Telephoto lens or short refractor?

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thesmiths
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Telephoto lens or short refractor?

Post by thesmiths » Sun Jul 02, 2017 1:37 am

Now that it's getting close, I am considering my options. Flying from Europe suggests travelling light. I did a dry run today with a Canon EF 300mm F4 IS camera lens vs an APM 480mm F6 telescope. The camera was a Canon EOS 100D. In terms of solar image size, I can see that the wider field of view of 300mm might be handy (I'm trying to imagine what the corona would look like). The 480mm is pretty nice also and would give better resolution of fine structure, I assume.

The camera lens is much smaller and lighter of course. But the big disadvantage I see with it is focusing. Auto-focus didn't seem to work well at all and manual focus was quite fiddly and my guess is would not stay put for long periods. The telescope was much easier to focus and images were much sharper. The Feathertouch focuser can be locked and then not worried about again.

I have attached jpeg files taken with 300mm camera lens and the 480mm telescope. These were taken with Baader film and are as they came from the camera. It's not so obvious the difference in sharpness unless you view the photos at 1:1 (which I don't think you can do on this webpage).
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IMG_1851.JPG (1.56 MiB) Viewed 1011 times
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IMG_1857.JPG (1.83 MiB) Viewed 1011 times
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1858.jpg (134.83 KiB) Viewed 986 times

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Montana
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Re: Telephoto lens or short refractor?

Post by Montana » Mon Jul 03, 2017 11:13 am

The second image is far superior and still plenty of room for the Corona. I am taking a small telescope and attaching to a DSLR, hopefully I can focus with the WL filter on and then not touch it. I had a dry run and flew it to Spain and it all survived and worked. I took the telescope in hand baggage and the mount in hold luggage. Just pack less clothes :)
Alexandra

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marktownley
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Re: Telephoto lens or short refractor?

Post by marktownley » Mon Jul 03, 2017 5:56 pm

The scope shot is a lot better, i'm taking my 300mm lens to America.
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Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

thesmiths
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Re: Telephoto lens or short refractor?

Post by thesmiths » Mon Jul 03, 2017 6:37 pm

Mark, in another post you wrote: "I'm probably going to use a DSLR and a 70/420mm refractor for my travelling setup." Did you change your mind? I actually thought around 420mm on a crop DSLR camera was a perfect compromise. I think that's was Alexandra is planning on using. The Tecnosky 65Q 420mm quadruplet she mentioned in another post looks really ideal. As I understand it, having a flat field is a big advantage.

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marktownley
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Re: Telephoto lens or short refractor?

Post by marktownley » Mon Jul 03, 2017 6:52 pm

Yes, one of the possible options, but my 70/420 really isn't in the same optical league as the tecnosky (and I have managed to put a deep scratch on the objective), i'm really more concerned with getting things visually than photographically and a few snapshots will do me. The 70-300 zoom i'm going to use will be convenient for the rest of the trip out there also. Guess its all about compromise!
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Solar images, a collection of all the most up to date live solar data on the web, imaging & processing tutorials - please take a look!

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