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01-29-2013, 12:39 PM   #1
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Pentax FA 100mm macro f2.8 + dslr help (k20d users input would be perfect)

Hello guys, i was invited to photograph this nice concert thats going to be tomorow, and like everywhere else it's all about canikon

but here am i with my trusthworthy k20d...

im gonna go with the kit lens, smc-m 50mm 1.4 and smc-m 35mm 2.8
(i have permission to photograph during the whole concert)
I've been able to use the 35mm 2.8 in past concerts, but this one im gonna be in the pit, so i decided to make a couple of calls and i got this superb lens lended from a friend that works in the photo services of a local college, the lens is quite the nice, but... autofocus is "crap"

maybe it's my k20d that needs servicing, i honestly dont know because im a manual shooter myself, even with the kit lens it hunts and hunts... my mirror is quite dirty, so i wonder if the focus system is also dirty, i've been only able to autofocus with it on broad daylight and most time it fails, it's not even a back/front focus isues, i have the focus limiter on and the clamp off, it starts hunting and then it locks... i have to manualy turn the lens all the way to infinity for it to try and focus again...
so can anyone give me anytips for optimal auto-focusing setup for my k20d as the show is tomorow night and my k20d is all configured for manual labor

Happy photographs, and if you leave pentax i will hunt you down like a mad lens!

01-29-2013, 01:10 PM   #2
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I'd definitely clean the mirror in the K20D. If it is not clean it could be scattering/degrading the light which goes through the mirror to the secondary mirror which goes to the AF sensors in the base of the body.

Macro lenses always have a large focusing throw (movement), and most of this movement is at the shorter focusing distances, very little at the longer focusing distances that you would be using in a concert. Compare this to a 100mm telephoto lens where more emphasis is in the longer focusing distances. I'd try and manually focus the lens in the concert as a way of getting the best results.


Chris Stone
01-29-2013, 02:09 PM   #3
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I have the FA100, and I wonder if it's not going to be too narrow a field of view. Anyway, it's a nice lens as a telephoto, but I've mostly used it in bright weather as such. I'd definitely clean that mirror and probably while in there, blow any dust off the sensor. Perhaps have a look around, I don't know if the prism could be dirty as well.
01-29-2013, 02:33 PM   #4
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I have used my FA100 (with K-x) for a school show and it went pretty well (depending on where you are situated relative the stage).
Having said that, I tend to use manual focus a lot in low light situations. LiveView can be a help focussing on a target area ready to take the shot.

01-29-2013, 04:50 PM   #5
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thank you guys for all the suggestions I'll be cleaning my cam and later if i have permission, some concert pictures!!
01-30-2013, 07:05 AM   #6
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Would not the focus limiter help at longer ranges?
01-31-2013, 11:43 PM   #7
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i ended up using good old smc35 mm for most shots, old reliable lens.. the focus trow is really small but hey...
and its really hard to focus as i dont haev a proper focus screen, but here are some pics..

i only ended up using the FA100mm macro 2.8 for that last shot of the Mad Alchemist

smc-m 35mm f2.8
smc-m 35mm f2.8
the 100mm

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