Louis D

It's probably under that tan piece of wood in the bottom of the mirror box. Most big Dobs designs have a board to protect the mirror from falling objects. I know my Tectron 15" does.

You could wrap the legs in the appropriate inner diameter pipe insulating foam for a bit of impact protection and to keep them warmer to the touch in winter.

I wrap my gear in bubble wrap and then put it in the gym bag(s) for transport. That way, it's somewhat protected from inadvertent bumps.

Were you taking images directly onto the camera sensor before with no taking lens in between? My guess is that the focus position changed dramatically with the 2x Barlow and 10mm eyepiece. That, and your image scale changed dramatically, dimming the objects to where you can't even see them with short exposures. Try out your imaging train in the daytime on a distant object. If you get that figure out, try it out on the moon next. If you get that working, try dimmer objects.

Sheds here in Texas can heat up in the direct sun to 20 or 30 degrees F above outdoor ambient temperature. That would be extra thermal load to dissipate at night.

Think how unfriendly it would be to mount a 16" APO refractor if you could get one made for you at any price. Imagine hauling that out to a dark sky site and setting it up by yourself. I'll take dealing with an f/4 or faster 16" or larger Dob's viewing position any day over that.

For most Newtonians, I favor f/5 to f/6 to keep the tube more compact without growing the secondary too much by using a low profile focuser.

I was wondering a similar thought last Thursday except I was wondering if adding a Zhumell Moon & Skyglow (Urban Skyglow) filter or a Tiffen CC50B color compensating photographic filter to various yellow filters would yield a more neutral color balance when combined with my DSLR's automatic white balance setting. The CC50B filter has just about the same density and color appearance (purplish) as a M&S filter despite not having that notch at yellow-orange. Basically, cutting yellow (M&S or purple CC filter) somewhat compensates for cutting violet (yellow longpass filter). Here are the results below: The Baader Semi APO is fairly neutral all by itself. It does a semi-decent job of cutting violet at night. The M&S plus either the Hirsch #12A or cheap Chinese Yellow yields a result very similar to the Semi APO and also does a decent job cutting violet at night. The vignetting in the cheap Yellow image is because I was using a 1.25" filter instead of 2" filter in this one case in front of the taking lens. The M&S plus Rokunar K2/#8 Yellow looks very similar to the daylight Contrast Booster images I've seen with that weird greenish sky. At night, it cuts all violet. The Tiffen CC50B plus Rokunar K2/#8 Yellow is very similar in color balance to the M&S/K2 combo as I expected. I don't recall trying this combo at night. Something to remember to try out next time. The M&S plus Meade #8 Light Yellow is closest to the original color balance, but doesn't do much to reduce violet. Again, I don't recall trying this combo at night, but I doubt I'll try it since the Meade #8 Light Yellow doesn't cut any violet that I can see. Overall, even a DSLR with sophisticated color balance algorithms couldn't correct out the weird color casts completely.

The Contrast Booster filter is basically a 495 Longpass combined with a Neodymium glass subtrate. You can get roughly the same results with a Yellow K2 filter stacked with a generic Moon & Skyglow filter. Transmission might be a bit lower than the CB.

I ordered some other filters from the ebay seller at the same time to experiment with to save on shipping costs. The cost for the K2 filter came down to $15.70 with tax and shipping.

Try a #56 green filter to block unfocused red and blue wavelengths on bright planets to see if it improves overall sharpness. It sharpens up Venus tremendously for me.

If you can find a new old stock 48mm Yellow K2/#8 photographic filter local to the UK, it will have roughly the same bandpass characteristics as the Baader 495 Longpass for a lot less. I have the Rokunar version, and it works very well with a distinct yellow cast, but not nearly as strong as a GSO Yellow #12 filter. The 48mm photographic threads are an exact match for astronomy 2" filter threads.

When importing expensive items into the US, it can sometimes be to the buyer's benefit to break-up the purchase into sub-$800 chunks to come in under the $800 de minimis allowance per day per person to avoid import duties/tariffs. The downside is paying multiple shipping fees. Thus, shipping accessories separately from a new OTA can avoid fees on them.

The GSO mirrors (the StellaLyra Dobs are GSO made) must be quite good because Teeter Telescopes used to list them as the base option for their telescopes prior to ending production.

Maybe it's trying to show something else like focus flatness across the field at all frequencies? I'm really not sure what it's trying to show. Perhaps @vlaiv might know?

Based on all of my "research" I really wish all companies would do like Baader and publish spectrographs/grams of each of their filters so we'd know what we're actually getting, not what we're supposed to be getting. The #8 Yellow is a major case in point.

