Small Etalon Improvement For Only $15 USD (13 Euros)

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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by marktownley »

Excellent, let us know how you get on Martin.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by christian viladrich »

A lot of excellent information here. Thanks for sharing !


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Oak »

Hi All,

Since it's been a while, I was wondering how these mods held up. Are you still using them? Any need to replace the rubber/felt elements? Any troubles with decontacting? I am considering doing this for my Lunt 40mm etalons.

Best,
Derek


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by pupak »

Since the etalon from PST was also mentioned here, I have a question. It is possible that the rubber pads damaged in this way ensure the correct functioning of the etalon, or there is some hidden intention. Thanks for every opinion.
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from two etalons
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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

First, let me say I have never owned or inspected an Ha PST. I have viewed Mark's video on the disassembly of a PST etalon chamber.

It would seem these defective seating pads would result in uneven mechanical pressure to the etalon peripheral spacers, and even result in some tilt. Indeed, any tilt that may be occurring with the PST seems to be a fault of the compression tuning implementation. I note in Mark's video there is quite a bit of slop that can occur in the etalon chamber, as the etalon appears completely free to float on the orange foam rubber ring as the nylon/plastic O compression ring is screwed down. I think the less friction from a roller bearing method would be better - maybe you can give that a try with the PST etalon.

In the larger SM90II rich view etalon I had a chance to play with, the lower etalon plate was fixed in its cell with the usual silicon blobs around the side to keep it from tilting. The PST etalon has no such fixation. This might be giving some of the unevenness (the sweet band) from unintended tilt that can be seen with PST etalons at times?

Another issue with the PST might be the compression ring has a bit of friction, and might therefore skew the etalon a bit because it is not secured in any way as compression is applied. This might be where the roller bearing methodology could be a better implementation for tuning of the PST etalon.

I any case I would be replacing those foam rubber gaskets with a more uniformly thick solution. This would seem to be even more important with the PST, since unlike the Lunt etalons, there are none of the silicone buttons around the side of the etalon plates that help secure it and maintain its position without any appreciable tilt as compression is applied.

Bob


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by pupak »

Bob Yoesle wrote: Tue Jan 31, 2023 3:00 pm First, let me say I have never owned or inspected an Ha PST. I have viewed Mark's video on the disassembly of a PST etalon chamber.

It would seem these defective seating pads would result in uneven mechanical pressure to the etalon peripheral spacers, and even result in some tilt. Indeed, any tilt that may be occurring with the PST seems to be a fault of the compression tuning implementation. I note in Mark's video there is quite a bit of slop that can occur in the etalon chamber, as the etalon appears completely free to float on the orange foam rubber ring as the nylon/plastic O compression ring is screwed down. I think the less friction from a roller bearing method would be better - maybe you can give that a try with the PST etalon.

In the larger SM90II rich view etalon I had a chance to play with, the lower etalon plate was fixed in its cell with the usual silicon blobs around the side to keep it from tilting. The PST etalon has no such fixation. This might be giving some of the unevenness (the sweet band) from unintended tilt that can be seen with PST etalons at times?

Another issue with the PST might be the compression ring has a bit of friction, and might therefore skew the etalon a bit because it is not secured in any way as compression is applied. This might be where the roller bearing methodology could be a better implementation for tuning of the PST etalon.

I any case I would be replacing those foam rubber gaskets with a more uniformly thick solution. This would seem to be even more important with the PST, since unlike the Lunt etalons, there are none of the silicone buttons around the side of the etalon plates that help secure it and maintain its position without any appreciable tilt as compression is applied.

Bob
I made a test precision silicone pad that will ensure the placement of the etalon in the axis of the case. If the sun ever shines here again, I'll try it. :)
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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

That looks great!


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by marktownley »

I love how additive manufacturing has benefitted the world of solar!


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by pupak »

I like the idea of pressure tuning the LS40. I would like to modify the LS40 to fit with the assembly.
I assume that the ERF is useless.
Does anyone know what the underside of the etalon rests on? Is there a stop, or does the etalon in the case only hold the silicone on the edges? If there is no lower support surface, then the compression of the etalon must be quite uneven, because the silicone is applied there rather irregularly.
I am mainly interested in reducing the dimensions and reducing the weight of the etalon.
Thanks for every opinion.
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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by marktownley »

Cunning. Thst works well!


