Am I correct that your 5/16 EP will give me 126x in my 39 3/8 focal length scope? Doing math with fractions does seem harder to me.

Knowing nothing of the history of this conversion, I have wondered why some scopes are manufactured or named in inches or millimeters. The C6 is, for instance, known for being a 6" scope, but officially listed as having 150mm of aperture, so designed and made in metric. The common 8" Newt, however, is listed as having 203mm of aperture, so it is made to a "round number" in English, not metric. We could be talking about two of the most common and versatile scopes out there being the 100 refractor and the 200 dobs, but these designs were rounded off to the English system and are instead 4" and 8" scopes. Whussup wit dat?

 

It sounds like you would like I-19, from Tucson, AZ to Nogales, AZ. It's the only metric road in the U.S. and all the distance markers and exits are in kilometers. At least the speed limit signs are in mph.

 

All I know is 9" = 228mm the Pearl!
Hey Keith welcome to the site and it is great to see you here.

(aveman

 

Thanks (caveman! It's nice to see some familiar names here.

 

The only time I go metric on scopes is when solving for a new weight and balance for an OTA. Mainly because the scales I have do either Pounds/Ounces or Grams. It's a lot easier to use grams instead of converting pounds and ounces into tenths of pounds.

 

I am an engineer, and feel your pain too. Working with military jet engine parts, everything is designed in U.S. Engineering (read: English) units. But when we have to incorporate parts made from European suppliers, all hell breaks loose... That said, I also think metric units are easier to work with. It's just that US citizens are not that exposed to them as in other countries. I don't know my height in meters, and when doctors tell my baby's weight in kilograms, I don't know if she doing fine or needs to eat more!

 

In the context of telescopes, I can deal with inches and I can deal with millimeters, but centimeters throw me. Someone says they bought a 6.5cm Goto and I'm thinking, "Wow, a 6" refractor. No, wait."

The change from inches to meters for the giant scopes makes sense, but it obscures the fact that that 1,000" scope we always dreamed of will soon be reality. (And here I reach for a calculator to check myself. Yup, the E-ELT will be over 1,500".)

 

My gas dynamics prof in college in the 70s refused to capitulate to the metric system. He often told us that if God had intended metric to be the standard, there would have been 10 apostles, not 12.

 

I can work in both imperial or metric, but from an engineering point of view I prefer metric, much easier on the grey matter when doing calculations.

Telescope apeture specs to me can be in either but it is easier to work out focal ratios in metric.

Being English I prefer my beer measure in pints but will buy wine by the litre.

Question: A US gallon is 0.8 of an Imperial gallon. Are US pints smaller too?

When I was apprenticed into the Royal Navy all of our engineering courses were taught in ISO units. Great....except my first submarine, an old diesal/electric boat, was all in Imperial...

 

1 US pint = 0.833 Imperial pint. And they say everything is bigger in the US.

Metric is definitely easier to use when you need to find the middle of a board on a woodworking project.

On a side note Frank, I lived in Suffolk for 10 years. The Mildenhall/Lakenheath area. The first six, I was in the Air Force, and stayed another four years after I retired. My wife grew up in Thetford and then moved to Beck Row, next to RAF Mildenhall. I miss a good English pint.