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Posts Made By: Ed Zarenski

January 13, 2003 01:22 PM Forum: Astro Binoculars

Cold night notes, Fuji16x70, Ober15x70, Ober20x80

Posted By Ed Zarenski

I had several pair of binoculars out back this weekend, all mounted. Included were Oberwerk 15x70, Oberwerk 20x80 and Fujinon 16x70. Some tests between these three revealed the relative ability to see. Skies were noted as 5.0 mag. And some important cold weather info is noted.

Resolution notes: For wide, open clusters, I carefully pick outline boundaries and count stars within to see how deep binocs can see. On the Christmas Tree cluster, NGC 2264, both the Oberwerks see 17*, the Fujinon see 19*. On M44, 15x70s see 71*, 20x80s see 73*, the Fujinon 16x70s see 80*. Several other clusters produced similar results.

On small dense clusters that often just look like a glow in binoculars, I saw a real difference. The Fujinons contrast and resolution made it easier to discern stars within the glow of tight clusters. On M36, Ob15x70 saw 4*, Ob20x80 saw 4*, Fuji16x70 saw 8*. On M37, the 15x70s saw 3* while the Fujinon 16x70s saw 8*.

The Fujinon can be focused to a finer point of light than either of the Oberwerks. The Fujinon contrast and resolution makes it easier to pick out the fainter stars and pick out the stars embedded in the glow of many in the small tight clusters.

Although all the binocs could see the Pinwheel, the contrast in the Fujinons made it much easier to see the faint diffuse light of M33. Last week, using the Fujinons, I found M31 in daylight about 30min before darkness. Saturn’s rings are separated from the disk in all three binocs. The Trapezium is resolved to 3 stars in all three binocs. A-B at 8.7” is not resolved, but several times did appear elongated in the Ob20x80 and the Fuj16x70.

Cold weather notes:
I viewed for about an hour or two on Saturday night. I left the binocs out over-night so the equipment would be set up for a 5AM session. Temperature in the evening was in low/mid 20s, by morning temp was 18°.

The Fujinons were exactly as I left them, focused and ready to go. Both the Oberwerks changed focus, had to be refocused. I did gain additional diopter range on the 80's, which I usually have at the max minus even with my glasses on. Didn't need them at max minus in the morning.

The Oberwerk 20x80 became nearly impossible to move the focus dial.

The Oberwerk 20x80s changed collimation. They were out by morning.
Could it be the mass and length of the steel barrles has such a coefficient of expansion that the 20x80s literally changed shape overnight?


February 26, 2003 05:56 AM Forum: Solar System Observing

Europa Shadow transit and GRS 2-25

Posted By Ed Zarenski

I went out last night to catch a few views around 8:00 EST and it was partly overcast, but with periodic breaks. Didn’t have high hopes. Took a quick look and saw Saturn and 2 moons, very well defined ring divisions. On Jupiter I saw 3 moons, but it started to cloud up. Left the scopes and went in to get warm. Temp was 12° with a little wind. Went back out later. The sky had a thin haze, I would say transparency was only 3/10. Castor and Pollux were easily seen, but some of the other stars in Gem were not. None of cancer was visible. Viewing started just after 10:00 EST.

Using my 5" G5 SCT, when I brought a 7mm ep it into focus I immediately saw the 4th moon had reappeared to the west, maybe only 5” past the disk and following closely behind was its shadow crossing the face of the disk. The shadow was a very dark spot about 5”-10” in from the west limb. As I watched for 10min or so I could see the moon moving away.

Just approaching the central meridian was the GRS, kind of a pale area, but an obvious big oval hole protruding south out of the SEB. The leading edge of the GRS was just a bit darker. The belt south of SEB was not seen complete to limbs. In the NEB following the GRS was a dark mass smaller than GRS, a small part of which protrudes north out of the NEB.

The center of the GRS crossed the CM between 10:30-11:00. By 11:15-11:20 the moon shadow disappeared off the west limb and the dark spot in the NEB was just crossing the CM.

