Whats better for me, a 1.25" or 2" barlow?

[7immy]

hi

im thinking of buying a barlow for my setup (SW200) but really not sure what size is better for me 1.25" or 2". My uses would be for normal viewing with 1.25" eye pieces but also (and this is a biggy for me) to use with my camera (canon 350D).

A 1.25" barlow would be good because my current eye pieces are all that size but I've heard of issues with SLR's at this size ie vignetting and lower light conditions due to smaller hole. Does any one know more about this?

My next option is a 2" barlow with a 1.25" adaptor so I can use my camera without worry and theoretically my eye pieces too.

Would there be any quality differences looking through a 2" barlow with a 1.25 EP and a 1.25 barlow with the same EP?

The barlows in question are: 1.25" 2* Tal and 2" 2* Revelation ED

Sorry for the long winded questions but I'm new and bit confused about all this.. hope someone can help me..

Many thanks

[sixela]

Well, why would you use a barlow with your EOS? Usually, the result is a scope+barlow that is hard to use for deepsky photography because of the long effective f/ratio and something which is not that suited for planetary photography because you can't easily take tons of frames in an animation (like you can with a webcam-type sensor).

The only thing I can think of is lunar photography at a different image scale, but have eyou actually tried it on prime focus and decided you wanted the same but bigger and that a webcam sensor without a barlow wasn't going to do?

But both the barlows you mention are pretty OK. The main advantage of the 2" barlow is that if you ever buy a large expensive 2" eyepiece you'll have two, but the combination is usually very bulky.

[7immy]

thanks for the reply sixela

That kinda makes sense. I suppose if you 2* the magnification your going to almost 2* the amount of light you need.

Could you suggest (or is there) anything to get in closer to deep space objects/ planets? I know I'm never ever going to get anything close to nasa shots but currently on prime focus orion for example is the equivalent of a 50p coin on an A4 piece of paper and i'd like to get in a little closer to get more detail without cropping images.

I havent tried webcams yet though, I'll give it a try!

I thought I'd be able to get in a little closer to these wonders.. are my expectations just too high.

[sixela]

thanks for the reply sixela

That kinda makes sense. I suppose if you 2* the magnification your going to almost 2* the amount of light you need.

Four times, because the area something occupies increases by the square of the magnification factor.

Could you suggest (or is there) anything to get in closer to deep space objects/ planets?

Getting closer to deep space objects with photography? Usually, each scope/sensor combination simply has its sweet spot, and you select the objects accordingly. Then it's a matter of making the signal to noise as good as possible, and for that a faster scope is more convenient. If you have an object that is slightly small you can just slightly rescale the image. If you have an object that's much too small, you really need either a sensor with a much smaller pixel size or another scope.

Mind you, you can try. But with a 2x barlow, you're going to end up with less subs (and some bad ones because tracking correctly wo'n't work) if you want the same signal/noise ratio in each sub, or with just as many subs but with a worse signal to noise ratio (or nothing at all). It might be useful for really bright DSOs like M42 and M13.

I know I'm never ever going to get anything close to nasa shots but currently on prime focus orion for example is the equivalent of a 50p coin on an A4 piece of paper

Uhm -- I'd bet you only have the central part on the image, then. M42 should fill up a sizeable chunk of the image if you have all of it, as it's 1° in size (assuming a 200mm f/5, that's 17mm large, which means it only barely fits on your 50D sensor; in fact, some parts would be clipped!)

I havent tried webcams yet though, I'll give it a try!

They're only useful for bright objects, though -- different kettle of fish, planets and the moon.