Louis D

11 minutes ago, vlaiv said:

This is probably first time I've seen 8" scope being used as finder.

I do worry that by the time I'd get up the ladder - target would move out of the FOV and I'd need to get back down to again align the scope

Actually, that's a 12.5" f/5 finder scope on that 40" Dob:

The 40-inch is 17 feet high when pointed at the zenith. It weighs over 800 lbs. Steve (Swayze) and Bruce worked for months grinding, polishing, and figuring the mirror. The truss tubes are covered with a black shroud during observing sessions, to enclose the tube and block stray light. The "finder" scope mounted piggyback on the mirror box, seen here on the right side of the photo, is a 12.5" f/5 telescope, also built by Steve. The first photo was taken at our Goat Mt. site, with Mt. Hood in the background. The ladder is a 16-foot orchard ladder built with extra steps. It is very stable, resting on 3 feet with a very wide base.

My point being that various folks have gone to great lengths to make faint objects bigger/brighter and small objects larger/higher resolution.  Anyone using an 8" scope is going to have to have tempered expectations.

13 minutes ago, vineyard said:

Hadn't thought of that either - is there any risk of the aluminium somehow creating reflections (even though its on the outside of the insertion barrel)?  Cheers

Probably no worse than a chromed brass barrel.

10 hours ago, semitte said:

I'm fulfilling a life-long dream of getting a good telescope to see the planets.  I have a Celestron NexStar 8se, with both a 40mm lens, and a 8-24mm lens; but both of them cause the planets to look very small, with no detail or color.  Yes, I can see Saturn's rings, but it's just a small image that I feel I could get using binoculars.  What am I doing wrong??

Get a 30" or larger Dob with a hand figured mirror and observe from a high desert location with good laminar flow.  Under those conditions, you can really push up the magnification to make planets look reasonably large. 😁

17 hours ago, Ships and Stars said:

Kayaks/paddle boards quickly sold out this summer and many retailers are struggling to restock it seems, even now.

Same with bicycles and bicycle parts.  Tires and tubes in particular are nigh on impossible to find even today.  My grown kids refurbished a couple of 25 year old mountain bikes the wife and I hadn't ridden together in decades.  Used bikes have become a hot commodity on Facebook Marketplace.  My son bought a road bike that turned out to have too large a frame for him, so he sold it on to my 6' 4" future son-in-law for what he paid for it.  For a while during the summer, area bike shops had a 3 week backlog of work, so you had to be patient while they refurbished your bike.

You might try aluminum foil tape on the insertion barrel.

2 hours ago, sputniksteve said:

I would take the refund and keep the scope.

You have to return the scope to get the refund. 🤔

The 12.5mm Morpheus is supposed to be quite nice and comparatively light.

The 22mm Omegon Redline SW (Astro Tech AF70) is a close runner-up to the 22mm NT4.  Once the eye cup is screwed off, it's easier to take in its 70 degree AFOV than the NT4's 82 degrees since it also has a 30mm eye lens.  It only starts to get astigmatic in the outer 10% of the field, but it's mild.  I prefer it over my 24mm APM UFF if I have a 2" focuser available.  I had to do a bunch of A-B comparisons with the NT4 before I made the decision to retire the AT AF70 to my B-team case.

3 hours ago, horseheadnebula said:

Too bad Morpheus eye relief is tight in 6.5 mm. I have to look something more expensive here unless Vixen SLV is solution. How important big field of view is with high magnification with non-tracking telescope?

Even if you only see 70 degrees with eyeglasses, it's still way more than the 45 degrees of the SLV.  Vixen claims 50 degrees, but all the LV and NLV predecessors from 7mm on down were all 45 degrees, and several reliable folks have confirmed that the SLVs are no different.  Wide field is a huge boon for non-tracking scopes at high powers.

Another good but relatively affordable option is the recently discontinued 6.5mm Meade HD-60.  It has a measured 64 degree AFOV and 15mm of usable eye relief.  I've found it to be a very respectable performer with no major issues.

5 hours ago, StarGazingSiouxsie said:

Beautiful observing location. 👍

20 minutes ago, Coyote00 said:

Well I got a deal on this because I bought it as a refurbished scope directly from celestron, but they said they will expedite repair as it arrived broken and not just being sent in for normal warranty work. 

What you got was a customer return that they just sent back out without doing any quality checks.  Unfortunately, this is pretty common in the US.  You have no way of knowing how long it will take them to "repair" it nor how well done those repairs will be made.  Once you agree to a repair instead of a return, you are then hostage to their timeline with no legal or financial recourse.

