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July 2, 2012

Crop Factor Tutorial – What Is It, and How Does It Effect Your Photography!!

Crop Factor - From the Lens perspective

Crop factor is one of those terms you hear all the time in the photography crowd, but you might not know exactly what it means and how it effects your photography.

Well let me break it down for you really simple. Crop factor is the size of your cameras sensor as it relates to the “standard” 35mm size. Due to film being 35mm for so long it became the standard size for a camera, and therefore “Full Frame” means equivalent to 35mm.

For example, if you were to purchase a full frame DSLR like the Sony Alpha A99, the sensor will physically measure ~35mm wide like the image below on the left. Crop Factor cameras like the Sony A57 for example will measure significantly smaller and usually have a much higher pixel density.


Compare Sensor Sizes

Crop Factor Explained - Sensor Sizes

Sensor Sizes

If your using a Full Frame Camera there is No Crop Factor = 35mm, so the lens focal length is what it actual says on it. If your camera does have a Crop Factor, your lenses effective focal length will have a “Multiplier” associated to it.

For example my Canon 70-200mm f/2.8 L IS lens on my Full Frame 5D Mark II has no crop factor because it’s full frame. However, if I slap that same lens on my Canon 40D, which has a 1.6x crop factor sensor, I would need to do some math to figure out the actual effective focal length of the lens. The simple math would be (70mm X 1.6 = 112) and (200mm x 1.6 = 320) In other words the lens effectively becomes a 112-320mm f/2.8 L IS on a 1.6x crop factor camera body. Pretty simple actually and incredible important if your looking to spend $1000 Plus on a lens!! πŸ™‚ Here is a link to a crop factor calculator.

The simple math would be (70mm X 1.6 = 112) and (200mm x 1.6 = 320) In other words the lens effectively becomes a 112-320mm f/2.8 L IS on a 1.6x crop factor camera body. Pretty simple actually and incredible important if your looking to spend $1000 Plus on a lens!! πŸ™‚ Here is a link to a crop factor calculator.

Looking from a lens perspective at my buddy Chubs up top, you can see how the full frame sensor size takes full advantage of the whole lens, while the crop factor sensors use more of the center area only.

Some say the crop factor takes advantage of the “sweet spot” of the lens. The center of the lens is proven to be the best based of all the sharpness test I’ve seen and it just makes sense from an optical perspective. I still prefer the full frame though for the other clear advantages. Although if you need more zoom for sports or something, the 1.6x crop factor might be the way to go to save cash on lenses! Keep in mind though, that the extra zoom you gain is amplifying the flaws of the lens. Sweet spot or not all lenses still have flaws. Chromatic aberration, Vignette, etc..

Until recently the Full Frame DSLR’s were extremely expensive. Then Canon introduced the 5D which although pretty expensive at the time, it had a Full Frame Sensor that aspiring Pro’s drooled over and could actually afford. Sony Also re-leased the A850 Full Frame camera around the same time. Now we have the Sony A99 and DSC-Rx1!!


Common Manufacture Sensor Size Info

Sony Info:

  • Full Frame sensor (24x36mm) – A900, A850, A99, DSC-RX1
  • APS-C sensor = 1.5x “Crop Factor” (23.5 x 15.6 mm ) – A77, A65, A57, A55, A35, A37, Nex-7, Nex-6, Nex-5r, Nex-5n, Nex-F3, Nex-3C

Canon Info:

Nikon Info:

  • FX sensor = Full Frame (~ 23.9 x 36mm) – D3X, D3S, D3, D700
  • DX sensor = 1.5x “Crop Factor ” (~ 15.8 x 23.6mm) – D90, D300S

Crop Factor Chart
If you study this illustration below you can see the effect of the lens crop factor pretty clearly. Also if you understand DOF, you could imagine how the focal length difference would also drastically effect the depth of field produced by the lens.

Crop Factor Explained

That was the simple explanation πŸ™‚ Beyond this I’m going to go into more detail on crop factors and the advantages of “Full Frame” sensors over crop factor sensors etc… So if you want to know more, please continue reading!


Full Frame Sensor Advantage

In this illustration below you can get a sense of the field of view advantage on the Full Frame Sensor.

