Louis D

This depends heavily on what distance your eyes are fixed focus at. In my case, my eyes focus somewhere around 8 to 12 inches without correction; thus, I just look under my distance-only eyeglasses to read things while at the scope. My eyes have yet to change from highly myopic to somewhat more farsighted as I age. The lower part of my bifocals has almost zero distance power, just astigmatism correction. Surprisingly, my 2.0 diopters of astigmatism don't bother me much at all when reading for short periods of time. I actually have my optometrist prescribe the reading part of my bifocals for focus at 18 to 24 inches so I can read things laying on a table without having to lift it. That also makes them handy for reading things on shelves in stores without having to get so close. However, I despise the near/far line intruding into my field of view with wide field eyepieces; so I have the distance-only pair for astro.

Telrads have a separate mounting plate than can either be stuck on with included double sided tape or bolted in place after drilling a couple of holes in your tube. ScopeStuff sells an adapter base to mount a Telrad into a Synta/Vixen finder base. There are triple finder mounts on ebay. I've got a couple of them. They are very sturdy. The Telrad and RACI would probably need to use the far opposite shoes to fit. The middle one might go unused.

I could have all sorts of eyepiece suggestions, but I would need more information to narrow it down. What's your budget per eyepiece and in total? Do you have strong eye astigmatism and need to wear eyeglasses at the eyepiece? Do you like really wide apparent fields of view or are you satisfied with somewhat narrower fields of view? What objects do you like to observe the most? Here's a group shot of my eyepieces I recently took, so there's plenty of choices in eyepieces out there:

There's also the GSO 2" Linear Bearing Crayford Focuser that might work for you. The JMI EV-1n might work for your needs. I have a similar single speed focuser from the 90s, and it works great under heavy loads. Of course, there's always Feather Touch focusers, but they're on backorder. If the focuser has a rack and pinion on it, you shouldn't have slip issues in my experience with a 2.5" focuser on my TS-Optics APO refractor.

I agree. However, Mars at the last opposition just looked like a featureless orange fuzz ball using it (as well as in my 5.2mm Pentax XL). I swapped it for my Arcturus binoviewer, Meade 140 Barlow nosepiece (to reach focus) operating at 3x, and a pair of vintage B&L 15x (17mm) microscope eyepieces. Suddenly, the image looked like a sharp photograph with a wealth of detail. I swapped back, and the image was as before. Two eyes were definitely better than one that night. The image of Mars also appeared bigger to my mind's eye with both eyes working together. I can also see a wealth of detail on the full moon with BVs that are simply swamped in too much glare with one eye. I think Mars at its brightest must have been similar.

I bought a pair of distance only eyeglasses online from EyeBuyDirect for $20 5 years ago. They rarely need cleaning, so they don't get much in the way of microscratches that my daily wear bifocals get. That, and the entire field of view is in focus at the same time with no intrusive line. I've never tried varifocals, but I can't imagine how they can show a 100 degree AFOV all in focus at once. I bought the lowest index plastic lenses because they introduce the least chromatic aberration at the edges of the view when not looking directly on-axis. Not true with long eye relief (>18mm usable ER) eyepieces for most folks. I have a tall nose bridge that also limits how wide of an eyepiece top I can tolerate. It also prevents me from using many fat eyepieces in my binoviewer even if they are narrower than my IPD. Here is Tele Vue's Dioptrx chart that is a good guideline for most folks: Since I'm a very picky observer and notice the least bit of astigmatism in the view, I would shift the line downward by 0.5mm EP for folks like me with 2.0 diopters of astigmatism or more. You will probably need a minimum of 17mm to 18mm of usable eye relief in my experience. Ask on here before trusting even Tele Vue's ER specs since they are quoting design ER from the center of the eye lens. That's not helpful for eyeglass wearers. Most of the BSTs have 12mm of usable eye relief due to eye lens recession. The 25mm is the lone exception with 17mm ER and is quite usable with eyeglasses. The others will require tipping your head a bit to see the edges. Probably true. You should be good without eyeglasses using a 25mm eyepiece, although just. You can use 2" eyepieces with a Synta 127 Mak with the proper Mak to SCT thread adapter, SCT visual back, and 2" diagonal to get to larger exit pupils. There will be some illumination falloff (vignetting) with eyepieces having a larger than 27mm field stop. I also see halo reflections off the inside of the rear baffle tube as bright stars pass the edge of it. Below is an image showing the difference in TFOV between a max TFOV 1.25" and 2" eyepiece and demonstrating the associated edge darkening.

