Don Pensack

2 hours ago, Gaurav Mk said:

I have the F/5 1000mm Newtonian

Well, my typical advice for a ~200mm scope is jumps of 50x magnifications between powers:

50x--low power, widest field, bright image.  good for large open star clusters, the largest nebulae (M8/M42/43), large star fields, carbon stars in fields.

100x--medium power, sharp image quality, great magnification for globular clusters, smaller open clusters, many nebulae, most galaxies, Moon, large planetary nebula (e.g. Helix)

150x--high medium power--not affected by seeing much, great for globular clusters, small open clusters, most galaxies, Moon, most planetary nebulae, planets when seeing is poor.

200x--high power--when seeing allows, great for planetary nebulae, globular clusters, many galaxies, Moon, planets, double stars

250x--very high power--when seeing allows, great for small planetary nebulae, small globular clusters, Moon, planets (especially Mars, Neptune, Uranus), double stars

You'll use 50x and 100x all the time.  150x will be used a lot.  200x will be used often, but it will depend on seeing conditions.  250x will be used only occasionally.

2 hours ago, Dippy said:

It depends on the target you wish to observe, planetary or wide angle. Let assume the wide angle low magnification eyepiece. With a non-tracking Dobsonian you need to nudge the telescope  more to keep the target in view if you go for narrower field. I would recommend a 100 degree eyepiece like APM HDC 20mm which almost cost the same as a Pentax XW. You can keep the target in view for about 2 minutes with this.  Or if you don’t want that much field of view, probably a Baader Morpheus 17.5mm 76 degrees is nice which would be about £60 cheaper and has excellent optics. Although it is very light weight which is essential for a Dobsonian to balance, it is weather sealed with neutral gas and can be used with a binoviewer due to its light weight. A Televue Delos is more than £300 new and has 72 degrees field of view. I have heard TeleVue  Ethos 21mm on some targets gives almost a three dimensional effect, thanks to its exotic glass material and coating, although I have not tested it yet myself. It will cost you about 2 Morpheus eyepieces plus a Maxbright II binoviewer.

To clarify your post: the 20mm APM XWA eyepiece is sealed.  The 17.5mm Baader Morpheus is not.

If the manufacturers just told us it would help, like Baader, TeleVue, Explore Scientific (though recently I discovered some of the ES data is in error), Pentax.

How about "Eyepiece Rest"?

Nope, too graveyard.

OK, how about "Eyepiece Waist"?

Given how porky some eyepieces are, it might be apropos.

How about "Eyepiece reference surface"?

That might need some explanation, however.

What about "Eyepiece barrel stop"?

2 hours ago, Louis D said:

These all get high ratings:

1.6x 1.25" Nikon EIC Barlow

3.0x 1.25" Televue Barlow

2.4x 2.0" Vernonscope Dakin Barlow

2.0x 2.0" AP BARCON (BARADV) Barlow

2.5x 2.0" Siebert Telecentric

2.0x 1.25" Carl Zeiss Abbe Barlow

Nice list.

I'd add the Baader VIP Barlow to that list.

1 hour ago, Naveen said:

thanks for your responses! If the views are superb - I am prepared to spend a bit but has to cost less than the scope

another issue i have is of alignment. I am in London and stars arent so visible really. However, i manage to point the scope to jupiter and normally it finds its way to saturn ( which are the two main in addition to the moon that are normally visible every night from my backyard/  Does that properly align the scope or I need to do star alignment as well? Any help and advice on alignment would be much appreciated, still new to this scope...

Too close together.  Your alignment stars should be at least 90° apart in the sky and different in altitude.

Use first magnitude stars like Altair or Vega or Deneb or Arcturus or Antares.

If you don't know those stars, your first mission is to learn some constellations and bright stars.

See Skymaps.com for a monthly star chart with planets.

I'm in Los Angeles, and even here the bright stars are visible.

If you have a computerized scope, look in the manual to see how to align on objects, too.  This can make your pointing more accurate.

