Louis D

The other most commonly mentioned filter for planets is a variable polarizer to cut the glare. Actually I would recommend two linear polarizers for your setup. One would go on the front of your diagonal and the other on the bottom of your eyepiece. Just rotate the eyepiece to vary the amount of dimming to the best level. I don't know if you've tried binoviewing, but I've found it really takes visible detail on planets up many notches. In particular, Mars at opposition goes from an overwhelmingly bright orange orb (haven't tried the above crossed polarizers on it yet) to loads of details in a BV. Same goes for the full moon. I'd recommend a #56 green filter or cheap Chinese green filter on Venus or on any planet low in the sky. It really cuts through the red/blue color separation/scintillation due to the atmosphere.

That just means it is FPL-51 equivalent glass when the term "ED element/glass" is used. Generally figure an FPL-51 triplet will have about the same amount of chromatism visually as an FPL-53 doublet, but with longer cool down time. I'm not sure how they would compare for astrophotography. For visual, I would go for an FPL-53 doublet to save weight and cool down time.

Is the Bresser/Explore FirstLight/JOC Dobsonian series so bad that no one mentions them as worthwhile of a look? I haven't tried one in person, but I like the look of those altitude trunnions and rotatable tube. I believe the focuser can be upgraded to dual speed.

It will still have the spatial resolution of an 8" which can be important for fine details. A central obstruction does not change this. Think about very long baseline interferometry. It has a huge central obstruction, and yet achieves very high spatial resolution.

Some folks over on CN have been using a 1.25" to 2" Step Up Ring screwed onto the 1.25" filter threads of their ASZ to prevent it from smashing into their diagonal optics, especially prism ones, when used in 2" mode. The ring's 2" outer surface will stop at the diagonal's 2" safety lip that prevents 2" eyepieces from inserting too far. It might also be useful for other hybrid eyepieces with extraordinarily long 1.25" barrels when used in 2" mode in diagonals without a lot of excess insertion distance.

Does the seller collect VAT and remit it to the UK on international sales? That's how sales tax works here in the US. Sales between individuals, even internationally, don't have sales tax applied unless the seller has a sales tax permit and meets various other location and sales threshold requirements. Technically, the buyer is supposed to remit use tax voluntarily when no sales tax is collected, but that rarely happens. Direct international sales are only subject to federal duties, tariffs, and excise taxes when no marketplace is involved. If you paid UK VAT, shouldn't your friend be able to get his Japan VAT refunded as a reseller?

Could you add Galilean wide angle or teleconverters intended for fixed lens digital cameras to the Seestar 50? I carefully epoxied a step ring to a fixed lens camera that had no filter/accessory thread so I could mount a fisheye adapter to it. It worked great. Would the software get all confused by the altered angle of view?

Look at how far the eye lens is recessed on the 25mm! 18mm of eye relief gone to waste. So much for any illusions of me using the 25mm with eyeglasses (low power + strong eye astigmatism = eyeglasses at the eyepiece for me). It's almost as bad as my 26mm Sirius Plossls. I have to really cram my eyeglasses against my face to see their meager 50 degree field of view. Needless to say, I rarely use my pair in my BV. I guess I'll rely on those of you with either little to no eye astigmatism or who wear contacts to give feedback on these.

As many others have said, mono versus bino viewing needn't be an all or nothing proposition. The two forms of viewing can coexist quite happily. As stated repeatedly by others, binoviewing works best on bright objects where putting two eyes on the target can trigger more parts of the brain's visual processing cortex; thus, revealing more subtle details. For Mars in particular, I find it goes from being an overexposed orange orb at opposition in monoviewing to a highly detailed, normal brightness object in binoviewing. The full moon is very similar. Suddenly, the washed out details on the face of the full moon snap into high contrast features going from monoviewing to binoviewing. Also, it appears sphere-like instead of circle-like. Monoviewing shines with fields of view over 70 degrees. You can't take in much more than about 60 degrees in a binoviewer. Additional field beyond that is strictly in peripheral vision because you have to view on axis to merge the two images. While it's nice for context, you simply can't scan around the field of view in a binoviewer. You will lose one or both images, ruining the effect. This is not an issue monoviewing. I really enjoy viewing the neighborhood around objects, especially in star cluster rich regions. It's also near impossible to keep two eyes aligned to a binoviewer while lazily scanning the skies in super wide to hyper wide eyepieces just to see what's up there like an aimless tourist. This happens to be one of my favorite activities monoviewing since I like to look for new to me asterisms, associations, and multiple star systems. I don't really care to find out what I've found, I just enjoy the moment and move on. I find it highly relaxing and rewarding.