Crop Factor Explained

Crop Factor Explained


Regardless of format, Full Frame sensors are all about image quality. The most obvious advantage of full-frame sensors is the ability to combine high resolution with large pixel sizes. Compare two sensors with the same number of pixels, one a full-frame unit and one smaller like a 1.6x crop factor. The pixels of the full-frame sensor are larger in comparison. Each larger pixel has a greater surface area available for gathering light. More light collected means less amplification needs to be applied to the output signal of each pixel for the purposes of read out and image processing. Less is better here because magnifying low-level signals inevitably entails picking up and increasing noise that will then have to be removed as thoroughly as possible in a later step.


Crop Factor Explained

Check out the diagram above you can see that bigger pixels offer higher sensitivity because they can gather more light in less time than smaller pixels. The diagram also shows that larger pixels are less inclined to light overflow or spill over because of their greater capacity, improving dynamic range!!! Finally, for a given quantity of noise, more light gathered means a higher signal-to-noise ratio and increased optical signal purity.


In the diagram below there is an example of the full frame sensor microlens gap. The Gap for all intensive purposes is good. All of this stuff is huge when it comes to image quality, and believe me it is is noticeable! Going from the 40D to the 5D Mark II was an incredible eye opening insight into the old phrase “you get what you pay for”. Once you go Full Frame you won’t go back IMO πŸ˜‰

Crop Factor Explained

Crop Factor Explained – Pixel Density


Depth of Field

One last thing about the full frame vs crop factor sensors is the effect on “Depth of Field”. DOF is a huge subject on it’s own, but basically what you need to know is this: Because of a smaller circle of confusion, if we shoot from the same subject distance with the same aperture, and same lens of course , the depth of field will be less on crop factor sensor than on a full frame sensor. However, that is just because of the increased focal length caused by the crop factor multiplier and the subject would appear much closer like in the illustration towards the top of this article. So the way that the crop factor effects the DOF can vary depending on the subject distance and/or focal length. Man that sounds confusion, but it’s correct!

I hope this article helped clear a few things up for those curious about Crop Factor!!


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  1. Thank you so much for this Jay!! I had just been thinking about this today and how I wished I could understand it!! I do have a few questions for you though! πŸ˜€

    Right now I have an NEX-7. I’m really getting into my photography and am doing some weddings this summer. I have also been tagging along with any photographer who will let me. Right now Sony doesn’t have a FF camera, which is fine because I wouldn’t be able to afford it right now anyway. A lot of people are saying the 7 really shouldn’t be used for any real shoots where you’re getting paid, do you agree with that? I know someday I’ll want a FF but I thought maybe I could earn money with my 7 until I can upgrade. I just don’t want to buy a bunch of Sony glass if I go to another brand.

    I really like the D800 and it seems like Nikon & Canon stuff is a lot more abundant than Sony and cheaper. It’s been such a struggle to find affordable flash options(Finally got a Metz 50) and a way to use TTL and HSS wirelessly. Is Sony pretty much on par with Nikon though? I just don’t want to get a bunch of Sony gear if I’m going to switch. Why did you switch to Sony over Nikon and Canon?
    Also, I wasn’t clear on wether I can get the same DOF on my 7 as I could on a FF(If I use the right lens and subject distance)?

    I know that was a lot, but I have so many questions!! Thanks again for all the great articles. I have your homepage saved in my tabs so it always pops up!

    • Jay


      I’ll get back to ya tomorrow in regards to your questions, Bedtime!!

      Thanks again for the comments and kind words πŸ˜‰

    • Jay


      Nex-7 for Pro Work Question

      Ok buddy here we go11 No, I don’t think doing weddings with a Nex-7 is a good idea!! The focus just isn’t good enough to get the shots that you “must” get. You really need an SLR that has much better battery life and build quality. You also want to look professional at Weddings in particular, looks do matter in that environment.

      On a regular portrait session, on the street session, or as a back-up I think the Nex-7 could absolutely be used. As long as you have enough time to set-up everything properly it will do just as good of a job as an SLR.

      You could use the Nex-7 for weddings if you got the LA-EA2 Lens adapter and some A-Mount lenses, but the ergonomics would kill you by the end of the day. Wedding work can be really hard, and time is so critical that equipment failure, or inefficiencies are Unacceptable in my opinion. People expect their day to get captured, and as a professional, that is our job!! We cannot fail at any cost when it comes to getting their images delivered safely. Phase Detection AF speed and Pro-Build quality are a must for weddings!! You get banged, equipment gets dropped, splashed with booze, etc..

