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Double extender 1.7x (for BTX)

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Old Saturday 4th May 2019, 07:16   #1
yves0071
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Double extender 1.7x (for BTX)

Dear Colleagues,
I found a BTX as second hand with my 95mm module. As magnification is 30x, it maybe a bit short to read label legs or see small details. I can use my existing 1.7 extender up to 51x.
Is there anybody who already tried to add a second extender and have up to 87x magnification?

(I tested it in the past with my Kowa 883 and 25-60 but quality decrease significantly at 153x)
Thanks for your feed back. Any experience is welcomed (even for ATX/STX!)
Regards
Yves
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Old Saturday 4th May 2019, 11:40   #2
jring
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Hi,

I know a person who has a very good BTX95 combo which is normally used with one extender but he also owns a second and uses it when needed. I have not personally seen the two extender version, but he said it's quite usable, which I believe.

Joachim
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Old Saturday 4th May 2019, 15:12   #3
Canip
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Quote:
Originally Posted by yves0071 View Post
Dear Colleagues,
I found a BTX as second hand with my 95mm module. As magnification is 30x, it maybe a bit short to read label legs or see small details. I can use my existing 1.7 extender up to 51x.
Is there anybody who already tried to add a second extender and have up to 87x magnification?

(I tested it in the past with my Kowa 883 and 25-60 but quality decrease significantly at 153x)
Thanks for your feed back. Any experience is welcomed (even for ATX/STX!)
Regards
Yves
Just small correction by the side:
The BTX provides 35x with the 95 objective module (not 30x), and the 1.7x extender brings that up to 60x (59.5x to be precise). A second extender boosts that up to 101x.

I do have a second extender but have not yet found a use where it makes sense to use two extenders (even for astronomy; the image gets rapidly too dark at these high magnifications with only one tube, the BTs (binocular telescopes) such as APM, Oberwerk, Vixen have a clear advantage there).

Canip
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Old Sunday 5th May 2019, 17:19   #4
DRodrigues
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Quote:
Originally Posted by Canip View Post
Just small correction by the side:
The BTX provides 35x with the 95 objective module (not 30x), and the 1.7x extender brings that up to 60x (59.5x to be precise). A second extender boosts that up to 101x.

I do have a second extender but have not yet found a use where it makes sense to use two extenders (even for astronomy; the image gets rapidly too dark at these high magnifications with only one tube, the BTs (binocular telescopes) such as APM, Oberwerk, Vixen have a clear advantage there).

Canip
I understand Canip but he is probably biased by his binotelescopes use...
You can see part of his experience for astro use at https://www.cloudynights.com/topic/6...-use/?hl=pinac

I never used the BTX with 2 extenders but from my experience with binoviewer use over 100x for cr-birding (see http://www.pt-ducks.com/cr-telescope...CR-binoviewing), a second extender can be useful "to read label legs or see small details", even if image gets dark. The comment "...Kowa 883 and 25-60 but quality decrease significantly at 153x" result not from the use of a second extender but mainly from the too high magnification for daylight use with a 88mm scope.
However this 2nd extender solution only should make sense for someone that doesn't have a ATX module.
Yves, in your case I would use the BTX with the extender and if you will need more power to resolve details, remove the BTX and put the ATX module - you get higher resolution and the zoom capacity...
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Old Sunday 5th May 2019, 18:51   #5
Canip
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Originally Posted by DRodrigues View Post
..... Canip .... is probably biased by his binotelescopes use...
.....
.....
.....)
Yes, he definitely is (and even somewhat proud of it )
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Old Sunday 5th May 2019, 21:57   #6
jring
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Hi,

I agree that 153x for the Kowa 883 is a bit over the top (at least visually - there some not too shabby images out there with two extenders on the Kowa), but 100x with a 95mm objective sounds quite ok.

Joachim
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Old Monday 6th May 2019, 06:09   #7
yves0071
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Hi,
Thanks to all of you for useful comments & experience.
Have a nice week.
Best regards
Yves
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Old Monday 6th May 2019, 13:20   #8
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It depends what one is looking at.
In the Sky and Telescope I just received a double star observer finds that he gets considerably closer separations than the Dawes limit with his Questar 3.5 and Questar 7.
I think that this is probably because a telescope with a central obstruction alters the diffraction pattern by putting more light into outer rings.

His standard magnifications for these close double stars are 160x with the 3.5 inch Questar, and 320x with the 7 inch Questar. But he says that if conditions allow he doubles this to 320x and 640x using the internal Barlow. I.e. 90x per inch of aperture.
He also tests for elongation rather than separation.
I note that observers have found that Questar internal Barlows range from 1.5x to 2.1 times depending on the eyepiece used and the year of telescope manufacture. The average seems to be 1.85x.

I think that 100x for a 95mm scope even with the light split for a binocular view is modest even for terrestrial subjects.

B.

Last edited by Binastro : Monday 6th May 2019 at 13:25.
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Old Monday 6th May 2019, 17:12   #9
jring
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Hi,

although it has to be said that the double-star crowd tends to use magnifications deemed absurd by everybody else and have quite relaxed needs for image quality - e.g. if they see a diffraction pattern looking vaguely like an 8, they cry separation and are happy.

Everybody else would not really love the view...

Joachim
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Old Monday 17th June 2019, 03:03   #10
horukuru
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I tested the ME 1.7x on my STX95 and the zoom starts from 50x up to 120x. Viewing was a pleasure and sharpness is great throughout the zoom range. I took pics unedited with Nikon V1 on the TLS APO 30 to showed the differences at 50x and 120x. Only resized for web viewing

Click image for larger version

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ID:	697815 Click image for larger version

Name:	DSC_6315 120x.jpg
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ID:	697816
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Old Monday 17th June 2019, 12:19   #11
jring
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Quote:
Originally Posted by horukuru View Post
I tested the ME 1.7x on my STX95 and the zoom starts from 50x up to 120x. Viewing was a pleasure and sharpness is great throughout the zoom range. I took pics unedited with Nikon V1 on the TLS APO 30 to showed the differences at 50x and 120x. Only resized for web viewing
Thanks for the heads up!

Joachim
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Old Monday 17th June 2019, 14:47   #12
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A little CA on the higher magnification, but still very good.

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