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EdZ
Professor EdZ


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Oberwerk BT100 - mini review
      #72001 - 03/15/04 01:04 PM

BT100

Here are my first impressions of my new Oberwerk BT100. I’ve had them for about a month now.

These BT100s fill a gap in my scopes. My good scopes jump from an 85mm ref to 125mm SCT to 150mm ref. The theoretical combined effect of the BT100, with two beautiful 100mm f/6.2 refractors, is like looking thru a 118mm scope from 21x to 69x. The visual effect seems more pronounced than that.

I would tend to agree the BT100 is a different animal altogether than any other 5# to 12# binocular in the 80mm to 100mm range. The BT100 at 26# (12k) is heavier than my largest telescope, a 4-5' long 6" refractor. The BT100 cannot be picked up while mounted on its tripod. You must first set out the tripod then attach the BT100s. You would not move it while mounted. You must first take the binocs off the tripod.

The BT100 is a straight thru viewing binocular. The standard tripod, a specially modified heavy-duty wood surveyor's tripod results in the need to sit in a chair under the binocs to view at high altitudes. Actually, I’ve found this is very comfortable.

The views are simply stunning. It does come standard with two sets of wide WA eyepieces, a 24.5mm = 2.5°Tfov at 25x and a 10mm = 1°Tfov at 62x. Both eyepieces have an apparent fov of 62°.

With the Oberwerk BT100 at 50x100 using 12.5mm UO orthos in mag 5.5 skies I was able to see stars to mag 11.9. The BT100 used with a pair of Televue 26mm plossls at 24x100 saw stars all the way down to mag 11.5, slightly better than seen at 25x100 with the stock 24.5mm WA eyepieces provided.

Best views yet with the BT100 were with the Televue 26mm plossl 2.0°fov and with Televue 20mm plossl 1.5°fov eyepieces. View is quite a bit narrower than the stock WA 2.5°fov eyepieces, but you can literally put objects right out to the edge of the field stop and still see a near perfect view with almost no distortion present. While both pretty good, neither of the supplied WA eyepieces provides the same degree of sharp view right out to the edge.

Some recent observations with the Oberwerk 20x80 standards as a comparison in mag 5.4 skies reached stars to mag 11.2. I still have not exceeded mag12 with any binocular or scope up to 5"SCT at 96x and TV85 at 120x.

The BT100 has a nice even coating with a green/purple tinge. A better indicator of the quality of antireflection coatings may be any reflections you can see when looking into them. Look into the objectives of an Oberwerk BT100 binocular telescope and you will barely see the outline of your head. You will not see any detail in your face. As a comparison, it is difficult to see any reflections at all in Fujinon coatings. Look into a binocular with lesser quality coatings and you will be able to see your full reflection in color with detail in your face. Any reflections you see is the reflected light coming off the lens and not passing thru the lens.

I compared the coatings on the Oberwerk 20x80 standards to several other binocs. At both the objective end and the eyepiece end:
20x80s reflect back less light than the Oberwerk 15x70/'03,
20x80s reflect FAR less light than Pentax PCF WP 16x60s.
20x80s are about the same as the swift Ultralite 8x42.

The Oberwerk BT100 reflects less light than either the Oberwerk 20x80 standards or the 15x70/’03. The Fujinon 16x70 reflects just a bit less than all of the above.

BT100s are equipped with non-rotating helical focuser, individual focus. That means if you have eyepieces with eye guard wings attached, the eyepieces don’t rotate as you focus. The focus diopter range seems unlimited. I haven’t found the end. Accepts any 1.25" eyepieces. Comes with two sets of WA eyepieces. It's FMC, very well baffled with coatings that rival Fujinon. BT100 has a 620mm focal length, nets f/6.2. The Inter-pupilary distance, IPD, has a range from 58mm to 80mm. It’s possible some very large eyepieces might hit together when used for a narrow IPD. However the supplied WA eyepieces are pretty large and these do not come in contact even at the narrowest setting.

The prism housings hold what are described as massive prisms. There are three separate covered openings into the prism housings to make adjustments to the prisms if necessary. This is not like the common binocular with prism tilt screws. Collimation is quite different, very precise and well designed. The massive prisms are mounted to plates that float on three points, each point finely adjustable. I have not needed to open the housing. Using a double star of known separation, I measured image separation between the objectives at approximately 40 arcseconds. Normally separation is measured in several arcminutes. Images readily merge at every magnification I’ve used.

