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Vincent33
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Reged: 09/18/07
Posts: 95
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Quote:
Give serious thought to accepting this very small field of view. Even all the 20x80s and 25x100s that I have used have a wider field of view than these.
Hi Ed,
do you think that an instrument like the one below:
http://cgi.ebay.it/Binocolo-Astronomico-GHT-20x80-Tripletto-FMC_W0QQitemZ230247947601QQcmdZViewItem?hash=item230247947601&_trkparms=72%3A758%7C39%3A1%7C65%3A12&_trksid=p3286.c0.m14
Google translation (I wasn't able to make a working tinyurl):
http://66.102.9.104/translate_c?hl=it&sl=it&tl=en&u=http://cgi.ebay.it/Binocolo-Astronomico-GHT-20x80-Tripletto-FMC_W0QQitemZ230247947601QQcmdZViewItem%3Fhash%3Ditem230247947601%26_trkparms%3D72%253A758%257C39%253A1%257C65%253A12%26_trksid%3Dp3286.c0.m14
with a declared 64° AFOV, can offer a 40° central view at the Pentax level?
Thanks.
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12341
Loc: Cumberland, R I , USA42N71.4W
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Sorry, I don't know anything about the instrument in that link, so really can't say. But experience tells me that just about any instrument has decent sharpness in the central 40-50% of the fov. the binoc would need to suffer from spherical aberration to degrade the central image, and some do, so there is no gaurantee.
Quote:
I am having a difficult time merging the two views into one image. I get two overlapping circular fields but not a double image. Not comfortable. I suspect this has more to do with the very small exit pupil than collimation
This has more to do with close focus than anything else and really has nothing to do with small exit pupil or collimation. Typical 20x binoculars, regardless of what is posted as close focus, have a real closest usable focus of about 75 ft. (20m). They will show the field circles of the barrels will not completely overlap at least out to 200 feet (60m). This is common to most binoculars, and especially prominent in higher powerd binocs. Typical low powered binoculars that have a close focus of 15-20 feet will show generally only 75% to 85% of the barrel views is overlapped at 20 feet. Roofs do much better than porros in this respect, with roofs generally showing 85% to 90% of the barrel views overlapped at 20 feet.
FWIW, I checked the edge of field in the barrels of this 20x60 and it matches perfectly when used on night sky at infinity.
Early evening, I spent most of my time viewing the moon. There was always some false color. depending on eye placement and even a slight change in angle of view, the color border on the bright edge of the moon could be made to change from yellow to green to blue. It was narrower than some of the most prominent false color models I've seen. It wasn't really distracting so much that it bothered me.
I noticed this Pentax 20x60 is very sensitive to having IPD set correctly. It is easy to see blackout in the eyepieces when this binocular is not adjusted to your IPD and ER. When I used this with the eyeguards in all the way, I could easily move side to side slightly and experience blackout. If I did not take care to set IPD, I could experience blackout easily.
With my eyeglasses (I typically find best eye relief between 12-15mm), I needed to have the eyeguard turned out one click for proper eye relief. Once I got the IPD and ER set properly, I spent the remainder of a 3 hour evening without experiencing any blackouts at all.
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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hallelujah
Carpal Tunnel
Reged: 07/14/06
Posts: 1563
Loc: Colorado Rocky Mt. High
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Quote:
I noticed this Pentax 20x60 is very sensitive to having IPD set correctly. It is easy to see blackout in the eyepieces when this binocular is not adjusted to your IPD and ER. When I used this with the eyeguards in all the way, I could easily move side to side slightly and experience blackout. If I did not take care to set IPD, I could experience blackout easily. Quote:
EdZ,
As I stated in my PM, the newer models on the market that I have looked through do not seem to be plagued with this problem. Perhaps Pentax made some necessary corrections on newer versions.
Stan
Edited by hallelujah (06/13/08 09:00 PM)
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12341
Loc: Cumberland, R I , USA42N71.4W
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about the only thing they could do would be reduce eye relief.
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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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12341
Loc: Cumberland, R I , USA42N71.4W
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Quote:
Quote:
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I am having a difficult time merging the two views into one image. I get two overlapping circular fields but not a double image. Not comfortable. I suspect this has more to do with the very small exit pupil than collimation
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This has more to do with close focus than anything else and really has nothing to do with small exit pupil or collimation. Typical 20x binoculars, regardless of what is posted as close focus, have a real closest usable focus of about 75 ft. (20m). They will show the field circles of the barrels will not completely overlap at least out to 200 feet (60m). This is common to most binoculars, and especially prominent in higher powerd binocs. Typical low powered binoculars that have a close focus of 15-20 feet will show generally only 75% to 85% of the barrel views is overlapped at 20 feet. Roofs do much better than porros in this respect, with roofs generally showing 85% to 90% of the barrel views overlapped at 20 feet.
