Louis D

I'm just pointing out how focal reducers work from a layman's perspective. Also known as telecompressors, they compress the image circle into a smaller area, increasing the photon flux per unit area, simultaneously reducing image scale. As you say though, what good is a faster acquired image if it is tiny on the sensor? However, if someone is after large, expansive, low resolution sky survey images acquired in the least amount of time possible, then perhaps the Starizona solution is for them. It's similar to a Schmidt camera which is used for such purposes.

Thanks for the info. I wonder what its wavefront error measurement is. If the weather ever clears up here, I'll try to do a careful star test on the GSO 6".

It can't, but it can increase the amount of light per unit area on a sensor by compressing the image circle as with a refractor. I get the whole pixel business, but if you take the imaging device out of the equation and simply look at the optics, the light flux per unit area at the imaging plane has increased. Hopefully their customers who are willing to pay their prices are savvy enough to understand this trade-off. If it was a $100 device, then I would be concerned about noobs being misled.

Ask @Don Pensack why he quit selling into Europe. I may be mistaken, but I recall reading a post of his where he decided the cost and overhead of VAT collection for EU sales to be too much for too little benefit in additional sales over US-only sales. He may still sell into Canada.

I'm curious what they are. Certainly there's uncorrected coma since 1.25" CCs are hard to come by. Are there others? I had thought about getting a Heritage 150, but decided I'd miss 2" eyepieces and CCs too much, so I recently picked up a used 6" f/5 GSO Newtonian with the dual speed focuser. I have been impressed with the quality of the mirrors. Our weather has been terrible, so it's been difficult to critically evaluate it, but so far it exceeds my expectations for about $300.

Are you also saying focal reducers are nonsense and don't actually reduce exposure time while simultaneously reducing focal length? I thought if aperture remains constant but focal length decreases, f-ratio must go down as well. When the f-ratio goes down, the exposure time required for the same exposure density also goes down. The HyperStar gets rid of the 5x magnifying effect of the SCT secondary mirror, reducing the focal length and f-ratio by 5x in the process. You're assuming the focal length remains constant, which it does not; and they make no claims that it does. Further down, they show the decrease in both in a table: The 25x comes from the squaring effect of f-ratios on light gathering. I think it is really 2**5 or 32x, actually. That much they did screw up.

I'm pretty sure if folks in the UK buy from overseas, someone from the government collects VAT upon arrival of your item in your country because it's a fixed nationwide tax similar to tariffs. That doesn't happen in the US. Americans are expected to keep track of sales for which no sales tax was collected and submit use tax instead on their own to their state and local governments since sales tax is not a nationwide tax. That pretty much never happens, though. It would cost too much in labor and overhead to create the government bureaucracy in every state and local taxing entity to collect the small amount due since the vast majority of Americans buy goods within the US. The exception are online marketplaces like Amazon and ebay which do collect sales tax for sales into the US on behalf of overseas sellers ever since the 2018 US Supreme Court ruling South Dakota v. Wayfair. By contrast, European countries are now requiring overseas sellers, not just online marketplaces, to collect and remit VAT on behalf of customers, creating a lot of undesired and expensive overhead, so many non-European sellers have simply quit selling into Europe.

I think the OP was asking, "Why do we put up with long f-ratio scopes just for high power usage? Why not just buy shorter f-ratio scopes and use Barlows or short focal length eyepieces to get to higher power." And the partial answer is, that would be great if optical quality didn't suffer at shorter f-ratios, particularly in refractors. However, as I stated above, shorter f-ratio scopes of high quality get real expensive real fast.

There are very short focal length Dobs made to be more ergonomic to observe with. Here's a Webster 28" f/2.7: Is this what you are suggesting? The problem is that it is difficult to make short focal length scopes with the same optical quality as longer focal length telescopes. As a result, they are more expensive aperture for aperture.

That's at least $85 cheaper than buying it here in the US. Add in the fact that sales tax isn't collected by FLO, and the deal gets even better.

May I ask why? The focuser on it is already basically a helical microfocuser. Adding anything above it would probably prevent you from reaching focus. I've not read of anyone trying to replace the original focuser with another helical microfocuser. There is this thread documenting adding a 2" Crayford focuser to one:

After using the blower, use a light rolling/flicking motion with a clean microfiber cloth like a vacuum beater bar does to carpets to get more stubborn particles lifted off the surface. DO NOT SCRUB THE FILTER SURFACE with any cloth. You will likely scratch it with unseen microdebris.

Well, you do live just 6 degrees latitude south of the Arctic Circle, so you're sort of asking for it. 😉 I live just 7 degrees latitude north of the tropics, and I'm fully aware of how hot it gets here for 8 months of the year. It makes for very hot and muggy nights of observing. When we do get a blizzard as in Feb. 2021, we shut down entirely and lives are at risk due to hypothermia. I'm sure you'll enjoy your CF 90. I really like my TS-Optics 90mm FPL-53 Triplet APO. After actually handling it, I'm glad I didn't go any bigger as it's quite dense. My DSV-2B mount has zero issues with it, though.

