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nellyleelephant
1,815 posts
104 months
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dibbly dobbler said: Thanks LQ  Unfortunately you lost me at the first sentence!  What does 'sensitivity to f5.6 mean' ? I can focus my 100L at f2.8 so this doesn't make sense to me sorry. If I understand your last point then if I get a 70-200 + 1.4 and just crop in a bit more then I should be good to go ? It means that a lens with a maximum aperture of 5.6 will autofocus, put an extender on that takes the max aperture to f8, it won't.
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dibbly dobbler
6,657 posts
67 months
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nellyleelephant said: It means that a lens with a maximum aperture of 5.6 will autofocus, put an extender on that takes the max aperture to f8, it won't. Thanks Sorry if I'm labouring this but surely I can focus at f16 (say) so how does that work ?
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nellyleelephant
1,815 posts
104 months
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dibbly dobbler said: Thanks Sorry if I'm labouring this but surely I can focus at f16 (say) so how does that work ? As far as I understand it the body does the focussing at the largest aperture the lens will go to. It stops it down when you press the shutter. So, if you're lens / TC combo gives f8, the body won't be able to focus....unless it's a pre 1DX 1 series.
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dibbly dobbler
6,657 posts
67 months
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Fab - thanks very much 
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2slo
1,591 posts
37 months
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mikef said: 2slo said: I use the 70-200 f/2.8 a lot on both a 7D and a 1D iv. I have nothing bad to say about the lens, it can produce superb results. Whilst I haven't tried it with the 2x TC I quite often use it with a Canon 1.4x TCIII and find very little loss of image quality. Happy to post some shots if you're interested. Yes, I would be interested, thanks, especially in performance at lower light (thinking ahead to early morning safari drives) Certainly. I shoot mostly birds and wildlife and do quite a lot in low light with high ISO. The two shots below are with the 70-200mm f/2.8 + 1.4x TC III: 1. Exposure 1/800sec; Aperture f/5.6; Focal Length 280 mm; ISO 5000:  2. Exposure 1/640;Aperture f/5.6; Focal Length 280 mm; ISO 5000: 
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LongQ
8,961 posts
103 months
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dibbly dobbler said: LongQ said: 60D has 9 focus points with sensitivity to f5.6 on all of them except the centre point which is more sensitive offering f2.8. So for the centre point you can add 1 stop to the lens maximum apperture and still have AF. Add 2 stops and it's no go. Using the f2.8 capable 70-200 lenses you can still get AF at the centre spot with a 2x extender. The later 1D bodies (Except the new 1D X apparently) allow centre point AF focusing sensitivity to work f8 so and f4 lens plus 2x Extender would be fine. Or, in theory, an f2.8 +2x extender + a bit of Polariser .... but the results cab be very, r, not as anticipated. Iirc the 7D and 5DIII have additional high sensitivity AF points in their arrays for the f2.8 level but nothing that allows sensitivity for AF at the f8 combined level. All of this can get rather confusing so so here's a nice little 'written for the person in the street' article that explains it comprehensively in a way that the average 8 year old child would understand. By that I mean that anyone much over 8 will probably end up with more questions than answers.  I read the Canon official explanation somewhere once. I'll see if can find it again. ETA: Most of the points (no pun intended) I made here were covered by others whilst I was off trying to find some understandable documentation .... oh well. BTW, on the 600D a very quick and dirty hand held test of moon shots a couple of weeks back suggested that there was little difference in the results between a 70-200 f2.8 IS MkII at 200mm (320mm in FF money) and the same lens with a 2x Extender MkII at 400mm (640mm in FF money) if the images were viewed at the same size on screen. However I was not entirely convinced by that so will be repeating the exeperiment if we ever get another night with the moon in the right place for my visibility absent street lights and no cloud. Thanks LQ Unfortunately you lost me at the first sentence! What does 'sensitivity to f5.6 mean' ? I can focus my 100L at f2.8 so this doesn't make sense to me sorry. If I understand your last point then if I get a 70-200 + 1.4 and just crop in a bit more then I should be good to go ? Ah, looks like I may have forgotten to include the link. I was quite proud that I got half way through it before confusing myself - or, rather, wondering whether the article was a bit confusing beyond the confusion that it mentioned it was trying to deal with - if you see what I