      At Minimum you want at least 2 fully capable camera bodies, and a solid back-up (nex-7 perhaps). Michele and I did our first wedding with a Canon 40D (I used) and a Canon Rebel XTI (Michele used). No back-up other than the rebel xti really. Not the best way to go, but I think we did a great job considering!! I also recommend using smaller memory cards and changing them often and numbering!! Cards do fail, and you can’t afford to lose any. If you only lose an hour it won’t destroy the bride and Groom! Small “Fast” cards are cheap!!

      The last wedding we did I had the Canon 5d mark II on my Flash Bracket Rig fully loaded, and a 40d with another lens on it around my shoulder. Michele then used our other 5D Mark II with whatever lens was required for her part in the given moment. I was pretty comfortable that if something failed I was good to go!!

      If I were you and seriously considering going Pro Wedding Photographer, I would get at least the A57 if not the A77!! They are both more than capable and have the build quality you need for weddings. The advantage of Killer HD video with AF would be a really nice perk for your clients πŸ˜‰ The Nex-7 could totally be a second shooter camera with a specialty lens on it!!

      You can’t go wrong with a used 5d Mark II or D700 either for wedding work!!

      Flash Question

      As far as flashes go, the Sony gear works wireless with it’s own technology similar to ttl. I don’t think and Sony camera supports TTL, but I could be wrong about that. I honestly don’t know that much about Sony Flash as I have minimum experience. What I do know is all you need is one Sony flash on your camera, and then you can wirelessly trigger other Sony Flash units with full auto exposure control!! It’s incredible powerful and works awesome on the Nex-7 and all the Sony flash capable cameras. I actually just read about it Gary Friedman’s Nex-7 book, which I highly recommend you get and read btw. He explains everything about the Sony Flash Technology, and how to use it in detail!! I’m not to familiar with the Metz, can it talk to other Sony Flash units??

      If you want to use Off Camera flash triggered by the Hot Shoe, you simply need a $20 dollar adapter to convert the Sony Hot shoe, then everything will work. Check out the Flash accessories guide I made over Here >> for more on that stuff.

      DOF Question

      As far as the dof question, to put it simple no. It’s a different Format is how you have to look at it. Same with Micro 4/3rds for example. In theory you can get a similar equivalent Depth of field, but the POV would be different etc.. The actually dof characteristic is unique to the format (sensor size) pretty much. If you wanted a similar DOF you could put say an f/1.4 lens on a crop factor camera and it would ruffly give you about f/2.8 or so. I’m totally guessing here for visualization purposes, as math can be done to get the exact value, but this is about how it seems to me going from a crop factor to a full frame!! I had to stop using f/4 and start using f/5.6, f/8 as the depth of filed was so much more shallow I could not believe it! With the same 70-200mm f/2.8 lens no less. That is what totally sold me on the Full Frame as images almost look 3d in comparison to the crop factor 40d camera I cam from. Hard to explain, but it’s the Format.

      I hope all this helps Brett, and please fire away if you have any more questions. Happy to help!!


      • Wow! Thanks Jay! You helped answer a lot of my questions there! I really appreciate your time!

        I definitely plan on getting a FF camera, as soon as I can save up the money. I know the NEX-7 may not be ideal, but could I get by with it until I can save up the money or should I just tell people that I can’t do it when they ask me?(until I can get the FF)

        Also I’m really liking Sony so should I wait for their FF? I’m looking at Nikon as well, but I’d like to settle on one brand so I don’t get a bunch of gear and then have to sell it all and buy it all again with a different brand. I know you said you switched to Sony, what made you change your mind?

        My Metz flash does communicate with other Sony flashes, but I’m not sure if it can be a controller or not. I have Phottix Stratto II sony trigger system now, but it doesn’t do ADI,TTL or HSS. I have heard Pixel King makes some that do though, so I’m thinking about trying them out. I guess it all comes back to wether I’m sticking with Sony or not. I don’t want to buy all these triggers and flashes for Sony if I’m going to switch once I get a FF.

        Thanks for helping me understand the DOF stuff too. I’ve heard a lot about it, but when I search boards it seems like people all have different ideas on it. That helps to know that there really is something different about the FF versus Crop that can only be achieved by having a FF camera.

        Thanks again!!

