[audiobomber]

I just recently upgraded to the 55-300 and it's the same speed as the 50-200

Not really. The 55-300 is F4.5 at 200mm, where the 50-200 is F5.6.

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Last edited by audiobomber; 02-03-2009 at 11:52 AM.

[awo425]

You can get used Pentax SMC F70-210 4/5.6 for $115 from the market section of this forum. It is for sale in the post "300+ lenses ..."
It is one helluva lens for the price, sharp wide open and better then Pentax DA 50-200. AF is noisy, but fast and IQ is great.
For macro I would look for a separate MF lens, or even a reverse focusing ring and Pentax 50mm prime lens.
I think decent lens in 70-210 range is more important in a kit then a macro.

[alohadave]

Not really. The 55-300 is F4.5 at 200mm, where the 50-200 is F5.6.

1/2 a stop difference. Close enough.

[audiobomber]

1/2 a stop difference. Close enough.

2/3 of a stop.

[Marc Sabatella]

2/3 of a stop.

If you do the math, yes, it might work out about that way in theory. But Pentax uses f/4.5 to represent the half stop between f/4 and f/5.6 - you can see that by going into Av mode with your camera set to use half stops and flipping through the choices. Of course, those numbers are also only approximate on a variable aperture zoom, but unless you've actually measured the exposures, the default conclusion from the specs would be that the 55-300 is 1/2 a stop faster at that focal length. And I assume there are also focal lengths where there is no difference at all. So the "average" improvement in speed would have to be *less* than half a stop.

[audiobomber]

If you do the math, yes, it might work out about that way in theory. But Pentax uses f/4.5 to represent the half stop between f/4 and f/5.6 - you can see that by going into Av mode with your camera set to use half stops and flipping through the choices.

My camera is set for 1/3 stops and it shows 4.0, 4.5, 5.0 and 5.6. Why would you set the camera for half-stops if you're trying to determine thirds?

I see what you're mean though. The 55-300 changes to F4.5 at about 120 and reports that nominal aperture until it changes to F5.6 at 210, so it's not actually F4.5 at 200mm, even though it says it is. So would that mean that the aperture has infinite stop positions in between the actual f-stops?

[Nick Siebers]

I have a Tamron Adaptall 70-150mm zoom that does 1:2.5 macro. I think you can get one, and a PK adaptall mount, for under $100. Then later you can get a 90mm Adaptall macro that is almost as good as anything out there.

[Marc Sabatella]

My camera is set for 1/3 stops and it shows 4.0, 4.5, 5.0 and 5.6.

Weird. My camera is set for half stops and shows 4.0, 4.5, 5.6. So I guess they use 4.5 as both the 1/2 stop and the 1/3 stop.

So would that mean that the aperture has infinite stop positions in between the actual f-stops?

I don't know how it works for apertures that are not wide open, but that seems plausible. Wide open, simple math - size of opening divided by focal length, or something to that effect - would seem to suggest the actual maximum aperture does change continuously with focal length. But then, that doesn't explain constant aperture zooms. I haven't yet been sufficiently fascinated by the issue to read enough to begin to understand...

[sabarrett]

So... to the OP... Are you thoroughly confused now? (grin)

[reeftool]

I have the Sigma 70-300. It came with the package deal I got when I bought my camera. While I have got some very nice shots from it, I find it very soft abovve 200mm unless its bright sunlight and I'm shooting at f/11 or f/16. I would wait a few weeks and save a little more and get the Pentax 55-300. Another option is to look for used deals on Ebay or a dealer like KEH.