M42 - 30mm - 23.2mm eye tube adapter warning.

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blekenbleu
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M42 - 30mm - 23.2mm eye tube adapter warning.

#1 Post by blekenbleu » Thu Aug 11, 2022 5:27 pm

This Cnscope adapter seemed ideal for adapting a 23.2mm centering telescope to 30mm eye tubes,
Image
https://www.ebay.com/itm/224158403124
...but the i.d. is nearer 26mm, too loose a fit IMO.

This was remedied using bits of HVAC pressure-sensitive aluminum tape:
Image
Metaphot, Optiphot 1, 66; AO 10, 120, EPIStar, Cycloptic

LouiseScot
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Re: M42 - 30mm - 23.2mm eye tube adapter warning.

#2 Post by LouiseScot » Fri Aug 12, 2022 10:28 pm

It says it's a C-mount internal thread = 1" = 25.4mm?

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

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Re: M42 - 30mm - 23.2mm eye tube adapter warning.

#3 Post by blekenbleu » Fri Aug 12, 2022 11:32 pm

LouiseScot wrote:
Fri Aug 12, 2022 10:28 pm
C-mount internal thread = 1" = 25.4mm?
There are internal threads, for about 6mm, in the tube at the end opposite the T flange.
It could not be used for a C-mount camera in a 30mm eye tube.
I lack C-mount stuff to verify that thread.
Tube length is about 28mm.
Metaphot, Optiphot 1, 66; AO 10, 120, EPIStar, Cycloptic

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Re: M42 - 30mm - 23.2mm eye tube adapter warning.

#4 Post by LouiseScot » Sat Aug 13, 2022 9:02 am

blekenbleu wrote:
Fri Aug 12, 2022 11:32 pm
LouiseScot wrote:
Fri Aug 12, 2022 10:28 pm
C-mount internal thread = 1" = 25.4mm?
There are internal threads, for about 6mm, in the tube at the end opposite the T flange.
It could not be used for a C-mount camera in a 30mm eye tube.
I lack C-mount stuff to verify that thread.
Tube length is about 28mm.
Yeah, I have some similar ones - more for astronomy really. The C-mount is probably intended for a filter. I think maybe the advert is incorrect though! If the od is actually 30mm it could maybe fit a 30mm microscope eyepiece tube. I've seen similar adapters that have an od of 23.2mm to fit a standard EP tube. My one actually has an od of 31.6mm so slightly too big to fit a 30mm EP tube but ok for a commonly used 1.25" astro fitting https://www.ebay.co.uk/itm/394107226337 ... BMjvHO5tJg. It has an id of 27.5mm. The one in your ad can't be both C-mount and 23.2mm for an EP and od of 30mm so is wrong. It could be the advertiser intended to offer a choice between 30mm and 23.2mm viz: https://www.ebay.co.uk/itm/334149957114 ... BMpKHd5tJg rather than an impossible hybrid! Still, at least they don't cost much!

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

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Re: M42 - 30mm - 23.2mm eye tube adapter warning.

#5 Post by blekenbleu » Sat Aug 13, 2022 2:41 pm

LouiseScot wrote:
Sat Aug 13, 2022 9:02 am
The C-mount is probably intended for a filter.
I was unaware of C-mount filters; thanks! I had supposed that
there might be some application for converting C-mount to M42x0.75 with 28mm of extension...
If the od is actually 30mm it could maybe fit a 30mm microscope eyepiece tube.
It is and does, now working for my 23.2mm centering telescope in a Nikon UW head 30mm eye tube,
as intended.
The one in your ad can't be both C-mount and 23.2mm for an EP and od of 30mm
I found an old JVC video camera with C-mount; it does fit, and the rest now also fits 23.2mm eyepieces.
Even before shimming, 22mm of the tube had a smaller i.d. than that final C-mount threaded 6mm, just not small enough.
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Re: M42 - 30mm - 23.2mm eye tube adapter warning.

#6 Post by Sure Squintsalot » Sat Aug 13, 2022 3:19 pm

I bought adapters as well.

