DX lenses & Hyperfocal Distance

[desmond5529]

I've a few questions regarding DX lenses and hyperfocal distance.

1. As I know DX lenses are designed for APS sensor on Nikon dslr. I'm using Nikon D40. When looking at the focal length scale on the lense, do I still need to multiple that with 1.5? Or the focal length on the lense has been adjusted for 1.5 magnification factor? e.g. When I turn to 35mm on the lense, does it mean the actual focal length is 35 * 1.5 = 52.5mm? or this 35mm is already the actual focal length?

2. This question is actually related to the 1st question. I've a hyperfocal distance chart based on nikonians.org that shows for me all hyperfocal focus points for a given focal length and aperture. According to the chart, at 35mm and f/11, the hyperfocal distance is 5.45m. My question is should I turn the lense to 35mm or 52.5mm (35mm * 1.5) for this hyperfocal distance?

[ExplorerZ]

1. no, don have to multiply...

2. still 35mm since focal length is that but you are just using part of the 35mm angle..

[knpan]

wow i thought when used with DX lens , must be mutiplied to prevent shutter blur.

i have been using shutter speeds higer than the 1.5 X of the DX lens all these while.

[XC Pictorial]

Originally Posted by knpan wow i thought when used with DX lens , must be mutiplied to prevent shutter blur. i have been using shutter speeds higer than the 1.5 X of the DX lens all these while.

If you meant the 1/focal length guideline then yes generally, better to stick to it.

But Depth which is dependant on dist, aperture, focal length remains same as in 35mm

[desmond5529]

Thank you very much.

Knpan has put up another good question. To summarize all

1. For hyperfocal distance, set the lense's focal length according to the focal length on the chart. NO multiplication needed.

2. For 1/focal length rule to prevent image blur, multiply the lense's focal length with 1.5 and set it accordingly.

[knpan]

ok thanks.

[JeeT77]

Originally Posted by ExplorerZ 1. no, don have to multiply...

So meaning those lenses that have "DX" on them have effective focal length range "etched" on the lenses already?
- If so how come on Nikon's website quoted on the AF-S DX 18-200VR:

Quote: The lens offers users the remarkable 18-200mm focal length range, which conveniently covers everything from wide landscapes to tight portrait shots. (The picture angle is equivalent to a 27-300mm lens in 35mm format.)

i'm confused now...

[Artosoft]

Originally Posted by JeeT77 So meaning those lenses that have "DX" on them have effective focal length range "etched" on the lenses already? - If so how come on Nikon's website quoted on the AF-S DX 18-200VR: i'm confused now...

DX lens mean that the lens is optimize for DX size sensor. The focal length remain the same. If they put 18-200mm, the focal length of that zoom lens is from 18mm to 200mm. Only when you are using on DX size camera/body, if compared to 35mm camera, the FoV (Field of View) became 1.5x (Nikon DX sensor 1.5x crop factor), or become 27mm-300mm (35mm FoV equivalent).

Regards,
Arto.

[JeeT77]

Oic..... so for effective focal length (35mm equivalent), then yes need to multiply, but for T/S usage, don need to multiply la..... thanks !

[lsisaxon]

Originally Posted by JeeT77 Oic..... so for effective focal length (35mm equivalent), then yes need to multiply, but for T/S usage, don need to multiply la..... thanks !

Try to change the mindset about the effective focal length. Think more in terms of angle of view because the focal length never changed. It's only the picture angle that has been reduced because of the crop.

[knpan]

for example i use the d70s DX kit lens on the d70s itself. i shoot at 18mm(on the lens). i dont need to set shutter speed to minimumly 1/30 sec to prevent shutter shake. just need to set shutter to 1/20 on the body is enough for non shaky pics.

but if i use the VR 8o-4oomm on the d70s( which is not DX lens ), i need to X 1.5 of the current focal length on the lens to prevent shutter blur

[JeeT77]

err... isn't what has been said i.e the functionality of the focal length on the lens itself is what it is (i.e be it your body is FF or APS-C, you need not to multiply) ?

Agree with your first statement, but I thought it would apply to the same Non-DX lenses (i.e. your 2nd statement).

[theRBK]

Originally Posted by JeeT77 So meaning those lenses that have "DX" on them have effective focal length range "etched" on the lenses already? - If so how come on Nikon's website quoted on the AF-S DX 18-200VR: Quote: The lens offers users the remarkable 18-200mm focal length range, which conveniently covers everything from wide landscapes to tight portrait shots. (The picture angle is equivalent to a 27-300mm lens in 35mm format.) i'm confused now...

notice they mention picture angle, not lens equivalent or any change in focal length...

[desmond5529]

I did a lot of readings on this subject these few days and came up with a conclusion. Correct me if I'm wrong.

