Solar Telescopes

I have a Coronado PST and enjoy viewing through it, especially after Meade rebuilt it under warranty a couple of years ago when the dreaded orange rust appeared on the lens.

I'm thinking of buying a better and larger solar telescope some time this year and wondering what would be a good choice. I've more or less discounted the Daystar SolaRedi after reading some very negative reviews on it and the etalon temperature issues and Coronado are too pricey. The Lunt LS60THa scopes look to be good value with a variety of models available and attract good reviews, although a few months waiting list for some models.

Can anyone please tell me is it worth considering a more expensive B1200 model over a B600 one and what exactly does the Pressure Tuner do? Again, is it woth getting a model with it?

Gordon

Gordon,

Forget the B600. It is a 6mm diameter blocking filter and will only cause vignetting of the image. B1200 is the one to get with the 60mm scope.

The Pressure Tuner uses air pressure to adjust the tilt of the filter. I haven't used it myself but have heard very good reports on it.
Here is a portion of an article Andy Lunt wrote about it:

The system works because the etalons used in the current Lunt designs are air spaced. These air spaced etalons are tuned to the Hydrogen-alpha line via several mechanisms.

The first is the spacing of the air gap between the high reflective surfaces of the ultra flat plates.
The distance of this spacing is generally held constant because the refractive index of the medium between the plates (air) is relatively stable at ~1.

The center wavelength can be manipulated by tilting of the etalon. This changes the angle of the light at the interface of the high reflector/air layer, having the effect of moving the center wavelength toward the blue.
Now assuming that the etalon was tuned in the normal incidence position, tilting can only shift the CWL in the one direction.

Slight changes in barometric pressure and/or a change in altitude will effect the CWL due to the change in refractive index of the spacer layer. These changes can be compensated for by tilting, provided the etalon is tuned to allow for those changes.
Taking an etalon that was tuned at 100ft to 10,000ft would not be within that range.

In the past I have manufactured sealed etalon system for space flight. These etalon systems were designed to work in a vacuum. They were manufactured as very high tuned etalons, by placing them under vacuum, the tuning lowered and we had to fine tune to ensure that at full vacuum the etalon was on band.
Additional fine tuning from there was done via heat due to the fact that the vacuum could not be adjusted.

Our technology utilizes air pressure and not vacuum.

We have enclosed the etalon system within a sealed cavity.
The sealing of the cavity is done via the collimating and refocus lens so that the etalon itself is isolated from differential pressure.
The piston applies from zero to a pressure that is equivalent to taking an etalon from -500ft to +12,000ft above sea level.
This essentially makes the etalon system altitude insensitive.
In addition the etalon can be used from -50 to +200 degrees Celsius due to the fact that the tuning can compensate for the very small changes that heat would have on the "feet" of the etalon.

I have gone into great detail regarding the compromises of tilting internal to a telescope. Only very small adjustments to the tilt can be done otherwise the etalon system will begin to suffer from the off axis rays of the collimated beam. People have noted that in internal tilt systems the CWL is very sensitive to even small adjustments of the tilt wheel.

By removing the need for tilt we have placed the etalon in the most optimized position possible.
We install a very accurately tuned etalon.
This etalon is tuned to the red side of the CWL.
Given that it is already tuned to the red, the user has the ability to shift the tune of the CWL to the Hydrogen-alpha line and then Doppler tune to the blue or back thru to the red.

Due to the fact that there is no tilt involved, the image field remains flat and precise.

Traditional tilting allows the Doppler shifting across the field in a plane perpendicular to the axis of light. The user can see a change to the image that allows for the viewing of proms or filaments.

True Doppler Tuning allows for a shift into and away from the user. Adding a 3D component to the viewing experience.
While it has minimal effect on proms due to their being at the edge, it does have an effect on filaments and active regions. While looking at a filament at the center of the Sun the user has the ability to Doppler shift from the base of the filament to the tip, following the filament thru it's structure toward you and away from you. The Tuning system provides an order of magnitude more precision to the tuning of the desired features.

Thanks Michael. That answers my question perfectly so it will be a B1200 then and the pressure tuner too if I can afford it.

Interesting article that. Explains a lot. Thanks for posting it. You still doing solar photography? I recall you taking many stunning solar pics.

Gordon

Gordon,

I'm in the middle of re-configuring my setup at the moment.
I bought a Paramount ME and have the 16" SCT on it.
However, I also want to attach my TEC140 on the mount.
I got plates made up for mounting it piggyback, but no joy.
Now I am exploring options for mounting the TEC140 side-by-side with the 16".

In terms of solar, I have a Daystar T-Scanner filter which I use with the TEC140.
I hope to get back imaging with that once I have the mounting configuration nailed.

BTW, in terms of Coronado, Meade have an outlet shop:
www.shopatron.com/home/index/1323.0
If you have somneone in the US or Canada who can handle a package for you, you could save a small fortune.
The Solarmax 90 looks tempting, although a BF15 would be best with that size filter.

Michael.

Nice setup Michael! Hope you get it all up and running soon with the sun getting more active.

I didn't know Meade had an outlet shop. I'll look into that.

Thanks,

Gordon