Posts Made By: Wei-Hao Wang

February 5, 2004 04:58 AM Forum: CCD Imaging and Processing/Solar System

Another Image from New Mexico

Posted By Wei-Hao Wang

Mark,

Very nice image, especially the vivid details in the nebulas.

I suppose the image should be much deeper with 5x20min of exposure. Is it possible to further enhance the faint nebulas without saturating the brighter parts?

We-Hao

February 12, 2004 08:45 PM Forum: Film Astrophotography - Imaging and Processing

Is Takahashi EM-2 usable for long time exposure?

Posted By Wei-Hao Wang

Hi,

It really depends on your optics. If its focal length is less than 200mm, perhaps you can guided it without touching the DEC axis for 30 to even 60 minutes. Of course this also depends on the accuracy of your polar alignment. The polarscope of EM2 has reasonable accuracy. I believe 30min of guiding for f<200mm is easy.

Wei-Hao

March 3, 2004 08:16 AM Forum: Takahashi

NJP mount questions

Posted By Wei-Hao Wang

Hi Sandy,

Perhaps I can answer some of your questions since I regularly use NJP for astro imaging.

1. The PE of NJP is about +/- 4". It's quite smooth.

2. NJP can afford about 70 lbs. I do long exposure (>1 hour) film imaing with NJP and I guide manually on a guide scope. I am confident that my guiding accuracy is better than 1".5.

3. NJP is very robust. Its mechanical part doesn't need too much care. I'm not sure if this is still true for the Temma version since it contains more electronics.

4. I cannot answer this one.

Hope this helps.

Wei-Hao

May 12, 2004 09:45 PM Forum: CCD Imaging and Processing/Solar System

IC 1318 in H-alpha

Posted By Wei-Hao Wang

Wow! Excellent!

I cannot refuse looking again and again at the fine details in those little dark nebulas.

Please do a wide-field mosaic and share with us!

Wei-Hao

May 18, 2004 05:23 AM Forum: Film Astrophotography - Imaging and Processing

Apeture & "f " stops

Posted By Wei-Hao Wang

Hi,

Do you mean prime-focus photography? If yes, and if you don't have a coma corrector for your Newtonian, the Schmidt Newtonian should give you better image quality because of its less coma. And, of course, the extra 2" of aperture helps too.

Cheers,
Wei-Hao

May 28, 2004 10:18 AM Forum: Film Astrophotography - Imaging and Processing

T-Max 3200 or other?

Posted By Wei-Hao Wang

Hi Roger,

Is the variable star a rapidly varying one? Since you have a eq platform, 30 sec of exposure seems a little short. Longer exposure may give you more than a higher speed film do.

T-Max 3200 is certainly a good starting point. However, you may want to try T-Max 400 as well. Although T-Max 400 has lower ISO speed, its much finer grain may help to detect faint stars, which are very small on the film.

Wei-ao

June 19, 2004 03:55 AM Forum: Film Astrophotography - Imaging and Processing

Light Pollution & Filter Question

Posted By Wei-Hao Wang

Hi,

IDAS LPS filter is the state of art. This is the one you should use for color photography. If the light pollution is very slight, a Kodak CC10M or CC20M filter will help to reduce the green background.

If you are going to do B&W photography, a red filter (e.g., Kodak Wratten #25, Kenko R1, or B+W 090) will work. These normal photographic red filters cut wavelrngths below 600nm. There is plenty of star light above 600nm but relatively little light pollution. If you are using TP and targeting red nebulas, a deep red filter (e.g., Kodak Wratten #92, Kenko R64, B+W 091, or Lumicon H-alpha) will give you the best results.

Wei-Hao

July 29, 2004 12:57 AM Forum: Film Astrophotography - Imaging and Processing

Kodak Ultra Color Pro

Posted By Wei-Hao Wang

Hi Mike,

I noticed Ultra Color a while ago. There are no reliable technical data on its reciprcity and I cannot comment on this part. Its red sensitivity doesn't peak at 656nm (where H-alpha is), unlike PPF. At 656 nm, its log sensitivity is 1.9. PPF has a log sensitivity of 2.5 at 656 nm. This means, 400UC is about 4x less sensitive to red nebulas comparing to PPF, if they have identical reciprocity. We all know PPF has very good reciprocity. Unless 400UC has a reciprocity 4x better than PPF (unlikely), it's not a good choice for deep-sky work.

This my conclusion after reading its tech data. Trying it is still the best way to get the final answer.

August 3, 2004 10:44 PM Forum: Film Astrophotography - Imaging and Processing

Milkey Way

Posted By Wei-Hao Wang

Beautiful!


August 14, 2004 11:01 AM Forum: Film Astrophotography - Imaging and Processing

How do you shoot a whole roll?

Posted By Wei-Hao Wang

Comparing to the cost on telescope and camera, film isn't that expansive. After coming back from the mountains, I usually process the film as soon as I can even if I only made one exposure in a roll.

If I really want to make good use of the negative, I made a series of exposures on a gray card. Negatives usually have best S/N when the exposure is as indicated by the light meter. By comparing the densities of the sky fog and the gray card exposures, I know how to adjust my exposure time when I next time go out and shoot stars.

Cheers,

Wei-Hao