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Garrett BT70-90 MK II's arrived!

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#51 Vondragonnoggin

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Posted 05 December 2010 - 02:23 AM

r u having trouble tightening the undercuts on the ep's? if so there was a thread in the ep fourm a while ago & members were buying some rubber tape form auto dealers, cutting it to the fit the undercut & sticking it in -problem solved


Good to know. this might have to be a solution if they can't offer one from Garrett. I will see what they have to say. They are aware of my first gripe and have been great responding. I just sent an email telling about the compression ring and assuring them I want to keep these and will not freak out anymore over sleeks that don't affect the quality of the views. They have responded above and beyond expected already, so I am happy I bought from them.

#52 peter k

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Posted 05 December 2010 - 03:17 PM

Eric, good to read that you are relaxing into full enjoyment of your new BT70. Sounds like you got a good copy. For me the undercut issue is a minor nuisance at most. If push comes to shove you can just not fully tighten the compression rings. The eyepiece shoulder should keep the eyepiece sufficiently square and centered (it does on mine), and one of the benefits of the 90* design is that there is very little chance of an eyepiece falling out.

It sounds like your copy is similar to mine in optical quality. The 9mm Expanse clones for 48x see a lot of use in mine. This power provides some resolution of the brightest globulars if your skies are dark, and is also useful for smaller galaxies and larger planetaries, not to mention Jupiter and the moon. The image is so good at that magnification that I'm considering trying 6 or 7mm EPs.

#53 Vondragonnoggin

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Posted 05 December 2010 - 04:38 PM

I would agree. These really are impressive in performance and I have settled down to just liking the views. Letting the eyepiece rest in the focuser works fine and I have some options after researching some ideas posed with aluminum tape or chrome tape on the undercuts. As long as both eyepieces are adjusted the same, both loose or both tight, they work great. This design is great becuase there is no opportunity for an eyepiece to ever fall out even if my mount could reach to full zenith.

Now about the performance again - Last night I had about 22 minutes between clouds to get some views in. the fact that I could get setup and take full advantage of 22 minutes viewing in comfort is exactly why I bought these. My dob has no chance in those conditions.

I took a look at Orion and surrounding areas, getting in views of the little beehive and several other clusters and M42, The Plieades, Hyades at 25x.

I noticed that 70mm and 25x provides a nice contrasty view. If I had another mount I would have setup the 25x100's next to them to compare, but it seems from memory to have a greater contrast due to smaller objectives and much more resolution than my 25x100's. I can usually resolve 3 stars of the trapezium in my 25x100's and on a good night (from my current light polluted location) see all 4. Last night was not ultra clear and I had no trouble seeing all 4 in the BT at the same power. I was equally excited by good CA control on Sirius and see less color fringe than my 25x100's.

There is less height adjustment with a right angle bino than straight through due to the more comfortable nature of looking down at the ep. Big bonus. particularly with my tripod that has non-geared center post.

I can't wait for a really clear night where I can view for several hours and try it out with my chair. I just picked up Nightwatch last week and now have some great charts and objects to seek out and I'm looking forward to extended viewing with these and not dreading a neck ache. I am really wanting to get my other 28mm to try some wider field views over 3 degrees. 25x puts the Plieades in the entire view edge to edge barely. I should have popped in the 22x Meade wide angles.

#54 Vondragonnoggin

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Posted 05 December 2010 - 04:58 PM

Some notes on the mechanics of 90 degree occulars:

These have a single screw type IPD adjustment that moves the occulars in or out in tandem. The housings are tight tolerances with all the parts, but I imagine is pretty hard to get the height of the collars to match up perfectly. Mine have about 1/16 of an inch difference in height.

I would not recommend eyepieces with these that have very little eye relief due to the small height difference. Longer eye relief pieces will allow for a more comfortable adjustment on the eye that uses the taller side. 1/16" is not much difference, but for a short eye relief piece, could be the difference in wearing glasses with unrestricted FOV or not.

If someone were to buy these, I would not expect the collars for the ep's to be at the exact same height and if you do get some that are, then you will probably be in a rare percentage that does have this. Mechanically, I think they have done a great job at getting them as close as they did. I have no idea how the 45 degree mechanics are or if they have the same design with a single IPD adjustment screw. To me, it makes no difference comfort wise. I cannot wear glasses with the supplied 25x eyepieces and small eye relief they provide.

The focuser works pretty well in fine adjustment though, and I am able to get fairly pinpoint stars without my glasses. I prefer to wear them and makes a difference because of my astigmatism. maybe I haven't figured out the eyecups correctly on the 25x supplied ep's but I see no way to roll them down and the lens is recessed a good 1/4 inch from the top of the ep.