mean. http://www.the-digital-picture.com/Photography-Tip...But basically, yep. The AF system has different ways of assessing focus and some are more sensitive than others. Fundamentally the system will work with lenses that, wide open before the shutter trips and the lens stops down to take the shot, allow at least f5.6 levels of light to pass. (Or, in the case of some Sigma lens for example, are told that the lens is f5.6 even if it isn't.) They sometimes have one, very occasaionally more than one, AF sensor point that is even more sensitive and can make use of f2.8 light levels if the lens provides such. An in the case of 1D bodies - but not currently the new 1D X - the system offered a centre point that allowed AF to work with an f8 level of light input. Think long f4 to f5.6 max primes with extenders. The key, basically, is that if the lens +extender +filter combination means light availability to the AF system is less than f5.6 levels phase detection AF will not work - or not relaibly. As I understand it Contrast Detection, as used for pocket cameras and, typically, Live View on DSLRs would still work but is usually slower though possibly more accurate. Phase detection systems are faster BUT to enhance the speed of response will take some decisions about how accurate the accuracy needs to be compared to the need to get the shot. The article repays several readings in order to get to grips with it.
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2slo
1,591 posts
37 months
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LongQ said: Ah, looks like I may have forgotten to include the link. I was quite proud that I got half way through it before confusing myself - or, rather, wondering whether the article was a bit confusing beyond the confusion that it mentioned it was trying to deal with - if you see what I mean. http://www.the-digital-picture.com/Photography-Tip...But basically, yep. The AF system has different ways of assessing focus and some are more sensitive than others. Fundamentally the system will work with lenses that, wide open before the shutter trips and the lens stops down to take the shot, allow at least f5.6 levels of light to pass. (Or, in the case of some Sigma lens for example, are told that the lens is f5.6 even if it isn't.) They sometimes have one, very occasaionally more than one, AF sensor point that is even more sensitive and can make use of f2.8 light levels if the lens provides such. An in the case of 1D bodies - but not currently the new 1D X - the system offered a centre point that allowed AF to work with an f8 level of light input. Think long f4 to f5.6 max primes with extenders. The key, basically, is that if the lens +extender +filter combination means light availability to the AF system is less than f5.6 levels phase detection AF will not work - or not relaibly. As I understand it Contrast Detection, as used for pocket cameras and, typically, Live View on DSLRs would still work but is usually slower though possibly more accurate. Phase detection systems are faster BUT to enhance the speed of response will take some decisions about how accurate the accuracy needs to be compared to the need to get the shot. The article repays several readings in order to get to grips with it. There are ways to get a lens + extender combination to AF on a non 1 series Canon body at apertures less than f/5.6, either with the canon TC where the pins are taped over to prevent the camera realising the TC is fitted or by the use of a non reporting extender ( one which doesn't supply data about itself to the camera) I've seen succesful use of Kenco extenders with Canon teles in this regard, even in one case stacked extenders giving, IIRC, f/16 and still AF. Very slow AF and a lot of hunting, but it did apparently work. Centre point AF on a 1Div with 400mm f/5.6 + 1.4x TC @ f/8 works fine by the way.
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LongQ
8,961 posts
103 months
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2slo said: There are ways to get a lens + extender combination to AF on a non 1 series Canon body at apertures less than f/5.6, either with the canon TC where the pins are taped over to prevent the camera realising the TC is fitted or by the use of a non reporting extender ( one which doesn't supply data about itself to the camera) I've seen succesful use of Kenco extenders with Canon teles in this regard, even in one case stacked extenders giving, IIRC, f/16 and still AF. Very slow AF and a lot of hunting, but it did apparently work. Centre point AF on a 1Div with 400mm f/5.6 + 1.4x TC @ f/8 works fine by the way. Indeed. Mentioned in the article, briefly. But then if it's really slow and potentially slightly compromised for accuracy (a pragmatic approach) one might as well focus manually or go the hyperfocal route (and variants) for wider angles. For many lenses with ND or poalrising filters fitted one could be in that situation anyway, though perhaps using AF first if the filter system allows it and ones technique is up to it. There are times when I miss the old split prisms focusing screens.
