Nikon FX lens on a DX body
Discussion
I'm trying to understand zoom levels and the field of view I can expect with different prime lenses on my DSLR. I have a Nikon D3100 and currently shoot almost everything with my 35mm f1.8G. 99% of my pictures are of my children and lots of those are indoors with poor lighting so I'm interested in fast lenses. I have no fixed budget but don't want to spend a huge amount. A few hundred pounds is the ball-park figure I'm hoping for. What I want is a lense for capturing head-shots from across a room (maybe 3-5 metres away). Trying to get close to the children disrupts their activities and being across the room means I need to drastically crop my current pictures.
The obvious candidates I'm looking at are the 50mm f1.8G and the 85mm f1.8G
What I'm stuggling to understand is what zoom these will give me compared to my 35mm because my current lense is DX and these are both FX. Am I right in thinking that they are equivilent to 75mm and 128mm DX lenses? If so, would they give me a the equivilent of a x2.1 zoom and a x3.66 zoom compared to the 35mm?
I've created this image to show the field of view for each of the 3 lenses. Is this right or have I misunderstood something?
The obvious candidates I'm looking at are the 50mm f1.8G and the 85mm f1.8G
What I'm stuggling to understand is what zoom these will give me compared to my 35mm because my current lense is DX and these are both FX. Am I right in thinking that they are equivilent to 75mm and 128mm DX lenses? If so, would they give me a the equivilent of a x2.1 zoom and a x3.66 zoom compared to the 35mm?
I've created this image to show the field of view for each of the 3 lenses. Is this right or have I misunderstood something?
The focal length is the focal length, it doesnt change because of the sensor size.
So 35mm you have now is the same as 35mm on a Fx body. You just get a cropped version of the image circle.
50mm is 50mm on your body, it will give you a field of view of about 85mm, as your 35mm gives you a reduced field of view of about 52mm.
So 35mm you have now is the same as 35mm on a Fx body. You just get a cropped version of the image circle.
50mm is 50mm on your body, it will give you a field of view of about 85mm, as your 35mm gives you a reduced field of view of about 52mm.
RobDickinson said:
The focal length is the focal length, it doesnt change because of the sensor size.
So 35mm you have now is the same as 35mm on a Fx body. You just get a cropped version of the image circle.
50mm is 50mm on your body, it will give you a field of view of about 85mm, as your 35mm gives you a reduced field of view of about 52mm.
I'm sure your answer is correct, but something still hasn't clicked in my head. I'll drop the 85mm for now and just talk about the 50mm.So 35mm you have now is the same as 35mm on a Fx body. You just get a cropped version of the image circle.
50mm is 50mm on your body, it will give you a field of view of about 85mm, as your 35mm gives you a reduced field of view of about 52mm.
Take the example where I stand and take a picture with my 35mm DX lens and it produces this entire picture. If I switch to the 50mm FX lens, do I get the outer green rectangle (35/50 = 70% of width and height) or the inner green rectangle (35/(50*1.5) = 47% of width and height)?
This web page form the excellent Cambridge in Colour web site may help you.
http://www.cambridgeincolour.com/tutorials/camera-...
There is a calculator section about half way down the page that will allow you to put in your parameters - distance to subject, size of subject that needs to 'fill' the frame and size of sensor and will give you a reasonable guide as to which focal length lens(es) you might find useful.
The rest of the page is handy too, as it the entire site!
To pick up on your question above - as Rob has observed a 50mm lens is a 50mm lens. What is the difference between an FX or a DX (or in Canon terms EF or EF-S? Mainly that the lenses dsigned for the smaller sensors are made smaller and so the circle of light will cover the sensor of a crop sensot camera (APS-C etc.) but would not cover a full frame sensor or, is it did, the edges and corners would likely be of poor optical quality and and have a lot of vignetting. The 'look' of the image produced would be the same but you would see less of it using a cropped sensor with either a full frame of a crop sensor special lens attached - as you correctly assume.
The benefit of the special smaller lenses for cropped sensors will mostly relate to size, weight and cost. All of which are likely to be reducded compared to full frame.
