Extender + crop factor ?

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Thomas Covenant

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John
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Might seem a daft question ( don't worry there's more where this came from !)
but if you use a 1.4x extender on a lens attached to a small sensor camera such as my 7D I take it that the 1.6 crop factor still comes into play ?
As I say, may seem daft but I've noticed sometimes when reading articles/forums where lenses plus extenders are used in this situation they only talk about the max focal length as affected by the extender
ie 300mm + 1.4x = 420mm and not 672mm inc 1.6 crop factor.
I could be having a Homer Simpson moment of course !
John :thinking:
 
Yep, you still take crop factor into account. So a 300mm lens on a 7D with a 1.4 extender would have an effective focal length of 300 x 1.4 x 1.6 mm. The crop factor is a property of the camera, so if the article is just talking about the lens, it wouldn't mention it most likely! :)
 
The crop factor will still come into play yes.
Think of it as two separate equations, one for the extender and lens and one for the sensor.
Easier that way that multiplying the crop factor by the extender magnification and then muliplying the focal length.
 
Thanks Chris and Andrew, much appreciated.
Its nice to get confirmation that what you are thinking is correct as I have read articles on various photographic topics where what one says seems to conflict with other articles on the same subject elsewhere.
John:thumbs:
 
The 'crop factor' is only a comparison of 'effective focal length' when compared to full frame. The actual focal length of the lens doesn't alter, though the effect on the framing is the same as if it had, due to the cropping.

The extender is an actual focal length converter. The focal length is actually increased by 1.4x, and the lowest f/number actually rises by one stop.
 
John, The confusion arrives because some people regard the small sensor as giving you an increased focal length but it does not in the true sense. A crop sensor does not alter the focal length at all but it does give you a field of view similar to a longer focal length. So a 300mm lens plus a 1.4 tc on a 1.6 cropper gives you a focal length of 420mm and a field of view of 672mm (some people call this 'effective focal length).
There is no doubt in my mind that a crop body gives an advantage over a full frame for things like bird photography when you are reach limited as it puts all of the pixels into the 'business' part of the shot.
 
My thanks to both of you too Richard and Roy.
It seems quite alien to me to have started a hobby which puts me instantly out of my depth and I lack the safety net of the picture painting where I pretty much knew what to expect using my chosen medium and technique although I am far from an expert artist either and have had many a mishap there also.
However frustrating its fun to learn.
John
 
If it makes it easier for you, after multiplication of the lens focal length x the extender, treat that as one thing and then multiple it by crop factor.

So 300mm x 1.4 = 420 - now treat this as one 420mm lens
420mm lens x 1.6 crop factor = 672mm

Just break it down into easier to manage chunks.
 
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