Lenses for Full Frame and Crop Cameras

[doggiej]

<p>I am about to make a major investment in new cameras and lenses. I will be shooting mostly landscape and outdoor photos. I want to purchase a main camera and a backup camera as well as lenses. I am torn between full frame and crop sensor cameras. My question is if I purchase both types of cameras can I purchase lenses that work on both cameras or must I have a diff set of lenses for each camera. I am considering the Nikon D800 full frame camera and the D7100 as a backup. Can I purchase lenses that wil work with both cameras. I appreciate any help I can get. Thanks Frank</p>

[owen_omeara]

<p>Frank;</p>

<p>I found myself in exactly the same situation. I have, and love my d7100 but am planning to add a d800 or d810 soon. When I made that decision I began buying both but FX glass and it works beautiful with the DX format. When I get the DX body I will be happy I made that decision. Good luck and let us know what you decided.</p>

<p>-Cheers</p>

[Andrew Garrard]

<p>Hi Frank. Lenses designed for film or for "full-frame" digital cameras will work on both the D800 and D7100. Lenses that are designed only to have coverage for crop sensor cameras such as the D7100 will fit on the D800, but will typically produce a dark/black or soft image outside the cropped image area. (You can put the D800 into "DX" mode, but it only captures the middle 16MP of the sensor at that point.) Lenses that aren't designed to cover the area of a full-frame camera are designated "DX" by Nikon; other manufacturers have other terminology (such as "DC" for Sigma).<br />

<br />

I trust you're aware that, by using a full-frame lens on a crop-sensor camera like the D7100, you're only going to see the middle of the image. This means that the lens is effectively longer (and slower, although you don't have to worry about this for ISO), as though you were using a 1.5x teleconverter on the larger camera. For example, a 40mm slight wide-angle on a full-frame camera is, on a crop camera, a slight telephoto (the equivalent of 60mm focal length in angle of view).<br />

<br />

I hope that helps.</p>

[Two23]

<p>While obviously any F-mount lenses will mount on any Nikon camera, it's the focal length that makes it useful or not. The D7100 is probably Nikon's best for wildlife, so longer lenses such as 80-400mm VR are a no-brainer. For landscapes, myself, I would want at least a couple of Nikon's tilt/shift lenses. Again, a no-brainer. If you're not buying those, consider skipping the D800. I say this because after looking at it myself, I ended up with a pair of D7100. The reason is I shoot some weddings and some commercial work. I want my back up body to be exactly the same so I don't accidentally screw up a setting during the "heat of battle." A more practical consideration for travel is with only one camera I have only one type of battery to buy and one battery charger to bring. My strategy has been to simply and slim down what I carry, and the amount of cash stuck in photo gear. You called it an "investment," but really the opposite is true. Modern DSLR cameras and even the lenses depreciate very, very fast. Since last year even my D7100's have lost $300 each in value. Instead of putting the bucks into a camera, I've put it into a first class Gitzo tripod & head, and excellent lenses that are a great fit for what I do. I simply plug a new medium cost camera into this system every couple of years. It's been working very well for me as the ratio of $$ to results is very favorable. Despite being a wedding photographer and a night photographer, I've never really jumped on the FX bandwagon. I use the money saved to travel to great places. I've been very happy with that. My standard line is I'd rather have a $100 camera and a ticket to Iceland than a $3,000 camera and no ticket to anywhere. I'll get more interesting photos with the $100 camera.</p>

<p>To answer your question more directly, there is no one set of lenses that will do the same thing on a D800 that they do on a D7100. You will need at least a wide zoom for the D7100 and a 50% longer lens for the D800. If you shoot both wildlife and landscapes with a thilt/shift lens, having two different camera systems might make sense. Otherwise, it complicates things, adds more cost to the system as well as weight.</p>

<p>Kent in SD</p>

[doggiej]

