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Lunt double stack

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#1 MAURITS

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Posted 24 January 2013 - 01:52 AM

Why did Lunt "stop" the production of the LS35FHa (double stack)filter for the little solar scope?

Thanks! :waytogo:

#2 neotesla

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Posted 24 January 2013 - 08:17 AM

Double stacked the Lunt 35 gets really dark and the image is very dim... The 35mm is more of a visual instrument as well, since there is insufficient in focus for using a CCD.

#3 MAURITS

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Posted 24 January 2013 - 10:21 AM

Thanks S C

#4 Fish

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Posted 24 January 2013 - 05:15 PM

Good afternoon,

It is too bad the DS module is no longer available. Although small and limited in some aspects, the LS35 is a nice grab 'n go scope.

I've had a DS SolarMax 40 telescope for 7 years now and I use it more than any other for quick looks. Small image scale but a solid performer!

Regards, Marc

#5 MAURITS

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Posted 25 January 2013 - 01:31 PM

Why is the double stack 35mm not good for visual?

#6 rdandrea

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Posted 25 January 2013 - 03:46 PM

Why is the double stack 35mm not good for visual?


See neotesla's post above. Because of the smaller aperture, the image would be very dark.

#7 Pawel

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Posted 26 January 2013 - 03:16 AM

Not true. Recently my friend bought two LS35Tha (complete sets) and took one etalon on another to double stack it. Works great!
Only rotating adapter is needed (it's simple, I have the same for my SM90 DS).Take a look:
CLICK

#8 BYoesle

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Posted 26 January 2013 - 07:54 AM

Nice adapter and SS v. DS images :waytogo:

#9 MAURITS

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Posted 27 January 2013 - 03:46 AM

Thanks Pawel for the very nice explanation with the movie!

#10 MAURITS

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Posted 27 January 2013 - 03:50 AM

Is the "double stack" filter "perhaps" somewhere in stock?

#11 Pawel

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Posted 27 January 2013 - 03:57 AM

No chance to get DS filter from stock. You have to find some used or buy another LS35THa. You can also use Coronado SM40, they will work together but SM40 has central obstruction and it will take some aperture.

Bob, we made the adapters after reading your topic about double stacking ;) Thanks for that! :)

http://www.cloudynig...4860184/page...

#12 BYoesle

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Posted 27 January 2013 - 10:18 AM

Thanks Pawel - good to see that it works for others too! :D

#13 Fish

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Posted 27 January 2013 - 07:45 PM

Good evening,

Once again - this time with no explanation unless someone asks! - I must caution against the use of a Lunt blocking filter with any Coronado etalon in the light path. The differences in the basic design do not support that configuration.

Regards, Marc

#14 Spectral Joe

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Posted 27 January 2013 - 09:13 PM

Well, someone's going to have to ask, so, why? I understand the design differences, and that the etalons have different free spectral ranges, but as long as the blocking filter is narrow enough to block the off band modes from one of the etalons things should be no worse than they were single stacked. Better, in fact if the two etalons have different FSRs.

#15 Pawel

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Posted 28 January 2013 - 12:32 AM

If Coronado + Lunt etalons are used in double stack, there is no difference which BF is used.

#16 BYoesle

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Posted 28 January 2013 - 02:43 PM

I must caution against the use of a Lunt blocking filter with any Coronado etalon in the light path. The differences in the basic design do not support that configuration. Marc

I understand the design differences, and that the etalons have different free spectral ranges, but as long as the blocking filter is narrow enough to block the off band modes from one of the etalons things should be no worse than they were single stacked. Better, in fact if the two etalons have different FSRs. Joe


:waytogo:

Note for newcomers: The free spectral range (FSR) is the distance between the primary etalon target wavelength peak (Ha @ 6562.8 Angstroms) and the side band (harmonic) peaks passed by the etalon.

For single stacking, I believe the original Coronado and current SolarScope filters have a FSR of 10 Angstroms, and the Lunt filters have and FSR of around 15 Angstroms. Thus using a Lunt blocking filter with a Coronado or SolarScope etalon would be inadvisable, due to the potential side band (continuum peaks) leakage of a wider bandpass filter of the BF with the narrower FSR etalon. The bandpass filter also has the potential of significant drifting with temperature changes, which could make the situation worse. This therefore could result in much decreased contrast and detail.

Using a Coronado or SolarScope blocking filter system with a single Lunt etalon would seem to be acceptable, as it likely has a narrower bandpass filter than the Lunt blocking filter, and thereby would be even less likely to pass the side band peaks.

For double stacking with say a Lunt and Coronado etalon with differing FSR’s, using either company's BF should work OK, as the bandpass filter portion of a blocking filter would seem to be rendered almost unnecessary. As Joe states the different etalon FSR’s should block, at least theoretically near the target wavelength, the offending side bands from either etalon.

If Coronado + Lunt etalons are used in double stack, there is no difference which BF is used. Pawel


Yes, but if the Coronado SMII etalon design changes have changed the FSR to that of or near the Lunt FSR, this would not apply. In any case it would be necessary to see if far off-band peaks line up.

Regardless of which blocking filter is used, the IR blocker (the Induced Transmission Filter) in the blocking filter would likely still be required for safety, as far off-band IR peaks for both etalons may line up and allow harmful IR radiation to possibly leak through.

Using a Lunt verses a Coronado blocking filter in place of a "rusted" Coronado BF: Unfortunately, the ITF seems to be the component of the blocking filter most likely to fail over time with the Coronado blocking filters. This is a relatively inexpensive component of the blocking filter*. If the bandpass filter of the blocking filter fails (the much more expensive part) it might be able to be dispensed with in a double stacked system with etalons of differing FSR’s - but you would still need the IR blocking component.

* I seem to recall reading that Coronado Meade is no longer replacing ITF IR blockers when they fail, and now require the replacement of the entire blocking filter assembly if outside the warranty period.


Single stack configurations:

Wide FSR etalon + wide bandpass blocking filter = OK

Wide FSR etalon + narrow bandpass blocking filter = OK

Narrow FSR etalon + wide bandpass blocking filter = Not OK


Double stack configurations:

Wide FSR etalon + wide FSR etalon + wide bandpass blocking filter = OK

Wide FSR etalon + wide FSR etalon + narrow bandpass blocking filter = OK

Wide FSR etalon + narrow FSR etalon + wide bandpass blocking filter = OK

Wide FSR etalon + narrow FSR etalon + narrow bandpass blocking filter = OK

Narrow FSR etalon + narrow FSR etalon + narrow bandpass blocking filter = OK

Narrow FSR etalon + narrow FSR etalon + wide bandpass blocking filter = Not OK


#17 MAURITS

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Posted 29 January 2013 - 01:44 AM

Thanks Bob, very instructive!

#18 Pawel

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Posted 29 January 2013 - 03:42 AM

Bob, :bow:

#19 MAURITS

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Posted 30 January 2013 - 11:38 AM

I have seen so many pictures of the little Lunt LS35THa scope ........ :), but why is the "brass wheel" sometimes "cutout in the white part" of the etalon, and sometimes is it "embedded in the black part" of the etalon?

Newer or older model?? :confused:

#20 rdandrea

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Posted 30 January 2013 - 01:19 PM

Mine is "embedded in the black part." It's relatively recent production, September of 2012.

#21 MAURITS

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Posted 31 January 2013 - 03:05 PM

Thanks all for the input!






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