Louis D

To raise up a Dob, lots of folks on SGL use a water butt stand:

I've found Dobsonian mounts very forgiving of slight slope because the center of gravity is directly over the azimuth rotational axis. Alt-az mounts are not at all forgiving of slight slope unless you're using a counterweight on the other side because the center of gravity is way off to one side of the azimuth rotational axis. This necessitates re-leveling the mount in the dark anytime you need to pick it up and move it to another location to dodge observing obstacles like buildings or foliage unless your entire observing area has the same slope and you keep your tripod oriented exactly the same from place to place. For Newtonians with focal lengths of one meter or longer, I generally recommend the Dobsonian mount over the alt-az mount in my experience. For shorter, just the opposite.

Simply a case of saying it's so doesn't necessarily make it so. My Baader Scopos Extreme 35mm says 70 degrees on the barrel, but it actually has a measured 66 degree AFOV and a 68 degree eAFOV.

The original Vixen LVs from 7mm on down were all 45 degrees. I can't remember if they changed the claim to 50 degrees with the NLV or SLV line, but the actual optical design didn't seem to actually change, just the claims.

Well, I finally found an affordable, high quality cyan BG39 (minus red) glass filter. It's a 1" (25.4mm) diameter bare disk, so I mounted it in a spare Meade UV/IR blocking filter mount with a just less than 1" clear aperture due to the retaining ring. I had to leave the original UV/IR glass in place to keep it from falling out the front. It's specified bandpass from the manufacturer (Newport) is below: At best, it has an 80% transmission at 500nm (teal or blue-green). Here's how it looks by itself and in combination with other filters through the spectrograph: As you can see, it does a fine job of completely blocking orange-red and red light starting right around 600nm as specified. I tried it out by itself and in combination with various other filters and in comparison to various other filters on Venus last night in my ST80: By itself, the Cyan BG39 filter transmits quite a bit of violet, but it does an excellent job of blocking red. I saw simply a violet fringed blue-green disk with no orange or red flaring. I'd say it was sharper than with any Yellow filter thanks to that. The best combination was with the Yellow K2 (#8) filter. All violet and blue fringing was blocked along with the orange-red flaring leaving a nice and sharp disk. The color cast was a pale blue-green. Next best was with the Hirsch Yellow #12A filter which left barely perceptible violet-blue fringing. The color cast was a a very slightly more blue blue-green disk than with the Yellow K2 filter. The combination with the Hirsch Light Green #11 yielded a slightly darker image than with either yellow filter above. It still had lots of violet-blue fringing, but no red-orange flaring. The combination color cast tended toward blue-green while the Green #11 by itself tends toward yellow-green. The Yellow #12 combination was rather dark in comparison and overly yellow-green. I wasn't a fan of it despite it blocking practically all poorly focused blue and red. I would rather use the Meade Green interference filter to achieve that goal. In comparison, the Rokunar Green X1 (#11) yielded almost identical results to the Yellow K2 or Yellow #12A, just with a yellow-green instead of a blue-green color cast. The best performing BG39/Yellow combinations both have sharper cutoffs and slightly higher combined transmission especially in teal/blue-green, but on Venus, it made little to no difference. I preferred the Green X1 simply for the simplicity of a single layer filter. The Hirsch Light Green #11 by itself simply does too little to block either violet or red to be of much use. The various yellow filters do a good job of blocking violet, but the resultant orange-red flaring is probably just as bad as the violet fringing. The violet fringing is well away from the disk while the orange-red appears as flares practically on top of the disk. It's easy to ignore the violet corona, but it is impossible to ignore the orange-red flares distorting the disk image. To try to break the Green X1 vs. Cyan-Yellow K2/12A tie, I tried the Green X1 and Cyan/Yellow combinations on the Orion nebula and the Trapezium. Alas, I couldn't tell a difference on such dim objects. No filtering was best by far for them. I simply couldn't see any fringing on them without filters, so why use them? On Sirius, I didn't find the color fringing all that objectionable. I tried the various filter combinations, but still preferred the unfiltered view. I've come to the conclusion that the poorly focused red and blue/violet light of fast achromats is really only a problem for bright solar system objects. Unfortunately, that's what most beginners first point these scopes at and are less than impressed by the resultant views. I'm sure at higher powers, it would also affect the ability to resolve globular clusters and close double stars, but most folks don't ever use these scopes for those purposes. I'm more convinced than ever that a high quality 470nm to 610nm (or 480nm to 600nm if the cutoffs can be very sharp) bandpass interference filter of high transmission would be ideal to market as a planetary filter companion for fast achromats. Now, we just have to convince some retailer to come to market with one.