<p>WOW ! As a side note I must say I really love this site , incredibly fast response and very helpful answers !! Thanks so much for the information so far. As I said in my original post I am starting from scratch, If I am correct in what I am reading If I get the D800 as my primary camera and then purchase the lenses for that camera. Those lenses will also work on the D7100 backup camera. In That case if I could get some recommendations on lenses for the D800 that would be great. I will be shooting mostly landscape and nature but I will also be shooting some portrait and social photos (to help pay the bills as they say)....Thanks Again Frank</p>

[ShunCheung]

<p>Frank, one thing to keep in mind is that Nikon has recently announced the D810, as a minor update to the D800/D800E. The changes are rather small so that it may be a good idea to buy the "old model" D800 with some discount. If you don't need 36MP, the D610 is also a possibility.</p>

<p>For wide landscape work, I can highly recommend the 18-35mm/f3.5-4.5 AF-S: http://www.photo.net/reviews/nikon-18-35mm-g-review/<br>

It is not particularly expensive but optically excellent as long as you don't need f2.8.</p>

<p>If you need a backup camera, I would suggest getting another FX-format body to backup an FX body such as the D800 or D610. And just in case you get a 24mm/f3.5 PC-E lens for landscape work, you will have a hard time mounting it on some DX body, and a lot of its tilt/shift capability are not usable. But that is a highly specialized, uncommon lens; it might not be your concern at all.</p>

[JDMvW]

<p>I usually carry both a FX and a DX body, with the telephotos on the DX and the regular and wide-angle lenses on the FX.<br /> I find this really convenient, if a little heavy. As it happens, I do have a DX wide angle and other DX-only lenses for when I want the relative lightness of the DX only set up. <br /> I don't see the cropping feature of some FX cameras with DX lenses as being a useful feature, YMMV.</p>

 

<blockquote>

<p>" A pixel is a terrible thing to waste"</p>

</blockquote>

[eric_arnold]

<blockquote>

<p> there is no one set of lenses that will do the same thing on a D800 that they do on a D7100. You will need at least a wide zoom for the D7100 and a 50% longer lens for the D800. </p>

</blockquote>

<p>Kent is right on the money with this. it's simply a hassle to use both DX and FX formats, because it involves compromises with lenses. IMO it's not really worth it to use DX lenses on FX bodies for the reasons Andrew mentioned. where you really feel it is in wide-angle; the 18-35 that Shun mentioned is an ultrawide on FX and a moderate standard zoom on DX. On the other hand, using crop sensor cameras with telephoto lenses does give you more reach, which may save you money, if you factor in the cost of 300mm and longer lenses. there are some focal lengths which work well on both formats: a 70-300 VR on DX gives you 450mm @ 5.6, which is pretty good; an 80-400 gives you 600mm @5.6, which is even better. a 24-70 or 24-85 is a standard zoom on FX but extends into the portrait range on DX, although you lose the wide end. if you go that route, which makes the most sense if you want to use longer lenses, you do have to be fairly careful with your lens selection. when i went FX, i had to get new zoom lenses in every category: UWA, standard zoom, telephoto. getting rid of my DX lenses wasn't an option for me, because i needed to have the basics covered, although i have only bought 1 new DX lens since then.<br>

<br>

another option is to get a d600 as backup. they're down to about $1400 new, which is only a few hundred dollars less than a d7100. if you're not shooting sports or wildlife, then it might make more sense for you to have an all-FX system. one thing to keep in mind, however, is that dedicated DX lenses tend to be less expensive and lighter than their FX counterparts, though this depends on the lens specification somewhat. <br>

<br>

finally, i have to ask the question of whether you need to go FX at all. obviously the d800 has superior resolution, but 2 x d7100 is nothing to scoff at and will free up more budget for lenses. if i had to choose between an expensive camera with an average to mediocre lens and a modesty-priced camera with an excellent lens, i would probably opt for the latter, especially because that expensive body will begin to depreciate the minute you take it out of the box, while lenses depreciate far less.</p>

[William Michael]

