Hello everybody,
 I live in Montreal, Canada which is a very light polluted site, and for a long time I was wondering what kind of images it is possible to obtain when the limiting visual magnitude of my site is somewhere around 2.5
    After searching the web for information that I never really found I decided to take the plunge and got myself a DSI-C followed by a DSI Pro and recently just acquired a DSI PRO II. Over the years I collected images showing what can be expected in a light pollution site. I just created a web site http://lightpollutedskyobservation.generalcybersystems.com/ that shows what to expect for people with similar light polluted sky.
   I am also starting to provide information which I either found the hard way or after tedious long searches on the Web. I hope this link will help people who might be skipping on astronomy because they think you can't see anything from a light polluted site.

   There is also a free software to provide the equivalent of a reticule for accurate centering during mount alignement procedure. It works with the latest envisage version 7.05 and works with the DSI I, II and probably III (I don't have one to test it). If it does not just reply to this message with a description of the problem (an image showing the problem is even better) and I will try to fix it.

I Hope it helps other people to become interested in astronomy in all the World's largest cities.

The web site has now been updated with the measured gain and Read Noise for the DSI-C DSI Pro and DSI Pro II. That's one thing I always wanted to know in order to compare with the SBIG other CCD cameras. The measurment method has also been added along with some picture showing the lower noise of the DSI Pro II. I was very much surprised to see that when exposed to the same light source both the DSI Pro and DSI Pro II showed about the same historgram levels since the Pro II is supposed to be more sensitive...

   Check out the differences link on the http://lightpollutedskyobservation.generalcybersystems.com/ 

Jim,

J'espère bien pouvoir ajouter sur mon site plus de photos prises avec la Pro II mais le ciel de Montréal n'est vraiment pas cooperatif depuis quelque temps et je n'ai acquise ma Pro II que depuis environ 2 semaines... S'il y a des choses ou information que tu aimerais voir sur mon site, tout commentaire sera grandement apprécié.

I know what you mean about the sky. I am in Rochester NY and between now and next Spring you can probably count the number of clear nights on one hand. And then it will be minus 15-20 C.

JimT

Jim,

After looking at your picture galery, you seem to be blessed with a much darker sky. All the pictures on my web site were taken from a sky with limiting visual magnitude of around 2.5 Can you tell me what your limiting visual magnitude is. Your Horsehead nebula is quite impressive compared to the few attempts I have made, where it is visible but with a very low contrast between the background brightness and the nebula itself. I am thinking of maybe showing the difference between various sky quality if I can get hold of a few pictures with the correspoding visual magnitude. Do you think that would be a good idea?

Vous êtes trop aimable au sujet des images dans ma galerie. There is a lot that can be done in post processing to improve the initial image. You should see the ones I don’t post.

We average about 20 clear nights per year when the moon is not a factor. Magnitude averages about 4.0. On really good nights (maybe five times per year) limiting magnitude is about 5.0-5.5 but I have a large shopping mall to the West and much neighborhood lighting so my eyes never totally dark adopt.

Clearly sky conditions make a difference but  unless you have images taken with the same equipment, exposure times, and processing there will be too many variables for a meaningful comparison.

Regards,

Jim,

You are right that the overall quality depends as much on the sky condition, equipement and post-processing done. But there are some aspects of the picture that are limited by the sky condition, mainly the sky fog. At my site nothing dimmer than magnitude 16-16.5 can be seen because that's the sky brightness. That's why I find your horsehead nebula impressive since at my site the sky brightness is so close to the surface brightness of the nebula that it is barely visible no matter how much post-processing I do on it. It is that aspect that I would like to be able to compare using picture from different site with their corresponding visual limiting magnitude.