If you have a Green #56 or Yellow-Green #11 filter on hand, try repeating the comparison on the moon with a filter in place on the ST80. I've found a light green filter will greatly suppress the violet and red-orange flaring going on in the fast achromat on bright objects. This then vastly improves sharpness by removing most of the veil of unfocused light splashed across the field of view. Sure, you're left with a greenish view, but it's a much sharper view. Try Venus next time. It really sharpens up nicely with a green(ish) filter in the ST80. It goes from a flaring blob of violet/orange-red light to a (mostly) sharp edged greenish disk in my ST80.

Is there a particular circumstance forcing you to use a diagonal in your imaging train?

Hey, let's keep my personal life out of this. 😉

I bought a display Meade 8x42 binocular 25 years ago for a good discount. It came with neither neck strap (I added a neoprene one) nor case. I've kept it in a $10, soft sided, padded lunch cooler all these years. It can sit out in its case, and no one thinks it's worth stealing. The case is a little too big, but it squashes down for storage. Something like this might work for your bins.

Plus, if an eyepiece has borderline kidney beaning (SAEP), a Barlow can exacerbate it, possibly making it unbearable. A telecentric won't have any such effect.

Perhaps try a quality Barlow or telecentric magnifier ahead of it to use the 5mm to 8mm settings at higher powers to take advantage of the more generous eye relief at those focal lengths?

Are you allowed to skip the sale and simply resupply at the sale period wholesale price? If so, when the sale is over, you still have stock to sell at a decent profit. If not, what about using shell companies to participate in the sale, buy at sale wholesale prices, but list items as out of stock, and then move that stock to the actual selling company after the sale? I wonder if JOC monitors their sellers closely enough to notice this stock shuffling is happening. I know NYC based photo retailers used to do a huge business with gray market items bought overseas to take advantage of differing sale prices and currency fluctuations. These items would be moved into the US to be sold at higher prices. This is the sort of stock shuffling I'm thinking of, but strictly within the US.

Correct. Mine arrived in a bubble wrapped zip bag as I recall. It was just tucked in with the wedge to the side. Yes, a single polarizer will work, but you have to get the rotation position angle right before you can start observing. This can be a pain in the eye when swapping eyepieces while solar observing. Setting a variable polarizer to a certain maximum brightness allows you to start observing right away when swapping eyepieces. If it's still too bright, rotating the eyepiece allows for further dimming just as with a single polarizer. Also, since the wedge is not at the Brewster angle, you're not getting perfect polarization, so full dimming with a single polarizer may not be possible. Thus, you might not be able to dim it enough for your liking, but the second polarizer in the variable filter guarantees you can get there. I'll have to try this out with a single polarizer on my Hercules wedge sometime to see how dim it can get. Again, single or variable polarizers are quite cheap from China via AliExpress or ebay, so no worries financially about replacing the missing one.

Photographically, I found the AFOV to vary from 58 to 61 degrees, so it qualifies as widefield, just not super wide field (SWA) which generally starts at 65 degrees. 6mm and 7mm are clearly different in AFOV. I went back and remeasured my photos. Sure enough, I was off on the 6mm for some reason. It actually works out to a 59.7 degree AFOV at 6mm. Mea culpa.

