Don Pensack

I'm working on a system to accurately measure the "effective eye relief" (from the folded down eyecup to the exit pupil) for glasses wearers. If it works well, it'll be possible to measure it on any eyepiece. I think glasses wearers will be surprised how little effective eye relief it takes to use glasses with an eyepiece. One eyepiece I have that has a design eye relief of 18mm and which I found *just* usable with glasses on had only 14.3mm of effective eye relief. When people look for eyepieces with 20mm of eye relief for glasses, that is not the eye relief from the rubber up, but the design eye relief from the glass, and the depth of the lens varies all over the place from eyepiece to eyepiece. One eyepiece with 20mm of eye relief had 12mm of effective eye relief, and another with 20.5mm of eye relief had 19.2mm of effective eye relief. On paper, both were glasses compatible. In reality, only one was.

So, buy used eyepieces, leave marks on them and sell them as used with marks. I've done that a few hundred times, and at 50% of the new price (not what I paid), they sold instantly. The difference between what I paid and what I received was a "rental cost". If there were an eyepiece rental service, I bet they'd be busy and marks wouldn't matter at all. So it is with eyepieces sold at 50% of new. No one cares about marks, boxes, or anything. If your finances are very tight (and I've been there), and you cannot afford to lose any money, use nylon screws to not leave marks and you can sell the eyepieces for about the same price you paid. All my eyepieces have marks except those in quasi-permanent adapters, and it's never inhibited the sales. The problem comes when you want to sell for, say, 80% of the new price and customers expect the eyepiece to be brand new.

It is always the distance up from the center of the top surface on the eyelens, the paraxial eye relief. I have also called it the Design eye relief, as the housing is usually not externally designed as the lens configuration is designed. IF the manufacturer quotes the eye relief correctly, measuring the depth of the lens will tell you the eye relief from the folded down rubber eyecup to the exit pupil, the "effective" eye relief for glasses wearers. See this discussion: https://www.cloudynights.com/topic/837363-effective-eye-relief-a-few-measurements/

The 17.5mm Morpheus focuses 2.5mm in relative to all the other Morpheus eyepieces. You can use a TeleVue In-Travel adapter (or similar from other brands) to compensate and make it parfocal.

Its design sacrifices 8mm of the 20mm eye relief when all the way down! It's a long eye relief eyepiece with the eyecup removed. I would find another regular eyecup of 49-50mm I.D. to replace the original eyecup with glasses. Without glasses, the OE eyecup works great.

The 13mm Hyperion at f/5.75 (my scope with coma corrector) suffered from minor astigmatism at the edge of the field (easily ignored) and Edge of Field Brightening (EOFB). This latter issue only shows up on very dark fields, as when looking at a faint galaxy or nebula, and not, really, on any brighter object. Star images and focus were quite good on axis to about half way out in the field (center 35°) and fairly good out to about 75% (center 50°) and only showed some noticeable aberrations outside that. With a coma corrector, my scope has a coma free field larger than the 13mm Hyperion's field of view. At f/6, without corrector, coma at the edge will bloat the stars to about 4x their diffraction sizes at the edge of the field in the 13mm. How large that will be to the eye, visually, is dependent on the magnification the 13mm provides. I would put it this way: the Hyperions are not as bad as many people make them out to be. The 21mm and 17mm are the best in the series, while the 24mm, 5mm, and 3.5mm are not even good at f/10.

The eyecup can be removed, saving a lot of weight. https://www.cloudynights.com/topic/635087-celestron-15mm-axoim-lx-how-do-i-decloak/ It makes the eyepiece a LOT smaller and lighter.

Can you? Yes. It improves star image quality and brightens the overall image. It doesn't create more light, though. So if you can use an eyepiece with a 46mm field stop at f/10, your maximum field eyepiece's field stop with the reducer is 46*0.63=29mm That's one of the reasons it is said: " 2" eyepieces at f/10, but 1.25" eyepieces at f/6.3."