I vaguely recall Tamiji Homma on CN doing a comparison via an eyepiece turret on his APO some time back. I don't have time tonight to search for it, but perhaps you could find it. This might be it, but I recall a longer post on the subject.

Precisely what I was thinking of when I asked if was possible to get rid of the long 1.25" adapter train. Why doesn't the Tak come with a 2" visual back and 2" to 1.25" adapter like most other fracs? How are you supposed to use 2" eyepieces in it straight from the factory?

I'm not familiar with that Barlow. It could be because it's a relatively short Barlow. Bummer that didn't work either.

The TV Barlows are not 1.25" filter threaded. They're somewhat smaller and won't engage.

Did you try putting the Barlow into the wedge? It's too bad the threads on the TV Barlow nosepiece aren't 1.25" filter threaded, then you could dispense with the long Barlow barrel and definitely reach focus. Why the long train of step down adapters (three by my count) on the back of the focuser? If it did the step down in one low profile go, I'm sure you could reach focus.

I use the nosepiece of a vintage Meade 140 2x Barlow on my Arcturus BV to reach focus even in my Dob which has only 20mm of in-focus left. It operates at 3x in that configuration. Check the astro classifieds and maybe put out a wanted ad. There are some other screw in Barlow/OCA/OCS/GPC options out there as well to help reach focus.

No applicable for Herschel wedge usage.

Dust has to be really heavy before it affects the views in any appreciable manner. You can stick your hand in front of a large Dob's opening while observing, and the most disruptive effect will be from the heat waves shimmering off your hand in cold weather, not the actual blockage. Overzealous cleaning of optics can lead to micro-scratches that will affect contrast by increasing light scattering. It's generally best to leave light dust evenly coating a mirror or corrector plate rather than trying to clean it off.

If your Dob is balanced to handle 30mm 82 degree, 40mm 68 degree and 17mm 92 degree eyepieces that each weigh over 2 pounds plus a coma corrector, you'll do fine with a binoviewer loaded with a Barlow/OCS/OCA/GPC nosepiece and two compact 15mm to 20mm eyepieces that your nose will fit between. I find that at 3x with the 2x Meade 140 Barlow nosepiece in my BV, I don't use my GSO coma corrector because it just adds axial spherical aberration without noticeably improving the edges. This lightens the load on focuser a bit. At an effective f/18, I find the SVBONY 68° Ultra Wide Angle 20mm eyepieces to work great:

I would get the 40mm ES-68 if you want to absolutely maximize your possible true field of view. It is the same optically as my 40mm Meade 5000 SWA. There is just a bit of astigmatism in the outer field of view. If you want absolute perfection, then the 41mm Panoptic is the way to go. The difference in price is only $56 here in the US. A lower cost alternative is the 40mm Pentax XW-R which has just a tiny bit more true field of view, a bit of field curvature (not visible to those with younger eyes that still focus properly), and a bit of edge astigmatism. It's $120 cheaper than the 40mm ES-68 here in the US. It's also considerably lighter. Stars will be a mess in the outer 25% of the field of view without a coma corrector at f/5 regardless of eyepiece. You would see a massive improvement with just the GSO/StellaLyra CC and a 25mm M48 spacer ring. It's been good enough visually for me that I've not felt the need to get a Paracorr II. It's much easier to take in a 68/70 degree field of view all at once than an 82+ degree presentation. It's hard to appreciate what is going on in the periphery once you get past 70 degrees without looking directly at it. At f/5, the exit pupil is going to be getting a bit large with a 40mm (40mm/5=8mm), so the sky will be somewhat washed out. This isn't a bit deal with bright star clusters like the Pleiades, but the hazy nebula within it will be hard to detect. You'd be better off with a smaller scope and smaller exit pupil to observe the dusty nebula around the stars to darken the sky background a bit. You could always bump up to a 20mm to 30mm eyepiece in your f/5 scope to darken the sky background and observe parts of the dusty nebula in sequence rather than all at once. At f/5, a 30mm eyepiece provides a 30mm/5=6mm exit pupil, which is much better, but still overly large. The background sky will still be somewhat bright. Personally, I prefer the somewhat washed out sky and easier to take in view of the 40mm eyepiece over the 30mm eyepiece. Another option are the various 20mm 100 degree eyepieces out there. There's the APM, Myriad, Astro Tech versions which are lighter, lower priced, and better performing than the ES-100 variant. You lose some true field of view while massively darkening the sky (20mm/5=4mm exit pupil). However, eye relief is tight and it is impossible to see the edge sharply without rotating your view way off axis. There's no magic bullet here short of mounting a smaller scope to your f/5 scope for wider true fields of view.

