Louis D

Betelgeuse has been resolved by several large observatory telescopes such as the European Southern Observatory's Very Large Telescope as in the images below highlighted on APOD earlier this year.

And then there's push-to with DSCs on a manual mount. Sometimes, I'll fire up the DSCs on my Dob when I'm having a difficult time locating a challenging object. Since I don't generally look for challenge objects, a purely manual mount works well enough 98% of the time. Full GOTO is handy if you're sharing the view, but so is plain old equatorial tracking. Most full GOTO mounts are nowhere near as smooth and easily controlled in manual mode as an equally priced manual mount. Of course, there are the high end mounts that start with a fine manual mount and then add DSCs and motors to achieve full GOTO allowing you to have the best of all worlds depending on your mood on a given night.

Well, I use mine visually, and it's quite nice. Star points are nice and tight and pretty much color free at best focus. Airy disks are apparent on one side of focus, but not so much the other. Is it a huge step up from my AT72ED (FPL-51 doublet)? No, it is more incremental. The big step up was from my ST80 to the AT72ED. Is it as color free as a Newtonian? No, but the tighter star images make up for it visually. Photographically? I think your money might be best spent elsewhere as others above have suggested. Visually, moving from ED to APO wasn't nearly the game changer I had expected. It's still not at the color free level of a Newtonian, but there's no central obstruction.

I read about another person allowing the Dob's mirror to dry in the sun after washing and rinsing. The angle was such that the sun was focused on the eaves and started to scorch it. As for the OP, this seems to point to using a Newt to project a solar image which is not a good idea.

However, back heavy scopes end up with short height rocker boxes, an extremely large swing in altitude height, super awkward usage at low altitudes, and a particular sensitivity to heavy eyepieces due to the long moment arm magnifying their effect on balance. I find it much better to weight the top end to counteract such back-heaviness to allow for a balance point more in the middle of the tube and thus a taller rocker box. If the weight is on the opposite side from the focuser, it also makes the scope less sensitive to not being completely level in azimuth when used with heavy eyepieces.

There was a recent APOD image of Thor's Helmet where it's obvious that images of different resolutions and sizes were successfully combined for an overall pleasing result:

I have the 9mm Morpheus and find it to be nearly the equal of my 10mm Delos, just with a wider AFOV. The 14mm is nice, but has some field curvature and astigmatism in the last 15% of the field. My understanding is that the 12.5mm, which I don't have, is somewhere in between performance wise.

For widest field, but not the best correction at f/5, I would go with the 35mm Aero ED. It nearly maxes out the field of view possible in a 2" barrel. For best correction at a reasonable price, I would go with the 30mm APM Ultra Flat Field (or Altair UFF). It has nearly the same true field as the 35mm Panoptic with more magnification, less field curvature, and less distortion. The 31mm Luminos has SAEP and EOFB to deal with. The SWAN eyepieces won't do well at f/5. The Aero EDs do better for similar money. The 34mm ES-68 is decent, but is regarded as the weakest of all the ES-68s.

The zoom might not be such a bad idea with kids. I've read that the Celestron and SkyWatcher versions are from the same Chinese manufacturer, so buy based on price if that is the case.

I have a sub-$20 Zhumell OIII filter which acts more like a light pollution filter than a true OIII filter like my 90s vintage Lumicon. Price does make a difference.

I'm assuming that's a UK law rather than an EU "law"? The OP's location is Alicante which is apparently in Spain. Who knows where it was purchased from. I'm curious to know what brand of Dob that is. The main two manufacturers are Synta (SW) and GSO (Revelation) with JOC possibly making Bresser.

