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beachchairbill
professor emeritus
Reged: 11/06/08
Posts: 507
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Rich V., Barry Simon,
Whenever I see your post or comments, I immediatly read yours first and what yu have said above is right on the money.
I for one tried and tried and tried to purchase a Miyauchi before I purchased the GBT 100/45. I even went as far as speaking to the Japanese Consulate, however, when your closed your closed.
So far, I have no problems with my GBT or Oberwerk and I will send a message to each vendor about what I have found with the hope that changes will be made in the future with the consumer receiving top rate QC upon purchase.
Now getting back to the original question Rich V what is the true aperture on my GBT for the record.
Thanks
BB
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Rich V.
Pooh-Bah
Reged: 01/02/05
Posts: 1394
Loc: Carson Valley, Nevada, USA
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Quote:
Now getting back to the original question Rich V what is the true aperture on my GBT for the record.
Well, Bill, you said above:
Quote:
At eight inches back from the ep the measuremennt has been corrected to four inches reather than three.
It sounds like your GBT is operating at the full 100mm aperture on the one side and 100mm minus whatever percent you're losing due to the "missing" areas outside of the flat intrusions you see on the other side. Hopefully not more than 10% of area on the "bad" side, which would work out to the equivalent of 95mm. Even if you have 15% obstruction it still equals the area of a 92mm objective. You shouldn't be able to notice that small an obstruction.
If it makes you feel any better, the Obie BT100 is reported to be operating at 91-92mm according to a couple of member's measurements. True aperture thread
Best regards,
Rich V
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Binoculars:
33/50/75/150x100 Saturn III, 16x70 FMT-SX, 10x50 PCF-V, 10x43 DCF-SP, 10x35 E2, 7x35 E, 8x30 E2, 7x26 Custom, 8x23AS Diplomat, 8x23 Travelite
Scopes:
C9.25, 6" f8 reflector, SV80S
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medinabrit
professor emeritus
Reged: 10/27/04
Posts: 648
Loc: medina ohio USA.
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Yes ive found 3 in the last 2 years.
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BarrySimon615
Pooh-Bah
Reged: 03/01/04
Posts: 1279
Loc: New Orleans, LA
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Quote:
Rich V, EDZ,
Barry, nice work and her is an update on the GBT 100/45 - At eight inches back from the ep the measuremennt has been corrected to four inches reather than three. If I can help with additional measurements, please say the word.
BB
I would be curious to see still another measurement. Reason? You say above that the GT 100 measures at 4 inches not three. Keeping in mind that these are 100 mm binoculars and 4 inches is actually almost 102 mm, something is still wrong. Remeasure with binocular objectives about 4" from the "projected to" surface and with the binoculars squared to the door. Try to get several readings with the light source at 8" back from the eyepiece (at infinity) and also at about 12", 16" etc. (These readings will hopefully be the same.)
I plan to measure some of my telescopes later to see what changes occur in going from straight thru at infinity to a 1.25" diagonal and then on to a 2" diagonal. Should be interesting.
Barry Simon
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14731
Loc: Cumberland, R I , USA42N71.4W
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I agree that result should be verified.
these comments from my original post in the original thread on this simple test
Quote:
I tried this simple test this morning and found it to be quite easly performed and also quite accurate. I took out a 15x70 that I know is 63mm. I used a small bright LED white light. Actually I found there is quite a bit of leeway in the angle of the light entering and I could still easily see 63-64mm on a scale placed directly over the barrel.
One caution is the instruction to keep the light a reasonable distance back from the eyepieces. That is important. With the light right up near the eyepieces, a mistake someone might make is to tilt the light from side to side slightly. This allows you to shine the light right out to the objective edges on both sides, showing a false apparent aperture of 70mm. With the light perhaps 6" to 8" behind the objectives, I could tilt the light a little to each side and the effect was to "move" the 63mm projected circle across my scale.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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beachchairbill
professor emeritus
Reged: 11/06/08
Posts: 507
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Hi everyone,
I will recheck my measurements later today and report my findings.
BB
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beachchairbill
professor emeritus
Reged: 11/06/08
Posts: 507
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Here we go again,
Here are the latest numbers and their are a few of them.
