Posts Made By: Roland Christen

M66, same as above

Rolando

M66, same equipment as above

Rolando

Hi Tom,

That is impressive. You are the first one to shoot with that combination of scope, compressor and that size camera. Gratifying to see an actual outcome from my design efforts. Thanks.

Rolando

That's not a bad result with the limitations of the RGB filters. For galactic nebulae you will have much better results if you go narrow band, even if you simply add a single Ha exposure to your RGBs as Luminance layer.

Here is an example, a narrow band color image taken with Ha as red, SII as green and OIII as blue. Scope used was a 140F7.5 Apo refractor operating at F5.7. You will notice that the stars get really small with narrow band filters, which allows the nebula to pop out from behind the bright Milky Way stars. It also brings out lots of knots and nebular detail that is missing in RGB.

Rolando

Excellent!

Rolando

You are welcome. I'm glad you are enjoying it.

Rolando

For your information, dispersion has nothing to do with color correction. Some glass has high dispersion, some medium, some low dispersion. Some glasses have high index, some medium, some low. None of these by themselves have any affect on color error.

What one needs to make any kind of lens is at least one high dispersion element coupled to one low dispersion element. generally the high dispersion also has high index, and the low dispersion has low index.

Color correction for any two glasses is usually going to be the same as any achromat.

The only way to get better correction is to use one glass which has a partial dispersion that is equal to or close in value to its mating element, so that the color error generated by the first element is neatly cancelled by the second element. Normal glasses cannot do this. It takes one glass that has abnormal dispersion to match a normal glass so that complete cancellation of color error can take place.

Therefore, it is the partial dispersions of the two glasses that is important, not whether they are low or high. Partial dispersion is the derivative of the dispersion, for those of you who are math nuts.

Look for marketeers to glom onto this term, "Partial Dispersion" in upcoming ads .

Rolando

Amazing that you can see such a small variation.

Rolando

I just came back from a short vacation on the French Riviera. I learned something about cars and fuel efficiency. Despite high population density along the Mediterranean coast in cities like Nice and Cannes, traffic moves fast and efficiently. There was no gridlock, even at rush hour. Streets are narrow and tight, yet everyone drove like banshees. There are almost no stop signs on any of the streets, and very few traffic lights. Most major intersections have roundabouts, so traffic keeps moving, never stops.

Our host during my stay there drove a medium size Renault SUV, similar to a Ford Escape. The engine was a 1.8 liter turbo diesel, which ran an efficient 40 mpg in our urban driving and an incredible 60mpg during our country outing. He did not drive gently at all, in fact he drove in a manner that would scare most US drivers. I joked that he was preparing for LeMans, him and everybody else down there. Speed limits were 110km/hr around the urban centers and 130-140km/hr in the countryside (68mph and 81-87mph). Most of the cars were going faster than that.

To summarize, almost 90% of the cars in France are turbodiesels. Even though they are paying the equivalent of $8.00 per gallon, the efficiency of these small turbodiesels allows them to pay out of pocket the same or less than we do per driven mile. Even large cars like our dealer's Mercedes station wagon, get excellent gas mileage (around 35mpg city, 45mpg country) thanks to a powerful but efficient turbodiesel. These are clean running cars with none of the sooty exhaust and smell that we have in our diesel powered school busses and big trucks here in the US.

I would like to see new engine development here, coupled with electric traction for commuter cars. They don't have to be small dangerous cramped vehicles. With double or triple our present average gas consumption, we could go a long way to solving our energy crisis.

Rolando

Nice wide field. Do you have a cropped closeup?

Rolando