I have been collecting eyepiece sets to use various other powers than those provided. A pair of 20mm TV plossls provides me with 31x with a 1.6° fov. The view is absolutely sharp right to the edge of the field stop. I have been enjoying my best views between 25x and 50x. I have used them with magnification as high as 69x with no detrimental affects. At this time, I do not have eps pairs to try them any higher, but at magnification this high, the fov is quite narrow.

I've had the BT100 at seven different magnifications from 26mm plossls = 24x, to 9mm orthos = 69x. One CN article author writes he has used them with barlows! I'm working on a set of 30mm Ultimas to get 21x with 2.5° fov and 4.8mm exit pupils, what I think will be an ideal system for viewing faint extended nebulous objects. The two sets of WA eyepieces that come standard with the Oberwerk BT100 are 24.8mm = 25x 2.5°fov and 10mm = 62x 1°fov. Both sets are pretty good. I like the WA, but Teleview plossls see more stuff, especially my pair of TV20mm plossls. I think the 30mm Ultimas are going to be a good match.

The BT100 tripod is not very tall. It’s similar in height to many EQ mount scope tripods. However, it is a heavy-duty surveyor’s tripod constructed out of nicely finished wood. The binocs stand pretty tall on top of the mount post and the binocs weigh 26#. I haven't tried any other mounting setup. So far, I've been doing all my viewing with them from a seated position. Yeh, I need to bend my neck, but that's no different than every other binocular I own. The tripod assembly permits only reaching to about an altitude of 75-80°. To get closer to zenith, I shortened the two back tripod legs a few inches tilting the entire mount assembly slightly. Be very careful here, as this whole mounted setup is really very top-heavy. An off-balance tripod could be a dangerous situation. The way I had it set, if they were to topple, they would be falling towards me.

The tripod mount assembly permanently attached to the binocular has an integral slow motion altitude dial. It has a locking dial, which when unlocked allows you to tilt the binocs in altitude with a little effort. They will not move on their own if unlocked, but the slow motion dial will not engage. The dial provides a range of several degrees of slow motion movement. I found this extremely useful when I was conducting critical observations recently in the M45 area at 50x. The modified tripod head has an azimuth lock. Best this is locked when viewing to prevent fairly easy swivel.

The BT100s come in a suitcase sized well-padded zippered case. They come with an easy to mount 7x (or8x?) 50mm finder scope. At magnifications below 40x, I have not need to use the finder. I’ve actually had very good luck just pointing them at objects like the Christmas Tree cluster at 30x to 40x, looking in the view and there it was.

Impressive views of M42 and resolved the four stars of the Trapezium at 25x. I must admit, the image of the M42 nebula in the BT100s at 36x was one of the most stunning views I have ever seen. The coatings and baffles in the BT100s seem to be a huge step up from anything I've seen. First impressions are I really like these. But for an instrument such as these, there will be more than just first impressions. I will be testing the performance of these BT100s and taking lots of notes. There must be 15 other aspects I want to measure. I'll reserve judgment until after more use, but initial impression is high.

The BT100 from Oberwerk comes complete with mount and specially modified surveyor's tripod, 2 sets of WA eyepieces and case for $1595.

edz


edit 3-16-04
last night I took these out again, with one purpose, to view Jupiter. The BT100 is a semi-apochromatic triplet objective.

The tripod is really not short at all. it's a full height surveyor's tripod and quite robust. When used to point high, the eyepiece end of the BT drops to about 3-4" below the tripod top mount plate. Hence the need to get under them with a chair. 45° eps would really show their value in this instance.

That 40 arcseconds of misalignment proved a little bit more of a problem on the extended images of the disk and moons. I was viewing at 50x with a well corrected 12.5mm UO ortho. The difference was much more noticable than it is when viewing a star field. That may be adjustment, not problem. I'm not yet ready to mess with that.

I had to question whether I was seeing any false color on the edges of Jupiter's disk. There may have been a minor blue fringe. very little.
See also my post explaining chromatic aberration in astronomical and terrestrial instruments.

I aslo took a quick look at M65-M66, pretty bright. Found them easily at 50x, nice pair. Tried to view Algeiba for a split but no see. However, the lowest limit with my 5" scope was 53x the other night.

The 7x50 finder scope is mounted to a precision dovetail which is pre-mounted to the top of the binoc. When I slipped mine into the dovetail and locked it in, it was perfectly aligned. It is not included in the total price above. it is an additional $89.95.

edz




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KennyJ
The British Flash


Reged: 04/27/03
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Re: Oberwerk BT100 - mini review new [Re: EdZ]
      #72034 - 03/15/04 02:15 PM

Great review Ed.

This sounds like a VERY useful binocular set -up.

Perhaps 45 degree angled eyecups arrangment would make it even more so ?

