Hello Marty, Ok, I see. Then the calculation is completely different since there is no telecentric or collimated beam falling onto the etalon. In the first case, you just have a f/16.67 beam. It means you will have both: - an enlargement of the FWHM (compared to its nominal value) because of the f/1...

Hrm, Any help with this? Mica spaced etalon, 21mm aperture (Quark Combo) 60mm aperture F16.67 telescope (1000mm focal length) Sweet spot size and general thoughts? I just rough calced it with n=1.6 and the result was 1.59 degrees approximately? This seems to agree with the graph above? I'm curious ...

I updated the formulae for mica-spaced etalon.

Hi all... This is quite the read, and need to go over it a few more times. I have a question about the sweet spot ration from the d/D ratio. Does the result, say .2, have any units associated with it or is it 0.2 of the actual field of view, or some other relative detail? Just trying to make sense ...

Hi all... This is quite the read, and need to go over it a few more times. I have a question about the sweet spot ration from the d/D ratio. Does the result, say .2, have any units associated with it or is it 0.2 of the actual field of view, or some other relative detail? Just trying to make sense ...

Beautiful FD image Mark !

Excellent Peter !!
I will try this method on my side.

BTW, there is also a possible combinaison with a double stack Lunt 80 mm internal etalon. I don't remember what is the actual diameter of this etalon.

Does that sound about right? Yes indeed ! As an example, you might remember Antonello Satta's refractor (not sure of his pseudo here). He made a 150 mm f/10 refractor with an internal Lunt 60 mm etalon. It was a kind of truss tube OTA. This is also the principle at work in the 140/90 mm famous Ha r...

Hello Marty, There is a simple rule for internal etalon in collimated beam : - in an "optimal" system, the sweet spot diameter is proportional to the ratio d/D, where d is aperture of the etalon (and collimating lens) and D the aperture of the refractor. Accordingly, the maximum diameter is acheived...

Beautifull refractors !!

BTW, Pedro I was wondering whether you could put a SSM on top of the water tower we see in the background ? It would be interesting to know the difference of seeing between ground level and up there (8 m high ?).

Very well reported Christian, and this is unfortunately the humpty dumpty story of solar filters! companies will not throw underperforming glass filters in the trash unless there is a severe defect; companies will attempt salvage of the rejects by allowing an extended acceptable tolerance range. Th...

This is a very promising start. Congratuations !

Nice set of images Stuart, with beautiful processing !

Hello Pedro,
Clavé helioscopes are collector items. I should have bought them years ago when I was a student. But ... I didn't have enough money ...

Hi, ************************************************************************************************************************************** To the moderators, I am not quite sure to what section this post belongs to, so feel free to move it in the correct one. ****************************************...

Yes indeed, it looks good on paper :-)

As explained by Bob, you can take any filter to observe/image the photosphere. As a general rule : - the contrast of granulation increases when going to the blue end of the spectrum, - turbulence increases when going to the blue end of the spectrum, - some refractors have a lower optical quality in ...

Just wondering whether you could post a larger version of the test report ?

Hi Peter, The only measure I know of a Lunt etalon is this one : https://luntsolarsystems.com/were-proud-of-our-etalons/ They say : Specifications: Lunt Solar 50mm Etalon Center Wavelength: 656.28nm Peak Transmission: 79.89% Bandwidth: 0.7 Angstroms (FWHM) R: 12.5 Angstroms https://luntsolarsystems....

As said by Bob, domes can have good or bad impact of day-time seeing. During the day, the heating of the dome surface will degrade the seeing. A difference of 2°C between the surface of the dome and the ambient air is sufficient to seriously degrade the image quality. You can check this with an IR t...

Hi Peter,
I am puzzled by the factor 2x between the "expected" and measured values. As you said, it could be because of the f/16 ratio used. I tested different values from f/1.8 to f/11. It was a good way to learn about the true optical quality of my lenses.

In my experience with tilt-tuned etalons, a large inner ring might indicate the etalon cannot be brought on-band, and even if it can, it might therefore be plagued by "banding" due needing excessive tilt from having a too high of a CWL. It might be just as important to define the outside limit for ...

Peter: excellent work, as usual. In the very good paper by Cyril Bazin and Serge Koutchmy, "Photometric properties of new solar Ha commercial Fabry-Perot etalons", they state: We consider the use of the commercially available Fabry-Perot etalons (FP) of Sidorin and Lunt type for the imaging of the ...

Excellent Peter ! Some comments : - if you take into account the lens focal length, then you can calculate the FWHM (and FSR) in Angstrom, - François Rouvière is working on a short paper presenting the associated calculation, - indeed, I found out that the quality of the lens is very important since...