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

I'd assume the LS40 is nearly identical to the LS35 (see first post of this thread), and the LS40 etalon will be supported equally and uniformly around the perimeter of each etalon plate, and the etaon is seated on the same type of silicon foam rubber pad as the PST and other etalons.

The ERF is an RG610 or 630 with dielectric IR blocking coatings, in a tilted ERF cell. This is required for all front mounted etalons. It's only useless if you are doing a DIY internal etalon implementation. But even there the ERF cell might serve a useful purpose for ancillary ERF duty, or support a circular polarizer if doing a DS internal implementation within a collimator or telecentric lens system,

I would be concerned that there will always be some friction from the Teflon/silicon/whatever ring(s) that will apply some level of torque that increases with compression to the etalon, and might have some detrimental effects as it does with the PST etalon. This is greatly reduced if not totally eliminated with the thrust bearing implementation which was originally posted about, and therefore would seem the superior method of applying any form of etalon compression tuning.
Next was deciding how to apply uniform pressure, and I struck upon the idea to use a very thin needle trust bearing with even thinner thrust races that would total only 4 mm thick when combined, which also had the appropriate inside and outside diameters, and leaving plenty of room for a thin (~ 2 mm) rubber gasket to apply uniform pressure to the etalon periphery. This would therefore translate rotational movement in to a uniform axial movement and pressure without any torque applied to the rubber gasket or etalon face.
Bob ;-)


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by pupak »

Your arguments are very reasonable. I understand that you want to avoid rotational force when tuning, but there are two circumstances where I don't think the use of a needle bearing is necessary.
First of all, no one knows what torque could damage the etalon. I guess this is just speculation or am I wrong?
Secondly, the rotational moment is very small, because it is only a fraction of the force in relation to the force acting axially, because the coefficient of friction between teflon, nylon, silicone and glass is very small, when we consider that the axial force is in units of Newtons, then the rotational moment comes out in mNm. The etalon is glued to the tube with silicone in several places and this effectively prevents the individual parts of the etalon from turning relative to each other due to a small rotational force.
If the etalon had a significantly larger diameter and was not divinely fixed, the needle bearing is really ideal, but it is probably not necessary for this particular design.
I'm not asking anyone to abandon your tried-and-true approach, just offering an alternative solution.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Valery »

Bob Yoesle wrote: Sat Feb 11, 2023 12:54 am I'd assume the LS40 is nearly identical to the LS35 (see first post of this thread), and the LS40 etalon will be supported equally and uniformly around the perimeter of each etalon plate, and the etaon is seated on the same type of silicon foam rubber pad as the PST and other etalons.

The ERF is an RG610 or 630 with dielectric IR blocking coatings, in a tilted ERF cell. This is required for all front mounted etalons. It's only useless if you are doing a DIY internal etalon implementation. But even there the ERF cell might serve a useful purpose for ancillary ERF duty, or support a circular polarizer if doing a DS internal implementation within a collimator or telecentric lens system,

I would be concerned that there will always be some friction from the Teflon/silicon/whatever ring(s) that will apply some level of torque that increases with compression to the etalon, and might have some detrimental effects as it does with the PST etalon. This is greatly reduced if not totally eliminated with the thrust bearing implementation which was originally posted about, and therefore would seem the superior method of applying any form of etalon compression tuning.


Bob ;-)
Thanks, Bob.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by pupak »

I tried to design a solution that does without the needle bearing and does not transfer the torque to the etalon.
The etalon is glued into the case with 6 tapes approx. 8 mm wide. The gap between the case and the standard is 1.5 mm. If I fit a duralumin ring (2) snugly into the housing with cutouts that fit into the gaps between the silicone strips and have cutouts for the silicone washer (1) on the top edge, this will prevent any torsional stress on the etalon during tuning.
The ring is firmly seated in the frame of the etalon and the silicon washer is anchored in the cut-outs of the ring, only the axial force generated by the threaded cylinder is transmitted.
This solution is more complex to manufacture than Bob's, so it is only suitable for someone with mechanical skills or a lot of friends.
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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by pupak »

