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Thread: Sensor talk.

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    Super Moderator NEF.D90's Avatar
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    Sensor talk.

    Ok when using a aps-c sensor you have a crop value IIRC it's 1.5 for nikon and 1.4 for canon.
    So does this mean my 35mm lense on my nikon dx body has a focal length of 50.2 and that my 300mm on the same body has a focal lenth of 450mm? Is that right? Or does it just mean that you can view the same as a 450mm? Please clear this up for me. Thanks everyone.
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    Administrator Aloicious's Avatar
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    it's 1.5 for Nikon 1.6 for canon, but it's not actually making your 300mm a 450mm, the only thing that modifies the actual focal length is a teleconverter. unless you're using a teleconverter, 300mm is 300mm is 300mm regardless of what body it is on...what changes is the angle of the view you are seeing, and the area of the image circle that is being recorded.

    a crop value is just that, its only a crop, so its just changing the view that you see, it would be identical to cropping the image in photoshop, it's just done with a smaller sensor. so people compare a 300mm lens on a crop body to a 450mm lens on a full frame body, what they're comparing is the field of view. they're saying (or they should be saying) that the view you see with a 300mm lens on a crop body would be similar to the view you see with a 450mm lens on a full frame body. given the same pixel density and sensor performance of both sensors, there is absolutely no difference between shooting on a full frame sensor and cropping it down, vs shooting the same thing on a crop sensor. (there is some difference when the sensors have different pixel density and/or different performance)

    here's a visual example, so the lens projects a circle of light (the image circle) onto the inside of a camera where the sensor is, the sensor physically covers and records only one area of that image circle, and the physical size of the sensor dictates how much of that image circle is recorded. in this image the circle is what the lens would project (this would be an FX coverage lens), the area inside the red rectangle is what a full frame sensor would record and the resulting image you would get in the memory card, the area inside the yellow rectangle is what a crop sensor would record and the resulting image from that sensor.



    so if this were a 300mm lens, you can see the image circle that is being projected isn't changing with the crop or full frame sensor, so it's not changing the focal length, its only changing the area of the image circle (or view, or angle of view) that is being recorded.

    things become more complicated when you get into varied pixel densities and such. but don't get too hung up on that. just understand that the difference between the sensor size only affects how much of the image is being seen and recorded.

    Hopefully that makes some sense.
    -Justin

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    Super Moderator NEF.D90's Avatar
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    Ok this is what I thought it meant but wasn't quite sure so I thought it would be a good topic for here so that myself and others could learn. Thanks for l
    Clearing that up for me.
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    Administrator Aloicious's Avatar
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    yeah for sure man, things with the DX vs FX get more complicated when you start looking at pixel densities too, especially with newer bodies because some cram more pixels into the yellow box than others have in the red box and vice versa.
    -Justin

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    http://www.slrlounge.com/multiply-ap...eid=3c58fdf9eb

    Oh this is a good short read, and be sure to watch the video extremely informative about this topic.
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    Administrator Aloicious's Avatar
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    yeah, what he's talking about is accurate, but he doesn't do a great job of explaining it IMO. he's only comparing background blur quality when he's multiplying the aperture, it's not in reference to the lens' light gathering ability...he also uses some strange language, he keeps saying things like '100mm becomes 200mm' which is flat out wrong, 100mm is 100mm, the focal length is a physical measurement of the lens, it doesn't change at all with a crop factor, but later in the video he starts saying things like '100mm becomes LIKE a 200mm' which is more correct because the crop factor is only a change of the field of view. he also talks about image quality, but what he's referencing isn't image quality, he's talking about signal to noise ratio....image quality is a large mix of noise, lens performance, operator ability, lighting, etc, etc so comparing ONLY ISO performance isn't fully accurate in the way he presents it using technical vernacular...so although the underlying principles he's trying to explain are accurate, he certainly goes about it a bit strangely, at least IMO. However Tony's books/videos definitely cater to the beginner, so he may have been trying to explain a complex idea in a way that could be more universally understood...
    -Justin

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    Super Moderator NEF.D90's Avatar
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    I liked the video it touched base on things we hadn't discussed. I know what you mean about misrepresentation of the multiplication factor and the focal length.
    From the things I've learned from you I understood what he was really taking about. Thank you justin for chiming in and kinda of defining certain parts for us.
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    So bringing this back up I am having some thoughts.
    Justin have you ever considered going back to a "crop" sensor (aps-c)?
    I'm looking at the ability of the crop in a while new light, so with the D7100/D7200 you have a sensor that has 24mp and no anti-alias filter. This means it should be sharp and full of detail.
    Putting a 600mm lens on an APS-C body will give you a 900mm F.O.V (field of view)
    So you now have a "900mm" at 24mp.
    So really an APS-C should be really good for wildlife... what do you think?
    I'm going to put my tamron 150-600mm on my dad's new D3200 that I got him for his birthday. I can't wait to see the results.
    If your going to dream, Dream Big!

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    yeah, if a really good crop body came around I'd consider it, but for the most part I find the crop bodies cut out some of the form and function that I prefer on the higher end FX bodies. honestly I'm kindof waiting to see what they come out with as a successor to the D810. there is rumor of a 54MP sensor in the high end body (54mp is the FX size sensor with the pixel density of a 24MP DX sensor, the same way the D800's are the FX size of the 16MP DX sensors like the D7000) plus there has been news of a 54MP sensor in development for some time, and with Canon coming out with their recent 50MP body, I don't see the next variation of the D8xx staying at 36mp.

    many people do prefer DX for wildlife but at least in Nikon land they haven't released any real successor to the high end DX bodies like the D300S. the D7100 has more limited controls, and severe buffer problems which I think the D7200 might improve on, but its still a lower end body setup, at least in my point of view.
    -Justin

    Bodies - D800E
    Lenses - Sigma 18-35 f1.8 DC | Zeiss 15mm f2.8 ZF.2 | Zeiss 21mm f2.8 ZF.2 | Sigma 35mm f1.4 Art | 105mm f2.5 AI-S | 70-200 f2.8G VRII | 200mm F4.0D Micro AF | 300mm f2.8 VRII

    My PhotographyWild Blog

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    I should mention that the d7100 and d7200 are fantastic cameras, its just the little details of change between them and my current D800e that detour me from them.
    -Justin

    Bodies - D800E
    Lenses - Sigma 18-35 f1.8 DC | Zeiss 15mm f2.8 ZF.2 | Zeiss 21mm f2.8 ZF.2 | Sigma 35mm f1.4 Art | 105mm f2.5 AI-S | 70-200 f2.8G VRII | 200mm F4.0D Micro AF | 300mm f2.8 VRII

    My PhotographyWild Blog

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