Honestly, ive been super satisfied with the Sony FE 85mm f/1.8 for a while now. Its very reliable and works well indoors too.

• Basically the 85mm focal length compresses the background so your kids will pop more in the photos.
• Stick with a native lens like this to ensure the eye-autofocus stays fast and safe for moving kids... never had any complaints with it.

Regarding what #1 said about the Sony 85mm, how large is the party venue? In my experience 85mm is often tight indoors so youll need space.

• Samyang AF 45mm f/1.8 FE
• Viltrox 85mm f/1.8 Mark II FE

> What prime lens is actually the best for portraits on a Sony a7IV? Adding my two cents here because i have been through this frustration before. Honestly, many of the options within that price bracket for the a7iv are pretty disappointing when you actually start looking at the raw files. I grabbed a cheaper wide-aperture prime for a family event last year, thinking the technical specs would translate to better low-light performance. Unfortunately, the chromatic aberration—that ugly purple fringing—was visible on every single highlight, and the linear motor just wasnt fast enough to track a toddler. I also found that the typical focal length people suggest for portraits can be a total nightmare indoors. I was constantly backing into furniture trying to fit more than one person in the shot. It really sucks when you realize the glass is holding back such a capable sensor... definitely check the minimum focus distance before you commit.

Saw this thread and wanted to chime in since i use the a7IV for family stuff all the time. Before giving a final word, how big is the space where the party is happening? If youre indoors in a typical house, an 85mm lens is usually too long, meaning you will have to stand way back just to get a kids head and shoulders in the shot. If space is tight, a 35mm or 50mm is much more versatile for portraits of kids playing. For your 600 budget, these two are your best bets for performance:

• Sony FE 35mm f/1.8: This is my top pick for the a7IV. It is fast, sharp, and the autofocus is native so it never misses. You can find these used for around 450 easily.
• Sigma 35mm f/2 DG DN Contemporary: Very well built and fits the budget. The image quality is excellent for the price point. Basically, the smaller the number (like 35mm), the wider the view. The larger the number (like 85mm), the more zoomed in it is. Let us know the venue size tho, because that really dictates which one you should buy.

Helpful thread 👍

I've been thinking about your situation for a bit because the a7IV is such a powerhouse that you really don't want to bottleneck it with a lens that has slow focus motors. In my experience, technical reliability is everything when you're shooting kids who won't sit still for even a second. Checking out the actual data is usually better than just guessing... if you want to see some actual charts on how different glass performs, you should definitely check out the reviews on Phillip Reeve or the technical forums over at Fred Miranda. They get really deep into the weeds with sharpness and AF tracking stats. To give you a better idea of what technical specs actually matter for your party, I've got two questions. Are you gonna be shooting mostly indoors in low light, or is this an outdoor thing? Also, how close can you get to the action without being in the way? Knowing the lighting and the working distance makes a huge difference in whether a specific focal length will actually work for you or just be a headache.

Basically those numbers like 85mm just tell you how much the lens zooms in. In my experience, for a kids party, you dont want a number that is too high or youll be backing into walls all day trying to get the shot.

• Go with Sony. You cant go wrong with their own lenses because the autofocus is the most reliable for moving targets and youll have less chance of missing the cake cutting.
• Sigma is the only other brand I really trust for portraits. Just get any of their primes that fit your budget and the quality will be great.
• Tamron is okay but I find their primes arent quite as snappy as the others when kids are running around. Just stick to those brands and youll be safe. Honestly, native glass is always the best way to go if youre worried about things going wrong. Let me know if you need help narrowing it down once you see whats in stock!

Gonna try this over the weekend. Will report back if it works!