Focusser - The differences?

[Redscouse]

Hi all,

Probably a bit of a silly question to ya'll professionals however I need to ask anyway. 
What is the difference between a £20 focusser and a £200 one? (apart from £180 - and no, I'm not buying one.)  
I don't get it. Is the eyepiece not the important bit? 

[Timebandit]

Hi and welcome to SGL

Obviously if you cannot get accurate focus then no matter what eyepiece you put in the scope then you are not going to get the best view possible 

That's why a lot of the better quality focusers have possible two speed focus adjustment, so you can make minute adjustment to get the best focus point possible. Obviously quality counts and the better the focuser the more it costs in general 

I hope this helps☺

 

[MarsG76]

I like to think that a more expensive focusers are more accurate and you do get what you pay for... but even the cheaper one will be an improvement over manual focusing, especially at high power.

[Paz]

The more expensive ones will allow more finely tuned focusing, they can be adjusted to focus with a lighter touch so you dont shake the scope so much when you're trying to focus, they are more rigid and can hold more weight safely and without going out of alignment, they will have compression rings rather than set screws so they won't ding your eyepiece barrels, they may be better baffled so they cause less scatter of stray light.

[Louis D]

Better quality focusers won't have backlash as you move forward and back through focus.  They also hold the tube in perfect alignment under heavy loads (no sagging).  They also have better lift capability under heavy loads (no slippage).  They also have a smoother motion with no notchiness.

[tooth_dr]

And they generally are more aesthetically pleasing 

[Alien 13]

4 minutes ago, tooth_dr said:

And they generally are more aesthetically pleasing 

I agree, the fit and finish of a nice focusser adds to the overall enjoyment.

Alan

[ronl]

One of the best things I have upgraded, I bought a Moonlite focusser, they are worth every penny,

makes fine focussing so much easier, and collimation too, keeps the Cheshire perfectly central.

Oh and it looks great too.

[niallk]

I've a Feathertouch on my 15", and it handles the weight/torque of a Paracorr 2, Powermate and Ethos EPs without issue. The dual speed adjustment is silky smooth.  Just lovely to use.

I've a stock focusser on my 10" Skywatcher dob, with an €80 dual speed upgrade kit.  It works beautifully: best accessory I bought for that scope after the Telrad and TV 13mm Type 6 Nagler  The fine adjustment feels pretty much as smooth as the FT, but I dont load it as much, using lighter weight 1.25" EPs in that scope - but it does handle my binoviewer very well.  No compression rings, just screws, but I wouldn't feel the need to truly upgrade to something more expensive.

I had the stock helical focusser on my Lunt LS50, which was usable, but suffered from sag with a diagonal/blocking filter and EP, and was not as easy to fine focus as it lacked a fine tune ring.  I got a Moonlight mini focuser to upgrade, and it is a real beaut: and the smooooooth fine focus is a real pleasure for teasing out the wisps in prominences and lovely surface detail on sunspots.

To me, a dual speed crayford is highly desirable for visual.  The imagers have their own requirements of course

[Stub Mandrel]

It's been proven that more expensive, colourfully packaged painkillers are more effective than generic ones, due to the placebo effect.

Presumably the same applies to focusers

More seriously, my rule of thumb is that quality increases roughly with the square root of price.

That would suggest a £200 focuser is three times as good as a £20 one, although these things are highly subjective and it really depends on what you value.

As an imager, it is largely irrelevant if it takes 20 seconds or a minute to get accurate focus,  the time is negligible compared to imaging time. If I was always mainly visual and always swapping non-parfocal eyepieces then investing in a top end focuser might make sense for me.

As it is I'm making a crayford focuser at the moment; their defining feature is that even very basic ones are vastly better than rack and pinion focusers and the main difference is how easy is fine adjustment, whether they can be adjusted to stay in place or not and if locking them causes any focus shift. My Skywatcher one is not perfect on the last of these.

[25585]

How do Baader Steeltrack focusers rate compared to Moonlites?

[alanjgreen]

14 hours ago, Redscouse said:

Hi all,

Probably a bit of a silly question to ya'll professionals however I need to ask anyway. 
What is the difference between a £20 focuser and a £200 one? (apart from £180 - and no, I'm not buying one.)  
I don't get it. Is the eyepiece not the important bit? 

If you dont know why you need one, then I suggest that you probably dont need one

Here is a quick benefits list...

1. Expensive one will be dual speed, allowing "fine" adjustment at the critical point.

2. Expensive one will hold a lot more weight i.e. large 2" eyepieces, binoviewer & 2 eyepieces, camera etc. Would you want £1000 worth of eyepieces and camera to drop to the floor?