The ability to use ANY 1.25mm eyepieces is a most enviable one .

I look forward to further reviews of your viewing experiences through this set -up.

I'm sure there will be several more !

I take it these are "keepers" then ? :-)

Regards , Kenny.

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Milton Wilcox R.I.P






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EdZ
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Re: Oberwerk BT100 - mini review new [Re: KennyJ]
      #72036 - 03/15/04 02:20 PM

45° holders would make these the ultimate viewing experience.

You can look forward to reading more about these in the future.

edz

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Anonymous
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Re: Oberwerk BT100 - mini review new [Re: EdZ]
      #72141 - 03/15/04 05:34 PM

Edz, Thanks for posting your mini-review of the BT100. I have been scratching my chin about the thought of a future BT100 purchase. Your review is extremely helpful....and timely. I look forward to the rest of it.

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nemo
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Re: Oberwerk BT100 - mini review new [Re: EdZ]
      #72158 - 03/15/04 05:58 PM

Ed,
Enjoyed your review since as you know I also have a pair of the same binoculars. Just thought to throw my 2c in. Very quickly I found that to maximize the potential in these bino's using different eyepieces was essential. The following are what I am using at this time:
Meade Super Wide Angle EP's in the following-
24.5=25x
18.0=34x
13.8=44x
Vixen LV 50degree-
9.0=68x
Vixen LV 45degree-
6.0=103x

Thus far I have personally enjoyed the 24.5 for wide views such as sweeping the milky way, the 13.8 and 9.0 for more detailed looks at messier objects and star clusters. Even though I have had my binoculars much longer than you (several years) I suspect you have already used yours more. Due to health and other considerations such as where I live my viewing time had been limited. I have been in amateur astronomy for over 40 years and I can say that I have never had a more incredible view of M42 at 44x than with these. Of course it was my first time looking at an Messier object through anything but a telescope so the 3D effect was -well unexpected. I highly recommend the Millennium Parallelogram mount as a cure for the stiff neck and zenith viewing. I will say though that with the weight of these binoculars along with the heavy duty tripod they need and a mount that weighs close to 50lbs. we are not talking about something you are going to just trot out the door with.This is more like a major large scope set-up although basically simpler to put together once you have the learning curve down.Thanks for your review Ed and will be interested in hearing what other observation you have as you use the BT 100's.
R/S,
Dan
"Experience is a wonderful thing. It enables you to recognize a mistake when you make it again."

--------------------
"Humility is not thinking less of your self-it is about thinking of yourself less."


Edited by nemo (03/15/04 06:05 PM)


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777Guy
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Re: Oberwerk BT100 - mini review new [Re: nemo]
      #72321 - 03/15/04 10:47 PM

Ed,
I am a new member to the Binocular Forum and appreciate the education you have given this group in Binocular optical sciences. I became interested in learning more about binoculars from this forum and am enjoying binocular astronomy as a result. I have had a 10x70 Fujinon for awhile and I have recently purchased a Burgess 15x70 binocular and tripod and have really enjoyed using them for both terrestrial and astronomical viewing. I am now intrigued with obtaining a binocular with at least 100mm objective for observing DSOs. Until I read your review I probably would not have considered the Oberwerk BT100.
Thanks for your professional evaulation and review.
Cheers,
Jim


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lighttrap



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Re: Oberwerk BT100 - mini review new [Re: 777Guy]
      #72413 - 03/16/04 05:19 AM

Good review, Ed. (as always)
You know I'm looking forward to hearing more adventures with these.

Don't you also have the Oberwerk 22x100's? If so, how do they fit into the mix?

Thanks,
Mike Swaim

--------------------
18" Starsplitter II f/4.5
8" Hardin Dob f/6
C5 workhorse mini SCT f/10 or f/6.3
70mm TV Ranger dual purpose birding/astro
77mm Leica Televid APO
16x70 Fujinons on UA Deluxe Mt.
12x50 Nikon SE
8x30 Nikon E2s
and many others


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Anonymous
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Re: Oberwerk BT100 - mini review new [Re: lighttrap]
      #72414 - 03/16/04 05:33 AM

Thanks for putting this review up, Ed.

Lookin forward to your insights when you have put the BTs through the paces.


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EdZ
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Re: Oberwerk BT100 - mini review new [Re: ]
      #72421 - 03/16/04 06:08 AM

Mike,

I don't have the 22x100s. I did have the opportunity to look them over real good one day while over at Larry P.'s UA shop, he's only about 30 miles away. The 22x100 is the old 20x80 Deluxe body with an extension added to the front to bring the lenses out further. Also, an objective crossbar has been added and improvements to coatings and baffling are apparent over the older Deluxe.