I think I should point out that all this info probably doesn't make a bit of difference if you don't wear eyeglasses OR you have all long ER eyepieces anyway.

#55 Jawaid I. Abbasi

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Posted 05 December 2010 - 05:49 PM

I can usually resolve 3 stars of the trapezium in my 25x100's and on a good night (from my current light polluted location) see all 4. Last night was not ultra clear and I had no trouble seeing all 4 in the BT at the same power.


Actually, trapezium is a good test for resolution. The "E" is really a test for your Binocular. With my APM-100; I went to 70x and I think that I saw the "E" component.

Since, I knew that where is "E" component and perhaps I was assuming that I saw "E" with no saperation.

Eric,
You said that you will buy a 6mm eyepiece so when you have a 6mm eyepiece then check again on trapezium to see if you can resolve at 80x.

Eric, if you do not mind then I would like to ask a question to eveyone.
How is "7mm Ortho Vixen/celestrom Japan" performance wise and what are the specification for it?

#56 EdZ

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Posted 05 December 2010 - 06:06 PM

I'm surprised you can't see 4 components resolved in your 25x100. Many people report they see 4 in 20x80s. I've seen all 4 in all the 22x binoculars in my report. I've seen them in several 20x and certainly in my Oberwerk 25x100.

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#57 GlennLeDrew

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Posted 05 December 2010 - 06:13 PM

A slight height difference in focusers will have no impact whatsoever, even if the oculars have small eye relief. The small angle at which the eyes would have to swivel due to the slight tilt of one's face is utterly trivial.

#58 Vondragonnoggin

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Posted 05 December 2010 - 06:17 PM

Jawaid, here is some info on your eyepiece, but haven't read through all the postings. Something about it being a symetrical eyepiece and not a true orthoscopic and some different users opinions on performance. Might help - Here

I'm glad you brought up orthoscopics as my previous post discussed the height difference in occulars in the BT70 and this ortho type and definitely plossl type ep's in the higher powers (I'd say 10, 9, 8, 7mm etc) would be where the difference could hinder shoving your eye into the small peephole (sorry, not a plossl/peephole fan in high powered even though I know they perform well in better models).

#59 Jawaid I. Abbasi

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Posted 05 December 2010 - 06:21 PM

Post deleted by Jawaid I. Abbasi

#60 Vondragonnoggin

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Posted 05 December 2010 - 06:22 PM

A slight height difference in focusers will have no impact whatsoever, even if the oculars have small eye relief. The small angle at which the eyes would have to swivel due to the slight tilt of one's face is utterly trivial.


That makes sense. I was thinking of plossl types really where you have a small enough margin already to view, but I suppose eyeglasses are somewhat squishable in minor amounts in just about any direction so it would not be an issue. hasn't been an issue with me, although the difference was enough in viewing to make me take a look at how it was setup to make that difference in the first place, so it is not entirely unnoticable.

#61 Vondragonnoggin

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Posted 05 December 2010 - 06:24 PM

I'm surprised you can't see 4 components resolved in your 25x100. Many people report they see 4 in 20x80s. I've seen all 4 in all the 22x binoculars in my report. I've seen them in several 20x and certainly in my Oberwerk 25x100.

edz


I don't know why that is either, other than maybe seeing on some nights or optical quality of the Tachyons or my inexperience. I have no issues with the Tachyons though and think they were a great deal for what I payed and built solidly. Again, some nights I do see 4 through them. The BT just seems a little more resolved at 25x.

#62 Jawaid I. Abbasi

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Posted 05 December 2010 - 06:28 PM

Eric,
Thank you for the link but it did not do any clarrification about 7mm which I just bought them from AM. It will probably arrive with 3 or 4 days but the specification not found anywhere.

I just want to compare with 7mm UWAN if it is more sharper then it.

#63 Vondragonnoggin

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Posted 05 December 2010 - 06:33 PM

I also wanted to point out the difference in height because, since it is noticable and made me look at the mechanics it might be noticable to someone else getting these and if they were like me and new (like trying to wrangle a puppy) I would not want them expecting heights to be the same for this type of mechanism. I think it is normal in the design.

#64 Rich V.

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Posted 05 December 2010 - 06:58 PM

Jawaid, Trap "E" is hard enough in a BT; "F" is a much tougher target due to its close proximity to "C". Are you sure about "F"? If this is so, you must have a great BT specimen there as well as excellent seeing. :confused:

http://www.astropix....NTER/TRAPEZ.HTM

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#65 Jawaid I. Abbasi

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Posted 05 December 2010 - 07:30 PM

Rich,
As you see I deleted that post. I was little confused (wokeup early :) ) it was infact "E"; I was talking about..

