Thinking forward on focusers for imaging

[discardedastro]

So I'm currently rocking the stock focuser, DC focus motor and Hitecastro DC focus setup on my 200PDS. I've dismantled, flattened and adjusted/tensioned the focuser and it works well by hand and the motor moves are all alright, but the DC focuser has a huge amount of backlash and slop so all of the AF software I've tried (Indi/Ekos, SGP) has failed miserably because of the poor position repeatability and resolution. I'm using the scope nearly exclusively for imaging, though I do occasionally enjoy slinging an eyepiece in and using it for visual.

Still getting my head around the focuser landscape in terms of products, what works where, interoperability, etc etc.

I'd like to upgrade the focuser mechanically because the stock focuser isn't fantastic - it can hold what I'm putting on it at the moment but it's clearly not fantastic in terms of stability and machining tolerances, which makes me concerned about flexure. I also want to upgrade the focus motor to a stepper.

The Primaluce Lab Senso focus motor appears a fairly sensible option since it isn't ridiculously expensive and looks like it'd work on the current focuser but also if I swapped for a Moonlite or Feathertouch. I also kind of like that option because if I swap the scope for a frac I'd be able to reuse it without having to bundle in a new focuser as part of the package for the new frac. I'm just wondering what I'm missing from the PLSS compared to, say, getting a Moonlite focuser with focus motor package. Is the PLSS likely to be adequate on a Tak or WO frac? Would you typically be looking to swap the focuser on a new frac for a Moonlite or similar? Is the PLSS well-regarded? I can't find out much information.

And additionally, in a perfect world (I'm intending to stick this all in an observatory for remote operation) I'd like a rotator or rotating focuser, but this looks like it's pretty much impossible on a 2" focuser? I think I have room on the 200PDS to insert a separate rotator into the optical train but obviously not to put a 2.5" focuser in, which seems to rule most out. Do most people just accept you get to go out and rotate the camera a bit every time you change targets in a night?

[wimvb]

On 23/02/2019 at 19:58, discardedastro said:

Do most people just accept you get to go out and rotate the camera a bit every time you change targets in a night?

I prefer the camera to be aligned with ra/dec. If it isn't it will be difficult to get a good alignment when imaging over extended periods, and it will be more difficult to reuse flats.

The focus motor I use is a Pegasus focuscube. It has a geared stepper motor. So far it hasn't let me down. When I used the sw dc motorfocus, I used it with a bahtinov mask, because of the severe backlash.

[discardedastro]

15 minutes ago, wimvb said:

I prefer the camera to be aligned with ra/dec. If it isn't it will be difficult to get a good alignment when imaging over extended periods, and it will be more difficult to reuse flats.

The focus motor I use is a Oegasus focuscube. It has a geared stepper motor. So far it hasn't let me down. When I used the sw dc motorfocus, I used it with a bahtinov mask, because of the severe backlash.

I hadn't even thought of flats being rotation-specific. Bleedin' obvious now you mention it... ? is there a reliable process for RA/dec alignment of a camera? I leave the scope outside but bring the camera back in once I'm done so would have to realign every night. I've been using the SGP field solving mostly so far, with manual rotation to align to a reference image.

The Focuscube seems to be pretty similar to the PLSS in design; I'm fairly sure the PLSS is a geared stepper, but can't find much in the way of details. Seems to be able to achieve good position quality and repeatability from what I've seen from googling. Just a bit worried I'll lob one on, and the focuser will turn out to still limit the performance substantially and have to dip back into the pot for a new focuser!

[wimvb]

Have you considered the Baader diamond steeltrack? Not quite as expensive as a Feathertouch, I believe.

To align the camera, take a longer exposure, and slew at siderreal rate in ra only. Rotate the camera until the star trails line up with the image edge. Afterwards you can make a small mark on the camera and focuser, making easier alignment next time.

[discardedastro]

I was thinking of a Moonlite over the Baader, just because the interface to the tube looks a bit more well-engineered; the Baader seems to involve a bunch of shims whereas the Moonlite has a plate adapter. About the same price as the Baader, still well below a Feathertouch. I've got a lot of Baader bits and pieces around and they're all well thought through, though, so maybe it's actually fine...

Alignment makes sense. I'll give that a shot. Can imagine there'd be some scenarios where I'd want to be offset, though, to fit a subject into the FoV.

[wimvb]

18 minutes ago, discardedastro said:

I'd want to be offset, though, to fit a subject into the FoV.

Yes, some objects will require rotation. But make those the exception, and not the rule.

I can't comment on Baader vs Moonlite, but maybe someone else can.

[Starflyer]

I haven't owned a Feathertouch, but I have owned a couple of Moonlites a Baader Steeltrack, and a few other 'premium' focusers. 

For me it's Baader all the way, the Moonlites just didn't cut it, poor repeatability poor lifting capacity and if you adjust them to lift a camera, FW, OAG etc then the coating on the drawtube wears very quickly resulting in a very rough drawtube. This is with autofocus btw, I only have experience of Lakeside and I love my two, but I'm hearing great things about the Pegasus Focuscube. 

Cheers, Ian

[Starflyer]

I manually rotate, I don't think I have room in the imaging train for a motorised rotator anyway. Its not a big problem and I rarely need to rotate manually to fit a target in. 

[discardedastro]

Interesting. Repeatability is the main thing I'm worried about, since that's going to put a fairly hard limit on the performance of any motor focuser and autofocus software. How do you find the Baader tube mounting, if you're using that on your Newts? It looks kind of awkward and like it'd leave gaps for light to leak around (although I suppose I could fix that with some neoprene or similar).

[ollypenrice]

On 23/02/2019 at 22:53, discardedastro said:

I was thinking of a Moonlite over the Baader, just because the interface to the tube looks a bit more well-engineered; the Baader seems to involve a bunch of shims whereas the Moonlite has a plate adapter. About the same price as the Baader, still well below a Feathertouch. I've got a lot of Baader bits and pieces around and they're all well thought through, though, so maybe it's actually fine...

Alignment makes sense. I'll give that a shot. Can imagine there'd be some scenarios where I'd want to be offset, though, to fit a subject into the FoV.

I wouldn't use a Moonlite for imaging and I know several people who've come to the same conclusion. One unlucky soul bought three for a triple rig before having to replace them all. It's the true Crayford design with the roller driving the slippery drawtube. This may be OK for holding EP's but it is no way to hold a camera. Baader's diamant has the roller driving a high friction industrial diamond flat surface for far more grip. I also used the earlier Steeltrack quite successfully but I'd go for the diamant now.

Good grip will be particularly important if you follow the expert Newt imagers in setting up the rig with the focuser's light path parallel with the counterweight bar. This keeps the dynamic balance consistent across the sky. Here's Pieter Vandevelde's example. 

Olly