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johnnyison
06-13-2005, 10:20 PM
Question about lens mm:

I understand that with the D70 if you use a regular Nikon 28mm lens, you must multiply by a factor of 1.5, so its really a 42mm lens.

What about the lens that is optionally included with the D70 kit, the 18-70mm lens, is it really 18-70 or is it a 27-105mm lens?

I really want to take panoramic pictures but I'm a little confused with this mm thing

TheObiJuan
06-13-2005, 11:12 PM
the 18-70 does not reflect the crop factor, so it is a 27-105mm lens.

erichlund
06-14-2005, 09:12 AM
No, it's still a 28mm lens. It just acts something like a 42mm focal length because the glass crops out the center of the image. There are some advantages and disadvantages to this.

Advantages: You get the longer focal length at the same speed of the wider glass. You lose a lot of the edge distortion artifacts common to much consumer glass. You have less weight than a real 42mm lens (this comes more into play with long focal lengths).

Disadvantages: It's much harder to get real wide glass because wide glass is more prone to distortion, vignetting and other bad things, so wide is costly. Some lenses (e.g. Nikkor DX) are designed for the new format, and they are useless if you later move to a full frame camera. This is especially true of the wide angle lenses.

Could go either way: Depth of field is greater because of the smaller sensor size. You're superb bokeh 85mm f1.8 may not work quite as well for portraits, but it's easier to get everything "in focus" on landscapes.

One thing that wasn't really answered the other day was whether or not the compression effect moves with the apparent focal length. In full frame, you use 80-120mm for portraits because it moves the camera away from the subject and it has a slight compression effect so things like noses don't look so "extended". For instance, the 50mm lens now has a 75mm lens crop. This puts it close to the ideal range for portraits, but does it now have 75mm compression or 50mm realism. I contended that with the crop, you now have to move further away from the subject, so the variations in facial depth are a smaller proportion of the overall distance from the focal plane, therefore you should have 75mm compression. But I don't have any evidence or physics to back it up, so I'm just guessing. Anybody?

Cheers,
Eric

Warin
06-14-2005, 07:49 PM
Depth of field and actual focal length dont change, so the 50mm lens @ an apparent 75mm field of view still is not the best portrait lens. My 85mm f/1.8 is extended to a 127.5mm FOV, but retains a very pleasing depth of field effect for portraiture. I just need to move back a little farther.

The actual optical properties of the lens dont change... just the apparent field of view.

thesween
06-14-2005, 09:12 PM
I'm totally digital now, but I can sure remember a time if you wanted to zoom, you zoomed with your feet. Interesting to see that the concept is stiill alive. In my 25+ years of photography, there are maybe five frames I am REALLY, REALLY proud of, and four of those were taken with a 50mm lens on a completely manual body. Okay, that aside, God, I love the D70!

jeisner
06-14-2005, 09:48 PM
I'm totally digital now, but I can sure remember a time if you wanted to zoom, you zoomed with your feet. Interesting to see that the concept is stiill alive. In my 25+ years of photography, there are maybe five frames I am REALLY, REALLY proud of, and four of those were taken with a 50mm lens on a completely manual body. Okay, that aside, God, I love the D70!

I think having to ZOOM with your feet (so to speak) actually more often than not results in a better picture as more thought has to go into framing the shot correctly.. Zooming to frame can make you lazy, well makes me lazy LOL, which is why I use primes 90% of the time...

D70FAN
06-14-2005, 10:53 PM
I think having to ZOOM with your feet (so to speak) actually more often than not results in a better picture as more thought has to go into framing the shot correctly.. Zooming to frame can make you lazy, well makes me lazy LOL, which is why I use primes 90% of the time...

90% of your shots are using a fixed focus lens? You must be one fast dude. Both running and changing lenses. ;)

With a zoom I can go from 18mm to 125mm in about a second and shoot, I'm not sure I could cover that kind of ground, in that time, physically.

While I agree that shooting with a 50mm or 105mm fixed focus lens can net some beautiful shots, I don't think I could take 90% that way.

Kudos for those who can.

jeisner
06-15-2005, 12:08 AM
90% of your shots are using a fixed focus lens? You must be one fast dude. Both running and changing lenses. ;)

LOL not such a fast runner, but I do change lenses reletively often, it all depends. I do have an assortment of primes to switch between though - 20mm, 28mm, 50mm, 105mm, 135mm, 200mm (I will get a 35/2 when I can afford it)...