The only reason I have the Baader Semi APO is because it came with an achromat. It actually does quite well visually. The previous owner said he left it on his diagonal continuously when using that scope. Make that #12A. I also have the #12 (GSO version), and it is quite aggressive at cutting out all blue as you can see from the lower right sub-image in my spectrogram composite image. It was my second attempt to cut violet. My first was over 20 years ago when I bought a "Minus Violet" filter, which, as you can see from the second sub-image down in the left column, is a very weak yellow filter. Any violet reduction it might technically accomplish is not detectable to my eyes. I then tried the #12 and found that it completely cuts all violet while imparting a very strong yellow cast to everything. So, I set off on my journey to find the Goldilocks of yellow/minus violet filters. The #12A and K2/Wratten #8 come closest. The former leaves a bit of violet without adding an undue yellow cast while the latter cuts all violet while leaving a pale yellow cast that I can tolerate while picking out fine details. For some reason, the #12A is not available in new production today, and the latter is only available in the 2"/48mm photographic size as new old stock. The current #8 Yellows are much closer to the 1990s Minus Violet I mentioned above as you can see from the third sub-image down in the left column. As I've said before, some of the cheap Chinese made "Yellow" filters from ebay are actually very close to the #12A as you can see from the fourth and fifth images in the left column. However, the one I have does induce some light scatter as is visible in that artificial star image to the right of the fourth image. Even the polyester film Rosco filters have less scatter (see R### yellows in that composite image). Of the Rosco filters, the R312 Canary was my favorite. It cut all visible violet while imparting only a mild yellow cast. It turns out it is nearly identical to the K2/Wratten #8 photographic filter as is obvious from the second and third images in the right column.

I stick with the GSO dialectrics (three at last count, one being a quartz) and haven't had any issues with any of them with regards to vignetting.

If the OP doesn't mind tight eye relief, it is an excellent performer between 5mm and 8mm. For the money, it would be a good buy to be able to exactly tune the magnification to the seeing conditions.

See the following post of mine below for more on SAEP vs. blackouts. It has some nice animations of each type of blackout by @Ruud.

I was thinking in terms of the GSO 6" and 8" imaging Newtonians available at various f-ratios versus the 152mm KUO achromat or even larger achromats (anyone know of any readily available?). Weight-wise and length wise, I find the 6" f/5 GSO Newtonian much easier to mount than the 152mm f/5.9 KUO achromat. Perhaps things change once you try to include a filter wheel and other imaging gear? Also, I could see if you simply want to image wide fields, the refractor route handily wins out.

Would any of that outweigh simply using a fast Newtonian with coma corrector instead of a fast achromat just to avoid a central obstruction? I can't imagine ever getting better results regardless of achromat filtering.

If imaging with a fast achromatic doublet like an ST80 or KUO 152, I would think you'd want an L cutoff closer to 470nm like the Yellow #12A to eliminate enough violet blurring to be useful for luminance. This would still leave the Hβ visible.

If you want information overload, take a look at this spectrograph of multiple violet reduction filters: I have the Hirsch 12A and find it just about the best compromise of the purely yellow violet-cut filters. There's still a tiny bit of violet fringe, but it is hardly noticeable. There is also very little yellow cast introduced. It also doesn't cut into the Hβ line much, so it could be left on with nebula within bright open clusters. The problem is, it isn't made anymore. The closest modern equivalent are some of the generic yellow filters coming out of China (which I have). The problem with them is that they tend to scatter more light than the older US, Japan, and newer Taiwanese filters like Meade, Hirsch, and GSO. The modern #8 Light Yellows are similar to the Meade #8 above (which I also have). It cuts a little bit of the far violet, but not enough to be effective. On the plus side, there's little to no yellow cast. The older, true Wratten #8 (Yellow K2) is very similar to the modern Baader 495 Longpass. However, the yellow cast is strong. It's not as strong as the modern GSO #12 Yellow, but still strong. I tried the GSO #12 first of all my yellow filters, and find it the least usable because it cuts all blue and some green, which is massive overkill. The Yellow K2/#8 filters are still available as new old stock 48mm (2") filters on ebay for under $20 if you want to try one. It cuts into the Hβ line, so not appropriate for those nebula that strongly emit it. The Baader Contrast Booster and Semi APO filters simply add a Neodymium glass base that cuts some of the yellow and yellow-orange part of the spectrum to compensate for the loss of violet. The CB is basically a #8/K2 Yellow or 495 Longpass combined with the Neodymium glass. The SA is somewhere between the Meade #8 and Hirsch #12A in cutting violet as you can see from the graph, and then adds the Neodymium glass. In my experience, the SA gets rid of enough of the violet fringe without adding a nasty yellow cast. My poor man's CB still shows some yellow cast and no violet fringe at all. The Baader filters add violet cutting coatings to the Neodymium glass to get higher transmission. However, this doesn't really matter all that much on the bright objects that display violet fringing the most. There's no violet-cut benefit to the Neodymium's suppression of teal-blue to green wavelengths just above 500nm. However, when combined with the yellow/yellow-orange cut, the Neodymium filters increase contrast by separating blue from green from red with bandgaps. Eyeglasses for the color blind work in a similar manner to cut notches between the colors they can't separate with their retinas. Here's some of my yellow filters run through my spectroscope. It also includes some Rosco yellows and my attempt to photograph an artificial star through my ST80 with some of these filters.

I can verify that when using my Meade RGB interference filters with my ST80 visually, I could get a sharp image in green, a reasonably sharp image in red with a bit of refocusing, and a somewhat fuzzy image in blue no matter how much refocusing I tried. I wrote it off to violet focusing too far from medium blue to bring them both into focus at the same time. However, spherical aberration in blue might have been what I was seeing as well. Regardless, I can't imagine a camera not seeing this same blue-violet fuzziness.