Louis D

We went round and round on this in another thread, and I tried to use large lenses and presented the mediocre results there, but the results were inconclusive. I will restate that the image from the camera phone exactly mirrors my visual impression of the field of view, right down to where some eyepieces have zones around 70% out that go soft and then get sharp again toward the edge. Visually, those areas look "jittery" depending on how you move your eye. Clearly, there's some sort of aberration going on at the exit pupil, possibly SAEP related. The one exception as I've previously stated is the portrayal of field curvature. Eyepieces with a curved field look much flatter in the small camera lens than to my presbyopic eyes. It probably mirrors how younger eyes perceive the field of view. I suspect the enormous depth of field/focus of these tiny, wide angle lenses are able to bring the curved field into focus from center to edge. Despite these lenses operating at f/1.7 to f/2.5, they still have lots of depth of field because of their incredibly short native focal lengths of around 4mm or less.

Doesn't it have a 3/8"-16 mount on the base underside to attach it to a wide range of photo tripods? If not, my apologies.

Don't overlook the 9mm APM XWA 100°. It's lighter and cheaper than the ES alternative, and most reports rank it as just as good if not better. Excellent choice. My preferred eyepiece at that focal length. The ES-82 is wider, but has issues with CAEP (Chromatic Aberration of the Exit Pupil) aka, ring of fire at the edge. You'll find yourself either leaving it in the focuser for extended observing periods or removing it. PMs and Barlows are just too clunky to be swapping in and out regularly. I would spend the money on dedicated eyepieces, myself. That, and you'll have a really long optics train hanging off your focuser. I would probably recommend 13mm and 4.77mm APM XWA 100° to fill the power gaps instead. The latter is 110° which will be really helpful at high powers with a nondriven Dob. Pick up a cheap moon filter off of ebay or similar if you feel the need. Pick up a quality OIII first and UHC second. Don't go cheap on either one. Astronomik, Lumicon, and several others are quite good. As long as neither of you has astigmatism (CYL correction), you'll both be fine without eyeglasses at the eyepiece. You can just focus out the distance correction. Depending on how strong the prescription is, the field stop may get a bit fuzzy because you're moving the image circle away from it to compensate for the observer's eye.

Don't ask, don't tell. It was the 90s afterall.

Found a good clip of the self-destructing tape for our younger contributors:

Also remember that as the f-ratio goes down, the central obstruction goes up, and contrast on planetary details goes down with it. Below is a simulation of the effect CO has on planetary details: The effect is subtle but real.

Does anyone know why Synta hasn't switched over to a GSO style focuser that actually makes sense when switching between 2" and 1.25" mode? It would prevent a multitude of problems for users of their Dobs.

One located in Australia or in orbit, I would think. Right now, the planets are a bit low from the northern hemisphere, so you really need to get south.

They're generally listed for $4000 to $5000 in the US astro classifieds, although that doesn't mean they sell for that. Thus, £2,000 would be a quite a bargain.

I've got that same situation with a $50 dielectric diagonal from Amazon. It's a very nice diagonal except for the fact it pushes all 2" undercut eyepieces up and out of the holder because the compression ring is too close to the top. I'll have to try removing the ring and replacing the screw with nylon one to see if that improves matters.

Just try to find eyepieces that you like the view through and are comfortable to use and you'll be fine.

Based on reports I've read, the BHAs would be decent buys if they cost around $100, not $200+. They are improved Erfles, but not enough to justify the additional cost. There is significant astigmatism in the outer 25% of their fields. The 1.25" adapter on them leads to heavy vignetting even in a true 2" light path, so not recommended. It's just too close to the field stop. The 30mm APM UFF, which is now sold under Altair, Celestron, Meade, and a few other brands, is insanely good for the same money when you get a true 2" diagonal. The 35mm Aero ED is a better deal than the 36mm BHA at around $100+ if you can find it in stock. They're recently discontinued, but there might be a few still available in UK/Euro stores. Don't back order them, they won't ever come in.

I agree it feels like 18mm in actual use, but the point where the image circle is smallest is 16mm from the flipped down eye cup using the projection method. I remeasured it a few times because it didn't align with my ER experience with it. It's not the only eyepiece with this divergence between measured and "feels like" distances. For instance, the 22mm AT AF70 also has a repeatably measured 16mm or usable ER, but feels like 18mm in use (eyeglasses just above rim). The 22mm NT4 has 14mm of measured ER, but feels like 16mm in use (I have to push in a bit on my glasses). The 17mm ES-92 has a measured 16mm ER, but feels like 17mm in use (eyeglasses just touching). The 35mm Baader Scopos Extreme has 16mm of measured ER, but feels like 18mm. That last one actually has about 35mm of design ER thanks to its 47mm diameter eye lens, but the eye lens is recessed about 17mm, IIRC. As an experiment I screwed off the top and put a flat lens retainer over it to get to about 30mm of ER. Even for an eyeglass wearer, that was too much ER! I had trouble holding the exit pupil because I had no frame of reference touching either my glasses or nose. I guess I need a measured ER and a "feels like" ER. The problem with the latter is that it is very subjective. I'm going to try to measure it someday with a cardboard tube wrapped around the eyepiece and pushing it down with the phone's camera until the field stop pops into view. I would then measure and record the distance from the top of the eyepiece to the top of the tube. After measuring a bunch of eyepiece ER distances this way, I should be able to come up with a constant offset that accounts for the location of the camera's entry pupil inside of it by comparing these numbers against the ER distances measured using the narrowest projected image circle.