<blockquote>

<p>I want to purchase . . <strong><em>a backup camera</em></strong> . . .</p>

</blockquote>

<p>Why?</p>

<p>*</p>

<p>I think that you should firstly reconsider the rationale for having a 'back-up' camera.<br /> Then secondly consider what the purpose of that camera actually is to be.</p>

<p>What I mean is, if the second camera body is truly a “Back Up” then to completely ‘back up’ (i.e. ‘replace’) the first - it must be the same or close to the same as the first as possible.</p>

<p>If this is the case then I would seriously consider the cost outlay for the expected returns. For example IF your (very expensive) camera goes belly up and needs to be in camera hospital for three weeks, would that be the end of the world and/or could you survive renting a similar body for that time? Is it necessary to outlay a whack of money to have another camera “on standby” just in case . . . maybe it is for you, I don’t know: It is for me because I still shoot some gigs for money and I cannot afford look stupid if my one of 5D’s die – so I take at minimum three DSLRs to all paying jobs: but at a family function or a long drive or a relaxed weekend away I take one camera.</p>

<p>If on the other hand when you wrote <em>‘back up’</em> you meant <em>“I want to use two active cameras when shooting”- OR – “I want two different cameras because I have diversely different needs”</em> then that is a different matter. And in this case I think that you need to look at what OUTCOMES you specifically want from using two cameras (as opposed to one) and let that drive the choice of which two cameras that you buy.</p>

<p>WW</p>

<p>Addendum: I just noticed you subsequent post about shooting 'Portraits and "social" ' - then I suspect that you do need a second camera body - but remainder of my above reamins for consideration - AND - especially if these paying gigs are infrequent (or not yet in the bag as contracts) then I see no rush to buy a second body if you can borrrow or rent (cheaply) </p>

[john_curlett]

<p>I would like to correct a statement made earlier in this thread. The "speed" or F number of a lens does not change with the format of the camera. A f/2.8 full-frame lens will provide exactly the same exposure on a FX camera as it does a DX camera. The only difference is the smaller field of view on the DX camera because of the smaller physical size of the sensor.</p>

[bebu_lamar]

<p>I agree with William W. that unless you intended to use your camera professionally I think there is no need for a back up camera. Sure Murphy's law stated that something that can fail will fail but how bad is it if you camera fail? For me the cost of buying or repairing the camera hurts more than the lost images. If you want a DX for a different purpose than back up then it's fine. For example you may want to have the D7100 for longer reach and higher frame rate. </p>

[Two23]

<p>If you are starting from scratch, based on what you've said so far, I'd suggest the following:</p>

<p>x2 D7100 (or one D7100 & one D7000)<br /> Tokina 11-16mm f2.8 or Nikon 10-24mm<br /> Nikon or Sigma 17-50mm f2.8<br /> Nikon 80-400mm VF AFS (if shooting wildlife) OR<br /> Nikon /SIgma 70-200mm f2.8 (if NOT shooting wildlife<br /> x2 Nikon SB-900/910<br /> one EXCELLENT tripod (Gitzo carbon fiber) and EXCELLENT ballhead (RRS, AcraTEch)<br /> Photoshop software<br /> 8gb RAM memory in computer to process the files<br /> a REAL graphics monitor that can be color calibrated<br /> polarizer<br /> 3 spare batteries</p>

<p>All of the above is a great system that will work together. There are no weak links. The classic beginner mistake is to spend a ton of money on an expensive camera and then have little left over for the important things, and in the end just about everything is more important than the camera.</p>

<p>A back up camera is essential if you are doing paid work. Saying your camera died in the middle of a job just isn't going to cut it. You could potentially even be sued. You're going to find two D7100 (or 1 D7100 & 1 D7000) to be a helluva lot more affordable than two D800. Bottom line is not one of your customers will ever know the difference between an image made with a D7100 (or even a D7000) vs. one made with a D800. For "event" work you want the back up camera to have the same controls/batteries/cards/etc. as the other camera. It's a big pain in the butt to have to stop and think about where a certain button is on one model camera vs. another when you switch off cameras, and can lead to your making an unfixable mistake. For casual shooting, a back up camera could be different since there is no pressure of having to get it right. You will still have more $$ tied up in lenses though, will be carrying more weight around, and will have different batteries and chargers to mess around with and pack. My whole strategy is to simplify, and it's worked very well.</p>