Using a 2" diagonal also allows for adding a TSFLAT2 ahead of the diagonal to flatten wide field views for edge to edge sharpness. In both my 432mm and 600mm ED/APO refractors, it makes quite a difference at lowest powers. However, I have to remove it at high powers to avoid the introduced spherical aberration from the flattener that is not visible at lower powers.

Probably minimal. Your f/10 scope at 8mm yields a 0.8mm exit pupil. I generally prefer to go no lower than 0.75mm. The Svbony zoom at 5mm would yield 0.5mm which is about my limit for seeing through my eye floaters. The other problem with your SCT is the very high resultant powers that would require very good seeing conditions (2000/8 = 250x, 2000/5 = 400x).

Are you sure about this? I found this blurb on the SkEye website: Whenever SkEye is in automatic scrolling mode, SkEye gathers data from two or three sensors in your Android device: the accelerometer, magnetometer and gyroscope (if available). I've found it accurate enough to put objects within 2 degrees of the optical axis. It's hard to complain about a free app.

I've taken some images through the KUO 152mm with various filters and compared it against other scopes I own in another thread. Here are links to the relevant posts:

Sounds like we have a volunteer to take one for the team. 😁 Let us know what you think of them.

Nope. Brightness of the projected image is entirely based on the exit pupil of the eyepiece/scope combination. Any 5mm will yield the same image brightness in the same scope. The long eye relief will make it easier to match the eyepiece exit pupil to the camera's entry pupil for afocal projection. I'm not sure it makes any difference for regular eyepiece projection that you're attempting. Be aware that most eyepieces not specifically designed for eyepiece projection will project a curved focal plane. You may find it impossible to get the center and edge in focus at the same time on a flat imaging sensor. This focal plane curvature is not an issue for afocal projection due to the taking lens's depth of focus.

Here's a composite of the KUO 152mm Achromat with no filtering and 8 filter variations to try to both cut violet and sometime red fringing in an effort to increase sharpness and contrast: The SemiApo is the Baader SemiAPO filter in 2" format. It's too bad the Hirsch filters are only available used because they had a bunch of unusual colors such as their Light Yellow #12A (Wratten #4) and Light Blue #82B (Light Cyan). The Green X1 (Wratten #11) and Yellow K2 (Wratten #8) filters are both 48mm Rokunar photographic filters. Both are still available as new old stock on ebay in 48mm size. The Cheap Yellow and Green filters came in a set of 6 colors from China for $13. They tend to cause a bit of light scatter and loss of image fidelity. The 600nm Shortpass filter (Minus-Red) is an uncut dielectric filter from China. As in my previous post, the Baader SemiAPO does a very good job at cutting most of the objectionable violet fringing while avoiding adding a harsh yellow cast. The Hirsch #12A does a good job cutting violet while adding very little yellow cast to the image. The Yellow K2 is a bit heavy handed. However, it cuts all but a tiny bit of violet fringing. I should try pairing it with my 48mm Moon & Sky Glow filter to make a poor man's Baader Contrast Booster and reduce the yellow cast. The Green X1 is a good compromise to cut both violet and red at a reasonable cost. The Yellow/Cyan and Yellow/Minus-Red filter combinations do a bit better than the Green X1 by having higher transmission over a broader passband while still cutting almost all violet and red fringing. However, the components are difficult to find.

I think this eyepiece line aims for high contrast and sharpness on axis with low scatter and stray light, similar to the Vixen HR line. I'm guessing they accomplish this through use of glass with very little bubbling or surface roughness from polishing. They probably also have carefully designed light traps to reduce stray light. If none of this is true, I, too, would wonder what makes them worth the premium price.

As promised, I went out last night and took more comparison images of the moon. This time, it occurred to me, how close would a 2x Barlowed smaller, but higher quality, scope show relative to the big KUO 152mm Achromat. I brought out my Astro-Tech 72ED and TS-Optics 90mm FPL-53 Triplet APO for comparison at both native and 2x magnification. I did the same with the GSO 150mm Newtonian as well. I skipped Barlowing the KUO 152m Achromat because it did so badly in that mode the night before. Here is a composited comparison image, this time with labels (ST152 = KUO 152mm Achromat). Make sure to click it open for a high resolution view. My impression at the eyepiece was that the 90 APO showed the sharpest, contrastiest views, even when Barlowed. The 72ED was a bit behind thanks to being an FPL-51 doublet. The 150 Newt was showing incredible detail, sharpness, and contrast as expected. However, the APO had more WOW factor due to the high contrast. All three Barlowed extremely well. The ST152 was just sad to look through. The Baader SemiApo filter helped it a bit, but there's just nothing that will make it a compelling bright object scope. The views were blurred, low contrast, and awash in false color. I included the "Typical Violet Fringe" image because it best captured how the view looks to the eye at the eyepiece. I will say that bright star fields looked decent in the ST152 with my 40mm XW despite there being some violet fringing on brighter stars. I'll have to do a comparison in that mode at some point. Perhaps it might "shine" for wide field sweeping.

