Louis D

I use a 2x nosepiece from a Meade 140 barlow to reach focus with my Arcturus binoviewer. It yields about 3x with the binoviewer. Thus, I typically don't go below about a 16mm wide field eyepiece pair in them. I also use a 1.25" diagonal to reduce the amount of in-focus required in my refractor. I can come to focus with just the 2x nosepiece alone in my dob. To get wider, though vignetted, fields of view, I add a 0.5x focal reducer to the nose of the binoviewer while attaching the 2x nosepiece to the front of the diagonal. It yields about 1.25x. For my dob, I put about 2 inches of extension between the two and screw them into the front of the binoviewer (again, 2x closest to the objective). It sort of works there as well. It's mostly useful for taking in wide vistas with both eyes. It's not appropriate for critical observing. My Mak can reach focus without anything additional while increasing the focal length less than 20%. I also have an older Siebert OCA that also yields at least 2x in the dob. It is too long for diagonals, however. It is quite sharp like the Meade 140 2x unit.

How cute. Each gets its own sleeping bag on campouts.

It's certainly not as compact, plus it's long since discontinued, but I prefer to couple my Speers-Waler 5-8mm zoom with my 8-24mm zoom for travel. The exit pupils and powers associated with 5-8mm work better for me than 3-6mm, and I really like the 80 degree AFOV. Perhaps someone should petition TV to make a 4-8mm or 5-10mm version of their Nagler zoom design. The 2-4mm version was just too much magnification for most users, thus it didn't sell well and was discontinued.

Reminds me of one of my cases where I've put pick-n-pluck foam squares back in after reconfiguring my case over the years. I always keep all my foam bits in a box with my small accessory boxes, like the ones for filters and small eyepieces. It seemed like hoarding until I needed to redo my case's layout several times. That foam (the high density version in particular) is expensive to buy separately.

Pretty much from a hand wavy description point of view, that's correct. That's also why Powermate style focal extenders (telecentric barlows) don't mess with the exit pupil. They have a second set of optics between the negative lens and the eyepiece to reconverge the light cone to a near parallel orientation so it doesn't mess with the eyepiece's exit pupil. Increasing the distance between them and the eyepiece has little effect on increasing the power. They're also handy if the eyepiece's fieldstop approaches the size of the eyepiece barrel. Ordinary barlows will tend to vignette the outer field of view while telecentric barlows are completely unnoticeable other than increasing power.

This diagram isn't perfect, but it helps to convey the diverging rays caused by a barlow lens. This diagram isn't too bad either showing the apparent increase in focal length.

Here's another trick to try with removable barlow optical sections. Thread it onto the front of your 1.25" diagonal for you refractor/CAT users out there. You'll get about 3x or so. Because it is a negative focal length lens rather than a positive focal length lens like a refractor objective. By diverging the light rays, it lengthens the effective focal length of the scope. A focal reducer is just the opposite. It is another positive lens and further shortens the effective focal length of the scope.

Some folks just have more discretionary spending money than others. I finally met one big spender who participates on CN. He's a retired executive VP of a well known computer company. Others I've met are full university professors at top schools or own their own businesses. Astronomy is just another hobby to them. Many also have very well equipped wood working shops, boats, vacation homes, motorcycles, etc.

If you leave it on continously, then yes, that's a good point in favor of the Telrad. I tend to turn either on for at most 10 seconds at a time, and then only a few times per night, so 250 hours is a very long time indeed. I picked up a couple of used Telrads for $15 apiece that were a little rough to replace my fried one. I just won't ever pay new prices for one again, though.

It is if it uses a power source susceptible to corrosion and there's insufficient shielding between the power source and the electronics to prevent damage due to caustic gasses from the power source. They could have chosen button cells like Rigel, but they didn't.

I have a Telrad with AAs that corroded in it. I haven't been able to get it working again even with a new battery holder soldered in. That happened in well under 10 years. My Rigel QF still has the same button cell going strong after 12 years and no corrosion evident.

What if you set your latitude to 90 degrees North? That way, it would track using only the azimuth axis while wedge mounted. You couldn't use it to locate objects, but it should track once pointed properly. Does this mount even have an option to set latitude or does it strictly depend on star alignment to track?

