Louis D

What is it about the Pan you didn't like? Was it just duplicating the 20mm APM's TFOV? I would suggest a 30mm APM UFF to increase your exit pupil for when you're using nebula filters. That, and the 70 degree field of view is easier to take in all at once than in a 100 degree eyepiece. I retired my 27mm Pan in favor of the 30mm UFF.

Good to know. What is the maximum weight you feel confident lifting onto a mount? What is the maximum weight you can hug against your body and confidently lift? Personally, I had to quit using my 15" Dob after an auto accident 20 years ago ripped up my back, and I couldn't hoist the 65 pound mirror box any longer. That didn't bother me as much as not being able to lift my own kids anymore. My back has healed up enough to lift 40 to 50 pounds with only some soreness afterward, so the 8" Dob is okay to use. I do better lifting if I can keep the weight close to my center of gravity and my back straight. That's why moving my 8" Dob isn't so bad. In contrast, trying to lift my fully rigged alt-az mount on a tripod with a 90mm APO and a 127 Mak is a whole lot more challenging due to the awkwardness of the whole rig despite it weighing about the same. It can't be hugged close to my body, it's top heavy, and it wants to catch on the doorway going out. I don't like rigging it up outdoors for multiple reasons, so multiple trips are not an option.

Are you saying the OTA is too heavy to lift onto a mount or that the OTA would be too heavy for your current mount? My 127 Mak was showing just as much detail on Mars the other night as my 90mm APO triplet, but not as much as my 8" Dob. I would lean toward a 6" f/8 for 8" f/6 Dob, perhaps mounted in aluminum rather than particle board if weight is an issue.

I can't recall any 9" Dobs, but Starmaster used to make an 11" Dob.

There's the 6mm TV Ethos and Delos, Vixen SLV and NPL, Tak Abbe Ortho and Starbase Ortho, Orion LHD and Edge-On Planetary, Antares Speers-Waler Series 4, Astro-Tech Hi-Grade Plossl, Fujiyama (KK) HD Orthoscopic, Burgess Optical Ultra Mono, Vernonscope Brandon, Baader Classic Ortho, Altair Lightwave LER, Smart Astronomy Sterling Plossl, many 58 degree TMB-type Planetaries, many 66 degree Expanse-type wide fields, and many 50 to 52 degree Plossls. So, agreed, there's not much to choose from at 6mm. 😉

I've used this eyepiece in multiple telescopes that are flat field or close to it and have never noticed any appreciable field curvature in it. The only thing I've noticed is that the last 5% to 10% starts to fuzz out which no amount of refocusing will correct. You can see this loss of edge sharpness in my eyepiece AFOV comparison image below: These were taken through an AT72ED refractor with a TSFLAT2 field flattener ahead of the diagonal at the proper spacing.

A simple way to check for atmospheric or local thermal effects on seeing is to focus on a bright star and defocus it to spread out its light into a circle. Is the circular image nice and steady or does it wobble and constantly change? If the latter, you're never going to get sharp images at high powers. I'm not saying that is what is causing your issue, but it can be easily diagnosed and eliminated as a cause with this technique.

Binoviewers introduce spherochromatism, not spherical aberration. Basically, GPCs reduce spherochromatism by slowing down the light cone. Also, increasing power by using GPCs instead of higher powered eyepieces reduces the appearance of collimation issues in the binoviewer. So, GPCs/OCAs/OCSs are a win/win all the way around. Binoviewers can introduce spherical aberration indirectly in certain telescope designs such as SCTs by increasing the required back focus to account for the binoviewer's additional optical path length. This is because SCTs have increasing spherical aberration the further off the designed back focus distance the focal point is moved by moving the mirror to reach focus. Again, a GPC can return the back focus to the optimal distance to minimize spherical aberration. However, the SA is not caused by the optics of the binoviewers, only its optical path length.

Here's a very recent thread on CN comparing these two eyepieces.

When did this happen???? 🤔

Someday I should try comparing the color correction differences between my f/5 ST80 achro, my f/6 72ED, and my f6.6 FPL-53 triplet 90mm on various subjects. How much contrast on various subjects is gained with each step up in color correction? I know that spherical correction also plays a big role as well. I'll have to figure out how to separate the effects of the two of them first.

You'll need to try decreasing the exposure on your phone. Pull up the image tools and look for EXP or similar and drag the slider to -2 at least. It's likely overexposing the image trying to make the black background 18% gray.

Focus on a star at the edge of the eyepiece and rack focus on either side of that best focus. If the star distorts into a tangential line on one side of best focus and a radial line on the other, that's astigmatism rather than coma you're predominately dealing with. If it looks basically the same on either side like a teardrop fanning out away from the center, that's probably coma. If the star splits into a rainbow radially, that's chromatic aberration.