Quote

 

This thread points out how to set up the GSO coma corrector:

https://www.cloudynights.com/topic/462985-setting-up-the-gso-coma-corrector/

APM is now saying the Noblex/Docter 12.5mm is now out of production.

Will there be another production?  It's a good question.

1 hour ago, Barry-W-Fenner said:

Hi Louis

That's spot on what  I am getting. The stars are fine points that turn more tear drop and a have a point at the bottom as they drift to the field edge.  Regarding coma corrector, what would be the best option for a 12" dob?

I've used a few, and can point out the convenience of use:

TeleVue Paracorr: easiest to use and dial in the correction for any eyepiece

Explore Scientific HRCC: wide range of adjustment, can be used for fine focusing, hard to use if eyepieces focus a distance apart, easy to use if eyepieces are nearly parfocal.

GSO coma corrector: hard to dial in for individual eyepieces, but fairly easy to use if eyepieces are parfocal.  More difficult to optimize than the 2 above.

Baader MPCC: unless you have a pile of spacers on the eyepieces, this one is very difficult to optimize for individual eyepieces.  Not great correction either.

https://www.astrofotoblog.eu/?p=856

I use the 14mm Morpheus in a 12.5" newtonian, with Paracorr coma corrector, so f/5.75 effective f/ratio.

I use (and require) glasses at this focal length.  I use the eyepiece as a 1.25" at setting A in the Paracorr. That's the setting.

In my setup, the 14 Morpheus provides sharp, pinpoint, stars right up to the field stop and only deteriorates visibly exactly right at the field stop.

The performance really impresses, and the eye relief is nearly perfect for glasses.

That means, of course, that the eye relief is long.  I suspect that just about ALL visual observers who don't use glasses would require the eyeguard extension ring provided.

After all, Baader didn't provide them on the original shipments and got a real dressing down over the unfriendly eye relief for non-glasses wearers.

as for adding a Barlow, it's entirely possible the Barlow isn't very good.  If the scope is collimated, and cooled to the ambient temperature, you shouldn't have had much issue with 214x

as long as that magnification is under ~25x/inch of aperture.

Also, unscrew the ring at the bottom of the eyeguard on the T4s or Radians and rough the felt liner up with a toothbrush.

It gives a much nicer positive feel to the eyeguard.

Yes, a 130mm f/5 has a very short focal length and a strongly curved focal plane.

Add coma from the f/5 mirror to that, and it's no wonder the edge deteriorates somewhat.

But, I'm glad it did as well as it did.

23 hours ago, Louis D said:

Sounds like a winner this time around.

One more thing:

The eye lens on the Delites is oversized.  The apparent field doesn't need the entire lens.

So they built an iris into the eyecup that covers the very outer edge of the eye lens.

When the eyecup is raised, as nearly everyone who doesn't wear glasses will do, the iris creates a "light trap", i.e. no peripheral light can reach the eye lens.

This improves contrast to almost the same degree as draping a black cloth over the head, or cupping your hands around the eyepiece, to block all light except that from the eyepiece.

And is one of the reasons contrast is so amazing in these eyepieces.

23 hours ago, Pixies said:

How do these compare with the Baader ClickLoks?

The Baader Click-Lock is a nice adapter, but:

--the internal collet is narrow, not wide, and may hit the undercut on the eyepiece

--the 1.25" narrow section on the eyepiece above the undercut may not be supported at all (it depends), and certainly is not tightened against.

--the Baader has an undercut groove on its exterior, while the Antares has a smooth exterior.

IMO, the Antares is a better adapter, though I admire the machining on the Baader adapter.

5 hours ago, Louis D said:

The DeLites are almost doppelgangers for the Radians, aren't they?  Hopefully, they don't have the SAEP of the Radians.  I was excited with the arrival of the Radians in 1998, but I couldn't get them to work for me in daylight due to SAEP (kidneybeaning), so I never bought any and stuck with the Pentax XLs.

The Delites do not.  No one seems to have any issues with eye placement except the inevitable person who doesn't use glasses and doesn't adjust the eyeguard up and experiences blackouts by getting inside the exit pupil.

