Louis D

11 hours ago, Alan64 said:

I can't help but to want to bypass the usual fare, and then to wonder as to viability of this 70mm f/4 achromat.  With a 32mm eyepiece inserted, 9.4x...

https://www.barska.com/30070-225-power-starwatcher-telescope-by-barska.html

I'm thinking that getting its optical axis aligned with the main OTA might prove challenging without tube rings of any sort.  That, and it's weight would making mounting it extra difficult.

Since you originally mentioned the Baader Hyperion-Aspheric eyepieces, and because I just remembered there being a decent comparison article, I'll add the following translation link for you to read up on them and their Aero ED SWA counterparts.

I would go with the 30mm APM UFF.  It has replaced my 27mm Panoptic in that range.  Better flatness of field, better edge correction of lateral color, much wider true field of view, and much better eye relief.  It might be a tiny bit less sharp in the center, but the 10% difference in magnification makes it a difficult comparison.

See below for some comparison photos of eyepieces around 30mm.

I used to use a 60mm f/4 binocular half with a 32mm Plossl and 90° Amici prism as a wide field finder when first starting out.  I found the weight (with the finder's tube rings) threw off the balance of my 8" Dob no matter where I put it, so I stored it away for nearly 20 years (being a pack-rat).  It added some field to the Dob, but at the cost of light gathering.  I found a Telrad or QuikFinder to be good enough for star hopping, especially once I added DSCs.

I dug it back out for use with my daughter's 127mm Mak.  This time, I put a 24mm APM UFF in it and mounted it close to the altitude axis's centerline.  The 127mm Mak and the 60mm finder make for a very complementary pair now.

1 hour ago, Alan White said:

Sorry Louis but all my glasses are now varifocal, not a single vision pair left.
 

I bought my single vision distance glasses from EyeBuyDirect after finding a frame of about the same dimensions and style as one I liked from the optometrist's store.  I think I paid under $20 for them, and they are of a surprisingly good quality.  The frame is actually much nicer than my wife's Ray-Ban frames.  You seem to pay for the name in the case of Ray-Ban.  They stay in a case in my astro toolbox along with my miscellaneous astro gear.

21 minutes ago, djpaul said:

My problem with wearing glasses is not getting much of the fov with my ethos and nagler eyepieces. 

So for that reason the dioptrx is perfect.

However I can see the whole fov wearing glasses with my 32mm and 25mm televue plossls.

The only eyepieces I have that issue with are my ES-92s.  The left and right edges are fine, but the top and bottom fall outside the corrected area.  However, it's pretty rare that I look up or down rather than left or right.

I can't use the Ethos or non-T4 Naglers with glasses because the eye relief is too short.  It's my understanding that you still need about 15mm of usable eye relief to use the Dioptrx successfully; so, for example, the 16mm Nagler T5 wouldn't be compatible with them.  My other thought is that my long eyelashes would probably grease up the Dioptrx corrector lens on shorter eye relief eyepieces whenever I blink.

Would you be willing to compare the view through single vision eyeglasses versus the Dioptrx sometime?  I found the biggest problem with eyeglasses was that older pairs have microscratches all over them, so I bought a brand new dedicated astronomy pair to remedy that.  As stars passed over those microscratches, they would suddenly have diffraction spikes, ruining all that work to perfect the eyepiece image with correctors, collimation, and premium eyepieces.

1 hour ago, Adam1234 said:

I can easily star hop to find my targets without giving myself a neck injury

I use a laser sight to get the scope on target because I can't twist my head around very well anymore.  Just be sure to check the skies before lighting it up and be aware of local laws and regulations (Australia in particular).

I've order some Baader items from Microglobe that were shipped to the US in the past.  There were some initial ordering hiccups with CC payment and removing VAT, but they came through in the end.

The Celestron f/6.3 Reducer Corrector Lens is available for $113 shipped and sales tax free to most states in the US from both Agena Astro and B&H Photo.  It would be a few dollars more shipped to the US from the UK once VAT is removed, especially since the GBP has recovered a bit off of its August lows relative to the USD.

The 9mm Morpheus is just about the equal of the 10mm Delos at f/6 in my AT72ED refractor.  The difference is quite minimal.  The 14mm has some edge astigmatism and field curvature, but is otherwise quite similar to the 14mm Pentax XL.  Neither suffers from any sort of SAEP (kidney beaning).  They're a great set of lenses by all the reports and reviews I've read.

Here are two comparison shots I composed through the AT72E of my 13mm-15mm and 9mm/10mm eyepieces I did a few weeks back that include the two Morpheus I own.  I don't have the 17.5mm version, but I do have the 17mm ES-92 which is a fantastic eyepiece if you can stand the weight, price, and bulk and have a 2-inch focuser.  See below for those comparison shots.

29 minutes ago, Alan White said:

@Louis D thank you for that link, made me smile as I had thought of exactly that mixture for my 10" Dob as well.
I prefer the price of the GSO (et al) CC to the Paracorr, but concerned I am wasting money trying.
I do like TV kit, just don't like paying the price required for that fine kit.

