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John

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Posts posted by John

  1. The edge distortions will depend on the spec of the scope that the eyepiece is used in. In an F/10 or slower scope, most eyepieces are sharp to the edge of the field of view. At F/4 most will show some distortion.

    Scopes also have some distortions of their own to add to the mix eg: coma with a newtonian and field curvature with refractors.

    I don't know what spec of scope Louis D's field photos were emulating. It would be interesting to know :smiley:

    • Like 3
  2. 23 minutes ago, Deisler said:

    Thank you.

     

    I have checked many threads here about TV Barlow vs TV Powermate. I understand the major differences, i.e. the eye relief. How much gain in visual I can expect between TV Barlow and PM?

    Am I right to say Powermate is a better long-term buy as I will never need to replace it? If so, I'd rather buy the Powermate. 

    In pure optical terms the differences might be slight or non existent . Barlows can vignette the field of view of eyepieces with wide field stops and push the eye relief outwards a bit. Powermates and Telextenders don't have these effects. There are other telextender options which cost less than Tele Vue though. The Explore Scientific 2x Focal Extender is one that is very good.

     

     

    • Like 2
  3. With the F/6 focal ratio of the 200P dobsonian you don't really need Tele Vue quality to get great results. If you eventually move to something a little faster which typically you need to do to get larger aperture dobs / newtonians, the edge of field correction becomes more important. The Morphus reportedly is pretty good though, even in faster scopes. It was not around when I was building my eyepiece collection.

    Scopes tend to come and go but a good eyepiece set can stay with you for life !

    • Like 2
  4. My regular eyepieces are Tele Vue and Pentax but I've owned and used a few BST Starguiders and I think they are really pretty good eyepieces for their cost (£50 new, £30 or so on the used market).

    The BST's are a significant improvement over the stock eyepieces in my opinion. Going beyond them to, say, £100 - £200 apiece eyepieces and the peformance gains are much smaller.

    Your £200 would get you 4 focal lengths in the BST Starguider range, or 3 plus a barlow lens. The Baader zoom is pretty good as well but the field of view at the 24mm focal length is limited so you would need something like a 30mm NPL plossl to get those wider / low power views and also something shorter such as a 6mm for the higher powers that the scope is capable of. Budget blown a bit I suspect !

    The Powermates are superb but one swallows up most of your budget and Powermating the stock eyepieces is not going to turn them into great eyepieces I fear.

    • Like 4
  5. 3 hours ago, Rob said:

    I had one of the WO -V filter and found the same John. I now switch between a Baader Fringe Killer & Wratten #8.. that said I often dont use one at all!

    I don't recall the Bresser 127-L that I had producing any really objectionable CA Rob. A good 5 inch achromat I thought :smiley:

    • Like 1
  6. I used a William Optics Minus Violet filter with a 150mm F/8 achromat refractor a few years back and compared the views of the moons limb with and without the filter. I found that the filter reduced  the visible violet fringe by around 50%. The flip side was a pale lemon tint to the overall view. The CA was still visible but it was reduced.

     

    • Like 2
  7. The Baader Semi-Apo filters get decent reviews and seem work well:

    https://www.firstlightoptics.com/baader-filters/baader-semi-apo-filter.html

    The Baader Fringe Killer does a similar job:

    https://www.firstlightoptics.com/baader-filters/baader-fringe-killer-filter.html

    As does the Baader Contrast Booster:

    https://www.firstlightoptics.com/baader-filters/baader-contrast-booster-filter.html

    I believe the Semi-Apo produces the most natural tint to the view wheras the other two do introduce a slight hue to the image.

    Here is some further discussion on these:

     

  8. 4 hours ago, JOC said:

    DSO's always seem a bit problematical for me in terms of EP.  The issue I find is the sheer range of sizes that they are and the range of visibility in the sky.  I often think that there is probably not a one size fits all DSO EP out there!  I have a full range of EP's still struggle to find many of them!

    I agree. Practially all my eyepieces have proved useful for observing DSO's of one type or another. Tiny planetery nebulae need a lot of magnification to differentiate them from stars. The Veil Nebula needs a field of view 6-7x as large as the moons disk to fit the whole thing in.

     

    • Like 3
  9. 3 minutes ago, Raph-in-the-sky said:

    Very interesting! How good is the GSO/Revelation coma corrector? Obviously I am not expecting Paracorr performance but how does it compare to other cheap coma corrector (SW, baader,...)?

    Would you care to eleborate?

    I realise that there is some relevance with this thread but I'm keen that we don't go off on a tangent on coma correctors when the original question was about eyepieces :smiley:

  10. 1 hour ago, davhei said:

    Thanks! Do you know the differences between the Vixen and the 22 mm T4 Nagler? I would assume there would be similarities and the Naglers are always held in high regard. Do the Nagler need coma corrector to get sharpness across the full field while the Vixen albeit with a smaller tfov has sharp stars almost to the edge?

    I've owned both the Nagler 22mm T4 and the Vixen 22mm LVW. They are quite different designs but peform equally well in terms of sharpness across the field of view. In a F/4.7 newtonian the Nagler will show more coma though because it shows more off axis field than the LVW. Not the fault of the eyepiece but the nature of fast newtonian optics. Both comfortable eyepieces with good eye relief and large eye lenses. Quite a bit difference in price though.

     

     

     

    • Like 1
  11. The relationship between the diameter of the eye lens and the size of the apparent field of view is quite complex eg: my Delos eyepieces have a 72 degree apparent field but their eye lenses are about 50% larger in diameter than my Ethos eyepieces with their 100 degree fields. I believe that the diameter of the eye lens is more connected with the eye relief of the eyepiece than it's field of view.

    Amongst the largest eye lenses out there belong to the ES 92 degree eyepieces, which also have long eye relief, considering their very large apparent fields.

     

     

    • Like 3
  12. 6 hours ago, Timebandit said:

     

    That would be an impressive eyepiece and diagonal in my eyepiece case or should that be cases.

    Christmas is on the way, that would be a great present from Santa😀

    Dare I ask the price ???😵

     

     

     

    I hope you have been a good boy this year :icon_biggrin:

    FLO list the 30mm / 100 ES at £860 and the 3 inch ES diagonal is $400 currently in the USA but I can't find it listed in the UK currently.

    So still less expensive than the TV Apollo 11.

     

    • Haha 2
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