The problem I always had with the Deluxe was the very short diopter range for the right eyepiece. The 22x100s I saw at Larry's (last June/July) had exactly the same eyepiece and focuser assembly as the older Deluxe. So even with my glasses on, I had reached the end of the diopter range. Those comments were posted here in the forum. Try a search of all posts. If I understand correctly ???, that eyepiece can be taken out and the diopter range can be reset with either more + or -, depending on what's needed.

But for me, I was looking for something different. I decided quite a while back if I was going to get a 100mm binocular, I wanted to consider interchangable eyepieces. I didn't like the idea of proprietary eps, so I started reading about the ITE and the Oberwerk. The Oberwerk won out.

edz

--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
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EdZ
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Re: Oberwerk BT100 - mini review new [Re: ]
      #73815 - 03/18/04 10:45 AM

As I go back through my notes on observations with the BT100, I found this:

Feb 13, mag 5.2 skies, BT100 with 26mm TV plossls = 24x, exit pupil = 4.2mm

M36 was fully resolved with a very tight double right at the center.
When viewing M45, did see faint glow around lower end of M45 (Merope)
Field of view with the TV26 is 2.1°

That's the first time I've ever recorded seeing the Merope nebula in M45. I've looked hundreds of times with ~20 different instruments. I've observed M45 dozens of times recently with Fujinon 10x70s, Pentax 16x60s, Oberwerk 15x70s, Fujinon 16x70s and Oberwerk 20x80 standards, sometimes in better skies than mag5.2. None of them showed the Merope nebula. This is a first.

edz

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Diego
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Re: Oberwerk BT100 - mini review new [Re: EdZ]
      #73876 - 03/18/04 12:59 PM

That's great Ed! It's a good example that NELM is not everything. Seeing conditions plays an important part of the game. Guess you were blessed with excellent seeing after all those years

Diego

--------------------
Diego
Celestron 80 mm f11.4
Oberwerk 20x90
6" f7.8 Reflector


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KennyJ
The British Flash


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Re: Oberwerk BT100 - mini review new [Re: EdZ]
      #73878 - 03/18/04 01:03 PM

Congratulations Ed !

It must have been quite a joyous experience.

The question remains though :

Was this because of :

(a) the increased magnification (from 20 to 24x) ?
or
(b) the sheer increase in aperture (from 80mm to 100mm) ?
or
(c) the combination of BOTH ?

You might guess what I'm going to ask next !

Could it be related to EXIT - PUPIL too ? :-)

Regards , Kenny.

--------------------


Milton Wilcox R.I.P






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EdZ
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Re: Oberwerk BT100 - mini review new [Re: KennyJ]
      #73886 - 03/18/04 01:25 PM

I tried with exit pupils smaller and larger without success. did not see it with 3.75, 4.2mm, 5mm or 7mm exit pupils at powers lower than the BT100.

I have had no other instrument as large as the BT100, other than scopes.

I have not seen it at low power in my TV85, C5-125mmSCT, 150mm SVD6Newt or 150mm CR150Ref.

Probably a combination of both aper and mag. exit pupil being large, I'm sure helped also, as I did not see it at 36x or at 40x or 50x in the BT100.

edz

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Anonymous
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Re: Oberwerk BT100 - mini review new [Re: EdZ]
      #74379 - 03/19/04 10:03 AM

Ed, Nice work. Your review reinforced my feeling that big binos with interchangable eyepieces would potentially be quite satisfying. I will be interested to learn if you are able to use some diagonals and how that may work out.

Thanks again for the valuable review. Nick


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EdZ
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Re: Oberwerk BT100 - Stock 24.5mm ep sharpness new [Re: EdZ]
      #76244 - 03/22/04 01:49 PM

4-21-04 Testing for edge distortions with the 24.5mm WA eyepieces at 25x

To check edge sharpness, first I used the 30” double Struve 855 about 5° or 6° WSW of the Rosette. It was still easily seen as double 80% to edge all the way around. It has a mag9+ C star which was lost from view at about 60%-70% out from center. I could still see the A-B clearly separated at 90%-95% out but the two stars had become fuzzy blobs.

For this magnification (25x) the 30 arcsecond double was too wide for the test. While observing M47, I found another much closer double.

The double at the center of M47 is Struve 1121, with components of 7.9-7.9/7.4” and it was cleanly split at 25x. It was still clearly seen as a separated double at 60% from center towards the left, right and bottom, and 75% towards the top.

