What are the advantages of a DSII over a single etalon?

[rimcrazy]

Please forgive my ingorance but I was curious as to what the advantages of have two stacked etalons (DSII) vs a single etalon.

[swisswalter]

Hi Phillip

welcome to that wonderful TOS free site. Have sun, have fun.

Not going into details the advantage of a second etalon is that you get more contrast on the disk, you see more details because the bandwith is narrower, if you stack two etalons. You trade that in with some loss of brightness.

[rimcrazy]

Ah, ok. That kind of leads me to my next question. I am putting together a proposal for a remote controlled solar observatory. Hooking up a camera and robotic focus to a Lunt telescope appears to be rather straight forward. My question however relates to hooking up robotic control to the etalon tuning knob. In theory, I don't believe it should be too difficult but honestly, I don't own a Lunt yet so I've not operated one. Has anyone done this and does it work from a practical sense as well as a mechanical sense. Any links to pictures/examples?

Thanks

Phil

[swisswalter]

Hi Phillip

yes that has been done and it works, but only on the old models with a tilting wheel. The newer models are pressure tuned, that is a little bit harder to do

[Montana]

Hi Phil!

A very warm and sunny welcome. I would start with a single stack, but if you have the money then get a double stack and you suddenly realise what you have been missing. A double stack gives breathtaking views compared to beautiful views from a single stack.

Alexandra

[astrodanco]

You probably would not want to try remotely turning the pressure tuner knob(s). The pressure tuner knob(s) might require considerable torque to turn. What you want for remote pressure turning is one of those pressure pumps that Lunt sells for this purpose or something like that which can be interfaced to software. I'm not sure if the Lunt pump can be interfaced to software or not.

[rimcrazy]

This is what is a bit confusing to me not having a Lunt. My cousin, however, does have the 60mm and I asked him specifically how hard was the pressure tuner to torque and he said it is very smooth, not unlike a crayford focus. This is why I'm not understanding why this would be difficult. If it is simply a matter of fixture, it is not an issue. I have access to a professional machine shop so I can fabricate just about anything mechanical that is required. Stepper motors, properly geared, have quite a bit of torque so it's simply a matter of fastening the motor to the knob. I can think of a half dozen ways to do that so I'm really not understanding the problem. I think I will give Lunt a call and see if I can talk to a technical support person. Thanks for all of the input.

[astrodanco]

Buy one and you'll see exactly what I mean. :cheer:

I'm using my double stacked LS80 as an example. Turning the pressure tuner cylinders is smooth, but that's relative. It certainly always requires more torque than, say, a focuser knob requires. (I know what you're thinking. I have indeed pressure equalized them by unscrewing them, then screwing them back on. I do that as a matter of habit, so that's never an issue.) When either of the cylinders gets near the bottom of its range, considerably more torque is required to turn it. And wouldn't you know it, my scope only goes on band towards the bottom of the pressure tuner's range. Big problem for a motor and belt and/or gears. They would likely slip and/or stall. No problem at all for a pressure pump. Lunt's remote control solution is a pressure pump. It's elegant and sensible.

[rimcrazy]

Just got off the phone with the good people at Lunt and got my questions answered. Basically they have a pressures control system that they sell for the DS80. The other Etalons are a tilt version but the 100mm, which I am interested in purchasing, should have one later this year. It sounds fairly trivial to hook up a remote control to the pressure control system so it all sounds quite feasible.

Thanks to all for the replies.

[swisswalter]

Hi Phillip

that is a surprice to mee. I have a LUNT 100 pressure tuned scope sitting here for over a year

[rimcrazy]

I thought that sounded strange when she (person at Lunt) told me that. She said the 100mm and larger had the etalon on the front and were tilt. You go on their website and you can see the tuning knob on the back so I'm at a complete loss. I live in Phoenix which is just a modest ride to Tucson. When things get closer to fruition on this project I believe I will make a trek down there to visit. They said no problem in stopping but just please call ahead. I too would like to get the 100mm model. It's about the optimum price/feature/fov point for my project budget.

On the pressure controller she said they had a button on the panel to raise/lower the pressure. Her tech said I could jury rig a solenoid to push the buttons but that's that hard way. If it's a switch I can rewire it with a relay and remote control it all day so I don't see an issue there.

[JimLafferty]

For remote imaging I would stick to a single etalon. Honestly, for any imaging (except for full disks, non mosaic) go single stack. The biggest advantage for double stacking is visually (much better contrast as Walter mentioned) or single avi full disk imaging. When you start to try to image in hi-res with a doublestacked system the resulting drop in image brightness can be problemmatic. Iam speaking only to coronado/lunt type systems. This of course could change as tchnology improves.

Jim

[rimcrazy]

From the postings and simply the complexity involved that is what I was planning on doing. Thanks.

