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12-24-2016, 10:09 PM   #1
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F number relativity

Dumb title, probably a dumb question as well as the more knowledgeable will probably do a sigh and think "how come that you don't know that?" ... So, let me make this question reasonably clear so I can expect an answer I'm actually looking for instead of ... well... everything else...

Scenario: shooting a portrait/headshot/beauty shot
Lighting equipment: available

Lenses: Pentax M Macro 100mm F4 (1:2), Pentax D FA Macro 100mm F2.8 WR (1:1), Tamron 90mm Macro F2.8, Tamron 70-300mm Macro F4-5.6 and Sigma 17-50mm F2.8.
(the wider lenses I have are not suitable for the job)

Let's say I set up the lighting, model, background etc to desired arrangement. Set the ISO to 100-200 range, distance from the subject as required by the framing/composition and depending on the lens from the list above. F number, for sake of the argument set to F8. (might go up to F11 or so if I want to get more DOF)...

Let's (theoretically) compare the 100mm Pentax lenses. Both set to F8 and same ISO. (both lenses have the same FOV angle on my APS-C K-3 II) ... So...

Question #1: Should I expect any significant difference in results as one is F4 and the other F2.8 when wide open?

For some shots I expect the 100mm lenses to be too much and I have the other ones listed available.

Question #2: Can I expect the cheap 70-300mm Tamron zoom to behave reasonably well at 70mm and set to F8 or so?

Background story: I get to spend about three hours with a model who is not a professional, I make no money, she gets no money from all this, the only gain is the result we are hoping for and also hope for some good time doing it. If all goes well, she'll have a few great shots so she can feel good about herself when she looks on the framed print I intend to give her as a compensation for the time, patience and effort, I also get the right to print a few shots which I pick and keep them for my own collection of shots I can be proud of (if any). I want to use the time we have together for shooting, not looking at bad shots. Of course, I might end up with 3 or 4 hundred shots, but I expect that and I don't expect all of them to be "Wow!" I expect one of those to be like that. The perfect one. So, learning and preparing in time is what I'm trying to achieve here.
I have my job (designer/engineer/problem solver in my own company) and have no intention to go pro on photography but also suffer from that need for perfection in whatever I do. I might get a second chance to get that young woman for shooting but definitely not if I don't end up with at least one "perfect shot" or something very close to that. We already spent some time together chatting, I paid a lot of attention to her face, skin, eyes (size) and gestures so I can expect her to be relaxed in my company and we'll have a make-up person around as well which I consider to be a must in cases like this. I'll have to compensate her as well, so before I waste everyone's time and my money... I ask you..

12-24-2016, 10:21 PM - 1 Like   #2
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Let's see...

Q1: These lenses will be quite different if both are wide-open. F4 to F2.8 is a whole stop, and on a full-frame camera, it will show on your depth of field (on APS-C, too, but more so on 35mm). The newer lens will be better controlled for various aberrations, sometimes this comes across as a 'clinical' rendering. I'm not familiar with the 100mm M, but they're both Macro lenses, so you should expect fairly sharp images from wide-open, some might say too sharp.

Q2: If it's this lens:

Tamron 70-300mm F4-5.6 AF Di LD Macro Lens Reviews - Tamron Lenses - Pentax Lens Review Database

It seems to get mixed reviews. I wouldn't feel great paying a model and shooting with it.
12-24-2016, 10:32 PM   #3
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QuoteOriginally posted by lithedreamer Quote
Let's see...

Q1: These lenses will be quite different if both are wide-open. F4 to F2.8 is a whole stop, and on a full-frame camera, it will show on your depth of field (on APS-C, too, but more so on 35mm). The newer lens will be better controlled for various aberrations, sometimes this comes across as a 'clinical' rendering. I'm not familiar with the 100mm M, but they're both Macro lenses, so you should expect fairly sharp images from wide-open, some might say too sharp.

Q2: If it's this lens:

Tamron 70-300mm F4-5.6 AF Di LD Macro Lens Reviews - Tamron Lenses - Pentax Lens Review Database

It seems to get mixed reviews. I wouldn't feel great paying a model and shooting with it.
A1: I know that at one whole F stop the results can't be compared, but I'm much more interested in what happens when the same focal length is used at the same F stop? Basically I almost never use any of the lenses wide open except the Sigma 30mm F1.4 for shooting in a theatre, but even then, I move it a bit away from wide open..

