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Old 20-07-2011, 10:45 AM
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Canon widefield lens advice

Hi everyone,

I've been enjoying taking star trails and widefields for some time with my Canon 350D. I've got an 18-55mm lens but I really struggle to get accurate focus and find my eyesight no longer good enough to confirm the focus on the back screen. I seem to have wasted many nights taking a series of shots that are too fuzzy to use. This seems partly because the focus ring on the lens goes part infinity.

So - looking for a fixed focal length (or short focal length) lens that focuses on infinity without having to step it back.

Can anyone suggest a suitable lens. I've heard good things about the Tokina 11-16. Does it focus easily?

Are there other recommendations?

many thanks

niko
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Old 20-07-2011, 10:54 AM
Poita (Peter)
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Use the zoom feature on the screen on the back of your camera to get the focus right and take a few pictures and keep adjusting the focus.
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Old 20-07-2011, 12:06 PM
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multiweb (Marc)
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Quote:
Originally Posted by niko View Post
Hi everyone,

I've been enjoying taking star trails and widefields for some time with my Canon 350D. I've got an 18-55mm lens but I really struggle to get accurate focus and find my eyesight no longer good enough to confirm the focus on the back screen. I seem to have wasted many nights taking a series of shots that are too fuzzy to use. This seems partly because the focus ring on the lens goes part infinity.

So - looking for a fixed focal length (or short focal length) lens that focuses on infinity without having to step it back.

Can anyone suggest a suitable lens. I've heard good things about the Tokina 11-16. Does it focus easily?

Are there other recommendations?

many thanks

niko
Lenses are a bit of a hit and miss. Sometime you get a good one. I focus with a mini-bathinov mask and keep the lens at full aperture so I don't get diffraction spikes in the way. Then I f-stop it. Some lenses are very easy to focus. Some have a very tight CFZ.
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Old 20-07-2011, 12:26 PM
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Omaroo (Chris Malikoff)
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Quote:
Originally Posted by niko View Post
Hi everyone,

So - looking for a fixed focal length (or short focal length) lens that focuses on infinity without having to step it back.
Not sure you'll find one Niko. I've heard from many that the reason they go beyond infinity at the final stop is to allow for expansion/contraction.

I've been using the mini-Bahtinovs for ages on my camera lenses, and with live view on the 5D-II it works very well as you can dial in focus on a bright star in seconds as you watch. The 350D, without it, will still work, but you need to expose for at least 10 secs at ISO800 on a fairly bright star to see the diffraction pattern well - which you need to center in frame as best you can so that zooming in to inspect the result doesn't require you to jog the object into view all the time.
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Old 20-07-2011, 03:33 PM
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Thanks everyone.

Chris/Mark - I tried the bahtinov mask without much luck at 18mm I just didn't get the spikes - I'll try again centred on a brighter star. I just find even zooming in on the camera's screen doesn't help much. Guess I will have to run it through the laptop so I can see a bigger piccie.

I went to look at the Tonkina 11-16 and the Sigma 10-22 - holy moly, wasn't expecting them to be so much. Guess you get what you pay for.

niko
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Old 20-07-2011, 05:37 PM
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Originally Posted by niko View Post
Thanks everyone.

Chris/Mark - I tried the bahtinov mask without much luck at 18mm I just didn't get the spikes - I'll try again centred on a brighter star. I just find even zooming in on the camera's screen doesn't help much. Guess I will have to run it through the laptop so I can see a bigger piccie.

I went to look at the Tonkina 11-16 and the Sigma 10-22 - holy moly, wasn't expecting them to be so much. Guess you get what you pay for.

niko
How thin are the slits? You need really thin ones. You get some good lenses on eBay. My Pentax 200mm costed $60.00 shipped. Best is to check pics and see what lens they were taken with,f-stop, etc... so you have an idea of what works and what doesn't. Don't go spend a lot then figure out later it doesn't do the job.
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Old 20-07-2011, 08:54 PM
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My copy of the Canon EF35mm f/2.0 focuses at infinity at the stop, and provides a good sized field.

