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Old 17-06-2021, 10:38 PM
Hemi
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Pentax 40mm XW-R vs Panoptic

Anyone care to share there opinion between these two?
Mostly for a c11. Want to max out my TFOV. Currently have a ES 30 82.

Cheers

Hemi
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Old 18-06-2021, 12:33 AM
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Stonius (Markus)
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I wouldn't have thought the field of view would be much different between them.


Markus
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Old 18-06-2021, 01:53 AM
astro744
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Field stop diameters (mm): (listed in increasing true field for any given focal length of telescope).

Tele Vue Ethos, 100 deg., 21mm = 36.2mm
Tele Vue Panoptic 68 deg., 35mm = 38.7mm
Tele Vue Type 5 Nagler 82 deg., 31mm = 42mm
ES, 82 deg., 30 = 43mm
Tele Vue Plossl, 50 deg., 50m = 46mm
Tele Vue Panoptic 68 deg., 41mm = 46mm
Ricoh Pentax XW40-R, 70 deg., 40mm = 46.5mm

True Field of view (deg) = Field Stop Diameter (mm) x 57.3 / Telescope Focal Length (mm).

You gain only a few percent more true field going from 43mm to 46 or 46.5mm. However you do gain a significant increase in exit pupil which at f10 is important.

Exit Pupil = telescope aperture / magnification
also
Exit pupil = eyepiece focal length / telescope focal ratio

ES 30 gives 3mm exit pupil
Pan 41 gives 4.1mm exit pupil
Plossl 55 gives 5.5mm exit pupil

A larger exit pupil gives a brighter image including background sky which will affect contrast. I think on an f10 SCT there is merit in going from 30mm to 40mm not so much to gain a few percent of true field but more so to gain a boost in exit pupil (unless you are in the middle of the city and require maximum contrast).

Edit:
I use a Panoptic 41mm on my C9.25. I have not used a Pentax XW. The 41 Pan is a heavy eyepiece and benefits from a diagonal that is single piece construction (Tele Vue) to avoid possible unscrewing of the diagonal nosepiece (as found on other diagonals). However I keep my Tele Vue diagonal in my refractor kit and use a WO diagonal on my SCT. As long as I keep the eyepiece vertical it’s OK. A drop of glue on the diagonal nosepiece thread would fix this but I would rather not do this. As for the views I find the 41 Panoptic gives excellent low power views in my all of my telescopes ranging from refractors, Newtonians and SCT. I have the 50mm Plossl too but prefer the 68 deg field of the Pan although the Plossl gets used at times.

Last edited by astro744; 18-06-2021 at 09:22 AM. Reason: Added last para. and corrected C11 from f11 to f10
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Old 18-06-2021, 06:51 AM
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mura_gadi (Steve)
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Hello,

Pure numbers, based on C11 Edge series using astronomy tools.

Pentax 40mm: 70mag/1 degree fov/3.99mm exit pupil
ES 30mm 82: 93.33mag/.88 degree fov/2.99 exit pupil

Either are good exits pupils, both are great pieces, eye relief is the biggie between the two.




Steve
PS. Reducer would be a good way to go maybe?
Pps. You will be hard pressed to get more than a degree (Es 25mm 100degree will get you .89degree fov) - Masuyama will get you a wider range of exit pupils, they have 40/50/60mm ep's at 46-53degree. The 60mm at 46degree would just fit inside the 40mm Pentax though (46.67mag/.99degree fov/5.98mm exit pupil).

Last edited by mura_gadi; 18-06-2021 at 09:11 AM.
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Old 18-06-2021, 09:27 AM
Hemi
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Thanks for the replies everyone.

I agree the TFOV would be similar in both, I was asking as to which users thought was better optically.
I personally think I will notice the FOV increase from .88 to 1 degree.
I like that the Pentax is smaller/lighter.

I usually base my EP range on Exit pupils, but these are same FL and in same scope so exit pupils will be the same, in this case 4ish, which is great.

Cheers
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Old 19-06-2021, 11:29 AM
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Quote:
Originally Posted by Hemi View Post
Thanks for the replies everyone.

I agree the TFOV would be similar in both, I was asking as to which users thought was better optically.
I personally think I will notice the FOV increase from .88 to 1 degree.
I like that the Pentax is smaller/lighter.

I usually base my EP range on Exit pupils, but these are same FL and in same scope so exit pupils will be the same, in this case 4ish, which is great.

Cheers
Didn't the Pentax 30 and 40 go out of production at one point? I think its only recently reinstated. That would have to be a consideration as well. Don't assume it will always be available.

Greg.
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Old 19-06-2021, 06:21 PM
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Stonius (Markus)
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Well, If you decide you *do want the xw40, I've been thinking of getting rid of mine. The exit pupil doesnt work with my dob, which is what I use for most of my visual observing. It's in good nick, with box . $550 would do it I think, if you were in the market for a second had one.

Markus
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