Eyepieces used 7.5mm Tak LE (thanks Shannon), 7.5mm Ultima, 7mm UO ortho, 15mm TV pl in 2.5 powermate. The Tak and UO produced best views. Finished off the night with views of Castor and Algieba, two very similar 4" doubles. Even though transparency was poor, based on diffraction rings, seeing was a IV out of V.

Checked this morning and found GRS crossed CM at 10:40 EST and Europa shadow transit ended at 11:13. This was the first time I’ve ever recorded seeing a moon shadow transit. I've got a nice little sketch in my log book. Those hazy clouds didn’t do much to hamper my night!

Did anyone else get to see this Tues night?


March 5, 2003 09:47 AM Forum: Equipment Talk

Re: Collimating a SCT

Posted By Ed Zarenski


I have a G5, same tube as the C5. The secondary should be secure within the corrector plate so don't try moving that.

Before you try loosening the retainer ring, take measurments as indicated below. If all measurements are equal then there may be something else going on. If measurements are not equal, go on.

Set your mount so the scope corrector plate is face up and lock the mount steady. With the corrector plate locking ring slightly loosened you will be able to gently grasp the back of the secondary and move the corrector plate around. You will need a good pair of draftsman's dividers or a compass or a micrometer. Careful of the corrector lens! Take a reading at all three screws, between the back of the secondary and the inside of the retainer ring, approx 1.75 inches. Gently move the secondary to slide the corrector plate around until the reading is exactly the same at all three points. try not to twist the orientation of the secondary.

This should fix your problem if it is the secondary that is off center. A few years ago celestron was putting out the C5/G5 tube with a lot of complaints about the corrector being loose. I had one. This is one way to fix that problem.


March 7, 2003 08:53 AM Forum: Astro Binoculars

Pentax PCF V same as WP ??

Posted By Ed Zarenski

Is the Pentax PCF V series one and the same as the WP series?

If not, is the only difference nitrogen filled in WP, or do the optics vary?


March 28, 2003 12:15 PM Forum: Equipment Talk

Seeing width in the Cassini Division

Posted By Ed Zarenski

Way back in early March this discussion gathered quite a few posts and here I link back to the original question.

I did some reading at the time and posted my opinions. Back then I posted a three part thread to cover what I found. Questions were raised and I left that thread hanging at that time saying I needed to do some additional reading. I have since done so.

I cannot possible post here all the info I have gathered, but I will post my conclusions. Hopefully in the very near future I will edit this post and provide a link to the complete article.

The original question was:
Aperture to resolve Cassini Division into gap?
can the Cassini Division be resolved into a *small* gap with a 4" aperture?

Some other questions raised as a result of the original question included:
What size scope and magnification is required to resolve the "gap" so that it can be readily perceived as having width?
Why can we see the Cassini division with scopes that would seem too small to resolve its width?
How does the Cassini division fit the criteria of an extended object?
Can we use point source criteria to judge the measurements of extended objects?

I would encourage you to return to this location for a link to the complete article, however the following post is the last page of the complete article, my conclusions.

thanks, edz

4-1-03 here is the link to the complete researched article

April 16, 2003 04:59 PM Forum: DVDs and Music and Books That You Recommend


Posted By Ed Zarenski

Pay It Forward

April 20, 2003 01:34 PM Forum: Solar System Observing

April 19 transit and GRS

Posted By Ed Zarenski

Saturday night April 19, 8:00 to 11:30

Outstanding night,
All night mag 4.5, by end of night mag 5.0* little dipper was vis
Seeing sometimes wavering, most times still, crisp.

Early on views of Saturn with TV85 Started out with TV19wf Titan vis
No Cassini with 12.5UO 48x or 9UO 67x But one more moon vis
7.5TakLE Cassini vis and 2nd moon.
One dark band on disk vis with all of these.

Later views with the TV85, Castor beautifully split wide
And Jupiter, not nearly as impressive as with the Cr150.