Since for me, realization is usually only hours away from the idea, the pressurized LM40 is ready for tests. The pressure is solved by a Teflon toroid, which is stored in a groove and lined with a precise silicone pad. In order for Bob to sand me less :) , the toroid is still coated with a small layer of Teflon paste on the side in contact with the glass. Friction should really be minimal. Tuning from the outside is currently via two M3 screws, which have a range of about 90 degrees. Inside there are 4 threads at 90 degrees, so finding the optimal position should not be a problem. I'm really curious about it. Hopefully the one day's work won't be for nothing. ;)
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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Oak »

Here is another version for the Lunt 40mm. Try as I might, I could not find thrust bearings to fit the 40mm etalon. Instead, I ended up going with 2-3 PTFE washers 2mm in thickness, 55mm OD and 45mm ID, centered in the cover using 3 pieces of velcro tape - under $10 USD total cost. The idea is that the two washers slide against each other, reducing rotational forces on the etalon. (The washers were : MECCANIXITY PTFE Flat Washers 55mm OD 45mm ID 2mm Thick Flange Gasket, White Pack of 5)

Seems to work well via hydrogen lamp, but clouds for the next week so no test under the sun yet… Images below.

-Derek
CompressionTuneLunt40.png
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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

Well done!


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by hopskipson »

I’m a little afraid of taking apart my etalon. I always end up touching something or doing something unintentionally that screws something up. I’m really afraid of decontacted etalons since they are so pricey to fix. Am I being too cautious or paranoid? How hard or easy is this mod?

Has anyone tried this out on a 90mm SM1?


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by marktownley »

hopskipson wrote: Wed Jun 14, 2023 11:26 pm I’m a little afraid of taking apart my etalon. I always end up touching something or doing something unintentionally that screws something up. I’m really afraid of decontacted etalons since they are so pricey to fix. Am I being too cautious or paranoid? How hard or easy is this mod?

Has anyone tried this out on a 90mm SM1?
If you don't feel confident mossing, you really shouldn't do so!

I've thought about trying it with my SM90 etalon, but never got round to it.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by hopskipson »

Oak wrote: Sun Jun 04, 2023 7:06 pm Here is another version for the Lunt 40mm. Try as I might, I could not find thrust bearings to fit the 40mm etalon. Instead, I ended up going with 2-3 PTFE washers 2mm in thickness, 55mm OD and 45mm ID, centered in the cover using 3 pieces of velcro tape - under $10 USD total cost. The idea is that the two washers slide against each other, reducing rotational forces on the etalon. (The washers were : MECCANIXITY PTFE Flat Washers 55mm OD 45mm ID 2mm Thick Flange Gasket, White Pack of 5)

Seems to work well via hydrogen lamp, but clouds for the next week so no test under the sun yet… Images below.

-Derek

CompressionTuneLunt40.png
Hi Derek
Did you ever get the chance to test your design? I just got a Lunt 40 and limited testing looks positive.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Oak »

Briefly though wildfire haze but the results were very good. No more sweet band in double stack. Is your 40mm fairly uniform?


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by hopskipson »

Oak wrote: Tue Jun 20, 2023 12:40 am Briefly though wildfire haze but the results were very good. No more sweet band in double stack. Is your 40mm fairly uniform?
I just got it today and had a brief time with a very stiff photo tripod. It looks pretty good from what I saw today. The full disk looked uniform on band. Looks like I’m in for a rough patch of weather for the next 8 days. :?

So you’re pretty happy with the operation? Do you notice any sticking of the washers or is it smooth threading?

Thanks for the update.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Oak »

hopskipson wrote: Tue Jun 20, 2023 2:03 am
Oak wrote: Tue Jun 20, 2023 12:40 am Briefly though wildfire haze but the results were very good. No more sweet band in double stack. Is your 40mm fairly uniform?
I just got it today and had a brief time with a very stiff photo tripod. It looks pretty good from what I saw today. The full disk looked uniform on band. Looks like I’m in for a rough patch of weather for the next 8 days. :?

So you’re pretty happy with the operation? Do you notice any sticking of the washers or is it smooth threading?

