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Posts Made By: Dan D DuBal

September 6, 2002 07:43 AM Forum: Astro Binoculars

roof prism vs porro prism

Posted By Dan D DuBal

Hi Bob.

Porro-prism binoculars don't have an inherent advantage in image fidelity, but it is "easier" & less costly to arrive at comparable image fidelity via porro prisms (versus roof prisms). An excellent 8x42 porro-prism binocular will very likely cost *significantly* less than an excellent 8x42 roof-prism binocular.

A roof-prism design gains very little beyond *potential* bulk savings, over comparable porro-prism designs. I stress the word "potential," because larger-aperture roof-prism binoculars can be just as bulky (if not more bulky) than comparable porro units -- particularly at or above 50mm aperture. As aperture shrinks, yes, the roof-prism design's advantage (bulk/weight) becomes more and more obvious.

If I were considering non-waterproof binoculars with larger aperture (say, 50mm), then I would eliminate roof-prism choices altogether.

If I required a waterproof design, I'd *still* go for a porro unit, so long as its weight/bulk and price remained reasonable (compared to comparable roof units).

The DCF 10x50 is indeed a nice binocular. However, the PCF WP (waterproof) 10x50 can be found for about half the cost of the DCF. The PCF WPs are fairly new, and I have no experience with them. If their optical qualities are shared with the standard PCF line, I'd expect them to yield equal or better image fidelity than the DCF. Of course, other factors are important: weight, bulk, field of view, fit/ergonomics. -Just an example, since you mentioned the DCF.

My own bias: for stargazing, I stick with porros.

Best wishes.

September 6, 2002 08:28 AM Forum: Astro Binoculars

Best compliment for a Telescope user?

Posted By Dan D DuBal

Hello Sven.

I can think of only two reasons NOT to choose a particular marine binocular:
1) its images aren't as good as those of another non-marine (or marine) unit.
2) its weight/bulk make it difficult to hold or carry.

Unfortunately, some marine binoculars *do* show a visible disadvantage, when compared with other marine (and non-marine) binoculars. -That's what I've read, anyhow. I have very little experience with compass-equipped binoculars, but I hear good things about the Fujinon and Nikon offerings.

The 20x80s aren't necessarily too big for beginners. They're just BIG :-) I consider high-mag. giants to be specialty binoculars, certainly NOT general-purpose/all-around instruments.

Your consideration of a combo-purpose marine/stargazing binocular is a good idea. Just make a point to try and test drive your candidates -- "in the hand" as well as "at the eye."

I don't consider myself a beginner, and I have three pairs of binoculars: 8x32, 7x50, & 10x70. (A fourth pair will likely be added before year's end.) There's no doubt in my mind that I'll continue to use all four pairs for many years to come. I'll never "outgrow" binoculars.

Best wishes and luck.

September 6, 2002 06:11 PM Forum: Astro Binoculars

Pentax 12 x 50, Orion 10x50, Oberwerk 15x70

Posted By Dan D DuBal

Ed, your impressions of the Oberwerk are that much more meaningful because you related them to your experiences with the Pentax and Orion units.

Now, go check out the 12x63 and 15x63 Mini Giants and the Minolta 12x50 Activas and report back to us -- say, in a week or so :-)

Thanks for sharing your impressions of this trio of very popular binoculars. You've helped give me a little more perspective on all three. I'm sure other readers feel the same way.

Best wishes.

September 8, 2002 11:06 AM Forum: Off Topic Discussions

Life without TV?

Posted By Dan D DuBal

I have not weaned myself from television, but I did cancel my cable-programming service, several months ago.

My TV intake is down to one or two hours per week (max).

I was a teenager during the "heyday" of late-70s/early-80s sitcom hell. Today's TV "landscape" -- to me, at least -- is far more insipid and inane.

I'm less concerned with the "manipulative" aspect of current TV; it's the overall air-headedness and stupidity of most programs which worries me more.

I'll keep my modest 19-inch Toshiba for viewing movies (repeat favorites and future rentals).

Best wishes and congratulations on weaning yourself!

September 8, 2002 11:55 AM Forum: TeleVue

Different FOV with two 4.8 Naglers

Posted By Dan D DuBal

Hi, Kevin.

Various factors could be at work, here. I'll make one critical assumption:
-the eyepieces' fields were compared in the *same* scope, using the *same* diagonal (if any). Is this correct?

Even "identical" scopes from the same manufacturer can have slightly different focal lengths. Different focal lengths will yield different magnifications with a given eyepiece, and (thusly) different fields of view will result.

Likewise, if the eyepieces themselves have slightly different focal lengths, they will yield different magnifications in a given scope.

Another possibility is that the field stops differ slightly in diameter &/or position. (I.e., their apparent fields of view differ.) You can't directly measure the Naglers' field stops (they're located between elements, within the eyepiece body), but you can look through both eyepieces (like binoculars) and compare the visible circular fields defined by their stops. As the circles begin to merge, you should be able to tell if one of the circles is larger than the other. The eyepiece with the larger circle (field stop) will yield the larger f.o.v. If both circles are the same size, then their apparent fields are also the same.

If the scope used for comparison was a moving-mirror SCT or Maksutov, then yet another wrinkle arises. If the eyepieces aren't exactly parfocal (i.e., if the scope needs to be re-focused when switching from one eyepiece to another), then the resulting effective focal length of the scope is changing --slightly-- for each eyepiece. Hence, different magnifications, different fields of view.

Assuming the same scope/set-up was used for comparison, then the different fields of view you noted were likely caused by differences in the eyepieces themselves (field stops &/or focal lengths). The fact that they're not the same age supports that possibility.

Hope this helps a little. Best wishes.

September 14, 2002 07:45 PM Forum: Telescope Making

My Giro Knock Off

Posted By Dan D DuBal

>>What do you think?<<

I think it's great. Very nice work. I'm usually not enamored with brass, but I *do* like the effect in this particular piece. I'm sure the machined finish is one reason why.

Might I ask a few ??s:

Can you elaborate/explain the function(s) of the six screws on either side of the az block?

How does the top tension bolt interface with the shaft -- i.e., is the tip of the (steel?) bolt in direct contact with the shaft? or is there another material involved (UHMW, Delrin/Nylatron tip, else)?

Anodized? Raw? Other?

Great stuff, Anthony. Thanks for sharing.

September 14, 2002 07:52 PM Forum: CCD Imaging and Processing/Solar System

Got Broadband? You'll need it....:-)

Posted By Dan D DuBal

I could babble and elaborate, but I think this pretty-much sums up my opinion:



September 19, 2002 02:31 PM Forum: Takahashi

Why the Tak .965 ep's?

Posted By Dan D DuBal

Points which come to mind (not necessarily theories or reasons why):

At 42 degrees afov, there's no need for the 1.25-inch format. (Indeed, the two HI-Or models, with their subdiamter negative field lenses, need even *less* diameter. Imagine a 0.4-inch format!)

Less bulky; lighter in weight.

Slightly less lightpath "eaten" by the smaller format (vs. comparable 1.25ers).

Converting/adapting them to the larger format would increase cost.


September 26, 2002 06:57 AM Forum: Deep Sky Observing

The Moon SEES me??!!

Posted By Dan D DuBal

Respectfully stated: I have no idea what you're referring to.

Unaided view? Binoculars? Telescope? What type of telescope? Which eyepiece(s)? Was an eyepiece filter involved?

If it truly resembled an eye, then it probably *was* an eye -- your *own* eye. Luna is quite bright and easily capable of producing visible reflections within a telescopic optic.

Best wishes.

October 2, 2002 12:16 PM Forum: Deep Sky Observing