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mikef
1,404 posts
121 months
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2slo said: Certainly. I shoot mostly birds and wildlife and do quite a lot in low light with high ISO. The two shots below are with the 70-200mm f/2.8 + 1.4x TC III Beuatiful shots. Lens arrived this morning and I'm looking forward to getting to know it.
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2slo
1,591 posts
37 months
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mikef said: Beuatiful shots. Lens arrived this morning and I'm looking forward to getting to know it. Thanks, good luck with it, I'm sure you'll enjoy it
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dibbly dobbler
6,657 posts
67 months
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Any thoughts on whether the IS is worth the extra? I'm looking at used f4s and the IS basically doubles the price! I would prefer to have it but... 
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2slo
1,591 posts
37 months
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dibbly dobbler said: Any thoughts on whether the IS is worth the extra? I'm looking at used f4s and the IS basically doubles the price! I would prefer to have it but... Depends what your intending to use it for and how you're going to use it. For instance, if it was going to spend most of it's time on a tripod, probably not worth having as you'd switch it off anyway. Remember it's a 2 stage IS, stage 1 attempts to stop all movement. Stage 2 allows horizontal movement (tracking birds inflight, panning race cars etc). It's a very fast IS system (certainly on the 2.8, I haven't tried the f/4)and I find it can save me lost shots in low light situations, hand held, by allowing me to use a far slower shutter speed than I could get away with without IS. In a nutshell, for wildlife, motorsports and anything moving IS is definately worth having. Landscapes and other tripod based uses, not much use at all.
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LongQ
8,961 posts
103 months
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dibbly dobbler said: Any thoughts on whether the IS is worth the extra? I'm looking at used f4s and the IS basically doubles the price! I would prefer to have it but... There is a little more difference than just IS. The optics are different and the IS version has better dust and moisture resistance ALTHOUGH it may be that later builds of the non-IS version have some tweaks in that area since the Canon web site makes claims for both lenses. Review (from 2005 and using a 350D for the body) here http://www.photozone.de/canon-eos/196-canon-ef-70-...Worth reading both and also maybe the IS version as re-tested on a 50D body.
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dibbly dobbler
6,657 posts
67 months
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LQ & 2Slo - thanks Gents, I have purchased myself a second hand f4 non-is. Ridiculously cheap for what it is so I am well chuffed  ETA - now to start looking for a 1.4 extender
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2slo
1,591 posts
37 months
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dibbly dobbler
6,657 posts
67 months
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2slo said: Crikey - a 1.4x III extender could cost me more than the lens! 
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nellyleelephant
1,815 posts
104 months
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dibbly dobbler said: Crikey - a 1.4x III extender could cost me more than the lens! To save a bit of cash, go for the 1.4II not the III. Apparently there isn't much difference between the two. The updated 2x is supposed to be much better though.
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dibbly dobbler
6,657 posts
67 months
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nellyleelephant said: dibbly dobbler said: Crikey - a 1.4x III extender could cost me more than the lens! To save a bit of cash, go for the 1.4II not the III. Apparently there isn't much difference between the two. The updated 2x is supposed to be much better though. Cheers. Actually further research appears to show that the Kenko 1.4 TC is the equal of the Canon item and half the cost so I have bid on one If all goes to plan I should have a mint 70-200 + 1.4x TC for roughly £400 - not too shabby
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flat-planedCrank
2,980 posts
73 months
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dibbly dobbler said: 70-200 + 1.4x TC for roughly £400 - not too shabby  Lot of kit for the money!
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RDMcG
7,138 posts
77 months
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When I travel I take a 72-200 2.8 and a 24-70 2.8. Heavy indeed but I use them constantly- tough as old nails. I use an EOS 5D.2 and this pretty much covers my needs. Heavy, sure, but pin-sharp.
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