[astrodanco]

The base LS80THa is pressure tuned. The DSII add on for double stacking the LS80THa is also pressure tuned. The DSII is relatively inexpensive.

The base LS100THa is pressure tuned, but requires a completely separate LS100FHa front mounted etalon to double stack. The LS100FHa is tilt tuned. At least I think it's tilt tuned. Note that the LS100FHa costs more than the LS100THa itself. You can save some cash there by double stacking the LS100THa using a Coronado SolarMax II 90mm Etalon (and an adapter) rather than a Lunt LS100FHa. That's the so called "Luntanado."

[telescopemaker]

I've got the Lunt80, it takes a LOT of torque to turn the tuner - I was originally thinking of remote controlling it, but I decided you'd need quite a gearing ratio to get what you need. So far I have just used my fingers- it can change from day to day depending on outside pressure anyway (or seems to in my setup). Every week or so it seems I unscrew it completely and let it equalize with outside air, then it goes to the same general area on turns to get the same general tuning of features. I hope that last sentence makes sense

[SimonM]

I thought that sounded strange when she (the person at Lunt) told me that. She said the 100mm and larger had the etalon on the front and were tilt. You go on their website and you can see the tuning knob on the back so I'm at a complete loss. I live in Phoenix which is just a modest ride to Tucson. When things get closer to fruition on this project I believe I will make a trek down there to visit. They said no problem in stopping but just please call ahead. I too would like to get the 100mm model. It's about the optimum price/feature/FOV point for my project budget.

Phil

When looking into the purchase of a Lunt, I found this an interesting read: https://luntsolarsystems.com/a-simplifi ... elescopes/

At the moment I have analysis paralysis and want to avoid buyer's remorse...

Faye, the customer rep was explaining to me that the pressure change is quite modest and the article by Andy Lunt makes this clear. Between -500 feet and 12,000 feet, the pressure changes very little e.g. around 15 psi at -500 ft down to 10 psi at 12,000 ft. the tire inflator you might use on your car has to cope with far bigger pressure changes. Being battery operated, their USB unit clearly can't have too much work to maintain and change the pressure if it runs for a day. Since you cannot compress water, if you like DIY, you might consider moving a volume of water to exert pressure (on a volume of air), and using a modest volume (a reservoir) would have a smoothing and dampening effect too. Of course, you don't want to flood your new scope...

I am envious of your location, with a solar manufacturer nearby (about 130 miles) the temptation to go and visit them must be very high. It would remove headaches/concerns if you can see the product you are buying and decide what works for you. The gas miles used, might be offset by what you don't need to buy. For me, a pickup in person is out of the question (from the not so sunny UK).

I'm approaching the purchase of one of their modular scopes at the other extreme, a 60 or 80, and SS or DS. It would have been nice to drop by and see what works and to what degree, or to inspect before paying for, their fine products. At the lower end, you may be surprised to see the cost of the refractor part - they range from $450 to $730, so not that expensive according to their website. For a particular version being 60, 80, 100, or 130, they offer a "basic" version. It might have been better if they had called it the "essentials" version. It actually has the stuff you need, so like a scope "package" where you leave off things in the box (if you already have them) to gather dust, it's a good choice.

Simon

[MapleRidge]

The DS option has a huge contrast benefit for disk features, so it isn't only a benefit to visual use. The longer exposures in DS mode are still more than manageable.

The new modular scopes use the pressure tune system, with the 130mm version using the etalons from the LS152 (single & DS modes), and the smaller modular scopes use an etalon similar to the DSII for the original LS80T. The front mount 100mm etalon could be used but it is more suited to mount on a standard refractor but will be very heavy. My 75mm etalon adds a lot of weight to the scope when I add it to the LS80T. With a good heavy duty mount it is ok. The pressure tuning knob tension is variable...warm weather it turns relatively easily...at cold temps it is very hard to turn (I've imaged at -26C and it is almost locked in place). This is my main reason to use the remote tuner.

Brian

[SimonM]

On the pressure controller, she said they had a button on the panel to raise/lower the pressure. Her tech said I could jury rig a solenoid to push the buttons but that's that hard way. If it is a switch I can rewire it with a relay and remote control it all day so I don't see an issue there.

Phil

You might want to ask someone else, how to control it directly:

Lunt USB PC.pdf

(845.39 KiB) Downloaded 27 times

If you wanted to "emulate" this yourself, then you might consider using a Raspberry Pi 3/4 or an Arduino, a 20 character (two-line) display, one/two pressure pump(s) e.g. "commodity" cost parts. For reliable connections to the pressure tuner you may want to order (or make some in your machine shop) some of these Lunt "spare" parts:

1x or 2x Cover-caps;
1x or 2x air pipe connecting sleeves.
1x or 2x "new" pistons (#1).

#1: it is not clear what they mean by the "new" piston" e.g. if it is really a new piston or it is the old piston with a hole (tapped) in it that allows air to pass through (but also be closed/opened with the addition/removal of a screw). Perhaps the German Importer (+49 (0) 2872 - 80 740) knows more about this particular setup?

