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vlaiv

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About vlaiv

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    Novi Sad, Serbia
  1. Are you certain that you are going to get 10 and 20mm with your Dob? Which one did you order? SW 8" Dob comes with 10 and 25mm eyepieces. 25mm is very decent eyepiece and you can use it for now for low power eyepiece. At some point you can think of adding 32mm plossl for wider views and as finder eyepiece. For around 18mm have a look at this one: https://www.firstlightoptics.com/ovl-eyepieces/skywatcher-extraflat-125-eyepieces.html (19mm is probably best option) A bit more expensive than Starguider, but supposed to be good. But if you get 20mm eyepiece with your dob - use that instead - very small change from 18mm and 19mm to 20mm. In this case add 32mm as wide field / finder eyepiece and just keep using 20mm as DSO eyepiece (but compare it to 32mm and see if it's good or needs to be replaced). 10mm that you get, might also be decent eyepiece, so don't discard it yet. Do get shorter FL eyepiece for planetary views, something like 6-7mm. This way you will know if your 10mm is good enough or you need replacement in this range (10-12mm). What I'm trying to say is: you don't need to rush into buying whole set of eyepieces until you had a chance to learn to observe and to see what sort of preference do you have in eyepieces.
  2. vlaiv

    Back Focus Issue?

    Almost, but not quite I also measured distance in pixels - or thickness of pattern and it's ~275px on right side and ~250px on left side. This is very big defocus pattern, so I can't tell how significant that difference is, if you want to make sure, maybe a take a series of smaller defocus patterns - starting with size of inner circle and doing 2 or 3 in decreasing diameter?
  3. If lifting heavy things is a concern, then think again about 8" dob. It's not the largest scope out there, but it's bulky. Basic version without goto is 26Kg - divisible in two parts. About 11Kg OTA (Optical tube assembly - or scope main tube) and about 15Kg base. OTA is somewhat bulky but easily carried by one person. Base is bulkier and you can carry it via handle - it feels like lugging around heavy bulky travel suitcase. Goto version is a bit heavier - due to motors on the base.
  4. vlaiv

    Back Focus Issue?

    This diagram explains nicely what happens when no flattener is in optical train - focus is shifted further away from objective. Indeed, with flattener it is the same thing - distance between flattener and sensor needs to increase (physical distance). This can be explained to same result in to different ways: 1. Flattener needs to be in certain position in converging beam after main lens (depending on primary lens focal length) and flattener does not really care what happens to the light after it passes thru flattener. It just sits there doing its thing. Since focus position moves away from lens, so does too from flattener - spacing between camera and flattener increases. 2. In above diagram we see that "physical path" gets longer than equivalent "optical path". Flattener needs to be placed at certain "optical path distance" from sensor, which in this case equates to longer physical path - hence longer distance from flattener to sensor.
  5. I don't think weight is going to be issue - but length might. I'm happy with HEQ5 performance with RC8" and all bits on it. That is easily over 10Kg of weight (bit less than 9Kg for ota alone). With that scope (125mm frac), setup is likely to be over meter long and that is quite arm momentum, so it could be a bit problematic in wind, but I don't have direct experience with such setup. I did mount 8" F/6 Newtonian that is over meter long, and total weight was certainly in 13Kg range (Ota is about 11kg and I used guide scope instead of OAG then - needed x3 5Kg CW to balance it), so it's doable but I would not call the performance reliable (I would not recommend anyone to take such combination seriously).
  6. vlaiv

    Back Focus Issue?

    Ah, my mistake - camera and the reducer - indeed that one should be increased to compensate for "decreased" focal position.
  7. vlaiv

    Back Focus Issue?