A2: yup, that lens. I'm perfectly happy with it as it was like 70€ and in mint condition, and I don't really use it a lot, but when I do I really have good reasons for that (not too friendly insects in larger numbers), and I usually do get good results as long as I avoid shooting into direct light or high contrast things like tree branches with really bright sky as background
12-24-2016, 10:32 PM   #4
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I would most likely use the 17-50 for the wide to short telephoto range. ISO would be good around 200 to preserve the image quality (avoid graininess). The shutter speed for a posing model might be good at 125 to accommodate slight movements. The F stop is going to depend on your lighting and what depth of field you desire. If you shoot wide open at F2.8 for example, you will have a shallow depth of field and detail in all areas of the image may not be satisfied. You mentioned F8, you may want to start with that and do some test shots, adjusting the F stop setting as needed, which can be done without or with the presence of your model. Shooting should be done in Manual mode to avoid any misinterpretation of an auto mode. The adjustment range of your F stop and other settings will be dependent on the extent of your available light.

12-24-2016, 10:35 PM   #5
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As regards question 1, using a f/2.8 lens at f/8, and a f/4 lens at f/8--they should be similar as regards amount of light and depth of field (if same focus distance). If instead you started at about f/16 of f/22 and opened up the lens, as you get closer to the wide open setting you may expect better performance, and then within a stop or two from wide open increasing uncorrected aberations. But individual lens design will affect any comparison--it not being only about light transmission and depth of field.

More specifically about the two 100 mm Pentax lenses--I don't have/use either one--but there will be differences that you may or may not see yourself. But I think your own choices about distance and fstop will be the deciding parameters--and not the lens design.

Last edited by dms; 12-24-2016 at 10:50 PM.
12-24-2016, 10:40 PM   #6
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QuoteOriginally posted by C_Jones Quote
I would most likely use the 17-50 for the wide to short telephoto range. ISO would be good around 200 to preserve the image quality (avoid graininess). The shutter speed for a posing model might be good at 125 to accommodate slight movements. The F stop is going to depend on your lighting and what depth of field you desire. If you shoot wide open at F2.8 for example, you will have a shallow depth of field and detail in all areas of the image may not be satisfied. You mentioned F8, you may want to start with that and do some test shots, adjusting the F stop setting as needed, which can be done without or with the presence of your model. Shooting should be done in Manual mode to avoid any misinterpretation of an auto mode. The adjustment range of your F stop and other settings will be dependent on the extent of your available light.
I already did some test shots with my daughter as a model but she is very different from the model (different tone of skin and not too interested to act as a model - rather sitting there like an egg) so I got the basic starting positions for the mono lights and have a complete set of various light modifiers we can play with...
I found F8 to be a great starting F number as that gives me a great chance to get a clear and sharp shot of both eyes even if the head is slightly turned aside. At F6.3 can't really get both eyes to be perfectly sharp...
12-24-2016, 10:41 PM   #7
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QuoteOriginally posted by stein Quote
A1: I know that at one whole F stop the results can't be compared, but I'm much more interested in what happens when the same focal length is used at the same F stop? Basically I almost never use any of the lenses wide open except the Sigma 30mm F1.4 for shooting in a theatre, but even then, I move it a bit away from wide open..

A2: yup, that lens. I'm perfectly happy with it as it was like 70 and in mint condition, and I don't really use it a lot, but when I do I really have good reasons for that (not too friendly insects in larger numbers), and I usually do get good results as long as I avoid shooting into direct light or high contrast things like tree branches with really bright sky as background
Gotcha. In that case, what I'd look for are some 'test chart reviews' that'd tip you off to where the lenses peak at. I think the D FA 100mm Macro peaks at around F4 or F5.6, and since the 100 F4 starts at F4, it likely doesn't hit its sweet spot until later. On the other hand, you're shooting portraits, and these are macro lenses, so the kinds of things that you'd gain from sweet spot apertures: increased sharpness and minimum vignetting, might not matter.

As for the zoom, as long as you know its limits and are personally happy with it, then that doesn't seem to be a problem, either.
12-24-2016, 10:51 PM   #8
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The Sigma could do just about everything from full body to head and shoulders for your shoot, Stein.

