amaury

I'll keep that in mind. A very wide EP would be nice to have at 4mm exit pupil. I believe the 21mm/100 degrees you mention is the TV Ethos. Way beyond my budget I am afraid.

I have a 25mm Plossl, with my 8" f/6 dob, it gives me a very narrow 1.04 TFOV at x 48 and 4.16mm exit pupil. Very narrow but sharp edge to edge. I'm about to buy the APM UFF 30mm, that gives me 1.75 TFOV (that's a much wider field of view relative to what I have) at x40 with 5mm exit pupil. Thanks, that is encouraging

your three EP set plus a barlow is what I am planning more or less. I'm about to buy the APM Ultraflat field 30mm 70 AFOV . Price scales up rather quick with those premium 80 AFOV eyepieces. I believe that eyepiece is a good balance between optical quality, field of view, exit pupil, eye relief and value.

Yes I have, very handy indeed. The only uncertainty I have is with this statement: "Most of us live under moderately light polluted skies. A large exit pupil could increase the sky background brightness so much that it appears light grey. Therefore, under moderately light polluted sky, it would be better not to have eyepieces with more than 4mm-4.5mm exit pupil" That seems sensible if you are observing from a bortle 6 backyard. I observe from a Bortle 4 area, I believe I can stretch that recommendation to 5mm exit pupil for my low power EP in that context.

@Rob_UK_SE I was thinking about this comment. I understand you don't observe benefits when going from 4mm to 5mm exit pupil in terms of observing more faint details but do you observe contrast detriment when going from 4mm to 5mm? I believe the other real perceivable advantage of going from 4mm to 5mm EP is the extra True Field of View, I just wonder how much the trade off is in terms of contrast from a Bortle 4 location.

@Spile The 12mm of the BHZ is pretty much bang on with a 2mm exit pupil. You x2.25 barlow it to 0.9mm exit pupil. That pretty much covers what I have in mind plus some extra high power alternatives (I mean x150 and x338). Do you use your x225 and x338 powers often?

@Second Time Around thanks for the input. I actually bought the Svbony 8-24 zoom based on your feedback some weeks ago. It's outstanding value for the money. The Baader is around 3X more expensive than my zoom, I agree is sharper and more contrasty but not even close to 3x better. It has a wide field of view only in the last two shortest focal lengths. Low power is subpar and the 16mm is plossl-like at best, which is not bad, I just have a hard time trying to justify a 3x price.

I was just watching a video from an astronomy club where they mention this is the best virtually-free hack you can do in astronomy. I'll give it a go. That is very interesting. I wonder if the hood would help you out to open more your pupils. I certainly see your point tho' I'll do my research eventually with a Barlow. I don't want it to be the weak link in my optics.

Would you say the ES68 24mm performs better that the APM UFF 24mm? they are priced fairly similar

I normally observe from a bortle 4 area in South Downs. Is that Dark enough to justify a 5mm exit pupil? Yes, 200mm aperture 1200mm focal length f/6 Skywatcher Dobsonian. I've read in many places that the 2mm is related to the average size of the retina we are used to during the day. Apparently that is the size of the most sensitive part of the retina and the one that gives the best visual acuity. So there is some science behind that "optimal" exit pupil size. It's pretty clear that dedicated eyepieces are preferred instead of Barlow. I'll go for a dedicated third EP then. Thanks. With excellent conditions sure it is achievable.

Hi all, I have been planning my eyepiece selection based on exit pupil. For context I have an 8" f/6 Dob. I am following a minimalistic/simplistic approach. Basically I am planning to have three magnifications. Low power: 30mm focal length eyepiece / 40X Magnification / 5 mm Exit Pupil Mid power: 12.5mm focal length eyepiece / 96X Magnification / Approx. 2 mm Exit Pupil (Apparently around 2mm exit pupil is the optimal exit pupil for visual acuity) High power: 2x Barlow the 12.5mm eyepiece or a dedicated 6mm eyepiece/ 200X Magnification / Approx. 1 mm Exit Pupil (to match my scope focal ratio) So basically two eyepieces and a 2x Barlow, or three eyepieces. Is it too simplistic? is there any point with going beyond 200x with my telescope in the UK? (I guess not) I am missing out something without a 1.5mm exit pupil or a 3-4 mm exit pupil?

I love the sense of humor of this community hahaha I agree that a planisphere is excellent when you are learning your way around the night sky.

Hi all, Do you guys bother changing the rubber O-rings that come in some primary collimation schemes with springs? or just with thicker o-rings? I feel the factory o-rings that come with the 8" SW Dob are so thin that they barely do anything to support. This is the only thread I've come across where this matter is discussed explicitly. https://www.cloudynights.com/topic/542406-skywatcher-8-dobsonian-collimation-where-are-the-screws/?hl=+skywatcher++mirror++cell#entry7307925 Sketch of the push pull system with rubber piece. Sketch taken from: https://www.cloudynights.com/topic/427605-disk-vs-coil-springs-for-loading-adjustment-bolts/

Sorry to deviate a bit (still relevant to the topic discussed here), do people use planispheres anymore at all?

