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08-14-2010, 08:32 PM - 1 Like   #46
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QuoteOriginally posted by Hannican Quote
I'm not doing portraits but "Candids".
There's a basic equation that involves subject and frame sizes, camera-to-subject distance, and focal length. The right single (prime) focal length for your candids depends on how far away you're shooting from.

The equation is: F = (i * d) / s

where F is focal length, i is image size, s is subject size, and d is distance

Let's say you want frame-filling head shots. Depending on the fatness of the hair, such a subject (portrait mode) might be 360mm / 14 inches wide. An APS-C frame is ~18mm wide (portrait mode). (I chose these numbers for simple calculation.)

If you shoot from 1m away, we get: F = (18 * 1000) / 360 = 50mm
If you shoot from 2m away, we get: F = (18 * 2000) / 360 = 100mm

Thus I suggest a Samyang or Helios 85/1.4. You can't argue with the numbers.

08-19-2010, 08:31 AM   #47
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QuoteOriginally posted by Hannican Quote
Each lens serves its purpose in my line-up, with the DA 50-135 being the only exception, since it's larger than I feel like carrying anywhere, and too intimidating to be bringing around to parties and such. It's given me some great shots of my cat and I got some amazing sand dune photos from Death Valley with it, but I don't want to lug it around if I can use something else.
...
Thanks for the advice everyone! I'm leaning toward that DA 40 now... the pancake sounds interesting =)
Pictures of your cat is also a purpose!!!
- I want to use it for candid portraits of my children!!!

QuoteOriginally posted by RioRico Quote
There's a basic equation that involves subject and frame sizes, camera-to-subject distance, and focal length. The right single (prime) focal length for your candids depends on how far away you're shooting from.

The equation is: F = (i * d) / s

where F is focal length, i is image size, s is subject size, and d is distance

Let's say you want frame-filling head shots. Depending on the fatness of the hair, such a subject (portrait mode) might be 360mm / 14 inches wide. An APS-C frame is ~18mm wide (portrait mode). (I chose these numbers for simple calculation.)

If you shoot from 1m away, we get: F = (18 * 1000) / 360 = 50mm
If you shoot from 2m away, we get: F = (18 * 2000) / 360 = 100mm

Thus I suggest a Samyang or Helios 85/1.4. You can't argue with the numbers.
I kind of double checked the physics/mathematics by going to a shop early this week and try it out myself, mainly because I was concerned that 50-135 would be too long for my purpose. Those F numbers are the F numbers on the lens, or do you still have to multiply them by 1.5x (crop factor)? You use APC-C frame sizes, so you should be right, but don't know if all the lens manufactoring companies know these physics...

Either way, I concluded that at 3-4 m, zoomed up to 135 mm on the lens (35 mm FF equivalent of ~200 mm) I could , fill view finder with A4 catelog (comparable to size of face). So within the accuracy of my experiment, I confirmed your theory .

But now I can also calculate how far away I have to be, to be able to catch full body length of my oldest daughter. Still less than one meter, but I want to use this lens for a couple of years, so let me take 1.5 m and lens zoomed out as much as possible.

F = (18 * Distance) / 1500 = 50mm
18 * Distance = 50 * 1500
Distance = 50 * 1500 / 18 = 4.2 m!!!

So if you want to do full body portraits with a 50 mm lens, you need to be more than 4 meters away from you model. (more than I expected...)

How would brokeh of DA*135 mm F2.8 compare with 50 mm F1.5 (and 30 mm F1.4, e.g. from Sigma)?

Last edited by JoepLX3; 08-19-2010 at 08:37 AM. Reason: Added a question
08-19-2010, 09:11 AM   #48
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QuoteOriginally posted by JoepLX3 Quote
So if you want to do full body portraits with a 50 mm lens, you need to be more than 4 meters away from you model. (more than I expected...)
I don't know anything about that formula, but the answer is about right. And it looks like the size of the sensor is part of the formula, so the formula is already accounting for the "crop factor". In fact, it would be an extremely odd formula if it only happened to give the right answer for one sensor size and required adjusting focal length to work with any other sensor size.

I think one of the previous posters had it right, I have to say - you really shouldn't be worrying abut which expensive lenses to buy until you gain some actual real world experience with what different focal lengths are like, also with how big different lenses are and how you feel about them, how you feel about changing lenses, and so forth. All the formulas in the world won't really be tell you what you need to know. I think you should just get a camera and the kit lens or lenses it comes with and use these for a while to gain the sort of experience you'll need to better understand your own requirements. Otherwise, chances are very good you'll end up making an expensive mistake, no matter how much research you try to do up front or what you end up deciding. Not that there isn't a possibility you'll happen upon the "right" answer for you, but it's just that without a little real world experience, it's really impossible to put all these numbers into context.
08-19-2010, 09:35 AM   #49
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Yeah Marc, I guess you are right. I have some experience (SLR + LX3), which is IM(h)O sufficient to go for Fast tele zoom (50-135/150 mm F2.8), but I indeed can't figure our which prime I should start playing with just now.