It is a project that I would contemplate attempting because I enjoy controlling things from a PC (preferably a Mac) rather than manually. A dual setup (with one control interface) would be my preferred configuration for controlling one (ideally both) pressure tuners. Water is "immutable" because you can't change the volume with pressure, and is an ideal medium to control with it acting as a "proxy" to control the pressure in an air chamber (acts like a capacitor as a reservoir, smoothing/stabilizing the delivery of pressure changes). There are also many air pumps used to inflate tires available too.

One thing that interests me is how two Etalons interact together e.g. if you retune the first Etalon, does the second Etalon get adjusted to first narrow the overall bandpass and then stay linked so that you can shift both of them in tandem for the Doppler effect? This "coupling" lends itself to computer control because it can be set up and modeled with ease.

Simon

[MapleRidge]

The control box for the remote tuner has a USB connection to a computer and the pressure can be adjusted via an app on the desktop. You can control this via a remote desktop if you need to be a significant distance away, or you can run the tubing from the control box to the scope. Lunt has 100' rolls of tubing available though I'm not sure how far you can run it in practice. I typically have about 25 feet in use.

The rotating knob that houses the piston that adjusts the pressure needs a quick mod from the manual setup as it is shipped. There is a small raised cap at the end of the knob which twists off. Once off it will show a small screw head. Un-thread the pressure knob completely and you will see the bottom of the piston. If you loosen the screw the piston can free from the body. Lunt will supply a small fitting that accepts the tubing...one end is the same thread as the screw you removed and the other is a pressure fit opening for the tubing...the centre of the adapter is open to allow air to flow through it. Insert the piston back in the manual knob body and thread the tubing adapter into the top of the plunger so it is back in place. They have a second cap to thread back on the top to cover it, but it has a hole to allow the push-fit end to protrude and allow you to insert the tubing into the modded pressure tuner. Re-install the tuner body by threading it all the way to the bottom, and you are good to go.

A couple of items to note...I am basing this on my own experience setting my remote unit up many years ago and Lunt may have made a few changes. I have a new conversion kit at the observatory and should double check that the cap with the hole is still the way they have the kit. I have always ordered a second plunger/twist knob assembly so that I can keep a manual knob available and not have to disassemble the tubing fitting in the event I don't need the remote unit...but that's just me.

As for tuning, I find that if I tune the primary etalon to give the maximum contrast (by eye or by camera) then add the DS unit and tune it until the best contrast is reached again. As I have it configured now, if I make adjustments to the DS unit it will tune into the Ha wings, but I don't use the double stack much this way. If I am in the single stack mode you get an incredible range of tuning from 0PSI on the remote up to 20PSI.

I will try to get some pics of the pieces and post them sometime today.

Brian

[MapleRidge]

I have pulled a few pics of the parts used to setup the remote pressure tuner from Lunt.

The first is a shot of the tuning knob on my LS80T with the cap on and with the removed to show the screw head that holds the piston in place on the right side. Once the screw is removed the piston can be removed when the outer shell of the knob is removed.

PT_Cap.jpg (636.46 KiB) Viewed 626 times

The pic below shows the parts that are included int eh conversion kit to switch from manual to the remote piston. The replacement piston has the tubing adapter threaded onto the end which allows the air tubing to connect to it. There are a set of o-rings which are fitted into the groves n the piston to make the seal with the inside walls of the tuner body. There is a closeup of the adapter at the bottom and replacement cap which allows the adapter fitting to protrude through the cap.

Piston_Parts.jpg (548.78 KiB) Viewed 626 times

The next pic shows the converted knob assembly with a piece of tubing fitted into the adapter. You can also see the base of the piston has a hole which duct the air from the remote compressor to pressurize the etalon and make the tuning changes we want.

Piston_Tubing.jpg (567.09 KiB) Viewed 626 times

The last pic shows the face of the remote tuner body with the controls and the control app running on the PC. The + and - pressure button can be depressed by the mouse and lets you set the pressure without touching the scope. This also has the advantage of not manually bumping the scope and when the knob is hard to turn it is a huge advantage.

Remote_Display.jpg (806.29 KiB) Viewed 626 times

One other item I thought of regarding the remote tuning. If you figure that this is what you want to use, I'd say an electronic/remote focuser is equally important. Fine focus is hard to adjust without the human touch induced vibrations and a motorized control will make it much easier to focus.

If there are any questions please let me know...this is a pretty quick overview of the setup.

Brian

[Highbury Mark]

I had the external Lunt pressure tuner for a while. Worked well. I was lucky to find one secondhand as they are very expensive considering the fairly rudimentary technology. Both the Lunts I owned only came on band right at the end of the manual tuner travel - where it required some force to push the piston to the required position.