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  #21  
Old 06-08-2018, 12:26 PM
morls (Stephen)
an endless wholeness.....

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I'm trying to find out. I've just called skywatcher, who couldn't tell me immediately, but they're going to call back.

It's a hard spec to track down, so I'm very interested to know exactly what the diameter is.
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  #22  
Old 06-08-2018, 04:41 PM
Wavytone (Nick)
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Stephen, sorry I forgot - Steffen is half correct - the aperture limiting the exit beam is the diameter of the hole at the backplate, you can measure that for yourself with a rule.
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  #23  
Old 06-08-2018, 05:40 PM
morls (Stephen)
an endless wholeness.....

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Well, I just measured it and the results are very interesting...

The diameter of the backplate exit is 1.25". I can see the diameter of the inner baffle from the secondary is also 1.25"

So it seems it doesn't have a 2" visual back as I'd come to believe after reading others state this as so. It's a 1.25" system.

Does this mean a 2" diagonal and 2" eyepieces are essentially a waste of money?
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  #24  
Old 06-08-2018, 07:12 PM
morls (Stephen)
an endless wholeness.....

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Thinking some more about this now...if the practical field stop of this scope is 1.25", let's say 32mm, then I assume this is the largest eyepiece field stop I can effectively use.

I've made up my mind to get a televue for wide views (at least as wide as the scope can provide). I think the 35mm Panoptic is out because of the 38.7mm field stop. This leaves me with a choice between:

27mm Panoptic with 30.5mm field stop, x100 mag, 1.8mm exit pupil and 0.65 degrees true field
22mm Nagler with 31.1mm field stop, x123 mag, 1.5mm exit pupil and 0.66 degrees true field

I have a couple more questions:

The 22Nag isn't listed on the Bintel site - has this been discontinued?

Would a 1.25" diagonal with 2" eyepiece adapter suffice, given the above eyepiece field stops?
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  #25  
Old 06-08-2018, 07:22 PM
Wavytone (Nick)
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Quote:
Originally Posted by morls View Post
Does this mean a 2" diagonal and 2" eyepieces are essentially a waste of money?
No, not at all. Personal experience is that it will usefully fill the field of 2" low power eyepieces with larger fields than what is possible in 1.25" barrels. As I indicated below your eye won't notice much until the vignetting exceeds 50% and that occurs when the field reaches about 40mm diameter.

For example the ProStar 38mm 70 degree UWA and Vixen LV50mm are both excellent in this scope.

But you are intent on using 2" eyepieces with no field stop at all, you will find the image is cut off by vignetting just inside the field stop. And example is the TMB Paragon 40mm which is also rebranded as various clone such as Titan II etc.

The same occurs in many newtonian telescopes - the size of the secondary mirror is often a compromise between the desire to deliver the full light cone over a reasonable field of view, vs the size of the central obstruction caused. The result is many opt for a diagonal that will cover a 20mm field but beyond that it starts to vignette.
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  #26  
Old 06-08-2018, 07:28 PM
morls (Stephen)
an endless wholeness.....

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Thanks Nick, I really appreciate the help. I'm on a bit of a learning curve here...
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  #27  
Old 06-08-2018, 07:42 PM
Wavytone (Nick)
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Here's an analogy.

Take the cardboard tube from a roll of paper towels or gladwrap.

Hold it up about a foot from your eye and look though it.

Move your eye side to side. You will notice the light passing through isn't cut off immediately your eye is in line with one side (or the other). In fact your eye can be significantly beyond the edge of the tube before you see nothing through the tube. So in other words the useable field of view is significantly wider than just the diameter of the tube.

You're not a bit OCD by any chance ?
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  #28  
Old 06-08-2018, 08:22 PM
morls (Stephen)
an endless wholeness.....

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Quote:
Originally Posted by Wavytone View Post
You're not a bit OCD by any chance ?
maybe a little...
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  #29  
Old 07-08-2018, 04:25 PM
morls (Stephen)
an endless wholeness.....

