Posts Made By: Dan D DuBal

What advantage(s), if any, would such a finder have over a standard o.t.a.-mounted right-angle finder?

Mind you, that's not a rhetorical question; I may simply be "missing" something. I can envision significant design considerations &/or potential problems, but advantages are escaping me.

Cheers & best wishes.
-Dan

Hi, Scott.
After years of small-aperture viewing, I feel I've trained my eye reasonably well and can do a good job of "seeing small" in my 75-80mm refractors. I myself would consider a 6mm aperture "gain" (over 70mm) to be insignificant, visually -- likely not discernible at all, in terms of angular resolution (assuming comparable fidelity). I have both a Sellarvue 80mm f/6 and a Pentax 75 EDHF (f/6.7), and the Stellarvue compares favorably.
Is it "as good?" No.
Could I "make do" with the Stellarvue alone? Probably.
Would I part with the Pentax? Never.
The EDHF was my first really useful/capable astronomical telescope, whereas the Stellarvue arrived some years later (after yet another couple scopes I haven't even mentioned here). If I were forced to part with either the Stellarvue or the Pentax, it would certainly be the Stellarvue. Again, this is not due to any optical shortcomings; my Stellarvue is an excellent 80mm achromat.

If there was an alternate timeline in which my first "real" scope was an excellent Ranger, and I'd spent many years with it, and I had no qualms about its 1.25-inch format and helical/draw focus mechanism...
...I don't think the TV76 would hold too much sway over me.

In the end -- even if the TV76 does not seem likely to satisfy your "bang for the buck" considerations, you may have to ask yourself an even-more-important question...

"Yeah, OK... But do I still want it!?" 8)

Never underestimate the power of emotional "bang."

Cheers & best wishes, wherever your decision leads you.
-Dan

Excellent color, Pete -- and I envy your southern vantage. This be guided, or did you just 'er go?

Notice how blue IC4665 appears (right edge, almost 2/3rds up from bottom).

Wonderful stuff, as always. Thanks for sharing.
-Dan

Wha-? Huh?...
Well, waddya know! We'd grown so accustomed to the 4-inch Tall Ron B[ee]...

You'll have to be patient, sir. It may take us a while to get used to the idea.

Seriously, though -- congratulations and kudos to you. I suspect the next few months will find you sharing countless hours with both of them, comparing views & virtues, and realizing even moreso how much wonder & enjoyment you get (and will continue to get) out of "Junior."

Cheers and best wishes!
-Dan

...maybe this one?
www.rednova.com/images/gallery/2mass_sky_survey/iras_060881909/24/79/index.html

Cheers.
-Dan

Dave, you said it yourself... "There's no downhill side to the learning curve." Hence, there are no silly questions, so long as they're sincere.

A typical 50mm binocular objective has a ~200mm focal length. I'm guessing you don't have a 20-inch f/40 Schiefspiegler, right?

Even paired up to make a Symmetrical/Dialsight/Plossl-type eyepiece, the effective focal length would be around 100mm.

To bring the effective focal length down to a more practical range, one or more "stronger" elements (shorter focal lengths) would need to be employed.

Cheers & best wishes.
-Dan

One big advantage of an intermediate extender is the increased distance between it and the eyepiece, which (when properly implemented) would reduce potential focuser-travel issues, compared with much shorter extender-eyepiece distances.

As for secondary obstuction: yes, implementing an intermediate extender into an existing primary/secondary system might pose a logistics problem. However, full aperture can still be maintained by altering that system (i.e. primary-to-secondary separation, diagonal size, or combo thereof). Even if such modification isn't practical, the scope's design & intended use may very well be able to "accomodate" a larger secondary obstruction with little/no significant reduction in resolution or contrast (fast astrographs come to mind). When used for visual astronomy, of course, a larger obstruction would impact resolution/contrast. The question would then be, "Would the impact be visible &/or significant?"

I suppose an intermediate reducer could be integrated with an existing slow objective (term includes primary mirrors) to allow for a more-compact structure, thereby perhaps reducing the capacity requirements for a given mount. -Sounds like a potentially reasonable solution for certain specific/limited scenarios.

Cheers.
-Dan

If you don't have access to a laser or Cheshire tool...

If the "squareness" of either end of the scope tube is untrue to a significant degree, a T-square or combination square may show it (remove the focuser from the tube). However, if the degree is too subtle for either tool, then another quick & sure-fire way to test the focuser/tube interface is to simply twist/rotate the focuser in its place while sighting a fixed target. For many scopes, this involves the removal of three screws that attach the focuser housing to the tube. Obviously, a very tight flange/tube interface can make for some stiff & stubborn rotation. Make sure the focuser/tube interface is maintained (focuser butted up against the tube end when rotating). If focuser rotation induces similar circular motion of the target within the field of view, then the focuser's optical axis is not parallel to the tube's/objective's optical axis.

Focuser/tube alignment is especially critical for faster refractors utilizing non-adjustable objective cells. If one or both ends of the scope tube are not perpendicular to the tube's ocular axis, realignment can be tedious. Both ends of my 60mm f/5 refractor tube are non-perpendicular, so realignment required shimming the objective within the non-adjustable cell and a focuser tweak. Luckily, the focuser tweak involved a simple 120-degree rotation of the focuser (screw holes in an alternate "clock" position).

Cheers & luck.
-Dan

Two questions:
1) What was the distance between the C8 & the artificial star?
2) What other hardware was installed with the r/c (i.e. extension tube, visual back, diagonal, etc.)?

If the artificial source required a significant shift in focus (primary pushed forward), the primary baffle tube (or perhaps the r/c itself, or another item nearer the eyepiece) may be interfering with the image field to a minor degree. Any movement of the fresnel pattern off axis would cause some "flattening" of one sector the fresnel pattern. Both the center of the pattern and the opposite sector remain undisturbed. I have seen this effect in moving-primary scopes as well as long/slow refractors, even when focused at infinity.

Cheers & best wishes.
-Dan

Hi, Dave.
The red felt hard case (brown, I'm guessing?) and 8x40 specs remind me of the classic Bell & Howell 8x40s from the '60s & '70s.

I've attached a photo of the B&H model.

My own B&H pair has the following specs/characteristics:
field of view = 510 ft. @ 1000 yds. (9.7 degs.)
BK7 prisms
MgFl coatings (quite blue)
pebble-grain "leatherette" covering
german/Zeiss style body (separate objective barrels; not one-piece Bausch & Lomb/American style)
leather hinge on case is fastened with 7 rivets (4 top, 3 bottom)

The right-side hinge area of my B&H (just off the front shoulder, where barrel joins prism housing) includes the Japan manufacturer code of "B191" -- this specifies either Seiwa Optical Co. or Yoko Sangyo as the maker of the completed binocular (likely Seiwa).

You should be able to find a similar "B" code engraved either on the hinge itself or snugged up against the front cover plate. Just to the left of the "B" code, there should be a slanted "J" with a right-leading horizontal dash. On my B&H, the bottom curl of the "J-" is hidded by the edge of the cover plate, so the character looks like a slanted "L" instead.

There might also be a serial number on the front hinge cap (mine is "BH-44293").

I learned my way around the sky with my parents' B&H 8x40s and an old hardcover edition of the "Field Guide to the Stars & Planets." (The B&H pair I have now is a replacement I picked up a few years ago.)

This URL will lead you to a list of Japan manufacturer codes:
www.home.europa.com/~telscope/jbcode.txt
I'd sure be curious to know if your Century Mark IVs are by Seiwa. Let us know what you find.

Cheers.
-Dan