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What is Inside a Focuser

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#1 b.bill.p

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Posted 15 August 2020 - 10:54 PM

The Crayford (?) type focuser on my 115 refractor was a bit sticky forcing me to take it apart to see whats inside.   The Crayford type is very common and are manufactured by different companies as explained on Wikipedia and a couple of Web pages on Agena Astro that helped explain the mechanism with a few detailed photos posted..   Its interesting to note there are NO optics in the focuser, just your optics in the form of the eye piece or imager at one end and the object lens at the other end.   The focuser in my attachment is a hybrid model using Rack and Pinion gear drive while other Crayfords might use friction drive between the focuser shaft and the focus tube.   So for the curious folks this is what it looks like.    

 

The only problem is that my photo is too large (apple ipad) so I have to use a Windows PC to shrink it under the required 500K image size for uploading.    Sorry but that will be done tomorrow.         


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#2 eyespy

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Posted 16 August 2020 - 01:02 PM

Hi Bill,

 

Looking forward to your photos.  No PC computer needed.  Easy way to reduce 'size' is to email it to yourself and adjust size to less than 500K's when prompted.  When you receive it, open and save it.  That's it.  Your can also do this this with multiple photos in one email.

 

Doug.....


Edited by eyespy, 16 August 2020 - 01:04 PM.


#3 b.bill.p

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Posted 17 August 2020 - 12:26 AM

6D9ADABE-AED5-4DEE-BCDA-0616B194A042.jpeg


Edited by b.bill.p, 17 August 2020 - 12:31 AM.

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#4 Cometeer

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Posted 17 August 2020 - 12:58 AM

The focuser in my attachment is a hybrid model using Rack and Pinion gear drive while other Crayfords might use friction drive between the focuser shaft and the focus tube.   So for the curious folks this is what it looks like.            

There is no such thing as a hybrid model Crayford focuser that is a rack and pinion. By definition, a Crayford focuser only relies on friction to move the drawtube. It is entirely different from a rack and pinion focuser. 


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#5 b.bill.p

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Posted 17 August 2020 - 10:53 AM

The original Crayford Eyepiece Mount was invented by John Wall and used friction drive which is a lot easier to hand manufacture than a rack and pinion.  Since I had to do a lot of research here and across the ‘net before taking the focuser loose from the OTA please refer to the manufacturer, longperng where the focuser is described as a ‘Hybrid’ .     

 

Never the less it works very well and should be of interest to others who are curious about the inner workings of the assembly and how the focus tube is firmly held in place yet glides so smooth.    Another point of interest is the construction of the focus tube inner walls to eliminate unwanted reflections.

 

Lastly it might be noted how easy it is to remove the assembly from the OTA if the need to remove dirt or dust becomes necessary.    Three screws in the case of my refractor but be careful because they are the type of screws that fly thru the air to hide forever in the carpet.


Edited by b.bill.p, 17 August 2020 - 11:08 AM.

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#6 SonnyE

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Posted 17 August 2020 - 02:59 PM

"they are the type of screws that fly thru the air to hide forever in the carpet."

 

LOL! Yep, sometimes those little boogers just dance until they hide forever!

 

After building my own Electronic Focuser, I found an Achilles Heal in my Crayford.

One night I was carrying in my telescope and do to my loosening the tensioner, the focuser tube slid clear in.

Not a happy moment. I had to re-zero my step counter to get things back to any sort of normalcy.

That right there taught me I think I like a geared focuser drive from now on.

 

My ED80T CF telescope has the tube threaded, and screws into the Crayford Focuser. Here is a good example.

The first year, a manufacturing defect cropped up. there are 4 sets of guide wheels inside the focuser. One of the wheels developed a crack in it.

Normally these tiny hardened wheels guide the tube straight and smooth. When the one wheel cracked, it began dragging and scratched some really ugly gouges into the focuser tube.

Not to mention how it screwed up the focusing entirely.

 

I disassembled the focuser from the main optical tube very, very carefully. Then removed the stop ring and got down to where I found the problem. I very carefully reassembled it and contacted Orion.

They took it in and replaced the entire focuser under warranty. Which is to say, the entire rear of the telescope. Problem fixed.

 

But it is my opinion a geared drive would be more reliable and accurate with an electronic focuser. Backlash would be easier to deal with than slippage such as a Crayford can have.

 

A friend of mine got an ED80T CF, and immediately installed a Moonlite focuser on his. He offered the new, but now unused OEM Crayford to me for a replacement for mine. Currently it is set up as a screw on replacement for Visual use.