More than likely, they'll send you a refurbished scope.  You can check this by making an indelible mark somewhere inconspicuous on the scope that you know to be unique to you.  The scope they return "fixed" will be someone else's return that went through the repair process earlier.  You'll be able to tell because it will have wear marks somewhere, and yet different from your original scope.  That, and your mark will be missing.  This happens a lot with warranty returns.  It's doubtful they would bother with reblackening the interior of the tube since they probably don't have the local facilities to do that.  Another problem is that the warranty return process can last 2 to 3 months because they're under no obligation to hurry.

I was thinking renting telescopes might not be such a bad business proposition if the fees are setup properly.

As Mike at Astronomics (Cloudy Nights sponsor) recently said in his mailing list as pertains to constrained product supply:

Due to unexpected demand in astronomy products from a stay at home pandemic, rocket launches, and a very bright comet all manufacturers are stuck in an awkward position that nobody could have predicted.  We appreciate your interest and your understanding in the matter as we are filling orders as fast as products can come in.  Astronomy is a hobby about patience, so please have a little with us currently.  Thank you. 

It reduced the focal length of the telescope as seen by the eyepiece or camera, but not the physical focal length of the telescope.  It does this by compressing the image circle into a smaller footprint.  That's why they're also referred to as telecompressors.

@10-7You never mentioned if you intended to use it with eyepieces or a camera or even with what type of scope.  The focal reducer/correctors for SCTs work pretty well with 1.25" eyepieces.  Refractor focal reducers are mainly intended for astrophotography.  The cheap, generic 0.5x focal reducers don't work well at all with most eyepieces and telescopes.  They are mainly intended for very small imaging chips.

@Alan64I thought Bresser is the European marketer of JOC products as Explore Scientific is in the US while Ningbo Sunny out-right owns Meade.

From my own experiences at f/6 or so:

30mm APM UFF: Very good, easy to use with eyeglasses

22mm Nagler T4: Very good, a bit tight with eyeglasses but still usable

17mm ES-92: Very good, easy to use with eyeglasses, very heavy

14mm Morpheus: A bit of field curvature and astigmatism in the out 15% of the field, but nothing too distracting, easy to use with eyeglasses

14mm Pentax XL: Quite a bit of field curvature, no edge astigmatism once refocused, easy to use with eyeglasses, only found used (discontinued since 2003)

12mm ES-92: A very tiny step down from the 17mm ES-92 in terms of edge correction, ease of use, and eye relief; slightly lighter as well

9mm Morpheus: Very good, easy to use with eyeglasses, fits in well with Delos (I have the 10mm)

9mm Vixen LV: Very good, easy to use with eyeglasses, claustrophobic after using 65 to 80 degree class eyepieces

7mm Pentax XW: Very good, slight chromatic aberration in the outer 10%, easy to use with eyeglasses

5.2mm Pentax XL: Very good, no aberrations, easy to use with eyeglasses, only found used (discontinued since 2003)

3.5mm Pentax XW: Very good, no aberrations, easy to use with eyeglasses.

All of the Delos except perhaps the 17.3mm are considered very good with no edge correction or eyeglass issues.

22 hours ago, TheLookingGlass said:

Explore Scientific 82° 30mm  eye lens is recessed too much for use with glasses.

Not the original mushroom top version that I have.  It was also marketed as the 30mm Meade 5000 SWA and 31mm Celestron Axiom.

Decloaked, far right (I never took a picture of it with the outer part still attached):

The 30mm diameter eye lens is basically flush with the top of the housing.  Measured, I get 16mm of usable eye relief, which is right at the limit of eyeglass usability.  It views similarly to the NT4s which also have 30mm eye lenses and 82 degree AFOVs.

5 hours ago, Second Time Around said:

One of several reasons is that, as Louis has pointed out, prescriptions change.  In fact mine changes every year, especially the correction angle needed.  With a Dioptrx one can keep up with these changes (even in mid-yea) simply by rotating it.

Yes, position angle is not a big deal with Dioptrx, but I was pointing out that you need to buy a new Dioptrx if your astigmatism diopter changes too much.  Sure it's slow, but mine has crept up from 0.5 to 2.0 diopters over 40 years.  I used to need mostly distance correction (0.75 diopters), but that has also crept up to 1.75 diopters.  I just wanted to point out that a Dioptrx might not be a once in a lifetime purchase for everyone.  Maybe once every 10 to 20 years or so, depending on your age.  Based on my own experience, I would hold off buying one around your mid-40s as that is when my prescription was noticeably changing year by year in both distance and astigmatism as presbyopia was also setting in.

