Posts Made By: Dan D DuBal

Hi Gary.

This is a specialized large-aperture achromat and will show vivid of chroma on brighter stars, planets, & the moon. However, it should really excel at its intended purpose -- dropping the viewer's jaw with deep, wide, sweeping views of star fields, clusters, & nebulae. This is certainly not a planetary scope, and Markus would be the first to say so. If the optic is fine (I'm guessing it's very good), then deep-sky imaging would certainly be an option, given a suitable mount (i.e. large, strong, & expensive), drive, imaging equipment, software, etc.

As for planetary views, I suppose one could craft a removable stop-down mask and have an excellent 4-inch (effective) f/12 achromat. But it's my opinion that this bird should always be allowed to fly at full aperture. Feeding this 8-inch f/6 achromat an excellent binocular viewer would also be a treat.

Several years ago, I had the opportunity to spend a few minutes "behind the wheel" of a 10-inch f/5 APM achromat (with a Pentax 40mm XL). Sweeping through Cygnus, Lyra, & Hercules was an eye-boggling experience. In that context -- visual observation of dimmer stars & star fields -- the inherent chroma wasn't at all obtrusive.

I won't dare guess a "fair price" for this rare bird, but if it were mine, I'd be looking for at least $4K -- likely more (again, that's just me). Component, design, & construction particulars would certainly be factors.

A comparable apochromat would (or should, if well designed & implemented) prove a much more versatile (& serious, & expensive) imaging platform.

Cheers & best wishes.
-Dan

As for higher mag "pushing," that's much a function of the optic's quality & aperture (for now, we'll ignore atmospheric effects & the human eye). For a given aperture, a more accurate & smooth optic should yield higher useful magnifications. Likewise, for a given optical quality, a larger aperture should yield higher useful magnifications. In this case (4- or 5-inch Maksutov; 80mm SV/WO), the 5-inch Mak should have the higher-magnification advantage (assuming comparable optical quality) -- again, that's "on paper," so to speak. Now, let's reconsider those previously ignored factors (seeing, eyes, et.al)... For observers on most scopes on most nights at most locales, the high-magnification limit is determined by the atmosphere &/or defects in the observer's own eyes (especially floaters).

I would not expect a typical good 4-inch Maksutov to show any advantage over an excellent 80mm refractor, with regard to available/visible plantary detail, regardless of magnification. A 5-inch Mak?, well, that's a bit more interesting. There's a definite aperture advantage, and that 150x-to-200x range will be more "easily" accessed, due to the the Maksutov's longer focal length. As for available/visible planetary detail, the Mak (if it's very good) may have a slight advantage, assuming conditions allow it. If we were to consider a 6-inch Maksutov, then the advantage would be more than slight.

Darn it; is there ever an easy answer?

My two cents...

Any experiments regarding insulative & conductive scope interiors would need to be standardized & controlled. With so many factors contributing to a particular scope's thermal "performance," it's easy to see how one or more aspects of the scope's design & construction might override the "interior composition" part of the equation. Significant considerations include: primary mass/thickness, cell design/mass, primary baffle design/mass, secondary assembly design/mass (including spider), baseline temps, etc.).

In the case of a classical or other open-tubed cassegrain, I would think an insulative interior might be more appropriate with a 1/16th-inch aluminum tube structure. Still, the practical contribution (insulative vs. conductive) may remain relatively insignificant. If you go with an insulative interior, consider a concrete form tube (i.e. Qwik-tube/Sonotube). I think they make much more sense than cork sheet -- much easier to implement (already tubular!), cheaper, and more durable.

Hmmm...how about a Qwik-tube interior surrounded by an intermediate air space (say, 1/8th-inch)?

Yes, the rear end (primary & cell/housing) should receive much of your design consideration. More mass => more heat.

I agree about the "blackness" of the interior: with proper baffling -- including the front end, ahead of the secondary -- even an aluminized interior (egad! 8O ) won't generate stray light at the image plane.

Cheers & best wishes.
-Dan

Very nice, Pete!

I'll keep mum about the target's popular name (or names, rather).

Thanks for sharing.
-Dan

Great photos, Pete -- all of them!

I especially like the image scale in your M101 photo. The background sky adds a wonderful perspective & context, and it's a refreshing change from the typical close-up "full bore" images of that galaxy.

Keep 'em coming, sir!
Best wishes.
-Dan

I agree with John. A long 5- or 6-inch acromat will require a more substantial mount. An Atlas or C6 is simply not up to the task -- not tall enough, either.

I'd get the biggest Maksutov both my budget and mount could comfortably manage -- likely from either TEC, Intes, or Intes Micro. If my budget &/or mount dictated a six-inch Mak, but I still wanted more aperture, I might very well opt for the Celestron 9.25.

Cheers & best wishes.
-Dan

-A wonderful photo, Pete.

I'm gonna go waaay out on a limb, here, and guess that...perhaps...just maybe...you're having loads of fun with your SN8 & LXD75. 8)

Of course, I could be misreading.

Clownfish? I'm afraid to ask...
I have four clown loaches, myself. They're called the Stooges.

Cheers and grins.
-Dan

Polar-mounted refractor, perhaps. Didn't the inimitable Oscar Knabb make one (among countless other scopes, of course)?

A decidedly inelegant (and perhaps impractical) notion: how about a scope-mounted screen tent? Imagine a large sheet of netting attached/draped over two quarter-circle or D-shaped hoop collars, each collar being at either end of a large dob, creating a 4- or 5-foot canopy over the observing side of the scope, front to back. The hoop collars could be small-diameter PVC piping, with two or three lengthwise connecting supports (from arch to arch -- one at the crest & one or two more further down along the hoops). The front end of the scope remains open, with the netting simply draping down to the ground around both you and the scope.

I'd imagine the total weight of the netting and PVC framing would be less than 10 lbs -- perhaps closer to five(?).

-And I'm sure it wouldn't draw any attention at all.

Cheers & best wishes.
-Dan

Sounds very cool, Rey. Congratulations!

I haven't used the TV60, but I do have a couple of 60mm achromats (one f/13, the other f/5) with excellent objectives, and I know what you mean. I think mine are great, and I get a big kick out of trying to see what they can do. No, neither of them can keep up with my Pentax 75 when the seeing is good, but they're still lots of fun -- definitely not poor performers. I'm keeping both of them.

I think you have the right idea: just keep enjoying that little overachiever. It's all about FUN!

Best wishes, & thanks for sharing.
-Dan

Great shot of one of my favorite globular clusters. Even in smaller scopes, M92 is wonderful.

As always -- thanks for sharing, Jim.
Cheers.
-Dan