Louis D

Despite reports noting a central stellar concentration with this comet, I could not see one even at high powers last Sunday night.  Sometimes I convinced myself that there was the slightest hint of one, but it was nothing like the strong stellar concentration I've seen with some past comets.  Basically, it was brightest across a fairly uniform, but ragged, circle that then tailed off to the background sky brightness.  The extent was larger in my accidental comet filter (Zhumell OIII) because it suppressed the background brightness.  I didn't notice any obvious elongation in any direction, which is fairly typical of comets I've seen from my suburban skies.

Lack of tracking definitely reveals more details about stray light control than having tracking.  For instance, when I move a bright star center to edge in my 127 Mak with a 2" visual back and widest field 40mm SWA eyepiece, I can see a reflection off some baffle tube in the scope revealing itself as a hollow, oval reflection of the star on the opposite side of the FOV that grows in size the further off axis I move the star.  If I had kept the star centered, I would have never noticed it.  If I had kept the star stationary off axis, I might never have made the connection as to what was causing the oval reflection on the opposite side of the FOV.

I'm always moving objects, sometimes rather rapidly, center to edge to observe changes to the FOV during eyepiece and telescope evaluations.  My eyes can pick up moving changes way easier than static details.

17 hours ago, Ratlet said:

Not sure if we can trust this.  The ruler is not even made of wood!

Funny you mention this.  I've noticed that the low contrast printing on my wooden rulers does make for a more stringent test than would (wood?😄) high contrast markings.  Also, the subtle wood grain is also a good indication of ability to render low contrast details.  The bar code on one of them is also handy for showing chromatic aberrations.  I suppose I could print up some sort of high contrast target and attach it to the rulers to be able to track chromatic smearing center to edge.  Ideally, a series of backlit pinholes in foil would also be a good artificial star test across the field.  I've just not had the time to work out the details yet.  That, and I'd have to do all my testing in near darkness.

Nicely done.  You've inspired me to hunt down some doubles sometime in the near future.

I'll have to look for scattering again when I get the chance.  I'd swear I was seeing a bit more in the Svbony than the S-W zoom on Capella, but it could also have been down to undetected dewing of one versus the other.

41 minutes ago, Stu said:

Maybe so Don, but I found that the 31mm Nagler is sharper than it at the edges when compared in my Genesis.

Someday I'll have to directly compare the much vaunted 31mm NT5 to the 30mm APM UFF.  My 30mm ES-82 has more bloated stars in the central region and spectrally challenged stars in the outer 10% of the field as compared to my 30mm APM UFF.  It would be neat if the 30mm APM UFF design could be extended to 82 degrees or more to compete more directly with the 82 degree class of eyepieces.

3 hours ago, Stu said:

Pretty sure that’s @Louis D

3 hours ago, F15Rules said:

+1 for that, it's got to be Louis😊

Guilty as charged. 

2 hours ago, Zermelo said:

I think he has copyrighted it, so no-one else is allowed do it.

That's right.  My lawyers are ready, willing, and able to fly around the globe to protect my worldwide copyrighted/trademarked style of eyepiece testing. 😁

I started doing it for my own edification because my eyes aren't what they used to be.  The aha moment came when I realized smartphone cameras were very small, wide field, well corrected, low linear distortion, high resolution, fixed focal length, and could take the place of my own eyeball to very accurately capture what I was seeing at the exit pupil.  Everything from SAEP,  CAEP, and vignetting to field stop sharpness and field sharpness center to edge could be examined in detail later via pixel peeping at the computer.

The only thing not accurately captured by a smartphone camera is field curvature because these tiny, wide angle cameras have vast depth of focus similar to very young human eyes.  Thus, the camera will often show what appears to be a blurry outer field to my presbyopically fixed focus eyes as sharply or nearly sharply in focus.  I generally try to note this difference in my imaging notes and reviews.

I'm guessing being in India that your budget is constrained by wages being well behind Western Europe and the US for comparable work.  As such, I would recommend saving up for a bit longer to stretch to a 6", f/8 Dobsonian from GSO or Synta (Skywatcher).  Such a scope would not disappoint and would keep you busy finding and observing objects for years to come.

I just remembered I had taken ruler test images through a few different eyepieces in the scope once I finished it.  I just now composited them.

