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Reverse
Crayford 2" Focusers
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RCF-1
Model 1
Newtonian Version
without Motor
RCF1
$119.00
Buy Now*
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RCF-1M
Model 1
Newtonian Version
with Motor
RCF1M
$259.00
Buy Now*
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RCF-K
Model K (Kit)
Newtonian Version
without Motor
RCFK
$99.00
Buy Now*
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RCF-KM
Model K (Kit)
Newtonian Version
with Motor
RCFKM
$239.00
Buy Now*
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RCF-1
A 2" Reverse Crayford focuser. Regular
motorized versions include a standard hand unit. (Specify
the Interchangeable Base options.)
See RCF Options, Focuser
Comparison Chart and Focuser
Accessories Page. (Specify all options and accessories when
ordering.)
Factory
Assembled without motor, Part Number RCF1
Factory Assembled with motor, Part Number RCF1M
(Kit
Version without motor, Part Number RCFK
Kit Version with motor, Part Number RCFKM
*
For all RCF focusers you must specify whether you want a flat or
curved base.
For curved bases, you need to specify the radius. If you
don't, you will get the standard size radius. Please
specify your selection by one of the two methods listed here:
METHOD 1
Select one of the options below to add your desired specs to the
shopping cart.
METHOD
2
Place a note in the shopping cart Comments area specifying
"Flat Base" or "Curved Base" and the
appropriate radius for the curved base.
(Diameter = 2 x Radius)
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NOTE |
When
using a laser collimator, keep in mind that there will be slight deviations in the laser
beam when moving the drawtube through the full length of travel. This deviation is
not noticeable visually, is only a small fraction of the amount present with a normal
rack-and-pinion focuser and is completely eliminated with the higher quality of most of
the NGF focusers.
Due to the design of this focuser, the knobs
are at a 90-degree orientation from most, placing the drive shaft perpendicular to the
optical tube when using a curved base.
The Kit versions of the RCF are shipped
unassembled. Proper assembly is the responsibility of the customer. JMI will
not be responsible for any damage during assembly. Kit versions can only be
purchased directly from JMI.
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Front view of 2" Reverse Crayford
Focuser. This focuser has the curved base option. |
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Back view of 2" Reverse Crayford
Focuser. A locking brake (thumbscrew) can be seen
on the back of the drive block. |
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Reverse
Crayford 1¼" Focusers
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RCF-mini1
Model mini1
Newtonian Version
without Motor
RCFMIN1
$99.00
Buy Now*
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RCF-mini1M
Model mini1
Newtonian Version
with Motor
RCFMIN1M
$239.00
Buy Now*
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RCF-miniK
Model miniK (Kit)
Newtonian Version
without Motor
RCFMINK
$79.00
Buy Now*
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RCF-miniKM
Model miniK (Kit)
Newtonian Version
with Motor
RCFMINKM
$219.00
Buy Now*
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RCF-mini1
A 1.25" Reverse Crayford focuser. Regular
motorized versions include a standard hand unit. (Specify
the Interchangeable Base options.)
See RCF Options, Focuser
Comparison Chart and Focuser
Accessories Page. (Specify all options and accessories when
ordering.)
Factory
Assembled without motor, Part Number RCFMIN1
Factory Assembled with motor, Part Number RCFMIN1M
Kit
Version without motor, Part Number RCFMINK
Kit Version with motor, Part Number RCFMINKM
*
For all RCF focusers you must specify whether you want a flat or
curved base.
For curved bases, you need to specify the radius. If you
don't, you will get the standard size radius. Please
specify your selection by one of the two methods listed here:
METHOD 1
Select one of the options below to add your desired specs to the
shopping cart.
METHOD
2
Place a note in the shopping cart Comments area specifying
"Flat Base" or "Curved Base" and the
appropriate radius for the curved base.
(Diameter = 2 x Radius)
|
NOTE |
When
using a laser collimator, keep in mind that there will be slight deviations in the laser
beam when moving the drawtube through the full length of travel. This deviation is
not noticeable visually, is only a small fraction of the amount present with a normal
rack-and-pinion focuser and is completely eliminated with the higher quality of most of
the NGF focusers.
Due to the design of this focuser, the knobs
are at a 90-degree orientation from most, placing the drive shaft perpendicular to the
optical tube when using a curved base.
The Kit versions of the RCF are shipped
unassembled. Proper assembly is the responsibility of the customer. JMI will
not be responsible for any damage during assembly. Kit versions can only be
purchased directly from JMI.
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Front view of 1.25" Reverse
Crayford Focuser. This focuser has the flat base option. |
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Back view of 1.25" Reverse
Crayford Focuser. A locking brake (thumbscrew) can be seen
on the back of the drive block. |
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Reverse
Crayford Options and Upgrades
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Interchangable Base
Flat Base or Curved Base (purchased as a separate item)
RCFBASE
$16.00
Buy Now*
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Interchangeable
Base (purchased as a
separate item)
All RCF focusers can be purchased with either a flat base
or curved base. (Specify RCF model and "flat" or "curved"
base.)
The base plate is removable. The curved base on a 1.25" RCF-mini focuser has a standard radius of
3.75 inches (7.5" diameter) or an optional radius of 6 inches (12"
diameter). The 2" RCF has a standard radius of 10 inches (20" diameter)
or an optional radius of 5 inches (10" diameter).
Purchased as a separate
item, Part Number RCFBASE
An option when purchasing a focuser, Part Number N/A (See
"Method 1" Below)
*
For all RCF focusers you must specify whether you want a flat or
curved base.
For curved bases, you need to specify the radius. If you
don't, you will get the standard size radius. Please
specify your selection by one of the two methods listed here:
METHOD 1
Select one of the options below to add your desired specs to the
shopping cart.
