JMI Online Store
Reverse Crayford Focusers for Telescopes

Home < Back

Product Index

Next Page >

Help


Product Index

RCF 2" Focusers

RCF 1" Focusers

RCF Options and Upgrades

Related Products

Focuser Accessories
Information Index

More Pictures

What is an RCF?

What is a Crayford?


Customer Comments

Questions (FAQs)

Compare Models

Focuser Comparison Chart

Find What You Want

Find What We Sell for Your Equipment using the Telescope Equipment Index

Find What You Are Looking For using the Key Word Index

View Shopping Cart

Reverse Crayford 2" Focusers

 
RCF-1
Model 1
Newtonian Version
without Motor



RCF1
$149

Buy Now*

RCF-1

A 2" Reverse Crayford focuser.  (Specify the Interchangeable Base options.)

See RCF Options, Focuser Comparison Chart and Focuser Accessories Page(Specify all options and accessories when ordering.)

* 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 the EV 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.
 

Front view of 2" Reverse Crayford Focuser.  This focuser has the curved base option.
Back view of 2"  Reverse Crayford Focuser.  A locking brake (thumbscrew) can be seen on the back of the drive block.

 


Reverse Crayford 1" Focusers

 
RCF-mini1
Model mini1
Newtonian Version
without Motor



RCFMIN1
$129

Buy Now*

RCF-mini1

A 1.25" Reverse Crayford focuser.  (Specify the Interchangeable Base options.)

See RCF Options, Focuser Comparison Chart and Focuser Accessories Page(Specify all options and accessories when ordering.)

* 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 the EV 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.
 

Front view of 1.25" Reverse Crayford Focuser.  This focuser has the flat base option.
Back view of 1.25" Reverse Crayford Focuser.  A locking brake (thumbscrew) can be seen on the back of the drive block.

 


Reverse Crayford Options and Upgrades

 
Interchangable Base
Flat Base or Curved Base (purchased as a separate item)



RCFBASE
$19
Buy Now*

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)

Flat Base for RCF-1
rcf_1_base10.jpg (34253 bytes) 10" Radius Curved Base for RCF-1
5" Radius Curved Base for RCF-1
Flat Base for RCF-mini1
3.75" Radius Curved Base for RCF-mini1

 

 
Flat Base
All RCF Focusers
Specify Flat Base



(FLAT BASE)
No Charge
Buy Now
Curved Base
RCF-1
Specify Std Radius



(10" RADIUS)
No Charge
Buy Now
Curved Base
RCF-1
Specify Optional Radius



(5" RADIUS)
No Charge
Buy Now
Curved Base
RCF-mini1
Specify Optional Radius



(6" RADIUS)
No Charge
Buy Now
Curved Base
RCF-mini1
Specify Std Radius



(3.75" RADIUS)
No Charge
Buy Now
Interchangeable Base Selection Using "METHOD 1" (at the time of purchase only)

Select your base here at the time of purchase of an RCF focuser.  "Buying" one of these bases only specifies the option you want and does not add any cost to your purchase.

NOTE

If you specify your telescope's OTA diameter in our shopping cart Comments area, we will double check your base selection.
 
This picture shows the RCF-min1 with a Flat Base, Curved Base with 3.75" radius and Curved Base with 6" radius for comparison.

 

 
Drawtube Upgrade
Upgrade RCF-mini1 Drawtube to 4.6" Length (at the time of purchase only)



RCFDTUPGRADE
$19
Buy Now

Drawtube Upgrades

RCF-mini1 focusers come standard with a 3" length drawtube.  This option is for upgrading the drawtube length to 4.6" at the time of purchase.  (A 2.5" drawtube length option is available for the 1.25" RCF-mini1 focuser at no additional charge.) 

NOTE

The 4.6" length drawtube was designed specifically for the Meade Starfinder telescope.  When replacing the Meade focuser with an RCF-mini1 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).

The 4.6" drawtube for the 2" RCF-1 is no longer available.  For the 2" focuser replacement we recommend converting to an EV focuser

 


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 EV 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.


What is the Crayford Design?

The Crayford Eyepiece Mount (CEM) was invented  by John 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.  Mr. Wall, who chose not to patent his idea, continues to design and build Crayford Focusers.


Customer Comments

"I only wish I had bought two [RCFs]."  (P. G.)

"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.)


Frequently Asked Questions (FAQ)


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.
   
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 Online Store.
   
Q. Will an RCF focuser work on my Meade Starfinder?
A. Yes.  See comments in the EV Focuser FAQ Section for more information.
   
Refer to the NGF Focuser FAQ Section for more information!