Thanks for the update.
Yes I am happy with it during my brief observing session. Reduced banding in double stack. I did not notice any sticking when I tightened the housing. I carefully cleaned the washers and tested how they slid against each other under pressure before using them - very little detectable friction. I was adjusting VERY slowly under diffuse illumination from the hydrogen lamp to watch the CWL shift. I haven't decided if it is better to loosen between uses or keep the compression in place. The etalon does sit on a foam or rubber ring that is somewhat compressible.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

My preference it to loosen when not in use, as this will allow the foam ring to "relax" back to "normal" and relieve any stress on the silicone buttons that constrain the the edge of the etalon plates.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by hopskipson »

I’m thinking of doing this to my SM1 90. Should I be concerned about not compressing the central spacer?


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

Depends on how far off-band the native CWL is. A small amount of compression would likely be OK. If it needs a lot of compression, the etalon gap without central compression will get pretty uneven, and the etalon FWHM will widen considerably.

Bob


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by hopskipson »

Thanks Bob

I will probably be using Teflon washers and some rubber just to give minimal compression and see if it reduces the amount of tilting needed.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by hopskipson »

Oak wrote: Tue Jun 20, 2023 12:40 am Briefly though wildfire haze but the results were very good. No more sweet band in double stack. Is your 40mm fairly uniform?
I was pleasantly surprised to a patch of clear skies this afternoon albeit only for about 45 minutes. The etalon visually is very uniform and requires minimal tilt. I got to see some nice dark filaments. One seemed like a long river meandering along the disk. I tried to double stack it with my Solar Spectrum and a 2.5x powermate but the image was very dark. It definitely increased the contrast but was very hard to get good focus.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by hopskipson »

I added the 3 Teflon washers to the Lunt 40 and tried to tune the etalon. It seems adding any pressure immediately makes the etalon off band. I didn’t get much time to figure things out but I’m guessing that the etalon is very close to being on band without much tilt to begin with. I’ll have to test this out more to minimize the amount of compression added before going off band.

I purchased a 2mm Teflon sheet and made 2 washers for my SM 90mm etalon. I also added a 4mm rubber washer and tried to use compression to tune it. It seems to add a lot of reflections to the image. I removed the Red ERF from the etalon but that didn’t help. More refinements need to be done. I think this may not be feasible as the erf cell is tilted and may prevent even compression over the entire surface.

I’m wondering if anyone else has tried this with larger etalons like this.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

If you're almost on-band with little tilt then there is really no reason to implement a compression tuning system for an external etalon use. It may also be unnecessary for double stacking with a telecentric arrangement at the focuser side of the optics. In ay event, very little compression is actually needed in most cases.

For the SM90; Hmmm... this is strange. The outer circumference of the ERF cell shouldn't be tilted, only the internal portion of the cell which actually encompasses the ERF itself should be tilted. I have not tried anything other than the LS35 etalon mod.

Bob


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by hopskipson »

I should have been more clear. With the erf in place it was unable to thread completely below the exterior ring that is squared making an uneven surface. When I removed the erf it would sit square but still produce the reflections. I didn’t have much time to experiment with this but I may just use it as a double stack without the erf with my other 90 when time permits.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Nik »

Has anyone tried it with PST etalon?


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by alpenglow »

hopskipson wrote: Sun Jul 09, 2023 9:14 pm I should have been more clear. With the erf in place it was unable to thread completely below the exterior ring that is squared making an uneven surface. When I removed the erf it would sit square but still produce the reflections. I didn’t have much time to experiment with this but I may just use it as a double stack without the erf with my other 90 when time permits.
My SM90I, Meade made, which is fairly red shifted.
Image

I think one solution is to reverse the whole ERF double ring assembly such that the label is facing inside. It might be tricky to screw back in but you'd be working with a larger flat surface.

Does anyone know if it matters which side of the RG630 glass is facing? I'm guessing that it might not be coated. If it does matter, it looks like it could be reversed as well.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

It looks like it might be AR coated. Once you remove the ERF cell and flip it you can reverse the ERF itself to maintain the OEM orientation.
Has anyone tried it with PST etalon?
See previous post in this thread. The PST is already similarly mechanically pressure tuned, but needs some additional support and possibly a sleeve around the etalon to prevent untoward tilting that can occur with the mechanical pressure. Using a more "slippery" surface to apply the pressure so as to not induce rotational friction and torque may help as well.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by alpenglow »

Thanks Bob. Figuring that it would be easier, I tried this first on my SM60I and flipped the rings to face outward and the ERF so that the coated side continues to face inward.