I my case the OD on one of them was 33mm. Managed to turn it down to 30mm but spent 2 hours using a hand drill as a lathe, in the sink, with 400 grit sandpaper.

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Re: M42 - 30mm - 23.2mm eye tube adapter warning.

#7 Post by blekenbleu » Sat Aug 13, 2022 5:03 pm

And I thought using a drill for turning down rubber and plastic was a hassle;
two metal turning opportunities await...
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Re: M42 - 30mm - 23.2mm eye tube adapter warning.

#8 Post by LouiseScot » Sat Aug 13, 2022 5:16 pm

blekenbleu wrote:
Sat Aug 13, 2022 2:41 pm
LouiseScot wrote:
Sat Aug 13, 2022 9:02 am

The one in your ad can't be both C-mount and 23.2mm for an EP and od of 30mm
I found an old JVC video camera with C-mount; it does fit, and the rest now also fits 23.2mm eyepieces.
Even before shimming, 22mm of the tube had a smaller i.d. than that final C-mount threaded 6mm, just not small enough.
23.2mm for an EP normally refers to the OD for the adapter to fit into the microscope standard EP tube. e.g. this add shows a 30mm one and 23.2mm one side by side https://www.ebay.co.uk/itm/140938461878 ... xyzHxRSxd~

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

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Re: M42 - 30mm - 23.2mm eye tube adapter warning.

#9 Post by blekenbleu » Sat Aug 13, 2022 6:16 pm

LouiseScot wrote:
Sat Aug 13, 2022 5:16 pm
23.2mm for an EP normally refers to the OD for the adapter to fit into the microscope standard EP tube.
e.g. this add shows a 30mm one and 23.2mm one side by side https://www.ebay.co.uk/itm/140938461878
I have seen those, but never understood their purpose;
what optic fits inside such a tube with 23.2mm o.d.?
How does a camera focus down an empty eye tube without some lens?
Metaphot, Optiphot 1, 66; AO 10, 120, EPIStar, Cycloptic

LouiseScot
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Re: M42 - 30mm - 23.2mm eye tube adapter warning.

#10 Post by LouiseScot » Sat Aug 13, 2022 6:36 pm

blekenbleu wrote:
Sat Aug 13, 2022 6:16 pm
LouiseScot wrote:
Sat Aug 13, 2022 5:16 pm
23.2mm for an EP normally refers to the OD for the adapter to fit into the microscope standard EP tube.
e.g. this add shows a 30mm one and 23.2mm one side by side https://www.ebay.co.uk/itm/140938461878
I have seen those, but never understood their purpose;
what optic fits inside such a tube with 23.2mm o.d.?
How does a camera focus down an empty eye tube without some lens?
I guess could use direct projection to a camera (though I never have) https://www.amazon.co.uk/Microscope-Eye ... C61&sr=1-8

Or may interface to a trinocular tube.

Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

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Re: M42 - 30mm - 23.2mm eye tube adapter warning.

#11 Post by blekenbleu » Sat Aug 13, 2022 9:12 pm

LouiseScot wrote:
Sat Aug 13, 2022 6:36 pm
direct projection to a camera
Direct projection wants a camera sensor is at a focal plane,
which, by design, is below the first lens in oculars or photo relays.
Refocusing objectives to increase their tube length 40mm or so exacerbates aberrations.
I just took these otherwise unedited 1:1 crops from images using the same APS-C camera, objective, target and illumination.
The first is from that 30mm-M42 adapter in an empty Nikon trinocular UW eye tube:
MTeyetube.jpg
MTeyetube.jpg (110.7 KiB) Viewed 3618 times
.. which required major objective refocusing from ocular focus.
The second is parfocal with oculars using a CF PL2.5X photo relay lens:
CFPL2.5X.jpg
CFPL2.5X.jpg (130.14 KiB) Viewed 3618 times
... which IMO has less chromatic aberration, despite requiring a speed booster lens
on the camera to get back to roughly comparable magnification and field of view.
A 5X objective was used (because easier to refocus),
but which is less liable to aberrations than high n.a. objectives.
Metaphot, Optiphot 1, 66; AO 10, 120, EPIStar, Cycloptic

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Re: M42 - 30mm - 23.2mm eye tube adapter warning.