In general, how a nebula filter works is to dim the background sky without dimming the nebula. So figure that all you are seeing is the nebula. As is the case with any extended object, it will appear to dim as the magnification goes up. You will see more details in the nebula, however, as magnification increases. So there is always a compromise between brightness and magnification when looking at any nebula. Otherwise, we'd all use the largest exit pupil possible with every nebula. The fainter the nebula, the lower the maximum usable magnification will be, with or without a filter. Nebulae that perform best with an H-ß filter are usually large and quite faint, which leads to better results with a large exit pupil, like 4-7mm. Nebulae that perform best with a narrowband (UHC-type) filter tend to be much brighter, so smaller exit pupils will be fine, down to perhaps 2.5mm at a minimum. Nebulae that perform best with an O-III filter fall into the large and faint (Crescent Nebula, Veil) or small and bright (many small planetaries). With the large and faint, exit pupils of 3-7mm seem to work best, while the small and bright might be suitable for as small as a 2mm exit pupil. though I would point out that many small bright planetaries show the most detail with exit pupils under 1mm, which is a magnification not suitable for filters. So the brightness of the object and its emission profile will determine how small an exit pupil you can use, and the emission lines will determine which filter will work best. Larger H-II star forming regions (M8, M20, M17, M16, M42 will work best with the narrowband filters passing both H-ß and O-III Planetaries, supernova remnants, Wolf-Rayet excitation nebulae will work best with an O-III filter. Large, faint, nebulae with almost exclusively hydrogen emission, will work great with an H-ß filter (example: NGC1499, IC434 behind the Horsehead)

The eyepiece is easy to use, light in weight, yields nice bright stars and has a near maximum 2" true field, with a well-behaved exit pupil. In your scopes, you will see astigmatism in the outer 50% of the field, but since it is such a low power, 15x in the NP101 and even less in the 48P, with a 6.7-7.2mm exit pupil, your own eye's astigmatism may dominate 😄 It isn't the equal of the Morpheus but it is basically OK as a very low power "finder" eyepiece. The field will remind you a lot of a binoculars image--very wide true field. Performance of the eyepiece gets a lot better at f/8 and longer. At f/5-f/5.4, it's being pushed a bit past its limits. I would use it when you want a truly larger true field view, especially of asterisms like the Coathanger, Kemble's Cascade, the Fairy Ring, etc., or large nebulae like the North America nebula, Veil Nebula, California Nebula, et.al.. It will sharpen up a lot when a nebula filter is added.

Brand new item. No economy of scale, yet. No amortization of the development costs yet. Still less expensive than Nikon, Leica, Zeiss, and Swarovski Zooms.

My IPD is 63.5mm and I have no problem at all with these eyepieces in a binoviewer. I've even used eyepieces 54mm and 58mm in a binoviewer with no issues. The larger one had a very long eye relief so my nose was nowhere near. But these? No problem.

If the O-III extends upward far enough to capture the 511nm and 514nm C2 lines, it could be a decent comet filter. The Starguy was (it's no longer made) identical to the Optolong. Not all the 18-28nm wide O-III filters (all too wide for O-III use) extend upwards far enough to catch those lines.

I noticed the light loss in daytime use in an 80mm Pentax ED spotting scope of f/6.5. Use of telescope eyepieces in that scope made the images so much brighter it was a different scope. It didn't matter than much in daylight use. At night, though......