Here's a thread about building a Dob mount for a bare Newtonian tube:

https://stargazerslounge.com/topic/356587-diy-sw-explorer-200p-dobsonian-convertion/

As far as eyepieces, you could add a Barlow to maintain eye relief or a short focal length Plossl to keep costs low at the expense of eye relief.  The 8mm or 5mm BST Starguider or one of the Sky-Watcher UWA Planetaries would make good choices to maintain eye relief and keep costs on the low side.

29 minutes ago, Don Pensack said:

The view of M8, M20, M17, M16, M42 are all better with a UHC than an O-III.

That's because these nebulae pass a LOT of hydrogen AND oxygen light.

Using either an H-ß or an O-III filter on these large H-II gas clouds merely reduces their sizes and darkens them appreciably.

On O-III targets, the narrower bandpass of the O-III filter helps improve contrast a lot.

It also depends on how savage the light pollution is that they're embedded in.  I'll have to try them out at a dark sky site someday to see if indeed the UHC performs better than the OIII under those conditions.

Perhaps if ordinary UHC filters were more like the OPT Triad Quad-Band Ultra filter with the intermediate wavelengths excluded, it would be more usable in light polluted skies:

3 hours ago, Baldor said:

H25mm (idk what's H here), H9mm, SR4mm (idk what's SR here again)

H = Huygens, SR = Symmetric Ramsden.  The difference between a Ramsden and a symmetric Ramsden is the former uses two different lens elements while the latter uses two of the same element.

Note the various eyepiece designs in the diagram below:

The above Ramsden is pretty close to symmetric as opposed to the one in the following diagram where one lens is clearly larger than the other:

Symmetrics, whether Ramsden or Achromat Pair, are cheaper to make than asymmetrical designs (such as true Plossls) because you only need to make half as many unique lenses or lens pairs.

16 hours ago, Pixies said:

2. I know the Oiii is the one-to-have for the Veil, but is the UHC more general-purpose and perhaps get more use in the long term?

In 20+ years of observing and having both Lumicon UHC and OIII filters, I find I rarely use the UHC.  Adding H-ß to the O-III lines just does not overcome the loss of contrast due to the wider passband.

3 hours ago, Nyctimene said:

Not cheap, but might be a lifetime investment:

https://www.teleskop-express.de/shop/product_info.php/info/p891_Tele-Vue-Astigmatism-corrector---0-25-dpt---DRX-0025.html

Stephan

 

Except that astigmatism correction tends to change with age.  That, and Dioptrx won't fit on many eyepieces and still requires about 15mm of eye relief.

1 hour ago, vineyard said:

time just blurs into one lump pre-virus

Here in the States, we liken it to being in the movie Groundhog Day.

59 minutes ago, AstroTim said:

Hi @Don Pensack,

Out of interest, how did you calculate that approximation? I have a C8 and have also been trying to work out the effect of various barlows and a Binoviewer. 

Given that you have to adjust the focus when adding a barlow (not sure if it’s inward focus or not) and that this in turn will alter the focal length of the scope (due to the mirror moving?), does that mean that a 2x barlow will not actually give a 2x magnification when used in a C8? I think I’ve also observed a difference between a nosepiece barlow vs the same magnification normal barlow, which I wasn’t really expecting, but maybe one of them is poorly specified.

Regards,

Tim

 

If you can reach focus without moving the mirror by sliding the Barlow in and out until reaches focus with the eyepiece, then any magnification change is entirely due to the Barlow.  This assumes the Barlow requires out-focus and not in-focus.  This is generally true for longer Barlows while the opposite tends to happen for shorty type Barlows.

Here's Tele Vue's table to help figure out if you need to wear eyeglasses at a particular eyepiece:

Exit pupil is simply the eyepiece focal length divided by the telescope's focal ratio while the astigmatism value can be read from your eyeglass prescription's CYL or cylinder correction value.  Basically, the more astigmatism you have, the smaller the exit pupil (higher power) you'll detect it in.  With my 2.0 diopters in my observing eye, I can easily see aberrated stars down to 1.0 to 1.5mm or so.  Below that, I find improved resolution wearing eyeglasses, but stars look okay.