Louis D

4 hours ago, apaulo said:

In fact i have even  considered using pliars on it

Don't.  I've twisted plenty of Chinese/Taiwanese sourced screws completely in two just using finger pressure.  Some others took using pliers to twist them in two.  Once twisted in two, you'll need to drill out the portion stuck in the device and retap larger threads.

13 minutes ago, johnturley said:

Now Jupiter and Saturn are moving higher up it will make less of a difference, I don't think many people bother using them for AP as you can correct any false colour due to atmospheric dispersion in the processing software.

Not completely true.  You can shift the individual RGB channels relative to each other in post, not the frequencies within each color band.  Blurring within each band cannot be corrected in post.

Here's an image from a rather thorough article about ADCs showing the improvement an ADC can make over doing the shifting in post:

10 minutes ago, bosun21 said:

Thanks. I was thinking about using it on my 12” dobsonian on an EQ platform. Thoughts?

You might not have enough back-focus to insert the ADC in the focuser.  If you have one of those Synta focusers with the high-hat 1.25" adapter, you could probably substitute it with the ADC with the proper low profile adapters to hold it in the bare focuser opening.

I only have 25mm of back-focus on my Dobs due to undersized secondaries and low profile focusers, so an ADC is not an option for me.

On 10/08/2019 at 20:49, Louis D said:

Optcorp is OPT, Oceanside Photo and Telescope.  They're one of the oldest and best astro retailers in the US.  The recently closed their retail store, so now they only do in person visits by appointment only.  They list their new address as 2245 Camino Vida Roble, Suite 102, Carlsbad, CA 92011.

OPT came under new management some years back.  Their service was going downhill already when the pandemic hit.  Their business model did not allow them to weather the storm, and they are now in liquidation bankruptcy.  There are now maybe half a dozen dedicated astro vendors in the US.

5 hours ago, rrb24 said:

I plan to take a Stowaway to Mexico next year for the solar eclipse and it looks just perfect for the trip.

Just make sure not to go to a cartel controlled part of Mexico unless you want to risk being kidnapped for ransom or just plain shot for being on their territory.  Perhaps you know someone there who knows their way around and can keep you safe.  The company my son works for just recently cancelled routine business trips to central Mexico to monitor their operations there.  He himself did manage to take an uneventful pleasure trip to Mexico City and the nearby Aztec ruins this spring.

20 hours ago, Highburymark said:

National Geographic was a not-for-profit enterprise until 2015, when it became part of the Murdoch empire. Then Disney bought 21st Century Fox in 2019, and became owner of the brand.

That probably explains why I let my NG subscription lapse in 2017.  I had been noticing a significant change in the type and quality of the stories in those last few years.  It wasn't the same NG I had grown up with decades earlier.

1 hour ago, Steve Ward said:

About 5000 visible to us , but the Earth gets in the way of a lot of them so we can never actually see more than about 2000 ... 😏

Definitely.  As I wrote that, I was thinking about how many stars will never be seen throughout the year from any given point on the Earth's surface.  You would need to travel to the opposite hemisphere and observe for a year there to catch all of the stars visible from both the northern and southern hemispheres.  I think that's why the number I looked up was so vague.  Even at the equator you would have trouble observing stars at or near the poles.

As a cynical American, I can say it's always all about the almighty dollar and the lure of a quick buck.  These organizations are dealing with changing times and declining revenue, contributions, or state funding.  They are doing whatever it takes to survive with little to no thought given to possible long term damage to their brands.  These branding arrangements are generally judged to be low risk by their governing boards.  In addition, merely getting their names out in front of the public is also seen as a form of advertising that may draw in new interest and funding.  In particular, a form that costs them nothing except reputation.

On 31/05/2023 at 12:45, jjohnson3803 said:

I've experienced that with wide angle, low power EPs from time to time.  Don't remember details, but I think there was a fair amount of field curvature visible and I was comparing the center of the field to the edges.  Ugh.

It was probably distortion you were experiencing rather than field curvature.  Field curvature causes the edges to go out of focus while on-axis is focused whereas distortion changes the placement of points relative to other points within the field of view depending on how far they are from the axis.  FC is obvious without having to move the field of view across the sky whereas distortion is generally not visible until the FOV is moved.  The exception is for extended objects like the moon placed near the edge.  It may be stretched into an egg shape or flattened into an oblate sphere.

