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Observing with the Pentax 20x60

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#1 EdZ

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Posted 16 August 2008 - 08:40 AM

I've recently had a 20x60 on loan to use for a period. This is an observing session from a very good night out. Someone recently asked, is the 3mm exit pupil rather small for deep sky? I leave it to you to decide for yourself.

The night was very clear, and there was very near a half moon. the moon was hidden below the trees from my point of view.

Looking completely away from the moon, I easily found M51. I could see both components and some distinct separation between. M101 was not seen, but I wasn't surprised about that. I rarely see it and especially when there is even a hint of a moon in the sky.

Globular Cluster were my main goal of the night. M3 was first, found by swinging west from Bootes, fairly large, then M5, also find by swinging west, but from lower Serpens. Then from the bright wide pair on the east of Ophiuchus (Yed), I turned east into its center. I easily found the dimmer M10 and then nearby M12. With a little more work I found the even smaller and fainter M14.

Moving south in Scorpius, I found M4, a broad patch, unlike the others seen so far. This time, I did not see NGC6144 near M4. Then I moved north a bit and easily found M9 below the sourthern point star of Oophiucus. Mear M9 and in the same fov, I saw the very faint NGC6356. The next one, to the west, M107, I think was the most difficult of the night. All of these are found by starting from bright stars nearby.

Swinging up quite a bit north, I viewed a few clusters. First was IC4665, then the more dense NGC6633, and the larger but fainter IC4756. I stopped around here to view a few double stars, 61Oph, theta Serpens, and a few more. Then I moved south to see M11. I also viewed M26, but did not see the very faint globular NGC 6712, nor to oc NGC 6664. Both of these are hampered by moonlight.

Afte that area I swung completely around to view M13 and M92, both quite bright. M57 was seen, although small and M27 was easy. I was able to pick out M71 in Sagitta. I stopped by for a look at The Coathanger and Albireo.

A few more doubles in this area, I saw 100 Herc and the double pair Stf 2470/2474 in Lyra. I could not make out Mizar.

All in all not a bad few hours of viewing. 13 globulars, 1 galaxy, 5 open clusters, 2 nebula and at least a half dozen different close doubles. This was a rather enjoyable session!

edz

#2 BobinKy

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Posted 16 August 2008 - 08:58 AM

EdZ--

Very good observing report. Did you have the Pentax 20x60 mounted? Were you able to compare the Pentax to your reliable yardstick--Fujinon 16x70?

Thanks for sharing your observations.

#3 Joe Ogiba

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Posted 16 August 2008 - 09:48 AM

The perfect mount for Pentax 20x60's is the Unimount Light Deluxe.
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#4 Obx

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Posted 16 August 2008 - 10:01 AM

I've read that it has very good optics with a flat field to the edge, but I would think that the narrow apparent FOV would be troublesome.

#5 EdZ

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Posted 16 August 2008 - 10:59 AM

I've previously compared the Pentax 16x60 (which I owned for several years) to the Fujinon 16x70 and the Oberwerk 15x70. I used tripod mounted for ease of moving. Although I have a Unimount deluxe, a Pgram mount would not have served me well for this viewing session. The narrow fov does not pose any problems to me, although I prefer wider. I had no problems doing some detailed star hops.

edz

#6 STEEL

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Posted 17 August 2008 - 04:22 AM

Finally I arrived the Pentax 20x60, unfortunately is slightly collimated evil factory Pentax. The image in the pipe right and slightly decentralized upward. I know another owner of Pentax is also him to the same problem the image slightly high in the right Eyepiece. EDZ can do a check on your Pentax?

#7 EdZ

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Posted 17 August 2008 - 04:57 AM

This one is fine.

edz

#8 hallelujah

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Posted 17 August 2008 - 06:26 AM

I used tripod mounted for ease of moving.

edz


Have you tried handholding the 20x60mm from a comfortable sitting position?

#9 EdZ

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Posted 17 August 2008 - 06:32 AM

Nope. Generally I don't handhold higher powers for more than a minute or two. I have a hard enough time keeping 12x and 10x steady.

edz

#10 hallelujah

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Posted 17 August 2008 - 06:41 AM

Steadiness is less of a problem for me, as I am mainly just 'scanning' the heavens. The vastness of the universe is still unfamiliar to me.

#11 EdZ

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Posted 17 August 2008 - 07:44 AM

Pentax PCF WP II 20x60 Minireview


Summarizing all my testing notes here

Exit pupil at the full aperture measures a 3mm exit pupil. This would lead most people to believe it is a full 60mm aperture. However, this measuremeent by itself is insufficient to tell anything about the actual magnifiaction and aperture.

Using a scale at the objective end and using a loupe to read clear aperture, I get a reading of 57mm.

Placing a 50.5mm aperture mask over the objective end and re-measuring exit pupil, I get an exit pupil of 2.65mm. With a 50.5mm aperture and a 2.65mm exit pupil, magnification must be 50.5/2.65 = 19.1x

Now getting back to my first measurement of exit pupil, if aperture is 57mm and if magnification is 19.1x, then I should see a full exit pupil reading of 57/19.06 = 2.99mm. This checks with my full aperture exit pupil reading is measured 3mm. These measurements and readings check between the two methods.

The Pentax PCF WPII 20x60 actually measures 19x57. There are no baffles interfering in the light path. From all indications, the aperture reduction is due to a too small prism shelf aperture.

Near close focus magnification is 20.5x.

Resolution is pretty good, not in the top tier but comfortably better than the mean.