I've read that Chinese eyepiece manufacturers (probably from Don) will make a run of eyepieces for you in your choice of livery with a minimum order of 300 per focal length. However, this is for eyepieces still considered to be in current production. I don't know about Japanese manufacturers like Vixen who have much higher production costs, though. It may simply be a minimum cost that they want to recapture regardless of order size. I know when the companies I work for send an ASIC out to a fab for build, the NRE (nonrecoverable/nonrecurring expense) has risen from $1.5 million to closer to $10 million or more over the past 25 years. I would think that restarting discontinued eyepiece production might incur a similar (if much smaller) NRE regardless of order size.

You're right. A narrow notch filter or dim to dark color filter actually works much better without the additional ND filtering. I've done that with my Optica b/c line filters that only transmit 30% over a <10nm bandwidth at best. They're much too dim to be useful otherwise.

Safe maybe, but usable or comfortable, not really. Where did I say it wasn't safe? I said it's intolerable. There are no features to be seen at that level of brightness. It's just basically a featureless white circle of intense brightness. There are plenty of features to see on the moon without a filter of any sort. In fact, I had to jerk my head away when I first tried looking through it without further filtration. It's nothing like viewing the moon without a moon filter. I've never experienced that sense of impending eye damage while viewing the moon. Maybe this wedge works fine in Canada without further filtration, but the noon summer sun in Texas is just too bright for my liking without additional filtration. It might be fine with the rising sun in a Texas winter, who knows? My horizon views are blocked, so I wouldn't know.

Don't even think about looking through it at the sun without the variable polarizing filter in place. The image is way too bright for human eyes to tolerate. I think it defaults to somewhere around an ND3 to ND4 brightness without additional filtration. You need to be at about ND5 for safety sake. I'm sorry your experience with it has not been as positive as mine has been. Everything was nice and tight and still is, and it came with the variable polarizer. It needs about an additional ND2's worth of dimming to be usable. I bought a Svbony ND3, but it was too much. A moon filter wasn't enough. I decided that the variable polarizer was still the best option. I set the variable polarizer to just about the brightest I can stand the image to be by trial and error (just take a quick peek off axis through the eyepiece to gauge the brightness). I then do final brightness adjustment by rotating the eyepiece in the holder to take advantage of the partial polarization caused by the wedge. Put another way, I dim down the view by eyepiece rotation to whatever level seems best for whatever feature I'm observing at that moment. If I can't get it dim enough, I'll take out the eyepiece and adjust the variable polarizer downward in transmission amount. I would go ahead an order in a variable polarizer from AliExpress or ebay. They're not that expensive in the 1.25" size.

The problem as I see it for professional usage, how do you keep an optically flat window perpendicular to the telescope's optical axis at all pointing angles and positions? It might be possible with a slit aperture in a domed observatory with some sort of expanding bellows to maintain the seal around it to avoid thermal air currents. Another issue would be thermal strain on the glass if there is a temperature differential between the inside of the observatory and the outside world. Also, reflected light could become an issue causing glare on the optical window. Perhaps with enough engineering forethought and post-implementation rework, it might be doable.

I wonder if that lower "TOE" image used to accompany the following Vixen comparison of the HR line to the 2.5mm LV: They basically threw the LV under the HR bus. Those Vixen pages seem to mostly be gone now that the HR line is discontinued. However, it might be the 2.5mm Vixen LV internal diagram despite the odd lens and group count.

Click the link and read the Wikipedia article? Basically, some of the largest and nearest stars have been professionally resolved. You didn't put any qualification on "best and largest telescope".

Not necessarily.

Kind of cool looking in a hyperspace jump or blackhole suction sort of way, though. 😁

Now that seems more plausible.

None of the ad photos show up anywhere else on the web using an image search, so that test of a scam posting fails. It begs the question, where would the poster have gotten the images from?