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05-07-2008, 09:26 PM   #16
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QuoteOriginally posted by k100d Quote
nice test steve ... good thing i got it right
maybe a lens isn't the best thing to use as a subject tho, too bad you didn't use ketchup bottles :P
So...which is which? There is a clue, but it is has nothing to do with perspective.

05-07-2008, 10:28 PM   #17
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QuoteOriginally posted by Kguru Quote
A person with a zoom lens framing the same picture once at 30mm and once at 45mm, he will get similar foreground in the pics but different perspective/background. Your statement is correct only for this case and it's nothing to do with crop factor, it's because the photographer moved.

OTOH, one person with 30mm on 1.5x crop and one person with 45mm on film camera shooting from same spot will get similar pics with similar perspective.

I need to turn this into my signature
How would pictures compare from the same lens?

One from a FF body and 30mm lens and one from a 1.5 crop body and a 30mm lens, both from the same distance.

I think I'm beginning to understand ... If distance dictates perspective, what is the difference between lenses of different focal lengths?

I'm guessing it's too early for me to understand bellows and such ...
05-07-2008, 10:48 PM   #18
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QuoteOriginally posted by superbass Quote
How would pictures compare from the same lens?
One from a FF body and 30mm lens and one from a 1.5 crop body and a 30mm lens, both from the same distance.
In this case the crop body gives a narrower view but similar perspective (ie. both foreground and background narrowed).

Another way to figure this is take this FF pic, crop the perimeter by 1.5x (=keep the inner 67%) you get essentially the same pic as from 1.5x crop body with same lens. Now you see why it's called 1.5x crop
05-07-2008, 10:54 PM   #19
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QuoteOriginally posted by superbass Quote
If distance dictates perspective, what is the difference between lenses of different focal lengths?
Easiest way to understand this: mount a zoom, stand at same spot, zoom in & out.

Longer FL = zooming in = narrower angle = larger subject (and larger background too).

05-07-2008, 10:57 PM   #20
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As this thread is headed towards yet another verbal discussion of perspective and varying opinions, here for the benefit of the threadstarter is a link to some photos by a Singaporean K20D user using a 30mm on Clubsnap. I think pictures says it all.

ClubSNAP Photography Forums - View Single Post - Please share your photos by a Pentax camera here :)

The images are great for full body shots but I would personally avoid using this focal length for torso or head and shoulder portraits. Because of the FOV care needs to be taken so that no background clutter intrudes in the framing.
05-07-2008, 11:03 PM   #21
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I noticed you used similar instead of identical, so I'm deducing that a 30mm lens on a 1.5 crop body will not give you the exact same picture as a 45 mm lens on a ff body at the same distance. However, it will give you similar perspective and framing when used from the same distance.

From what you just said, will the difference between the two pictures will be a slightly narrower angle and the background blur (I remember reading somewhere that higher focal lengths give you a blurrier background) ?

By the way, thanks for explaining this and sorry for thread jacking, but it's somewhat relevant information for lurkers and myself.
05-08-2008, 04:16 AM   #22
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QuoteOriginally posted by stevebrot Quote
Ok...tell me my penance and I will comply...I have erred...

Here are two images taken with the kit lens at identical distance, angle, and camera setting. One was taken at 55mm and the other at 35mm. Both were cropped to enclose the same subject matter.

Tell me (without looking at the exif), which is which:
Steve
The lower is the 55mm shot. It's easy
05-08-2008, 07:37 AM   #23
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QuoteOriginally posted by gkopeliadis Quote
The lower is the 55mm shot. It's easy
And the prize goes to gkopeliadis. The perspective is similar (identical?), but the depth of field is not.

Steve

05-08-2008, 07:38 AM   #24
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QuoteOriginally posted by superbass Quote

By the way, thanks for explaining this and sorry for thread jacking, but it's somewhat relevant information for lurkers and myself.
This little aside has been useful for me as well.

Steve
05-08-2008, 12:15 PM   #25
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I wasn't entirely clear in the first post.
I'll shot full body or upper body portraits most of the time and I'm not afraid to do a little HEAVY cropping. You'd be surprised to find out how large you could print an 1.5-2 MP image using fractal based resizing software.
I know the Pentax 50mm f/1.4 if the better lens but the 30 mm Sigma is casting some kind of magic on me. Maybe is the fact that I'm attracted by the wider end of the optics.
Right now the balance is (PENTAX)(45%)<----->(65%)(SIGMA).
Edit:
QuoteOriginally posted by creampuff Quote
As this thread is headed towards yet another verbal discussion of perspective and varying opinions, here for the benefit of the threadstarter is a link to some photos by a Singaporean K20D user using a 30mm on Clubsnap. I think pictures says it all.

ClubSNAP Photography Forums - View Single Post - Please share your photos by a Pentax camera here :)
That is EXACTLY what I'll shot the most.

Last edited by quantum; 05-08-2008 at 12:26 PM.
05-08-2008, 12:44 PM   #26
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FA31 is the Pentax way to go then
05-09-2008, 07:05 AM   #27
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24mm on a FF camera

QuoteOriginally posted by stevebrot Quote
The issue with feature exaggeration is a real one. Noses tend to grow and chins to recede. This is not a matter of distortion. Rather, it is a matter of perspective and cannot be corrected with PP.

Cheers!

Steve
steve, I do use 24mm on a FF camera a lot and it works out well. 24mm is a great focal length!



05-09-2008, 07:07 AM   #28
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QuoteOriginally posted by quantum Quote
I wasn't entirely clear in the first post.
I'll shot full body or upper body portraits most of the time and I'm not afraid to do a little HEAVY cropping. You'd be surprised to find out how large you could print an 1.5-2 MP image using fractal based resizing software.
I know the Pentax 50mm f/1.4 if the better lens but the 30 mm Sigma is casting some kind of magic on me. Maybe is the fact that I'm attracted by the wider end of the optics.
Right now the balance is (PENTAX)(45%)<----->(65%)(SIGMA).
Edit:

That is EXACTLY what I'll shot the most.
I have used sigma 30mm f1.4 for 3 years or so, especially on a trip to Thailand as well. This lens is great but it often lacks the impact and contrast needed in certain situations where it is needed.

But it is so compact and light. I actually kind of miss it in fact.
05-10-2008, 01:49 AM   #29
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I'm now 100% away from 50 mm lenses.
Now I just have to decide between the Sigma 30 mm or the fa31 ltd.
Considering the fact that I HATE using flash I may go for the sigma since it is a little faster. As for the lack of contrast... there is always Photoshop to give it some microcontrast/colordepth/anything else as long as it capture enough detail.
I also forgot to mention that the 31mm ltd is nowhere to be found in my country so I'll have to order it overseas.

Last edited by quantum; 05-10-2008 at 01:57 AM.
05-10-2008, 01:56 AM   #30
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I wouldn't worry about that difference between f1.4 and f1.8....honestly you're going to want to use these lenses stopped down to f2 AT LEAST for most portraits...just to sharpen up the image, and get any kind of workable DOF.

For portraits, I'd be most concerned with bokeh...I would think the 31/1.8 would have the edge.
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