Color presentation is also more balanced--no one describes the Delites as "warm" in tint.

21 hours ago, Stardaze said:

Thanks Don. Apologies up front, but what’s the of 1.4 decipher?

The idea is to yield the same increase with each change of focal length.  Dividing by 1.4 = a 40% increase in magnification.

That is where Pentax came up with the 20--14--10--7--5--3.5mm focal lengths for their XW eyepieces, as one example.

There is nothing sacred about a 40% increase--some people like more, or less.

But since you posted you had a 16mm and 6.7mm, I was trying to find an in between focal length that would yield a fairly even change in perception.

Ricochet explained it quite well.

The exit pupil is the image of the primary mirror.

As you approach the eyepiece (we'll assume it is in focus), you see the truncated field until you are at the exit pupil, where you finally see the field stop.

Essentially, when you were farther out, the edges of the lens vignetted the field with a hard stop because the rays from the outer parts of the field hit your eye outside the pupil and you could not see the entire field.

If you move your head back and forth when outside the exit pupil, you can see different parts of the field.

At the exit pupil, all the light of the field goes into your pupil and you see the entire field.

When you move inside the exit pupil, your pupil is now smaller than the light cone from the lens to the exit pupil and once again your pupil sees only part of the field.

But now there is no hard edge to the field created by the aluminum surrounding the lens.  You do not see the entire field, but you see blacked-out portions of the outer field floating around because

your head and eye are always wandering.  Unlike the top of the eyepiece, there is nothing outside the visible field to focus on, so the blacked out areas appear vague and amorphous as they float around.

Now, if the exit pupil is smaller than the pupil of your eye, you do have some freedom to drift in and out relative to the eyepiece and still see the entire field, though you may need to refocus as you do so (depends on your age and your ability to accommodate).  Likewise, you can drift back and forth laterally slightly and still see the entire field, though we instinctively try to hold out eye in the center so our foveal vision can examine the image.

If the light rays enter the eyepiece parallel, they are bent by the eyepiece and the image at the exit pupil is a certain distance from the lens.  If the light rays enter the bottom of the eyepiece diverging, as, for example, after a Barlow lens, 

then the bending of the rays that occurs in the lenses will still occur to the same degree but because the incident rays are diverging, the image formed at the exit pupil will be extended outward from the eye lens.

I can't see the stars in the field of an illuminated eyepiece until the reticle is so dim I can't see the reticle.

I started using the defocused star in the early '60s--defocus a star until the crosshairs appear black crossing the donut shaped star image.  Works great.

But, about 10 years ago I realized I could estimate the center of a circle well enough I didn't even need crosshairs.

On my refractor, I can center the star in the field of the finder (no crosshairs) and it's in the field of view of a 3mm eyepiece.

Perhaps 57 years of doing this have given me the ability to line things up without crosshairs--I also align my DSC with just a visual estimate of the center of the field in the eyepiece,

and my alignment error is almost exactly the same as when I used to use a crosshair eyepiece--the trick is to use a very high power eyepiece to align the finder to the scope.

Lower powers all will appear centered.

Of course, that's for visual use.  Guiding a photograph is a whole different thing.

16mm / 1.4 = 10mm.

10mm / 1.4 = 7mm

It looks like 10mm is the better choice for an in between focal length, though a (non-existent) 9.5mm would be OK too.

The 10mm Delos is a fantastic eyepiece.  Here is a review of top 10mm eyepieces:

https://web.archive.org/web/20130829052725/http://www.cieletespace.fr:80/files/InstrumentTest/201306__6_oculaires_10mm.pdf

And if a positive lens follows the negative lens, the rays can be made parallel as they exit the lens.

Yet, the increase in image scale will still occur.

