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A go with the "nifty fifty".


GrantEb
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Hi all

Again, nothing spectacular. I had a quick go with the "nifty fifty" above Sadr.

This only clears the neighbors roof at 02h45, so I only had about an hour and a half to get as much as I could before sunrise.

Nifty Fifty on the 1000d, f1.8, 66 x 1min30 secs exp iso 800.

I think next time will be at f4, iso 1600 and slighty longer exposures, to have better shaped stars.

(Slightly cropped)

post-21699-133877596731_thumb.jpg

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f3.5-f4 should sort it .. you can do a quick test by putting a bright star in the corner and changing the aperture value whilst in zoomed liveview... then a quick slew so it goes round the corners and into the center will confirm the lowest workable aperture value...

Peter...

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I haven't really done much with mine yet.. not anything deep I am finding that stopping them down to 4.5-5.0 helps but its a zoom (admittedly quite a nice one) ...

One think I noticed for the first time the other night (and explains some disappointing results) is that where they are parafocal for normal use on an un-modded camera they ain't on a modded camera with additional in body LP filters... so focus at the FL you are going to shoot rather than zooming in focusing and then zooming out...

Its something I want to get a better handle on ...

Peter...

Edited by Psychobilly
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Grant Parafocal - I was talkign about the zoom lenses... not the fixed FL primes... With a normal camera the zooms dont need to be refocused when you change the FL...so for critical focus you would zoom in , focus , then zoom out to shoot... with the LP filters behind the lens they do.. so you cant get accurate focus by focussign zoomed in and then zoom out... the 24-105 f4L on the Filter replaced 1000D with a Hutech IDAS MFA filter focuses slightly short of the infinity mark at 105mmm but if you zoom it back to 24mm the same target comes into sharpest focus between the 3 and 5m marks...

With the Nifty at f4 you can correct any residual error using the lens correction tools in CS... but you will end up needing a very slight crop as well...

Peter...

Edited by Psychobilly
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Looks good Grant... I guess that parfocal is only on the premium zooms Peter... I've read that most zooms are not parfocal, and you should zoom to the correct focal length you want to use before focusing, of course, that may make know difference given the working distances involved...

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The Ls are parafocal... (normally).. I will run the problem past the otical wizard that is Ken...

The Canon EF 24-105mm f/4 L IS USM Lens’ autofocus is driven by Canon’s excellent Ring USM (Ultrasonic Motor). It is internal, fast, quiet – and accurate. The 24-105 L is a parfocal lens – “There’s a cam inside the 24-105mm lens that is designed to maintain an accurate focus when the lens is zoomed from tele towards wide.” [Chuck Westfall, Canon USA]

Edited by Psychobilly
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Yeah, I understood what you meant Peter. Just never knew the L lenses are parafocal, and haven't used mine a lot yet. (And I didn't know the difference between parafocal and parfocal)

It seems a bit more difficult to find a bright enough star to focus on when @ 70mm, but I'll get it right eventually.

Thanks again.

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  • 2 months later...

I've often wondered if an external aperture mask would work insead of using the artefact-inucing diaphragm. I have a Belgian guest at the moment who showed me a Dutch imaging forum and it seems that this trick is popular over there so I mean to try it. In the posted images it certainly worked.

The nifty fifty has done well here, I'd say. Very promising.

Olly

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