Edit: I just remembered that due to the extreme field curvature of a 300mm refractor, I added a TSFLAT2 to the nose of my 2" diagonal for these images.

First, I used a Meade Series 5000 SWA 40mm for the widest field and best possible correction.

Second, I used an OVL Aero ED 35mm for near widest field and decent correction at a much lighter weight.

Third, I used a Pentax XL 5.2mm for near highest possible power just to see how it would perform.

I took images at both full aperture and reduced aperture.  Unfortunately, I don't remember what reduced aperture meant.  I might have used the aperture stop that came with the scope for this purpose.  If so, the 30mm effective aperture increased the scope's f-ratio from f/4.3 to f/10.

As you can see, at widest field of view, it does a pretty good job with a highly corrected eyepiece and slightly less well with a somewhat less well corrected eyepiece.

At high power, it is pretty soft until stopped down, and then it's not too bad.

Overall, I was pleased with the objective's quality for $25.

I was out viewing comet C/2022 E3 (ZTF) Sunday night before the full moon washed out my skies.  The best views with commonly available filters was with the Svbony UHC filter.  It reaches far enough right into the blue-green to pass the C2 lines associated with comets.  The Svbony CLS filter would probably give similar, but slightly more washed out views.  The UHC filter darkened the background without darkening the comet's coma, making the extent of it easier to see.

My older Zhumell OIII filter is defective and actually passes the C2 lines like the Lumicon comet filter instead of the OIII lines.  It worked really well to darken the skies and show more coma extent.  However, they've been unavailable for about a decade.

I tried a few blue and green color filters, but they just generally made matters worse, making the comet more difficult to see.  As I said above, you really need a teal/cyan blue-green filter.  Blue and green filters tend to both attenuate the C2 lines which lie between blue and green.

Would this be better categorized as imaging rather than eyepieces (visual)?

They're decent, entry level Plossl (symmetrical) eyepieces.  The older ones from the 90s like I have were made in Taiwan (by GSO?) and were MgF2 singly coated.  You can tell this because the only lens reflection is pale violet.  They're not quite as good as my GSO Super Plossls which do seem to have slightly better correction to the edge and are multicoated (several color reflections like green and red from the lens).

Those two eyepieces should serve you well for quite some time.

I bought one of the 70x300mm scopes back at the beginning of the pandemic for $25 off of ebay for this purpose.  The scope has a 0.965" focuser, diagonal, and eyepieces.  I will say that the focus tube is very long and narrow which in and of itself probably would cause vignetting of the objective.  However, they stuck an aperture stop partway down the focuser tube to choke down the aperture and improve performance.  On top of that, they put about a 30mm diameter aperture stop directly behind the objective for the same purpose.  So, as shipped, it is not very useful as a 70mm finder scope.  You'd be better off with a GSO 8x50mm RACI.

Undaunted by the mechanical surprises, here's the steps I went through to convert it to a 2" eyepiece capable 70mm finder scope.

1. I got to work and disassembled the whole thing.  It's just held together with screws.
2. The focuser went back in the box.  Maybe I'll figure out something to do with it someday.
3. I pushed out the aperture stop behind the objective (it's pressure fit) which scratched up the tube blackening.  So, I sprayed flat black paint in there and let it dry a few days (the paint really stinks).
4. I mocked up a 2" focuser from 2" PVC plumbing parts, thumb screws, and more flat black paint.  I'll have to work out something better someday.  I'm not into 3D printing yet.
5. I screwed the PVC plumbing parts inside the original tube which is close to 70mm in diameter.  I still need to work on getting the centering better with spacers.
6. I put a cheap Amazon 2" diagonal in the PVC focuser.
7. I put a 40mm Pentax XW in the diagonal and slipped the diagonal forward and back until it came to focus and then tightened the thumbscrews.
8. I attached a Vixen rail to the photo block on the tube so it could be mounted on the other side of my alt-az mount.
9. It's not perfectly aligned, but at 7.5x and 9 degrees, it doesn't matter all that much.  You just make a mental note about how far off-center and in what direction something is when centered in the main scope.