 

I haven't tried a Paracorr in my Dobs, but I notice right away when I forget to put the GSO CC in the focuser and start observing.  My first thought is, why are my premium eyepieces showing so much aberration at the edges?  Then a moment later I realize I had forgotten the CC.  I slip it in, and all is right with the world again.  It does so well, I never feel the need to upgrade it.  Just remember to remove it for high power viewing (below about 1mm exit pupil).  I find the views sharper without it, but YMMV.

If you are having to deal with light polluted skies, I suggest getting a UHC or OIII filter to make seeing nebula easier.  Galaxies are going to be all but impossible to see except possibly for their cores (M31 comes to mind).

Higher powers will make globular clusters stand out better from the background as @Mr Spock suggests.

3 hours ago, Alan White said:

@Louis D, do you think the Baader 28mm spacer would be ok.
FInding a 25mm in the UK is being a pain or costs a great deal more.

https://www.firstlightoptics.com/baader-planetarium/BhyperionTuningRing-2.html

The Coma Corrector from GSO branded Revelation Astro is on offer in the Uk at present, so very tempting.

Yes, the 28mm would probably be close enough for starters.  It's only a 3mm difference, and would only affect eyepieces focusing significantly above their shoulder.  There was an interesting thread on the GSO CC on CN recently and how screwing the optical nosepiece onto the bottom of the Baader 2" ClickLock with 2" CL Extension 47mm gives exactly the desired separation and you have a much nicer eyepiece holder to boot.

4 hours ago, joe aguiar said:

Seems to cheap I have bought these for 169 plus taxes almost 200, with the name brand models. I also just sold a brand new one just last week that came with my skywatcher 100ed f9 that I just got like 2 weeks ago.

I sold it for 125 it wasn't used I just didnt need it as I have my own but still has to be cheaper than someone buying from store.

So is skywatcher meade celestron and Orion just making 3x what they should off us? Or is this Amazon to cheap and it's not a real dielectric?

Joejaguar 

It is definitely a more lightly built 2" diagonal than the GSO equivalent.  Optically, I didn't notice any major differences, but I also haven't done a critical back to back test of the two.  I'll add it to the list of things to do in my copious free time. 😉 

I was just looking for a low cost 2" diagonal for my daughter to take with her camping observing kit, but was unprepared for such a design oversight.

I finally found the discount dielectric diagonal I was referring to above.  It is still listed on Amazon for $49.99.  What's deceptive is that you can't see the position of the 2" thumbscrew or compression ring from the photos relative to the top of the eyepiece holder.  They are very near to the end and work terribly with undercut 2" eyepieces as described above.  Otherwise, it's a fine diagonal.  It's a shame it's marred by poor design.  It is somewhat usable if you slip a parfocalizing ring or rubber O-ring on each 2" eyepiece prior to putting them in the eyepiece holder to lift them slightly out of the holder to allow the compression ring to align with the undercut.

6 hours ago, rl said:

but to be fair the correction is good enough over a wide range of adjustment so as to just leave it set for your favourite low-power eyepiece. 

Sounds similar to the GSO/Revelation CC in this regard.  Only my 12mm NT4 shows coma because it focuses about 19mm from the shoulder which is well beyond the 10mm on either side of the best correction zone which I've centered on shoulder focusing eyepieces.  The rest of my well corrected eyepieces focus within that 20mm band of best correction.

6 hours ago, rl said:

I always felt the Paracorr had the edge over the ES for visual use...the image was a little cooler and more transparent (the ES added a very faint sepia tint).

I've noticed a color tint when swapping the GSO/Revelation CC in and out of the focuser.

4 hours ago, Alan White said:

So a question to add please @Louis D, do you still use the GSO unit or has it been replaced with something more exotic?

Still using it.  The only quibble I have with it is that one of the thumbscrews stripped in the eyepiece holder because they're made of pot metal instead of brass or steel.  Luckily, there's a second one.  Don't over tighten the screws.

21 hours ago, celestron8g8 said:

Any time you  add more glass  to your line of viewing it will reduce incoming light .

Unless that glass is increasing the magnification, and assuming that glass is properly multicoated, the light lost to additional glass elements in the path is minimal and below the threshold of human perception.  In fact, if that added glass is a focal reducer, it actually increases the amount of light on a per area basis.

One thing to be wary of with the cheap dielectric diagonals.  The locking screw or compression ring is often very close to the lip which causes many eyepieces with undercuts to be pushed up and out at an angle.

8 hours ago, Praseodyymi said:

The finder was okay, but I found it slightly difficult to use as the image is also upside down. Not sure if it would be easier if I get a finder that shows the sky as it is (to first pick object by naked eye, then from the finder and so on) or if it is just matter of learning, any suggestions/thoughts?

