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Posts Made By: Eric Cusson

December 31, 2002 04:22 PM Forum: Astro Binoculars

Russian 20x140mm Big Binos?

Posted By Eric Cusson
Hello,

I read Markus Ludes appraisal of a number of big binos earlier this year and was wondering if anyone has had any direct experience with the Russian 20x140mm binoculars since.

Markus seemed to give the 20x140mm binoculars high marks but does it give the same yellow images like its bigger brother (30x180mm)?

Also, Markus, do you still have the 20x140s? If so did you ever put it on a fork mount and are there any plans to sell modified versions of this binocular that will allow the user to use interchangeable eyepieces?

Regards,

Eric

May 18, 2003 03:40 PM Forum: Astro Binoculars

FOV Calculation

Posted By Eric Cusson
Hi,

I'm curious as to how the focal ratio for a binocular would be calculated for a given true FOV (not apparent FOV)?

For instance, if I wanted a binocular that would provide a fixed magnification at 30x and provide a FOV of 3 degrees, what would my focal ratio have to be and what role would the eyepieces play in this calculation?

Thanks,

Eric

June 11, 2003 11:50 PM Forum: Astro Binoculars

Binocular and mirror aid

Posted By Eric Cusson
Not sure if anyone knows the answer to this one but here goes...

How accurate does the surface of a mirror have to be (used in conjunction with straight through binos for easier viewing) to support powers say between 25x-75x?

For example, a front surface mirror figured at 1/4 wave would support up to what power?

Thanks,

Eric

August 3, 2003 10:07 PM Forum: Astro Binoculars

TFOV and 1.25"/2" eyepieces.

Posted By Eric Cusson
Hey guys,

For binoculars using interchangeable eyepieces, it would seem that one would want to obtain an eyepiece with the largest field-stop and AFOV possible to obtain the widest TFOV of the heavens. Is this assumption correct?

If so, it would appear that many of the 1.25" eyepieces on the market have field stops that do not exceed 30mm while 2" eyepieces have considerably larger field-stops but would seem to be out of the running due to thier physical size.

Any comments or experiences with eyepiece/binocular combinations?

Thanks,

Eric


August 21, 2003 10:41 AM Forum: Eyepieces

Eyepiece Field Stop Question

Posted By Eric Cusson
Hi,

I'm hoping someone can clear this up for me.

I've noticed the 30mm Widescan III eyepiece has an advertised 44mm field stop which would seem to provide the potential for a generous TFOV for any given focal length.

However, what happens if the field stop of this eyepiece (or any eyepiece for that matter) is not fully illuminated by the light cone of a given focal system? What role does off-axis light play in all of this?

The way I understand it, a 30mm eyepiece focuses 30mm beyond the focal plane of the converging light cone for a given focal system, say f/5, but if thats the case, the diverging light cone 30mm beyond the focal plane does not fully illuminate the field stop of an eyepiece like the Widescan III.

What am I not getting here?

Thanks in advance for any help,

Eric

October 23, 2003 03:19 PM Forum: Astro Binoculars

Oberwerk 22x100

Posted By Eric Cusson
Hey Guys,

Just wondering if anyone has had any recent experience with the Oberwerk 22x100mm binos. Are IPD and collimation still an issue with these?

I'm looking to spend 1K on a decent bino setup having at least 3.5 deg TFV, good light gathering ability for deep space objects and decent magnification (20x).

Any suggestions?

Eric

December 14, 2003 07:32 PM Forum: Eyepieces

F-Ratio and the effects of field curvature

Posted By Eric Cusson
Hey Guys,

At what F-Ratio (fast) do the effects of field curvature become apparent?

In your experience, what eyepieces handle fast focal ratios best, say F/5.5, with minimal edge distortion, coma etc?

Regards,

Eric

January 16, 2003 12:38 PM Forum: Astro Binoculars

New APM binocs.....

Posted By Eric Cusson
Hmmmm...

How about 45 deg Fujinon 150mm bodies with hand picked (TMB designed) lenses for a fraction of the cost of a Fujinon!

Wishful thinking I suppose...


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