[PePe]

What is too slow and what is not ? It really depends on what you shoot, and where.
In most cases f:4 for a 300mm lens is just fine.
I went for a f:2,8 because I do a lot of wildlife shooting. Animals have an annoying tendency to show up at dusk or when the light is low. Eventually you run out of light no matter how fast the lens is. Another area where I think there is a clear justification for f:2,8 is shooting motorsports, where the need to freeze motion may force you to choose wide apertures.
But for general use f:4 is just fine.

[msatlas]

The general optical quality of the DA* 300/4 and F*/FA* 300/4.5 is a lot higher than the zooms you've got in that FL range. So you're much more likely to be able to get sharp results at or close to the maximum aperture.

[Just1MoreDave]

At 300mm, F4 is probably the fastest we mortals will ever contemplate. As others have said, 300 2.8 is HEAVY, scarce and EXPENSIVE..

Exactly. It's like a car with a 12 cylinder engine. Nice, I'm sure, but an exclusive club. The closest thing to affordability is the Tamron Adaptall-2 300/2.8, which is often less than 4 figures. I have the SMC Pentax 300mm f4, and it's really pretty good. It's more than two pounds, 77mm filter, same as the DA* 300/4.

[reeftool]

I have the K300/4. It's a pretty big beast. Big enough that I don't use it as often as I could, opting for my SIgma 70-300 which is slower but also much lighter. I've seen a 300/2.8 on a Canon and it looks like a cannon (pun intended). It's also big on the wallet. However, if you need it....

That's always the big question. Do I need it? Considering the prices involved here, this is an instance where renting makes perfect sense before any purchase is decided on. Will the higher ISO quality of a newer body like the K5 make up the difference? The only new 300/2.8 option we have is the Sigma and that's over $3K.

[Lowell Goudge]

Look in the Sample photo archive, I have posted shots with a K300/4attached to a SMC-F 1.7x AF converter, and also using a Nikkor-H 300/4.5 on its own

You be the judge

[bdery]

I do not shoot f4 on any of my lenses. So, that isn't going to be a problem, now is it?

With a 70-200 or 60-250 lens, or a 300 prime, you can shoot at f4 with some confidence.

[Lowell Goudge]

With a 70-200 or 60-250 lens, or a 300 prime, you can shoot at f4 with some confidence.

In sharpness at the point of focus yes, but even a chickadee or small finch shot at an angle is not all in focus

[rvannatta]

In sharpness at the point of focus yes, but even a chickadee or small finch shot at an angle is not all in focus

as an owner of the faster long lenses---my comment is that the questioner has asked the wrong question. The occasion for needing
a photo at 2.8 is rare. However, that is not the reason for buying them. Rather the reason for buying them is that they
make a platform for converters, which eat f stops like candy.

However life has been made much easier and the need for really fast lenses has been mitigated considerably by the advent
of high ISO cameras such as the K-5.

If you are adamant that the only good photo are ones take at 100 ISO then you better look for the fast glass, however insufficient
depth of field is the worst driver of bad pictures on long lenses, with camera shake being the next culprit. I finesse this vice
with elevated ISO--- usually 800 or 1600, but even so you have pushed the envelope---profoundly if you want to use a 2x converter if the lighting is weak.

[Lowell Goudge]

as an owner of the faster long lenses---my comment is that the questioner has asked the wrong question. The occasion for needing
a photo at 2.8 is rare. However, that is not the reason for buying them. Rather the reason for buying them is that they
make a platform for converters, which eat f stops like candy.

However life has been made much easier and the need for really fast lenses has been mitigated considerably by the advent
of high ISO cameras such as the K-5.

If you are adamant that the only good photo are ones take at 100 ISO then you better look for the fast glass, however insufficient
depth of field is the worst driver of bad pictures on long lenses, with camera shake being the next culprit. I finesse this vice
with elevated ISO--- usually 800 or 1600, but even so you have pushed the envelope---profoundly if you want to use a 2x converter if the lighting is weak.

i wholly agree, and while you can pixel peep to your heart's content, when printed, the noise is no where near as obvious.

Even the K7 was capable under the right conditions of producing a good shot at ISO1600

[photolady95]

First of all, I don't use teleconverters mainly because where I shoot they are not needed. The birds I shoot are usually less than 20 feet from the end of my lens/es. And I agree, I didn't ask the right question, as I believe, I got all the wrong answers. Right now I'm not sure how to ask what I was thinking when I said faster.

Unless it's sunny outside, I don't shoot at ISO 100. Usually, ISO is set to 200, 400 or even 800 (cloudy days).

[Lowell Goudge]

First of all, I don't use teleconverters mainly because where I shoot they are not needed. The birds I shoot are usually less than 20 feet from the end of my lens/es. And I agree, I didn't ask the right question, as I believe, I got all the wrong answers. Right now I'm not sure how to ask what I was thinking when I said faster.

Unless it's sunny outside, I don't shoot at ISO 100. Usually, ISO is set to 200, 400 or even 800 (cloudy days).

When birding I set auto ISO on my K5 to top out at 5000 and shoot Tav mode when not on a tripod, for the DOF I want and shutter I want. I would rather have a minor amount of grain than either motion blur, or shallow DOF on my birds.

[photolady95]

Well, I shoot totally in manual, so all the settings are set by me, ISO, shutter and aperture. And I don't have a k-5, mine is a k-x until next year at least. I don't think I get bad results shooting this way, The only time I use a tripod is either when using the Samyang or it's super windy outside. There are trees around (palm trees) that I can lean against or prop the camera on, to reduce shake in windy conditions. The Samyang is a M lenses, the longer zooms are autofocus and A lenses.

[Transit]

Not feeling any slowness with my exceptional new F*300/4.5
surprised how bright it is wide open

[jpzk]

Not feeling any slowness with my exceptional new F*300/4.5
surprised how bright it is wide open

OK, so I have been using this DA*300/4 as a permanent fixture on my K5 for the longest time.

Because of the K5 ability to handle high ISO quite well, I shoot wide open a lot (F4) and TAv.
I have yet to complain about any "slowness" with this lens/camera combo.
The F4 images shows some very sharp details ...
Anyway, not at all "slow" in my books.

You can have a peek at my signature below: a lot of images of BIF were taken that way, often not under the best lighting conditions. (see "Flickr" in the signature especially vs. PPG).
Also, nearly all of them (maybe all of them, come to think about it) were done without a tripod.

JP

[derekkite]

A 2.8 will give you more light for focus. In low light that is usually the issue, not enough for either manual or auto focus. And you can put tc on it without losing the ability to see enough to focus. Rarely would anyone with a 2.8 soot wide open unless the conditions were such that you could see exactly where the focus was.