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Thread adapters

Briny River M42 to M48 step-up ring (390-EG)

A step-up ring converting the T-2 thread to M48, so that 2 in filters and M48 accessories can be fitted to T-2 components.

Briny River M42 to M48 anodized aluminum step-up ring

Briny River M42 to M48 step-up ring (390-EG)

A step-up ring converting the T-2 thread to M48, so that 2 in filters and M48 accessories can be fitted to T-2 components.

Slot count and filter size
M42 × 0.75 male — the T-2 thread · M48 × 0.75 female — the 2 in filter thread
Optical path length
The listing gives none
Manual or motorized operation
A thread adapter — no optics, and not a filter wheel
Light sealing
Aluminum alloy, anodized
Power
Not published by the maker.
Software support
Not published by the maker.
Amazon reference
DE B0FM49SGJH · US B0FM48JF46 · GB B0FM48JF46 · FR B0FM48JF46 · IT B0FM48JF46 · ES B0FM48JF46
EAN
4895264934644
  • Both threads are named precisely with pitch, which is what an adapter listing must do
  • Anodized aluminum resists the corrosion that ruins a thread left damp
  • No length figure, and every adapter consumes back focus

Best for: Putting an M48 filter or accessory onto a T-2 threaded component

Check price on Amazon

Specifications

Slot count and filter size
M42 × 0.75 male — the T-2 thread · M48 × 0.75 female — the 2 in filter thread
Optical path length
The listing gives none
Manual or motorized operation
A thread adapter — no optics, and not a filter wheel
Light sealing
Aluminum alloy, anodized
Power
Not published by the maker.
Software support
Not published by the maker.
Amazon reference
DE B0FM49SGJH · US B0FM48JF46 · GB B0FM48JF46 · FR B0FM48JF46 · IT B0FM48JF46 · ES B0FM48JF46
EAN
4895264934644

Two threads, both named properly

M42 × 0.75 male in, M48 × 0.75 female out. Naming the pitch alongside the diameter is what distinguishes a usable adapter listing from an ambiguous one — and it is also what distinguishes T-2 from the superficially similar M42 × 1.0 lens mount.

What it is for

T-2 is the thread most camera adapters and small accessories carry. M48 is the thread of 2 in filters and of larger imaging components. This ring bridges the two, in the direction that lets bigger accessories attach to smaller ones.

What it cannot do

Widen the light path. The M42 side remains the narrowest point, so a large sensor behind it will vignette regardless of the M48 accessory in front. Step-up rings solve mechanical problems, not optical ones.

The unpublished figure

Its length. Every part between telescope and sensor is subtracted from the back focus budget, and an adapter with no stated length has to be measured on arrival.

Availability

American Amazon catalog holds a record for it that nobody is selling.

Figures as Keepa reported them on the day this page was last updated. Stock and pricing shift without warning.

What gets asked before buying

Does stepping up to M48 remove vignetting?

No. The narrowest part of the path still limits it, and here that is the M42 side. A step-up ring makes a larger accessory attach; it does not widen the beam that reaches it.

Why does the missing length matter?

Because every component between the telescope and the sensor is subtracted from the back focus budget. An adapter whose length is unpublished has to be measured before the train can be added up.

Is M42 × 0.75 the same as an old M42 lens mount?

No. The lens mount is M42 × 1.0 with a different flange distance. They start on each other and bind, and the standards page on this site sets out why.

What barrel it suits

More filter wheels

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    Positions
    Five, numbered 1 to 5, for any standard 2 in filter
    Housing
    Aluminum, described as stiff enough for heavy cameras, without flexure or tilt
    Light sealing
    Interior stated as light-tight, for imaging without reflections or stray light
    Telescope side
    2 in adapter supplied for the focuser
    Camera side threads
    Not stated on the Amazon.com listing; Astromania's European listings name T-2 and M48
    Inward focus needed
    22.5 mm (0.89 in) from the normal focus position, per the Amazon.com listing; the French and German listings say 20 mm
    Weight
    594 g (1.3 lb), in Amazon's product details
    Storage
    The box doubles as a storage case
    Power and software
    None: a manual wheel
    Amazon reference
    B0140UA9F6
    EAN
    6970019290355
    • Publishes the inward focus it consumes, the figure that decides whether it works at all
    • Light-tight aluminum housing, stated stiff enough for a heavy camera
    • 22.5 mm (0.89 in) of inward focus is more than some refractors can give

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    Check price on Amazon

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    Transmission percentage
    Not published by the maker.
    Neutral or tinted dimming
    Not published by the maker.
    Fixed or variable design
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    Thread size
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    Glass flatness
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    Cell depth
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    Amazon reference
    B07VQKLGZ8
    EAN
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    Transmission percentage
    Adjustable from 1% to 40%, stated
    Neutral or tinted dimming
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    Fixed or variable design
    Variable: rotate the lower ring
    Thread size
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    Glass flatness
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    Cell depth
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    Amazon reference
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    EAN
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    Transmission percentage
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    Neutral or tinted dimming
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    Fixed or variable design
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    Thread size
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    Cell depth
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    Amazon reference
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    EAN
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All filter wheels

Any figure written into the body of this page was true on the day it was written. The amount shown next to each instrument is requested from the retailer as the page loads, and it is that amount, not the text, that stands.