softbox vs umbrella, catch box and light control

I am shooting with a pair of ab 800s, and shoot through umbrellas. It was to my attention that my catchlight are a little small
1. The size of catch lights is in part a function of their distance to the subject, correct?
2. Is 24 inch by 36 inch is generally considered a good size soft box, for 1-2 people portrait? should I go bigger?
3. Am I less likely to get hot spots from a soft box than I am getting from my umbrella?
4. Any other advantage of one over the other? (light spill over,....)
I would be also very appreciative of any useful links.

You might have your lights positioned too close to the umbrellas, and your catchlights might be too small as a result of the light coming from the strobe not covering the whole umbrella. How large are your umbrellas?

As to what size softbox to get, it depends. Different modifiers are used for different effects. Your suggested size should be fine for a portrait of one or two, but will be too small for a full length portrait. It all depends what you want to do with it, and how far away your lights are from the subject (and how hard the light is as a result).

I prefer the control of softboxes to the light scatter of umbrellas. That said, I use umbrellas when I need the ultimate in portability, or when appropriate (I bounce the light from umbrellas to cover larger groups sometimes). Once again, each have their place.

I believe the catch light is dependent on light distance from subject and size, yes. I think the intensity of the catch light is also dependent on the power of the source. One more thing to note: After seeing lots of magazines with professional photos, I no longer subscribe to the theory that the best place for a catch light is always 11 or 1-o-clock, and there should always be only one. Many great photos are taken with multiple catch lights, or lights from angles other than the "ideal."

As it seems to me, to achieve even lighting with a soft box, a good rule of thumb would be to make sure the softbox is just about as tall as the area of the subject in your frame in order to have the most even lighting on the subject. The same would probably apply to other diffusers, but I don't know how a full-body umbrella would work.

I think you're probably less likely to get hot spots from a soft box; it seems to produce more even lighting.

Lots of professional portrait photographers like softboxes for control and softness of light, and I'm inclined to believe that I would also prefer softboxes...if I had any of a reasonable size. The huge one I have puts out a swath of soft light that does a really nice job on a headshot or probably even full body photos, but it's extremely unwieldy and I wish I had smaller ones. If I want the absolute best quality light I will probably use it for my main; otherwise I use shoot thru umbrellas very often and they do a very nice job. Not quite as softening to a more character-laden face, but I can do some of that in photoshop.

Worth noting is that I don't have a set studio, and I'm fully mobile. Umbrellas are much faster and more convenient for me.

An as-yet unedited photo using 4 lights: two in front butterfly style white shoot-thru umbrella setup w/upper 2 stops higher power than lower, 1 hair light thru corrugated plastic grid, and one light with blue gel against thunder grey background paper. Lights on subject were all Sunpak 383S, light on bg was speedlite 580.

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thank you for your inputs.

I just also discovered maybe what I should have already known. If I take off the reflector from ab, the light is a lot softer and more diffuse. it takes a little bit of power hit, but still plenty of juice. are we supposed to take off the aluminum reflector when mounting the umbrella?

Optional, much less light going to the umbrella; I think the softness could be from bouncing light off other sources being reached by your now omni-light.

certainly could be. however, standing if front of the umbrella with the modeling lamp on, the umbrella is much more evenly lit without the reflector vs with the reflector.
sample single light, just testing, and getting the flash closer, shot 1/200 sec, 1.8, iso 100, around 1/20 on power. I think I am going to play with this some more. not sure if a softbox is necessary.

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Quality of light can also be determined by distance and size of the diffuser from the subject. In closer softer light (dependent on source) When doing single portraits I like to work with a large soft(main)box in close feathered and a reflector for fill.

Heres a couple using 1 main light (30 X 40 soft box) in close reflector for fill and B/G light all shot on location. Gray muslin...

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love the 3rd one

Thanks, I showed 1 & 2 to illustrate how one light used right with a reflector can be a good choice on a single subject.

I am such a big fan or 1 light and a reflector. Less IS more.