Moderator: E.J. Peiker

All times are UTC-05:00

  
« Previous topic | Next topic »  
Reply to topic  
 First unread post  | 4 posts | 
by MND on Wed Jul 18, 2018 1:19 pm
MND
Forum Contributor
Posts: 584
Joined: 1 Jan 2007
Location: Pennsylvania
When it's midday, hot and sunny I sometimes will reach for my IR converted old Sony A7R with 16-35mm f/4 lens. This combination leaves a hot spot right in the middle of the frame starting at around f/5.6. It doesn't take much work to reduce it but anything to automate the process is going to help speed things up.

In E.J's Summer 2017 Newsletter he explains about Lens Cast Calibration profiles.  In his Autumn 2017 Newsletter he explains how it helps eliminate the Hot Spot in IR photography. I understand most of it but some of it is not clear to me.

What I am not clear on is the technique involved. I get it that you take a picture, then you place a piece of translucent white acrylic over the lens and take another shot using exactly the same parameters as the first shot. In Capture One you apply this second image as an LCC to reduce color casts etc to the first frame. 



My question is :- Do you need to produce a second image using the white acrylic for EVERY shot you take if you alter any camera/lens parameters?

If you can just take a white image at every f stop and apply that to any image I can see that is doable. To do it every time you take a photograph, forget it.
 

by E.J. Peiker on Wed Jul 18, 2018 2:53 pm
User avatar
E.J. Peiker
Senior Technical Editor
Posts: 86761
Joined: 16 Aug 2003
Location: Arizona
Member #:00002
Hi Mike,

From that Newsletter article:

"Many technical camera photographers do this for every frame but I find it is not necessary for DSLR and mirrorless photography, even medium format photography. Instead, I have built a library of LCC shots for lenses that need it at every aperture and then apply those in my Capture One Pro workflow."

I agree it would be unwieldy for every frame so here is what I do, For the lens in question I will create an LCC image at 16mm, 20mm, 24mm, 28mm, and 35mm and then do it for every aperture I am likely to use.  Then in Capture One, under the Lens Correction tab (by default unless you have moved it) I create a preset for each of those LCC images (you do that in the little icon with three horizontal lines next to LCC).  Once they are all added it's as simple as adding that preset to any image taken in the future from  clicking on the same icon with the three little lines - that will now produce a drop down and you simply select the LCC profile that most closely matches your focal length and aperture for the shot.  you can certainly do it at every millimeter and every third of a stop but that's an overwhelming task and just not necessary.

Here's an example of what it will look like when done.  So as you can see, it is important to name each one clearly so that you don't get confused later.  It takes the name from the file name that you give it when you save the LCC profile.  While the example isn't an IR image but you can see the profiles there for both my Irix 11mm and 16-70mm lenses that I use with my IR camera.
Image
 

by MND on Wed Jul 18, 2018 6:37 pm
MND
Forum Contributor
Posts: 584
Joined: 1 Jan 2007
Location: Pennsylvania
Thanks for the very detailed reply E.J.

One further question. If I take a sample image at my all my normal f stops and focal distances what sort of background do you suggest for the LCC images? For my IR shot's I normally take foliage and clouds.

BTW Your Newsletters are always a great read, thanks for taking the time to write them.
 

by E.J. Peiker on Wed Jul 18, 2018 7:15 pm
User avatar
E.J. Peiker
Senior Technical Editor
Posts: 86761
Joined: 16 Aug 2003
Location: Arizona
Member #:00002
Thanks :)

Just point it up at the sky, and then prior to generating the ICC, click the white balance dropper at about 1/4 of the way in from the left or right.
 

Display posts from previous:  Sort by:  
4 posts | 
  

Powered by phpBB® Forum Software © phpBB Group