I have not been successful in my initial searches for a needle thrust bearing (ID>=60mm OD<=80mm) and may go with something like PTFE spacers.

As an aside, I pressed on the center dot with my finger and found that it did not take much pressure to bring the etalon on band (held over a H spectrum lamp). This was true from either side.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Bob Yoesle »

Indeed, the small amount of physical pressure needed to effect a gap spacing change is remarkable.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by jannickz »

alpenglow wrote: Tue Sep 12, 2023 3:17 pm Thanks Bob. Figuring that it would be easier, I tried this first on my SM60I and flipped the rings to face outward and the ERF so that the coated side continues to face inward.

I have not been successful in my initial searches for a needle thrust bearing (ID>=60mm OD<=80mm) and may go with something like PTFE spacers.

As an aside, I pressed on the center dot with my finger and found that it did not take much pressure to bring the etalon on band (held over a H spectrum lamp). This was true from either side.
You haven't found a suitable needle thrust bearing (with specific size requirements) and are considering alternative solutions like PTFE spacers.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Dennis »

Oak wrote: Sun Jun 04, 2023 7:06 pm Here is another version for the Lunt 40mm. Try as I might, I could not find thrust bearings to fit the 40mm etalon. Instead, I ended up going with 2-3 PTFE washers 2mm in thickness, 55mm OD and 45mm ID, centered in the cover using 3 pieces of velcro tape - under $10 USD total cost. The idea is that the two washers slide against each other, reducing rotational forces on the etalon. (The washers were : MECCANIXITY PTFE Flat Washers 55mm OD 45mm ID 2mm Thick Flange Gasket, White Pack of 5)

Seems to work well via hydrogen lamp, but clouds for the next week so no test under the sun yet… Images below.

-Derek

CompressionTuneLunt40.png

Tested today with the Quark and lunt 40 etalon with the teflon washers and works great. Much more transmission now without the need to tilt the etalon.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Dennis »

Dennis wrote: Thu Feb 29, 2024 8:39 am
Oak wrote: Sun Jun 04, 2023 7:06 pm Here is another version for the Lunt 40mm. Try as I might, I could not find thrust bearings to fit the 40mm etalon. Instead, I ended up going with 2-3 PTFE washers 2mm in thickness, 55mm OD and 45mm ID, centered in the cover using 3 pieces of velcro tape - under $10 USD total cost. The idea is that the two washers slide against each other, reducing rotational forces on the etalon. (The washers were : MECCANIXITY PTFE Flat Washers 55mm OD 45mm ID 2mm Thick Flange Gasket, White Pack of 5)

Seems to work well via hydrogen lamp, but clouds for the next week so no test under the sun yet… Images below.

-Derek

CompressionTuneLunt40.png

Tested today with the Quark and lunt 40 etalon with the teflon washers and works great. Much more transmission now without the need to tilt the etalon.

Another test today with velcro tape to keep all in the center. Not good, got banding. I assume the velcro caused a bit of friction on the washers which made them slide not so well -> torque (?) on the etalon. Next test without velcro again.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Oak »

Seems odd. Did you try with just the Lunt 40 or only in double stack? Probably the Velcro tape is not totally necessary anyway.


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by Dennis »

Oak wrote: Sat Mar 02, 2024 3:42 pm Seems odd. Did you try with just the Lunt 40 or only in double stack? Probably the Velcro tape is not totally necessary anyway.
Its weird, last time there wasnt any banding (always in ds with the quark). Today i had it and i was wondering what happened. Then i tried to slide the washers manually.. and then i realized it. Didnt know those etalons are that extreme sensitive to pressure and torque..


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Re: Small Etalon Improvement For Only $15 USD (13 Euros)

Post by marktownley »

If there is banding the etalon has too much tilt, ie the CWL is sat at is in the red.


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