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Topics - PeterJ

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Lenses / 24-70 versus 24-105 AF performance
« on: November 28, 2012, 02:02:19 AM »
I've got a 24-70 f/2.8L (original version) and I've been thinking about a 'cross-grade' to a 24-105 f/4L. With a crop I used to use it a lot for portraits but since moving to FF (now own a 5D3) I normally use a 70-200 for that and 24-70 only gets used at f/4 or above most of the time anyway and often for things where IS would be a benefit. I use a 50mm if I want something faster.

Anyway I know a f/4 lens will technically focus slower in low light than a f/2.8 but just wondered from someone who's used both how low light AF between the two compares? I thought maybe despite f/4 the 24-105 may have a more modern / faster AF drive so maybe not too much of a difference in practice?

EOS Bodies - For Stills / 5D3 and odd problem focusing telescope
« on: November 09, 2012, 10:20:55 PM »
I just bought a cheap 2nd hand Dobsonian 6" telescope with a T-mount and Canon adapter. Anyway just set it up during daylight hours to have a play around and all fine through the eye-piece but couldn't get anything to focus through the camera. So I pushed the focuser on the telescope in so the 5D was pretty much as close as it would go to the telescope body and moved it around to find out where it was focusing. It turned out I could focus on a power pole a little under 20 meters away, so now I have a nice photo of an insulator (actually was suprised how well it turned out).

Anyway I decided to remove the T-mount and hold the camera towards the telescope, then realised it would attach directly to the thread on the telescope without the T-mount. When mounted that way now I can focus out to about 4KM. I've never used a telescope before so maybe it's all normal and it will focus on very distance objects OK because the light will "cross over" one more time or whatever the right term is? Will find out tonight I guess.

Another interesting thing was to get a decent live-view image I could use to focus I had to select a 1/15 shutter speed whereas the metering reported 1/250 was correct which turned out to be about right.

Australia / Legal question on photography
« on: October 20, 2012, 03:11:25 AM »
I'm thinking of going to a cricket test match at Bellerive (Tasmania, Australia) a bit later in the year and was just checking Bellerive has the same 200mm lens limit as elsewhere, which it does. I noticed in the terms & conditions of entry that you can't publish photos anywhere and it specifically mentions Facebook, Twitter and the like. Anyone know if that is likely to be legally binding?

My understanding of Australian contract law was that conditions had to be pretty clearly set out in advance, not just on some web site I may or may not have read. I can't remember buying a ticket and have them run through the conditions, like they do when say getting a bank loan. It's a bit different to say taking your own beer where because it's private property they can deny entry / ask you to leave and it's trespass if you refuse.

Lighting / Infrared reflectivity
« on: September 19, 2012, 04:32:46 AM »
Not really a photography question but I know there's a few optical wizards about so thought I'd post away :). I'm working on a system that uses a 850 +/- 10 nm infrared photodiode and what I'd like is an easy way to bench test the device. It'll be illuminated and if it worked in the visible range I'd use black, 50% grey and white cards to test it with, it doesn't have to be very precise just a way to take a few readings across the range of realistic readings, as opposed to putting in an enclosure or pointing at a mirror.

Because the filters on infrared remote controls are visibily dark and farily transparent to IR but designed to block visible light I know the rules of play are quite a bit different at that wavelength. I wondered if anyone had ideas on materials to use or maybe some reference to a database of how reflective various materials are at various wavelengths?

Third Party Manufacturers / Eye-fi card and 5D3 experiences
« on: August 22, 2012, 08:32:08 AM »
Hope this isn't a dupe but all threads I found regarding the 5D3 and Eye-fi were when the Mk 3 was either speculation or had just been released. I wondered a few months out how users  found the combination?

The Canon WFT is a bit expensive for my amateur use but I'm considering one of these. Use would be just to transfer RAW images from a another room to save carting the camera back and fowards for food and product types shots. Transfer and burst speed isn't much of an issue, anyone found any other issues? I assume when out and about if I disable writing to the Eye-fi it wouldn't affect writing to the CF card speed wise?

Canon General / 5D mark II versus 7D spot focus
« on: September 27, 2011, 08:52:18 AM »
I bought a 7D a while back over a 5D II and my main reasons at the time were the more advanced autofocus system plus higher fps. I'm an amateur but now I'm finding myself more confident I rarely take the camera out of manual, tend to meter based on a point of interest and for focus just about always use spot towards the center of the frame and recompose.

I've seen some complaints about the 5D autofocus but I'm guessing they are mainly about the lower number of focus points and less cross-type. Anyway I guess my question in general is from anyone that's used both would spot AF be noticeably different on either body? All my lenses are f/2.8 or faster, but sometimes I do take some photos in low-light conditions without AF assist where the 7D does hunt a while.

Lenses / Filter for direct sun photography
« on: September 04, 2011, 05:10:04 AM »
In a few months they'll be a partial eclipse visible here in Tasmania and I'd like to take a few snaps of it. I don't want to fork out too much for the excercise so will be using my existing 7D + 70-200 + 2x TC but don't mind buying a filter which I'm sure I'll find other uses for. While I don't want to fry my 7D sensor I'm even less inclined to fry my eyes so after some Googling so far my thoughts are:

Purchase a Hoya NDx400 77mm filter which is a 9 stop / 1/500 filter and shoot at around f/11. I've got no intention of looking through the viewfinder so thought I'd quickly compose and focus in live view so the sensor isn't exposed a long time and then switch back to normal mode, lock the focus and take the shots using an intervalometer for a time lapse sequence. I haven't worked it out properly yet but guess at 640mm effective length the sun will be small enough and won't move enough in the 5 minute period to need me to recompose the shot.

Anyway I just thought I'd post and see if anyone sees any holes in my plan or better filters and/or techniques I can use? One possible thing I could do is 10 mins before starting is focus the lens on something at infinity and lock it, but seem to remember reading that somewhere that apparently large objects in the sky may not require infinity focus, but can't really remember the theory and if it was a reputable source.

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