Remote Focusing

Focuser Refractors Acquisition Remote Astrophotography Deep Sky
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Jerry Gerber avatar
Jerry Gerber avatar
Hey!

I'm placing a 151mm refractor at a dark site to operate remotely.   At home, I notice that if I do not lock down the focuser with the focus-lock knob at the bottom of the rack & pinion focuser, the drawtube can slide toward the ground if aimed near zenith, due to the weight of the camera, filter drawer, etc. 

When imaging remotely, I will not be able to lock down the focuser as that will prevent the electronic focuser from working.   How do I deal with situations where the scope may be aimed toward, or close to, zenith?   Is there a "middle-ground" where I can keep the focus lock loose enough so that the electronic focuser can work, but snug enough so that the drawtube doesn't slide out all the way due to gravity?

Thanks!
Jerry
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Arun H avatar
Arun H avatar
What focuser are you using? With a high quality focuser you would not need to use a "focus lock" knob to keep the focuser from sliding so long as you are within weight capcity. Especially if you are doing this remote, you should invest in a good focuser. If your 151mm is from Stellarvue - did you get the Stellarvue focuser, or did you specify the Feathertouch? The Feathertouch is very well worth the extra cost, and I say that having used the Stellarvue focuser on my 80mm and two Fetahertouch focusers on two other scopes. With either focuser though, you can call the manufacturer and they could provide suggestions.
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Jeffery Richards avatar
Jeffery Richards avatar
Some more info would be helpful such as actual scope in use and the focuser (stock or aftermarket) and the focus motor used. It is pretty much never a good idea to use a lock screw on a rack and pinion focuser that has a focus motor attached. Now if we were talking about a crayford focuser then yes, tensions can be adjusted to prevent slippage.
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Nick Grundy avatar
Nick Grundy avatar
Hi Jerry, I'm guessing you aren't using a auto-focuser on your current 130phq? 

Whichever autofocuser you install on your new rig, it should hold at the position regardless of orientation. That is, provided your imaging payload is within the weigh limit of the auto-focuser. 

In this config, you don't use the focuser lock at all (in fact, it needs to be open to allow the auto-focuser to move in and out freely)

Did you identify a focuser for your new rig yet? For something like yours, I like the esatto 3". They are pretty easy to work with and quite precise. I also have an optec leo on my Epsilon, which is fantastic. (but doesn't make sense for that rig i think)
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Jerry Gerber avatar
Jerry Gerber avatar
Thanks for the replies everyone! 

I'll be placing an Askar 151phq on a pier at the dark sky site. The focuser is a 3.4" R&P and it's the same focuser as in the 130PHQ, which I use at home. 

It's a hefty focuser. Sites that sell the scope say the load the focuser can handle is 17 lbs, but Askar says it's 11lbs. The weight of my image train will be less than 5 lbs, well within limits. The focuser also has a tension screw that I've never used but it may come in handy once I get set up. Since the focuser of course must remain unlocked with the electronic focuser, I believe that's what the tension screw is for. Am I right?
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Daniel Carter avatar
Daniel Carter avatar
Jerry Gerber:
Thanks for the replies everyone! 

I'll be placing an Askar 151phq on a pier at the dark sky site. The focuser is a 3.4" R&P and it's the same focuser as in the 130PHQ, which I use at home. 

It's a hefty focuser. Sites that sell the scope say the load the focuser can handle is 17 lbs, but Askar says it's 11lbs. The weight of my image train will be less than 5 lbs, well within limits. The focuser also has a tension screw that I've never used but it may come in handy once I get set up. Since the focuser of course must remain unlocked with the electronic focuser, I believe that's what the tension screw is for. Am I right?

What kind of EAF are you using? Some EAFs have stronger/better motors that can handle the heavier weight of an imaging train without slipping.
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Jerry Gerber avatar
Jerry Gerber avatar
Daniel Carter:
Jerry Gerber:
Thanks for the replies everyone! 

I'll be placing an Askar 151phq on a pier at the dark sky site. The focuser is a 3.4" R&P and it's the same focuser as in the 130PHQ, which I use at home. 

It's a hefty focuser. Sites that sell the scope say the load the focuser can handle is 17 lbs, but Askar says it's 11lbs. The weight of my image train will be less than 5 lbs, well within limits. The focuser also has a tension screw that I've never used but it may come in handy once I get set up. Since the focuser of course must remain unlocked with the electronic focuser, I believe that's what the tension screw is for. Am I right?

What kind of EAF are you using? Some EAFs have stronger/better motors that can handle the heavier weight of an imaging train without slipping.

I've chosen to use the Primaluce Sesto Senso 2. The motor is apparently much more robust than the ZWO EAF.
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Leonardo Landi avatar
Leonardo Landi avatar
Sesto senso is a wanderful focuser, but as far as I know permits to focus with the coarse knob when engaged, so maybe it's not designed to hold loads. I know that's far more expensive, but if you want to go remote i suggest you to have a look at the Esatto line. It's not expensive as a nightcrawler but it's extremely strong and has no backlash issues. I found one by second hand few years ago and never regret the money.
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Jeffery Richards avatar
Jeffery Richards avatar
Agree with Leonardo, the Sesto senso is a great focuser but is also one of the few that will allow manual focusing so it might not hold loads very well.
Jerry Gerber avatar
Jerry Gerber avatar
OK thanks for the heads up. I'll check out the Esatto focusers.  By the way, does anyone know what the load capacity of the Sesto Senso 2 focuser is?  I've looked around and can't find it.


Jerry
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Maxim avatar
Maxim avatar
ZWO EAF has a reductor with pretty high reduction ratio(like around 1:70) It won't allow to rotate the knob after it's installed and will serve as a lock. It's not backlashless as esatto but it's 2-3 times cheaper and works just fine.
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Nick Grundy avatar
Nick Grundy avatar
Jerry, I've been using the ZWO EAF with my TOA-130 for a year or so now and it's been really successfully. It's a 4in focuser, but not much different mechanically than the 151phq's. 

since the EAF is relatively inexpensive (compared to the build you are doing) I would suggest picking one up and using it with the 130phq at home or espirt100 (whichever you end up keeping)

I've found the EAF's to be pretty resilient and with the correct autofocus settings in Nina, almost always produce a good AF curve for me. 

for the smaller Tak focusers, or the Epsilon stock, I wouldn't recommend the EAF though. Those ones really rely on the focusing lock (screw) to keep from shifting.
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