Louis D

With a Heritage truss type Newt, you'd have to make sure they're using a well fitted shroud around the truss poles to keep stray light out of the light path for daytime usage. This is especially true if you're going to do solar observing with a full aperture solar filter. What good is a filter if the sun can come in from an angle via the open tube?

Glad to hear you got it sorted enough to resume observing. You may want to fill in the undercuts with pinstriping tape to make it easier to get good alignment when swapping eyepiece pairs in the dark.

If you use a very high quality Barlow, the combination would probably work very well. You do end up with a long lever arm sticking out of the diagonal which can complicate balance at high altitudes.

But your original post on the subject simply stated that "false colur becomes more of a problem the shorter the focal length" without reference to holding the aperture constant. This made it sound like any shorter focal length scope will have higher CA than any longer focal length scope as is the case for field curvature (shorter always has more FC for a simple doublet design regardless of aperture). More accurately, the shorter the focal ratio (or commensurately, focal length) for a given aperture increases the amount of CA.

Agreed. My 14mm Morpheus gets little use because it is just too close to both the 17mm and 12mm ES-92s I use. I then jump to either my 10mm Delos or 9mm Morpheus. I kind of want to get an 8mm Delos to bridge to the 7mm Pentax XW I have.

CA (chromatic aberration) is a function of aperture and focal ratio. Focal length alone won't give you any indication of a scope's CA. The following table shows how CA behaves as a function of aperture and focal ratio: You can cross reference individual telescope's specs with this table to get a feel for how good or bad the CA will be for it. Additionally, moving to FPL-51 or FPL-53 doublets or even triplets allows the green and yellow areas to slide to the left. Field curvature is strictly dependent on focal length. It's roughly FL/3.

@Don PensackHow does the APM 12.5mm compare to the Apollo 11mm?

M4 is the width and thread pitch combined (technically, M4-0.70). Length? Probably no more than 5mm assuming thin wall tubing for the refractor. Just measure the thickness of the scope's tubing and the depth of the threads in the focuser (thickness of the focuser flange) and add them together. It's probably okay to go a few millimeters beyond that. You just don't want long screw tips protruding into the light path. I'd also get stainless steel screws to avoid corrosion issues.

The 22mm Nagler is nice. I was able to find one second hand for about $270, IIRC. It has a ding on the outer housing, but the optics and insertion barrel are fine. I find I do have to touch my glasses to the top of the eyepiece and push in slightly to see the entire field (the eye lens is only 30mm in diameter compared to 36mm/37mm for the Morpheus). However, it does not have the finicky exit pupil of its 17mm and 12mm stablemates, so it is usable to the field stop. It feels about like 16mm of usable eye relief compared to the Morpheus's 18mm or more of usable eye relief. The ES-92s are right in between at about 17mm of usable eye relief with their 43mm eye lenses. If you don't push in, you can easily see 70 degrees as with the AT AF70 (both have 30mm eye lenses).

Probably would make for an interesting discussion in the lounge as to why Bresser and TS-Optics don't market their wares more in the US.

If it's a GSO focuser, they're M4 sized.

Excellent. Unfortunately, neither made it to this side of the pond. 🙄

Getting off-topic (sorry OP and mods) Indeed, yours looks similar to the one on my TS-Optics FPL-53 triplet 90mm APO minus the camera angle adjuster. However, the one in the Bresser description and the CN review describe it as single speed with plastic wheels: Did you mod those features with aftermarket parts? You're right, though, that 2.5" focuser is nicer than the 2" AT72ED focuser in that it doesn't slip because it is a R&P focuser: Otherwise, they're very similar in smoothness and resistance to tilt.

I have similar Arcturus binoviewers that I have to keep the diopter adjusters tightened all the way down to avoid wobble and decollimation. I also have to push undercut eyepieces tightly into the collets while tightening them down to avoid them tilting in their holders. If I spin the diopter adjusters upward, I can watch the image in that eyepiece decollimate and trace a circle back to its starting position once it's been rotated 360 degrees. Maybe you'll get a mechanically better unit with an exchange, but I would temper my expectations. These binoviewers cost 1/3 to 1/4 what the Maxbrights cost, so it may not be reasonable to expect the same level of mechanical perfection in both.

The problem you'll run into around 18mm to 20mm is it's a no man's land when it comes to wide field and long eye relief in large part if you avoid the various 17mm offerings (Morpheus, ES-92, and . There's the 20mm Pentax XW with field curvature that can be an issue for folks with presbyopia (bifocal wearers), the 22mm Vixen LVW which has long been discontinued but otherwise excellent at 65 degrees, the 22mm Nagler T4 which is expensive and a bit tight on eye relief, the above mentioned 18mm and 20mm UWAs which all have very limited eye relief, and the 22mm Astro Tech AF70 which is also known as the Celestron Ultima LX, Olivon 70, Omegon Redline SW, Skywatcher 22mm SWA-70, and several other brandings. It is very comfortable with eyeglasses, flat of field, and sharp out to 90%+ of the field at f/6 with a true 70 degree field.