The Pentax PCF WP II 20x60 has extremely narrow field of view. Also since it has a field flattener it has minimal depth of field. Pentax PCF WP II 20x60 is among those with the least curvature, in other words it has one of the flattest fields.

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.

The Pentax 20x60 has a 2.2° fov, actually measured 2.18.
The triangle of Vega, epsilon and zeta Lyra is just barely seen all at once.

62 arcsec nu Draco is easily seen everywhere.
21 arcsec (61 Oph) is seen out to 90-95% of fov
14.2 arcsec (100 Herc) is seen out to 80-85% of fov.

Off axis sharpness is among the best. I generally compare the usable fov measured to 600 arcseconds. The 20x60 is a better 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. This outer field sharpness rivals the best binoculars, but do keep in mind this is the narrowest fov binocular of any I have ever seen. Even all the 20x80s and 25x100s that I have used have a wider field of view than these. However, if comparing this 20x60 Pentax to the 20x80 Garrett Gemini TWP, while the Gemini starts out with a 3.2° fov, it is sharp (by the same measure of 600 arcseconds) only out to 60% of the fov. So, by equivalent measure of comparison, the usable fov to 600 arcseconds sharpness of the Garrett TWP 20x80 is only 1.9°, while the Pentax 20x60 is a wider 2.1°.

There was no indication of misalignment. Images merged instantly.

The barrel images do not overlap at close focus, but almost no binoculars do. 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 powered 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.

Close focus in this binocular is 27 feet. The fov of one barrel at close focus is 2.1°, but the barrel images overlap only 80% of the fov. That’s normal. FWIW, I checked the edge of field in the barrels of this 20x60 and they match perfectly when used on night sky at infinity, completely overlapped as it should be.

There was always some false color on the moon. 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.The color band is narrower than some of the most prominent false color models I've seen. It wasn't really distracting so much that it bothered me.

17mm of usable eye relief. Works best for me with eyecups turned out one notch.

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 all the way in, 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.

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.

This binocular performed very well, better than some wide-field 20x80s that I've used. Compared to two different low cost, wide-field 20x80s that I've tested, both of which have a 3.7° fov, this 20x60 Pentax outperforms them both in almost every respect. It maintains adherence more closely to stated specifications, in one instance equals the sharp fov of a 3.7° binocular!, has better build quality, longer eye relief, lighter weight, better coatings, better beam transfer, less internal vignette, and it surpasses resolution and contrast.

edz


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#12 EdZ

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Posted 17 August 2008 - 07:59 AM

Well, these binoculars now know there way around a bit more. They are boxed up and ready to ship out Monday. Perhaps the next time you use them, they'll take you to places you haven't seen before. :)

Thank you very much for the loan.

edz

#13 hallelujah

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Posted 17 August 2008 - 08:17 AM

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 all the way in, 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.

edz


Ed,

This is where my problem lies. I think the combination of IPD and E.R. had me baffled. :confused:

Now that I know what's happening, and how to correct it, the viewing experience should be much more enjoyable.

Thank you very much for all your time and testing.:waytogo:

I really appreciate your 'clearing up' the problem. :applause:

Hopefully, it will spend less time sitting in the case. :)

You're very welcome!!!!!!!!!!!!

Stan the Happy Bino Man :grin:

#14 hallelujah

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Posted 17 August 2008 - 08:37 AM


:)

Thank you very much for the loan.

edz


Ed,

So, what would you like to test/review next? :cool:

Stan

#15 STEEL

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Posted 17 August 2008 - 09:31 AM

Thanks EDZ,
It difficult to make the collimation in Pentax?

#16 EdZ

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Posted 17 August 2008 - 11:54 AM

Thanks EDZ,
It difficult to make the collimation in Pentax?


Yes, I see no apparent way to do so. BUT, I've owned 3 different pentax and used this 4th pair. In six years of use, I've never seen the need in any Pentax to adjust.

edz

#17 EdZ

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Posted 17 August 2008 - 11:56 AM

So, what would you like to test/review next?



I'm already in to my next. You'll read about it eventually.

edz

#18 STEEL

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Posted 17 August 2008 - 04:04 PM

Would you like to say that if there is a slight decentralised as collimation, I must leave it like that?

#19 EdZ

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Posted 17 August 2008 - 04:46 PM

Either that or send it to a technician for repair. Ii don't see any way for the enduser to adjust a Pentax.

edz

#20 STEEL

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Posted 17 August 2008 - 06:17 PM

This attachment is a simulation of my binoculars 10cm away from my eyes.

Attached Thumbnails

  • 2587170-Immagine24.JPG


#21 Scanning4Comets

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Posted 17 August 2008 - 08:39 PM

If you can merge images and you don't get any eyestrain, they should be fine.

#22 STEEL

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Posted 18 August 2008 - 03:57 AM

When I am close with eyes everything seems ok, I see only one circle and the images are not doubles. While 10cm to the problem exists. I do not want that assistance Pentax tells me that is a decentralisation but remains in their tolerances.

#23 oneaudiopro

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Posted 18 August 2008 - 02:55 PM

Thanks ed for a great review on such a wonderful pair of binos. I've owned mine for about 2yrs now and use them all the time. I was't aware, or didn't pay close enough attention to, the built in field flattner that you mentioned. That would explain why I had to adjust the click stop diopter yesterday when I used them at an air show here in Calif when the planes were flying towards me and away from me. I never found that to be an issue for astronomy use as I always focus them once then lock the focus adjustment knob and call it a day. Looks like you learn something new every day. Thanks again!


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