As far as image quality, the 70mm achromat is actually quite good for wide angle views.  They really didn't need to stop it down for wide angle usage.  It is pretty bad at mid to high powers due to extreme false color, but not because of its figure, polish, or coatings.  The achromatic doublet objective lens cell comes with a nice dew shield.  The original main tube is also good quality metal with a nice paint job.  Mine came in a sparkly sky blue that my wife commented was really nice looking.  That's a high compliment.  She doesn't think anything else in my astro collection is attractive looking. 😃

I need to flock the whole thing.  Reflections off of everything in there are pretty bad on bright objects.

It does sound kind of stupid to hang over $400 of eyepiece and diagonal off of a $25 scope, but I generally have them sitting around unused.  I'll have to try the 40mm Lacerta ED in it which I didn't have back in early 2020 when I went through with this project.  I think I may have tried my 24mm APM UFF in it with similar success.  I don't care that the exit pupil is 9mm with a 40mm eyepiece.  I was just going for maximum possible true field.

I haven't been using it much, if at all, since.  It was more of pandemic project for me.  I'll have to revisit it someday.

14 hours ago, F15Rules said:

Now, I decided next to check for sharpness to the edge, going north to south and vice versa. The result was the same, in that the Meade pair were sharper than the WO clones moving from the centre to the edge.. however, I did notice that the "sharpness from centre to edge" for both pair of eyepieces was significantly worse moving North to South than for moving East to West..sharpness north to south definitely seems less good than east to west.

Did you rotate you whole head 90 degrees to either side to eliminate the possibility it was something to do with your eyes or perhaps even your visual processing complex?  That way, you're looking side to side along both axes of the eyepiece/diagonal/telescope combination.

2 hours ago, Mr Spock said:

Do we need eyepieces to be sharp to the edge though? Mostly we are looking in the middle so really the last 5% isn't that great a loss.

At lower powers, yes.  But as power increases in a non-driven mount, having wider field, "sharp to the edge" eyepieces helps to increase dwell time between nudges.

I just checked my spectrograph test images, and the Svbony UHC does indeed go far enough right in blue-green to completely encompass the Zhumell OIII's passband.  I even have a stacked image showing little to no change in the latter's passband when stacked with the former.  This actually agrees with what I observed last night with the comet.  The Svbony UHC made it easier to see the comet's coma against the sky background while the Zhumell OIII improved contrast even further.  The Lumicon OIII just made everything darker when observing the comet.  Thus, the Svbony UHC and Zhumell OIII were showing the C2 lines while the Lumicon OIII was blocking them.

If you're not short of cash or storage space, go ahead and hold onto that ED80 and FF/R for a bit.

I'm a bit of a hoarder myself (don't ask).  However, it saved me this weekend.  My upgraded receiver for my stereo system suddenly died (went into protection mode), so I swapped in my old one that I was getting ready to sell.  It turns out, it works well enough to hold me over until I can figure out my next step to replace or repair the upgrade one.

I'm not saying your new triplet APO is going to "die" at some point, but something else could happen to it (dropped, stolen, fungus, etc.).

My two OIIIs are both narrow enough to not cover both sets of lines, thus I found myself having to swap between them based on the object.  Stacked, they pass barely any light and view darkly on all objects.

At least I finally found a good use for my decade old Zhumell OIII filter.  It was never very good for its intended purpose.  It was only once I saw where its passband fell in my spectrograph imagery that I had my aha moment it might make for a good C2 line filter.  Last night I confirmed it.

I don't know if I'd pay $100+ for a Lumicon Comet filter just to get the views I was getting last night of Comet C/2022 E3 (ZTF), but if Svbony would market one for under $40, I'd probably recommend it.  They could add it to their UHC, CLS, and M&SG filter package.  I have no idea if their OIII filter is any good.  Hopefully it is on-band like my Lumicon and not off-band like my Zhumell.  Basically, any OIII rejects that have a too far right passband could find a new home this way.

I bought a 127 Mak for my grown daughter to use on camping trips with her family.  It's rugged and compact.  I have one myself, but for home use I tend to use my 8" Dob for planetary viewing.

Another option not mentioned so far would be a GSO/StellaLyra/TS Optics Classical Cassegrain, either 6" or 8".  The late, great @johninderby really liked his 6" and 8" CCs and talked about them often on SGL.

