QHY5L-ii and 5 x Barlow too much?

[hobsey]

When I go on my dark skies holiday in September, Neptune and Uranus will be at a good height to have a go at imaging them.

Would a 5 x barlow be too much for the QHY5L-ii and my C8?

I'm looking at this one as I'm happy with the quality of the Revelation 2.5.

http://www.telescopehouse.com/acatalog/Revelation_Astro_5x_Barlow_Lens.html

Many thanks.

[oldpink]

I bought the same on but have had no success with it so far
I tried it on Jupiter but was pushing my system past its max
on Mars I could just about make out the disk but the frame rate was way too low to be of use due to the longer exposure time required
but I have really bad LP here and to be of any use I'd need really good seeing conditions so its very rarely out of its box

I've yet to try it on the moon to see how it works on a bright object

[Andy Milner]

Interested in opinions on this too. I'm considering a 5x or 4x powermate.

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[ChrisLX200]

I've used a 5x Powermate on a 10" SCT and a 300mm f/5.3 Newt for planetary work. It works well and produces good results - but only when the seeing is good enough. When the seeing is not good enough you're wasting your time anyway (sadly, often the case where I am). A lower magnification will just give you a smaller image scale and thus hide the poor resolution so you would not be any better off, but this is not visual this is imaging we're talking about so what you are aiming for is a sensible image scale in relation to the CCD chip you're using, if the planetary disk fills (say) 2/3 the FOV you can do no better.

ChrisH

[hobsey]

Thanks for that Chris,

I really am hoping the seeing will be good then because I purposely booked that side for dark skies and good seeing.

They are showing out of stock at the moment so I will buy one nearer the time.

Cheers.

[Andy Milner]

Be clear a powermate is known to be better than a barlow. It let's more light through. I'm no expert but a 5x powermate will give much better clarity. This is why I'm willing to pay extra as at higher mag I want the best for imaging.

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[hobsey]

I would love a powermate but unfortunately my pocket don't go that deep.

[JamesF]

What's really of interest where planetary imaging is concerned is focal ratio.  Basically you want to know that you're capturing as much detail as your telescope can resolve.  Once you reach that point there's no real benefit from getting a larger image on the sensor as you could just do the same thing in processing and have a lot easier time capturing the data.

Because that's the kind of guy I am, I did the maths to work out how I could decide the optimal setup for my SPC900 and was surprised when it turned out that focal ratio is pretty much the determining factor given the pixel size of the camera.  When I switched to the ASI120 (same sensor and therefore pixel size as the QHY5L-II) it was simple to redo the calculations.  There's a fair bit of leeway in the general case because actually the calculations depend on the wavelength of light that you're capturing, but for the ASI120 and QHY5L-II I'd suggest that you want to be somewhere around the f/20 mark.  I like to go a little higher though I try to stay below f/25, others prefer a little lower.  As I said, there's a bit of leeway

So, given an f/10 C8 I'd say no, there's no point using a 5x barlow.  A decent 2x or 2.5x will be quite sufficient.  A larger multiplier barlow might give you a larger image, but it won't give you any more detail (and you'll be spreading the light around more, so probably need more gain which in turn means more noise in the captured data), so you may as well scale the image up in processing if you want it larger.

With my SPC900, which has much larger pixels, I used to aim for around f/35 and used a Revelation 2,5x barlow with some extensions to reach that.  Since getting the ASI120 I've abandoned even the 2.5x Revelation, good as it is, and bought a 2x Tele Vue barlow second hand.

James

[oldpink]

I'd love a teleview powermate 5x but at £150 it was a bit too rich for me this time around
maybe when I have more funds available I'll drop the hammer and buy one
but I have a long list of (Expensive) equipment thats higher up my priority list just now

the Revelation at £35 was a stop gap to see if it would work

[riklaunim]

QHY5L-II has small pixels, smaller than previously cameras and webcams with Sony ICX098/618 sensors. Smaller pixels means that you get optimal resolution at faster f/ratio. 5x Barlow would be good only for something like a f/4 telesope - giving around f/20 or slightly more.

[Andy Milner]

I have a f5 that will get f20 with a powermate x4. I'm thinking of a 4x powermate but it's very heavy due to being 2" and 1.25". I'm thinking if the powemate x5 for next years planetary season. As with near perfect conditions f25 ol should be fine. I may go for the x4 for now and trade in next year. Think this is sensible?

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[riklaunim]

You don't need powermate (or meade telextender) to do planetary imaging. They don't add anything to the images. They only offer fixed or almost fixed magnification with distance to the sensor. You can go with a short GSO/Revelation 2.5x Barlow and with adding some distance between it and the camera you could easily get 4x. Other option is Baader Hyperion Zoom Barlow which screwed to a typical long camera nosepiece will easily give somewhere between 3 - 5x

[Andy Milner]

Thanks rik. I will try the small extender that the qhy5l-II cane with.

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[Merlin66]

Rule of thumb....

The focal ratio target should be x5 the pixel size in micron.

For the QHY5II (3.75 micron pixel) this would mean around f20 - a x2 Barlow on the SCT......