      • Jay


        I definitely plan on getting a FF camera, as soon as I can save up the money. I know the NEX-7 may not be ideal, but could I get by with it until I can save up the money or should I just tell people that I can’t do it when they ask me?(until I can get the FF)

        For a wedding, unless you can barrow and practice a bit with a Phase detection DSLR for a back-up at the very least, I would say No. I personally wouldn’t take the chance, but I sorta have a established name as far as my photography business is concerned. It’s currently shut down, because I’m doing this and Life (Layla, Michele, both work full time) etc.. But, I would still say no.

        Seriously, the Nex-7 is completely capable of doing it, but it is just not designed for super low light fast focusing situations. It also doesn’t have the battery life longevity you Must have.

        If you want to use the Nex-7 for weddings, here is what you gatta do in my opinion as a bare minimum. Get a back-up camera of any kind!! You will need the Sony LA-EA2 Lens adapter for certain situations, but once you see how much faster it is, your going to want to leave it on. You going to need some serious spare batteries!! atleast 5-10 as they take for ever to charge, and only last about 1 hour under heavy shooting/ video. That means multiple chargers, as well. Need a really good flash unit. Then you will need a few A-Mount lenses which will work with your full frame camera once you get it.

        As you can see, this will ad up very quick. For the same money you could buy the A57 probably!! Then have a great back-up when you purchase the full frame. This is the way to go in my opinion. Bit the bullet Brett if your serious πŸ˜‰

        Also I’m really liking Sony so should I wait for their FF? I’m looking at Nikon as well, but I’d like to settle on one brand so I don’t get a bunch of gear and then have to sell it all and buy it all again with a different brand. I know you said you switched to Sony, what made you change your mind?

        That is really up to you Brett. I already have a Full Frame camera so its easy for me to say wait. The Sony FF is going to be around $2500-$3000 I hear, so it won’t be the cheapest FF. You cannot go wrong with any of the top guys. Seriously, Canon, Nikon, Sony, Olympus and Pentax are all awesome camera systems!!

        My Metz flash does communicate with other Sony flashes, but I’m not sure if it can be a controller or not. I have Phottix Stratto II sony trigger system now, but it doesn’t do ADI,TTL or HSS. I have heard Pixel King makes some that do though, so I’m thinking about trying them out. I guess it all comes back to wether I’m sticking with Sony or not. I don’t want to buy all these triggers and flashes for Sony if I’m going to switch once I get a FF.

        Why not sell all that stuff and just use Sony flash units? It all work together just like you want?

        Thanks for helping me understand the DOF stuff too. I’ve heard a lot about it, but when I search boards it seems like people all have different ideas on it. That helps to know that there really is something different about the FF versus Crop that can only be achieved by having a FF camera.

        No problem at all Brett πŸ˜‰


      • Thanks Jay!

        I want to bite the bullet πŸ™‚ I just can’t right now. But I am saving up for it!

        Is this book as good as the one you recommended?

        The problem I have is that several of my friends and family are seeing my photos and now are asking me to do their weddings. I have a backup camera(my wife’s Olympus 4/3) and several batteries.

        I want to get the LA-EA2 and a Sigma 70-200mm f/2.8(So I can use it on FF). Does that sound like a good combination?

        The other problem I have is not being sure which system I want to be tied down to. I don’t want to buy Sony lenses and flashes if I’m going to switch. I love how Sony seems to be at the cutting edge and how I could use lenses between a Sony FF and my NEX-7. But Canon and Nikons are cheaper systems overall in terms of flashes,accessories, etc. It also seems like there is a lot more help for Canons and Nikons.

        I know I can’t go wrong with any of the majors, but how do I make sure I get into a system I’m happiest with? They all seem to have different strengths and weaknesses.

        I guess I have a little while to deicide though since Sony doesn’t even have a FF right now.

        I really appreciate all your time and I’m sorry if I’m taking up too much of it! You’re my Sony guru though and I don’t know anyone else to ask!

      • Jay

        You might want to wait for the Sony Full Frame Bro!! Look at these specs Andrea over at Sar just re-leased from his 100% solid source!!!

