Here is the place to talk about all those equipment(Telescope, Mounts, Eyepieces, etc...) you have. Not sure which scope/eyepiece is best for you? Trash it out here!
Sam, I'm thinking of replacing my Celestron 2x Ultima Barlow (1.25") with this one to use with my 2" EPs (TV 2" barlow is way too expensive!). Any performance differences compared with Ultima?
Arief, i bought a 2" barlow (scopetronix) from sam, my first impression is that it is has a brighter image, The contrast however is not as good as the 1.25 ultima barlow. (i also have the ultima barlow) Same picture taken of saturn with the same speed on camera yield a brighter pic from scopetronix. ( I could not understand why). Maybe apo barlow have more lens. There is also a bright spot in the centre of the image too, anyone comments from other users.
2" barlow gathers more light, that's why i think it's brighter. can post the two pictures side by side? i'm curious about the bright spot in the centre of image.
2" barlow gathers more light, that's why i think it's brighter
I don't think a 2" barlow will gathers more light... a 2" barlow is use to maintain the large FOV that the 2" eyepiece give.
Anyway, I haven't come across a barlow that have internal reflection. Most of the time it is cause by the eyepiece and will only visible on very bright object, such as planets. Have you try use a different eyepiece??
Have a nice day.
Yang Weixing "The universe is composed mainly of hydrogen and ignorance."
scopetronix 2" barlow, Nikon d70 SLR, F9.8, speed 100, please note white central patch at sea. colour appear warmer, magnification appear a little lesser.
Last edited by wucheeyiun on Wed Sep 22, 2004 6:55 pm, edited 1 time in total.
big mistake in evaluting the barlows. anyway, everything is going off-topic, mods pls move this.
distance from the barlow elements to F(point where the light is being focused) greatly affect magnification. when couple with an eyepiece, the barlow will usually gives it's stated magnification. put a diagonal between the barlow and eyepiece will bring it to maybe 3x.
often 1.25 barlows are smaller, the length of the barlow is shorter and the power of the barlow elements are often greater.
2" barlows are big, the length are much longer. the power of the barlow elements are weaker and being compensated by the longer tube to achieve the same magnification.
when placed infront of extension tubes, t-ring and camera, the distance is greatly increased. for a 2x 1.25 barlow, it can easily go to 3-4x. but for a 2x 2" barlow, only slight magnification change occurs(since the barlow elements are not as powerful), maybe 2.5x.
since u do photography, u will realise that aperture makes big difference in exposure. a 3x barlow with that f/10 scope will give u f/30 but for a 2.5x barlow only f/25. very very big difference in exposure, abt 1/2 stop. thus explaining why everything is dimmer.
anyway, i'm quite surprised that u did not note the relation of the difference in magnification and exposure.
"The universe is composed mainly of hydrogen and ignorance." 