<p>--->Think in terms of the total SYSTEM. Look at photo gear as not just a camera, but a SYSTEM. The pieces must work together.</p>

<p>Kent in SD</p>

[Dieter Schaefer]

<p>The D7100 is actually the "higher resolution" camera - smaller pixel pitch means higher Nyquist frequency and hence ability to resolve fine detail.</p>

<p>I often wonder if for landscape photography the often cited FX advantages are really field relevant and lead to a clear distinction of images taken, for example, with a D7100 and Tokina 11-16 or Sigma 8-16 (which I consider the best DX UWA zooms currently around) and a D800E/D810 and the 14-24 (which is generally accepted as the golden standard for FX UWA zooms)? And is that difference - if it even exists or is important for ones work, worth the 2.5x price differential?</p>

<p>I acquired an FX camera particularly for use with the 16-35/4 - where VR allows me to take images that I otherwise could not (because I either didn't bring a tripod or am not allowed to set one up) - there is no equivalent lens for DX. It also essentially eliminated one lens from my bag - instead of 11-16 and 16-35 or 17-55 for DX, the 16-35 does all I need on FX. </p>

<p> </p>

[Two23]

<p>There is another combo that would have some compatibility. It would be a D600/D610 and D7000/D7100 as cameras. I'm assuming they take the same battery and assuming their menus/buttons are pretty much the same. For D610 have a 24-120mm VR and maybe a Samyang 14mm. For the D7100 have either a 70-200mm f2.8/Nikon 70-200mm f4, OR if you do wildlife something like an 80-400mm AFS. Still need an excellent tripod & head, still need two SB-900/910 flash, still need good computer software and a for-real graphics monitor, and the RAM to handle the big files from the D7100. When you start adding up the cost of a SYSTEM that will do what you are wanting, it comes up to a pretty big pile of $$. The idea is to make it a balanced system.</p>

<p>Kent in SD</p>

[dan_south]

<p>If you're just getting started, consider the D610 (as others have suggested). Use it for a while. Later, you can add the D7100 (or whatever model is available) if you'd like the extra crop for distant objects (wildlife). Or look into a D810 if you need the extra resolution.</p>

<p>The 24MP of a D610 is a lot of resolution. You might not need more. Many of my favorite photos were captured with a 21MP Canon sensor. People always comment on the level of detail that they see in the prints from those files.</p>

[William Michael]

<p>On your point about: “<em>I will also be <strong>shooting some portrait and social photos</strong> (to help pay the bills as they say)”</em></p>

<p>If you are starting from scratch buying ALL your gear, then you’ll need to allocate some funds to Lighting Gear.</p>

<p>WW</p>

[marklcooper]

<p>I fully agree with Kent Staubus. I use a D300 (12 megapixel) with a Tokina 11 - 16 f/2.8, Nikkor 17 - 55 f/2.8, Nikkor 70 - 200 f/2.8, and a Sigma 30 f/1.4. I have an SB-900 for flash. I've printed a landscape taken with the 17 - 55 handheld at 24" x 36."</p>

<p>Keep things simple by staying with the same model camera. Don't mix FX and DX. FX lenses can be used on DX cameras.</p>

<p>Because of my style of shooting, the 17 - 55 f/2.8 is on my camera most of the time. I do a lot of low light shooting. I'm starting to use my SB-900 more and more.</p>

<p>For examples of my style of shooting, go to http://www.mlc3.com/f440228339</p>

<p>Thanks,<br>

Mark</p>

[Two23]

