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pregulla

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About pregulla

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    Star Forming

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    Israel
  1. There is a confusion between two things in this thread. First - decrease in image brightness as a result of increased magnification/decreased exit pupil. Everyone agrees on that, but this effect is not unique to Barlow. If you just use eyepieces with different focal lengths the effect will be the same - dimmer image at higher magnification. Second is reduced light transmission due to extra glass added. With good quality Barlow this effect is too small for human eye to detect. It is unrelated to all the principles described above and this is what people mean when they say Barlow doesn't decrease brightness. Lets say you use 20mm eyepiece. Then you add 2x Barlow. The image got 4 times dimmer because of increased magnification and say extra 3 percent dimmer because of light transmission loss. Now you just use 10mm eyepiece. The image is still 4 times dimmer compared to 20mm just without the extra 3 percent loss. If you compare 10mm to 20mm+2x Barlow you won't be able to tell the difference in brightness. So we can say Barlow doesn't decrease brightness, now that we have taken the effects of magnification out of the equation.
  2. The article is poorly worded (or the author is decieving on purpose?). Doubling the magnification will reduce the brightness by a factor of 4 (or by 75%). It doesn't matter if it is done by using a barlow or a shorter focal length eyepiece. The article makes it sound like a barlow robs you of 75 percent of light that would be there if you just used an eyepiece, which is false. Quality barlow with modern coatings will only loose few percent of light.
  3. I replaced mine with bellville washers. 16mm OD, 8mm ID IIRC. 3 in series on each screw, depending on how much travel you need.
  4. Try rotating the laser or the cap inside the focuser. If it changes how your collimation looks you know they are off.
  5. You probably won't be able to tell the difference between 92% and 99%. Though I think Meade comes with erecting prism, then getting a star diagonal will be benefitial. I woudn't bother with filter yet. It helps a little, but doesn't iliminate light pollution. With my 8" dob the difference is pretty marginal - it helps to bring out a little more detail or detect what can't be seen at all without a filter, but not even close to what it is like under dark skies. Plus with 70mm under light polluted skies you are pretty much limited to brighter clusters, and UHC won't help you with those.
  6. From a city (Bortle 8 ) with 8x42 binoculars Andromeda looks like very faint, barely detectable fuzzy patch, no core or other details. As skies get darker it gets brighter, larger and the core becomes visible
  7. How long do you plan to spend there? For one night 3 hours extra sounds like a lot and I would probably settle on bortle 3. If it's more than that I'd go for as dark site as possible or you will keep wondering how would it be under darker skies. Bortle 3 is the darkest available for me. I live under bortle 6 skies and the difference is huge. I can barely detect the milky way at home, at bortle 3 site it looks very detailed and impressive. My first night I spent more time with binoculars than a telescope. Obviously DSOs look more impressive too and fainter ones can be seen.
  8. So I got 120mm in the end. AZ3 is pretty solid, at least at lower powers, but the balance is an issue. The scope will nose-dive near horizon and butt-dive near zenith. And that's before even getting 2" diagonal. Seems like it should be decent enough if I can fabricoble a ciunter weight.
  9. There are many good options. It all depends on what you are looking for. How much would you like to spend? How much eye relief you want/need? Do you observe with glasses? Do you prefer a zoom or single focal length eyepieces. How wide of a field do you want? I would start with getting 2" diagonal if it doesn't come with one, 2" Wide filed eyepiece in the 30-40mm range, a zoom eyepiece and a quality 2x barlow. That will get you covered from low to high power until you figure out what your preferences are and have a better ideas what eyepieces will suit you best. If you buy used you can swap later at minimal loss.
  10. I am using 40mm with mine. All 2" eyepieces I tried come to focus with it (Aero ED 35mm, Meade QX 26mm, ES82 30mm, SkyWatcher SWA70 32mm). I also use it with 1.25" to 2" adapter which is about 10mm tall and all my 1.25" eyepieces come to focus. I also know that 50mm was too much for SkyWatcher SWA70 32mm, I didn't try with others.
  11. Having multiple eyepieces with cracks would make me wonder if I store/handle my eyepieces properly. I also never came across eyepiece that I would describe as dirty on the inside. I didn't have a whole lot of cheaper eyepieces, 10 total maybe. Some may have had a spec of dust or flake of paint between lenses. But nothing so bad that I would call it dirty. I am sure there are some out there as a result of poor QC of the cheaper products, but they don't tend to be this way from my experience.
  12. The 35mm works fine in my F/5 12". I may be loosing some aperture with it, but I don't notice any negative effects. I also have ES82 30mm, but I feel it's a "little" overweght for this task. I think on steel tripod AZ5 should be fine. On the original aluminum tripod I am afraid 120mm will be too much for it. How is the AZ4 with it's original aluminum tripod? Overall I get a feeling from all the reading that AZ5 is better with short scopes. AZ4 is sturdier and more convinient with longer scopes. Since I am getting AZ3 with the scope anyway I may try to make it work first. I have seen reports that after balancing it was acceptable for 120mm. If I was going to pay for the mount, "acceptable" woudn't be something I want, but for a freebie I will give it a shot.
  13. ST120mm just shower up on a used marked locally. Comes with AZ3, but the price is right. For 120mm I feel less confident with aluminum legs, so I'll probably get AZ5 with steel legs, especially since the difference when buying just the mount (head+tripod) and not the scope combo is not that big.
  14. OK, AZ3 is out of the question then. Turns out Telescope-Express were underestimating shipping costs for AZ4 (it's like 100 EUR extra), so AZ4 doesn't fare well against AZ5 price-wise. Looks like AZ5 is the way to go.
  15. Hi All, I have decided to get a fast achromat to complement my dobs for low power wide field views. The SW Startravel 102mm seem like a perfect choice . I plan to get 2" diagonal for it and use it with 35mm Aero ED eyepiece (about 360g). The question is what mount would be the best choice? I plan on buying from Europe, since buying locally is way too expensive and options are very limited. The options I have thought about: - OTA+AZ3 bundle, about 270 EUR. Cheapest option, but AZ3 seems like not the best fit for purpose. From what I understand it goes out of balance at higher altitudes and gets inconvenient to use. I may still get the package and upgrade later if I don't like it. The problem is I'll have to pay for shipping again. - OTA+AZ4/AZ5 with aluminum tripod. about 400 EUR - Getting separately the OTA, AZ5 and stainless tripod: About 490 EUR. - AZ5 Shipped separately if I want to upgrade from AZ3: 257/288 EUR with Al/SS tripod - SS tripod shipped alone - 143EUR I am leaning towards getting the AZ5 with Al tripod. Should be fine for the Startravel 102. Upgrading to SS later will cost 50 EUR more than buying it straight away, but I will have the Al tripod too, so not too bad. Any comments? Are there other options that I am missing? Maybe there is a different OTA that comes with better tripod and would make a better deal as a package (Something around 100mm F/5 - F/6, 2" focusser)?
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