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I've found the info I need, so thanks to everyone for trying to help. My questions centred around whether a 35mm Panoptic and 2" diagonal would work, which a lot of people have already commented on .

It was a post from user Tanglebones (Stu) (in stargazerslounge.com back in April 2016) that finally convinced me, so I'll copy it in here just to finish this thread.

Thanks to all who helped. and apologies for the barrage of posts!

Stephen

In one of my last posts I mentioned wanting to try the Panoptic 35 (P35) on M42 and I had my chance a few weeks ago out at a darkish-sky site. First though, here is an entry from my observing log taken on the 27th of September 2014, which is the first time my eyes ever looked at M42 through a telescope - "I have to say, M42 was a bit underwhelming and Iím not sure why.Ē Contrast this with my entry on Friday, 11th of March 2016, which is when I went out to the dark sky site::

Tonight, there is only one word I can use to describe M42. Two words. Absolutely stunning. Oh, how my comment of 2014-270/21 comes back to haunt me ("I have to say, M42 was a bit underwhelming and Iím not sure why.Ē). I have never seen M42 looking so beautiful and I think I am just a little bit in love. And not just with M42, the TV35P was pretty much my only eyepiece for the majority of the evening. Using it, I saw the Trapezium as clearly as if I was there. Pin-sharp and very bright, surrounded by fold after fold of billowing nebulosity. That nebulosity seemed to take on a 3D perspective, even though I knew I wasnít seeing it as such. It looked like it had depth to it, though, like it would look as I approached it.

The fish mouth was dark, far darker than I think Iíve seen before in other scopes. As too was the dark nebulosity that separates M42 from M43. I also saw the swept-back Ďwingsí for the first time, matching what I see in peopleís images. And those three distinct stars all lined up underneath the starboard wing. And all this was before trying the UHC and OIII filters. Under the UHC filter, the Trapezium stars were a bit harder to see but I attribute this to the extra nebulosity I was observing, which only enhanced the 3D-like experience. The stars all had a blue-green tint to them, but strangely this didnít detract from the view. It gave it an unearthly, surreal perspective. I then switched to the OIII filter and there were less stars again and I noted the nebulosity had a different shape to it.

It amazes me that this hauntingly beautiful sight was right there for me to view my entire life, and until just over a year ago I never took the time. Iím so glad I finally did.
The views through the two DeLites are *almost* as good, but not quite, which I attribute to illumination of field. They are just as sharp and clear as the P35, but not quite as well lit. That Panoptic 35 is now my go-to eyepiece and it is always the first one I reach for. I haven't noticed any vignetting at all. If it is present then it is very subtle. So if any others find themselves wondering which eyepiece will give them the widest possible field of view in a Sky-Watcher Mak 180, with a minimum of distraction, then I highly recommend they look at Tele Vue's Panoptic 35. In this particular telescope it gives some lovely, lovely views.
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  #30  
Old 07-08-2018, 04:29 PM
Wavytone (Nick)
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I'd also suggest you refrain from cross-posting here on IIS and on CN. One or other will achieve what you want as many read both sites.
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  #31  
Old 07-08-2018, 04:34 PM
morls (Stephen)
an endless wholeness.....

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Sorry, my mistake. I've just emailed CN mods to get that post removed.
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  #32  
Old 12-08-2018, 05:42 PM
Kunama (Matt)
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The actual visible differences in real life are very small, often not visible at all.
The only exceptions I have found are the Baader BBHS coated prisms and mirrors.

The Baader ones also have their ClickLock eyepiece holders which are superb.

The views through the various dielectric ones are very very very similar...

I did not see any difference between the AP dielectric and the Baader dielectric when testing on my TOA130....
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  #33  
Old 12-08-2018, 05:57 PM
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LewisM
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Quote:
Originally Posted by Kunama View Post
I did not see any difference between the AP dielectric and the Baader dielectric when testing on my TOA130....
Maybe - just maybe - that's because Baader makes the MaxBright for AP (just buy the Baader badged one and save about $50)
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