<p>I'll add that probably half the photographers out there at one point say they'll shoot portraits etc. to pay for the gear. The reality is this is more difficult than you might think. First, there are dozens if not hundreds of others out there doing the same and if you don't have a marketing angle you really aren't going to be making that much. Second, this kind of shooting requires that you really understand how to use flash--and have a good one (plus a spare.) Portraits from paying clientele almost always involves off camera flash, flash modifiers, and a solid understanding of it. Yes do-able, but the learning curve is steep and there are costs. It might take a year or so of daily shooting to get to where you're proficient enough to be taking money. To keep things simpler you might consider just taking photos for yourself and family while learning. That way you can avoid the expense of a 2nd camera, 2nd flash, and moderately expensive calibrated graphic monitor (and portrait software.) Most people start with a basic photo system and add to it over several years. You're more apt to make wiser purchases that way as you'll know what you want.</p>

<p>Kent in SD</p>

[georges_pelpel]

<p>If you shoot portrait you also have to consider depth of field.<br>

A 50mm lens will have a smaller field of view on a DX camera than on a full frame body as it will be a 75mm equivalent but it will have the same depth of field.<br>

So the same lens has a 50mm f/1.4 lens DOF on an FX and still a 50mm f/1.4 DOF on a DX camera. If you are looking to achieve shallower depth of field on DX you need to choose an actually longer lens.<br>

For portraiture 85mm is a favorite on full frame systems. Using a 50mm f/1.4 on a DX will provide you with the same focal but you will get a wider DOF than the FX combo provides.</p>

<p>With long lenses DX has some advantages as you can reach smaller field of view (longer focal) with a lot lens weight. A 300mm f/4 used on a DX is like a 450mm f/4 on FX with a weight reduction of probably 60 to 70%, that's huge. It will also provide you with a little bit more DOF at the same aperture.</p>

<p>The reverse is true with wide lenses where the advantage goes to the FX format.</p>

<p>So to answer your question, yes you can have a 100% FX lens system that will cover all situations.</p>

[Wouter Willemse]

<p>While I never subscribed to the view that landscape equals wide angle, it's the wide angles where you'll find serious problems mixing FX and DX. A lens as the 18-35 that Shun mentioned is really wide on a FX camera, on a DX camera it's much like a kitlens with less range - nowhere near as special and pretty expensive compared to DX options that exist.<br>

Kent's shopping list makes a lot of sense, though for landscape photography, I'd get the 16-85VR as it's excellent for that. It is, however, a lot less suitable for event photography. But I also happen to agree with Kent's last posting. Keep things simple. Get one camera, get very familiar with it, and in time see if paid jobs come up. There is an awful lot of people trying to make a few extra dollars with photography these days (see the forums here and you get an idea) - and I think you may find there is a lot less clients out there as there may seem to be.</p>

<p>If you go for a single camera, you could consider the D610 (a D800 only if you're sure to print very large, or if you find the D610/D7x00 style body too small, most people do not). 18-35 f/3.5-4.5 and either 24-120 f/4VR or the kit 24-84VR (if landscapes is your main goal) or something as the Tamron 28-75 f/2.8 (more versatile for events, less range though; a 24-70 f/2.8 Nikon but try in a shop if you are happy with its weight), a SB910 or SB700 and a seriously good tripod. This would mean a lot less money spent, and hence a lot less urge to recoup the money shooting paid jobs... two birds with one stone.</p>

[Andrew Garrard]

<blockquote>I would like to correct a statement made earlier in this thread. The "speed" or F number of a lens does not change with the format of the camera. A f/2.8 full-frame lens will provide exactly the same exposure on a FX camera as it does a DX camera. The only difference is the smaller field of view on the DX camera because of the smaller physical size of the sensor.</blockquote>

 

<p>I would like to correct John's correction. An f/2.8 full-frame lens will require the same shutter speed and ISO for the same exposure on DX and on FX. However, the FX camera is receiving 2.25x as much light (1.5x crop factor, squared) in total than the crop camera. ISO is defined as light falling on a given area of the image (flux), so the stated ISOs for the cameras are correct, but - with the additional light - the FX camera will be just over a stop better in performance, exactly as though a 1.5x teleconverter was being used on the FX camera.<br />

