The importance of non-equivalence

I've been doing a lot of dog photography, specifically shooting agility practice at my girlfriend's relatively advanced lessons with her dogs and other student's dogs. It's all good fun, for me anyway, and they appreciate getting "nice" photos of their dogs in action.

Anyway, that's the context, and now the reason for this post. In the example I just provided there was a lot of cropping because the Nikon AF-S NIKKOR 70-200mm f/2.8G VR I was using was maxed out at 200mm, so I'm switching the camera I use on my Tamron 150-600mm g2 lens from my D500 to my D850, and now I have an issue with covering FOV wider than 150mm on the FX camera with a lens for my D500. Theoretically, I need a good zoom lens that goes up to 100mm (more would be better, but absolute overlap can be made up with some cropping). I have a very nice Sigma Art 50-100mm f/1.8, but the AF motor isn't up to the task (not even close).

At the extreme, during pre-lesson practice, I've been using my Nikon AF-S NIKKOR 24-70mm f/2.8G (non-VR version) which I got mainly for its AF performance and these sort of shots:

The above was 34mm using my D500. I'm going to try a Nikon AF-S DX NIKKOR 18-140mm f/3.5-5.6G VR, which sounds like it's going to accomplish the task (testing will tell), and in the meantime I do have a Nikon AF-S DX NIKKOR 16-85mm f/3.5-5.6G VR. While all of this could be moot, and the AF performance of the DX lenses under the conditions I'm going to use them in is going to be the most critical factor (otherwise, the Sigma 50-100 would be a no-brainer during the lesson shots), I was curious about filling the existing gap so I did a little image quality testing today using what I have.

All of this brings me to the point of this thread, and my apologies for the lengthy set-up. For sharpness the 24-70mm at 70mm beats the 16-85mm at 85mm shooting at f/5.6, but that doesn't tell the whole story. As I was looking at the comparison of the three options I have at about 20 feet (or about 6.5 meters) I noticed the whole bokeh/background blur issue became relevant (to my eyes anyway).

From left to right: my 24-70mm, my 16-85mm, and my 150-600mm choices. The actual focal length and apertures are inputted into the calculators and show the diameter of the lens pupil below each crop (all resized to match the 100% crop on the left). This is why I'm hoping the 18-140mm can prove useful from around 50mm to past 100mm at f/5.6, and I expect to know more within the next couple of weeks – so more to come. In the meantime, I welcome any feedback or insights.

just bought a tamron 18 300 for my a6300 for all the reasons your missing out on 😁 image quality is great, feather detail is excellent on the birds i have tested it on so far.

heavily back lit ,i was very happy with the results.

I like to keep things simple and not worry too much about equivalence.

I simply put on the lens that has the focal lengths that will give the FOVs I need remembering that the smaller the sensor size of the camera the lens is attached to, the larger the DOF will be resulting in less bokeh and background blur.

I'm unimpressed by the bokeh. Also, I find your snarky comment extremely offensive.

I started out thinking only about the FOV and detail, not concerning myself with equivalence. However, and quite by accident, I noticed how starkly different the background was between the 70mm and 85mm lenses, which really surprised me – thus, the title of the thread and its placement here. I now want to do a more well controlled comparison between those lenses as I think some of it comes down to lens' character, which also surprises me because I would have thought the bigger lens would have a more pleasant bokeh than the extraordinarily inexpensive DX lens.

Yes, the quality of the background blur and/or bokeh does to some extent depend on the quality of the lens.

In any case, you can create customised very realistic blur and bokeh in Ps so I personally don't try to think too much about it when taking the shot.

You serious .its beautiful, show me any bokeh balls from your zooms that better it.

You are providing more proof that you struggle to cope with people who have a different opinion to you.

I'm not impressed with the bokeh either. You have 3 ugly balls "attached" to both sides of the bird. On first glance it looks like the bird has some sort of growths on it.

I would have either moved or removed them in post, both very quick and easy to do.

You chose to leave them there because in your opinion the bokeh is beautiful and that's fine as it is your opinion to have.

But for you to expect everyone to then also like the bokeh is just plain stupidity and laughable from my point of view.

You do not get to decide for other people what they like and not like.

With posts like yours it's no wonder you were sandboxed over at DPReview.

On a side note, was your bokeh created by the lens or in post?

When you crop a photo, you not only change FoV (= equiv. focal length) but also equiv. f-stop.
Given your setup (cropped 70mm vs. 85mm) you'd better open up to f/4.5 @ 70mm for equivalent background blur (or close down to f/6.8 @ 85mm).

Bokeh (quality of out-of-focus rendering) should not be confused with blur (quantity of out-of-focus rendering)

🥱

....😉

I will take that as you accepting

Your bird photo looks much better with the balls moved away from the bird.

Yes, which is why I included the aperture diameters in the comparisons, and why I titled the thread "The importance of non-equivalence." It's also why I mentioned doing a more well-controlled test of the lenses.

BTW, I was mistaken about the aperture used on the 150mm shot, it was f/5.6 too, which made the pupil diameter nearly 27mm (a substantial difference). It's not like I'm fixated on attaining equivalence – I'm not looking to use an 85mm lens at f/3 and crop it to match the FOV of a 150mm shot. As a matter of fact, I practically crop every shot at every focal length I use because I would rather not have any part of a fast moving dog out-of-frame unless I choose to do that.

Nor should they be conflated, even if they can be related. I've noticed a difference in the transition from slightly out-of-focus to completely out-of-focus of the same scene and focus distance that's different on different lenses that have the same focal length and are using the same f-stop, more often than not it is negligible.

tell me what lens this is ? lets just say its a high-end 2.8 zoom

screen grab not to give it away.

As a matter of fact, I am serious. I'm not going to argue with you about your opinion, if you say the bokeh in that photograph is beautiful then I will take your word on that. That said, I think it's ugly.

The bokeh balls have rings around them, which I think makes them look busy. Also, the light reflecting from the background branches have a weird blurring to them, which I would attribute to image stabilization (it's that, or the lens is just weird that way).

Well, it's not like I set out to shoot bokeh balls with a zoom (or any other lens for that matter). About every time I do have bokeh balls in a photo, it came when using a prime. Therefore, I have to resort to a test I did over seven years ago with three lenses I was using at that time. For whatever reason, I can't embed the full-sized comparison I did here, so here's a link to it.

I have no interest in what lens it is because it doesn't change what I posted earlier.

you have missed the point the image i just posted is a center crop, not the boarder.

I see no point in the crop you offered, and I wasn't addressing that in my last reply. Frankly, both are examples of poor bokeh, but for different reasons.

I got rid of a Nikon AF-S NIKKOR 85mm f/1.8G because it had the same issue as your latest submission, clearly visible aperture blades as soon as it was stopped down. I also got rid of a Nikon AF NIKKOR 105mm f/2 DC in spite of its stellar bokeh because it wasn't sharp enough at wider apertures and I couldn't justify owning what I considered a one-trick-pony (great bokeh but not sharp enough until it was stopped down to f/4). As it so happens, I own three Tamrons, and all of them have good to excellent bokeh, as did the Tamron 24-70mm f/2.8 that I didn't keep (its AF was too slow for what I wanted to do with it).

You want a real-world example of what I consider better bokeh than what you showed? Here's one from the agility lessons I shoot at and was the purpose of this discussion before you hijacked it with your static bird shot and snarky comment about me "missing out."

Do even know what bokeh balls are ? or how they are formed. because it doesn't sound like you do.
"missing out " you were complaining about 50 lens not being the right one 🤨 so i posted an image from a single 18 300.

would you like me to post the 20 meg version.

A great photo!

David