That's the only one I don't have. How have you found it to perform under the stars?

My typical go-to A-team favorites would be as follows: 40mm Meade 5000 SWA decloaked 17mm ES-92 12mm ES-92 10mm Delos or 9mm Morpheus (hard to pick between them) 5.2mm Pentax XL 3.5mm Pentax XW While I really like my 30mm APM UFF, it just doesn't have the wow factor of the SWA for some reason. Perhaps because it gives up too much (~10mm) in field stop size to the SWA. 🤷‍♂️

I just google image translated it as 4 microradians (see below), which again would be astonishing if it is 1000x better corrected than an improved Plossl. Why would they use an Airy disk, which is typically in the 2.5 to 5 milliradians range, for the upper images, and then switch to 4 microradians, 1/1000ths of a typical airy disk, for the lower images? An apples to oranges comparison is very confusing. Text: Center spot diagram comparison LE12.5 The circle is an Airy disk, 11 wavelengths from 436mm to 656nm are synthesized, and the objective is an aplanatic optical system. (C) TAKAHASHI SEISAKUSHO Ltd. TPL-12.5 Spot Diagram Apparent field of view (half angle) 0° 5.5° 11° 16.5° 22° A circle is 4 microradians Afocal calculation of 11 wavelengths from 436mm to 656nm (C) TAKAHASHI SEISAKUSHO Ltd.

This article goes on to say the following: You can take active countermeasures too. A 4- or 7-watt light bulb inserted into a blanketed telescope makes a nice low-power heater. Well, the article should probably be updated from its original 2006 published version to specify a 4 W incandescent light bulb because I've got a modern 4 W LED light bulb that is a 40 W incandescent lumen equivalent that emits no infrared radiation, which is I think the form of heating the article desires. It does emit waste heat from the LED itself, but that is mostly confined to the base and would eventually reradiate as far infrared radiation. However, an LED light bulb is less efficient at immediately converting electricity purely to heat than an incandescent light bulb because it is optimized to convert electricity into visible light that doesn't warm things very quickly. I suppose the visible light photons, if contained within a light tight enclosure, would eventually warm whatever they strike in there, so an LED light bulb still might be 100% efficient at converting electricity to heat in the long run.

All the rebrands of the current KUO 4mm UWA should perform similarly. For example, it's also sold in the US under the Astro-Tech name by CN's sponsor. Aside from cosmetics, I would think the optics are identical. I did find this blurb which appears to be a factory-style release statement since Sky Rover is KUO's factory brand: Compared with the old UWA eyepiece, the new version has mainly made the following improvements: 1. The optical system has been slightly adjusted; 2. The design of metalworking part has been changed. The main body is slender in shape, and the cannula made of stainless steel has better texture. 3. Silicone folding eye cup is adopted, which makes observation more comfortable. SKY ROVER’s second generation UWA series ultra wide-angle eyepieces, with high-grade optics and impeccable appearance, are products that astronomy enthusiasts are keen on. Its success lies not only in providing an ultra-wide angle view of 82 degrees, but also in its reasonable price. Especially suitable for observing planets and deep space targets, and also suitable for observing ground targets. So, it's possible the current KUO UWAs are slightly better optically than the original flat top style, assuming the "slightly adjusted optical system" improved rather than degraded the performance. Notice they didn't explicitly say "slightly improved", so there is wiggle room as to what they did to the optical design. Perhaps it was slightly adjusted to make it cheaper or easier to produce at the same image quality level.

If indeed Tak has managed to reduce the aberration spot size by a factor of 287 over a typical improved Plossl (TV, Clave, Brandon), I will be insanely impressed.

@Marian M Here's some more comparison images from last night using the same setup except with a Parks GS 2x Shorty Barlow, so roughly 144x (achromat) and 120x (Newtonian): Top Row, Left to Right: GSO 150 f/5 Newtonian unfiltered, KUO 152 Achromat unfiltered, KUO 152 Achromat with Baader Semi-APO filter Bottom Row, Left to Right: KUO 152 Achromat with Yellow K2 filter (Wratten #8), KUO 152 Achromat with Green X1 (Wratten #11), KUO 152 Achromat with Hirsch #12A Light Yellow (Wratten #4) and Hirsch #82B Light Blue (Light Cyan) This shows that filtering the unfocused violet and red ends of the visible spectrum can help to sharpen up the achromat's image. However, I stand by my original assertion that the 150 Newtonian stomps all over the 152 Achromat for image sharpness, contrast, and color fidelity on bright objects. I'll try and get out tonight to see if I can improve on the achromat's performance any.