To barlow or not to barlow (not Ken)

[Guest devil74]

Ok so i know you will have been asked this a million times and i am  just being silly but I have one of those stupid questions, so sorry in advance 

 

Would there be any reason to use a 10mm EP instead of a 20mm with a x2 barlow?  Its just i have read a few posts (not on here) where some folk seem to prefer one over the other...I like to understand reasoning behind it if there is any.

[Brantuk]

The reasoning behind that is simply to reduce the amount of glass in the light train. You loose a tiny piece of the transmitted light every time you refract it through another coated lens. It's particularly relevant with lower grades of lens found in the cheaper eyepieces.

[Guest devil74]

Ok understood thanks Kim..I suppose its similar to transmitting sound really then..one piece of speaker cable is better than 5 joined.

 

Cheers

[Brantuk]

Good analogy

[Guest dawson]

From my little bit of research on the same topic, it seems the best option is alwys to get an eye piece at the desired focal length. Anything to alter the effective focal length of an eye piece will either: reduce the amount of light transmitted to your eye; and/or introduce optical imperfections.

It seems a powermate introduces fewest imperfections and least hinders light transmission. A conventional Barlow will likely result in more imperfections and reduce more light loss.

Just put a fancy 10mm on the credit card and hide the statement from the Mrs

Jd

[Doc]

I never use barlows, in my opinion they make the view darker, and spoils the enjoyment.

 

Less glass is the way to go.

[+RonC]

The only reasoning I can see (from the original question) is if you have an expensive WA 20mm ep and don't want to fork out the money for an equally expensive 10mm ep!!

[Guest]

I guess as most objects I view with a Barlow are quite bright anyway, I don't see light loss as much of an issue. For webcamming Jupiter, a Barlow is essential, as the bright light needs to be spread out.

 

When I view DSOs through my telescope (not that often), I don't use a Barlow but even go the other way and use a focal reducer. Of course, these introduce some light loss, too but they also concentrate faint objects into a smaller area.

 

I might consider a Powermate but I don't have a motor drive for my mount. I've managed to hand guide a webcam exposure with a 3X Barlow but it drives me nuts (or at least more nuts than I am already).

[Guest dawson]

 

For webcamming Jupiter, a Barlow is essential, as the bright light needs to be spread out.

 

I think that depends upon the fundamental speed of your OTA.

 

The term 'essential' is a bit like 'always' and 'never' in MCQ exams, and those questions are usually wrong as there are often exceptions.

 

I've had more success imaging Jupiter WITHOUT a Barlow [or Powermate], but I have slow optics (currently f/15).

 

I know nothing about DSOs.

 

James

[Rusty Strings]

I regularly use a power mate and I can't see the difference with or without

[Guest]

I think that depends upon the fundamental speed of your OTA.

 

The term 'essential' is a bit like 'always' and 'never' in MCQ exams, and those questions are usually wrong as there are often exceptions.

 

I've had more success imaging Jupiter WITHOUT a Barlow [or Powermate], but I have slow optics (currently f/15).

 

I know nothing about DSOs.

 

James

My OTA is about F/13. I have done webcamming at F/5 and even F/2.5 of DSOs. I don't do much DSO observing because I'm not often at proper dark sites. I did the Messier objects out of curiousity but would say that many of them are more things to cross off the list before one dies than great but there were some nice surprises.