Louis D

For emission nebula, an OIII is the most aggressive and often yields the best view.  The slightly less aggressive UHC types also show the H-Beta line and sometimes include the H-Alpha and SII lines as well.  However, more light pollution is let in due to the wider passbands, decreasing contrast on low surface brightness nebula.
 

OIII passband:

Typical UHC passband including H-alpha and SII:

Other DSOs don't really benefit much from filtration.  Open clusters tend to be "large" and high contrast, so no issues there.  Globular clusters tend to be small and compact and do best with high power (200x+) and at least 6 to 7 inches of aperture to start to resolve them into tiny pinpoints.  Planetary nebula tend to be compact and benefit from high power as well because that reduces the background skyglow.  Galaxies really need dark skies because they emit light across the entire spectrum, so no filter helps to increase contrast with them in light polluted skies.

One of the brands they're sold under in the US is Astro Tech Paradigm Dual ED (possibly the first here).  I've got the 5mm to 25mm set as shown below with the Meade HD-60s behind.  They are no doubt identical to the BST Starguiders and Astro Essentials.

I don't know about longer eye relief on longer f-ratio scopes, but I do notice much stronger SAEP and CAEP in longer f-ratio scopes as I showed in this thread.

I have the 10mm Delos and 9mm Morpheus, and there's not a whole lot to choose between them other than a wider field of view on the Morpheus.  I can't use the NT6s due to needing to wear eyeglasses to correct 2.0 diopters of astigmatism in my observing eye, so I can't give you any advice on them.

The APM UFF 30mm is really nice.  I highly recommend it.

On 23/07/2020 at 16:03, bomberbaz said:

All my stuff is stored in the conservatory

Off topic, but it seems like everyone in the UK has a "conservatory" which I take to mean an non-heated/non-cooled sun-room or enclosed patio rather than a music room.  They're pretty rare here in Texas because it would be over 130° F in there for much of the year.  I take it they're much more pleasant there.

On 24/07/2020 at 17:55, russell slusher said:

I don't know why people are not mentioning it.  With a large Dob that is an F-4.5 you need a coma corrector. GSO (in Taiwan) makes a very good 2" coma corrector. They make them for several different brands. I bought one for my 14" Dob.  AgenaAstro sells them. for $115.  I recently bought a 180mm Maksutov.  I'm going to do a side-by-side comparison viewing of the planets when we get some clear sky.

I have the GSO coma corrector, and it works great in my 8" f/6 Dob, but I need to take it out for highest power work with planets because it seems to add a bit of spherical aberration on axis.  The views are definitely sharper on axis without it.  I have noticed the same thing with my TSFLAT2 in my ED and APO refractors.  Highest power views are sharper without it in the optical path.

Glad we got that all sorted out so quickly.

I would recommend the 5mm BST Starguider as good step up from the included eyepieces.

As far as the phone holder, the Celestron NexYZ 3-Axis Universal Smartphone Adapter gets good reviews here on SGL.

1 hour ago, DanielC said:

Thanks. Can you help me understand this? For the SCT that I'm planning to buy, the focal ratio is F/10 so the exit pupil is 

pupil = (focal length of eyepiece) / 10

So the 40mm eyepiece would give me a 4mm exit pupil and the 32mm eyepiece would give me a 3.2mm exit pupil. So I googled for "exit pupil" and I saw that apparently a larger exit pupil means that there's more light going into your eye. But I don't understand that. If both eyepieces are already at the maximum field of view that the telescope can produce, aren't they both giving me every last photon that the telescope can collect?

Thanks!

Correct about the total light flux, but the lower powered eyepiece is putting that same number of photons into a smaller area leading to a brighter image per unit area, albeit at a lower magnification.  Besides a smaller, bright object image, the background skyglow will also be brighter, washing out low surface brightness objects unless that skyglow can be reduced via a selective filter.

Relatedly, there is the Zarkov Cloud Gun for punching observing holes through the clouds until the cloud filter becomes a reality.  Order yours today. 😚

7 hours ago, JeremyS said:

Well I never knew that Dave. I thought the waler was something to do with misspelling of whaler cos the eyepiece is so big. And The Speers was actually spears, so something to do with whale hunting. Oh well! Or should I say, Oh whale?
:-)

Speers is for Canadian optical designer Glenn Speers.  Due to the unfavorable exchange rates between US and Canadian dollars, he wanted to create a home-grown line of affordable wide field eyepieces for Canadians who couldn't afford Tele Vue Naglers.