First, I put a white sheet of 8 1/2" by 11" paper on a wall and kept the front of the right tube 8 1/2" away from the paper. With the focuser all the way in and the ep out, I placed the flash light right against the focuser and the full circle measured 4 1/4" in D. With the focuser all the way out the measurement was 4 1/8"
I then placed a 20mm ep into the focuser and performed the same test with the flash light at 8" away and again at 16". Here are my measurements:
Please refere to the picture provided by Rich V, because the circle did not reach a full circle. With the focuser all the way in and the flash light at 8" the measurement was 3 3/4". With the flash light at 16" the measurement was 3 1/2". These numbers held true with the focuser all the way out.
I hope this helps
BB
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Rich V.
Pooh-Bah
Reged: 01/02/05
Posts: 1394
Loc: Carson Valley, Nevada, USA
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Bill, I was hoping EdZ or Barry would respond before me because I don't get why you get a 3.75" circle with the light at 8" but a 3.5" circle with the light held at 16". I've tried the same distances with my Miyauchis and the projected circle doesn't change a bit whether the light is held at 6" or even 24". Only the brightness of the circle changes, as expected.
I can only guess, then, at your actual effective aperture. 3.5"=89mm and 3.75"=95mm so your GTB is somewhere in that range. If you calculate the segment areas that are missing from the circle on the one side based on the images provided by planet-beaver in the above linked thread, then you have approx. an additional 15% light loss making the effective aperture of the obstructed side somewhere in the 82mm to 87.5mm range.
That's about the best I can make of it. Thank your wife for being so patient! 
Rich V
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Binoculars:
33/50/75/150x100 Saturn III, 16x70 FMT-SX, 10x50 PCF-V, 10x43 DCF-SP, 10x35 E2, 7x35 E, 8x30 E2, 7x26 Custom, 8x23AS Diplomat, 8x23 Travelite
Scopes:
C9.25, 6" f8 reflector, SV80S
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medinabrit
professor emeritus
Reged: 10/27/04
Posts: 648
Loc: medina ohio USA.
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Heh you guys .Try looking out of the small end .Its much more enjoyable.Ha Ha.
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Rich V.
Pooh-Bah
Reged: 01/02/05
Posts: 1394
Loc: Carson Valley, Nevada, USA
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I hear you, Brian, sometimes these complexities just get out of control!
A night under the stars puts it all back into perspective.
Rich V
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beachchairbill
professor emeritus
Reged: 11/06/08
Posts: 507
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Brian,
Funny, however last night was a total rainout and the Rangerss lost, not a star in the night sky with the exception of my falslight.
Rich V. I'm sure that EDZ and Barry will respond in due time. Did you try the flash light with the focuser all the way in and then all the way out?
Also Glen M has the GBT 100/45 as well and we should ask him
if he could check the numbers as well.
Brian, do you have a flash light that you would like to try?.
A light loss of between 18mm and 12.5mm is something that needs to be further verified by others.
My wife Gerry gets her reward today for helping me this kind of fun project. She gets to shop most of the day today with my one and only 31 year old daughter Laura. Shop till you drop.
BB
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medinabrit
professor emeritus
Reged: 10/27/04
Posts: 648
Loc: medina ohio USA.
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Actually i am the same with flashlights as i am with Scopes & binos Must have at least a dozen.
But im off to France in the morning so flashlight games will have to wait.
Had beautiful clear sky here this morning .
Got some great views of the half moon.
Brian.
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beachchairbill
professor emeritus
Reged: 11/06/08
Posts: 507
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Thanks B for the quick response and enjoy your trip to France. Hope you get to see Kenny along the way.
With so many bins and telescopes, the flashlight games would reveal some interesting findings especialy with your GBT 100/45.
Enjoy the trip and the wine.
BB
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Erik D
Post Laureate
Reged: 04/28/03
Posts: 3196
Loc: Central New Jersey, USA
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Quote:
Actually i am the same with flashlights as i am with Scopes & binos Must have at least a dozen.
Brian.
That statement brought a smile to my face. Some of us on this forum seem to have the same affliction. Mine was with maglites. Let's see, I had the 2 AA, 2 AAA, 1 AAA, 2 C, 7C, 4D, 6 D. I use to order 2 AAA mag lights by the dozen and give them away for the holidays. I must have had every color 2 AAA mag lite ever made. Use to mix and match green and red for Xmas. ;-))
I have no intention of starting an LED collection. No way....
ERik D
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