This is how the telecentric barlow works:

https://www.cloudynights.com/topic/712460-barlow-lens-gives-two-possible-focus-points/?p=10263173

On 24/07/2020 at 11:57, steveex2003 said:

I have all but the 14mm in Morpheus. To my (inexperienced) eyes they all are a little loose at the field stop (compared to on-axis) and the 4.5mm has noticeable EoFB. My favourites (for whatever it's worth) are the 17 and 9mm. I ignored the 14mm as it seemed the most problematic across amateur and more serious reviews. For whatever reason it seems that the 14mm has noticeable detractors across their respective ranges for the Pentax XW, Morpheus and Delite EP's. As and when I can afford, and get around to it, I am confident that the Delos is the 14mm I want to try with the required eye-relief I need.

Last Saturday night, I used the 14mm Morpheus extensively in my 12.5" f/5 (coma corrected f/5.75) dob and used it with glasses to correct my astigmatism.

My wife also looked through and used her glasses, and we were happy to discover neither of us had to refocus when switching positions.

Her almost immediate comment, and I said nothing until she looked, was how incredibly sharp the eyepiece was from edge to edge.

I saw that too, and it yielded superb contrast.  Stars just in from the field stop focused to tiny little points when the center was in focus, indicating the field was very flat.

Bear in mind that my coma-corrected dob has an equivalent 1826mm focal length, so it should be flat.  If the field was curved with that long a focal length, it would have to be pretty curved,

and it was flat as far as both of us could see.  I used it all night to look at a lot of objects (mostly larger, since the true field in that scope is 36'--larger than the full moon).

The measured apparent field is 78°, and field distortion (geometric distortion seen, usually, as angular magnification distortion) is a tiny 0.84%, so very very good, and definitely designed as an astronomical eyepiece.

I saw no EOFB, though the night had a tiny bit of ground haze that made your peripheral vision see the sky brighter than the center of vision, and this showed in all the eyepieces as well that had apparent fields over 75°.

That is not the same as EOFB which, as far as I can tell, this eyepiece does not have in that scope.

In comparison, the 17.5mm had a little more sensitivity in eye placement, though this was solely due to an even longer eye relief.  The 17.5mm can be used with glasses even if the extender ring is added.

Due to the lower power, I didn't use it much, so I will spend more time with it later, but it, too, looks promising.

BTW, I found an easy technique to tell you if glasses will improve the image at a particular focal length: defocus the star on either side of focus.  If it stays round without glasses, glasses will make no improvement.

If it goes oval as you defocus, but stays round with glasses on, you need glasses at that focal length, or, more exactly, glasses will improve the image quality of stars.

Seeing astigmatism in focus is a different thing, and there is a high likelihood you won't see in-focus astigmatism at a longer focal length than the defocusing test shows.

I see the star image, when defocused, go oval as short as 6mm, whereas I can tolerate the astigmatism in focus up to 12mm.  If I'm looking at planets, I'll use my glasses with 8mm, for example,

but for any other object, I won't.

Also, if you are talking about the 127mm scope, when reduced, a 24mm 68° might become a better low power eyepiece than a 30mm.

Aha!

Well, then, I presume you are talking about a 30mm 1.25" eyepiece, since a 2" 30mm would be incompatible with a reducer (too large a field stop).

In which case, a reduced 1.25" 30mm might work just fine as a low power, especially if the reduction is not more than 35% or so.

You will see some vignetting of the field edge, but it would likely affect only that eyepiece.

Unthread the illuminator and see if the edge of the reticle is visible there (try a bright light).

It's possible the reticle's retaining ring has gotten loose, allowing the reticle to move.

The LED has to be at the edge of the glass to illuminate the reticle.  Even a millimeter off could remove the efficacy of the illuminator.

Basic set of 4, no glasses needed:

40mm 68°, alternative 35mm 68°

20mm 100°  This will be the most-used eyepiece.

13-14mm 100° for nearly all DSOs with a larger blow-up and more details visible.

9-10mm 100° your high power eyepiece that is usable all the time.

Basic set of 4, with glasses used:

40mm 68°, alternative 35mm 68°

22mm 82°  Again, the most-used eyepiece.

14mm 76° A fine, and frequently used focal length

9mm 76.  Excellent high power eyepiece