To be more exact, the only issues owners of the Ultrablock filter have encountered is that the bandwidth can be slightly misplaced, clipping either the 486nm H-ß wavelength or the 501nm O-III wavelength at a much lower transmission. My lab-tested sample had transmission % at 486 of 85.9%, at 495nm (O-III/2) of 95.4%, and at 501nm (O-III/1) of 82.8% The bandwidth wasn't misplaced in the spectrum, as FWHM bandwidth was 482nm -508nm (26nm), plenty of room to get transmission above 90%. That bandwidth is similar to TeleVue, Lumicon, and Astronomik. It just wasn't a good curve. A test of 8 of them here: https://searchlight.semrock.com/?sid=a08a1af9-84ee-49d2-959d-153d7e7c0eb8# showed H-ß transmissions from 70.3% to 97.4% and at 501nm (O-III/1) of 82.4-95.6% That variability is why the Orion Ultrablock is not considered one of the premium filters. Nonetheless, 2 of 8 were superb, and 4 of them had nice bandwidths, just with a bit lower transmission % than the higher priced filters. That would only be an issue if used on a small scope of 80mm or smaller. So your odds of getting a decent one look to be 75%, and a superb one of 25%, based on the 8-filter sample. Last, Orion uses a different thread on their filters, so threading them into regular eyepieces can be problematic. Know this: At only 7g for a 1.25" filter, only 1 thread really needs to catch to hold the filter on. So if it doesn't thread in more than a couple threads, that is really not a problem. Internet Forums make a big deal out of that, but I've used Orion filters on and off for decades, and never had one fall off. Yes, the wider UHC filters (ES, Optolong, StarGuy, Astronomik UHC-E, etc.) do not provide the contrast enhancement you want. They're less expensive, which is why they've sold. Here is a US-oriented listing of available nebula filters (though pretty applicable in the UK): https://www.cloudynights.com/topic/817105-2022-nebula-filters-buyers-guide/ I note there are some photographic filters now that perform as credible narrowband UHC-type filters, but they are also not inexpensive.

The XL (on the right) was very significantly darker at each focal length than the corresponding XW fixed focal length eyepiece--almost the difference of adding a neutral density filter. It's OK in bright daylight, where the light loss doesn't matter as, for example, in spotting scopes. But for astronomy? My advice is to look elsewhere.

Orion's official name is "Sky Glow Ultrablock" filter. That's confusing, because they also have a Sky Glow Broadband filter. So everyone just refers to it as an "Ultrablock". It is Orion's narrowband "UHC-type" filter and is comparable to other "UHC-type" filters. Someone may just call it a "UHC" to avoid confusion with broader filters. That's not a bad thing--good for the seller. It will be used at powers from 10x/inch and lower, so if your low power eyepieces are 2", get a 2" filter. A 2" filter will fit the bottom of many 1.25" adapters for a 2" focuser, and also thread on to the front of a 2" star diagonal, so 2" is the universal size if the scope has a 2" focuser. If the scope is 1.25" all the way through, including the focuser, then 1.25" filters are appropriate, of course.

The William Optics is a re-packaged Norin binoviewer. As such, it has the disadvantages of a low end unit: --small clear aperture (20mm) --The WO OCA has significant chromatic aberration and spherical aberration. Use another brand if you can. It's probably a good "gateway" to see if you like binoviewers. If you like binoviewing, it won't be your last binoviewer, though.

This may end up in a grey area, but I have found that apparent fields wider than about 68° do not work well in a binoviewer. Why? Well, in a mono-viewing situation, if you want to look at the edge of the field with direct vision and the field is 70+°, you slightly roll your head over to look since you need to keep the pupil of your eye at the exit pupil of the eyepiece. It's no problem at all to do so. You can't just simply move the eye to look directly at the edge with foveal vision because that moves the pupil of your eye away from the exit pupil of the eyepiece. The head movement is so slight, most people don't even notice the movement. Therein lies the issue with ultrawide fields and binoviewers. You need to roll the head slightly to look directly at the right and left hand edges of the field. If you do so, one eye gets lifted away from the exit pupil and that side goes dark. You can simply ignore the edge and only focus on the center, but that means you cannot follow and object across the field from edge to edge in an untracking scope. But if you stick to 68° and smaller in binoviewers, you can see right and left edges of the field by merely moving your eyes and you can track the object from edge to edge. This is the main reason, I believe, that it is a very rare binocular that has an apparent field in excess of 65°. So how wide an apparent field can you use? Therein lies the grey area. If you don't care about looking at the right or left edge of the field with direct vision, then the only limit is your IPD and the scope's focuser's ability to handle the weight. If you do care about seeing the entire field with direct vision, then smaller eyepieces of up to 68° will work best. 60° eyepieces are almost universally bino-friendly, and because they are modest in price, having dual copies of each will likely not be much of an economic hardship. And many of them are quite good.

