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Archive 2014 · flash hot spots!

  
 
peterski
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p.1 #1 · p.1 #1 · flash hot spots!


I'm getting a few hot spots in the middle of the frame on some of my shots. Is this usually sunlight or reflected flash light hitting the leading lens element? I'm using a reversed lens with a lens cap holed out for protection. The flash sits right on the end of the cap but angled outwards and I'm usually holding the subject in my left hand and out of direct sunlight. This shot is minor but others have a more diffused over-exposed circle of light in the middle.
http://farm4.staticflickr.com/3931/15248313157_85a51abb99_b.jpg
cheers,
peter



Oct 04, 2014 at 03:00 AM
philshoots
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p.1 #2 · p.1 #2 · flash hot spots!


Not really seeing it, perhaps post another - a worse case example. As I understand it you've made a lens hood from a rear cap, the cap interior surface is often very shinny and reflective. Have you painted it flat black, as well as the lip/ od of your hole? Maybe this is the source light bouncing inside the cap back onto the rear - in your configuration 'front' element. Also in your reversed set up I'd think the rear flange surrounding the rear element could act as one big shinny ring. If you're going to use this lens reversed permemently can you paint these areas flat black? If it's not coming in the front via reflection it's a light leak coming in at one of your flange joints, this will happen in bright sun even when using flash as your key, you could black out/wrap your joints to see if this is the source of the flare. Good luck sorting it out.

Phil



Oct 05, 2014 at 05:54 AM
philshoots
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p.1 #3 · p.1 #3 · flash hot spots!


Another thought, your homemade lens cap hood may be causing exposure vignetting of the image. The standard field if view of a 24mm requires quite a wide hood but since your using it reversed I'm unsure of the actual field of view or how one would calculate it or determine the correct portal size/OD and length of a homemade hood. Other than trial and error. Any bright sparks want to weigh in?

Quite interesting as a brain teaser.....



Oct 05, 2014 at 06:52 AM
coder
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p.1 #4 · p.1 #4 · flash hot spots!


You mean that bit of glow under the hover's eye?

Have you tried some indoor test shots without flash and see if it is still there?

My guess would be the flash and you need a hood of some sorts.



Oct 05, 2014 at 08:35 AM
peterski
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p.1 #5 · p.1 #5 · flash hot spots!


coder wrote:
You mean that bit of glow under the hover's eye?

Have you tried some indoor test shots without flash and see if it is still there?

My guess would be the flash and you need a hood of some sorts.


Yes, the glow under the hover's eye. It's worse in other shots. I can't hood the end of the lens too much as I'm pretty close to the subject and this would block the light. I'll check for leaks and reflections.
thanks



Oct 05, 2014 at 07:04 PM
peterski
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p.1 #6 · p.1 #6 · flash hot spots!


philshoots wrote:
Not really seeing it, perhaps post another - a worse case example. As I understand it you've made a lens hood from a rear cap, the cap interior surface is often very shinny and reflective. Have you painted it flat black, as well as the lip/ od of your hole? Maybe this is the source light bouncing inside the cap back onto the rear - in your configuration 'front' element. Also in your reversed set up I'd think the rear flange surrounding the rear element could act as one big shinny ring. If you're going to use this lens reversed
...Show more

Thanks Phil. Good idea. I'll check for leaks and reflections. Only happens with the flash and usually with sunlight.
cheers,
peter



Oct 05, 2014 at 07:06 PM
e6filmuser
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p.1 #7 · p.1 #7 · flash hot spots!


Most likely flare on the front element. Try moving your flash back a bit towards the camera. There are a lot of white elements in the image, any of which could contribute to this specific example.

Harold



Oct 06, 2014 at 04:35 AM
peterski
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p.1 #8 · p.1 #8 · flash hot spots!


e6filmuser wrote:
Most likely flare on the front element. Try moving your flash back a bit towards the camera. There are a lot of white elements in the image, any of which could contribute to this specific example.

Harold


Thanks Harold, will try that as well.
cheers,
peter



Oct 07, 2014 at 01:19 AM
Dalantech
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p.1 #9 · p.1 #9 · flash hot spots!


Two things:

First that area of a hoverfly's head is extremely reflective and it's normal to see a flash reflection there.

If you're concerned about light from the flash getting back into the camera (which would cause a loss of contrast and not necessarily a reflection problem) then set your camera to display the histogram when you view an image (all three primary colors). Make sure that the lens is to max magnification, the ISO to 100, and the shutter to the max sync speed for your flash. Set the flash/diffuser at the angle you normally use it, and go outside so you can point the camera at the sky (away from the sun) and take a photo. Now look at it on your camera's display. What you want to see is all three primary colors hugging the left hand side of the histogram and a completely black frame. If you see any of the histogram output to the right, even the slightest bit, then light from the flash is getting back into the lens.



Oct 13, 2014 at 01:48 AM
rw11
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p.1 #10 · p.1 #10 · flash hot spots!


There is a trick with using polarized light and unpol. light but I can't recall it. It is in the book:

Light--science & magic : an introduction to photographic lighting
by Hunter, Fil
Publisher, Date: Boston : Focal Press, c 2007.
Description: xii, 308 p. : ill. ; 25 cm.
Call Number: 778.72 HUNTER 2007

which is outstanding BTW.



Oct 13, 2014 at 09:14 PM
peterski
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p.1 #11 · p.1 #11 · flash hot spots!


Dalantech wrote:
Two things:

First that area of a hoverfly's head is extremely reflective and it's normal to see a flash reflection there.

If you're concerned about light from the flash getting back into the camera (which would cause a loss of contrast and not necessarily a reflection problem) then set your camera to display the histogram when you view an image (all three primary colors). Make sure that the lens is to max magnification, the ISO to 100, and the shutter to the max sync speed for your flash. Set the flash/diffuser at the angle you normally use it, and go outside so
...Show more

Thanks John. I tried it a few times and all 3 colours hugged the left hand side of the black frame as you said. Looks like no flash light is entering the front of the lens. Most of the shots I've been taking have been of insects and spiders sitting on white flowers. This may reflect some of the light around. Also I've upped the flash ETTL to +1/3 for some of the darker subjects. This may over-expose the flash as well. Will keep experimenting.
cheers,
peter



Oct 15, 2014 at 12:03 AM
Dalantech
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p.1 #12 · p.1 #12 · flash hot spots!


Sounds like you're on the right track Peter


Oct 15, 2014 at 02:00 AM





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