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Pentax and Delos 3.5mm eyepieces


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1 hour ago, Dantooine said:

I’m at the same point in deciding which ones to keep. Someone will get some bargains at some point. The biggest expense in this hobby is the ones you sell 🤔

Or just never sell and become an astro hoarder like me. 🤪  I enjoy going back to compare newer acquisitions against older ones.  My grown daughter also gets to borrow some really nice eyepieces without having to spend any money at all, so there is that as well.

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22 hours ago, markse68 said:

wasn’t the XO range astro specific? they went to great trouble to minimise internal reflections in those I think

I really don't know about that, I have never had my hands on one, though I have seen people on site talk highly of them.

Alan

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1 hour ago, vagk said:

Is Pentax XW 3,5mm a good choice for maximum magnification in combination with SW ED80 (planetary and double stars)?

It gives 171x.

Mine is certainly sharp enough, but I rarely use it.  The exit pupil gets super tiny with scopes slower than about f/5 and my eye floaters become intrusive.  I have to keep flicking my eye to get them out of the way for a fraction of a second to get a sharper view.  Bright planets and the full moon tend to get washed out looking at those high powers for some reason.  You'd think the high power would take the brightness, but it doesn't.

I got much better views of Mars at the last opposition using an entry level binoviewer and a pair of vintage 15x microscope eyepieces with a nose piece from a vintage Meade 140 Barlow to reach focus and to boost power by 3x.  Depending on how much you pick up the various pieces for, it might be a wash cost-wise.

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22 minutes ago, Louis D said:

Mine is certainly sharp enough, but I rarely use it.  The exit pupil gets super tiny with scopes slower than about f/5 and my eye floaters become intrusive.  I have to keep flicking my eye to get them out of the way for a fraction of a second to get a sharper view.  Bright planets and the full moon tend to get washed out looking at those high powers for some reason.  You'd think the high power would take the brightness, but it doesn't.

I got much better views of Mars at the last opposition using an entry level binoviewer and a pair of vintage 15x microscope eyepieces with a nose piece from a vintage Meade 140 Barlow to reach focus and to boost power by 3x.  Depending on how much you pick up the various pieces for, it might be a wash cost-wise.

I have also a SW 12 dob f/5. Pentax XW 3,5mm will give 428 mag. I am sure I will rarely use it (when seeing is perfect), but I have eyepieces 70° and above with 4+ elements so I avoid using barlow. That's why I am thinking of it. For ED80 it is on the limit. 

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2 hours ago, vagk said:

Is Pentax XW 3,5mm a good choice for maximum magnification in combination with SW ED80 (planetary and double stars)?

It gives 171x.

As Louis says, the scope will take it, the question is will your eyes? That combination gives a 0.47mm exit pupil and will show up any floaters that you have. If your eyes are good with minimal floaters then on nights of good seeing it would be worthwhile. Otherwise binoviewers are well worth considering although these can be quite a personal choice as to whether you get on with them or not.

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34 minutes ago, Stu said:

Otherwise binoviewers are well worth considering

Are you saying using binoviewers allow you to see smaller exit pupils more easily than one eyed viewing?

I had very floater free vision until a year or so ago - since when I've had to limit my very high magnification / small exit pupil viewing.

I miss it very much... maybe a binoviewer would help?

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Binoviewers help in six main ways I've found:

  1. With two eyes, the brain selectively filters out floater blockages from one eye with information from the other eye creating a much better image.  It has its limits when floaters in each eye obscure the same part of the view.  Try closing one eye for a while and look at a clear blue sky.  You'll see obvious floaters.  Now open both eyes and look again.  Fairly quickly, the obviousness of the floaters dissipates quite a bit.
  2. Overly bright objects like the full moon, the solar disk, and planets at opposition are much improved with two eyes.  I chalk it up to the brain not being able to combine a super bright image with a pitch black (or nearly so) image.  On both the full moon and Mars, I have gone from seeing a washed out disk to high contrast, detailed views just by switching to my binoviewers.
  3. Two eyes working together is much more natural for the brain to process, and low contrast details just seem to pop in binoviewers that were all but indiscernible with one eye, even with dimmer objects that aren't washed out in monovision.
  4. Eye strain disappears and viewing become very relaxing with binoviewers once you get everything dialed in perfectly (which admittedly can take some trial and error).  I stared at Mars for 20 to 30 minutes at a time without fatigue.  It was an amazing feeling.
  5. The apparent field of view appears about 5 degrees wider than when monoviewing with the same eyepieces.  My 60 degree AFOV microscope eyepieces appear to show about a 65 degree AFOV.  I think your brain normally stiches together two images of slightly different viewpoints into a wider TFOV image (try closing one eye to see how much TFOV you lose); so instinctively, you perceive a two eyed view as being wider even if it is showing the exact same view as monovision.  As such, I don't feel compelled to search out ever wider AFOV eyepiece pairs.  Besides, you can't see the edges except in peripheral vision because the moment you look off axis, you lose one, and sometimes both, eyepiece views.
  6. You don't need ZAOs, TMB Monocentrics, Vixen HRs, or Tak TOEs to see low contrast, fine detail with binoviewers.  Fairly basic eyepieces that are well executed give excellent views in BVs in my experience.
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