<br />

From a creative perspective, the depth of field of a DX camera is less than that of a longer lens of the same f-stop used on an FX camera. The depth of field reduction from using a lens on DX is exactly that of reducing the f-stop of a 1.5x longer lens on an FX camera by a factor of 1.5. In other words, the exact behaviour of using a 1.5x teleconverter on the FX camera.<br />

<br />

I said:</p>

<blockquote>and slower, <b>although you don't have to worry about this for ISO</b></blockquote>

<p>Apologies for not being clearer. You don't have to worry about the "teleconverter" effect of DX on aperture for the purposes of exposure calculation. You should consider it for depth of field and for the amount of noise in the final image. I hope that helps remove confusion.<br />

<br />

As William and others said, if you want a camera <i>to complement</i> your D800, a D7100 is a very good choice, expanding the flexibility you have with a given set of lenses. If you want a <i>backup</i> to a D800, that's probably a task for another FX camera, for which a D600/D610 is the obvious budget option. (A used D700 would lose a lot of functionality for the style of shooting you say you want to do.)<br />

<br />

Lenses depend heavily on your budget (and a D610 with good lenses is likely a better idea than a D800 with cheap lenses, unless you're planning to expand your system. For landscapes, I tend to want a wide angle available (that's not to say that longer lenses aren't useful for landscapes, but those I'll cover below), which in my case is a 14-24 - though many would suggest that the difficulty putting a filter on that lens is an issue (as, for me, is field curvature, but I'm not sure whether my sample is unusual there). The Sigma 35mm f/1.4 is also very good, and doubles as a standard lens on a DX camera. For portraiture, an 85mm (f/1.8 AF-S or f/1.4 Samyang on a budget, f/1.4 Nikkor or Sigma if not) is a short portrait lens on FX and a long one on DX. A 70-200 f/2.8 is good for social shots, for the flexibility. For most wildlife, longer is better - a 300mm f/4 being the quality budget starting point (possibly with a TC-14E) or an 80-400 AF-S - and very expensive glass if you want more capability than that. All of these are just lenses to consider, not authoritative. Unfortunately, "landscape, wildlife and portrait" means you probably want "wide, long and fast" respectively, which means the expensive extremes of the lens range. But I'd probably start with something more affordable and extend the ends of your range as you see where you need more functionality - I've always bought a lens when what I got won't take a shot, not "just in case". I hope that helps.</p>

[lornesunley]

<p>Umm Andrew</p>

<p>"I would like to correct John's correction. An f/2.8 full-frame lens will require the same shutter speed and ISO for the same exposure on DX and on FX. However, the FX camera is receiving 2.25x as much light (1.5x crop factor, squared) in total than the crop camera. ISO is defined as light falling on a given area of the image (flux), so the stated ISOs for the cameras are correct, but - with the additional light - the FX camera will be just over a stop better in performance, exactly as though a 1.5x teleconverter was being used on the FX camera."</p>

<p>I cannot understand how this can be correct. The same amount of light is falling on a "given area of the image" - say a 10mm square of the sensor - regardless of whether or not the sensor is FX or DX, and according to this logic an 8x10 view camera will perform many many more stops better in performance (whatever that is supposed to mean). </p>

<p>Each pixel (given that the FX pixel pitch is larger) can have better dynamic range because the pixel area (which will be larger on the FX sensor) will receive more light during the exposure, given all other aspects of the sensor technology are equivalent.</p>

[Andrew Garrard]

<p>I appreciate that we're going off-topic, although I hope that Frank finds it useful...</p>

 

<blockquote>I cannot understand how this can be correct. The same amount of light is falling on a "given area of the image" - say a 10mm square of the sensor - regardless of whether or not the sensor is FX or DX, and according to this logic an 8x10 view camera will perform many many more stops better in performance (whatever that is supposed to mean).</blockquote>

 