The wide open problems of all the lenses should disappear stopped down a couple of times.

As you say, you have to stop down anyway for DoF, you have good lights for f8 where the differences between lenses are minimal. Leave the ISO on 100, the shutter speed on 1/180s.

With the simple setup you're completely in command of, you can concentrate entirely on rapport with your model, getting the poses and expressions right.

Don't let an awkward silence happen, engage with her, not your camera, until the shots for each setup are finished.

The looks on her face will match her attitude towards you, so let optimism, warmth and creativity win over uncertainty and fiddling with camera gear. Ain't no one got time for that.

Good luck with it all!


Last edited by clackers; 12-24-2016 at 11:03 PM.
12-24-2016, 10:54 PM   #9
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QuoteOriginally posted by dms Quote
As regards question 1, using a f/2.8 lens at f/8, and a f/4 lens at f/8--they should be similar as regards amount of light and depth of field (if same focus distance). If instead you started at about f/16 of f/22 and opened up the lens, as you get closer to the wide open setting you may expect better performance, and then within a stop or two from wide open increasing uncorrected aberations. But individual lens design will affect any comparison--it not being only about light transmission and depth of field.

More specifically about the two 100 mm Pentax lenses--I don't have/use either one--but there will be differences that you may or may not see yourself. But I think your own choices about distance and fstop will be the deciding parameters--and not the lens design.
Thanks. This is what I was looking for

Color rendering and final appearance of the shot will always be different with different lenses but I was definitely more into the technical aspect of the apperture thing...

There is one more thing (at least when the M and the D FA are in the game) but that is something I'll have to figure out on the way as I'm used to do all my macro shots with manual focus and manual settings. If I get a good connection with the model, I might use manual focusing as well... Then only the difference in color rendering will be the difference between the two lenses.

---------- Post added 12-25-16 at 07:41 ----------

QuoteOriginally posted by clackers Quote
The Sigma could do just about everything from full body to head and shoulders for your shoot, Stein.

The wide open problems of all the lenses should disappear stopped down a couple of times.

As you say, you have to stop down anyway for DoF, you have good lights for f8 where the differences between lenses are minimal. Leave the ISO on 100, the shutter speed on 1/180s.

With the simple setup you're completely in command of, you can concentrate entirely on rapport with your model, getting the poses and expressions right.

Don't let an awkward silence happen, engage with her, not your camera, until the shots for each setup are finished.

The looks on her face will match her attitude towards you, so let optimism, warmth and creativity win over uncertainty and fiddling with camera gear. Ain't no one got time for that.

Good luck with it all!
Thanks

I have two Jinbei 300WS mono lights (adjustable in 60 steps independently) plus several other constant sources of light (for additional lightning if required), several backgrounds and all the its and bits I could need (soft boxes, reflectors, color gels, diffusers) and of course, sufficient amount of "juice" (D-BG5 with two sets of batteries) and two 32G SD cards in my K-3 II so I'm good with that. Making photos of people is much like driving a car - 80% psychology, 20% technical stuff. those 20% should not be the obstacle but should simply be something you simply do or don't for reasons you shouldn't think about while you do it. Those remaining 80% is the harder part if you have problems with your approach to people. I don't think I'm one of those. If I'd decide to approach someone and say "I'd like to make photos of you" I would most likely end up beaten up in a small and dark street. I never do that. I can't tell how I do that because it always depends on many things, but so far, I'm okay and all the woman I have ever asked for shooting decided to say yes, I'd like that... Guess there is something in the way I behave and the fact I never have the camera in my hand when I make an approach for the first time.
There is a set of rules I have and I clearly explain all of them when we get to the point that they ask me "how does it work?"... I'm pretty much serious and explicit about these things... No nudity or "adult content" is expected from the model. If they want to get their nude shot, they have to tell me that and ask for it - I will never suggest or ask for that. I'm married for like 30 years and have a wife and daughter so I'm not interested to get in any sort of relationship with the potential model except for being behind the camera. No touching. If I ever need to get close and say, move/straighten the hair, I do that with my left hand in a white cotton glove. I always suggest that the model comes with a friend or someone who will give additional feeling of being safe but that person should not interact by any means except with being there in the "background". I always explain what I want to get, and ask the model is there anything she wants to get in terms of final results (some woman do have really clear ideas about that, some have absolutely no preference) and then we agree on my sign language and what does mean when I ask her to turn her head to one or the other side or something like that. I use a whole set of movements and gestures to do that as they usually have absolutely no clue which side is "left" when I just say "left", so I move my head and my hand in front of my face in the direction I want them to move their head. Of course, I never forget to show them some of my printed/framed work and show them visually what I'm looking for so they can understand as clearly as possible what do I mean when I say "like it was shot in the 20's or 30's years of 20th century" And there are other things we discuss in order to get no mess anytime later...