#12 Post by LouiseScot » Sat Aug 13, 2022 9:25 pm

blekenbleu wrote:
Sat Aug 13, 2022 9:12 pm
LouiseScot wrote:
Sat Aug 13, 2022 6:36 pm
direct projection to a camera
Direct projection wants a camera sensor is at a focal plane,
which, by design, is below the first lens in oculars or photo relays.
Refocusing objectives to increase their tube length 40mm or so exacerbates aberrations.
I just took these otherwise unedited 1:1 crops from images using the same APS-C camera, objective, target and illumination.
The first is from that 30mm-M42 adapter in an empty Nikon trinocular UW eye tube:
MTeyetube.jpg
.. which required major objective refocusing from ocular focus.
The second is parfocal with oculars using a CF PL2.5X photo relay lens:
CFPL2.5X.jpg
... which IMO has less chromatic aberration, despite requiring a speed booster lens
on the camera to get back to roughly comparable magnification and field of view.
A 5X objective was used (because easier to refocus),
but which is less liable to aberrations than high n.a. objectives.
I didn't say it was a good idea! But would work ok with an adjustable trinocular which could a suitable projection eyepiece
Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

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Re: M42 - 30mm - 23.2mm eye tube adapter warning.

#13 Post by blekenbleu » Sat Aug 13, 2022 10:47 pm

LouiseScot wrote:
Sat Aug 13, 2022 9:25 pm
would work ok with an adjustable trinocular
Indeed, Nikon's photo tube is 3 pieces screwed together;
unscrewing the top 2 would make the focal plane below photo relays
available for direct projection to mirrorless camera sensors. Sadly,
Nikon applied some sort of cement to those threads
that I have yet to overcome.
PhotoTubeUW.jpg
PhotoTubeUW.jpg (47.2 KiB) Viewed 3605 times
Metaphot, Optiphot 1, 66; AO 10, 120, EPIStar, Cycloptic

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Re: M42 - 30mm - 23.2mm eye tube adapter warning.

#14 Post by LouiseScot » Sat Aug 13, 2022 10:51 pm

blekenbleu wrote:
Sat Aug 13, 2022 10:47 pm
LouiseScot wrote:
Sat Aug 13, 2022 9:25 pm
would work ok with an adjustable trinocular
Indeed, Nikon's photo tube is 3 pieces screwed together;
unscrewing the top 2 would make the focal plane below photo relays
available for direct projection to mirrorless camera sensors. Sadly,
Nikon applied some sort of cement to those threads
that I have yet to overcome.
PhotoTubeUW.jpg
I was thinking more of the Amscope cheapo, basic but adjustable trinocular tubes.
Louise
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

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Re: M42 - 30mm - 23.2mm eye tube adapter warning.

#15 Post by blekenbleu » Sun Aug 14, 2022 12:48 pm

LouiseScot wrote:
Sat Aug 13, 2022 10:51 pm
Amscope cheapo, basic but adjustable trinocular tubes.
I lack Amscope experience; perhaps this tube is comparable e.g. when used with Nikon F-trinocular:
Image
https://www.ebay.com/itm/274696367794
... as suggested by @Scarodactyl.
Nikon's F trinocular (presumably intended for fluorescent photomicography)
https://blekenbleu.github.io/microscope ... scope-head
adds no glass between objectives and APS-C mirrorless camera sensor
for truly direct parfocal projection. It seems less popular than trinocular T or UW heads,
because lacking simultaneous ocular and camera viewing
and unusual twist-to-switch operation,
but final focus e.g. by HDMI monitor works well after finding and composing objects in oculars.
Image
Metaphot, Optiphot 1, 66; AO 10, 120, EPIStar, Cycloptic

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