3. Expensive one will be adjustable and can be collimated

4. expensive one will be smooth as silk for as long as you own it

5. Different focusers may offer a range of draw tube lengths depending on how much adjustment you need available for your usage. If you are both binoviewer and single eyepiece then a focuser with more travel gives greater chance of reaching focus with all your equipment. It was for this reason that I specified a Feathertouch with 2.5" drawtube on my dob. (Standard is 1.5" drawtube)

My Lunt LS60 came with a crappy chinese standard focuser (about £20 was all it was worth), it was not strong enough to hold my binoviewer and eyepieces and used to slip under the weight . An upgrade to a Baader Steeltrack resolved that issue. Now, i need never worry about an expensive "drop" to the ground! I could have paid more but the steeltrack was a cheaper alternative to a Feathertouch (at about half the price) and has served me well.

I do have Starlight Instruments Feathertouch focusers on my 20" dob and on my Borg89. But they were the focuser of choice from the start. They are just a class above anything else on the market. If you've invested in great eyepieces then you need a great focuser to get the best out of them or be prepared to never by happy with the view . Better to buy once and never need to think about it ever again!

As an additional note, the best focuser accessory that I have bought has been the "oversize" fine focus knob for my feathertouch. It really allows you to adjust the focus in miniscule amounts

https://www.firstlightoptics.com/starlight-instruments-feather-touch-accessories/starlight-instruments-large-fine-focus-knob.html

Thats £24 just for a BIG knob! But Wow it makes a huge difference to my enjoyment at the eyepiece  Highly recommended upgrade if anyone is considering adding one... (but do consider whether it will fit? David Lukehurst added a 1" riser to allow the big knob to fit  )

 

Alan

[Redscouse]

2 hours ago, alanjgreen said:

If you dont know why you need one, then I suggest that you probably dont need one

True indeed!  
I wasn't in the market for one. Reason I asked the question I saw FLO advertise a Crayford something or other. When I clicked it it was a focusser and that got me thinking to why, other that cosmetics, you would need one. 

Your explanation gives plenty of reasons I never even thought of such as slipping and dropping. 
Thanks Alan, very much appreciate your time and explanation.

Pete.

PS: Thanks to the rest of you for your explanations also. 

[RT65CB-SWL]

If you attach a Crayford or other 3rd party focusser to the back of a Mak or SCT it will help prevent 'mirror flop' or 'mirror slop' because you are not moving the primary mirror up and down the baffle tube when focusing. On Mak's or SCT's the primary mirror rely on the focus shaft to push & pull to focus and over time the primary locking ring can/may work loose. It normally is a case of removing the front cell/corrector plate or removing the backend from the tube and tightening it back up and collimation.

NOTE: the ETX90/105/125 are not easy 'scopes to collimate - refer to http://www.weasner.com/etx/techtips/collimating.html

My 're-modded' ETX105 with a Crayford and Celestron focal reducer being used as a spacer and attached to an ETX to SCT adaptor, (photo below), as the ETX focus shaft & knob does not have enough clearance to fit it directly to the backplate.

 <--- The attached ETX to SCT adaptor.

[Merlin66]

The Meade focus design on their SCT is inherently more sloppy than the fixed screw focuser used in the Celestron,

I’ve used both....

The mirror slop can be reduced by regularly running the mirror through the full focusing travel - this re-spreads the grease along the baffle tube.

I used the Feathertouch 10:1 micro focus upgrade on the C9.25 and the C11 and was very impressed with the performance.

[RT65CB-SWL]

11 hours ago, Merlin66 said:

The mirror slop can be reduced by regularly running the mirror through the full focusing travel - this re-spreads the grease along the baffle tube.

I do the same too, when my ETX105 & C6, (and fully rotate the helical focus in & out of focus on my Ranger), when they come out or during periods of hibernation.  

[alanjgreen]

8 hours ago, Merlin66 said:

The Meade focus design on their SCT is inherently more sloppy than the fixed screw focuser used in the Celestron,

I’ve used both....

The mirror slop can be reduced by regularly running the mirror through the full focusing travel - this re-spreads the grease along the baffle tube.

I used the Feathertouch 10:1 micro focus upgrade on the C9.25 and the C11 and was very impressed with the performance.

Yep, agree. Celestron SCT do not really suffer from the issue @Philip R describes. Better design used.

I would not recommend external crayford for Celestron SCT as you are just making the scope very back heavy (leaving you with balance issues). As @Merlin66 says Feathertouch microfocuser is the way to go with Celestron SCTs.

[DeepSkyMan]

12 hours ago, 25585 said:

How do Baader Steeltrack focusers rate compared to Moonlites?

Ive no experience of the Moonlight, but I’ve had the Baader Steeltrack on my 8” Edge for the past couple of years and its excellent.