Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Messages - Scott Bentley

Pages: [1] 2 3 ... 10
ATM, Optics and DIY Forum / Re: String Telescopes
« on: February 09, 2018, 11:35:59 AM »
Several folks here in Portland have built string telescopes - Dan Gray is the original creator; David Nemo built a 20" string telescope and had a build thread here.

Link to my archived buildthread:

Last year I had the mirror reground to around f3.5 - as I got tired of moving and climbing a ladder. Rebuild was a snap. Just shortened the strings and poles, and good to go.


Things have sure changed since I visited in 2005. Back then there was another rental company that would allow driving on unpaved roads, Saddle road (before it was upgraded) and up Mauna Kea. I rented a 4x4 from them because of that. Went on the Saturday tour (which it looks like they no longer offer). The tour back then included one of the Keck's and the UofH 22-inch (full tour of the latter).

Back then you had to have a 4-wheel drive vehicle to join the tour. I am surprised that anyone was ever let up the mountain without one, even independent of the tour. Even now I see it is still just a recommendation. How many deaths are required before it becomes mandatory (with gate control to the summit past the visitor's center)?

Although this was before the 30m controversy, even then there was native opposition against the telescopes. But AFAIK no protesters, at least not on a regular basis.

The Saturday tours halted when the protesters arrived.

General Astronomy & Observing / Re: Is it possible to have unstoppable dew?
« on: February 09, 2018, 06:34:40 AM »
Just curious why so many folks seem to work so hard covering/uncovering, etc. in an effort to avoid using dew heaters. Maybe it's because I observe in Florida where dew heaters are a given that you just use them and not have to worry - other than covering whatever is lying on the table.

Eyepieces Questions & Recommendations / Re: Delites are awesome
« on: February 09, 2018, 06:23:55 AM »

The 17 Ethos is special. I like it better than the 21mm.
The 18.2 Delite, though, has pretty close to the best contrast I've ever seen in an eyepiece.
I use it all the time in my 4" apo at 39x as a star cluster eyepiece (1.53°) and it frames objects very well.
But, if you liked the 17 Ethos, I foresee other 100° eyepieces in your future.

I don´t know how to describe it. The overall image of the 17E was a bit brighter, including the background. That means that the Ethos has better transmition? The DeLite showed a darker background, but it was my impression that the targets too were a bit dimmer. Again, just my impression.
The wider field could give the impression of a higher transmission.
Since the 18.2mm Delite yields a larger exit pupil, the image should actually be brighter in the 18.2mm.
Plus, it has fewer elements.
The darker background is likely due to substantially less light scatter. And the smaller spot size will yield tighter star images (not that the 17 Ethos is bad in that regard),
which could make DSO details smaller and tighter.
It has often been speculated that a narrower apparent field, in which the field stop is more visible, will seem to yield a darker image, even though lab measurements may actually show
a higher light transmission.
One thing that I have seen happen with me is that a wider field seems more engaging and immersive, so it seems more impressive. The brightness difference is almost assuredly a psychological phenomenon,
though, since for a transmission difference to be noticeable the difference would have to be 10-20% and there might be as much as 2-3% difference here, but certainly not 10-20%.

One other thing: there could be a spectroscopic difference in transmission curves that favors one end of the spectrum in one more than the other. Not having such data, however, I cannot speculate how
that could impact what is seen.

Mounts Questions & Expirience / Re: Polar Scope Reticle Image
« on: February 09, 2018, 03:37:39 AM »
Now i see, thanks!

The instructions included with the OIII filters like the one I have from Orion recommend for scopes 8" apertures or greater.

Folks' experience has pretty well rendered that bit of wisdom obsolete. Many, Many posts to the contrary.

Beginners Forum / Re: Thoughts on 10 yr old Orion intelliscope dob
« on: February 02, 2018, 04:16:28 PM »
Is this a push-to scope, meaning it does not use motors to automatically track objects?
If so, the extra field of view offered by an 82 degree eyepiece vs a 50 degree eyepiece, for example, would be a welcome plus.
I enjoy my Dob, but without my wide field eyepieces (about 70 degrees), it would be bothersome. Just my thoughts.

It seems quite a few premium eyepieces have very sensitive eye placement issues with blackout and kidney bean. My 11 DeLite was picky, and so is my 17mm ES 92. Conversely, my Panoptics, Plossls, and 12mm Nagler Type II are extremely easy to look through and have no eye placement issues.

Is it just something inherent with long eye relief eyepieces?

ATM, Optics and DIY Forum / Re: Bluetooth NEQ6 control
« on: January 31, 2018, 10:53:37 AM »
I've read some of the Chinese PCB silk screen masking have RTX and TX reversed.


I don't see any rubber or foam between mirror and puller, correct...?(image 3)

Hi Chriske, I do have the neoprene foam between my aluminum puller and the mirror - directly from Adler's article and the flex.exe output. There's blue masking tape around the puller plate/ foam assembly in the picture prior to gluing up the mirror itself.

Eyepieces Questions & Recommendations / Re: Delos 14mm vs. Pentax 14mm ?
« on: January 31, 2018, 04:41:21 AM »
the strong points of the 14xw
-eye placement
-on axis transmission

the strong points of the 14 Delos
-overall FOV correction
-sky background darker
-star saturation pop

my pick is a easy one here Delos!

I did polar align using the scope (btw Skywatcher: you can make it better!) and my wedge shows about 42°.... while I'm on 37° ?! How can this be?! EQ6 that badly manufactured?

Eyepieces Questions & Recommendations / Re: Advice on next eyepiece
« on: January 30, 2018, 03:07:45 AM »
What we often hear from folks in your area is that conditions limit useful magnification pretty severely. I can't see where you need any eyepieces unless you think you can push the magnification. You should have been able to test for that via the T6/Powermate combo. The 4.7 Ethos is akiller. Great eyepiece.
Like others, I think your kit includes a lot of duplication and could stand thinning. But there's nothing wrong with becoming attached to your gear and keeping it because you like it and you want to keep it.
I'd say go get that new refractor, sell all those Plossls and then consider adding a few Tak Orthos (maybe an 18mm/12mm combo with your Powermate) to really take best advantage of your new optics.

ATM, Optics and DIY Forum / Re: What did you work on today?
« on: January 26, 2018, 07:01:44 AM »
Three hours of testing hypotheses about why the collimation shifts on my dob as I move it away from zenith. Found a lot of things are AREN'T the cause...

Mounts Questions & Expirience / Re: Tree for a pedestal? Surely I jest...
« on: January 25, 2018, 10:20:11 PM »
A tree stump for a telescope pier isn't a new idea. There are pictures of such a setup in "Amateur Telescope Making," first published in 1926 by Scientific American magazine.

Yeah, but they made car frames out of wood back then too
Glad to know it has been done before - I hate being the first to do something crazy (although it happens)!

Pages: [1] 2 3 ... 10