You might want to get a 3.2mm to 4mm eyepiece for nights of exceptional seeing. I haven't tried the 3.2mm Starguider, but the 3.5mm Pentax XW is very nice. If you have the money, I'd go for a 17mm ES-92 to replace the 18mm Starguider and a future 18mm to 20mm UWA like a 20mm Nagler T2/T5, 20mm Meade UWA, or 18mm ES-82. The ES-92 eye relief is very generous, the contrast if phenomenal, and edge correction is excellent.

Optically the same, but with a stainless steel barrel making it heavier than the APM version. I would lean toward the 12.5mm. I've found I like observing around 75x quite a lot with the aperture you're using because it yields a near optimal 2mm exit pupil. As for Morpheus vs. APM, I'd probably lean toward the Morpheus since from what I've read, it has more comfortable eye relief for eyeglass wearers and slightly better edge correction. The APM seems to excel at central contrast and resolution like the 12.5mm Docter/Noblex it tries to emulate.

You can't even use long focus Barlows in a refractor's diagonal because they require more in-focus than most of them have to spare. The difference is that a Newtonian focuser essentially has no bottom (at least until you hit the secondary) while a refractor's diagonal only has about room to accept the first 1.5" of a barlow before bottoming out on a hard stop or hitting the diagonal's mirror/prism in a 2" unit. Thus, you can just keep inserting the Barlow in the Newtonian focuser until it comes to focus which is usually before you contact the shoulder. This can be 2" to 3" or more. This just isn't an option in a diagonal, thus the popularity of shorty Barlows which can be used in either.

Yes, not sold in the US, so not familiar with it at all. I think I'll stick with my AT72ED for widest field scanning of the skies. I don't think I'd want to trade off excellent color correction, two speed focuser, and all metal construction for an additional 30mm of aperture, though. It would be intriguing if they went with an FPL-53 triplet to bring down the false color to at least ED levels. Of course, the price would be at least $1000 higher.

After reading the review's mention of field curvature, I'd have to recommend budgeting for a TSFLAT2 to flatten the field if you're going to use it for widest field scanning of the skies. I use one with my 432mm FL 72ED to good effect. Screwing it onto the front of the rather long 2" diagonal insertion tube of my 2" GSO 99% dielectric diagonal resulted in slight overcorrection, causing field curvature of the opposite sign. Since that diagonal has SCT threads, I replaced the nosepiece with a 15mm SCT to M48 adapter tube and thread the TSFLAT onto the end of it. The resultant field is just about perfectly flattened.

Rather confusingly it claims "Richfield telescope with ED glass lens" and is also an "Achromatic Refractor". If it has a 4" ED lens for that price, I'd be very impressed. I wonder at low powers how much violet fringing would be visible. I also wonder how well spherical aberration is corrected. I'm just trying to figure out if it might work well enough with a 35mm Aero ED if there's all sorts of other aberrations to deal with. The outer 25% of the field would be a bit fuzzy with it, but if there's a bunch of other stuff going on out there, it might not seem so bad. It would definitely come close to maxing out the TFOV possible.

What refractor are you using that's a 100mm f4.6? Either it's an exotic ED/APO (Borg/Pentax?) or it's an achromat that has loads of color fringing. The problem at f4.6 is trying to keep the exit pupil below 7mm. A 7*4.6=~32mm would be your max usable eyepiece focal length to possibly make full use of your available aperture. Another problem is finding an eyepiece that can handle the steep light cone. I agree that the 30mm APM UFF would probably be a good bet for you. However, you're only going to get about 4.7 degrees TFOV, a bit shy of the 5 degrees you desire.

I'm glad someone got some use out of this old thread. @Pawel only posted once and hasn't even visited since that first day he/she joined and posted, so didn't even ever read all the responses.

One problem, the 40mm Aero ED has been sold out worldwide for several years now. There's been no sign of new production. The 35mm Aero ED is nearly as wide, TFOV-wise, and wider AFOV-wise. Correction isn't quite as good, but it's not bad compared to some other offerings in this price range. Eye relief is a bit tight on it because the eye lens is recessed 7mm for no apparent reason. It is nice and light, so it won't throw off your scope's balance. The 40mm ES-62 is basically the same as the 40mm Meade 5000 Plossl. It's great in the inner 50%, and then gets worse toward the edge. However, it lacks much distortion, so the moon stays nice and round as it moves across the field. Eye relief was great on the Meade and will probably be very good on the ES-62 as well. Here's a comparison image of a bunch of my widest field eyepieces taken through a field flattened 72ED refractor:

I generally only clean when I notice bright objects noticeably blurring as they move across the field of view. I then back away and try to identify the culprit which is usually a smudge or eyelash goo.