I actually also have the same Sigma 18-125 lens you have and I do use it from time to time, I guess it is just a personal preference, it depends where I am too, sometime it is not feasable to keep changing lenses (and take my time) and I will use the 18-125 in those situation and I am considering buying the Sigma 135-400 too...

I do think the fact that it forces me to take my time is the major benefit to me personally, it just slows me down a notch or two ;-)

D70FAN
06-15-2005, 06:58 AM
LOL not such a fast runner, but I do change lenses reletively often, it all depends. I do have an assortment of primes to switch between though - 20mm, 28mm, 50mm, 105mm, 135mm, 200mm (I will get a 35/2 when I can afford it)...

I actually also have the same Sigma 18-125 lens you have and I do use it from time to time, I guess it is just a personal preference, it depends where I am too, sometime it is not feasable to keep changing lenses (and take my time) and I will use the 18-125 in those situation and I am considering buying the Sigma 135-400 too...

I do think the fact that it forces me to take my time is the major benefit to me personally, it just slows me down a notch or two ;-)

I guess that my objective over the years is to travel as light as possible. Having logged almost 2.5 million miles in the past 15 years it has become almost obsessive. I do pack the 50 and the 70-300, but rarely use them when I'm traveling.

Guess it's different strokes, but I can appreciate why you use primes as much as possible.

Again, Kudos.

erichlund
06-15-2005, 09:34 AM
Depth of field and actual focal length dont change, so the 50mm lens @ an apparent 75mm field of view still is not the best portrait lens. My 85mm f/1.8 is extended to a 127.5mm FOV, but retains a very pleasing depth of field effect for portraiture. I just need to move back a little farther.

The actual optical properties of the lens dont change... just the apparent field of view.

OK, I understand that, but it doesn't really answer the question. The question is, is the compression effect a lens property, based on somthing like glass shape, or is it simple geometry. I contended above that having to move further away to frame you subject is what causes the compression effect, not the nature of the lens type.

Part of this contention is because the net "curve" shape of the 50mm lens on a dSLR has to be at least approximately the same as the curve of the 75mm lens on the ff slr, because they must both focus the same object at the same distance. I can see some obvious reasons this contention might be wrong (front of lens to focal plane differences, for one), and I don't even want to think about the math to prove it, either way. But, I think there's room to contend that compression effect is a geometry issue, not an optical property. I guess I'll have to think about some sort of practical test.

Cheers,
Eric

Warin
06-15-2005, 10:17 AM
I have no way to prove it, but if it were simply feometry, then the 50mm @ 75mm on a DSLR should move you back far enough to make it a decent portrait lens, which it doesnt (from personal experience). I think it is a property of the optics. Perspective is different though. Longer lenses change perspective at the same field of view, and that is pure geometry.

TheObiJuan
06-15-2005, 11:47 AM
OK, I understand that, but it doesn't really answer the question. The question is, is the compression effect a lens property, based on somthing like glass shape, or is it simple geometry. I contended above that having to move further away to frame you subject is what causes the compression effect, not the nature of the lens type.

Part of this contention is because the net "curve" shape of the 50mm lens on a dSLR has to be at least approximately the same as the curve of the 75mm lens on the ff slr, because they must both focus the same object at the same distance. I can see some obvious reasons this contention might be wrong (front of lens to focal plane differences, for one), and I don't even want to think about the math to prove it, either way. But, I think there's room to contend that compression effect is a geometry issue, not an optical property. I guess I'll have to think about some sort of practical test.

Cheers,
Eric


but optics do play a role. when shooting at specific scene with a 50mm on a 1dsmk2 and 20D you will get very different pictures. When the 20D is moved back to adjust for the difference in field of views, the actual look will be diffrent still. Popular Photography & Imaging did a test like this and the results are very obvious.

If you put sigma's new 30mm and adjust slightly for the difference in focal length, the 2mm I believe, then you still will have different images.

The Duke
06-26-2005, 06:37 AM
The 18-70mm lens supplied with your D70 has a true focal length of 18-70mm (+/- 5%).

Because the majority of DSLR owners have come from a 35mm background manufacturers quote a 35mm equivilent figure, (in this case 27-105mm) but the box will always state the lenses true focal length.

If you use the Nikon AF 28 f/2.8D lens on you D70, you will still retain the same depth of field but will have the apparent view of a 42mm lens. (1.5x)

To fully understand Focal length click here (http://bobatkins.photo.net/photography/technical/measuring_focal_length.html)