Louis D

I was thinking for use in my Mak to get to a 50mm/12 ~= 4mm exit pupil. I wonder why the 45° AFOV? 55/56mm Plossls have 50° AFOVs. Perhaps it's design was some sort of Abbe orthoscopic variant?

Or maybe it was the use of an f/10 system to make the comparison that leveled out the differences? Had you made the comparison in f/6 or faster scopes, your impressions might have been different.

I have both the 35mm Aero ED and the 40mm Lacerta ED. The 40mm is noticeably better corrected than the 35mm. However, the 35mm has a noticeably wider AFOV and nearly the same TFOV thanks to its 44.4mm field stop diameter. If I had to guess, the 35 ED is probably a bit better than the 36mm BHA, but not substantially better. It will probably have a significantly wider TFOV. The old, massive 35mm Baader Scopos Extreme that was replaced by the 36mm BHA is sharp edge to edge at f/6 and probably close to that at f/5 being a massive negative/positive design not much affected by fast f-ratios. Take a look at my Lacerta ED 40mm write-up. I think I have an image showing all three FOVs for comparison somewhere in it. I've never been even remotely interested in the 36mm BHA due to poor correction reports and high price, so I cannot directly comment on how it compares.

The one low powered LV/NLVW that I'd like acquire someday would be the 50mm LV. By all accounts I've read, it was an excellent ultralow power eyepiece with no modern peer. The problem is, unless you come across one as new old stock in some small, old, out of the way astro/photo shop, you'll never be able to purchase one new or used. I can't recall the last time I saw one up for sale on CN or anywhere else used.

FPL-51 in my 72ED pretty obviously shows violet fringing at higher powers. It's only going to be worse at 102mm even at the same f-ratio. My 90mm FPL-53 triplet doesn't show violet fringing at pretty much any power, but it has red-green out of focus images on either side of best focus that merge to white in focus. It's definitely not reflector-like. I don't know if FPL-53 doublets behave this way as well. Overall, I much prefer the 90mm to the 72mm scope.

Avoid the illuminators that have the fat back end. I've had nothing but problems with the switch desoldering from the wiring. I've had much better luck with the slim, straight style illuminators found on Celestron eyepieces.

How hard would it be to find a matching doublet and the correct distance to place it in the tube to make a poor man's Petzval or Aplanat design?

The BSE 35mm is fifth from the left below and the fifth ruler image down from the top in the FOV images. Notice the fairly low radial edge distortion in the BSE 35mm. It's 17% versus 47% for the Meade 5000 SWA 40mm. This makes viewing objects like the moon more enjoyable because they are distorted less as they drift across the FOV in an undriven mount. The BSE 35mm is in the back row, second from the right, to the immediate right of the ES-92 17mm. Weight and size wise, it's a good observing companion to the two ES-92s as I said above. I don't have an image of the eye lens, but it is the largest of all my commercially made eyepieces at 47mm. Even with 17mm of eye lens recession, it still has 17mm of usable eye relief. I once unscrewed the top to see what 34mm of usable eye relief would feel like. It felt like way too much eye relief even while wearing eyeglasses. 😅 Here's a CN user's image with the top removed from the Orion Stratus 35mm version in a CN thread about it: You don't dare turn the eyepiece in that state. That eye lens will drop right out without the top screwed on. I created a low profile top from a large pill bottle cut to size and with the threaded neck cut off. I rubber band it on top against the rubber grip to hold the eye lens in place when I remove the top.

That's a great deal, but they don't ship to the US. Explore Scientific (the US Vixen distributor) still has it at $249 before tax.

Interestingly enough, the price before Christmas went as low as just under $100 before taxes on ebay-US for a day before bouncing back up again. I'm guessing someone was testing the waters to see if the demand would noticeably go up if the price went significantly down. Hopefully they don't try price testing in the opposite direction to see what the market will bear. Explore Scientific certainly has done this in recent years with most of their offerings.

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.

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.

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.

Guilty as charged. 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. I got to work and disassembled the whole thing. It's just held together with screws. The focuser went back in the box. Maybe I'll figure out something to do with it someday. 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). 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. 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. I put a cheap Amazon 2" diagonal in the PVC focuser. 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. 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. 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.

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.

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.