If you pair the 40mm with a nebula filter such as an OIII, the larger exit pupil may make the nebula appear brighter than it would with the 32mm.  This is especially important with longer focal ratio telescope such as CATs that produce small exit pupils with most eyepieces.  For example, to get a 6mm exit pupil with an f/15 Mak would require a 90mm eyepiece. 😲  Good luck finding one of those.

Try working your way up to higher powers to see if the image starts to break down instead of jumping from 25mm to 6mm straight away.  A Skywatcher/Celestron/Meade zoom eyepiece might be a good option to help gauge the seeing conditions.

On 24/07/2020 at 00:55, lee g said:

No I don’t use 127mm scope anymore. I now use a sct 8” and I wouldn’t use the focal reducer with the 30mm

Update your signature equipment list so we won't keep getting confused about what scope you intend to use these eyepieces in.

Highest power for me is determined by the exit pupil.  For me, I max out at about 0.5mm to 0.7mm.  Beyond that, the floaters in my eye become too problematic to see around.  As I recall, you have an f/10 SCT from the other thread, so that would mean a 5mm to 7mm eyepiece would be my absolute maximum power eyepiece in your scope.  In my f/6 scopes, I use up to a 3.5mm eyepiece for high power, but very infrequently.  My point is, highest power eyepiece usage is highly scope dependent.

Undercuts weren't much of an issue before the advent of compression rings.  However, brass compression rings can become distorted by undercuts and can actually come out of their grooves and wedge the eyepiece in the holder for good.

The narrow bands in cheap, self-centering collets also won't always work with undercuts when they are not at the same depth/location relative to each other.  This causes eyepiece tipping in binoviewers which makes image merging all but impossible.

10 hours ago, vlaiv said:

You can't really change focal length of a barlow lens, but you are right - if you place barlow lens so it is it's own focal length away from focal plane of telescope - irrespective of any other lenses that come after - you have created a collimated beam of light because in that case barlow lens diverges incoming rays in exact same extent as scope converges them and they end up being parallel again.

This case could be considered as infinite magnification because parallel rays converge in infinity ... (abstract math stuff, I know ).

That has to be what I misremembered.  Place the barlow lens its own focal length away from the focal plane of the telescope, not the eyepiece the barlow's focal length away from the barlow lens.  My mind is getting to be like Swiss cheese.  Being confined at home 24/7 isn't helping matters.

All I can figure is I was misremembering something about this.  Based on the formula, all I can figure is if the barlow focal length is extended enough, you end up with parallel rays and you've created a relay lens that you terminate with a focal reducer/condenser lens.

7 hours ago, AstroMuni said:

This would work upto a point. i.e. you cant increase the distance beyond a certain point to get more magnifcation. 🙂

And that distance is the focal length of the barlow, IIRC.

5 hours ago, Barry-W-Fenner said:

I think the Morpheus will serve me well to be honest as I have no experience with "high end" eye pieces so doubt any of the above will be of much concern to my eye. From a performance point of view did you think the Morpheus performed well for the in relation to there cost? Would I notice the step up from say my 15mm BST for example?

The 14mm Morpheus is way better corrected in the outer field in faster scopes than the 15mm BST.  On axis, the difference is much more muted.  See my comparison image below taken through my f/6 AT72ED with field flattener.

The 5mm BST Starguider is pretty good for the money, and it has comfortable eye relief with a 60 degree field.

Agreed with Don above.  Try turning the eyepiece upside-down and looking up into it with the illuminator turned on and inserted to see if the reticle drops back to where it should be and lights up properly.  If so, you'll need to tighten a retaining ring under the reticle.  You might need to tap the eyepiece to get the reticle to move.

Please clarify a couple of points for me.  Is there red light coming out of the end of the illuminator's threaded barrel?  Can you see the reticle in the eyepiece in daylight without the illuminator?

I've kept my ST80 refractor in a gym bag wrapped in bubble wrap in both my closet and in my trunk on trips with no ill effects for 20 years.  I know there are custom, padded bags from Oklop and Lacerta for telescopes available in Europe if you want a more purpose built item.

19 minutes ago, lenscap said:

BTW I think the "2/3 of new price" mentioned above can be a fair asking price when selling recent gear I think it would be rather generous when buying kit of this age.

Right, unless it's highly desirable kit like AP refractors and such.