<p>Yes, that's correct. If we consider film cameras, ISO100 film (for example) has the same grain size no matter the size of the sheet of film. If one makes a 10x8 (okay, call it 10x7-ish for the aspect ratio) enlargement of 35mm film, you get very large (enlarged) grain. Make a contact print of an 8x10 exposure and it'll be much less grainy. As grain increases with film speed, this can be considered very similar to the noise difference caused by varying ISO in different sensors. Though I don't know enough about film chemistry to be able to vouch for whether the behaviour is quite so linear as with the digital case.</p>

 

<blockquote>Each pixel (given that the FX pixel pitch is larger) can have better dynamic range because the pixel area (which will be larger on the FX sensor) will receive more light during the exposure, given all other aspects of the sensor technology are equivalent.</blockquote>

 

<p>Yes, although the dynamic range also has to consider the saturation capacity - see <a href="http://www.sensorgen.info">sensorgen</a> for measurements. The sensitivity and dynamic range of the D800 and D7000 sensor, which are roughly the same generation and have similar sensor site sizes, are very similar <i>per unit area</i>. However, the D800 sensor covers a larger area - there are more pixels in total - which means that the total image it captures tends to have more dynamic range and certainly more sensitivity. This advantage goes away if you start cropping bits off the image, just as you you take a 35mm crop out of a 10x8 exposure, it'll be just as grainy as 35mm film.<br />

<br />

Incidentally, I'm ignoring the fact that 10x8 film is typically also <i>thicker</i> than 135 and 120 roll film in order to stay rigid. I don't believe this affects the grain, although it may affect the resolution. I defer to those with more view camera experience than me!</p>

[john_curlett]

<p>Andrew - I have read your responses several times and stand by my original comment. I would like to address your second paragraph:<br>

"From a creative perspective, the depth of field of a DX camera is less than that of a longer lens of the same f-stop used on an FX camera."<br>

Doing a quick calculation of a 50mm lens on a DX camera at f/4 with the subject 20 ft away will have a total depth of field of 8.04 ft. A FX camera with a 75mm lens at f/4 and a subject 20 ft away will have a depth of field of 5.22 ft. Clearly the DX camera has the advantage of a significantly greater depth of field.<br>

I have no interest in arguing these points with you. It is what it is.</p>

<p>John</p>

[Andrew Garrard]

<p>John - my apologies, I my-typed - or at least, did my comparison backwards (twice); you are quite correct, and I was probably thinking "absolute aperture size" in my head instead of "depth of field". The depth of field of a DX camera with the same lens is, as you say, greater than that of an FX camera at the same f-stop and a lens offering an equivalent field of view (whether you see that as an "advantage" is another matter - you can always stop down the FX camera!)<br />

<br />

Nonetheless, to achieve the same field of view and the same depth of field on an FX camera and a DX camera (i.e. "the same image"), the FX camera will need a focal length 1.5x longer, and an f-stop 1.5x smaller. A 100mm f/2 lens on a DX camera behaves like a 150mm f/3 lens on an FX camera, from the perspective of depth of field - which is equivalent to using a 1.5x teleconverter on the FX camera with the same 100mm lens. (Using a slower lens on the FX camera also negates the "ISO sensitivity advantage" of an FX camera, though there remain debatable advantages in dynamic range, resolving ability, and ease of designing lenses with slower apertures, and portability, AF area coverage and price advantages to the DX camera.)<br />

<br />

There are different comparisons if we consider the effect of using the same lens from the same distance on each camera (the DX camera has <i>less</i> depth of field because producing the same image size involves more enlargement, and the subject will be larger in the DX frame) or the effect of moving the camera to match the subject size with the same lens. However, neither of these produce "the same image" in the way that a change of focal length does. Absolute values of "depth of field" depend on viewing conditions, but we can compare the effect of different cameras.<br />

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In Frank's case, this is most likely to be an issue for portraiture, for which a reduced depth of field is sometimes considered creatively welcome. A DX camera will give more reach with a cheaper lens for wildlife, but at the cost of reduced light capturing ability, which may require longer shutter speeds and lower ISOs for the same noise levels. It may not be an issue at all, but it's worth being aware of if considering lens choices for a two-size camera system.</p>