20 replies to this topic

[Jon Isaacs]

Hello all...

Being cheap and a being a mechanical engineer are pretty much standard operating procedure.

The new two speed focusers are quite nice and one gets accustommed to the ease of achieving a sharp focus. In the old days, when Crayford was a word rarely heard and a two speed was a bicycle, we put up with some pretty crude focusers and made them work. With today's fast scopes and good optics, a fine focuser is a real help in getting the good views.

But a standard two speed focuser is not so cheap and as they say, there are many ways to skin a cat. Gears are only one of the various methods of allowing for a fine focus, gears are really just a complicated lever. Historically levers have also been used for fine focusing, the closepin on the ETX is one example.

The problem with the lever is that it needs a clutch so that you can engage it to fine focus and disengage it to use the normal focusing. My design over comes this problem by partially splitting the lever, one merely pinches the focus lever to engage it and then releases it when done. The spring action is provided by the lever itself.

In principle, this can work with just about any focuser, Crayford or Rack and Pinion but the ones I have made are for the Orion Single Speed Crayford. It fits over the smaller section of the focuser knob. I have made several, wood works as a material but is vulnerable if it gets hit so I made the last two with Lexan (polycarbonate = bullet proof glass) and they seem to be very durable.

With a cheap band saw and a drill press it takes about 10 minutes to make one. The only critical dimension is the hole, I use a 15/32nds drill and it seems to provide a good balance between a reasonable pinch force and a free release.

Installation is a bit tricky, one needs a long allen wrench but otherwise the entire process is quite straightforward.

There is really not much to using them and I find that it really does provide a useful fine focus. It is not as sexy or slick as a two speed but it is inexpensive, easy to make and can be made to work with most any design, it could work quite nicely with an SCT or MAK.

I don't know if this is a new design or simply a repeat of something already out there but in either case, I think it provides a viable option for anyone wanting better control over the fine focuser, is a bit handy with tools and is not in a position to spend the money to buy a two speed.

Here's a photo of the unit in action, a drawing follows.

Questions and comments are appreciated. I just want to get this out there so people can make use of it....

Best wishes to all

Jon Isaacs

PS: I have thought of calling it the RCPF the Reverse Clothes-Pin Focuser, a bit of a play on the JMI RCF ie Reverse Crayford Focuser...

Attached Thumbnails

• 

[Jon Isaacs]

Hello again:

This is the drawing of the focus lever for the Orion Newtonian Crayfords. I believe it should also work for the Orion ED-80/100 forcuser. I cannot guarantee the dimension of the hole other than it is what workes on my two focusers.

Best wishes to all...

Jon Isaacs

Attached Thumbnails

• 

[o1d_dude]

Great idea, Jon!

Along those lines, is there any chance you have a standard recommended tune up process for the common Synta refractor focuser?

I'd certainly appreciate some guidance. My CR-4 focuser is not as responsive as it could be.

Thanks!

[Glassthrower]

Wow, Jon!

Simple and effective.

If I wasn't operating at f/15, I would give that a try. But finding a crisp focus is pretty easy for me.

Well done and thanks for sharing.

[Arbacia]

I use a simmilar artefact.

A clamp from the rear red lights of a bicycle (in this case it is made of nylon reinforced with fibers), a piece of about 20 cm lenght of 3mm in diammeter fiber-glass rod (I has already, but a chopstick is OK) and a couple of rubber tips.

I remove the screw of the clamp and replace it with the stick. The stick is keeped in place thanks to the rubber tips.

As simple as that.

The clamp is about the same size of the whell of my crayford focuser. I take the clamp with a hand and keep open with a finger, the is mounted on the wheel. The presure of the clamp is enough to keep in place. The stick becomes a microfocuser and is easily removed with a finger...

[Jon Isaacs]

Great idea, Jon!

Along those lines, is there any chance you have a standard recommended tune up process for the common Synta refractor focuser?

I'd certainly appreciate some guidance. My CR-4 focuser is not as responsive as it could be.

Thanks!

There are some webpages discussing how to rework the Synta rack and pinion focusers. This is a short summary of what I do:

First turn the scope in the mount it is flat and the pinion shaft is on top.

Remove the 4 screws the hold the pinion plate cover in place, I remove the plate, the spring plate underneath and the pinion shaft and gear. The draw tube can now be removed, the pad that the lock and the adjustment "gibs" ride on is now free and can be removed.

