Prime lenses for the dSLR

HarveyMushman · March 10, 2005

I need some schooling.

My Nikon D70, like a lot of dSLR cameras, has a magnification factor of 1.5, which essentially means all my images are cropped by the Nikon software before I even see ‘em. It is said that a dSLR user should take the focal length of a given lens and multiply that number by 1.5 to determine the “actual” or “effective” focal length. I’m leaving a lot out here, I know. My question: Is a 28mm lens on my D70 optically equivalent to a 42mm lens on a 35mm SLR? Does a 70mm “become” a portrait-friendly 105mm on my camera? Or are things not that simple?

As you may have guessed, I’m considering shopping for some (used) prime lenses, but I want to know what I should be looking for first.

Harryb · March 10, 2005

Hey Tim,

The Nikon cameras have a 1.5 mag factor so my 3000mm becomes a 450mm my 50mm becomes a 75mm and so on .Thta is a factor you will have to consider when choosing your pirmes.

Shay Stephens · March 10, 2005

For all practical purposes, yes, a 70mm lens can be treated like 105mm lens and a 28mm can be treated as if it were a 42mm. Just take the focal length of whatever lens you are considering and multiply by 1.5.

However, it is not a software issue, this is a hardware/optical crop. The portion that is cropped is outside the image sensor and is never recorded.

HarveyMushman wrote:

I need some schooling.

My Nikon D70, like a lot of dSLR cameras, has a magnification factor of 1.5, which essentially means all my images are cropped by the Nikon software before I even see ‘em. It is said that a dSLR user should take the focal length of a given lens and multiply that number by 1.5 to determine the “actual” or “effective” focal length. I’m leaving a lot out here, I know. My question: Is a 28mm lens on my D70 optically equivalent to a 42mm lens on a 35mm SLR? Does a 70mm “become” a portrait-friendly 127mm on my camera? Or are things not that simple?

As you may have guessed, I’m considering shopping for some (used) prime lenses, but I want to know what I should be looking for first.

HarveyMushman · March 10, 2005

Shay Stephens wrote:

However, it is not a software issue, this is a hardware/optical crop. The portion that is cropped is outside the image sensor and is never recorded.

Thanks for the clarification. I told you I needed schooling.

bkriete · March 10, 2005

We'll learn you up real good.

cmr164 · March 10, 2005

HarveyMushman wrote:

I need some schooling.

My Nikon D70, like a lot of dSLR cameras, has a magnification factor of 1.5, which essentially means all my images are cropped by the Nikon software before I even see ‘em. It is said that a dSLR user should take the focal length of a given lens and multiply that number by 1.5 to determine the “actual” or “effective” focal length. I’m leaving a lot out here, I know. My question: Is a 28mm lens on my D70 optically equivalent to a 42mm lens on a 35mm SLR? Does a 70mm “become” a portrait-friendly 105mm on my camera? Or are things not that simple?

As you may have guessed, I’m considering shopping for some (used) prime lenses, but I want to know what I should be looking for first.

"Portrait friendly" is really defined by the perceived perspective in the features and that is determined by how far you stand from the subject. The lens the gives you the best use uncropped of the frame thus becomes a portrait lens. For the tiny sensors in consumer dcams that might be 9mm and for a medium format (6x6) it might be 300mm. (note #1) The 35mm and the APS sized D70 or drebel fall inbetween.

All of which is to say yes you can just multiply by 1.5 for your 35mm equivalent. HOWEVER, when considering depth of field (DoF) the actual natural focal length of the lens should be considered.

NHBubba · March 10, 2005

For what it's worth, my own experiences.. I previously had a Pentax K1000 film camera fitted w/ a 50mm f/2 lens. Nothing special, yet a great combo in my mind and it was a lot of fun to play w/ this lens. When I finally found the pennies and dimes to get a digital I settled on the DRebel, which has a 1.6x 'crop factor' much like your Nikon's 1.5x. I planned on getting the kit lens w/ the camera but wanted a simple fast prime to play w/. Basically I wanted to use my Pentax 50/2 on my Canon. Well, that just isn't gonna happen, so I went out and bought a Canon 35/2 instead. The crop factor makes the 35 just a touch more tele than 50mm on my DRebel, but I find it just as useful. The FOV and DOF both seem comparable. .. So yeah, I'd say things are really that simple..

HarveyMushman · March 10, 2005

NHBubba wrote:

For what it's worth, my own experiences.. I previously had a Pentax K1000 film camera fitted w/ a 50mm f/2 lens. Nothing special, yet a great combo in my mind and it was a lot of fun to play w/ this lens. When I finally found the pennies and dimes to get a digital I settled on the DRebel, which has a 1.6x 'crop factor' much like your Nikon's 1.5x. I planned on getting the kit lens w/ the camera but wanted a simple fast prime to play w/. Basically I wanted to use my Pentax 50/2 on my Canon. Well, that just isn't gonna happen, so I went out and bought a Canon 35/2 instead. The crop factor makes the 35 just a touch more tele than 50mm on my DRebel, but I find it just as useful. The FOV and DOF both seem comparable. .. So yeah, I'd say things are really that simple..

Exactly. I can get a Nikkor 28/2.8 or 35/2 for not too much money. I want a simple, good lens that I can just walk around with and experiment. The lack of zoom or telephoto will force me to use my head and feet to compose a shot. Back to basics with my digital camera.

ridetwistyroads · March 11, 2005

HarveyMushman wrote:

Exactly. I can get a Nikkor 28/2.8 or 35/2 for not too much money. I want a simple, good lens that I can just walk around with and experiment. The lack of zoom or telephoto will force me to use my head and feet to compose a shot. Back to basics with my digital camera.

I hear ya there HM. The ONLY lens I have currently for the d70 is a 25 sumthin y/o nikkor 50mm prime. No AF, no data for the camera. It turns the camera into a 25 sumthin y/o camera, more or less! But it is alot of fun, the lens is SO clear, and it really, really makes one work for their shots. I have enjoyed the limitations, actually.

I didn't get the kit lens because I had a very sweet deal on body alone (new - $675), so I'll be adding some different glass sooner or later. I had my eye on a 24-85, and maybe something longer as well, but, I have a hard time being motivated! I love that 50mm lens, it's just so crisp!! (Course, having things like AF and the ability to actually USE that camera like it was intended do come into play. I don't even have a meter!)

Prime lenses for the dSLR

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