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07-28-2012, 12:40 PM   #1
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lenses suitable for IR

Hello i bought IR 720nm filter and used on A 28/2,8...
there is one of first tries:

problem is the hot spot in the center, i am unhapy from it... IMHO kit 18-55 is not giving that spot, right?
my next question is, if you know, that A 50/1,7 isd giving this fault or not? very thanks! )

07-28-2012, 01:31 PM   #2
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I don't really see the hotspot. Perhaps it is my monitor but I don't see it. Now, if you see it then it must be an issue. I have had the same issue arise under certain light conditions (and it can be quite irritating). It does not happen all the time just under certain harsh light and depending on the f-stop. (I usually go with f11-16)

I take IR images with a converted K-x and use a number of lenses. For instance, the kit lens works well as do the Sigma 10-20mm, Auto Sears 55mm f1.4, Porst Weitwinkel Auto F 28mm f2.8, Tamron 75-250mm f3.8/4.5 Adaptall-2 (104A), and the SMC Macro Takumar 50mm. These are my favoritie lenses with IR.

My converted IR body is full spectrum (clear glass) so I use various filters in front of the lenses.

What camera body are you using? It could also be the filter. I have an Opteka IR 720nm that produces hotspots unlike other filters. Just a thought.
07-28-2012, 03:07 PM   #3
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it is not strong, but it is there!
here see:K-r + A28/2,8 & F8 (my first ir image... )

there is hotspot more visible...
it si irritating... okay... i maybe will use kit lens... but without DOF scale it willl be harder.... :/

my filter: Green-L 58mm IR 720nM ... costs about $23 ...

i hope, that with A50/1,7 (i gonna to buy) it will be ok...

by the way: how process in Adobe Camera RAW are you using?
i used wb on 2000K , lowered saturation of oranges and hue for oranges to yellow, yellow to green...
07-28-2012, 03:52 PM   #4
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I used a Hoya 72 and the SMC Pentax-F 28mm f2.8 for this one. It was at f8, 0.5 sec, ISO 200 and an unmodified *ist DS. Processing was a quick 2000K temp., -72 tint, +0.35 stop exposure, 25 blacks, and a little luminance NR in ACR, then swapping the red and blue channels in the PS5 channel mixer.

The F28/2.8 is supposed to be the same design as the A version but I think Pentax changed the coatings somewhat on the F series. I haven't seen a hot spot with my lens but that doesn't mean much.

07-29-2012, 01:18 PM   #5
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very thanks for your help, situation looks that, i'll mark hyperfocal distances on my kit lens and it will be it

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