The debenefits are that smaller and lighter means less glass and so less light and thus slower lenses. On the other hand with the full frame glass you add wieight, size and cost and, on a cropped sensor body, throw most of the light away! However you do end up working with the optical quality in the centre of the lens and so to some extent concerns about edge sharpness and vignetting that one might have to consider for full frame are likely to have no relevance on a crop sensor body. The BIG obvious benefit is that the lenses can be faster for use in low light situations - but you pay for it. You also have the potential for great control over depth of field but to get that readily in your 'typical shot' scenario is likely to require a significant investment and may be more than you feel you want to try to justify at this time.
One could get into discussions about pixel densities of sensors and thus IQ and cropability ... but realistically I don't think that would matter for your purposes based on what you expect to be shooting the mostl. You are unlikely to be pushing the quality boundaries for the subject matter at the shooting distance you have mentioned.
HTH.
ETA:
If you skip any detail that gets too technical and is beyong the scope of your question ... then there are a coupld more pages (lonked form the original page a above as a starting point) that take the discussions somewhat further and may help understanding in some ways.
http://www.cambridgeincolour.com/tutorials/lens-qu...
In fact this next page may be a better starting point for the answer to your question - working backwards from the sensor size to what lens you may find is best suited to your need.
http://www.cambridgeincolour.com/tutorials/digital...
They are all worth reading - enjoy!
http://www.cambridgeincolour.com/tutorials/camera-...
There is a calculator section about half way down the page that will allow you to put in your parameters - distance to subject, size of subject that needs to 'fill' the frame and size of sensor and will give you a reasonable guide as to which focal length lens(es) you might find useful.
The rest of the page is handy too, as it the entire site!
To pick up on your question above - as Rob has observed a 50mm lens is a 50mm lens. What is the difference between an FX or a DX (or in Canon terms EF or EF-S? Mainly that the lenses dsigned for the smaller sensors are made smaller and so the circle of light will cover the sensor of a crop sensot camera (APS-C etc.) but would not cover a full frame sensor or, is it did, the edges and corners would likely be of poor optical quality and and have a lot of vignetting. The 'look' of the image produced would be the same but you would see less of it using a cropped sensor with either a full frame of a crop sensor special lens attached - as you correctly assume.
The benefit of the special smaller lenses for cropped sensors will mostly relate to size, weight and cost. All of which are likely to be reducded compared to full frame.
The debenefits are that smaller and lighter means less glass and so less light and thus slower lenses. On the other hand with the full frame glass you add wieight, size and cost and, on a cropped sensor body, throw most of the light away! However you do end up working with the optical quality in the centre of the lens and so to some extent concerns about edge sharpness and vignetting that one might have to consider for full frame are likely to have no relevance on a crop sensor body. The BIG obvious benefit is that the lenses can be faster for use in low light situations - but you pay for it. You also have the potential for great control over depth of field but to get that readily in your 'typical shot' scenario is likely to require a significant investment and may be more than you feel you want to try to justify at this time.
One could get into discussions about pixel densities of sensors and thus IQ and cropability ... but realistically I don't think that would matter for your purposes based on what you expect to be shooting the mostl. You are unlikely to be pushing the quality boundaries for the subject matter at the shooting distance you have mentioned.
HTH.
ETA:
If you skip any detail that gets too technical and is beyong the scope of your question ... then there are a coupld more pages (lonked form the original page a above as a starting point) that take the discussions somewhat further and may help understanding in some ways.
http://www.cambridgeincolour.com/tutorials/lens-qu...
In fact this next page may be a better starting point for the answer to your question - working backwards from the sensor size to what lens you may find is best suited to your need.
http://www.cambridgeincolour.com/tutorials/digital...
They are all worth reading - enjoy!
Edited by LongQ on Saturday 15th September 02:39
alock said:
Take the example where I stand and take a picture with my 35mm DX lens and it produces this entire picture. If I switch to the 50mm FX lens, do I get the outer green rectangle (35/50 = 70% of width and height) or the inner green rectangle (35/(50*1.5) = 47% of width and height)?
At a guess, the green line. The 50mm will give you noticeably more magnification.Whether the lens is DX or FX makes no difference, it's the camera body that counts.
However, for 'head shots across a room in low light' I'd use a 70-200mm f2.8.
