Thousand Oaks H Alpha

Meng Lee · Post by **Meng Lee** » Tue Jun 12, 2007 9:50 pm

Hi all, I need your advice on Thousand Oaks Optical H-Alpha SOLAR filters.

http://www.thousandoaksoptical.com/halpha.html

The question is, they are much cheaper than Coronado but of course with larger (0.9 Angstrom) bandpass, so is it only good for prominences and nothing else?

Thanks for the advices!

mrngbss · Post by **mrngbss** » Tue Jun 12, 2007 11:22 pm

I have used a TO H-alpha on a Nexstar 5i side by side with a PST. (comparison made using C5 scope w/TO H-a unit)

On very good seeing conditions, you will see prominences on both units.
On poor seeing conditions, you will only see the prominences on PST.

I have never seen the features on the Sun (except Sunspots) through the TO H-a unit and seldom see prominences through it before. I have tried several attempts to view prominences, but only succeeded twice.

Using the PST is a 'always see features' on the Sun and the prominences. Thus, my conclusion is that spending so much/little on TO H-alpha unit is questionable.

However, do note that I used a SCT 5". I have not tried using the TO H-a unit on refractors yet. Results may vary widely.

If you are thinking of imaging the Sun in H-alpha, go for more established brands.

Happy H-alpha viewing!

Meng Lee · Post by **Meng Lee** » Tue Jun 12, 2007 11:29 pm

Hehe was thinking H-alpha next time. But now no funds, so got to concentrate on certain areas only.

By the way Lumenera max exposure is 3mins, if you match the focal ratio, you can use it for deepsky also. I will be testing it for deepsky next. Its low noise is really amazing.

mrngbss · Post by **mrngbss** » Tue Jun 12, 2007 11:32 pm

Meng Lee wrote: By the way Lumenera max exposure is 3mins, if you match the focal ratio, you can use it for deepsky also. I will be testing it for deepsky next. Its low noise is really amazing.

Can you explain a little more on matching the focal ratio? SImple example please?

Meng Lee · Post by **Meng Lee** » Tue Jun 12, 2007 11:35 pm

To make full use of the 3 mins exposure, go for the lowest focal ratio that makes the histogram bunch up around 1/3 the dynamic range, in short, choose the fastest focal ratio that does not cause too much skyglow in the 3 mins exposure.

In this way, you can go to the deepest possible imaging given the camera and light pollution.

mrngbss · Post by **mrngbss** » Tue Jun 12, 2007 11:39 pm

Sounds like aperture? the camera got built in aperture???

Meng Lee · Post by **Meng Lee** » Tue Jun 12, 2007 11:48 pm

Oops, not aperture, sorry about the misunderstanding. Let's have a flow diagram:

deepsky needs long exposure, but Lumenera at most can only expose 3mins.

small f-ratio --> faster imaging ---> but records sky glow also ---> so, compromise by picking f ratio that does not saturate the camera in 3 mins.

I hope I am not confusing you.

mrngbss · Post by **mrngbss** » Tue Jun 12, 2007 11:52 pm

Understooded. I didn't catch fully the meaning of your posts. thanks.

Meng Lee · Post by **Meng Lee** » Tue Jun 12, 2007 11:54 pm

I have the tendency to explain and make confuse, so you must pardon me for that.

Tachyon · Post by **Tachyon** » Wed Jun 13, 2007 2:33 pm

Meng Lee wrote:To make full use of the 3 mins exposure, go for the lowest focal ratio that makes the histogram bunch up around 1/3 the dynamic range,

Just to clarify, it doesn't matter if they are bunched up to the right or left?