PST double stacking

[canuck]

Hi Folks,

I've been given a scrapped PST without an HRF, so it's unusable. Is it possible to use the individual parts to double stack a functioning PST?

Please keep in mind I have no intention of risking my eyesight or dismantling my working PST! It's not something I'm going to experiment with, so if a straightforward solution is not possible, the damaged PST will be scrapped.

Any input welcome.

[PeterW]

Not possible. The PST has a small (?20mm) etalon, for double stacking you'll need a 40mm etalon for the front of the working one.... and you have to get the tilt right.... I don't think you'll have much luck.

Anyone know the current cost of double stacking a PST normally??

Cheers

PEterW

[Paxo]

Anyone know the current cost of double stacking a PST normally??

Cheers

PEterW

Current price at telescope house £639 for the Coronado Double Stack Filter + TMax For PST or just over £1000 including the pst.

http://www.telescopehouse.com/acatalog/Coronado_Double_Stack_Filter___TMax_For_PST.html

Steve..

[Xunil]

Not possible. The PST has a small (?20mm) etalon, for double stacking you'll need a 40mm etalon for the front of the working one.... and you have to get the tilt right.... I don't think you'll have much luck.

Double stacking 40mm etalons on a 20mm PST and then getting the tilt right...hmm....nope, I'm clueless.

Sorry to be a tad "Greeny McNoob" at you all, but can someone convert this to English for me?

[Kaptain Klevtsov]

Yup. The etalon (the good bit) in a PST is 20mm diameter. Its inside the tube somewhere. The double stack add-on bit has a 40mm etalon and screws on like a camera filter to the front of the PST. The add-on etalon has to be aligned to within plus or minus about nothing for it to work, so bodging one together isn't going to happen, even if it were big enough.

Kaptain Klevtsov

[PeterW]

Also putting a 20mm aperture onto a PST gives you so little light to play with, you might as well give up (double stacked images are darker anyhow). Save your pennies and get a proper one. I see that Lunt ..?... are bringing out a new PST challenger... so we'll hope that competition brings the prices down.

Cheers

PEterW

[Astroman]

The "etalon" is the front filter and consists of essentially two layers of glass with metal coatings on both surfaces. When light enters the etalon, it reflects off the inside glass, back onto the outside glass and back through the inside glass to the diagonal filter. In doing this, the etalon cuts out all light except that of the very specific H-Alpha band. The precision of this filter is crucial and depends on the distance between the etalon elements, the reflectivity of the coating and the angle at which the light enters. Simply placing two filters in line will not guarantee the precision of the two most important elements overall namely the reflectivity and angle, and won't necessarily give good results.

Now, read this again, slowly, and you'll see what it means. :shock:

[PeterW]

The flatness of the glass and the exact even spacing are measured in nanometers.... (light wavelength 100's nanometers). These little guys really are very high spec components, hence you only get a little one in your PST and why a 90mm one casts a wee bit more. Wikipedia explains the general concept....

http://en.wikipedia.org/wiki/Fabry-Perot

The etalon gives a very narrow transmission at the H-alpha band and the other filters ensure that the other etalon transmission does not get to your eye (messing up the image).

Cheers

PEterW

[Xunil]

Thanks for the info both, that's a little clearer now - the wiki page did leave me well behind - I think I grasp the phase being used to cancel out unwanted light but it made my head hurty shortly after.

@ Astroman - I read it several times, at various speeds - I even tried to rotate my head a little to get out of phase with my lack of understanding

..back to PST's & Etalons - In the practical world, is there a major advantage with using one instead of a scope with a sun filter on it?

[Astroman]

A PST allows you to see prominences, (flares), filaments and other very faint HAlpha features on the Sun. A "regular" solar filter lets you see sunspots, plages, and other white light features. Look at the Solar Imaging section for the differences.

[GazOC]

What do you make of this kit AM?

http://www.luntsolarsystems.com/

How good is a 0.7 Angsrom Ha filter?

[Astroman]

The narrower the bandpass, the finer detail you'll see. If you got 1.0 Angstrom out of a PST, you're probably doing well, just because of the small aperture and low price. The 60mm Coronado I use from time to time gets down to 0.6 A in good seeing, (~$5000), while a better one can get to 0.3 A or so. I'd say the 0.8 A and 0.55 A filters listed would work well.

BUT I don't generally like to rate or review equipment unless I see it in action. Spec sheets can say anything they like, but you can't really tell if it lives up to it unless you a) know what it should show, and actually see it show it.

HTH.

[GazOC]

Do you think these are OK in principal AM ?

http://luntsolarsystems.com/ls50f_ha.html

[Astroman]

Sure, but you need the blocking filter, too. I looked at those when I was there before.

The width of the HA line is very close to 2 Angstroms, including what's called the "wings". What happens on the Sun is, features are moving. Prominences shoot out from the surface at many times the speed of sound, traveling millions of kilometers per hour, potentially. This causes the line of the feature to Doppler shift to the blue or red side of the baseline. If your filter is only capable of 1.0 A resolution, you may only see the part of the feature that falls in that wavelength. If you have a narrower band filter, you'll see even less of the whole feature, but careful tuning will bring out more details as you tune to either side of the baseline.

It's a difficult concept to grasp, and you have to take into account the actual, physical size of the features you're viewing, along with how far it can travel in a given time. Don't know what else to tell you.

[GazOC]

Thanks AM. I think I understand.

[Tiny]

If you look at the Daystar site it has examples of what you see at 0.8, 0.7, 0.5. A double stacked PST is around 0.5 while a single is above 0.8.

The Lunt scopes specs and prices imply you can buy a Lunt for a lot less than a PST given Lunt offers a 60mm for not much over the price of a 40mm PST. Of course no Lunt's exist for testing yet but if they work as the pre build information implies...