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Paz

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About Paz

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    Sub Dwarf

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    Midlands, UK
  1. Paz

    180 Mak Focuser

    I use one of these focusers on a maksutov and an SCT and they do make it easier to get the focus spot on. They add quite a bit of weight though so if you have a mount that is being pushed already then one of these will exacerbate the issue. I have a dovetail balancing weight that I use to offset the weight with my 127mm maksutov, but with a bigger scope like your 180 it probably won't need one.
  2. Paz

    Eyepiece repurpose

    I got myself a second hand small cheap achromat and the various plossls that come with scopes are all in a small bag with that as my smallest grab and go set up. If you have any matching ones they could get you started with binoviewers.
  3. Paz

    Oops

    Maybe eating cables adds a bit of excitement and variety to their day?
  4. Paz

    Wider FOV eyepiece for Mak

    My own experiences around this are I use a 32mm plossl for wide fields in my 127mm maksutov and 200mm SCT. I have a 32mm plossl because it has more eyerelief than the 24mm/68 degree options I've looked at and it gives a darker background than a 40mm plossl. If it wasn't for the eyerelief issue I'd have a 24mm. I've got an 0.63 focal reducer for the SCT but I admit I don't use it, it's more glass in the light path and although it's been a while since I tried it I think I recall seeing the secondary or a shadow from it if trying to go really low in magnification. For finding things I use a 9*50 finder and this makes it possible to leave the main scope on very small fields of view and still find things ok. If you want to stick to one scope and make it as flexible as possible a focal reducer will expand its capabilities a bit, and is a lot smaller, cheaper, and simpler than getting another scope, but I would recommend considering just getting a 32mm plossl or a 24mm wider field eyepiece.
  5. Paz

    Televue Dioptrx

    The Dioptrx has at last had its first run out. I tried it with an ST120+Baader Mk4 Zoom+1.5x Barlow at 24mm all the way through to 8mm. I really struggled with getting it aligned in the field in the dark, and although it does fit on the Mk4 it's not as solid as I would like. In the end I would hold it up to the moon directly, rotate it around to the correct alignment and the try to go back on the eyepiece without losing the orientation. I thought this was quite a bit of hassle and it will be sensible to somehow mark the right orientation so I can feel it with my fingers in the dark and line it up easily. I found it really hard to notice a difference but the seeing was poor, thin cloud was not lifting and my scope was not cooled because I was lazy. Using a light mount (again too lazy to get out a heavier mount) meant vibes every time I adjusted it and this put me off trying for too long. I then tried a 4.5mm Delos. The fit was much better but it is a hassle removing the rubber eyecup on the Delos in order to put on the Dioptrx. Again I could not see a noticeable difference but the conditions were still poor. This is disappointing so far but probably not the fairest of tests. I realised while packing up that at small exit pupils the benefits get less and that may also play a part. The next time out I aim to have the correct orientation marked, and pick wide field clusters or star fields observing them with large exit pupils and better conditions. That ought to be a better test.
  6. Paz

    Lovely moon.

    It does look good, It's thin cloud for me but I've got a scope on standby in case the cloud clears.
  7. I think aperture is the first thing to consider, you can use different eyepieces to achieve the same magnification from different focal length scopes but the aperture of a scope can't be increased other than by buying a bigger scope. Size and ease if handling is another consideration. I have scopes similar to example 1 and example 2, and in practice the scope similar to example 1 gets more use as it is less bulky (by which I mean the tube is shorter), even though the quality if the views is slightly poorer.
  8. Apologies for going slightly off topic but I was interested to know what is that scope?
  9. The f/ratio is the same but the question is despite the f ratio being the same is the image quality the same. I was thinking not because, taking say spherical abberation the spread of the focal points is a certain amount with full aperture (say "a" in Diagram A below), less with an on axis sub aperture ("b" in diagram B below), but, and this is the key bit, it goes back to being the same length with an off axis sub aperture ("c" in Diagram C below) as it was with full aperture. If this was the case (and that is an if) then you don't get f-ratio related benefits from an off axis sub aperture as you would with an on-axis sub aperture, although you may get other benefits such as eliminating a central obstruction(?).
  10. I see what you mean, the angle between the edge rays is the same but then say in diagram 4 for the off-axis sub-aperture one of the edge rays is on-axis and the other edge ray is further from away from on-axis than with diagram 2 where the edge rays in the on-axis sub aperture are not as far away from on-axis - would that make any difference.
  11. I have been thinking about off axis apertures and the effect they have on f-ratio and aberrations and am not sure what to make of it. I would be interested in any insights and seeing what others think as I may be confusing myself! Here's where I have got to... I've drawn some pictures below and the commentary refers to them... Diagram 1 and 3 - Taking a scope with a 1cm clear aperture and a 5cm focal length as the reference point, 5/1=f5 (diagram 1 being a refractor and diagram 3 being a reflector with a central obstruction and secondary vanes) Diagram 2 - An on-axis aperture stop in a refactor of half the aperture leads to 5/0.5=f10 (diagram 2). Diagram 4 - However, what does an off axis aperture of half the aperture do??? In one sense (and this may or may not be faulty thinking) the aperture is still 0.5 so 5/0.5=f10 (diagram 4). This is what I have been wondering ... The light cone in diagram 2 with the on axis sub-aperture looks like an f10 light cone, with a nice slow angle of rays arriving at the focal point, but the light cone in the off axis sub aperture in diagram 4 just looks like half of an f5 light cone, i.e. the light arriving at the focal point is still a fast/steep cone. I thought if this is the case then the off axis aperture won't provide any benefits driven by improving the f-ratio and therefore any aberrations driven by f-ratio would remain the same. But if that line of rationale is correct then why bother with off axis apertures? I then thought on any refractor I've seen an aperture stop on it is always central - and this would make sense as that would give the best f-ratio improvement, whereas I've only seen off-axis sub apertures on scopes with central obstructions. I know under a number of conditions/circumstances I get sharper / better views with an off axis sub aperture in my VX14 and had always had f-ratio improvement as one of the reasons but what if the f-ratio is actually no better? I am wondering if it is just because of the elimination of the central obstruction and spider vanes (and maybe sometimes the smaller aperture just works better with the seeing). Diagram 5 - The last diagram shows how the off axis aperture in a scope with a central obstruction has to be less than half the full aperture in order to not overlap the central obstruction, which leads to a small difference for scopes of this nature. In this case say the actual aperture is 0.4. Then the light cone genuinely is actually slightly slower than the full f5 light cone because it is less than half of the aperture. The simple maths of focal length / aperture leads to f12.5 but in fact is it more a case of an effective focal ratio somewhere close to but slower than f5? In the end I got to thinking in refractors does an on axis sub aperture just provide the benefits of an improved f-ratio whereas off axis sub apertures on scopes with central obstructions just provide the benefit of having no central obstruction???
  12. Paz

    Televue Dioptrx

    In testing it straight through I have figured out the right orientation for both my eyes and I've practiced removing and replacing the rubber eye cups so that I can do it in the dark without doing a finger-plant on a lense by mistake, it's now just a case of waiting for a clear sky - which could be some time! Trying it out just looking at a distant street light in the dark isn't the most scientific of tests but it looks very promising.
  13. I'm only middle aged so can't talk about experience over 70, but I can say my children always beat me significantly on how faint they can see.
  14. Paz

    A Theft, Check Your Insurance

    I agree with the idea of trying to prevent anyone knowing you have anything of worth. Any half decent theif is going to steal anything they want and mostly get away with it.
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