For example, this is one of requests I had and the model was absolutely amazed and really happy about it...

Passion 2 | Robert Stein | Flickr

Last edited by stein; 12-24-2016 at 11:43 PM.
12-24-2016, 11:42 PM   #10
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A decent lens stopped down is hard to tell apart from a great lens. Check out the post Your favourite image, 35mm images.
12-24-2016, 11:46 PM   #11
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Q1: Your depth of field on both 100mm lenses will result in identical depth of field. Differences in sharpness will be virtually undetectable. However, the f/2.8 will give you a brighter viewfinder and even shallower depth of field while focusing and thus aid in either manual focusing better or faster more reliable AF. So technically no difference, but the f/2.8 may in practice give you better results because youʻll nail the focus.

Q2: Yes, you can expect the 70-200mm Tamron to give you decent results at 70mm f/8 as long as youʻre not comparing it to a prime or for example, cropped similarly to the 100mm prime. Keep in mind that technical results are meaningless if a softer lower contrast rendering improves your aesthetic goals.
12-25-2016, 12:13 AM   #12
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QuoteOriginally posted by Alex645 Quote
Q1: Your depth of field on both 100mm lenses will result in identical depth of field. Differences in sharpness will be virtually undetectable. However, the f/2.8 will give you a brighter viewfinder and even shallower depth of field while focusing and thus aid in either manual focusing better or faster more reliable AF. So technically no difference, but the f/2.8 may in practice give you better results because youʻll nail the focus.

Q2: Yes, you can expect the 70-200mm Tamron to give you decent results at 70mm f/8 as long as youʻre not comparing it to a prime or for example, cropped similarly to the 100mm prime. Keep in mind that technical results are meaningless if a softer lower contrast rendering improves your aesthetic goals.
I wouldn't compare the cheap 70 Tamron zoom with any 500 prime, no expectations of that sort. Just thought asking is it worth using it at all. The answer is yes.
I shoot RAW and like it or not, do have to work on images after shooting, sometimes less (preferable) but sometimes more and the better choices I make in advance, the less time I'm wasting on lens changing, light moving/adjusting...
If I was a young woman sitting in front of a camera and watching the photographer being all messed up with his gear I'd start to feel uncomfortable. Definitely. So, I can't afford to that. It should be fun to do it and a sort of nice experience for both me and the model... One day somebody could offer me to do this for some financial compensation, but I don't hope for that neither is that my dream, goal, ambition, whatever. Still, I'm simply used to do it right. Sometimes I can afford smaller mistakes, but sometimes not... I can always afford to investigate and learn about something I know nothing about

---------- Post added 12-25-16 at 08:34 ----------

QuoteOriginally posted by swanlefitte Quote
A decent lens stopped down is hard to tell apart from a great lens. Check out the post Your favourite image, 35mm images.
Kind of ended up picking the DA 35mm prime, even though it wasn't the winner in the poll Tastes, tastes...
12-25-2016, 12:42 AM - 1 Like   #13
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You're sayin' all the right things, Stein, so fingers crossed for some nice keepers, you deserve them!

12-25-2016, 09:40 AM   #14
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In fact - if there's not any time limitation for either you or the model - you can try all the different lenses. And I'm sure this could be main part of the joy.

Don't forget to share the resulting portraits with us.
12-25-2016, 04:32 PM   #15
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QuoteOriginally posted by zzeitg Quote
In fact - if there's not any time limitation for either you or the model - you can try all the different lenses. And I'm sure this could be main part of the joy.

Don't forget to share the resulting portraits with us.
With extra time, and having nailed some standard shots needed for both your portfolios, wouldn't you use the now good relationship to attempt more adventurous poses, lighting setups and expressions?

I think we may have different philosophies, Zzeitg!

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