Out front with CR150 on UA HD Surveyor damps in 3-4sec
started with 27Pan on M44 counted 130* in M44 field with 27Pan 44x 1.5°fov

Front set-up was primarily for viewing Jupiter. Shortly after 8:00 I spotted a moon’s shadow transiting and nearly exiting. I only got to see the transit for maybe 20 minutes. But while that was going on I could see the GRS coming around the turn. One half a very dark thin band stripe below lower eq belt preceding the GRS, the trailing edge of this dark stripe leading the GRS by about 1 to 1 ½ hours. The leading edge of the eq belt preceding the GRS was very dark, slanted upwards into the equartoral region and it appeared the whole dark band in that area was slightly pushed into the equatoral region. By my estimate the GRS was on the meridian just after 10:30 EDT. The GRS itself was totally washed out pale sandy tan, What was visible was the darkened pushed out areas of the band. This entire view was with 8.8 UWA. Outstanding sharp detail. 136x exit pupil 1.1mm

Last views with the CR150 was M65 and M66

I had a very nice night of viewing in Rhode Island last night. edz

April 20, 2003 01:55 PM Forum: Astro Binoculars

Two eyed vs one eyed

Posted By Ed Zarenski

Saturday night April 19, 8:00 to 11:30
Start night mag 4.5, by end of night mag 5.0* little dipper was vis
Darker skies towards SW, the area I was viewing.
Seeing sometimes wavering, most times still, crisp.

Last night I used the Fujinons 16 x 70s to do a left eye, right eye, both eyes test. Squinting closed I saw far less out of the other eye. Standing and leaning back I wavered a bit too much and again saw less. Finally, I went and got a lawn chair, set it under the UA Unimount Light. After I put a pillow behind my neck I had a nice comfortable seat, nice sturdy rig, settled in, little bumps damped in 2 seconds. Then I was able to concentrate on the task at hand.

Earlier I verified that M44 was rich in faint stars. I counted 80 stars in the region with my Oberwerk 20x80s and I counted 130* in the same region using my CR150 with a 27Pan. There were more than enough faint stars that I would not be able to reach the faintest magnitude stars in the area and be counting all there was to count. I found a stream of faint stars to the right of center from the NW to the SW of approx 20 of the faintest stars seen in the binocs. This was my test area.

When I first started, I wasn't being exact counting and I was convinced I was seeing all there was to see whether with two eyes or one eye. Finally, I recorded four or five successful counts with each eye and with two eyes. The counts varied with each attempt, but I always got counts of 14 or 15 in my right eye 15 or 16 in my left eye (my scope viewing eye) and 18 or 19 with both eyes.

Rather than close one eye in a squint, I covered my other eye with a thin black glove. The most notable difference is it was just so much easier to sit back and look with two eyes that everything popped into view and a few averted vision stars appeared in the two-eye viewing. There were a few stars in the sorrounding fileds that I did not see when I was standing. I was very clearly able to see better settled in the lawn-chair with all motion quieted down. The end result is I did see more in my test area with two-eye viewing. My results spread from a minimum difference of 16* to 18* all the way up to a maximum difference of 14* to 19*. The difference between the best reading with my scope eye to the best reading with two eyes of 16* to 19*, was an improvement of almost 20%.

In the past I never really accurately measured this. Regardless of what I thought in the past, this clearly indicates to me the degree of improvement with two-eye viewing. Certainly it will vary with the individual but this is at least an indication that it’s not just a marginal gain but more of a factorable increase.


May 2, 2003 11:16 AM Forum: Deep Sky Observing

The Airy Disk (groundwork)

Posted By Ed Zarenski

The Airy Disk
!!!!!EDITED 5-3-03!!!!!

This discussion progressed substantially elsewhere. The primary outcome that I will note here is numerous published works have incorrect explanations of these various criteria, Dawes Limit, Rayleigh Limit and Airy disk. I edited out any information from incorrect sources. If you have a desire to know more about this topic, contact me and I will forward the extent of the discussions pertaining to this. Thank you. edz

Dawes Limit = 4.56/D inches = 116/Dmm. D.L. is the first point at which a double star is elongated enough to suspect the presence of two stars.

As aperture increases, the diffraction disk gets smaller and hence the greater the resolving power. Dawes limit is not used to measure an achievable black space between two point sources.