FWIW, I checked the edge of field in the barrels of this 20x60 and it matches perfectly when used on night sky at infinity.
As a follow up to these comments, I checked the close focus field of view overlap in the Pentax 20x60. First of all the close focus measured 27 feet. So at a distance of about 30 feet I measured barrel view overlap. The total width of view at 30ft is 13 inches across. Only 10 inches is seen overlapped in both barrels. Therefore, similar to many other binoculars I've checked, close focus overlap is about 80% of the FOV.
As I mentioned before, I checked the edge of field lap in the barrels of this 20x60 focused when used on night sky at infinity and it matches perfectly, fully 100% overlapped.
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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AV in CMH
sage
Reged: 11/07/05
Posts: 282
Loc: Columbus Ohio
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Just in case anyone is interested.
I have had a chance to use the Pentax 20 x 60mm a few times and I can say now that these binoculars are more than I expected.
The ergonomics make them surpisingly easy to use. The sharpness is as noted noted on this forum - great. Yes, the eye alignment is quirky. Quirlky in the way a telescope is when using a barlow.
The only down side to owning these is that now I am wondering how much better could the 70mm Fuji binoculars be? Someone else posted that the trouble with good optics is that using them opens the door to more expensive and yet better optics or something like that. I could not really relate to the post when I first saw it but do now.
Regards,
Anthony
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Dave Hederich
sage
Reged: 09/12/07
Posts: 237
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"Surprisingly easy to use" is one of the reasons that I selected the Pentax 20x60s over the various 70-100mm options. In addition to celestial viewing, I also use them a lot in the daytime. I was recently viewing an airshow from a nearby hillside, and passed the 20x60s around to several other people. Without exception, they were blown away by the quality view of the parked aircraft at the airport about half a mile away.
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Celestron C4-R 102mm Refractor
Tasco StarGuide 4 102mm Mak
Stellarvue BV3 Binoviewer + SV23mm EPs
GSO 1.25" 2X Barlow
Pentax 20x60 PCF WP II Binoculars
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charen
scholastic sledgehammer
Reged: 05/28/05
Posts: 770
Loc: New Zealand
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Yes I use mine for day time use just as much as night time use. I use a monopod to help steady the image. The ergonomics are very good - they feel relaxing to hold. These are my 3 rd. pair as I have sold others on odd occasions to finance other equipment. These ones I have now are keepers. The image and build quality for the price is excellent. The ‘narrow’ FOV does not concern me - for others it is an issue.
Chris
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35 binos.
80mm Cat.
WO66ED
SV NH 80mm / EQ3
Meade 8in.LX90
Skywatcher Equinox ED120 / Goto HEQ5.
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GlennLeDrew
sage
Reged: 06/18/08
Posts: 467
Loc: Ottawa, Ontario, Canada
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Quite often I've seen this phenomenon of field stop circles overlapping, even when looking out to infinity. It indicates that the eyepiece optical axes are tilted with respect to each other. When the instrument is collimated so that comfortable merging of the images can be accomplished, the eyepiece tilt is well revealed as overlapping field edges. I find this to be an intolerable problem.
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Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV
Mediocre minds discuss people. Good minds discuss events. Great minds discuss ideas.
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12341
Loc: Cumberland, R I , USA42N71.4W
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A few more tests on these WP II 20x60s.
Resolution is pretty good, not in the top tier but comfortably better than the mean.
Off axis sharpness is among the best. I generally compare the usable fov measured to 600 arcseconds. The 20x60 is only 400 arcseconds at 95% out and has a usable fov right to the edge, giving it a usable fov wider than some 20x80s I’ve tested.
17mm of usable eye relief. Works best for me with eyecups turned out one notch.
Laser test shows good light beam transfer. Although one barrel had an optical axis more tilted than the other, the overall beam transfer was pretty good.
Aperture measured at 57mm. Magnification checks at about 19.5x to 19.8x.
Near close focus magnification is 20.5x.
Pincushion extremely low, among the least measured, may mean this binocular is a bit more difficult in most terrestrial observations as a lack of pincushion may translate to a greater rolling ball effect, (Although to my eyes, no rolling was seen).
Depth of field very shallow, another factor which may work against terrestrial use.
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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