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Post by ChrisV on Jan 2, 2019 10:14:09 GMT
So I GOTOed an EQ5 a while ago. Would now like to try some wide field - live viewing and AP. I'm thinking 50 - 100mm focal length to get the right FOV?? I've got an canon lens adaptor and mount for my ASI071 (APS-C sized sensor). So what sort of canon compatible lens should I get, or what should I look for? Brand, F ratio, ? I have no idea. All suggestions appreciated
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Post by howie1 on Jan 2, 2019 13:15:36 GMT
Gday Chris ... Rokinon lens with Canon fitment. Rokinon is also sold badged as Samyang lens. Same lens. Many club AP'ers use them for widefield as many of their lens are f/2.0 or f/2.8! Reviews reckon they are as good or even better optics quality than name brand lens in that low F ratio range. Ie great bang for buck. Google for Astrobin images and also google for reviews. They don't auto focus but can't use that when doing AP anyway ..... or can you .... read my comment further down in this post . Quite a few AP'ers out at club nights use the 14mm for wide field. I'd say the 14mm is the one most widefield club members are using. One or two have the 23mm. And I have the only 135mm in the club. We've swapped or borrowed each others lens at diff times .... so we've got a cheap "quiver" of good qual lens that way! Ha ha! The f/2.0 135mm was a Xmas pressie in 2017. I immediately took it out and made a video ... link down below was shot Jan last year. It shows a single, unstacked, unguided 90 sec frame of flame and horsie across to M42. Well actually, the first 'opening' image on the screen was a 60 secs single frame. Ken rightly pointed out an error when he viewed it, so at 1 min 5 secs into the video I showed a comment saying the grey "cloud" was the large Magellanic cloud .... but was in fact the Giant Molecular cloud associated with Eta Carina. My bad. OK auto vs manual lens focus ... you've no option but to save money and get manual as you are fitting to ASI. But, so people know this trick .... Mark in NZ uses lens with motorised focus with his Canon ... Ie Canon lens, Sigma lens which have the auto focus. So in Canon EOS Utilities on the Live View screen, there is a Manual Focus 'button' on the screen. So if the lens has motorised focus then you can live view a star in 5x or 10x zoom mode and click that Manual Focus button. It opens up a + - set of buttons so you can mouse click + or - until the smallest blob results and focus is achieved. And done by sitting there just watching liveview and clicking the mouse. It's nice because you don't touch the lens by hand so there's no bouncing when using the liveview focus button. Its a neat trick! Also dont forget my trick of using a flyscreen mask with a manual non-motorised focuser. It's pretty much mandatory to achieve great focus with a manual lens. It lets so much light through that it throws great diff spikes in order to focus. I just built one the other day hoping that one day I'd get out again with a lightweight/ easy on the back rig. I'll post up a photo of it. Anyway here's the vid.
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Post by ChrisV on Jan 3, 2019 2:38:10 GMT
Thanks Howie and nice video. I was actually thinking of the samyang 85 or 135mm. The 85 is cheaper, but I'm thinking the 135mm. I like it's fov and with drizzle integration its resolution isn't too shabby either.
How do you find it at the low f ratio setting? Is the image okay out to the edges or do you have to stop it down a bit.
I gotta a voucher from Christmas which is burning a hole in my pocket!
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Post by howie1 on Jan 3, 2019 13:40:30 GMT
Thanks Howie and nice video. I was actually thinking of the samyang 85 or 135mm. The 85 is cheaper, but I'm thinking the 135mm. I like it's fov and with drizzle integration its resolution isn't too shabby either. How do you find it at the low f ratio setting? Is the image okay out to the edges or do you have to stop it down a bit. I gotta a voucher from Christmas which is burning a hole in my pocket! No probs Chris. I tried f/2.0 and f/2.8 and really cant notice any difference. However, I'd read somewhere on the web ages ago when I got the lens that f/2.8 is the sweet spot for as low as you should go with it. I never did see any difference. In trying to re-find that article/comment (which I didnt find it), I did however find this article ... Review Rokinon/Samyang 135mm f/2 ED lens
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