        I got the 100% reliable specs of one of the pre final FF SLT prototype camera. Please keep in mind that these specs can variate with the final firmware. Here we are:
        24 MPX sensor
        All cross 102 phase detection AF
        ISO 50-25600 (can be extended to 102.400 with the final firmware)
        Live view – evaluative & subject recognition lock-on AF
        1200 zone live-view evaluative metering
        1920Γ—1080 60p and 24p
        simultaneous recording of still&movie
        921K True Black 3 way tilt LCD
        Shutter Speed 1/8000
        New iAuto
        Smart Tele converter
        Magnesium body
        Weather Sealed body
        Built-in Flash

        There will be a vertical grip too!

        The rumor is coming from a top source. I hope to get the 100% final specs soon.

        It’s worth waiting if these specs are true and the camera costs around $2500-2800 πŸ˜‰ Other wise if you must have full frame I would go with the Nikon as you seem partial to it over the Canon.

        The 70-200 is and awesome lens, but it may be a bit tight for you on the crop factor Nex-7, 70mm = 105mm or so. You may be better off with a 24-70 f/2.8 for the nex-7 and that will also work perfect on the Full Frame. In fact the 24-70mm, 16-35mm, 70-200mm, 70-400mm, 50mm f/1.4, 85mm f/1.4, and the 135mm f/1.8, would be on my want list for that Full frame.

        That book is very good, but not as good Gary’s in my opinion πŸ˜‰


  2. This is great coverage on the difference in sensor sizes and the crop factor effect between various cameras, but it is not the only issue, or what I consider to be the significant consideration between the two.
    To compare this, a 70mm lens on a canon 5d(ii) produces a 21 megapixel image and frames the same picture as a 50mm lens on a Sony A77 producing a 24megapixel image. In comparing this alone one would assume that the crop sensor on the A77 would actually produce a better image in that it has more pixels for the same image/frame. I state this aside from the variables in lens sweet spots and depth of field etc as outlined in great detail above.
    But this is not the greatest issue, the other factor not explained above is the result of a larger sensor allowing more light to hit it overall and to each of those individual pixels specifically – more light means more detail, less noise and better control and result. A full-frame sensor (I am told because I dont have one yet) provides much better depth to the image than a crop sensor can do – even with more pixels or newer technology . There are other factors to this, not all full-frame sensors are equal, the Mark ii compared to the Mark iii for example has other changes in the layers preceding the sensor itself, helping to intensify light onto the plane and other more really technical stuff but my comment is to state, that even with the other lens/framing and megapixel issues aside, a full frame (larger) sensor will provide a much better result.

    • Sorry, to add to that it was explained but my browser (page-down) skipped it. I think the image depth and quality from a full-frame is the most important issue aside from the lens framing factors. Unless your measuring your focal lengths, framing your subject is done by eye and not with concern of these differences.

      • Jay

        Hey Warren,

        Thanks for your comments!! I think your correct in the end! Image quality and depth on a Full Frame camera is significantly better. In fact it gets better as you increase the sensor size from the ultra compacts all the way to the FF. Hence the New Sony RX100 with it’s huge sensor (for and ultra compact) is destroying the competition!! You cannot beat large sensors, you just can’t.


  3. phun-ky


    Thanks for your explanation. There is one thing that still confuses me about the effect of crop factor though.
    Looking at the tree illustration, let’s say I’m using a 100mm lens on a FF body. I frame the picture such that the tree takes up half of the frame (that’s perhaps 12mm on the sensor). Now I switch to an ASP-C body with 1.5x crop factor and I will shoot from the same position. Assuming the same flange to sensor distance, the size of the tree on the sensor will be still 12mm, correct?
    Is it correct to say that the field of view is that of 150mm on the smaller sensor but the magnification is still of the 100mm i.e. mounting the 100mm lens on the smaller sensor won’t buy you the power of 150mm?

    • Jay

      Hence the “Crop Factor” Yes you are correct!! It’s hard to wrap your mind mind around though, and I had to think about it for a minute πŸ™‚

      Pretty nutz right? So technically it is getting you “extra magnification”, but it’s because of the relationship between the sensor size and the flange distance.

      This also relates to Macro Photography as a real Macro lens has at least 1:1 magnification. Meaning on a full frame sensor the bug will be the same exact size it is in real life on your camera sensor. On a 1.6 it would be the same size, but take up more of the actual sensor, therefore giving extra magnification!!


  4. Hi Jay!
    I just wanted to thank you again for your help and let you see how it turned out! I ended up buying the A mount adapter and renting a 24-70mm Zeiss lens. It was stunning!! I ended up buying the lens too after selling my Leica lens I had.
    There’s the link if you want to take a look and thanks again for your great advice that helped everything go a lot smoother!