Cheers,
Jason.
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Old 20-07-2011, 09:26 PM
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I use the Tokina 11-16, great lens for real wide field however focus on stars is some where about the infinity symbol meaning you still need a mask or live view. Lately I have just been connecting up the Acer Iconia tablet and using the nice large 10" screen when adjusting the focus.

Cheers, Peter
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Old 20-07-2011, 09:35 PM
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I went to look at the Tonkina 11-16 and the Sigma 10-22 - holy moly, wasn't expecting them to be so much. Guess you get what you pay for.
I have one complaint about my Tokina 11-16. The FOV is so huge I can't use it at home because either the house or trees get in frame and they are illuminated by street lights. Up at Glenhaven I get some part of the Sydney skyglow no matter what direction I point it.

Image included just to give you some idea of what it covers. Unprocessed apart from resize to 25%. The eastern horizon is just out of frame at the bottom. Sydney is towards bottom right. Scorpio occupies about 20% of the frame.

File Modification Date/Time : 2011:06:24 20:47:24+10:00
Exposure Time : 25 sec
F Number : 2.8
Exposure Program : Manual
ISO : 800
Focal Length : 11.0 mm
White Balance : Daylight
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Old 21-07-2011, 07:11 AM
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I have one complaint about my Tokina 11-16. The FOV is so huge I can't use it at home because either the house or trees get in frame and they are illuminated by street lights.
Same problem at home. I usually have to sigma reject my house gutter the first few subs looking east.
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Old 21-07-2011, 08:16 AM
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Originally Posted by PeterO View Post
I use the Tokina 11-16, great lens for real wide field however focus on stars is some where about the infinity symbol meaning you still need a mask or live view. Lately I have just been connecting up the Acer Iconia tablet and using the nice large 10" screen when adjusting the focus.

Cheers, Peter
That is a handy suggestion!,to the OP I have the 10-22 mm Canon EF-S wide field lens-I am amazed the sharpness of it,and could very much recommend it.I have heard very good things about the Tonika 11-16 mm,and I think it would be a lot cheaper than the Canon one.

Here is a 15 minute exp with my canon copy.
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Old 21-07-2011, 08:31 AM
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many thanks again guys

I think maybe the slits on the bahtinov are too wide
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Old 27-07-2011, 08:01 AM
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Just to add on the focusing side of things, what I had done as I didn't have a bhatinov mask. Is focus the lens in daylight (eg building/tree etc) to infinity then lock it in place with a couple of pieces of masking tape. That way I just needed to setup and shoot. Depending on the weather and atmos conditions, sometimes I would get a minimal amount of subs out of focus.

Moving forward for lens, I too am deciding on getting the tokina as I have heard veryngood things about them, so I'm sure you cannot go wrong.

Rob
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Old 27-07-2011, 07:39 PM
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Hello Niko,

Ever since I have been in this hobby a friend put me onto this program called Focusassist and I think that this is the website. http://jstanley.pingerthinger.com/focusassist/

I also downloaded a magnifyer program that allows me to zoom in. The focus assist allows you to take an image at different ISO and times and then downloads the image to the screen of the program. So you can see the stars and then I move my magnifyer program over a selected star ( i have the zoom set to about 8x and look at the focus of the star. If it looks fuzzy I adjust the focus, keep the magnifyer there and shoot again and the new image downloads and I can see if the adjustment was OK and then I keep going until the star will basically resolved to like a single pixel or close enough. I have done this for ever and it is very easy but have not used a batinov mask at all so can not compare.

Mark
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Old 27-07-2011, 08:22 PM
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Octane (Humayun)
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Canon EOS Utility Remote Shooting enabled; tick the 200% zoom box. Pop on your Bahtinov mask and load the free Bahtinov Geabber software, and you're set.

H
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