That amount of flex should be easier reproducible just by extending the focuser tube and pushing sideways on it.  That seems excessive.  Just adding a plate behind the focuser may just transfer the flexure further away.  Ideally, you want a stiff reinforcing ring around the entire inside of the upper tube.

Now I don't feel so bad having a Sonotube for my Dob's tube.  It doesn't flex at all that I've ever noticed.

A few previous Heritage light shroud threads for more ideas:

3 hours ago, neil phillips said:

Not so easy to figure good ones. As we would like. Agreed

And yet the Far Eastern optical shops have been cranking out consistently well figure parabolic mirrors for some time now.  Why has this level of optical prowess eluded their refractive optics figuring lines of business?

1 hour ago, knobby said:

Blimey, doesn't time fly ! just found the Moon pic I took through an imaging Ha filter ... 

 

3 years ago 🙂

 

 

That's very cool.  I wonder if an IR-pass filter would work well?  It doesn't seem like there's much scattered light in IR in a daytime sky.

2 hours ago, doublevodka said:

How's your French? https://gallica.bnf.fr/ark:/12148/bpt6k65067013/f233 You can find almost anything if you dig hard enough 😂

Very cool. To translate to English, I just clicked open the Text Mode (OCR) tab on the left and right clicked in Chrome and selected "Translate to English".  Not the best translation, but I certainly got the gist of most of the descriptions.

It's obvious he had insufficient aperture to resolve even the showpiece GCs or to detect the faint nebulosity associated with some OCs.  However, he was able to detect lots of galaxies that are mostly lost to light pollution in all but the darkest skies.  It must have been an interesting time back then.  Nice dark skies, but very crude and small instruments.

It's also obvious he had no idea what he was looking at other than the star clusters.

However, this source does provide the OP with an "authentic weblinks for the Messier Objects' Catalogue" as requested.

37 minutes ago, John said:

or use a newtonian ?

you can get several of those for the price of a chromacor 🙂

I actually bought both a used 6" f/6 KUO achromat and a used 6" f/5 GSO Newtonian and have compared them side by side on the same objects on the same night on my DSV-2B mount.  The Newtonian with a GSO CC walked all over the refractor with a TSFLAT2 except for the spider diffraction spikes on all objects I observed.  The lack of CA and SA really tipped the scales in the Newt's favor.  It also weighs about half that of the refractor, making mounting much more stable.  Crazily enough, the Newt cost 1/3 the price of the achromat!  I would struggle to recommend the fast refractor over the fast Newtonian aperture for aperture.

I'll have to find a tight double sometime to see if the refractor's lack of a central obstruction yields a better split or if the CA and SA negates that benefit.

19 minutes ago, neil phillips said:

 I am probably going a bit off topic now. So back to the virtues of achromats and filtering to reduce CA and minimize damaging effects of out of focus light on imaging or viewing. I liked my Baarder 495 it did seem to sharpen up the image. And without too much of a transmission loss. But your the one whos doing the testing so will know much more than me about any of that

I've found that cutting all violet and blue as with a true Wratten #8 or K2 filter (same as a Baader 495) gets you 95% of the way to the sharpest image possible in fast achromats on all but Venus.  Venus really needs a deep red cut filter like a cyan filter to get all the way there because the violet/blue cut filter only gets you about 80% of the way on Venus.  The unfocused deep red is really strong on Venus once you filter out the violet/blue.

I don't know why, but the other planets, the moon, the sun, and Sirius really don't improve all that much with an additional red cut filter like Venus does.  Dimmer objects often don't seem to improve at all with violet/blue cut filtering.  If anything, they sometimes get too dim to observe.

Basically, try various filtering options on each object with an achromat to see which yields the best view to your eye.  It may not be the same as when imaging the object.

On 29/05/2023 at 04:04, knobby said:

I've used my imaging set up to capture the Moon during the day using the Ha filter, quite surreal to see it looking like midnight during the day. Might be worth a bash if anyone has an Ha filter ?

