rich




If true, the apparent aperture on these would be an error that is both glaring and fundamental.

Many times I have heard a somewhat Elitist view expressed than only "expert" reviews can be trusted (code word for glossy astro mags).

Sadly, gushy reviews appear to be the magazine norm instead of the exception.


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GlennLeDrew
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Re: BT-70s on way.... new [Re: Jeff Morgan]
      #5910673 - 06/09/13 12:22 AM

Indeed, I fear that magazine reviews, if not based in ignorance, may well willfully ignore deficiencies which do not directly impact the *perceived* quality of view. In isolation, poorer illumination can so easily be overlooked by the average observer. We lot here on CN are now inoculated against such fundamental oversight. At least I like to think so...

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Rich V.
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Re: BT-70s on way.... new [Re: Jeff Morgan]
      #5910694 - 06/09/13 12:40 AM

It's a shame that many binoculars are sub-par regarding effective aperture. Many popular inexpensive binos sold as 70mm actually measure 63mm, similar 80mms are really around 73mm and 100mm and 88mm RA BTs have measured closer to 80mm effective. You likely will not get what you think you're getting.

These BT-70s are just another instance of the industry wide marketing of sub aperture instruments. The manufacturers get away with their claims because the objectives DO measure 70mm or whatever; it's just that the full objective aperture isn't making it to the eyepiece. I'd sure like to see vendors step up to the plate and verify that the products they sell really are what's claimed in the ad copy. Many are no more than a warehouse operation, though, and couldn't care less about the actual specs.

Few "reviewers" give more than a cursory look at the true specs of the binoculars they review. EdZ is one of the rare reviewers that actually doesn't take an instrument at face value. Since his retirement from moderating and organizing this forum, I miss his in-depth reviews and measurements but thank him for all the work that he has left here with us...

Rich


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GlennLeDrew
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Re: BT-70s on way.... new [Re: Rich V.]
      #5910703 - 06/09/13 12:46 AM

Ed Zarenki... a pioneer! And a critical observer after my own heart.

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Mr. Bill
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Re: BT-70s on way.... new [Re: GlennLeDrew]
      #5910715 - 06/09/13 12:58 AM

A huge amount of what I've learned about binoculars (and critical thinking about optics) since joining CN I owe to EdZ....



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KennyJ
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Re: BT-70s on way.... new [Re: Mr. Bill]
      #5910813 - 06/09/13 03:11 AM

< --- many vendors --- >
--- < couldn't care less about the actual specs.>

Rich,

What a refreshing change to see a North American write that rather than the usual and confusing "COULD care LESS"! :-)

Kenny


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Rich V.
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Re: BT-70s on way.... new [Re: KennyJ]
      #5911068 - 06/09/13 09:56 AM

Thanks, Kenny.

Not all of us over here carelessly trample over the English language. Just trying to do my small part...;^)

Rich


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Jarrod
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Re: BT-70s on way.... new [Re: KennyJ]
      #5911130 - 06/09/13 10:49 AM

Quote:

< --- many vendors --- >
--- < couldn't care less about the actual specs.>
What a refreshing change to see a North American write that rather than the usual and confusing "COULD care LESS"! :-)




There are more than one of us, even - this is a pet peeve of mine. Usually I refer people to this graphic:

http://www.doobybrain.com/2008/09/09/the-caring-continuum/


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SMark
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Re: BT-70s on way.... new [Re: Jarrod]
      #6351722 - 02/02/14 05:20 PM

Has the clear aperture issue with the BT-70 ever been addressed, or are we just going to have to settle with this being a "BT-60" instead?

Also, has Mr. Harrington ever made any additional comments on this? Not that it's necessary, I suppose. But it sort of gives any further reviews on his part less impact on my future purchases, and I suppose it would for others as well...


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JustaBoy
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Reged: 06/19/12

Re: BT-70s on way.... new [Re: SMark]
      #6351823 - 02/02/14 06:19 PM

"Also, has Mr. Harrington ever made any additional comments on this? Not that it's necessary, I suppose. But it sort of gives any further reviews on his part less impact on my future purchases, and I suppose it would for others as well..."

Mark,

He reviewed the 15x70mm Skymasters too - Liked em:-)

http://www.amazon.com/Celestron-SkyMaster-Binoculars-Tripod-Adapter/dp/produc...

I think that he's really at his best when writing about observing.


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GlennLeDrew
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Re: BT-70s on way.... new [Re: JustaBoy]
      #6352383 - 02/03/14 12:50 AM

The newer BT-70 Mk II does work at or at least very near to full aperture. It has been given larger pentaprisms, which required a visibly larger back end on the body.