Focal length is defined as "distance from the middle of the lens to its focal point". So the distance from from the middle of the lens to the camera's sensor is same regardless of whatever camera you use, dslr or 35mm. If you are using 50mm on a 35mm camera, the focal length would also be 50mm when you use it on dslr as the distance from the middle of the lens to the sensor is the same.

In regards to the sensor size, what actually change is the field of view (FOV), not the focal length. The dslr sensor is smaller than 35mm, basically a crop of 35mm. So your focal length will only change if you want to achieve the same FOV.

The conclusion is regardless of whatever camera you use, no changes are needed for the hyperfocal distance chart or 1/focal length rule.

[psychoatom]

Originally Posted by desmond5529 I've a few questions regarding DX lenses and hyperfocal distance. 1. As I know DX lenses are designed for APS sensor on Nikon dslr. I'm using Nikon D40. When looking at the focal length scale on the lense, do I still need to multiple that with 1.5? Or the focal length on the lense has been adjusted for 1.5 magnification factor? e.g. When I turn to 35mm on the lense, does it mean the actual focal length is 35 * 1.5 = 52.5mm? or this 35mm is already the actual focal length? 2. This question is actually related to the 1st question. I've a hyperfocal distance chart based on nikonians.org that shows for me all hyperfocal focus points for a given focal length and aperture. According to the chart, at 35mm and f/11, the hyperfocal distance is 5.45m. My question is should I turn the lense to 35mm or 52.5mm (35mm * 1.5) for this hyperfocal distance?

1. The focal length remains the same. The image is "cropped" in the case of a DSLR when using a non-DX lens, so the size of the subject remains the same (no magnification) except that the overall image area captured differs from a 35mm film camera and a DSLR. But a DX lens is optimised to be used in Nikon DSLRs, so when put on a 35mm film camera, you get a "smaller frame".

Some interesting reading:
http://www.dpreview.com/learn/?/key=...gth+multiplier

http://www.luminous-landscape.com/tu...dslr-mag.shtml

2. It is still the same focal length. But in this I assume you want max DOF when taking wide angle landscapes etc to convey a sense of depth yet keep foreground/background in focus. So it should still be 35mm.

Some great articles:
http://www.barbeephoto.com/articles/...hyperfocal.htm

http://www.vividlight.com/articles/3513.htm

[lsisaxon]

Originally Posted by desmond5529 I did a lot of readings on this subject these few days and came up with a conclusion. Correct me if I'm wrong. Focal length is defined as "distance from the middle of the lens to its focal point". So the distance from from the middle of the lens to the camera's sensor is same regardless of whatever camera you use, dslr or 35mm. If you are using 50mm on a 35mm camera, the focal length would also be 50mm when you use it on dslr as the distance from the middle of the lens to the sensor is the same.

This is fundamentally correct except that the lenses we use for photography is more complex than that. Thus, it is possible to obtain a 50mm lens which the focal point to the centre of the lens when at infinity is less than 50mm. So just take note of that.

Quote: In regards to the sensor size, what actually change is the field of view (FOV), not the focal length. The dslr sensor is smaller than 35mm, basically a crop of 35mm. So your focal length will only change if you want to achieve the same FOV.

Correct.

Quote: The conclusion is regardless of whatever camera you use, no changes are needed for the hyperfocal distance chart or 1/focal length rule.

I think you got the point with the exception that hyperfocal distance is also a function of circle of confusion which in digital has to do with actual pixel size also.

[calebk]

Originally Posted by knpan for example i use the d70s DX kit lens on the d70s itself. i shoot at 18mm(on the lens). i dont need to set shutter speed to minimumly 1/30 sec to prevent shutter shake. just need to set shutter to 1/20 on the body is enough for non shaky pics. but if i use the VR 8o-4oomm on the d70s( which is not DX lens ), i need to X 1.5 of the current focal length on the lens to prevent shutter blur

No, because, as mentioned before, focal length never changes on a DX sensor or FF sensor.

It's just a cropping of the effective angle of view.

18mm will always be 18mm no matter where you mount it on. The only difference is when you mount it on a DX sensor camera, you are getting an angle of view similar to a 27mm lens, BUT the focal length is still 18mm. DX lens or not, it's still the same rule. You still have to factor in the cropping.

[knpan]

so...whats the minimum shutter should u use when shooting 18mm( the kit lens) to prevent shutter blur. able to shoot at 1/20 on the d70s?

[lsisaxon]

Originally Posted by knpan so...whats the minimum shutter should u use when shooting 18mm( the kit lens) to prevent shutter blur. able to shoot at 1/20 on the d70s?

I think you should be able to handhold it at 1/20s on D70s. D200 would be more unforgiving. This has also to do with the circle of confusion.

[desmond5529]

Now crystal clear. Thanks to all the experts.

Focal length remains the same regardless of whatever sensor I use. The only thing I need to change is CoC from roughly 0.03 to 0.02 when calculating the hyperfocal distance.