Tonight, I was viewing Comet C/2022 E3 (ZTF) with the Svbony 3-8mm zoom getting good views in my GSO 6" f/5 Newt under Bortle 6/7 skies before the full moon overwhelmed my skies.  My Speers-Waler 5-8mm zoom was also showing it well.  However, when I swung the scope over to nearby Capella, I noticed that the Svbony seems to show more scatter around this bright star than the S-W zoom.  I'll have to investigate this further on other nights with other objects.  I don't recall scatter being a big issue with Jupiter in my earlier testing.

If anyone else has seen increased scatter in the Svbony compared to other eyepieces (zoom or not) on bright objects, please post your observations on here.

I was alerted in a PM that there is also the possibility of it viewing slightly darker than other same focal length eyepieces, like the Vixen LV eyepieces of the 90s.  I think I may have seen this effect, but it is subtle if it exists.  I definitely think the Orion Nebula showed up better in the Svbony than in the S-W zoom possibly because of this background sky darkening effect.

Again, post on here if you're seeing the Svbony zoom viewing darker than other eyepieces at the same focal length(s).

On 15/01/2023 at 21:08, Louis D said:

The Zhumell barely does anything for OIII being too far right of the lines, but might work as a comet filter and the C lines.

I verified tonight that my old Zhumell OIII does indeed work quite well as comet filter when viewing Comet C/2022 E3 (ZTF) tonight in my GSO 6" f/5 Newt under Bortle 6/7 skies.  I was able to see the greatest extend of its coma with this filter in place.  The Lumicon OIII just made things worse by blocking the comet's light, so it's definitely the right shifted nature of the Zhumell bassband working to let through the C lines.  Too bad they aren't sold anymore.  I wonder if any currently available cheap OIII filters have this same off-OIII band performance.  I'm glad I kept it around.

The Svbony UHC was second best, helping to increase the amount of coma visible by blocking light pollution.  The Zhumell Urban Sky (Moon & Skyglow) filter helped a tiny bit, but not enough to want to go back to it a second or third time.

On the Orion Nebula, the Lumicon OIII was best with the Svbony UHC very close behind by also passing the H-Beta line.  The UHC provided a more pleasing view by showing stars better.  The Zhumell OIII made it somewhat more difficult to see the nebula because I think it is passing only one of the two OIII lines, and then just barely.

All of this was done early before the full moon completely washed out my skies.

I tried out several filters on the Orion Nebula (M42) tonight in my 6" f/5 GSO Newt under my Bortle 6/7 skies before the full moon overwhelmed everything, and the Svbony UHC struck the best balance between seeing stars and nebula and seeing only nebula.  The Lumicon OIII did a slightly better job at improving contrast by making the sky background even darker without attenuating the nebula significantly (by blocking H-beta).  My Zhumell Urban Sky (Moon & Sky Glow) filter didn't do much to block light pollution.  Maybe a bit, but not enough to want to continue to use it.

Based on that, I would recommend the Svbony UHC for certain as a light pollution filter when viewing nebula.  The Svbony CLS is going to pass a bit more blue and red while still blocking all green/yellow/orange (where the majority of light pollution resides), so it should perform similarly.

For galaxies, which emit broadband light similar to LED lighting, dark skies are the only real answer.  You can try a UHC/CLS filter on them, but don't expect miracles.

Are your local streetlights low pressure sodium (yellow-orange) or LED (broadband white)?  The former can be effectively filtered while the latter cannot.

As for which to choose, I went twice with the Synta 127 Maks because I used to be able to pick them up used for $200 shipped off of CN classifieds here in the US.  Now, they tend to fetch $300 to $350 which is still quite a bit cheaper than new, if you can find one in stock.

The ES/Bresser 127 Maks never come up used here in the states, and I'm not about to start buying new now at today's inflated prices and 25% special tariff.

22 hours ago, bosun21 said:

Both the mirrors are the same size as is the aperture. It’s just that the Skywatcher doesn’t utilize the entire mirror due to its optical design. 
The Bresser specs below show a 127mm mirror the same as the SW

 

In the case of a Mak, objective diameter refers to the front corrector plate, not the primary mirror diameter, so FLO got it right.

Thanks for the effort.  It is appreciated.