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#7 Phutatorius

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Posted 17 August 2020 - 04:03 PM

"What is inside" (fill in the blank) has always interested me.  So thanks for the photo.  I have a new scope with a Crayford.  The indefiniteness of the focusing movement, especially in the fine focus is already annoying me.  I hate to give up on the Crayford without understanding more about it, but already I'm wondering whether a Moonlight focuser or motors for my mount will be my next purchase. 


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#8 Suavi

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Posted 17 August 2020 - 04:12 PM

Q: What is Inside a Focuser?

A: Mostly air.

 

 

Sorry, I couldn't resist flowerred.gif


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#9 Jon Isaacs

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Posted 17 August 2020 - 05:15 PM

The original Crayford Eyepiece Mount was invented by John Wall and used friction drive which is a lot easier to hand manufacture than a rack and pinion.  Since I had to do a lot of research here and across the ‘net before taking the focuser loose from the OTA please refer to the manufacturer, longperng where the focuser is described as a ‘Hybrid’ .

 

 

Technically I believe Hybrid is a valid description but since it doesn't use a friction drive, it wouldn't be a Crayford.  I believe they're called Hybrids because they combine the bearing support system of the Crayford with a rack and pinion gear drive.

 

You photo is nice.. I like fooling around with focusers. The Feathertouch is the cleverest design.

 

Jon


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#10 gnowellsct

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Posted 17 August 2020 - 09:25 PM

I seem to have moved completely out of crayfords.  I had one on my former Vixen refractor (Moonlite).  One on my Newt (Moonlite).  One of my Tak FS128 (Moonlite).  

 

They were better than what they replaced but I didn't like the default bearings.  I cracked a few.  I have very little understanding of roller bearing design and manufacture but spent a lot of time looking at more options than I dreamed possible at BOCA BEARINGS and finally selected a bag o' bearings that looked to be made to a high spec from the load bearing point of view.

 

I never cracked one of those.  Was I just cautious, lucky, or were they stronger?  Who knows.  I suspect they were higher spec than what Moonlite puts out the door, but that's just a guess.

 

Now I'm on to R&P:  On two AP scopes, on the CFF.  The Vixen ED81s also has R&P.  I actually like R&P better, am retrospectively surprised I detoured into Crayfords for so long (probably on the order of 12 to 15 years).  The CFF 92 mm focuser (3.5") is massively over spec'd and it is my favorite.  Love using it.

 

I'm used to seeing the bearings in plain view on the Moonlites and am wondering where they are here.  On the other side?

 

Greg N

 

p.s. on a desk top right click the photo.  Click "open with" choose PAINT.  In upper left find the re-size utility.  Depending on how big the original is, 25 to 35% will (making it 25% of the original) will usually do the trick.  Save as some other name if you don't want the original over-written.


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#11 gnowellsct

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Posted 17 August 2020 - 10:17 PM

"What is inside" (fill in the blank) has always interested me.  So thanks for the photo.  I have a new scope with a Crayford.  The indefiniteness of the focusing movement, especially in the fine focus is already annoying me.  I hate to give up on the Crayford without understanding more about it, but already I'm wondering whether a Moonlight focuser or motors for my mount will be my next purchase. 

To the best of my knowledge Moonlite makes ONLY Crayfords, but I haven't checked out their offerings in a few years.

 

GN


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#12 gnowellsct

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Posted 17 August 2020 - 10:18 PM

Technically I believe Hybrid is a valid description but since it doesn't use a friction drive, it wouldn't be a Crayford.  I believe they're called Hybrids because they combine the bearing support system of the Crayford with a rack and pinion gear drive.

 

You photo is nice.. I like fooling around with focusers. The Feathertouch is the cleverest design.

 

Jon

FT Crayford, or FT R&P?  I've seen and used both.  --GN



#13 b.bill.p

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Posted 18 August 2020 - 04:27 PM

Thanks for all the replys, suggestions and link.   I looked at the Moonlite focusers for refracters and have a question, what is the biggest reason to upgrade from a stock focuser that is operating properly for its price class ?    



#14 Phutatorius

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Posted 18 August 2020 - 08:25 PM

To the best of my knowledge Moonlite makes ONLY Crayfords, but I haven't checked out their offerings in a few years.

 

GN

Showing my ignorance; I thought Moonlite made rack and pinion focusers.  Lots to learn, I guess. 