So the 24.5mm Oberwerk WA eyepieces that come standard with the BT100 give 25x with a 2.5+ Tfov and they provide 25x7.4= 185 arcseconds resolution at 60%+ out from the center of the fov. That’s better than many people have as a limit of visual acuity even at the best resolution at the center of the fov.

Confirming a similar result to what Barry Simon found in his last report, I was able to see this 185 arcsec degree of resolution all the way to 75% out from center when placing the test object near the TOP of the fov. I had a more difficult time with side-to-side movement of my eyes. I found it very easy to look UP in the fov without eye-strain. I believe that is what allowed seeing further towards the top. I will be testing for this from now on.

edz

--------------------
Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
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KennyJ
The British Flash


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Re: Oberwerk BT100 - Stock 24.5mm ep sharpness new [Re: EdZ]
      #76264 - 03/22/04 02:47 PM

This "advantage top edge" phenonema is not totally new.

I have DEFINITELY read about it before , and recall doing a little experiment with it myself at the time ( about 3 years ago with my Heath Robinson 50mm scope at 40x )

It IS true -- and there is a reason for it , but I cannot recall the source of the article.

I'm almost certain though that it was either Carlin, Nagler or Bartle.

Regards , kenny.

--------------------


Milton Wilcox R.I.P






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nemo
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Re: Oberwerk BT100 - Stock 24.5mm ep sharpness new [Re: EdZ]
      #76403 - 03/22/04 06:23 PM

Ed,
One of the things I found with my Oberwerk 100 BT was that when using the 62x EP"s that came with them I had problems getting the two images to merge. I am extremely near sighted and do my viewing with my glasses off. Also my IPD is around 58mm(eye's are close together) and I am gifted with a beautiful large proboscis. The EP's from Oberwerk I am sure you will agree are massive for 1.25 oculars. I solved my problem by using the 13.8 meade SWA's and the Vixen 9.0 LV's. Don't get me wrong the eyepieces that come with the binoculars seem like a very good value but I do believe that one can get more of the potential out of these bino's by using other quality EP's which is of course true most of the time with any optical device. Thanks again for your research on this and I continue to enjoy your examination of the Oberwerk 100 BT's.
R/S,
Dan

--------------------
"Humility is not thinking less of your self-it is about thinking of yourself less."


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EdZ
Professor EdZ


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Re: Oberwerk BT100 - Vignette test new [Re: KennyJ]
      #84862 - 04/04/04 09:03 PM

Testing for Vignette
Apr 4, 2004

Just recently I tested a number of binoculars to determine the amount of vignette in the system. Of nine I tested, among the best was the Fujinon FMT-SX 16x70. For the 16x70, the test shows only the central 50% diameter of the objective fully illuminates the exit pupil. By the time the light from the very edge of the 70mm objective passes completely through the binocular light path it only illuminates 40% of the exit pupil.

None of the binoculars I’ve tested so far had more than 50% diameter of the objective fully illuminating the exit pupil. Also, no binocular provided more than 40% illumination to the exit pupil from the extreme edge of the objective. The Oberwerk 15x70 and Oberwerk 20x80 Standard had less on both points.

Having found this exists to some extent in all the binoculars I tested, I was curious to test the Oberwerk BT100 for the same. When using the exact same methods employed on all the other binoculars, the BT100 showed these results:
90 to 95% of the objective is fully illuminating the entire exit pupil. The BT100 has an aperture stop baffle located close (~50mm) behind the front aperture. This ring is effectively reducing the aperture to ~96mm. At the extreme edge of the full aperture, at the edge of this ring, the objective is illuminating about 85% to 90% of the exit pupil.

These are very nice results indeed, worthy of note!

edz

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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
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Anonymous
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Re: Oberwerk BT100 - Vignette test new [Re: EdZ]
      #85084 - 04/05/04 08:29 AM

EdZ, thanks for reporting the vignetting on the BT100. Your findings agree well with the performance you have previously reported.

But then again, didn't you in the vignetting thread state that the BT100 prisms experiences 100% light obstruction when the aperture is viewed from the edge?

Edited by night watch (04/05/04 08:37 AM)


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EdZ
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Re: Oberwerk BT100 - Vignette test new [Re: ]
      #85093 - 04/05/04 09:04 AM

Are you referring to the the aperture stop I spoke of. At first visual inspection it appeared to me to opaque about 5-6mm of the lens all around. When tested with the laser light, it was found to be far less than that. In my vignette test above, I report the results to the edge of that aperture stop, not the edge of the 100mm lens. In the first post to the vignette thread, I was referring to the full 100mm aperture. That was when I first discovered the aperture stop.

edz

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