Should I sale my 85mm 1.8

When family is involved I find wider angles tells a story more so than a detailed tele photo shot.

OP, I'd keep the 85mm because its a great lens. You can get fantastic portrait photos with the 85mm w/ crop body.

Exercise the use of foot zoom in conjunction with using a zoom. For primes you have not choice but to use your feet My point is you'll learn composition much quicker if you force yourself to work the camera using your feet .

Stop being a bokeh junkie and stop down the lens to land the shot.

I'd rather buy a mint used Canon 24L before buying a sigma 35mm. On a crop I find the 35mm range to be too "normal" and isn't all that wide. The difference in perspective between a 24mm and 35mm is HUGE.

Document your child at every phase of development. Dont risk too wide an aperture all of the time. If you must be a bokeh junkie at least shoot wideopen and immediately stop down to get another shot with more dof. It sucks when I look at peoples shots with one eye sharp wishing they stopped down. The photog is usually the most critical while most will appreciate the facial expression/smile/pose and put less weight on "ooooh ahhhh creamy bokeh". You must balance your wants and assure hammering the shot!!

I vote 24L on a crop !!

love my 85mm 1.8, as much or more on my XSi than I do on my 6D

I'd work on composing the subjects, as said, getting them on the same plane. I would also look at exactly where the camera tends to focus. It might be a little in front or behind where you think it is. Look closely at your wife's hair and see if it looks like the furthest bit is in tack sharp focus, if you see that it is in better focus than your child's ear/hair around her ear you may be back focusing a bit.

also, the 85 @ 2.8 should be much sharper than the zoom wide open

http://www.dofmaster.c​om/dofjs.html

Crop camera
85mm f/2
Subject distance 12 ft

Depth of field
Near limit 11.8 ft
Far limit 12.2 ft
Total 0.45 ft

In front of subject 0.22 ft (49%)
Behind subject 0.23 ft (51%)

Hyperfocal distance 624.1 ft
Circle of confusion 0.019 mm

^^^not much wiggle room

vengence wrote in post #16407106
Sell*

definitely.

AlanU wrote in post #16408783
Exercise the use of foot zoom in conjunction with using a zoom. For primes you have not choice but to use your feet My point is you'll learn composition much quicker if you force yourself to work the camera using your feet .

I consider this to be very bad advice.
'Foot zooming" is a nonsense. In no way does altering subject distance equate to altering focal length. The key difference is the effect on perspective. Altering distance changes this; altering focal length does not.

If, through selection of a prime lens of some arbitrary focal length you are forced to stand at a particular distance to achieve framing, all that has happened is that you have given up all control over perspective, needlessly, and that is a key, if perhaps subtle part of composition.

Far better, in my view, is to choose where you need to stand to achieve the perspective (and general composition) you desire, then select a focal length to achieve the necessary framing. This is why I believe that zooms are a far better tool for learning composition than primes, since adjusting FL is trivial; indeed, this facility is why zooms were invented.

Once position and FL are selected, aperture is adjusted to achieve the desired DoF, then shutter speed and ISO to achieve correct exposure.

Of course, if there is no optimal solution for all parameters, then some compromise in one or more of them will be required.

Now, it transpires that for particular formats, certain FLs happen to allow suitable framing only at a distance sufficient for perspective effects to be unobtrusive. This gives rise to the "portrait lens" range. For APS-C, this is typically around 50-150 mm; for FF around 70-200 mm (It's no coincidence that there are so many 70-200/2.8 zooms around). The 85/1.8 therefore is a decent portrait lens on either format.

I think the OP is working with a very common misperception that DOF and background blur have a 1:1 relationship. They do not, especially when we are talking about different focal lengths.

Even more importantly, what the OP is thinking about is directionally backwards. OP wants to blur the background. He also wants adequate DOF to include two subjects.

The way to do this is to back up and shoot with a long focal length and a slower aperture. If the 85/1.8 is the wrong choice, then a 35mm lens is worse. The right lens might be a 70-300 1:4-5.6!

Here is one key understanding. Suppose you shoot the two subjects with three setups:
1) Shoot at 50mm focal length from 5 feet away at f/4
2) Shoot at 100mm focal length from 10 feet away at f/4
3) Shoot at 200mm focal length from 20 feet away at f/4

Here is what is interesting. All three shots will have the same subject framing at the plane of focus. All three shots will also have the same DOF (same framing + same aperture = same DOF). But the progression from 50mm to 100mm to 200mm will progressively yield a blurrier background.

The way to get more DOF while still blurring the background is to use a long lens and move back. Stop down as needed for DOF.

xarqi wrote in post #16409125
I consider this to be very bad advice.
'Foot zooming" is a nonsense. In no way does altering subject distance equate to altering focal length. The key difference is the effect on perspective. Altering distance changes this; altering focal length does not.