As I've said in a previous post somewhere on SGL, I can't observe standing because I hover above my eyepieces. I never use eyecups because they smudge my eyeglasses. When sitting, I don't find it to be an issue at all. My backyard is dark enough that I don't have issues with stray light. If my wife flips on a light in a backroom of the house while I'm outside observing, then yes, it can be a problem. I just cup my hand around the edge of my eyeglasses and that usually takes care of it until I can get her to turn the light off again. I haven't ever noticed reflections from the outer casing or the eye lens, just my eyeglasses. The one thing that is annoying about that large flat top is that you have to tilt your head to the side to get your nose out of the way to get your eye in close enough to see into the eye lens. It's even worse with the original mushroom top ES-82/Meade UWA.

Having tried plenty of 40mm-ish widest (or near widest) field 2" eyepieces over the years, I recommend you skip the mid-range eyepieces being recommended and go for the Explore Scientific MaxVision 68° Eyepiece 40mm (2") while they are still available. You'll get near TV 41mm Panoptic performance for a fraction of the price. If you decloak it, you'll bring the weight and girth down to the same level as the Panoptic. I can attest that once you decloak it, you'll have about 29mm of usable eye relief. It's basically sharp to the edge at f/6. I also have no problems holding the view with eyeglasses.

Don't feel bad. I have four cases now. A-team, B-team, binoviewer and eyepiece pairs and OCS, and starter eyepieces not worth selling but kept for sentimental purposes and to compare with how far I've come in 19 years of observing. Then there's the large tool box of odds and ends like T-mounts, extension tubes, Tamrac folding filter wallet, 45 and 90 degree erect image diagonals for spotting scope duty, single vision infinity corrected observing glasses, etc. Sometimes I wonder if I'm an amateur astronomer hoarder.

I think being OCD is not unreasonable when dealing with an eyepiece collection worth thousands of dollars for some observers. I'm also OCD with my camera equipment for similar reasons.

For the most part. I just drop the end caps into the slot where the eyepiece would normally be for safe keeping. When I put the eyepiece back, it just lays on the caps until the end my observing session if I know I'm going to using it again. For my upright-stored eyepiece cases, I'll sometimes pop the top cap back on but not bother with the bottom cap since it can be hard to fish out of the depths. I keep my cases (yes, I usually have two cases open at once) at arm's reach from the telescope, so no need for pockets and such to store eyepieces temporarily. At the end of the session, I methodically put everything back together and in the correct spots. Tedious, but worth it.

Yes, and steviebee was first describing a classic ghost image, but then started describing a classic comatic image. It's certainly possible both can be caused the objective being spaced incorrectly and/or tipped.

Ah yes, I see that now in the original posting. You're probably correct about the objective. My only other thought is that a short refractor will have field curvature that looks like coma until the star is refocused.

Is this similar to your scope? If so, it's an f5 parabolic mirror and that's probably where your coma is coming from, although it seems a bit excessive from your description. If you were in the US, I'd recommend you watch for a second hand GSO coma corrector to clean up most of this for not a lot of money (usually under $90). However, I've yet to find anyone selling it in Europe under any brand. Maybe someone more familiar with European retailers could chime in here.

Is this similar to your scope? If so, it's an f5 parabolic mirror and that's probably where your coma is coming from, although it seems a bit excessive from your description. If you were in the US, I'd recommend you watch for a second hand GSO coma corrector to clean up most of this for not a lot of money (usually under $90). However, I've yet to find anyone selling it in Europe under any brand. Maybe someone more familiar with European retailers could chime in here.

Were you using the 45 degree Amici prism diagonal? They can cause a diffraction spike when a star crosses the center line. Is the comet tail the same color as the star or is it more of a rainbow? If the former, it's coma. If the latter, it's chromatic aberration. Does it grow longer the farther the star is from the center? Does it always point back to the center as the star is moved around the FOV? How does it look on either side of best focus? Which way does it point when the star is dead center? Have you swapped eyepieces to make sure it's the eyepiece and not miscollimated or pinched optics?

I think you're absolutely correct. Everyone is always saying they're shortening the path with a prism to increase available backfocus, when in fact they're lengthening the light path in glass to increase backfocus. You want to shorten the air part of the path as much as possible with stubbier connectors, but you want to increase the glass part as much as possible.

I'm no optical expert, but that diagram seems to show the exact opposite of what is common knowledge, that prism diagonals shorten the path length over a mirror diagonal. I'm still working out what is going on. The angles of refraction seem correct. The converging beam is actually made to diverge somewhat within the prism, lengthening its path while in the glass. I always thought just the opposite was happening and accounted for the shortened path length.

Have you seen this same ghosting using other eyepieces? How about the same eyepiece in your Skywatcher 200P? Based on the above sentence, it is possible you're seeing a reflection of the moon's image reflected off of your cornea back into the eyepiece. Try to narrow down which element is introducing the reflection.