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Posts Made By: Wei-Hao Wang

December 2, 2002 01:33 AM Forum: Telescope Making

field flattener or focal reducer for refractors

Posted By Wei-Hao Wang

Hi,

I'm thinking about getting a MEADE 178ED to do astrophotography. What I need is a field flattener (or focal reducer) to correct its field curvature. Does anybody know how can I design and make one for this telescope?

Thanks a lot.

Wei-Hao Wang

May 12, 2003 09:30 PM Forum: Film Astrophotography - Imaging and Processing

Kodak PPF

Posted By Wei-Hao Wang

Hi

I saw lumicon.com still has Kodak PPF for sale.
How do you think about them? Aren't they expired?

Thanks,

Wei-Hao Wang

July 26, 2003 06:47 PM Forum: Film Astrophotography - Imaging and Processing

Very good ISO 400 color negative

Posted By Wei-Hao Wang

Hi everyone,

I have found a very good ISO 400 color negative for astrophoto -- Konica Centuria Super 400. It has resonably fine grains and most importantly, very high red sensitivity.

It was occasionally used by some random Japanese astrophotographers. Their results looked OK. I did some test of this film last month, on North America Nebula and some Milky Way regions. My test confirms the very good reciprocity property of this film. It's extremely sensitive to red and blue nebulas. Its color balance under long exposure is somewhat toward magenta. Probably it's not good for planetary nebulas, which have green colors. On the other hand, if you have to take pictures under slightly light-polluted sky, this film will not give you greenish background.

The only concern about this film is, I'm not sure if it can be found in US. I asked my freind from Japan to buy them.

The picture in the link below is taken by this film. I'm processing the one on North America Neb. Next week I will post it to my website, too.

http://www.ifa.hawaii.edu/~wang/gallery/picutres/m16_to_24.htm

Wei-Hao

July 30, 2003 04:37 PM Forum: Equipment Talk

Buying telescopes from Japan

Posted By Wei-Hao Wang

Hi,

Had anybody considered buying telescopes from Japan. I'm talking about Japanese telescopes (such as Tak, Vixen, Pentax), of course. I found that the prices of these Japanese telescopes in US are amazingly high compared to those in Japan. For example, you can buy round-trip tickets to Japan and buy a Tak FS128. Probably the total cost is still lower than buying it in US.

Wei-Hao

October 15, 2003 06:08 PM Forum: Film Astrophotography - Imaging and Processing

EPSON 3200dpi Scanners

Posted By Wei-Hao Wang

Hi,

I learned that there are two 3200 dpi scanners from EPSON: Perfection 3170 and 3200. I wonder what's the exact difference between these two models.

According to the specifications, these two are both 3200 dpi with Dmax 3.4. 3200 can scan 4x5 films but 3170 can only scan median format films. In terms of speed, 3170 is significantly faster than 3200 (8.7 msec/line vs 14.3 msec/line at 3200 dpi). The CCD type and light source are the same for these two models. 3170's price is <$200. 3200's price is <$400.0.

Do they have the same image quality? If yes, perhaps I will go for 3170 and save $200. On the EPSON webpage, they mention that 3170 has a densitometer function. I think this function would be useful. However, they never mention this on the webpage of 3200. Does 3200 also have this function?

Any thoughts about these two scanners?

Wei-Hao

March 12, 2004 01:41 PM Forum: CCD Imaging and Processing/Solar System

Re: another quick question: adaptive optics

Posted By Wei-Hao Wang

I guess not. AO7 only corrects the shift of image due to seeing. By using webcam and frame selection in registax (for example), one not only corrects the image shift but also rejects frames that suffer from high order distortion caused by seeing. AO7 doesn't correct for the high order distortion.

Furthermore, according to SBIG website, AO7 corrects the image shift at a speed up to 40 Hz. The normal guiding rate is a even smaller 10 Hz. This is lower than (or comparable to) the readout rate of webcam.

If AO7 cannot correct image shift faster than webcam + registax and if AO7 cannot correct for high order distortion, I see no reason to use AO7 with webcam.

How to find a bright guide star for AO7 when doing planetary imaging is another problem.

Cheers,

Wei-Hao

June 13, 2004 01:46 AM Forum: Takahashi

Re: new mount EM-11 (update for EM-10?)

Posted By Wei-Hao Wang

It seems the main upgrade is that it uses bearing now, like EM-200. This brings its max load from 7kg (EM-10) to 8.5kg. The polar scope is now 6x (was 5x).

Some more pictures here: http://www.takahashijapan.com/PURODUCT/Mount/Equatorial/EM11/EM11TEMMA2/EM11TEMMA2JR.htm

Wei-Hao

August 14, 2004 04:19 AM Forum: Film Astrophotography - Imaging and Processing

Duplicating Slides

Posted By Wei-Hao Wang

Hi,

Now most people process their film images in digital dark rooms (PhotoShop etc.) and then print the images out. This is also what I usually do. However, I have a slide projector and I do enjoy watching the large projected image. For this purpose, I still need high quality slides. It's expansive to output digitally processed images to slides. I thus decide to try slide duplication.

Attached image is my first result. The left one is the original. The image is taken by a 4" F9.3 telescope with a 67 camera. The film is Provia 400F +2 push and exposure time is 2 hours. Apparently the contrast is low (even after +2 push!!). The right one is the duplicated image taken by a 645 camera. The film I use for duplication is E100G +2 push. These two images are scanned with identical setting and are not furthered processed after being scanned. What you see on the monitor should be very close to what I see on a lightbox.

Now I can enjoy this image on the large screen.

Wei-Hao

October 12, 2004 05:42 AM Forum: Film Astrophotography - Imaging and Processing

Star Trails #1

Posted By Wei-Hao Wang

Hi,

Just scanned several of my new star-trail pictures. All of them used Mamiya 645 and Kodak E100VS. Taken on 2004/09/25 under an almost full moon. Enjoy.

Wei-Hao
http://www.ifa.hawaii.edu/~wang

#1 35mm/3.5 @F5.6, 30 min exposure

October 12, 2004 05:43 AM Forum: Film Astrophotography - Imaging and Processing

Star Trails #2

Posted By Wei-Hao Wang

#2 35mm/3.5 @F5.6, 15 min exposure