Lens f/stop info

[Journeyman]

Good day,
I am new to the forum, I mainly take bird photos. Some experience and some reasonable photos.

I would like to ask about the higher f stops on longer lenses.
In the case of a prime lens with an f stop of f8, is most of the light control then completed by the electronics on the camera? With shutter speed/iso/aperture making it possible to shoot in lower light conditions?

Thank you for your help and indulgence,
Kind regards,
Dennis

[ameerat42]

Yes, if you have the camera set on A(perture) Priority.

But properly exposed shots will only be possible until the other parameters have
ceased adjusting. Ie, there will come a point when you will just have to use a
"lower" f-stop, or for that matter, yet a higher one.

Also: I will shift your thread to "Shooting Help" for better topic coverage.

- - - Updated - - -

PS: I just noticed this is your first post here, so
welcome to AP.

[Tannin]

Hi Dennis.

It all depends!

There are many ways to set your camera up. The most common way is aperture priority. Here, you set your desired aperture (f/8, for example), and leave your ISO setting fixed (typically, for bird work, you'd use ISO 400 or a little more). The camera measures the light level and selects a shutter speed to ensure correct exposure. It is up to you to keep an eye on the shutter speed, and if it drops too low, to take some action, such as selecting a wider aperture (f/5.6 or f/4), or a higher ISO.

In general, avoid lenses which can't open up to a decent aperture. For birding lenses, f/4 is excellent (but very expensive), f/5.6 is good, f/6.3 OK, and anything higher (f/8 or f/11) hopeless. (Note that you don't always use a lens wide open. You might, for artistic reasons, decide to use an f/5.6 lens at f/11, for example. But it is very important to have that choice.)

[Journeyman]

Thank you for the replies. Much appreciated.
I use a Tamron 18-400 at the moment. Great lens however it can’t be lengthened using a teleconverter. I had a 1.4 in mind for a little extra gain. The Tamron won’t accept the converter with any success.
Back to research I guess.
Kind regards,
Dennis

[swifty]

Hi Dennis, I don't specifically shoot birds and in fact that's one genre I haven't really touched.
But just a generally comment about larger f-number lenses.

Considering DSLR lenses, the PDAF system generally only work til either f/5.6 or f/8 depending on the AF point due to the way the AF system works in a DSLR. It doesn't mean the AF system can't use the higher f-numbers but it will autofocus at the larger aperture and stop down to your selected aperture when you take the photo.

Considering mirrorless lenses, the OSPDAF system generally work to much smaller f-numbers. I haven't seen any specific minimum but I believe it's around f/11 hence we're starting to see lenses for mirrorless systems with a max aperture of f/6.3, f/7.1 or even f/11 for some Canon's latest consumer 600 and 800mm primes.
It does mean they will AF but its still not a bright lens by any means so your exposure settings will be limited, increasing the need to raise your ISO.

[Tannin]

Cheers Dennis. It might be helpful to think of a teleconverter this way. It is a device which trades reach for quality.

A modest teleconverter, let's say a 1.4, turns a 400mm lens into a 560mm lens one grade inferior to the 400. It is one f-stop slower as well, but that is a different question: the thing we are interested in here is that the picture quality is decreased. On a really first class lens - a 500/4 for example, which costs around $12,000, you have such superb quality in the first place that it is still very good indeed even with the 1.4 converter. On a very good lens, say a 400/5.6 (around $3000 for a good one), results are only good. (At best.) On a fair lens like a 150-600/6.3, results are poor. And on a poor lens (any 18-400, no matter what brand, is pretty poor at 400mm), the result is very poor.

A more ambitious teleconverter (a 2.0) provides double the reach, and two grades lower quality. It makes a superb 500/4 into a good 1000/8; anything below that level (even a 400/5.6, never mind an 18-400) become something somewhere between poor and unusable.

In every case, you are spending quality to buy reach. You can only do this successfully when you have such high quality in the first place that you can afford to give some of it away.

But don't despair! There are no shortcuts to the better birding glass you want, but there good answers just the same. Look for a made-for-purpose telephoto lens in the 400mm class. Canon and Nikon make some outstanding ones at (considering what you get for the money) quite reasonable prices. Tamron and Sigma are also worth considering.

There are two ways to buy a birding lens.

Method 1: Try a teleconverter. Throw that away and try a cheap 70-300. Buy another teleconverter for that one. Throw all that away and buy a good lens.

Method 2: Buy a good lens.

Method 2 is faster, easier, and quite a lot cheaper.

[Journeyman]

Good day Tannin, thank you for the insight.
I have a Tamron 18-400, all things considered it does offer fairly good quality shots. However it does have reach limitations that I now understand can’t be overcome with a converter. I am confined to a less expensive lens than the Canon prime lenses.
Not to give up, my thoughts are moving to a better camera or a Sigma 150-600.
As you say biting the bullet for a more expensive lens right off may work out cheaper in the long run. With photography one is never bored, things change quickly.
Kind regards,
Dennis (Journeyman)