Here's some daytime images comparing various fringe killer filters: Most folks find the Baader Contrast Booster the most aggressive. And this one shows how much of the spectrum different filters suppress: The Contrast Booster works so well because it effectively cuts all violet and a bit of green-yellow-orange in the middle to reduce color shift.

If you want to do it justice, then you'll just have to get the TV Paracorr T2.😉 If you want to go cheaper on it, then there's the Explore Scientific CC or the GSO/Revelation CC. I have the latter, and it just needs a 25mm extension tube to clean up 95% of the coma at f/5 to f/6. It does need to be removed for high power work because it contributes a bit of spherical aberration that the TVPT2 doesn't.

Dobs are dirt simple to operate. Just point and look. Then nudge-nudge-nudge to keep the object in view. The harder part is learning where objects are on the sky, and what to look for through the eyepiece to know you're on an object. Collimation is a learned skill that takes a few tries to work through and become proficient at, but it's not difficult to do. Once done, most Dobs hold their collimation pretty well and might just need a slight tweak to it over time.

We certainly have lots of clear, stable nights. However, I'm near enough to the Gulf that the high heat and humidity all night long during the summer can make observing miserable. Winters are nice compared to up north. No jet stream or subfreezing temperatures to deal with.

That's why I say to double your aperture to see a massive improvement. I went from 3" to 8" to 15", and the improvement at each step was very noticeable. I just can't fathom a 30" at this point. 😆

Yep, Texas. Yee-haw, y'all. 🤠

I have a 3x that I bought first and have almost never used since buying a 2x. It's just too much power for most conditions. Power isn't so much the name of the game, it's aperture. If you want to increase power while maintaining the quality of the view, you also have to increase the aperture of your scope. That's why large Dobs are so popular.

Based on my Meade HD-60 6.5mm (which is a little tight on eye relief), I'd say only 10% of the field at most would be a bit difficult to see. And yes, they'd be quite close in magnification. 5mm would be a much better step if you could find an older 5.2mm XL or an XW. I've measured the 22mm AF70/Redline/Omegon/Ultima LX/etc. field stop to be 28.4mm, or just slightly larger than that possible in a 1.25" barrel. It weighs 16.8 ounces and has exactly a 70 degree AFOV. However, due to slight distortion, it has a 74 degree effective AFOV. I'm guessing this is because magnification decreases slightly near the field stop, allowing more field to be squeezed in.

In my experience, secondary shadow is only an issue during daytime (solar) observations because your eye's pupil is so constricted that it approaches the size of the secondary shadow. For instance, if you are using an eyepiece that provides a 6mm exit pupil, and you have a 35% by diameter secondary obstruction, the secondary shadow is 0.35*6mm=2.2mm. Guess what, your eye's pupil constricts down to around 2mm during the daytime. As a result, all you see in the center of the field is the shadow. You literally have to move your eye off center and try to look "around" the secondary shadow to see anything at all. The two problems with large exit pupils are that they lead to bright background skies and potential loss of usable aperture if your iris doesn't dilate enough to take in the entire exit pupil. On the other hand, they're often the cheapest way to get the maximum field of view possible when choosing a "finder" eyepiece to help with centering objects in higher power eyepieces. The eye cup is super rigid and won't fold down. Since it's a 43mm thread, you could substitute a Morpheus eye cup if you're worried about scratching your eyeglasses. I've done it myself just to prove it works fine. I use many eyepieces without eye guards of any sort and haven't scratched my glasses yet. If there's enough eye relief, you just hover above the eyepiece never touching it. The one time I scratched an eyeglass lens was years ago with a 27mm Panoptic . It had too little eye relief, yet I was determined to see the entire field of view, so I jammed my eyeglass lens into the top of the eyepiece, scratching it on the exposed eye lens retaining ring. I was furious Tele Vue designed it that way. It claims to have 19mm of eye relief when in reality it has only 14mm of usable eye relief with a sharp metal edge around the eye lens.

Yeah, apparently there's a lot of love of astronomy circulating around the UK. 😄

Apparently, it's a Mak in the UK and an achromat in the US. However, I did find that Harrison Telescopes sells the achromat version: https://www.harrisontelescopes.co.uk/acatalog/celestron-nexstar-102-slt-telescope.html

It's like everything in Europe relative to the US. To cover all the costs associated with highly restrictive business laws, goods tend to be more expensive in Europe than in the US. VAT alone adds costs just because every single business in the goods chain has to maintain meticulous tax records should they be audited. This requires additional personnel to maintain those records. In the US, sales tax is only collected when the item is sold to the end consumer. Wholesalers are tax exempt and don't have to maintain any tax records because they never collect any taxes. That's why most wholesalers in the US post "for sale only to the trade", otherwise they'd have to collect taxes on some sales.