    Should that not be decreasing distance ?
  8. My bad! For some reason I read wrongly what has been advertised on FLO website, but here it is: It looks like you get 15% off for 4 or more and 20% for 7 or more
  9. I think that it's the same scope as following two (if that helps for finding reviews): https://www.teleskop-express.de/shop/product_info.php/info/p8637_TS-Optics-PHOTOLINE-80-mm-f-7-FPL53-Apo---2-5--Focuser.html and this one: https://www.stellarvue.com/stellarvue-sv80-access-ed-apo-refractor-telescope/ I'm myself considering "older brother" - 102mm F/7 version (also branded by TS, Stellarvue and AltairAstro - was looking at TS version). I think reviews on 125mm F/7.8 have been very positive (same series of scopes also branded by those three vendors). I'm not 100% certain that scopes are indeed the same optically as TS for example advertises them as being Lanthanum + FPL53 glass, while AltairAstro does not mention lanthanum glass (they don't state glass type as far as I can tell) and Stellarvue states it's "FCD100 and Lanthanum" combination. Other than that, specs are identical and they look exactly the same except for branding (AA version might have different looking focuser casing on closer inspection, but I believe internals are the same).
  10. I'm not sure about combination - someone who actually has these eyepieces and tried them with barlow will probably give more definitive answer, but here is my concern: BST's already have plenty of eye relief at 16mm. Adding barlow lens will cause them to increase eye relief even further. If it stays below or at about 20mm it will probably be fine, but if it's increased further - it might make observing difficult. It's hard to keep pupil centered at very long eye relief and you will not be able to see complete field from that far away. Some longer focal wide field eyepieces start to vignette when used with barlow - so that is also something that needs checking out. BTW, FLO is offering discount of 20% if you purchase 4 or more items in BST range (eyepieces and barlows), maybe three eyepieces and one barlow (x2) would be better option to consider?
  11. vlaiv

    Back Focus Issue?

    Ah, there is one more thing to check, since it's EdgeHD (I wrote above with refractor in mind) - collimation, make sure it's as good as it can be.
  12. vlaiv

    Back Focus Issue?

    I would say tilt. Not sure how sound is meridian flip as tilt can be due to gravity. Let's say we have two types of tilt - loose one and firm one. Loose one will depend on scope position - so aiming straight up should show even stars in all corners. Firm one would not change with scope orientation (there is tilt but sensor is not affected by gravity and does not change tilt in respect to optical axis). It could be de-center as well, sensor not being square on optical axis. There is "logical" way to assert this, and you can probably test it via flats. For logic application - compare sensor size to fully corrected circle of your setup - if it's just right with no room to spare - sensor of optical axis means one of the corners is outside corrected circle - and this is why one corner is most affected. This way is not very reliable - since spec for fully corrected circle are often misleading (inaccurate, or different meaning of word "corrected" is used ). Other way to check de-center (and I'm not meaning lens de center - but sensor center not being spot on optical axis) is to examine flats - these should be center symmetrical. Don't know how reliable this method is but I would try it. Do you have laser? You can put it instead of eyepiece and observe where it hits front lens - it should be in center (make some sort of paper circular mask with marked center to help you out). Mind you, laser should be well collimated, but you can check this by rotating laser - if spot stays in the same place, it's collimated properly. There is small chance that tilt + de-center will put laser spot in exact center of the front lens (angles of tilt and de center distance need to match perfectly). HTH
  13. vlaiv

    Compass Points

    I think easiest way to orient your sketch is to let target drift for a moment. Direction of drift is always in RA and it drifts towards west - so you have two points straight away - E-W direction. Then you just think about how your scope is providing image - is it upside down (like in newtonian and straight thru refractor) or not inverted vertically (scope with diagonal) and mark N and S accordingly (this probably changes on south hemisphere, but not completely sure ).
  14. vlaiv

    M31 - my first attempt

    Yes, this is better. Dust lanes definition improvement is noticeable. Still quite a lot softness, but as Olly pointed out - is probably due to seeing (and having tough time trying to focus in poor seeing), and not much can be done about that.
  15. vlaiv

    FTX Enhancements

    T, A, K, A, -huh H, A, S, H, I What an odd way to spell binoculars
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