Anyways, I just ordered 12mm Paridgm eyepieces when I read EdZ report. I was looking for T6 11mm until I found reports from CN and other websites that they are very good.

#66 Vondragonnoggin

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Posted 06 December 2010 - 03:04 PM

Just got off the phone with Garrett Optical. There is no quick replacement of a compression ring, but have another solution ready to try with some aluminum or chrome or teflon tape. As Peter said, having the ep's rest on the shoulder and not tightened works fine anyway.

Garrett's customer service was definitely above and beyond. They have been great both in email responses and over the phone. definitely will buy other products from them.

Bottom line on GT70-90 mk II's:

I am happy and the views are great.

#67 Goodchild

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Posted 06 December 2010 - 04:20 PM

I also wanted to point out the difference in height because, since it is noticable and made me look at the mechanics it might be noticable to someone else getting these and if they were like me and new (like trying to wrangle a puppy) I would not want them expecting heights to be the same for this type of mechanism. I think it is normal in the design.


Von,
Thanks for this info. I wouldn't have known that that was normal for a BT.

#68 Vondragonnoggin

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Posted 06 December 2010 - 04:35 PM

It has to do with the connecting arms to the turrets from the single IPD screw. One is over the other under. The chance that you'll get spacer placement exactly level with each other is probably slim. As Glenn said, the small difference will not matter. I don't have any idea about mechanics on the 45 degree BT. I would think that if redesigned, they would use a single attachment rather than over/under with both arms connecting turrets the same height. I obviously am not a binocular designer though, so have no idea if that would work. From a plain old mechanical perspective it looks to be possible as the action and movement would not change.

You would have to have a slotted connection on the turret for my idea to work to accomodate inward and outward arm travel if the arms were connected at the same height to the mechanism on the IPD screw

#69 GlennLeDrew

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Posted 06 December 2010 - 06:29 PM

The over/under arrangement of the IPD adjustment mechanism's arms is not what's responsible for the different focuser/eyepiece heights. Assuming both eyepieces are focused identically (as would be the case if only one of your eyes was used for both), any height difference is a sign of one or both of the following:

- A difference in objective focal length. This can be as large as ~2% before the difference in image scale becomes perceptible. (If we assume roughly 70mm f/6, and hence 420mm f.l., the difference in f.l. between the two objectives can be as large as ~8.4mm.)

- A difference in the optical path length through the prisms. Not all prisms are necessarily made to identical dimensions. A physical difference 'X' in path length results in a shift of the focal surface by ~1/3X.

I would think objective f.l. differences would be the biggest contributor here.

#70 beachchairbill

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Posted 06 December 2010 - 06:56 PM

Von,

It has been noted several times in past that the 45 GBT has the same focuser height difference. You should find it on your right focuser. Several have had issue with it, however I have had no issues with it todate.

BB

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#71 Vondragonnoggin

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Posted 06 December 2010 - 07:10 PM

Maybe the pictures would help. I have closed the focusers - they are bottomed out on both sides. Same with the collars and being tightened. Here is the difference with a ruler weighted down over the taller side. You can see the gap easily as I have highlighted the bottom of the ruler in red.

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  • 4232807-DSCN0345.jpg


#72 Vondragonnoggin

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Posted 06 December 2010 - 07:12 PM

Here is a shot focusing on the top of the turret and also highlighted in red. One is set lower than the other.

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#73 Vondragonnoggin

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Posted 06 December 2010 - 07:14 PM

I don't know if this still relates to focal lengths being different still, but maybe the pics will clarify it. To me it looked like a design limitation. The lower turret is the one with the arm on the bottom connected to IPD adjustment screw.

#74 Vondragonnoggin

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Posted 06 December 2010 - 07:17 PM

On another note - I ordered a second Edmund RKE 28mm. They come to focus with plenty of room. I tried the baader zoom and it bottoms out on focuser just shy of coming to focus. I played with the skirt and screw in barrel and still just shy of focusing fully. Close focus, the zoom works great, but astro focus, then forget about it. I am thrilled about the RKE though. Twice that weird floaty view and 16x power. Should be really cool.

#75 Vondragonnoggin

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Posted 06 December 2010 - 07:23 PM

I just want to reiterate that Glenn was correct in that this height difference will not affect the performance. I think it would be safe to assume that a perfectly level set of turrets is probably rare. Maybe not in some Kowa Highlanders, but these are 1/10 the cost of the Kowa's. I don't care about the difference in height, I just wanted to post pics so you can see what I was referring to.


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