I could see where that works because most of the scattered light of a blue sky is blue to teal blue to shades of bright green while the Ha (C line below) has much less scattered light:

16 minutes ago, John said:

The drawback with filtering of course is that it removes light that ought to be contributing to the contrast and sharpness of the image.

Of course, the drawback of not filtering is that it leaves unfocused light flooding across the image reducing contrast and sharpness.

For instance, I was out looking at Venus in my ST80 last night comparing various filters, including a few new ones.  Without violet and far red filtration, it was difficult to discern its phase.  With both in place, it was quite clear what phase it was in.  However, Venus is sort of the acid test for a fast achromat, thus making the filtering challenge that much more fun for me to research.

I have reflectors, a Mak, an ED, and an APO I could have used, but I was interested in finding out how much can be teased out of a fast achromat by properly filtering unfocused wavelengths.  I'm not going to put a wanted ad on CN to try and secure a used Chromacor for the price of a nice APO to fix the chromatic focus of a fast achromat.  What would be the point of that given my scope collection?  Instead, I want to be able to make recommendations to beginners on how to get the most out of their fast achromats since they are so commonly bought by them as starter scopes.

You are right that filtering out certain wavelengths for low contrast objects will make it more difficult, if not impossible, to see certain features.  In those cases, it may take using a series of complementary filters to tease out various features, refocusing for each filter.

On 28/05/2023 at 17:47, Littleguy80 said:

Really worthwhile experiment and something I would never have thought to try without this post so thank you! Will definitely use this approach with Venus again. Not so sure on the Moon but, as you say, there may be some features where it helps. 

Try it on the full moon to see if features are easier to discern thanks to the dimming effect.  I find binoviewing really helps with observing the full moon thanks to putting two eyes on the target instead on one on the target and one eye closed seeing blackness.

11 hours ago, Billy Bob said:

Thank you so very. I'm sure I can find a few yoga mats from my beautiful wife 

Check the crafting section of Hobby Lobby or Michaels or the countertop section of Home Depot or Lowes and look for thin, opaque, flexible plastic-like material to bend around (or inside) the struts.  Once cut to size, the ends can be fastened with self-adhesive strips of Velcro along the length of the seam.  For truss Dobsonian secondary cages, folks have used Kydex, Formica, or even Protostar Flocking Board to bridge between the upper and lower rings.

6 hours ago, Ravi Hegde said:

What are the authentic weblinks for the Messier Objects' Catalogue?

Unfortunately, I don't think Messier ever published his list on a web page; and if he did, it is probably long since defunct.  The Internet Archive only goes back to 1996, not 1774, so we're out of luck there as well. 😉 

Anyone know why this scope was designed to barely work with a mirror 1.25" diagonal?  Most of my refractors come to focus with the focus tube halfway out using a 2" diagonal, and even further out with a 1.25" diagonal.  The lone exception is my 23 year old ST80 which doesn't have enough in-travel to accommodate a 1.25" Herschel wedge.  I'm betting the OP's scope wouldn't, either.  With such a gently sloping cone of light at f/12.5, I can't imagine it was done to avoid vignetting.

4 hours ago, jjohnson3803 said:

IIRC, a research observatory (University of Michigan?) tried observing through optical grade Mylar and the results were decent.  No idea of the cost or if the stuff is even manufactured anymore.

Sounds a bit like the aforementioned Baader TurboFilm.

If you have a big scope (8" minimum), and if you can get it on target, big/nearby globular clusters will resolve at high powers (>200x) even under moderately light polluted skies (Bortle 5 to 7).  They aren't as spectacular as under dark skies, but they are certainly visible as more than just a smudge.  In smaller scopes, they generally just remain smudges due to resolving power issues.

Compact open clusters also resolve nicely at higher powers in smaller scopes under moderately light polluted skies as has been mentioned above.  Smaller, more distant OCs will require more aperture and higher powers to resolve as with GCs.

Even brighter nebula benefit from using line filters in light polluted skies.  The Veil Nebula goes from invisible to wow with a premium OIII filter in my 15" Dob under Bortle 5 conditions.

I'd have loved to have had a peek at the moon last night, but the mosquitos are swarming thanks to a very wet spring here.  I really need to move to a more arid climate to enjoy astronomy better.