Telescope Focuser Comparison Chart

JMI Focuser
Comparison Chart

Focuser Model

EV-

EV-XT

RCF-

Type

Part Number

XTn

XTc

MIN1

Telescope-Specific Design

Newt
and
Gen

Cass

Refr

Newt
and
Gen

Cass

Refr

Newt
and
Gen

Cass

Refr

All–
(Build
Your
Own)

Newt
and
Gen

Cass

Newtonian
and
Generic

Inside Diameter of Drawtube

1.25"

Picture Link (may not match your options as ordered)

Body

Modular Design

Yes

Semi

Black Anodized Aluminum

Yes

Std

Yes

Gold Anodized Aluminum

Opt

Base

Base is Interchangeable

Yes

Refractor Base

Yes

Opt

Cassegrain Base

Yes

Opt

Yes

Combination Base (for surfaces from the specified radius curve to flat)

3.625"

Opt

10"

Curved Base with the specified radius (standard/optional)

10"/
5"

3.75"/
6"

Flat Base

Opt

Black-Wrinkle Painted Metal Base

Yes

Drive

Dual Speed with Dial Indicator — 0.064" and 0.58" of Travel per Revolution of Knob

Yes

Opt

Yes

Single Speed — 0.58" of Travel per Revolution of Knob

Yes

Opt

Yes

Rubber-Grip Gold Knobs

Yes

Opt

Yes

Knurled Aluminum Knobs

Yes

Opt

Yes

Vertical Load Capacity

8 lbs

4 lbs

8 lbs

8+ lbs

2+ lbs

Motor — Integral Miniature

Opt

Quick-Release Manual Override included with Optional Motor

Yes

Locking/Drag Brake on Motorized Version

Yes

Locking/Drag Brake on Manual Version

Yes

Drawtube Bearings — Sealed Stainless Steel Ball

Yes

Drive Shaft Bearings — Sealed Stainless Steel Ball

Yes

Drive Shaft Bearings — Nylon

Yes

Drive Shaft Pusher Bearing — Sealed Stainless Steel Ball

Yes

Opt

Yes

Drawtubes

2.0" Drawtube (L)

Yes

Opt

2.5" Drawtube (L)

Opt

3.0" Drawtube (L)

Yes

Opt

3.4"

Yes

4.6" Drawtube (L)

Opt

5.75" Drawtube (L)

Yes

Opt

Compression Ring in Drawtube

Yes

Formula Variable (D)

L-3

Formula Constant (X)

3.25

3.5

Maximum Extension (E)

4.0"

3.0"

9.0"

4.0"

3.0"

9.0"

4.0"

3.0"

9.0"

Var

4.9"

5.1"

X+D

X+D*

Minimum Height (H)

2.3"

2.4"

4.5"

2.3"

2.4"

4.5"

2.3"

2.4"

4.5"

Var

3.7"

4.0"

1.8+D

1.9+D*

Drawtube Travel

1.7"

0.6"

4.5"

1.7"

0.6"

4.5"

1.7"

0.6"

4.5"

Var

1.2"

1.48

1.62*

Maximum Penetration

0.7"

0.0"

1.2"

0.7"

0.0"

1.2"

0.7"

0.0"

1.2"

Var

0.0"

L-1.8

1.1*

Weight

Total Weight of Standard** Focuser without Motor (oz.)

Var

Total Weight of Standard** Focuser with Motor (oz.)

Var

Mounting

Spacing of Mounting Holes (Square Configuration)

2.75

Var

2.75

2.625

Cassegrain Bases — 2" (EVBASC)

Yes

Opt

SCT Large Format Visual Back Bases — 3" (EVBASL)

Opt

SCT Large Format Visual Back Bases — 4" (EVBASX)

Opt

Refractor Base (EVBASR)

Yes

Opt

SCT Large Format Visual Back Adapter — 3" (ADPT3XT)

(Opt)

Std

SCT Large Format Visual Back Adapter — 4" (ADPT4XT)

(Opt)

Opt

Other Telescope-Specific Mounting available (see Build-Your-Own EV Focuser)

Opt

Output Adapters

1.25" Eyepiece Adapter (ADPT2-1.25)

Std

Opt

Std

Opt

Std

Opt

1.25" Eyepiece and T -Thread Adapter (ADPT2-1.25T)

Opt

Std

Opt

Std

Opt

Std

Opt

2" Eyepiece Adapter (ADPT3-2)

Yes

SCT Threaded Output Adapter — 2" (ADPT2THREAD)

Opt

Std

Opt

Std

Opt

Std

Opt

SCT Large Format Threaded Output Adapter — 3" (ADPT3THREAD)

Opt

Upgrades

EV-1 Upgrade (EVUPG1)

Opt

EV-75 Upgrade (EVUPG75)

Opt

Accessories

Digital Read Out (DRO)**

Opt

Type

Telescope-Specific Design

Newt
and
Gen

Cass

Refr

Newt
and
Gen

Cass

Refr

Newt
and
Gen

Cass

Refr

All–
(Build
Your
Own)

Newt
and
Gen

Cass

Newtonian
and
Generic

Part Number

XTn

XTc

MIN1

JMI Focuser
Comparison Chart

EV-

EV-XT

RCF-

Focuser Model

Definitions

Std = Standard Feature
Opt = Optional Feature
Var = Varies Depending on Options Chosen

Cass = Cassegrain Telescopes (including SCTs)
Newt = Newtonian Telescopes
Refr = Refractor Telescopes
Gen = Generic Application

Input is the end in which the light enters ( >[] ) and Output is the end from which the light exits ( []> ).

Some values in the chart are shown as formulas, including variables or constants (see example 1 below). You can find each variable or constant (shown in parentheses) along with its description in the left column (see example 2 below). The value of the variable will be listed in the description in the left column (see example 3 below) or will be listed within the chart itself as a value or formula (see example 4 below).
1. 2. 3. 4.	E-H Maximum Extension (E) 3" Drawtube Length (L) L+X	To calculate this value, subtract the value of the variable H from the value of the variable E. The variable E represents the maximum extension of the drawtube. L=3 Drawtube length L plus formula constant X (which differs depending on the particular focuser).
See picture (below) showing dimensions, including some of the formula variables. All lengths are in inches. If the formulas in this table are more frustrating than helpful, please contact us for the information you need.

Miscellaneous Information

* For an RCF-mini focuser with a 2.5" drawtube, Maximum Extension (E) is 3.0, Minimum Height (H) is 1.9, Drawtube Travel is 1.1 and Maximum Penetration is 0.6.
** Please note that additional options, such as DRO and DFC, will increase the weight and decrease the number of knobs on the focuser.
Output adapters and extension tubes are not included in weight and height values but mounting adapters are included.

We recommend using software like NEWT for optimizing the aftermarket placement of our focusers on your telescope. NEWT is a Newtonian telescope design program that lets you quickly try various design parameters and see the results by casting rays through a telescope model on the screen.

For best results printing this chart, select landscape mode under print options. You may wish to disable any extra header and footer information placed on the page by your browser.

JMI Online Store Telescope Focuser Comparison Chart
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