Some good advice above.
Regarding the question of lens choice, 50mm won't cut it. It'll give you the equivalent of two or three strides [edit: over the 35mm]. The 85mm is a better bet but don't discount the 105mm f/2 or the 135mm f/2. You might find a used copy of the shorter 105mm for about the same money as a new 85mm G; the 135mm goes for closer to £900.
I've used the 135 on a DX sensor and it was great, with fantastic bokeh. You'll find the extra stop of light over any f/2.8 lens invaluable on your body, allowing you to keep the ISO manageably low.
Regarding the question of lens choice, 50mm won't cut it. It'll give you the equivalent of two or three strides [edit: over the 35mm]. The 85mm is a better bet but don't discount the 105mm f/2 or the 135mm f/2. You might find a used copy of the shorter 105mm for about the same money as a new 85mm G; the 135mm goes for closer to £900.
I've used the 135 on a DX sensor and it was great, with fantastic bokeh. You'll find the extra stop of light over any f/2.8 lens invaluable on your body, allowing you to keep the ISO manageably low.
Edited by AndWhyNot on Monday 17th September 09:50
The FX / DX focal length ratio stuff has been pretty well explained, so I've a different suggestion: Get the 18-200VRII and have a solution for most situations. Will give great images on a D3100, and particularly good at the focal lengths you've asked about. The only issue might be lack of shutter speed as you can't go as wide as a prime. Sharp as hell for a superzoom though....
Thanks to all the replies above. I think I finally understand which lenses will give me what I want.
1) Just get a 55-300 for the occasional longer shot.
2) But the 70-300 isn't much more and has much faster auto focus.
3) If I'm spending that much then the 18-200 would be a better walk-about lens and do I really need the last 100mm.
4) Sigma/Tamron offer smaller, lighter, cheaper walk-about lenses.
5) Sigma/Tamron offer heavier, larger, faster lenses like a 70-300 f2.8.
6) Reality-check, I don't need a lens like that. My wife would never want to carry it. 99% of my pictures are of my children and my only problem is the 35mm is too wide.
7) 85mm 1.8G is looking good.
8) If I'm spending >£300 on a lens, then wouldn't a zoom be more practical than a prime. Back to item 1 above.
I know what's going to happen.... within 12 months I'll have a 85mm 1.8G and the 18-200mm. I'll then be back here asking about lenses which are at least 300mm
AndWhyNot said:
Regarding the question of lens choice, 50mm won't cut it. It'll give you the equivalent of two or three strides [edit: over the 35mm]. The 85mm is a better bet but don't discount the 105mm f/2 or the 135mm f/2. You might find a used copy of the shorter 105mm for about the same money as a new 85mm G; the 135mm goes for closer to £900.
I've used the 135 on a DX sensor and it was great, with fantastic bokeh. You'll find the extra stop of light over any f/2.8 lens invaluable on your body, allowing you to keep the ISO manageably low.
I think your point above that the 50mm isn't different enough from the 35mm is the crux of my issue. I don't think those other two lenses have AF-S (which the D3100 needs for auto focus) and that would be a very hard sell to the wife. And if I'm honest I think I want auto focus as well.I've used the 135 on a DX sensor and it was great, with fantastic bokeh. You'll find the extra stop of light over any f/2.8 lens invaluable on your body, allowing you to keep the ISO manageably low.
Simpo Two said:
However, for 'head shots across a room in low light' I'd use a 70-200mm f2.8.
I know this is probably the default choice, but due to cost, size & weight, this is never going to happen.trackdemon said:
The FX / DX focal length ratio stuff has been pretty well explained, so I've a different suggestion: Get the 18-200VRII and have a solution for most situations. Will give great images on a D3100, and particularly good at the focal lengths you've asked about. The only issue might be lack of shutter speed as you can't go as wide as a prime. Sharp as hell for a superzoom though....
Don't get me started on this. At the moment I go full circle about every 3 days. It goes something like this:1) Just get a 55-300 for the occasional longer shot.
2) But the 70-300 isn't much more and has much faster auto focus.
3) If I'm spending that much then the 18-200 would be a better walk-about lens and do I really need the last 100mm.
4) Sigma/Tamron offer smaller, lighter, cheaper walk-about lenses.
