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Tachinidae Mintho

 
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qanunji



Joined: 29 May 2011
Posts: 36
Location: Haifa, Israel

PostPosted: Sat Jun 11, 2011 10:26 am    Post subject: Tachinidae Mintho Reply with quote



Hi,
having listened to Rik's advice, I've stopped my front stacked lens to F4.
my setup is 7D with 50 mm 1.8 stacked on 55-250 mm, 130 photos, dMap.

Here is 100% crop:



still, i got some issues:

as you can see in the following frame, there are a lot of white vertical lines.
what are those? sensor dust? burnt sensor pixels?



thanks[/img]
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rjlittlefield
Site Admin


Joined: 01 Aug 2006
Posts: 19240
Location: Richland, Washington State, USA

PostPosted: Sat Jun 11, 2011 10:55 am    Post subject: Reply with quote

This now looks good for sharpness and chromatic aberration. Striking improvement from your first ones. Nice work.

Quote:
as you can see in the following frame, there are a lot of white vertical lines.
what are those? sensor dust? burnt sensor pixels?

Sensor dust is dark on light background, and the spots spread over several pixels. The trails of light spots I see here look like "hot pixels". Hot pixels are pixels that are functional but accumulate charge from random noise faster than the surrounding pixels do. Typically they are no problem with short exposures (1/30 second or less) but become progressively more obvious with longer exposures.

What illumination method and exposure times are you using here? What type of camera?

--Rik
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qanunji



Joined: 29 May 2011
Posts: 36
Location: Haifa, Israel

PostPosted: Sat Jun 11, 2011 11:04 am    Post subject: Reply with quote

thanks for your answers Rik.

This one was around 0.6", using a desk lamp....

you wrote "random noise", but this one is not random, its advancing with the stack, am i right?
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rjlittlefield
Site Admin


Joined: 01 Aug 2006
Posts: 19240
Location: Richland, Washington State, USA

PostPosted: Sat Jun 11, 2011 11:35 am    Post subject: Reply with quote

qanunji wrote:
This one was around 0.6", using a desk lamp....

This makes sense. I used to have similar problems with my 300D, becoming visible at about 0.5 seconds and very obvious at 5 seconds.

Making the illumination brighter will help. Using flash instead of continuous illumination should make the trails disappear altogether. The problem is also worse at higher temperatures, so it's likely to be better at the beginning of a long photo session than at the end.

Quote:
you wrote "random noise", but this one is not random, its advancing with the stack, am i right?

Sorry, I was too brief.

The spots appear at fixed pixel positions in the original source files. Due to alignment of source frames during stacking, the spots march together and form trails that are more or less similar depending on details of the alignment and where in the frame the spots appear. One common pattern is parallel trails as seen here.

The phrase "random noise" refers to the electronic process by which certain pixels accumulate charge and become brighter than their surrounding pixels.

--Rik
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NikonUser



Joined: 04 Sep 2008
Posts: 2540
Location: southern New Brunswick, Canada

PostPosted: Sat Jun 11, 2011 1:18 pm    Post subject: Reply with quote

For an entomologist these images have a big 'ouch' factor.

We are used to see light coming from above, so that the dorsal surface is lighter than the ventral.

With your fly's head upside down, you get an unnatural light ventral surface (top in your images) and an unnatural shaded dorsal surface (below in your images).

Apart from the upside feature which bothers me, the lighting effect is all wrong.
_________________
NU.
student of entomology
Quote – Holmes on ‘Entomology’
” I suppose you are an entomologist ? “
” Not quite so ambitious as that, sir. I should like to put my eyes on the individual entitled to that name.
No man can be truly called an entomologist,
sir; the subject is too vast for any single human intelligence to grasp.”
Oliver Wendell Holmes, Sr
The Poet at the Breakfast Table.

Nikon camera, lenses and objectives
Olympus microscope and objectives
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qanunji



Joined: 29 May 2011
Posts: 36
Location: Haifa, Israel

PostPosted: Sat Jun 11, 2011 4:07 pm    Post subject: Reply with quote

thanks for your feedback, although i liked the composition.
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