On the other hand I know I want to push my development by not going for a 18-250 mm lens. And with the fast tele zoom icw with 18-55 mm kit lens, I also want to add a fast prime in 16-60 mm range and later maybe also something very long e.g. 500 mm F8 or a very wide like fisheye. Guess it will be best to start with my fathers 50 mm F2 manual focus lens!!! And/or a cheap use one a little wider,

08-19-2010, 09:40 AM   #50
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If you are on a budget, then you cannot go wrong with a 50mm manual focus, on a digital camera with the crop factor they are excellent lenses for portraiture
08-19-2010, 10:06 AM   #51
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I will buy my father a special beer!!!
08-19-2010, 08:49 PM   #52
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Yes, a Fast Fifty (or three) is always good to have, and manual primes are still CHEEP!! Or in your case, an absolutely free 50/2. That's a good place to start. Other handy and cheap glass will be 2.8's around 24-28mm, 35mm, and the ever-amazing Helios-44 58/2 for ~US$25 (a bit more in PK mount).
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _

The formula, rewritten (courtesy of FIELD PHOTOGRAPHY by AA Blaker) -- Let's take a different approach. What's the shooting distance for a full-body shot at various focal lengths?

d = (F * s) / i

where d is the camera-to-subject distance, F is the focal length, s is the subject size, and i is the image size (on the sensor/film frame). In portrait mode, the APS-C sensor is ~24mm high, and we'll take 1m current height and 1.5m projected height of your daughter as the subject sizes. Let's use the kit lens at 18mm. We get:
d = (18 * 1000) / 24 == 750mm = 30 inches, that's 2 1/2 feet
d = (18 * 1500) / 24 = 1125mm = 45 inches, just under 4 feet
To get my 76 inches / 1.9 m into the shot, you'd have to back up a bit more:
d = (18 * 1900) / 24 = 1425mm = 57 inches, just under 5 feet
So the 18-55mm kit lens is quite appropriate for both full-body and full-face shots within the 1-2m distance range. Just don't shoot me; your lens will likely break. Anyway, keep track of which focal lengths you use on the 18-55; that will give you an idea of what primes to go for.
08-19-2010, 09:01 PM   #53
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My favorites for K mount portraits, FWIW,

1. FA77Ltd/1.8--keeps a respectful distance on APS-c, great bokeh and large aperture focus, pixie dust. Nice on my LX as well. My hands-down favorite for kids.

2. Cosina 55mm/1.2. Great low light lens, and the OOF effects at F1.2 are super. For some reason, it also seems to be one of the more consistent manual lenses for green button exposure.

3. SMC K 135/2.5. Another pixie dust lens for me. It is great for the sneaky portrait from across a large room on APS-c, and for a slightly long portrait on film. It seems to draw character out of a face. I especially love it for older subjects.

I use all of these for film or digital. My other favorite is the 150mm for the 645, but that is another forum.

08-20-2010, 12:17 AM   #54
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QuoteOriginally posted by GeneV Quote
My favorites for K mount portraits, FWIW,

1. FA77Ltd/1.8--keeps a respectful distance on APS-c, great bokeh and large aperture focus, pixie dust. Nice on my LX as well. My hands-down favorite for kids.

2. Cosina 55mm/1.2. Great low light lens, and the OOF effects at F1.2 are super. For some reason, it also seems to be one of the more consistent manual lenses for green button exposure.

3. SMC K 135/2.5. Another pixie dust lens for me. It is great for the sneaky portrait from across a large room on APS-c, and for a slightly long portrait on film. It seems to draw character out of a face. I especially love it for older subjects.

I use all of these for film or digital. My other favorite is the 150mm for the 645, but that is another forum.
my favorites are almost the same as yours except it's a different version but are somehow identical in a way of what you have and like about them.

1. M85/2 - about as good as your 77.
2. A50/1.2 - same aperture speed opening. but with different character.
3. FA 135/2.8 - slightly slower cousin of the K135/2.5 and a bit less sharp but renders the same awesome results.
08-20-2010, 01:01 AM   #55
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That means if I go for the DA*50-135 mm F2.8 then I need to get a 50 mm F1.x?
- To replace/upgrade/extend the 18-55 kit lens I was thinking about something wider (30 mm F1.y), but I will start with my fathers 50 mm F2 (manual focus)

Can I decently use the DA* 50-135 mm F2.8 for marco's as well (probably icw extention tube)?

Joep
08-20-2010, 06:28 AM   #56
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QuoteOriginally posted by Pentaxor Quote
my favorites are almost the same as yours except it's a different version but are somehow identical in a way of what you have and like about them.

1. M85/2 - about as good as your 77.
2. A50/1.2 - same aperture speed opening. but with different character.
3. FA 135/2.8 - slightly slower cousin of the K135/2.5 and a bit less sharp but renders the same awesome results.
I could be happy with that set.

Since I got first the DA15 and then the DA12-24, I'm also getting more interested in wider angle full-body portraits taken from a lower perspective. The main problem with these shots is that it is hard to isolate from the background without pp or a very specialized lens.
08-20-2010, 10:06 AM   #57
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QuoteOriginally posted by GeneV Quote
I could be happy with that set.

Since I got first the DA15 and then the DA12-24, I'm also getting more interested in wider angle full-body portraits taken from a lower perspective. The main problem with these shots is that it is hard to isolate from the background without pp or a very specialized lens.
that is also the concern about wider lenses as far as subject isolation is concerned. but anything with a background, the wide lens is perfect. I think the Sigma 20/1.8 is the closest we have for a wide angle that has the best full body subject isolation capacity.
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