METHOD
2
Place a note in the shopping cart Comments area specifying
"Flat Base" or "Curved Base" and the
appropriate radius for the curved base.
(Diameter = 2 x Radius)
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Flat Base for RCF-1 |
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10" Radius Curved Base for RCF-1 |
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5" Radius Curved Base for RCF-1 |
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Flat Base for RCF-mini1 |
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3.75" Radius Curved Base for RCF-mini1 |
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Drawtube
Upgrade
Upgrade RCF-mini Drawtube to 4.6" Length (at the time of
purchase only)
RCFDTUPGRADE
$12.00
Buy
Now** |
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Drawtube Upgrades
RCF focusers come standard with a 3" length
drawtube. (A 2.5" drawtube is available for the 1.25" RCF-mini1
focuser at no additional charge.) This option is for upgrading the drawtube length to
4.6" at the time of purchase of an RCF focuser.
**
Only available for the 1.25" focusers (right side of
picture). The 4.6"
drawtube for the 2" RCF-1 (left side of picture) has been discontinued.
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NOTE |
The 4.6" length drawtube was
designed specifically for the Meade Starfinder
telescope. When replacing the Meade focuser with an RCF focuser you can
use the standard 3" drawtube and an extension tube
or upgrade to the 4.6" drawtube. The extension tube option is best if
you plan on doing prime-focus photography (see the NGF
FAQ information).
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What is a Reverse
Crayford Focuser (aka Monorail)?
The Reverse Crayford Focuser (RCF) is a
light-weight, low-profile focuser with a new revolutionary design — JMI's low-cost,
high-quality answer to plastic focusers. In the reverse Crayford design,
the drive-shaft pressure is applied to a bar which "pulls" the
drawtube against its supporting bearings as apposed to directly
"pushing" the drawtube as seen in the normal Crayford
design. This design gives zero
image shift and zero backlash as with our NGF focusers. (U.S. Patent No. 6,297,917)
Please see the Focuser Comparison
Chart.
The motor, gear box and
drive train of every RCF motorized focuser is warranted by JMI Telescopes (Jim's Mobile, Inc.) to be free from defects in
material and workmanship for a period of five years from the date of original
purchase. JMI will repair or replace a part found to be defective, provided the
defective part is returned to JMI freight prepaid with proof of purchase.
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What is
the Crayford Design?
 The Crayford Eyepiece
Mount (CEM) was invented by John ("Jack") Wall. The
Crayford name comes from the Crayford Manor House Astronomical Society
(UK) to
which he belongs. The Crayford design
uses high pressure on a metal drive shaft pressing against a metal drawtube
which is held by bearings on the opposing side. This direct
surface-to-surface drive mechanism eliminates backlash and shifting of the
drawtube as seen in other designs such as the rack-and-pinion focuser and
allows for very fine adjustments.
JMI
recognized the benefits of this design and was the first company to bring
it to the amateur market in a commercial product.
Click
on the picture to see one of J. Wall's original drawings.
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Customer
Comments
"The RCF-mini1 focuser
is great. There was very little trouble fitting it onto my small
scope. Works great! ... Where is the deviation when
collimating? I have none, but that's good." (G. G.)
"Just a quick thank you
for the prompt and excellent service in delivering my latest JMI purchase,
an RCF focuser kit. JMI is proving now, more than ever, to be a real
leader in amateur astronomy. Thanks again. (R. M.)
"Many
thanks to you. The order arrived in very good time, is assembled
(and wowed a number of friends with the high quality parts and design) and
is to be installed in my dob... Congratulations on an excellently
made product." (F. H.)
"I just wanted to
thank you people for producing an excellent low-cost focuser. I purchased a Monorail
focuser a few weeks ago and I am impressed with the quality of the design. I am a
quality control manager of a machine shop in Texas and have seen a lot of mechanical
products and know that this focuser is an excellent quality focuser. I recommend
that anyone who needs a high quality focuser at an affordable price should purchase one of
yours." (R. N.)
"Received my
replacement part and the new invoice today. Thanks. As always, it's a pleasure
dealing with some of the best 'good guys' in the astro business!"
(R. M.)
"After a long and
exasperating search, I have not been able to find a better deal for this type of
focuser. It appears that JMI puts great emphasis in the quality, function and
reasonable price of their instruments. I truly look forward to receiving my order
and seeing for myself what the rave is all about." (M. D.)
"The whole
amateur community owes companies like yours a very great deal; uncompromising quality at
the cutting edge is what has driven this hobby forward so amazingly in the last twenty
years and where our entire future lies." (J. K.)
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Frequently Asked Questions
(FAQ)
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| Q. |
What are the
differences between the NGF and RCF focusers? |
| A. |
The RCF focusers are
based on a new revolutionary reverse Crayford design (U.S. Patent No.
6,297,917). This new
design allows us to produce light weight metal focusers that are price competitive with
plastic versions. Another difference is the ability to change out the base of the
focuser by removing two screws which makes it easy to change between a flat base and a
curved base. The bases are made from formed aluminum rather than machined aluminum.
One more difference is the orientation of the knobs. On NGF focusers with a
curved base, the drive shaft is normally parallel with the optical tube. The design
of the RCF focuser places the drive shaft perpendicular to the optical tube when using a
curved base. |
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| Q. |
Can I add
a Motor to my RCF focuser at a later date? |
| A. |
Yes, the
Motor attaches very easily. A gear slides onto the drive shaft and is secured with a
setscrew and the motor unit attaches to the drive block with two screws.
See Motor for
JMI RCF Focusers in our JMI Catalog. |
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| Q.
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Will an RCF focuser work on my Meade
Starfinder? |
| A. |
Yes. See comments
in the EV Focuser FAQ Section for more information. |
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Refer to the
NGF Focuser FAQ Section for more information! |
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