TeleVue still offers the Naglers for sale in 31mmT5, 22mmT4, 16mmT5, 13mmT6, 9mmT6, 7mmT6, 5mmT6, 3.5mmT6 In the last few years, , the 26mmT5, 20mmT5, 17mmT4, 12mmT4, 11mmT6, and 2.5mmT6 were discontinued, to joint the originals, and type 2s in history.

The 'evidence' I've seen is almost completely anecdotal, as an endlessly-repeated comment from Vernonscope about Brandon eyepieces and why they have single layer anti-reflection coatings. The coatings explained: https://www.edmundoptics.com/knowledge-center/application-notes/lasers/anti-reflection-coatings/ https://www.edmundoptics.eu/knowledge-center/application-notes/lasers/an-introduction-to-optical-coatings/ I've read over a hundred studies about this, and the conclusions investigators come to are that the scatter is almost totally dependent on the smoothness of the surface the coatings are put on, not the coatings themselves. When you stop and think about it, if the surface reflects LESS light, how could scatter be MORE unless the surface becomes rougher with each layer? I guess I could see that a rough lens surface will scatter more light, but it's hard to see how a multi-layer coating will scatter more light unless the multicoating adds to the roughness of the coated surface. That is possible, but comparing a cheap eyepiece with multi-coatings to an expensive eyepiece is likely comparing surface smoothness more than it is the coatings. Brandon eyepieces have low scatter because of a higher end lens surface roughness figure. And Zeiss uses multi-coatings but has superior lens surface polish. This explains the main rating used for surface smoothness: https://www.advancedoptics.com/scratch-dig-specifications.pdf

Synta Maksutovs (90mm, 105mm, 127mm, 152mm, 180mm) are sold under many labels in the world. I have seen the whole line sold under the SkyWatcher brand in many countries. Most of them have a V-sized dovetail.

JOC was a supplier of Meade from the late '90s to 2011, but they never owned Meade. Meade was owned by Sunny until the recent lawsuit. Meade is now owned by Orion in the US. They do own Explore Scientific, however, and are a supplier for Bresser. How Bresser and JOC relate in the financial sense other than for purchases, I don't know. The UK has a couple sellers who import from JOC.

Not, I suppose, a giveaway bargain, but £83 is a pretty inexpensive eyepiece. It's a nice Japanese eyepiece for the price of a Chinese eyepiece. FLO has a lower price than many of the EU dealers.

Brightness is directly related to the area of the exit pupils. The brightness ratio would be the ratio of radiuses squared, i.e. r²(1) / r²(2) where 1 and 2 are the compared exit pupils. So a 5mm exit pupil, compared to a 3mm exit pupil has a brightness comparison of 6.25/2.25 = 2.78x, so the 5mm exit pupil is 2.78x as bright as a 3mm exit pupil. Pretty much, a 0.5 magnitude difference becomes a minimally different brightness difference. That is an increase of exit pupil area by 1.58x, so if you start with an exit pupil of 6mm at the large side, the next exit pupil would be 4.8mm and the next would be 3.8mm, etc. At the low end, that would probably yield magnifications that are too close together, but it would result in a visible change in field brightness. A typical narrowband with a narrow bandwidth will increase contrast for the nebula by about 2.4-2.5 magnitudes. A narrow 2-line O-III filter will increase contrast for a O-III emission nebula by about 2.9 magnitudes. Those increases in contrast are why the nebulae become more visible, because nebula filters do not make them brighter at all. It just seems like they do. Contrast diminishes sharply above about a 10x/inch magnification (2.5mm exit pupil), so nebula filters are low power accessories. If you like to look at small planetaries at 500x, you won't be using a filter.