    • Jay

      Hey Brett,

      Thank you so much for taking the time to reply with all the updated info!! It’s awesome to hear, and your photography is outstanding!! The images look professional to me, no question and I really enjoyed looking at them. In fact, perhaps you may want to check out the new SonyAlphaLab Forum?? It’s in it’s infancy, but I’m on it every day sharing pics and stuff, and it would be great to keep in touch regularly with photos etc.. I have some wedding photos I took a while back that I need to add.

      It’s nice to see quality wedding photos like these, as these days I find less and less good wedding photography on the web. I must admit, I was nervous about you using the Nex-7, but it did a fantastic job for you and it’s a testament to the quality when matched with killer optics and in the hands of a good photographer!!

      I’ll catch up with you later Brett, and thanks again for the link.

      Keep up the great work as well!!


      • Thanks Jay!
        You’re very welcome! I just figured that since you had helped me so much you might appreciate seeing how much you helped me! Your kind words are really encouraging to me! One of the photos was out of focus a little, but for my first paid Wedding I figure that’s not to bad. I tried to check out the forum, but for some reason it won’t let me register.

        This is the error I get:

        “The following errors were detected in your registration. Please correct them to continue:
        The solution of task you submitted was incorrect. Please read the instruction and try again.”

        But I don’t see any instructions.

        Again, thanks for your encouraging compliments, I was a little nervous too, but I felt a lot better once I started looking at the photos!

        Thank you for such a great site! I love coming here for the tutorials, tips, etc. It seems hard to find good Sony resources and you’ve been so helpful. I am so glad I talked to you and you convinced me to get the adapter. I was out doing some shooting without it and I could tell such a difference!

        Thanks again and talk to you later!

      • Jay

        Hey Brett,

        Right-on, and thank you so much πŸ™‚ Only one blurry picture is incredible good. I’m going to get my really good friend Kelly Lyle to to jump on the Forum. He is a master wedding photographer and one of the best teachers I’ve ever met!! Wait to you see some of his work!

        On the forum there is a Anti-Spam verification image you need to put together. It’s like a drag and drop type thing. Did you put the picture together? I may have to change that as Michele said it was really weird.


      • Ya! That was it! In Safari the image wasn’t showing up! In Chrome it worked fine and I’m in!

        Well I had more than that one, but I’d say 80% were good, no focus issues πŸ™‚

        Thanks again! It made my day to read how you were pleasantly surprised with my photos! I even sent what you wrote to my wife! Sometimes you just wonder if what you’re doing is really very good and it helps to have some validation!!

      • Jay

        Awesome to hear Brett Thanks πŸ™‚


  5. Aric

    Hi Jay! Thanks for the great explanation of the crop factor. I have a few questions now that I understand it a bit better. I’ve heard that the 50mm lens is great because the perspective is closest to the human eye. Now I’m currently using the NEX-6 which has a 1.5x crop factor. Does this mean that I should use a 35mm lens with the NEX-6 instead of a 50mm to get that “human eye” perspective (works out to be 52.5mm)? Also, do the advertised focal lengths of the E mount lenses take the crop factor into consideration? For example, if I use the E mount 50mm f1.8 OSS (SEL50F18) lens on the NEX-6 is it going to be 50mm or will it be more like a 75mm lens on the NEX-6?


    • Jay

      Hi Aric,

      Thanks for the comments and really good questions you have which will help firm up your understanding of the crop factor πŸ˜‰

      The human eye’s perception of focal length in comparison to camera’s, is really hard to put a number on. We actually “see” pretty wide if you include the peripheral vision, but if you look with one eye open, or focus on a specific object, I find it’s about equivalent to 35-50mm on a full frame camera sensor. Mind you this is not factual, just my perception as we have binocular vision and can control where we focus ect..

      Now, 35mm on the Nex-6, or any 1.5x crop factor sensor camera, will have the effective focal length of 52.5mm as you wrote above. This also means a 50mm lens or any lens would need to be multiplied by 1.5x and ~70mm ect..
      All lenses, as far as I know, read from the standard 35mm format. So, you will always need to factor that in unless you are using a 35mm full frame camera body. When on a full frame camera the focal length reads what the lens says!!

