Posts Made By: Wei-Hao Wang

http://www.aoc.nrao.edu/~whwang/gallery/picutres/m8_m20-2006.htm

Any comments are welcome.

Wei-Hao

http://www.aoc.nrao.edu/~whwang/gallery/picutres/summer_triangle_2006.htm

I think this image (the larger version, which is linked at the end of the page) explains why I am still shooting film.

Comments are welcome.

Wei-Hao

Hi,

This is my newest film M31:
http://www.aoc.nrao.edu/~whwang/gallery/picutres/M31_film_2006.htm
Please feel free to comment on it.

I wonder if there is any digital device that is under $1000 can reach both this depth and wide-field in 12 hours.

Wei-Hao

Hi,

I realize that my NJP has terribly bad Dec backlash. It wasn't like this before. Does anybody know how to adjust it?

Thanks.

Wei-Hao

Hi,

I am looking for eyepieces in the 10-25mm and 30-35mm ranges.

For the 10-25mm range, I found Vixen LVW 13mm/22mm and Orion Stratus 13mm/21mm have very similar specs. They have 65/68 degrees FOV amd 20mm eye reliefs. LVW is $250 and Stratus is $130. How do you guys think about these two? Does their difference in performance justify the price difference?

For the 30-35mm range, I found Vixen LV 30mm and Meade 5000 PL 32mm. Again their FOV and eye reliefs are similar. The Vixen one costs $200 and the Meade one costs $150. Which one do you suggest?

Any inputs are appreciated.

Thanks,
Wei-Hao

Hi,

I had wanted to take this picture for a long time, and finally got a chance about 10 days ago. It was taken under moonlight.

Wei-Hao

Hi,

Since I am a DSLR beginner, I tried two most popular beginners' obnjects.

M31:
http://www.aoc.nrao.edu/~whwang/gallery/picutres/M31-2008.html

M42:
http://www.aoc.nrao.edu/~whwang/gallery/picutres/M42-2008.html

Comments are welcome.

Cheers,
Wei-Hao

Hi,

Many Japanese people use 4x5 film on refractor telescopes. I also saw some 4x5 picture by Tony Hallas. The results look very nice.

Instead of the Graphlex 4x5, perhaps you can consider using a pure 4x5 film holder directly attached to the telescope. The structure of most 4x5 camera is not strong enough for astrophotography, especially under long exposure time (>30min).

This is what I found from a US website. The camera (actually is it just a 4x5 film holder and some adapters) is made in Japan.
http://www.sciencecenter.net/hutech/mitsub/ac4x5.htm

Hi,

Even if you have two holes with identical sizes and with perfect collimation, the two spots will not cancle each other.

Light will only disappear when it goes through two polarizers with orthogonal polarization states (e.g., two perpendicular linear polarizations, or left-hand circular plus right-hand circular polarizations). On the other hand, when light with different polarizations meet each other, their intensity will simply add together, but not cancels each other. These are very different situations.

Wei-Hao Wang

Hi Barry,

I couldn't tell you what photographic limiting mag (LM) you will reach, without knowing the sky brightness of your site. Here let me summarize several basic facts about photo LM.

1. Unlike visual LM, photo LM hardly depends on the aperture of your telescope. Eyes cannot do long exposure but film can. Thus aperture is not an issue.

2. Film speed is not an issue, either. High speed films reach the LM earlier than low speed ones. But no matter which one you use, you get the same LM.

3. Although not a function of film speed, photo LM is a weak function of film grain. Films with finer grain have slightly higher (fainter) LM. From this point of view, using low speed films helps you to go deeper. (You need to expose for longer time, though).

4. The primary factor about photo LM is the sky brightness. Whether a faint star can be identified on film depends on the contrast between that star and background sky. If a star is not significantly brighter than the background fog on film, that star never appears.

5. Photo LM also depends on your focal length (again, hardly depends on aperture). With a longer focal length, you will have higher photographic resolution. This helps to concentrate the starlight against the background and therefore will bring you higher photo LM. For the same reason, good seeing also helps.

6. If you know how bright the sky is at your site (M mag per square arcsec), as a rule of thumb, the photo LM is roughly M-2 to M-3 for >1000mm focal length. Again, the details depend on the film grain, focal length, seeing, and very slightly on aperture.

You can take a look at the book Advanced Manual of Celestial Photography. There is a formula for photo LM. That formula is kind of old and it is more suitable to professional observatories. But you can use that as a starting point.