In the 30mm ES-82, the outer 10% has CAEP, chromatic aberration of the exit pupil. The red and blue ends of the spectrum focus above and below the average exit pupil distance. The effect is to impart a color cast at the edge. At night, you can't see it unless you move the moon or a planet out there. A neutral colored planet like Jupiter splits into distinct red and blue images. Each is fairly sharp, but they do not coincide in the field of view in my experience. If you strictly keep objects centered and only look on axis, you will never notice this. However, if you have an undriven mount and let objects drift from edge to edge, you will see it. The field of view is very flat and sharp, it just has these slight issues at the outer part of the field. That, and there is a bit of astigmatism out there, but it is relatively minor. What's your budget and what are you hoping to view with any of these eyepieces and with what telescope?

Do you need to wear eyeglasses or not at the eyepiece due to astigmatism? I prefer my 30mm APM over my 30mm ES-82 and 27mm Panoptic due to much better eye relief. That, and the APM is sharp edge to edge at f/6 with no ring of fire like the ES-82. The ES-82 gives a more immersive experience, but is tiring to use unless you pull back to the same field as the APM. The 35mm TV Pan has been produced in two versions, one with a recessed eye lens, and one that's closer to flush mounted. If you buy used, make sure to inquire which type it is. Those who don't wear eyeglasses prefer recessed while those who do prefer flush mounted. I've used the 35mm Pan at star parties, and find it very well corrected and usable with eyeglasses if flush mounted. I prefer my 40mm Meade 5000 SWA or 40mm Pentax XW for widest field views. At 35mm, my favorite is the discontinued Baader Scopos Extreme. It is quite usable with eyeglasses and extremely sharp in the inner 60% of the field, and just barely falling off in sharpness to the edge.

Thanks guys. Makes total sense. I forgot about the lack of IR filtering and high IR sensitivity on those cameras. I have an old Olympus C-2000 that I use with an R72 filter for poor man's IR photography. It was the last (or nearly so) Olympus digital camera without an IR-cut filter ahead of the sensor. It's so sensitive to IR, I can use normal shutter speeds to photograph objects and people without motion blur.

I hope this isn't a stupid question, but why does the no filter image have the most color shift of the four images (I see it as pink on my monitor)? Did you use a weird color balance on your camera for all four images, and it balances out the color shift of the filters on the other three but ruins it for the no-filter one? It just seems counter intuitive that the filtered images are more neutral than the unfiltered image.

I'm glad to see the LV/LVWs in there to complete the collection. Very nice indeed.

Is there a reason you're averse to using a 1.25" to T2 nosepiece adapter? There's one one ebay UK for £7.99+S/H: Are you super concerned about edge vignetting or image train tip/tilt/sag to want it integrated into the Barlow?

Right there with you. Other than looking at large star clusters/fields, they aren't all that useful. Everything is jumping about because your own jitters are being amplified 6x to 15x, so you can't see anything but the brightest stars and planets/moon. If you're going to put the binoculars on a tripod, you might as well put a telescope on there. The viewing angle will be much more comfortable unless you bought a dedicated pair of astro bins with 90 degree prisms for $1000+. At that point, why not just buy a telescope? I had bins for years, but it took a telescope to really get me going on amateur astronomy in my 30s.

Maybe a nice used 12" to 15" custom truss Dob. They come up used on American astro classifieds for a fraction of new price all the time. As long as you're willing to drive part way to pick-up, they're a good deal.

Talk it over with @Olli who just went with a Sky-Watcher SkyMax-127 AZ GTi after starting the below thread trying to replace a Dob: