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11-27-2012, 01:17 AM   #1
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f4 on a 300mm too slow

Is it? I found one and thinking about buying but want to know if f4 is too slow and wouldn't be good in low light situations.

11-27-2012, 01:39 AM   #2
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Generally it's not too slow. 300mm f/2.8 is so much bigger, heavier, and more expensive that you need to make sure you really need f/2.8 before buying one.

The K-x is pretty good with low light, so you should be fine for most situations. A K-30 (or better yet, K-5 IIs) would do slightly better, but they're probably not worth the investment if you're getting good results with the K-x. Honestly, I hardly noticed the difference when I went from my K-x to the newly released K-5. Two years later I barely think I got my money's worth out of the K-5 (although it still has helpful at times).


As you can probably tell, I'd advise not getting a new camera until your lens collection is fairly complete. So unless you find an unusual bargain (possibly on the MF Tamron 300/2.8), a 300mm lens faster than f/4 is not a realistic option for many of us. I have the F*300 f/4.5, and it's quite good - certainly one of Pentax' better lenses. I've been using it a lot lately for action shots, and it's been fast enough. So if the 300/4 looks good, give it a try!

Last edited by DSims; 11-27-2012 at 01:47 AM.
11-27-2012, 01:51 AM   #3
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Thanks. I'll tuck this into my wish list. I have about seven lenses in my kit now but was thinking I need a long prime. This one is fairly cheap. And I have a Pentax AF360FGZ flash I can sell because I never use it that would help buy the 300mm. And out of those seven only one is a DA lens. Three are A lenses and the rest are M lenses.
11-27-2012, 02:00 AM   #4
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I have the 300mm f4.5, and I had the same pb initially. I tend to use more manusl control, in particular boosting the ISO to compensate for f4.5. It tends to work fine with my K-7 and would work even better with the newer Pentax dSLRs.

The FA*300m f4.5 is a grest lens and the DA*300 f4 is also well regarded. Great IQ and that is important.

Food for thougth.

11-27-2012, 02:12 AM   #5
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Using telephoto isn't all about letting in more light, although that's always desirable.

In real use you may often have to trade off letting in more light for getting the depth of field right, so that more of your subject may be in focus. Wide open at 300mm, DOF can sometimes be razor thin, which may not always work for the subject. I've rarely shot my DA* 300 f4 faster than f5.6-f8 recently.
11-27-2012, 02:16 AM   #6
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f4 is not slow.
Better use the 300mm with newer dslr models like K5 at high iso. SR is very good when using with long focals.

f2.8 weight like 4x f4-lenses, and not cheap.
11-27-2012, 03:56 AM   #7
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QuoteOriginally posted by photolady Quote
Is it? I found one and thinking about buying but want to know if f4 is too slow and wouldn't be good in low light situations.
The da300mm f4 is pretty good at f4 and works really good with the 1.7x afa, if there is plenty of light. The da300 is not real fast to focus though. The 1 stop you get with a 300mm f2.8 will cost a lot. I had the tamron 300mm f2.8 and it had to be stopped down because of fringing, so the f4 was better as it had AF. I wanted a f2.8 also and even sold my motorcycle and bought a FA*300mm f2.8, beautiful lens, too bad it was not sharp and pentax refused to fix it. (when they did their own service) I found the best option for good telephotos was with canon, I wasn't sure about the sigma's and the teleconverters being useable with the SDM focus. Back then the price of the canon 300mm f2.8 was $4K, but the new one is a lot more.You can get a used canon lens from fred miranda or keh and use it a while, and sell it later for what you paid for it, so it kind of makes sense if you can swing it. They do have good service too, which is important to me. I would like a K5 with a EF lens mount. If we hit the powerball, a 400mm f2.8IS vii will be mine.

Here's one that needed f2.8
11-27-2012, 04:17 AM   #8
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That works fine with that amount of depth. Nice snap.

F4 really really really isn't a dirty word these days. Your depth is still tiny, and your sensor is strong enough to compensate.

Viv la f4

11-27-2012, 04:59 AM   #9
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At 300mm, F4 is probably the fastest we morals will ever contemplate. As others have said, 300 2.8 is HEAVY, scarce and EXPENSIVE. I picked up a M*300 F4 a couple of months back but haven't used it much as yet due Single in... Challenges keeping other lens on the front of the K-x. Will spend some time with it over the Christmas break. DOF at 300mm 2.8 would be frightening to work with - it's skinny enough at F4 at birding type distances. F4 at ISO 800 on the K-x to get 1/500th+ shutter speeds in everyday situations is very do-able with some well tuned noise reduction back at the 'puter. To date, I've mostly used a DA55-300 to get 300mm and aperture is F5.6 with that focal length and that's ok in sunlight to modestly cloudy. In really poor light, flash infill probably needs too be considered, eg under forest canopy, in shady glens etc. Also where you live, you're not going to be fighting the cooler seasons' gloom that more northerly shooters have to deal with.
11-27-2012, 06:16 AM   #10
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f4 on my 60-250 at 250mm was plenty yesterday evening when at the pool to shoot my son's swimming lessons. And that's with a K20D at ISO 400.
11-27-2012, 06:42 AM   #11
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Well, I will be finding out sometime today, as the post office tired to deliver my "new" A*300/4 yesterday and my wife had stepped out for a bit. No one was home to accept the package. Most of my other lenses are f4 other than my older manual focus f2.8's. The field of view is much smaller - its a telephoto, but I shoot with a lot of ambient low level light usually on a tripod, so I am not thinking that I am going to be seeing much difference, especially when compared to my current 55-300. I am expecting that the IQ will increase though.

11-27-2012, 06:52 AM   #12
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what are you planning to use it for? i have one which i use for wildlife (birds,etc), some sports, great for macro shots and i am very happy with it...i would also highly recommend the 1.7 adapter...the 2 combined work very well together
11-27-2012, 08:44 AM   #13
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Thanks to all for your input. FYI, I never shoot wide open on any of my lenses. My two telezooms are f4.5-5.6. Both are not tack sharp at 300mm and both are not shot at the most wide open. I usually shoot at around f8. Though sometimes, like in my shaded back yard, I've had to drop that down to f7.1 to 6.3 and I don't like that because I don't get enough DOF that way. The below bird was shot with my rebadged/rebranded Quantaray (Sigma) 70-300mm at 300mm @f8:

11-27-2012, 08:52 AM   #14
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One thing to think of is that while F2.8 is a stop faster than F4, you may have to compensate for the weight with higher shutter speed if you aren't using a tripod or monopod. DOF-wise, F4 on a 300mm is going to be pretty thin regardless.
11-27-2012, 09:10 AM   #15
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I do not shoot f4 on any of my lenses. So, that isn't going to be a problem, now is it? For heavy lenses I use a tripod. I have only one really heavy lens and that is my Samyang 100-500mm f7.1 and I use the tripod for it. For more of my techniques, see my flickr photos.
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