Rayleigh Limit = 5.35/D inches = 136/Dmm.

Resolving power is dependant on wavelength of the light observed and the diameter of the objective.

Beiser: the angular width of the RADIUS of the diffraction (Airy) disk central point is represented as: A = 1.22 h / D, where
A in radians = 1.22 x h(lambda) / D (aperture of scope in meters)
Lambda is the wavelength of light = used avg of 500um or 500 nanometers = 500 x 10^-9 meters.
Visible light is between 420um and 600um. Some sources use 550um for this calculation.

For a 150mm scope, then A = 1.22 x 500 x 10^-9 meters / 0.15meters = 0.000004 radians
Converting radians to arcsec, then 0.000004 x 360/2pi x 60 x 60 = 0.83 arcsec.

Based on Rayleigh limit criteria, 5.35/D inches or 136/Dmm(some sources use 5.45/D or 140/D:
Resolution for telescopes of D: 4” = 1.33arcseconds, 5” = 1.09 arc”, 6” = 0.89arc”, 7” = 0.76arc”, 8” = 0.67arc”, 9” = 0.59arc”, 10” = 0.54arc”. To confirm the ability of your telescope to achieve these results, it would be necessary to observe and record various results for doubles near and beyond the projected limits for your scope.


May 18, 2003 04:26 PM Forum: Astro Binoculars

Visual Acuity - What’s Yours?

Posted By Ed Zarenski

Visual Acuity is a limiting factor in the eye’s ability to achieve resolution and magnification is employed to make an image large enough for the eye to perceive. If your visual acuity is 200 arcseconds, you need 12x mag to see a 17” double or 20x mag to see a 10” double.

Acuity is the apparent separation results for a range of varying doubles measured with one or more pieces of equipment. The results will fall into a fairly narrow range. This would be the observer's acuity range.

“The resolution of the eye is 3 to 5 minutes of arc; therefore a minimum magnification must be utilized to enlarge the image sufficiently to exceed the eye’s resolution.” C. R. Kitchin, “Telescopes and Techniques” Springer-Verlag, 1995. Other sources will quote lower limits. My personal records of many doubles puts me right in the middle of this range. Possibly some observers can achieve better results.

In my best binoculars I can rarely achieve apparent separations of less than 200 arc-seconds. I’ve recorded many observations between 210 and 240 arc-sec. Some telescope results are slightly better, possibly attributed to the better resolution of telescopes. The best results I’ve achieved with very good optics was about 160 arc-sec, equivalent to a 2” double at 80x. The closer the doubles or the wider the mag delta, the harder it becomes to achieve these results.

So my usual visual acuity is 3 to 4 arc minutes. I am not capable of seeing separation in a 4 arc-min pair naked eye; I cannot see e1-e2 Lyra (207") as separated. Optics improve the point source resolution and contrast making it easier to see separation.

I've read one binocular observer was able to split doubles of 4 seconds magnified 20x = to apparent separation 80 arcsec. My results do not indicate this cannot be accomplished, but they indicate it’s clear if we wish to compare our ability to perceive resolution with our instruments, we must first establish the visual acuity of the individuals. Anyone ever split Castor 4” or Algeiba 4.4” with 20x or 25x binoculars?

We could test acuity with a list of doubles. Some that might get better success with binoculars are 17CrB at 6” or 7CrB at 6.3”, E(sigma)953 in Mon at 7.1”, Mesartim y Ari at 7.8” or y Del at 9.6”. A wide range of binocs might be able to see these close matched doubles. Smaller binocs try 100Herc at 14.2”, or E2470 and E2474, the Double’s double in Lyra at 13.4” and 16.2”, or a multitude of doubles in the 20” range.

Some may achieve acuity of 2.5 arc minutes or 150”, or less, requiring a magnification of only 150”/9.6” or 16x to see separation in yDel.

I’m very interested in collecting results from binocular users that might lead to some realistic conclusions concerning acuity. Having determined acuity, we should be able to compare results of resolution tests from various individuals, as long as all other measurement criteria are held constant.

Please Email results to