You might look into a unit power finder such as a Telrad or QuikFinder.  Their bases can just be stuck on the tube with double sided foam tape if you don't want to drill additional holes.  They do require cranking your head around, but it's manageable for the young and young at heart.  These finders make star hopping to your target much easier than trying to sight along the tube.  Once in the general vicinity, a RACI (Right Angle Correct Image) finder will be much easier to use.  I find trying to use a RACI by itself to put the scope in the general vicinity problematic because you're looking at the tube, not the sky, as you line it up.  I like to think of RACI's as low power refractors; and as such, most useful for picking out objects invisible to the naked eye but just detectable with it for centering.

On 09/10/2019 at 22:51, celestron8g8 said:

But in reducing FOV will help remove or reduce coma at the edges of the FOV .

Remember, coma does not decrease with increasing power.  As long as the AFOV remains the same, coma at the edge will remain the same apparent size.  Coma increases linearly center to edge, so it is more noticeable in ultrawide field eyepieces.  Going to a shorter focal length will double the magnification at the edge, bringing the apparent size of the coma right back to where it was at the lower power's edge of field.

That said, I have noticed that eyepieces with built in Smyth lenses (a matched Barlow in essence) tend to decrease the visible coma.  For instance, I see no difference in visible coma with my 10mm Delos in an f/6 Newt with or without my GSO coma corrector (that is to say, none is visible either way).  The difference with and without is quite noticeable in my 9mm Kellner, which has no Smyth component, despite its much narrower AFOV.

10 hours ago, celestron8g8 said:

Oh sorry , parfocal is what i meant . Meaning that very little if any refocus is needed when changing different EPs’ with the same barlow . My bad  

No problem.  I've never heard of parfocalness having any effect good or bad with respect to barlows.  Conjecturing here, it might reduce pushing the eye relief outward, and as a result, not introduce any added SAEP.

I did not know that the Celestron Ultima Barlow (the Japanese made shorty, I presume) was parfocal with the Ultima eyepieces.  You're saying that little to no refocusing is necessary when adding that Barlow to the optical chain?  That would be very useful for refractors in particular.

If funds are an issue, I'd do what I did and get the GSO/Revelation CC with a 25mm spacer tube.  It has a 65mm to 85mm separation distance where correction is quite good, so there isn't much need to find tune the separation visually.  I'd say for most eyepieces that focus within 5mm of the shoulder, I get about 95% or more reduction in coma, which is plenty good for visual usage for me.  I need somewhere between 10mm and 15mm of inward travel, so not bad at all there.

18 hours ago, celestron8g8 said:

Just wondering if that difference is noticed with a barlow that is parabolic with same brand EPs’ ?? For example i have a set of Celestron Ultimas in 18mm , 10mm and 7.5mm . My barlow is also the Ultima and is parabolic with the EPs’ .  Wouldn’t it effect the FOV rather than the eye pupil exit ? However all barlows reduce light by 75% . But in reducing FOV will help remove or reduce coma at the edges of the FOV . 

Not a clue what you mean by a barlow being parabolic with same brand EPs.  Do you mean parfocal?  Mirrors can be parabolic, but I've never heard of a parabolic barlow or eyepiece.  Parabolic describes a curve, not a relationship between two optical items.

Yes, TFOV is halved with a 2x barlow.  AFOV remains the same, assuming no vignetting as described above.

The exit pupil is also halved with the doubling of the power.

10 minutes ago, Merlin66 said:

Hmmmm

Only for extended objects.....

Yes, for extended objects and the sky background brightness (which is technically a huge extended object).  As I recall, point sources will also start to dim as well once the magnification resolves the Airy disk.

18 hours ago, Merlin66 said:

RonL,

Not sure where the "" However all barlows reduce light by 75% "" comes from.

I could measure the actual transmission with the spectrograph, but I'm sure with today's coatings it's much better than 75%

 

I think he means by doubling the power, the brightness is quartered, that's all.

15 hours ago, Ships and Stars said:

Thanks very much John! My two lowest-mag eyepieces have relatively huge exit pupils in an f4 scope, don't want to miss any photons, but lunar views with these two EPs are incredible. 

Cheers

Be aware that barlowing low power eyepieces can lead to vignetting, sometimes difficult to hold exit pupils due to extending eye relief, and sometimes adds spherical aberration of the exit pupil.  Televue's Panoptic Barlow Interface (PBI) was created to use with TV's Big Barlow to eliminate these issues.  I can verify it also works well with the GSO 2" 2X ED barlow.  Alternatively, telecentric magnifiers like the TV Powermate and ES Focal Extender work in the same way but as a single unit.

16 hours ago, Ships and Stars said:

If I 2x barlow an eyepiece, what effect does it have on exit pupil and coma?

In other words, if an EP's exit pupil is 10mm in a fast scope (say f4) and produces some coma around the edges and I want to reduce it, would adding a 2x barlow reduce exit pupil size by 50% and would it reduce coma as a result by making the effective aperture f8?

Anecdotally, I notice much reduced coma when using a 2x barlow with or without the PBI.  I have to use it without the coma corrector because I can't reach focus with both at the same time.  It's not reduced astigmatism because there wasn't any to start with when using the coma corrector alone.