#15 b.bill.p

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Posted 18 August 2020 - 10:03 PM

This photo is the focusers interior showing the focus tube surrounded by guides inside the outer casting.   I am not sure of the bearing composition but they appear to be some type of pad instead of a roller bearing.    The focuser seems solid and supports the ZWO 178 or Nikon 5600 with a Televue Powermate 4x and extension tubes hanging out to obtain focus.    This combination on a 115mm refractor seems the limit for my Celestron AVX.  

Attached Thumbnails

  • BB812A71-64E4-43AC-A54A-43524782D8C8.jpeg


#16 gnowellsct

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Posted 18 August 2020 - 11:54 PM

Thanks for all the replys, suggestions and link. I looked at the Moonlite focusers for refracters and have a question, what is the biggest reason to upgrade from a stock focuser that is operating properly for its price class ?

in some price classes operating properly means not operating at all so you spend some money and get a focuser that's operating. there is problems like rough focus, wobble in the focuser, inability to handle a 2-in eyepiece well, run out when pointing at zenith are among the things that people try to get away from by buying a focuser. And to a large extent they succeed. The other thing many people are looking for is to have a dual focus mechanism, not all scopes come with that and it's very important for focusing at high magnifications which we define as exit pupils under 1 mm. And in some cases focusers do come with fine focus but it's not a fine focus that works particularly well.

Other reasons to upgrade a focuser are when you find out that the stock focuser is unable to serve your requirements when your observing needs expand. You may start hanging more weight on the focuser for astrophotography. Or you may start doing solar viewing with your scope and the H alpha filter and powermate and eyepieces to get all of that to work may put substantially more leverage on a focuser than just tossing in a 32 mm plossl.

Edited by gnowellsct, 19 August 2020 - 12:45 AM.

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#17 25585

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Posted 20 August 2020 - 09:36 AM

Tele Vue use black or dark gray sandpaper flocking inside their focuser draw tubes, probably the same as in their OTAs. It works.

 

Has anyone improved or modded anti-reflection in any focuser? What focuser & what did you use?



#18 25585

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Posted 20 August 2020 - 09:44 AM

Thanks for all the replys, suggestions and link.   I looked at the Moonlite focusers for refracters and have a question, what is the biggest reason to upgrade from a stock focuser that is operating properly for its price class ?    

In a word, load.

 

If you use heavy optics or imaging hardware, an OE focuser can be inadequate as they are designed for mid-weight loads. Imaging oriented scope specs always have big chunky focusers, more expensive but worth it IMO.   


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#19 25585

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Posted 20 August 2020 - 09:56 AM

FT Crayford, or FT R&P?  I've seen and used both.  --GN

How do their Crayfords compare?

 

From motoring media, I have read some really rubbish bearings come out of China, and IIRC Canada & other countries ban import of products from certain makers & outlets since road safety is affected by bearings mashing up etc.

 

I am sure makers like Moonlite & SI who rely on reputation, would buy proven quality bearings though. ES92 + 4× 2" Powermate + AP Maxbright diagonal as a load, what would you choose, Crayford or r&p? 



#20 howardcano

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Posted 20 August 2020 - 10:40 AM

in some price classes operating properly means not operating at all...

Words of Wisdom and Experience!



#21 gnowellsct

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Posted 20 August 2020 - 11:09 AM

How do their Crayfords compare?

From motoring media, I have read some really rubbish bearings come out of China, and IIRC Canada & other countries ban import of products from certain makers & outlets since road safety is affected by bearings mashing up etc.

I am sure makers like Moonlite & SI who rely on reputation, would buy proven quality bearings though. ES92 + 4× 2" Powermate + AP Maxbright diagonal as a load, what would you choose, Crayford or r&p?


I personally am done with crayfords.

I don't know if feather touch continues to make crayfords. Think I may have seen them on the website but I would not have paid much attention because I was totally focused on R&P.

I had a stellarview telescope with lomo optics a nice overbuilt triplet apo. It had the feather touch rack and pinion. It had very little focus travel and was unsuited for solar viewing. And in fact I think my friend sold it to me because he found the same focuser to be inadequate for astrophotography, in terms of focus travel.

In addition it was a heavy build which is a thing that I might admire under most conditions but for putting it up on top of my c14 it posed a number of issues. The c14 and the refractor just went over some threshold of manageability and I did not think I could safely balance the telescope with that lomo tank up on top.

When I got my CFF 92 mm one of the reasons I wanted to get a 92 mm was because I wanted a triplet but I wanted to keep the weight down. CFF allows you to set the specifications for the focuser you want and so I went for a 3.5-in feather touch with a lot of focus travel. I think it is something on the order of 180 mm.