I was out with the 8" Dob last night and tried the Meade MWA 26mm again with and without the GSO coma corrector. It turns out there's surprisingly little difference other than the fuzzy true field stop without the CC that I mentioned above. It's so difficult to use the outer field, that any significant difference is just too difficult to tease out. I would say the biggest benefit of the CC was the field flattening effect. Even with the CC, there is still slight field curvature in the MWA. CC or not, it was tiresome trying to keep the blackouts at bay while scanning star fields, even at the "easy view" distance with eyeglasses. I could always see an incipient shadow ready to rear its ugly head as my head/eyepiece alignment varied during scanning. It displays a pleasingly sharp and false-color free view in the central region, but the always imminent SAEP is really a bummer.

The only ingredient in it that concerns me is the blue food coloring. Hopefully, it all wipes off. For really grungy eyepieces on old eyepieces, I've had to disassemble them, note the order and direction of each element and spacer ring, and wash the elements with dish detergent over a thick towel (in case it slips out) in the kitchen sink using my fingertips as scrub pads. I then lay them on a dry, clean cotton cloth to dry it, giving them a light wiping to avoid spotting. That's the only way I've found to git rid of some tough grime.

Al Nagler has recommended Windex in the past. I've used it and it works well.

Lumicon had an issue with some of their filters oxidizing from the outside in. There are tests of H-Beta and O-III oxidized filters on the SearchLight website showing how much they have shifted off of their emission lines.

@bomberbaz How of the field of view is visible when wearing eyeglasses in the NAV-HWs? I would estimate about 80 degrees or so.

I assume the OP has both OTAs right now and can swap the primary mirror cells between the two before sending the original with the chipped secondary back. I'd probably take them both out and do some critical observing with them to see if there is any difference between them first. Perhaps one primary has a better figure than the other.

Here's a design plan for a Dob along the lines of what you want to accomplish. Here are some instructions for building a Dob. The structure instructions are toward at bottom under "A Dobsonian Mount".

I would try to make the trunnions as large as possible like the Bresser Dob's. It really improves the altitude motion a great deal. Also, try to mount the scope dead center to minimize the swing from horizon to zenith and to get the best possible balance. This may mean adding weights somewhere for balance (likely at the top end). There's not much reason if any to cantilever the mount backward as shown in your diagram. Straight up and down is perfect. Nylon chair slides can also work great for the bearing surface. Teflon can sometimes be too slippery. A matte to satin pebbly surface for the bearings is ideal. Smooth glossy is actually too "sticky" in use. It doesn't want to let go easily to track an object. Some smooth satin surfaces will also work, depending on the material. Think about a chair sliding on a floor with those glides on the bottom of each leg. You can actually try out different combinations with this method. The Dobsonian design at 8" f/5 excels when used while sitting. You want to be bending over the telescope when viewing about 25 degrees above the horizon, typically about as low as you'll want to go. You want to be sitting straight up when viewing at (or near) the zenith. This is why minimizing the swing is important. Mounting it too far back causes a large low to high swing. That 1000mm focal length will be just about perfect if you can mount the scope's trunnion's center point about 27 to 28 inches about the ground in my experience. I'm 5' 8", so your comfortable mount height might be higher or lower depending on your height. Here are some examples of what I'm describing:

Seems like having multiple co-mounted scopes with dedicated cameras would be less troublesome.

Has anyone tried those new dual, tri, and quad band nebula filters intended for single shot astrophotography visually? They're pretty expensive, but if they work under light polluted skies, they might be worth it.

And yet actually successfully fabricating an advanced refractor objective design seems to be much more difficult and expensive. It can't just be about the vast amount of expensive glass involved, or perhaps it is.

Very cool looking effect. Now your scope is unique and you can ask for a premium sales price should you ever decide to sell it. 😉

Yes, but I have never been able to detect it in use. Naked eye, I was able to clearly see the orange/red ring, but not the other ring colors. The camera was way more color sensitive. I was flabbergasted when I reviewed the image. Apparently, it's actually a ring of rainbow rather than fire, but the non-orange/red colors are harder for the human eye to detect.

Here is Ernest's post about CAEP on CN. I've reproduced the image here: That is the exact same version of the ES-82 30mm (mine is decloaked) that I shot my rainbow AFOV image through.