Barllow Recommendation?

[Astrosurf]

I used a friend's 3x Tal Barlow recently and it was wonderful. They don't seem to be made any more and I can't see any for sale. Is there a 3x Barlow that you would recommend that's equivalent and not silly money?

Alexxx

[JamesF]

There's the TV 3x barlow. They're not exceptionally expensive second hand. Or if you're willing to drop down a little, the Revelation 2.5x?

James

[Astrosurf]

Thanks James. I would rather have a 3x minimum for planetary. I'll have a look at the TV. Ta muchly.

[JamesF]

2.5x + extension would give you more than 3x with even a relatively short extension, I reckon, if you wanted to do it that way.

Give me a few minutes and I'll do some maths.

James

[Astrosurf]

Thank James. I forgot about an extension tube!

[JamesF]

Ok, my image of Jupiter taken within a few days of opposition last year is about 190 pixels across. That's 1.064mm of my SPC900 sensor. Jupiter is about 50 arcseconds across at that time, so that would be about 46.99 arcseconds per mm. The effective focal length is therefore 206265 / 46.99, or 4389mm. My 127 Mak has an effective focal length of 1500mm, so the 2.5x barlow plus the 40mm extension is giving me a smidge over 2.9x.

I thought it was more than that when I measured it last. Perhaps I misremembered.

The advantage of the lower multiplier barlow is that if you find conditions just aren't up to the higher magnification you can always drop down a bit. Or you drop down to use a camera with smaller pixels. With my ASI120 for instance, I only use a 2x barlow to get an image that's pretty much the same size as the 2.5x barlow and extension with the SPC900.

James

[Astrosurf]

Phew James! Many thanks for that. I'll digest it into my slow brain after a few readings. Maths and I don't get on! I do hope to get a decent planetary camera one day, in place of my Phillips webcam.

Do you use a TeleVue Barlow?

[nightfisher]

Antares make a x3 long barlow, i had one but never used it so sold it on, not expensive about £25 if you can find one

[JamesF]

I have the TV 3x, but the problem with the larger barlows when imaging off the EQ3-2 is keeping the planet on the sensor when swapping from eyepiece to camera. It's so easy to miss it.

I tend to find the target with a wide field eyepiece, switch to a 12mm with illuminated reticle and centre, then add the barlow and centre again, before adding the extension and centering once more. At that point I switch to the camera and I can be fairly sure I'll see the target on the screen.

James

[Astrosurf]

Yep, that's similar to what I do. I don't suppose you have any planetary images through the TV Barlow that you can post here?

[JamesF]

I've hardly taken any. This is a not particularly well-focused one that I took at the start of 2011:

James

[Astrosurf]

Even unfocused you can see more detail than I get with my poxy 4x Imagemate!

[JamesF]

I gave up trying to get my ImageMate to work. I think I just don't have enough aperture with the little Mak, and the slightest inaccuracy makes the target impossible to find on the sensor after aligning with the eyepiece.

I shall try it again when I have a more permanent setup.

James

[Astrosurf]

I think possibly the 4x Imagemate is pushing it a bit for even my 200P. You need such good seeing.

[JamesF]

You'd still only be hitting 4m focal length there, which I manage with the 127 Mak no problem. And you have aperture on your side, too. Perhaps it's the ImageMate that just isn't up to it

James

[SnakeyJ]

Astrosurf,

another possibility is the Explore Scientific 3x focal extender - http://www.explorescientific.com/focalextenders/ - pretty sure this would be available via Europe. I haven't seen a review on this, but nice and short looks very solidly built and the price looks very reasonable (US price currently 89USD against the RRP of 149USD). You could certainly use an extension tube, though depending on how much weight you have at the business end and the quality of the focuser.

I'm pretty sure though you will see a Tal 3x come up on ABS or SGL Classifieds if you can bide your time - though prices will probably rise.

[russ.will]

No point in using an extension tube with a telecentric.... 3x is 3x, regardless of extension.

I can vouch for their visual quality though. I don't get on with barlows for visual purposes, but the ES FE just disappears in the visual chain.

As for worthy successors to the TALs? Revelation 1.25" 2,25x 3 element Apo at £38? I've only had a chance to point mine at terrestrial targets, but blimey it's tidy. I tried a TAL 2x barlow some time back and don't remember being particualrly fussed about it. Good for £35, but the important part of that statement was £35.

Russell

[Astrosurf]

You'd still only be hitting 4m focal length there, which I manage with the 127 Mak no problem. And you have aperture on your side, too. Perhaps it's the ImageMate that just isn't up to it

James

I think you're right there.

[Astrosurf]

Thanks for the suggestions guys.

Russell, is this the Barlow you were referring to?

http://www.telescopehouse.com/acatalog/Revelation_Astro_2_5x_Barlow_Lens.html

[JamesF]

That's certainly the one I have.

James

[Astrosurf]

It's one of those difficult situations where you either need a resounding, 'This is brilliant!' plus with lots of images to compare, or trying one out for yourself!

I'll have to take things slowly and not rush out and buy one!

[russ.will]

Thanks for the suggestions guys.

Russell, is this the Barlow you were referring to?

http://www.telescope...arlow_Lens.html

Yes.

Russell

[JamesF]

It's one of those difficult situations where you either need a resounding, 'This is brilliant!' plus with lots of images to compare, or trying one out for yourself!

I'll have to take things slowly and not rush out and buy one!

All of the images I've posted in the planetary imaging section of Mars and almost all of Jupiter (saving those taken with the ASI120MC) were created using the Revelation 2.5x barlow. I don't think there's really any doubt that it's worth the money. I found it easier to use (because it makes finding the target easier when jumping up in steps) than the TV 3x too, which is why I stuck with it and the extension rather than just using the 3x.

If you're not sure though, perhaps it would make sense to wait for one of either to come up second hand. That way you could try them out and if you didn't like them sell on at pretty much what you paid.

James

[Astrosurf]

Many thanks James. Your images are great. I'll keep an eye out for second-hand TV 3x and TALs, whichever comes first! I want to get some decent imaging in as soon as this blasted weather clears!