Thank you all. I've decided to go for APM UFF. I am still flipping a coin between the 24mm or the 30mm (4mm and 5mm exit pupil respectively with my f/6) The Altair re-brand is a bit cheaper, just a bit heavier. Some shiny internals have been reported. Doesn't seem to affect its performance. Any thoughts on this? https://www.cloudynights.com/topic/715544-shiny-internals-on-30mm-uff-especially-altair/ I haven't seen a single one of these EPs showing up in the second market in the UK, I believe the design is too new. I guess I'll have to buy brand new or wait for an ES 68 (or clones) to show up in the second hand market.

Never mind, looks like the Hyperion Aspheric struggles a lot at f/6 as reported by @John

That is very true @KP82, I think I'll be patient and get a second-hand ES68 when one becomes available. This is a really a high quality eyepiece indeed, 9 elements in 5 grous. I may get one of those. What about the Baader Scopos? lookk pretty solid edge to edge in your comparison. A quick google search tells me now they are called the Hyperion Aspheric and they are really well priced. https://www.firstlightoptics.com/baader-planetarium/baader-hyperion-aspheric.html That's my impression too. Still a solid eyepiece I believe @Louis D mentioned it just before you did, thanks anyways. They certainly don't get much attention, everyone seems to recommend ES before anything else. That APM looks really good.

That's exactly what I said when I contacted the person (haven't received an answer yet), it must be a ES62 32mm or a discontinued model I haven't heard of

@John thanks, I am looking for something between 30 and 36mm. I came across the one below but haven't got an answer yet. https://www.astrobuysell.com/uk/propview.php?view=172006

I would love to get a Pentax or a TeleVue Panoptic at some point. No quite yet. Maybe for the next Christmas as well. XD

That's is good to know. I think I'd be happy with 68°. A wider field of view means more coma and a more expensive eyepiece too. Is there any other eyepiece option of the quality/price ratio of the already mentioned Explore Scientific / Meade 5000 / MaxVision? The Aero ED looks ok but the ES is noticeable better. William Optics SWAN apparently don't perform nearly as good the ones above either.

Thanks @Louis D. I haven't really used a wide field eyepiece yet. I am hopping for things to normalize so I can interact more with my local astronomy club and test a couple of things I have in mind. Like how bad the coma is in my f/6 with a wide afov eyepiece. Most people don't bother with coma correction until they get to f/5 focal ratios. I believe there is a strong matter of personal preference there too. I am still in the process of forming my own opinions when it comes down to preferences in my telescope.

Thanks @michael.h.f.wilkinson and @Louis D So Meade 5000 and MaxVision have the same optics as the Explore Scientific. That's good to know in case the show up in the second hand market. I can certainly see the Meade 5000 SWA is objectively superior. Based on those images I would still choose any of the 32mm Plossl (the Orion or the GSO, pretty sharp from edge to edge) over a simple under-performing wide FOV. @Louis D maybe it's a silly question, what's the implication of using a f/6 refractor compared to my 8" f/6 reflector? Should I expect similar relative performance? Does it change the analysis in any way?

@vlaiv Thanks for that, It looks like a good middle ground. I'll keep my eyes open for a second hand ES68 too. Interesting @Pixies, is the 35mm better?, or just because it has lower magnification there's more FOV close to the centre relative to the 30mm? If that is the case I much rather have a high quality Plössl that is sharp edge to edge

Hi again, I'm still learning a lot about this, but every time I take my Dob out I wish I had a lower magnification with wider field of view. I think this is the very first thing you realize as a beginner that is shockingly counter-intuitive at first. Now I am totally decided to get a low power wide AFOV for my 8" f/6 Skywatcher. I was doing my research and read in several places that fast scopes struggle with wide field of views, showing aberration at the edge of the field of view. Only premium eye pieces seem to have good edge performance with fast telescopes. I will quote what I read "If you have a fast focal ratio scope, you basically have three choices: (1) pay the price for premium wide-field eyepieces; (2) limit yourself to Plössls and similar older designs, which have narrower apparent fields but are sharp to the edge even in fast scopes; or (3) buy inexpensive wide-field eyepieces and resign yourself to very poor edge performance" Article where I read this: https://www.oreilly.com/library/view/astronomy-hacks/0596100604/ch04s07.html If that is true then, option 3 is really a waste of FOV and I much rather go with option 2. My question is, how bad edge performance would I have with an affordable low power wide AFOV like the one below (30mm 68 AFOV) https://www.firstlightoptics.com/stellalyra-eyepieces/stellalyra-30mm-2-superview-eyepiece.html would an equivalent Explore Scientific (34mm 68 AFOV) have much better edge performance considering that it's 3x the price of the stellalyra for around the same specs on paper? https://www.firstlightoptics.com/explore-scientific-eyepieces/explore-scientific-68-degree-series-eyepieces.html Thanks in advance, Amaury