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04-24-2013, 08:02 AM   #16
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QuoteOriginally posted by screwdriver222 Quote
Forgive me if i am wrong but isn't a 85mm lens on 35mm film still an 85mm lens on APS. The difference only being the cameras APS sensor only captures a cropped portion of the image. The cropped image appears 1.5 times larger. So should we still use a 85mm lens but stand further back?

Please correct me if am wrong, i am only trying to learn like everone else.

Regards Jeff
The focal length of a lens on APS-C to FF will not change. I.e an 85mm lens is still 85mm, however as the APS-C sensor is smaller (typically 23mmx15mm or so) they have what is called a "crop factor". What this means is say you're using a 50mm Rikenon or an old 50mm Pentax M (or A, or any lens that isn't a Pentax DX or lens that is made for the APS-C size) it will have an equivilent focal length of roughly 75mm. The way I have always been taught is take the focal length of the lens, and multiply it by 1.5, and this will give you an equivilant. So, if I have a 50mm on an APS-C camera, I would need a 75mm (so match the focal length) of an APS-C camera. That seems kind of vague.

Basically say you are taking a photograph of a model, and you are 8 feet away, using a 50mm lens on an APS-C camera. You would be zoomed a bit closer than a 50mm lens actually is. Now say you have the same model and you are the same distance away from her. This time, you are using a FF camera. With the same 50mm lens. Your focal length remains the same, but the 50mm focal length appears a bit "wider" than it did on the APS-C.

04-24-2013, 08:16 AM   #17
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I shoot with DA*55/1,4 and I love that lens!

Every needs to look, compare and choose his own best focal length,
but - I think - it is 55 mm the right lens at APS sensor.
04-24-2013, 08:22 AM   #18
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I personally shoot portraits using my Ricoh Rikenon-P 50mm and it works great. However I do know people who use anything up to 300mm lenses for portraiture. Personally I wouldn't suggest anything beyond 150mm.
04-24-2013, 12:28 PM   #19
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QuoteOriginally posted by Bcrary3 Quote
The focal length of a lens on APS-C to FF will not change. I.e an 85mm lens is still 85mm, however as the APS-C sensor is smaller (typically 23mmx15mm or so) they have what is called a "crop factor". What this means is say you're using a 50mm Rikenon or an old 50mm Pentax M (or A, or any lens that isn't a Pentax DX or lens that is made for the APS-C size) it will have an equivilent focal length of roughly 75mm. The way I have always been taught is take the focal length of the lens, and multiply it by 1.5, and this will give you an equivilant. So, if I have a 50mm on an APS-C camera, I would need a 75mm (so match the focal length) of an APS-C camera. That seems kind of vague.

Basically say you are taking a photograph of a model, and you are 8 feet away, using a 50mm lens on an APS-C camera. You would be zoomed a bit closer than a 50mm lens actually is. Now say you have the same model and you are the same distance away from her. This time, you are using a FF camera. With the same 50mm lens. Your focal length remains the same, but the 50mm focal length appears a bit "wider" than it did on the APS-C.
Therefore, focal length effects you see on the links I posted should be the same on an APS sensor or full frame camera. No need to add a 1.5 crop factor to the images as many of the websites suggest. I'm thinking correctly here aren't I?

Tim

04-24-2013, 12:34 PM   #20
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QuoteOriginally posted by atupdate Quote
Therefore, focal length effects you see on the links I posted should be the same on an APS sensor or full frame camera. No need to add a 1.5 crop factor to the images as many of the websites suggest. I'm thinking correctly here aren't I?

Tim
I'm not shure exactly what it is you're asking here. From everyone I have always asked, they have all told me that a majority of lenses are made for FF. Pentax DA lenses are speciffically made for APS-C sensor cameras. Many other lenses (if it doesn't say it is designed for APS-C) are likely for FF, in which case, the crop factor does apply.
04-24-2013, 12:41 PM - 1 Like   #21
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Sorry for the double post.

I found this

Basically, a smaller sensor means that a lens that isn't designed for the smaller sensor not be as wide. A lens not designed for this will also be longer longer on the APS-C format, as that same lens would be wider on FF. So say for example you have a 300mm lens meant to be used on a 35mm film camera body (which is FF) and you put it on a Pentax DSLR body (which has a crop factor of 1.5x) that 300mm lens would have the same reach on an APS-C camera as a 450mm lens on FF would have. (I could be wrong, but this is just how I've learned it. I'm not an expert :P )
04-24-2013, 02:11 PM - 1 Like   #22
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QuoteOriginally posted by atupdate Quote
Therefore, focal length effects you see on the links I posted should be the same on an APS sensor or full frame camera. No need to add a 1.5 crop factor to the images as many of the websites suggest. I'm thinking correctly here aren't I?

Tim
Yes and no.

Focal length is just that, it's the distance between the focus point and the film or sensor plane. It's an absolute measurement made with no regard to crop factor. So whether you're shooting a large format view camera, a medium format camera like the 645D, a full frame camera like the K1000, or even something as small as the Q, the focal length is measured from the same two points, the film plane, and the focal point in the lens. Where it gets a little confusing is when one starts describing lenses as "normal" or "wide" or "tele" or "portrait", you have to qualify those terms with the format that you're shooting. For example 300mm is considered a standard telephoto length for 35mm film and full frame digital, and a super tele for APS-C, but you may be surprised to learn that it's considered a "normal" lens on an 8x10 view camera. That's because the diagonal of an 8x10 inch negative is 325mm. Therefore a 300mm lens on a large format camera will create the same amount of perspective that you would observe with your own eyes if they were in the same position as the film plane. (Notice I didn't say the same angle of view, only perspective)

I looked at all three articles, and they are all using full frame cameras. So the focal lengths that they give are in terms of that format.

Now, to calculate for APS-C, such as current Pentax cameras utilize, you could do one of two things. You could crop the image by 33%, which would show you the image as it would be viewed on an APS-C camera taken from the same position as a full frame; or you could multiply the focal length given by 1.5, and that would give you the perspective that you would achieve with the same focal length and same framing on APS-C as on a full frame.

Last edited by maxfield_photo; 04-24-2013 at 02:25 PM.
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