By the looks of it, the newer BSC filter is indeed NIR safe. If it didn't cost so much, I might try it. I do have a vintage Optica b/c green line filter with ~30% transmission somewhere in the green part of the spectrum. I tried it briefly with my wedge, but I wasn't convinced the view was any better than without it, so it did nothing to whet my appetite for the BSC. I started using the UV/IR cut with my 8" Dob and Visual ND5 Baader Solar Film. It always felt like my eye was getting cooked over time. Based on the logarithmic spectrum of BSF shown below, it's no wonder I felt that way. Clearly, it's ~ND5 at visible wavelengths, but only ~ND3.7 to ~ND4.5 in NIR. That is more than a 10x increase in NIR transmission over visible transmission which is enough to cause discomfort for me. The Baader UV/IR filter (similar to my Meade photographic UV/IR filter) has the following transmission characteristics on a log scale: So it will definitely help with the BSF in my Dob where I need it most, in the NIR. That extra ~ND2.5 in NIR really helps make things more comfortable when solar observing. Interestingly, notice how a Baader ND3 starts to go off the rails toward ND2 above 1500nm in the IR part of the spectrum: Thus, a 10x increase in IR transmission in that region. I wonder how similar the ND3 filters packaged with Herschel wedges are to the Baader. Here, notice how crossed polarizers (similar to those packaged with my Hercules solar wedge) never block IR at 900nm and above regardless of crossing angle. That's just downright scary! I'll take the UV/IR cut filter as one more line of defense for my aging eyes, thank you very much.

Worst case, the UV/IR filter cracks or shatters for whatever reason, you clean out the mess, and try a different UV/IR that is reflective rather than absorptive. It's not like you're in any danger of shattered glass getting in your eye or being exposed to the full force of the sun's light. It's not much different than the more focused light cone after the wedge (4.6% of the pre-wedge energy) hitting the ND filter, which is absorptive rather than reflective. The ND filter is very near to the scope's focal plane. I will say that any finger grease on the UV/IR could lead to differential heating, and that might lead to an issue with cracking. Thus, keep it spotless.

I'm curious why Baader hasn't seen fit to put their mechanical engineers to task to find out what is causing the lock-up and fix it once and for all.

I put the UV/IR cut filter ahead of the wedge as someone on here suggested, and nothing bad happened. It didn't even get hot. Now I just leave it on there full time as a safety precaution for my eyesight.

Line filters can leak light from outside the visible spectrum without it affecting visual performance. Take a look at this thread which specifically tested two generations of the BSC filter. One version seriously leaked in the NIR: That could cause a serious amount of discomfort to one's eye while observing. Here's what it looked like combined with a UV/IR filter: While another BSC version did not leak NIR light:

The general consensus is that JOC reissued the Meade 5000 Plossl series as the ES-62 series since the specs and focal lengths are so similar. If that is the case, I can speak to the 40mm focal length since I own the Meade 5000 Plossl version. It is super sharp in the inner 50% at f/6 and then rapidly fuzzes out moving to the field stop due to astigmatism. On the plus side, the moon doesn't distort much at all moved from center to edge. The design is basically a variation on the Zeiss Astroplan opened up to 60/62 degrees. Even if it had been limited to 50 degrees, their design would still have had edge issues since that would only eliminate the outer 17% or so. Normally, these Astroplan variations are sharp to the edge at f/6 over a 50 degree AFOV as with the old Celestron Ultima, Parks Gold, Orion Ultrascopic, and Baader Eudiascopic "Plossls". The view through the 40mm Meade 5000 Plossl in my field flattened 72ED is shown below relative to others. Since it is a scaled design, all of the other focal lengths except for the 5.5mm, which has 6 elements, should perform similarly.

Don't ask me, ask the OP why he has "fallen in love with the big eye glass on the let". I've assumed it has to do with the relaxed view from longer eye relief that doesn't require mashing your eye into the eye cup to see the entire field of view. I know I can barely use my 7.2-21.5mm zoom due to its small eye lens (16mm diameter) and tight eye relief (9mm - 11mm) even without eyeglasses. My eyelashes keep brushing the top of the eyepiece whenever I blink. With eyeglasses, it's like looking through a soda straw. Without eyeglasses, my 2.5 diopters of astigmatism make for spiky star images. Also, the zoom action is so stiff that I have use two hands to zoom. Are the Svbony zooms' zoom actions silky smooth enough as to require only fingertip pressure?

Prism diagonals will always have a shorter optical path than mirror diagonals of the same size. It has to do with the physics of how light travels through glass versus reflecting off of a surface. The 1.25" diagonals will all have shorter optical paths than their 2" equivalents due to physical dimensions. If there isn't enough back focus for a 2" Herschel wedge, and your scope's aperture is 100mm or less, you could look into getting a 1.25" version. I use a 1.25" Hercules solar wedge myself.

Do any of them have a big eye lens for relaxed viewing as put forth by the OP? I've read that the APM SuperZoom has good eye relief due to a largish eye lens, but I'm not sure about the Svbony zooms.

Mark Ackermann here in the US designed the 30mm APM UFF as he describes in this CN post. It's not clear that Markus Ludes of APM commissioned him and paid for the design. KUO built it, did they pay Mark? It's not clear that APM ever had an exclusive right to sell the eyepiece based on the design. Perhaps APM had a limited time exclusive right to sell it, maybe a few years. It seems like that time period has expired, and now KUO can sell it to anyone wishing to market it.

I doubt if the holder can be rotated as that would probably unscrew it.

Unless @FLO can take a picture and demonstrate that their version of the curvy neck 1.25" diagonal does NOT have a constrictive ring at the bottom of the eyepiece holder, I would err toward getting a GSO made 1.25" dielectric diagonal. They are sold under the iOptron brand in the UK. They don't have a constrictive ring at the bottom of the eyepiece holder. I have a WO carbon fiber 1.25" diagonal that has the curvy neck, and it has the constrictive ring at the bottom that causes vignetting with widest field eyepieces. Since I only use it with a 22mm clear aperture binoviewer, I'm okay with it, though.