5) Sigma/Tamron offer heavier, larger, faster lenses like a 70-300 f2.8.
6) Reality-check, I don't need a lens like that. My wife would never want to carry it. 99% of my pictures are of my children and my only problem is the 35mm is too wide.
7) 85mm 1.8G is looking good.
8) If I'm spending >£300 on a lens, then wouldn't a zoom be more practical than a prime. Back to item 1 above.
I know what's going to happen.... within 12 months I'll have a 85mm 1.8G and the 18-200mm. I'll then be back here asking about lenses which are at least 300mm
alock said:
I know what's going to happen.... within 12 months I'll have a 85mm 1.8G and the 18-200mm. I'll then be back here asking about lenses which are at least 300mm
Of course. That almost always happens to anyone who is half serious about their image capturing and stays around here!If you are really committed you may well be sucked into macro stuff as well, though that seems to be more the domain of Canon users for some reason ...
alock said:
I know what's going to happen.... within 12 months I'll have a 85mm 1.8G and the 18-200mm. I'll then be back here asking about lenses which are at least 300mm
Sound to me like you just need to invest in one decent 'do it all' lens 
Whilst I have a small collection of 'nice lenses' such as a 70-200 2.8 etc, the best lens I have bought in the last 5 years is the 18-200 VR, no question about it.
By best I mean best for me and my needs, and I think that's far more important than technically or optically best.
It is the lens that stays on my camera 90% of the time and I have captured tens of thousands of photos with it.
I've taken heaps of nice photos using it that I wouldn't have got otherwise due to not being able to change lenses, or simply not having the 'right' lens with me at the time.
Of course optically it is a bit of a compromise like any superzoom, it is also very plastic, and pretty expensive, but as other owners on here will also testify, it's bloody good.
It's been splashed, rained on, dropped out of the back of a pickup truck onto concrete, bashed about over a five year period, dropped into snow, survived a snowmobile crash... and only this week I used it to take a night photo of Miami Bay which when I looked at it on my laptop shocked me by its colour, clarity and sharpness.
Don't bother with the 18-200's from Sigma/Tamron and the like. A few couple of people I know have bought these instead of the Nikon to save money because "they are just the same really". Wrong sadly. They produce noticeably inferior images and have poorer autofocus motors etc.
Buy one lens you can (mostly) leave on your camera that you will be happy with, and then you can forget about it and just enjoy taking the photos
Just my two pence worth!
Simpo Two said:
You have to decide which is more important, results or practicality. Either you get the best lens for the job, or you get a compromise. How much can you chop off and still get the results you want?
FWIW, I bought a 50mm F1.8 for my D80 a while back and simply love it. (I did a PH thread for it, here.) For me, the crispness and the fact that it is small and very portable when on the camera are great plus points; the best camera in the world is the one you have in your hand when you want to take a photo, and I take my camera with me much more now I have a nice, small lens on the front of it. Not expensive. And highly recommended.
Oli.
One more point about the 18-200 fwiw: Get the MkII version (has zoom lock and gold lettering) it's much superior (than the MkI) than it's £125-150 extra price on ebay would indicate. I have genuinely nice clean crisp shots @ 200mm/f5.6 from Goodwood this w/e that my old mkI (good as it was) couldn't hope to match, and neither would the Tokina/Sigma alternatives.
trackdemon said:
One more point about the 18-200 fwiw: Get the MkII version (has zoom lock and gold lettering) it's much superior (than the MkI) than it's £125-150 extra price on ebay would indicate. I have genuinely nice clean crisp shots @ 200mm/f5.6 from Goodwood this w/e that my old mkI (good as it was) couldn't hope to match, and neither would the Tokina/Sigma alternatives.
The Mk1 and Mk2 versions of the 18-200 are optically and mechanically identical.The only differences are the zoom lock switch and allegedly some 'improved lens coating', that's it.
The 'which one is better' questions prompted back to back testing by various photography websites and has shown that the image quality between the mk1 and mk2 is absolutely identical, as you would expect from identical optics.
I would suggest that if you have noticed a distinct improvement from the mk1 to the mk2 then your original one may sadly have been a duffer to begin with?
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