Thoughts and opinions?

[ollypenrice]

A rack and pinion is, in effect, a round gear wheel driving a flattened out one. It won't slip. A Crayford uses a smooth roller driving a a smooth strip. In the silliest examples, and this includes my own Moonlite, the dirven strip is made of slippery anodized aluminium. When the rig is pointing upwards all the weight of the camera pulls down and they tend to slip. They are popular because they are cheap to make but have cultivated such a bad reputation that William Optics and others have gone over to R and P. A well made Crayford like the Baader Steeltrack or, better still Diamant, has a high friction strip and can be OK. They are nice for visual because they are very smooth.

(Moonlite: the orthodoxy is that they are excellent because they are so pretty. A friend ordered three for a multi rig and ditched the lot of them. I'm faffing around with mine as well. Excellent? Certainly not.)

Olly

[RayD]

There you go.  

R&P is clearly the way to go so you're best just looking at the OTA's with R&P focusers on 

[Yamez]

I've just been looking at some R&P focuses and they're all a bit pricey. I found this crayford with a adjustable friction using a hex key. Also offers a clamp to lock down the focus, what do you guys think: https://www.firstlightoptics.com/skywatcher-focusers/sky-watcher-dual-speed-2-crayford-focuser-for-sky-watcher-refractors.html

[RayD]

No looking at Olly's post it seems Crayford's by design are no good for imaging as they all slip unless they're Baader Steeltrack or Diamant, which I suspect would also attract a premium.  If you want to get really good images you'll have to have a R&P focuser.

[alacant]

34 minutes ago, Yamez said:

just been looking at some R&P focuses

Hi. Your chosen telescope already has a big no slip two speed super smooth rack and pinion focuser. Even at the zenith, it holds my Canon 700d fine; set the tension you like -there's a thumb screw on the focuser- and forget it. HTH.

[RayD]

27 minutes ago, alacant said:

Hi. Your chosen telescope already has a big no slip two speed super smooth rack and pinion focuser. Even at the zenith, it holds my Canon 700d fine; set the tension you like -there's a thumb screw on the focuser- and forget it. HTH.

No unfortunately the Equinox 80 Pro has a Crayford, which was what the OP was looking at getting (see later posts).  Shame though as the review on FLO for this scope is really good, specifically the Crayford focuser.

http://www.opticalvision.co.uk/documents/74.pdf

[Steve Ward]

The SkyWatcher Crayfords are easily fine-tuned to work well and not slip , a simple honing of the machined flat on the tube. 

[Steve Ward]

 

[RayD]

I'm a Consultant Engineer by trade, and did my Masters in mechanical engineering, so generally understand the mechanics of each type of focuser, with Crayford, R&P and helical being the ones I know of.  However, at the moment I know relatively little about AP, which is why I tend to take a keen interest in posts like this, which help me to note not only opinions, but the reasoning behind them.  

It's an interesting topic as I have looked in reasonable detail at each type of focuser, and there are mechanical flaws in each, with the slippage issue and focus shift on a Crayford, and backlash (could manifest itself as slippage depending on the direction of the last focus rotation) and high manufacturing costs on a R&P.  In theory there is absolutely no way of completely eliminating the flaws in each in their current guise, and they will only worsen as the components wear.  With regards to the image and focus shift when locking a Crayford, surely there can be absolutely no difference with a R&P, albeit with this type you may not need to actually use the lock, but see comment above should you chose not to.  To totally avoid slippage in a R&P focuser (without locking) you would have to make sure that your last focus rotation is in, similar in a way to positioning your mount, where your last movements are usually North and West (that may be back to front).  I assume high end manufacturers such as Feathertouch will have minimal backlash, but it will most certainly be there.

The perfect focuser I guess would incorporate a linear drive permanent magnet motor, which would encompass magnetic lock (no focus or image shift or slip).  This would entail the focuser tube being a permanent magnet, and the outer part (don't know what that's called) being a linear motor.  This of course would need to be powered, but could be manual also with a battery operated maglock lift.  I doubt that this is going to happen any time soon within the financial capabilities of most of us, but an interesting project.  

I don't have any issues with my 2 Moonlite focusers currently, but then I don't hang that much off the back, don't use them very much, and they are relatively new.  However, as a new imager I could't quantify the cost of a high end R&P, and frankly, looking at the mechanics, a cheap R&P is highly likely to be worse than a reasonable Crayford as there is simply more to go wrong.

I'm enjoying the comments and views, and can feel a little engineering project coming with a linear drive focuser 

[Yamez]

A huge thanks to everyone for being so helpful, it's greatly appreciated!

Here's what i have now and i think i'm very happy with it:

Scope: https://www.firstlightoptics.com/equinox/skywatcher-equinox-80-apo-pro-ota.html

Decided to go with the equinox 80ed, very good reviews and i've seen sample images and some look fantastic (better work on my processing skills). Gives a lovely wide field of view at F/6.25. I can always invest in the R&P focuser when that one starts to wear.

 

Mount: Still deciding on the NEQ6 or the HEQ5, more sided towards the NEQ6 for the long run. 

 

Guide scope/Guide camera: https://www.firstlightoptics.com/touptek-cameras/guide-scope-bundle-suitable-for-piggy-backing.html

Instead of side by side setup, I took your advice and went with a piggy back system to avoid hitting the mount. Also the guide camera is mono therefore i can also image the moon with it.

 

Accessories: StarSharp Bahtinov Focus mask for perfect focus. Skywatcher 2" field flattener (quite essential for a refractor I've heard). Tube rings to piggyback the guide scope onto main scope. Lastly i will probably need a 2" light pollution reduction filter for where i live.

If anything is missing please let me know  

[Starlight 1]

Seen one image that you have done and I think you take to Ap like a duck to water. Hope every thing go well .

[Yamez]

4 minutes ago, Starlight 1 said:

Seen one image that you have done and I think you take to Ap like a duck to water. Hope every thing go well .

Thank you for the compliment, though i still have a lot to learn. But i absolutely love the astrophotography I've done so far and it is very enjoyable both the imaging and the processing. I look forward to getting a dedicated AP setup!