If you have an optics test bench as Ernest does, you just move a vernier to slide the eyepiece side to side independently of the image forming lens. Something along the lines of putting this: on this: If I came across some well priced, surplused equipment in this realm, I might go this route someday. However, I'm not really that serious about getting exact results. Actually, I just remembered I have one of these macro focusing rails that could be used for this with a few clamps:

I believe Ernest uses a telescope with micrometer eyepiece to look into the exit pupil of the eyepiece to measure the aberration spot sizes. I also believe he always uses the center of the lens and moves the eyepiece across its central axis to take measurements so lens edge aberrations do not figure into the equation.

I've measured the Morpheus 9mm to have a 78° AFOV both via projection and image photography. The 14mm comes in at 77°, and the 30mm APM UFF comes in at 72°. Usable eye relief was measured to be 20mm, 18mm, and 16mm for the three, respectively. Your observations about AFOV and ER match up pretty well with my measurements.

I thought SA referred to Spherical Aberration, a common issue with mass produced, short tube refractors. My ST80 from 1999 has loads of it.

It boggles my mind that my ancient (90s vintage) Sky Commander DSC can do a bang-on two star alignment every time without leveling, polar alignment, or geo location. Date is only need for solar system objects. Objects are always within a few degrees with rough initial alignment that I then refine with "realign on object" for each centered object. Modern DSCs should be miles ahead of it by now in accuracy. Can you realign on an object once you center Jupiter or M31 and get good gotos after that?

I'll agree, that's more what I was expecting. It's the first time I've gotten such a disappointing used eyepiece.

I have more problems with the 2" compression ring in the GSO CC and 2" 2x ED Barlow than with any 1.25" adapter. I have toyed with the idea of getting a BCL with 47mm extension to replace the GSO CC eyepiece holder, but I've read of several horror stories of BCLs getting stuck in the lock position over the years. There seems to be no agreed upon way to easily release it when that happens.

That's my point, I've never come across one. Does anyone remember what brand or style he recommended? Or, could someone post a link to the original suggestion? It just struck me as a very odd idea based on my experiences with plastic totes over the last 30+ years. I'm not saying the idea doesn't have merit, because it does solve two problems at the same time. I'm just not aware of any decently rigid, and yet affordable, plastic storage bins. If the suggestion had been for a flight case as used for transporting music gear for traveling bands, I'd have been in complete agreement as they are very tough and rigid. Perhaps I'm not thinking of the correct thing when some says plastic storage container. I think of the following: Which are no where near as rigid as a tripod or pier, or even a picnic table. However, a professional flight case flipped upside down or on end and off its wheels might be suitably rigid:

Reminds me of an episode at work. During a meeting, our team lead said "We've got a long way to go" and I finished his thought with "and a short time to get there" from the theme song to Smokey and the Bandit (1977). Another old timer says to me "You're showing your age Louis". We then did a quick poll of the room, and we were the only two who got the reference. I felt so old at that moment.

Vintage binoculars were sometimes made with magnesium frames and touted how light weight they were. Despite this, they were very heavy by modern binocular standards, probably due to often using oversized porro prisms to allow for very wide angle views. I've also bought some of the tungsten carbide (I think that's what you meant) rings. They are pretty awesome. They can't normally be scratched (Mohs 9.0) and the dark reflection is really cool looking. Their heft is pretty incredible as well. Silicon carbide is fairly light, actually less dense than diamond. It is known as Moissonite in the gem trade. It has lots of industrial uses when not gem grade thanks to its extreme hardness (9.5 on the Mohs scale). However, it is not a metal. I have a brushed titanium band that looks really industrial thanks to that metal's rather unappealing shade of gray. I never bought another because of that.

It reminds me of the original IBM PC keyboards that had a hefty steel plate in the bottom. At some point, it was removed and everyone immediately equated the lack of heft to being poorer quality despite everything else being the same.

Brass is barely heavier than SS, especially as either compared to aluminum or delrin. However, SS could be made with thinner walls than brass to yield similar strength characteristics. In that case, it would definitely be lighter overall than brass. I guess you haven't seen all the nice SS jewelry coming out of China lately. I've bought quite a few bands and faux gemstone rings through ebay for cheap, and the SS they're using takes a very high polish and doesn't seem to tarnish at all in my experience. It's a different "whiteness" from sterling silver, but still quite mirror-like.