At this point clean the "grease/glue" from the all parts. There are various techniques and solvents, I won't recomment any, that stuff is tough and I normally end up cleaning it off as best I can.

When everything is clean, I am ready for reassembly. Normally the problem with these focusers is they shift a bit when racking them in and out.

The way to avoid this is to adjust the drawtube "gibs" without the pinion gear in place. First locate the 'gibs" which are two small allen head screws in line with the focuser lock. Lightly grease with light grease the lock block and put it in place. (I have been known to make a new block from teflon.) Very lightly grease the drawtube and slip it back in place.

Now you need to adjust the gibs. Make sure the lock is loose and adjust the gibs until drawtube does not rock but is still reasonably free. This part may take some experimentation.

Once you are happy with that, it is time to reinstall the pinion assembly. Lightly grease the shaft and install the pinion. Next put a touch of grease on the contact of the spring plate and install it followed by the cover.

Play with the adjustment of the 4 cover screws until the action is smooth, reasonably easy and relatively free from backlash. These last steps may take some fiddling and tweaking until you are happy with the action.

When you are happy with the focuser, put a drop of crazy glue next to the head of each pinion screw to lock it in place.

Jon

[Sky Captain]

Great idea Jon! I like the design.

[o1d_dude]

Thanks, Jon.

That's what I was looking for!

[helpwanted]

excellent idea Jon.... i have the XT8 with the same focuser... so how much to make me one?

[Roy McCoy]

Thanks for sharing your idea Jon!

[Happy-Idiot]

PS: I have thought of calling it the RCPF the Reverse Clothes-Pin Focuser, a bit of a play on the JMI RCF ie Reverse Crayford Focuser...

Very cool idea, simple yet effective, you can't ask for anything more. But how about a flashy name like the "Clothespin-point focuser"_

. Im sorry i know its corny, but great job none the less. Its on my list of to do's.
Thanks,Brian

[GeorgeDuke]

Here is another simple easy and cheap fine focus mod.

Attached Thumbnails

• 

[Jon Isaacs]

Here is another simple easy and cheap fine focus mod.

So how do you engage and disengage the lever?

The neat thing about the split lever design is that it is normally disengaged and so the focuser operates normally but when you want to use it, you just pinch it between your fingers and make the fine focus adjustments and then releasing it frees it up again.

Jon

[gnome54]

Jon, good idea. Now I need to find something around the house to make one. I like inexpensive ideas that are simple to make.

[DarrylS]

Thanks Jon! I was trying to figure out a way to do something like this, and was thinking of trying a clothespin or some variant, but I like your solution much better

Darryl

[DonR]

Here's a similar mod I made to my Orion 8" newtonian with rack and pinion focuser:

http://www.pbase.com.../image/87292307

It allows for the critical focus needed for long exposure astrophotography. All parts came from Lowes and cost less than US$5.

[JPDeTombe]

Funny how sometimes you think you have a brilliant idea, only to find someone has done something similar already!

I was thinking on the same problem with my Orion single speed focuser, here is what I came up with.

Due to house modifications (read renovations) I had some black pipe hangers laying around the house and an inspiration hit me.

Attached Thumbnails

• 

[GeorgeDuke]

Jon, note the thumb nut! a tiny turn and it is free wheeling, also, slight move to the side and it is off completely.
Actually I use Accufocus motors myself.

[JPDeTombe]

I imagine that this can be done with something akin to a wire clothes hanger as well. I made sure to make the bent ends just a tad wider than the holes in the focus knob, that way there is outward pressure when it is in place.

Here is the raw piece:

Attached Thumbnails

• 

[Clive Gibbons]

Neat idea, Jon!

[Art Bianconi]

I don't know how I missed this Jon but it's a wonderful idea. I rank this right along the hack saw blade trim device that Burt Rutan developed for his novel and ground shaking Vari-Ese airplane of the 70's.

Instead of heavy and cumbersome wheels, bell-cranks and pulleys to adjust the aircraft's pitch trim in flight, he simply attached a hack saw blade to a spring that was then attached to an elevator horn, slipped the other end of the saw blade through a narrow slit in the instrument panel, teeth facing down. The saw blade rested on a sharp piece of metal and was preloaded with a simple spring.

To trim the aircraft, you merely lifted the saw blade against the spring tension to clear the sharp edge, moved it back or forth as needed and when you let it go, it locked in the new position.

Be careful Jon, you may be a candidate for addictive airplane building!

Art