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SMark
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Re: BT-70s on way.... new [Re: GlennLeDrew]
      #6352415 - 02/03/14 01:25 AM

Quote:

The newer BT-70 Mk II does work at or at least very near to full aperture. It has been given larger pentaprisms, which required a visibly larger back end on the body.




Glenn,

I don't see Oberwerk calling this a Mk II on their website. Or are you referring to the Garrett BT-70?


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RichD
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Re: BT-70s on way.... new [Re: SMark]
      #6352596 - 02/03/14 06:17 AM

It just goes to show that you get what you pay for. I think it's unrealistic, even from a chinese manuf. to get two doublet achromatic refractors, mounted in a rigid steel/alloy body,collimated, plus prisms, plus eyepieces for $850 and expect them to be on a par with higher end gear.

When you consider that you can pay triple that for a pair of high end binos of 40-50mm aperture...


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RichD
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Re: BT-70s on way.... new [Re: SMark]
      #6352597 - 02/03/14 06:17 AM

It just goes to show that you get what you pay for. I think it's unrealistic, even from a chinese manuf. to get two doublet achromatic refractors, mounted in a rigid steel/alloy body,collimated, plus prisms, plus eyepieces for $850 and expect them to be on a par with higher end gear.

When you consider that you can pay triple that for a pair of high end binos of 40-50mm aperture...


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Mr. Bill
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Re: BT-70s on way.... new [Re: RichD]
      #6352976 - 02/03/14 10:52 AM

IF Oberwerk's BT70 has indeed been redesigned to yield a full 70mm effective aperture, I will purchase them, but I want someone here to confirm that.



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Eric63
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Reged: 06/16/12

Loc: Ottawa, Ontario
Re: BT-70s on way.... new [Re: Mr. Bill]
      #6353141 - 02/03/14 12:15 PM

I got mine in December and they have 63mm aperture.

Eric


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GlennLeDrew
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Re: BT-70s on way.... new [Re: SMark]
      #6353221 - 02/03/14 12:56 PM

Quote:

Quote:

The newer BT-70 Mk II does work at or at least very near to full aperture. It has been given larger pentaprisms, which required a visibly larger back end on the body.




Glenn,

I don't see Oberwerk calling this a Mk II on their website. Or are you referring to the Garrett BT-70?




Yep, it's the Garrett. But don't these things come from the same factory?


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JustaBoy
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Reged: 06/19/12

Re: BT-70s on way.... new [Re: GlennLeDrew]
      #6353831 - 02/03/14 05:45 PM

Yes they do, but one is 45 while the other is 90 - Totally different design.

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Eric63
professor emeritus


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Loc: Ottawa, Ontario
Re: BT-70s on way.... new [Re: JustaBoy]
      #6353981 - 02/03/14 06:45 PM

Yep, mine are the 45 degree model.

BTW Chuck, I was in Orlando last week accompanying my wife at a conference. I brought some 10x50's with me, but I think I also brought the clouds and the cold. My observing bad luck just continues this winter.


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JustaBoy
Carpal Tunnel


Reged: 06/19/12

Re: BT-70s on way.... new [Re: Eric63]
      #6353997 - 02/03/14 06:58 PM

So that was YOU that did that to us, Eric:-(

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Eric63
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Loc: Ottawa, Ontario
Re: BT-70s on way.... new [Re: JustaBoy]
      #6354015 - 02/03/14 07:05 PM

Just call me Eeyore, that grey cloud follows me everywhere. But at least the temperature was on the plus side.

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JustaBoy
Carpal Tunnel


Reged: 06/19/12

Re: BT-70s on way.... new [Re: Eric63]
      #6354049 - 02/03/14 07:14 PM

"But at least the temperature was on the plus side."


Eric,

You call that PLUS??? - It was 32 here...

I'm still trying to get thawed out:-(

The 80+ that we have had the last two days are starting to help a little bit though.

Ideal for me is 90 in the daytime and 70 for the low at night.

Sadly, I'm not gonna find that anywhere on a consistent basis:-(

I've seen it -24 F when I lived in Ohio, so I moved to Tennessee to get warmed up, and saw -21 there:-((

I've been in Florida for 6 years now, and the coldest I've seen was +17 - Brrrr!@

Hmm... Seeing that I live in "God's Waiting Room" now, I wonder if Heaven is gonna be any better? - Sure hope so:-)


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Mr. Bill
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Re: BT-70s on way.... new [Re: GlennLeDrew]
      #6355417 - 02/04/14 12:19 PM

Check out the Garrett website....the product line has been severely pruned since the Big Binocular takeover.

Wonder if the new APM 100 design is in the future...after all, I imagine that its not exclusively manufactured for APM just as the current model is a BA6 model.



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