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Introduction to DSLR's and Wide-angle lenses
http://www.boltonastro.co.uk/forums/viewtopic.php?f=4&t=791
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Author:  DRatledge [ Wed Sep 23, 2015 11:37 am ]
Post subject:  Introduction to DSLR's and Wide-angle lenses

In last night's excellent talk on an introduction to DSLR cameras, Dave Walker suggested that clip-in filters were unsuitable for wide angle lenses. These are the filters made by Astronomik that fit inside the body of a Canon camera - behind the lens. There was a short discussion after - I thought the opposite - so I have done some more investigation.

What I have found is that in general clip-in filters are the only filter to use with wide-angle lenses. Front mounted filters just don't work because of the wide-angles involved with these lenses - they are not designed for light at an acute angle.

I have tested my clip-in filter with the following wide angle lenses: Canon 28mm, Pentax 28mm, Pentax 20mm and the ultra-wide Sigma 10mm-20mm. All these focussed fine with the filter inside - the infinity mark was no longer the correct position but they all focussed to infinity.

The problem lens is the Samyang 8mm Fisheye lens. The design of this lens is most peculiar. No amount of re-focusing changes the back focus distance so it cannot be used with a clip-in filter. Note this lens is sold under many other brand names and has even been copied by the Chinese. So this lens can only really be used at dark sites such as Kelling Heath - see the gallery. This is a shame as its performance is superb.

Author:  bbones [ Wed Sep 23, 2015 12:41 pm ]
Post subject:  Re: Introduction to DSLR's and Wide-angle lenses

I have to agree, even though I knew quite a bit about the camera functions It was nice to hear about the lenses and the LPF's, I have a Canon 600D and was thinking about getting a LPF to fit on my lens, however following the presentation / discussion and having read David's comments above I'm now looking at the clip in LPF as the camera than can be used with my 18-55 canon lens and my telescopes. Would I be correct in thinking that the one from Rother Valley Optics is the one I require?
Model: 9H00IC
Brand: Astronomik

http://www.rothervalleyoptics.co.uk/astronomik-cls-ccd-deep-sky-light-pollution-filter-canon-eos-clip-fit.html

Cheers Bill

Author:  DRatledge [ Wed Sep 23, 2015 1:52 pm ]
Post subject:  Re: Introduction to DSLR's and Wide-angle lenses

Bill,
Just as one telescope doesn't do it all then one LPR filter doesn't either. I have both the Astronomik UHC and CLS clip-in filters. The former is what I normally use but in the spring when I am imaging galaxies then the CLS is a bit better. If I had to use only one then it would be the UHC. it is brilliant on most nebulae and really reduces light pollution.

Bear in mind zoom lenses are not ideal and will probably need stopping down to f/8 if you want pointy stars.

Author:  bbones [ Wed Sep 23, 2015 4:51 pm ]
Post subject:  Re: Introduction to DSLR's and Wide-angle lenses

Thanks David, I will take a look. I normally stop down to f/5.7 so will try f/8 next time

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