      I hope that helps πŸ˜‰

      • Aric

        Hey Jay! Thanks for clarifying. I did a little more reading and I’m still confused on one point. Does the crop factor affect the aperture of the lens as well? For example, given that the f-number is entrance pupil over the focal length, would a 50mm f1.2 be like a 75mm f1.2 or will the maximum f-stop be different as well since the effective focal length is different?

      • Jay

        Hi Aric,

        The crop factor has no effect on the aperture of the lens, but does effect Depth of field which is a bit confusing πŸ˜‰ So in your example the 50mm f/1.2 would be a 75mm f/1.2. The aperture would not change ans the lens is physically the same. The only thing different is the sensor size, hence crop factor!!

        I hope that makes sense as it is a lot to grasp!


      • Aric

        Thanks again for the reply Jay! Yea I figured the aperture would stay the same physically but perhaps what I meant is would the “effective aperture” or “effective f-number” be different since the effective focal length is different. Maybe I’m just thinking about it too much haha. I think I’ll re-read the info on apertures/f-numbers and how they’re defined.

      • Jay

        No worries at all Aric!! It’s a lot to wrap your head around for sure. What you need to remember is the “effective” depth of field and focal length is what changes. Not the physical attributes of the lens like the aperture or actual focal length. The depth of field is a factor of aperture, sensor size, focal length, and distance to the subject. F/4 is f/4 all day long as far as the light coming into the lens is concerned, but F/4 as far as depth of field is concerned, is not the same. The smaller the sensor, the less depth of field you will get with that lens assuming the aperture is the same. Just remember aperture is a fixed value just like ISO and shutter speed. F/2 on a Micro 4/3rds camera for example is awesome, because it’s fast!! However, as far as depth of field is concerned, it’s not that great. The sensor is so small, that the relation to the larger aperture f/2 lens is not enough to yeild the same depth of field. In other words you would need like a f/1 lens on a micro 4/3rds sized sensor to yeild the same effective depth of field as a f/2.8 lens on a full frame camera. I’m totally ball parking it here just to make the point, but hopefully it makes a little more sense?? Or perhaps I just confused you more with my ramblings??


  6. Aric

    Thanks again for the reply Jay! That makes sense. I think what I’m still caught up on is the trying to work out the logic and math of the whole thing!

    Logically, since there’s light spilling over the sides of the sensor in a cropped-sensor camera, there’s light that’s been lost so less light is reaching the sensor than anticipated by the lens rating which assumes the lens will be used on a full-frame. As such, it should be equivalent to stopping down the lens to allow less light to reach sensor.

    On the math side, I figured since the f-number is the focal length of the lens divided by the diameter of the aperture, if the effective focal length were to change, so would the f-number even though the diameter of the aperture remains unchanged. So for example, a 50mm f/2 lens has an aperture diameter of 25mm wide open. However, if the effective focal length of the lens on an APS-C sensor is 75mm, the f-number becomes 3 (75mm divided by 25mm).

    I don’t know if that makes sense and if my reasoning is sound. It would be great if you could comment on this. Perhaps others could chime in as well if they see this.

    • Jay

      Ah Ha!! That is where your logic is off Aric. The light does not spill over the sensor like you are thinking. It’s simple focused by the aperture for the smaller sensor. This is where the crop factor comes from pretty much πŸ˜‰


      • Jay

        You Know I think I’m totally wrong here Aric. The more I think about this the more I am confusing myself. The light must be spilling over the sensor if your using a non crop factor designed lens. So a Full Frame lens on a crop factor camera body would have extra light spilling in around the sensor. Otherwise it would not get to the full frame sensor if it was there.

        I believe your math is also correct, but it’s still only the effective depth of field that is effected I believe, although it seems like you might be correct on that as well.

        Thanks for the hard questions πŸ™‚


      • Aric

        haha yea I’m still scratching my head over this one. What initially got me thinking about this whole thing (other than this article) was using various adapters and lenses with my NEX-6. That’s when I came across the Metabones Speed Booster. Looking into the Speed Booster, I found that it’s a focal reducer and they claim that it not only allows a crop sensor camera to have a field of view that’s closer to a full frame camera, it also increase the max aperture by one stop. I thought to myself, how is that possible? That’s when I really started digging into the issue to find out how this might be possible. Then I think I just got more and more confused! =P

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