Although moonlite probably has been using decent bearings the fact is I've cracked a few. This comes from the natural but highly unfortunate habit of grabbing the telescope by the focus tube when you want to move it to another part of the sky. That is going to crack your moonlight bearings. The substitute bearings I got had very high specifications but I don't know the specifications of moonlights bearings and so there's not much to say on this point. Plus after I've spent an hour or two researching bearings and then going through the hassle of replacing them on the moonlight focuser it is kind of like getting traffic tickets for speeding eventually you decide the game is not worth the candle and you reduce your speed. what that means for a refractor is that you begin to think that grabbing your scope by the focus tube is a real bad idea, which it is.

However it is a sloppy operational procedure which you can do with a feather touch just fine because they are that strong.

As for how your should upgrade I don't have much to say. As you can see there were multiple considerations with the l o m o refractor and had I gotten it a rack and pinion focuser with a longer draw tube my weight problems would have gotten worse not better. so it was time to realize that putting money into that refractor was not going to allow it to do what I wanted it to do.

If you think you're going to get into astrophotography and solar observing then it might be worth your money to get a feather touch. And in particular if you have multiple scopes you might just want to get one feather touch focuser and a whole bunch of adapters for different tubes.

eventually you have to decide whether in fact the refractor that you happen to have today is in fact a forever refractor. You can save significant money by getting a moonlight or a Chinese aftermarket focuser. As time goes by you may discover that the telescope has not just one but several limitations and that it is time to move on to something else.

Of course nothing prevents you from keeping the OEM focuser and when the time comes to sell your scope put it back on. Then you can keep the moonlight or the feather touch and put it on the next scope if the fit is right or you can sell them independently.

But you do need to be alert to the fact that if you stay in hobby your needs and requirements of a telescope may change. When I bought my Daystar quark H alpha equipment for solar viewing I thought I was dropping a couple of grand to make my refractor able to look at the sun. Well I do have refractors that can use that equipment. But what I also discovered was that I had to refractors that absolutely could not use that equipment. One was the vixen with the moonlight focuser. They're the problem was that the focuser could not handle the load. The problem with the lomo was that the focus are probably could have handled the load but did not have the travel to allow me to reach focus.

So venturing into H alpha viewing had the unexpected impact of making not one but two refractors obsolete at least as far as I was concerned. You're observing may take you in some direction that you do not anticipate today and the same thing may happen to you.
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#22 Phutatorius

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Posted 20 August 2020 - 12:29 PM

Q: What is Inside a Focuser?

A: Mostly air.

 

 

Sorry, I couldn't resist flowerred.gif

Can you get a discount if you order one without the air?


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#23 25585

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Posted 20 August 2020 - 12:58 PM

 And in particular if you have multiple scopes you might just want to get one feather touch focuser and a whole bunch of adapters for different tubes.
 

Thus I may well do. Of the refractors I may keep, most, TV & Tak, have r&p focusers already.

 

Of my reflectors, depends how long their mirrors last. They usually get my heaviest eyepieces, + Paracorr 2 or Barlow. OE Chinese Newt focusers have less options, so a FT might be more relevant there.



#24 b.bill.p

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Posted 20 August 2020 - 01:21 PM

When i first began astroimaging I put the camera body (Nickon 5600 or ZWO178MC) on top of the diagonal and worse yet adding the Televue Powermate 2X or 4X, the combination looked bulky and dangerous so from then on I put the camera body + Powermate at the end of a combination of 35mm or 50mm extension tubes straight into the focuser.  The focuser had to be extended roughly 1/3 to 2/3 out but the Astrotech AT80EDT seemed to handle it fine.   After receiving a larger AT115EDT the focuser was a bit chunky feeling so I disassembled it to see whats inside and that began this discussion.

 

So from this discussion I’ve become aware of a LOT such as focuser bearing issues, draw length and Load Limits which concern me that OVER TIME I am stressing the stock focuser.   Where is the Focuser Load Limit described ?   

 

The Feather Touch and Moonlite focuser have been mentioned and another writer mentioned buying ONE good focuser and multiple OTA adapters, a good idea in my book especially because I want the convenience of a motorized focuser (my arm is of normal human construction) and possible autofocus.       Currently the ZWO autofocus motor is attached to the AT80EDT but its a bear to swap back and forth between scopes.        Comments ?       


Edited by b.bill.p, 20 August 2020 - 01:22 PM.



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