If, through selection of a prime lens of some arbitrary focal length you are forced to stand at a particular distance to achieve framing, all that has happened is that you have given up all control over perspective, needlessly, and that is a key, if perhaps subtle part of composition.

Far better, in my view, is to choose where you need to stand to achieve the perspective (and general composition) you desire, then select a focal length to achieve the necessary framing. This is why I believe that zooms are a far better tool for learning composition than primes, since adjusting FL is trivial; indeed, this facility is why zooms were invented.

Once position and FL are selected, aperture is adjusted to achieve the desired DoF, then shutter speed and ISO to achieve correct exposure.

Of course, if there is no optimal solution for all parameters, then some compromise in one or more of them will be required.

Now, it transpires that for particular formats, certain FLs happen to allow suitable framing only at a distance sufficient for perspective effects to be unobtrusive. This gives rise to the "portrait lens" range. For APS-C, this is typically around 50-150 mm; for FF around 70-200 mm (It's no coincidence that there are so many 70-200/2.8 zooms around). The 85/1.8 therefore is a decent portrait lens on either format.

Rather bold of you to call my advice bad. I do not recall mentioning foot zooming as a replacement in FL selection...Please read carefully before passing judgement on an informative website.

Perspective is somewhat "built in" to a fixed prime lens.

"foot zooming" using a zoom lens can give a huge variety of perspective while changing different FL. Perspective is what "one" feels when they look at a photographers style.

How often do you see a lazy/new photographer frame a shot with a zoom by zooming in and out without concentrating on the other component of "perspective". The photog has an easier time framing the shot and composing a photo but typically just framing the photo.

With a prime lens foot zooming forces a photographer to work for the shot. This is where IMO has more potential of developing the "eye" for photography. If a photographer concentrates on perspective while using a zoom this is where a "zoom" can be a potent tool. Often you'll see people forgetting/uninformed how important perspective is while using a zoom while they flick their wrist to quickly grab a fl to frame a shot.

AlanU wrote in post #16409898
Rather bold of you to call my advice bad.

What a drab world it would be if all opinions were equal. I disagree with you. It's not personal.

"Foot-zooming" in any context, is a nonsense.

I do; then I think; then, if I have what I consider a valid opinion, I post. Much the same s you do, I expect.

Perspective is not built in to ANY lens. It is dictated solely by distance.

Again, "Foot-zooming", which I take to mean altering position to achieve framing, is a poor technique indeed, and I don't believe that "nonsense" is too strong a label to apply, so I do. You are of course welcome to have a different opinion.

Perhaps we also differ on what is being meant by perspective, indeed, your definition is quite alien to me. To me, perspective is the transformation of the geometry of 3D objects onto a 2D space, here, performed by a lens projecting an image onto a sensor. "Feeling" has nothing to do with this.

Quite the reverse. Zooming in and out to achieve framing implies that the photographer has established the perspective they wish, and the general composition, and is now refining framing. This is not laziness, this is correct technique, again, in my opinion.

Because the other aspects have been addressed already.

Well, I can't really comment on this as I don't think our working definitions of "perspective" are congruent, other than to say that I agree that a variable focal length lens (a zoom), is indeed a potent tool, but for correct framing of an otherwise well composed shot.

Over and out.

"Quite the reverse. Zooming in and out to achieve framing implies that the photographer has established the perspective they wish, and the general composition, and is now refining framing. This is not laziness, this is correct technique, again, in my opinion."

If a person stands in one spot and zooms in/out this will frame the shot but this does not always achieve the desired perspective since you are not varying the distance between subject/camera.

The last time I checked photography evokes emotions/feelings via subject matter, composition and perspective, etc. I think many will understand what I mean about perspective instead of a carbon copy definition found in a dictionary. When there's a discussion regarding a photographers "eye" its based on a specific style or look. Perspective carries alot of weight when you view an image.

I'm not so eloquent in my writing. I hope the op learns something from these posts.

I shoot at faster f/ stops to keep my shutter speed up and avoid using higher ISO. This is why I purchased a fast prime. I know full frame is the answer to my ISO problems and I plan on purchasing it in the future. Until then, I will have to start bumping up my ISO and shooting at a higher f/ stop. I was wrong about dof on the 35mm being better for me. I still plan on buying the Sigma 35 because it is a focal length in most of my pictures with the Tamron.

http://www.dofmaster.c​om/dofjs.html

This is a little cool tool to let you know what you're settings should be

Just using Depth of Field using the usual formula (sensor pixel size as CoC) just doesn't cut it here.

Going after a baby and somebody else at the same time will not get you "complete DOF" unless you use a nuke flash and very small aperture. What matters at that point, having exceeded the dof, is how much the areas right behind the DOF are "shredded". That improves significantly when you go with a shorter focal length and compensate by getting closer (given same f-stop rating, which is a different absolute size aperture for these two lenses). It also makes the background you don't want more recognizable, that's the drawback.