www.photomacrography.net :: View topic - Easy to overexpose when using darkfield illumination?
www.photomacrography.net Forum Index
An online community dedicated to the practices of photomacrography, close-up and macro photography, and photomicrography.
Photomacrography Front Page Amateurmicrography Front Page
Old Forums/Galleries
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 
Easy to overexpose when using darkfield illumination?

 
Post new topic   Reply to topic    www.photomacrography.net Forum Index -> Beginners Micro
View previous topic :: View next topic  
Author Message
dragonblade



Joined: 18 Oct 2014
Posts: 56

PostPosted: Sun Nov 05, 2017 9:05 pm    Post subject: Easy to overexpose when using darkfield illumination? Reply with quote

Ive been reading up on darkfield illumination and there's one bit of information someone mentioned in a youtube video which I haven't heard before. According to the video's uploader, it's very easy to get overexposure in darkfield images while shooting through a microscope. And sure enough, there were a few cases of overexposure in the darkfield video.

Is this likely due to the increase in contrast in darkfield imagery? I did note in the video that there was a water flea with some parts of the animal being correctly exposed but a large proportion of the 'stomach' area being overexposed. So it looked like there was a lot of contrast in the imagery. During another point in the video, there were a group of eggs that were very overexposed.

It could be possible too that the person who shot the video was using auto exposure. If that's the case, then all that large expanse of black would easily cause overexposure in many cases. As for myself, I plan to use full manual exposure when I get my equipment set up. As I'll be shooting video, I'll be forced to keep my shutter speed at 50th and the aperture wide open. I guess I'll have to adjust my iso setting to change exposure. If I get overexposure at the lowest iso setting, I'll have to use an ND filter to compensate.
Back to top
View user's profile Send private message
rjlittlefield
Site Admin


Joined: 01 Aug 2006
Posts: 18250
Location: Richland, Washington State, USA

PostPosted: Sun Nov 05, 2017 9:59 pm    Post subject: Re: Easy to overexpose when using darkfield illumination? Reply with quote

dragonblade wrote:
It could be possible too that the person who shot the video was using auto exposure. If that's the case, then all that large expanse of black would easily cause overexposure in many cases.

The same thing happens if you do manual exposure but fall into the trap of believing a metering system that relies on averaging. The only safe approach is to check for blown brights in the captured images, preferably by loading them into a computer where software can zoom in as required. Histograms in camera give a pretty good indication, but if you have small bright spots, the blowouts may not be evident in histogram either.

--Rik
Back to top
View user's profile Send private message Visit poster's website
dragonblade



Joined: 18 Oct 2014
Posts: 56

PostPosted: Sun Nov 05, 2017 10:27 pm    Post subject: Re: Easy to overexpose when using darkfield illumination? Reply with quote

rjlittlefield wrote:

The same thing happens if you do manual exposure but fall into the trap of believing a metering system that relies on averaging. The only safe approach is to check for blown brights in the captured images
--Rik


Exactly. With my Panasonic G6 Micro 4/3 camera in video mode, I judge exposure in live view and then adjust accordingly (in real world situations.) I'll try the same technique when recording through a microscope.
Back to top
View user's profile Send private message
dragonblade



Joined: 18 Oct 2014
Posts: 56

PostPosted: Tue Nov 07, 2017 2:07 am    Post subject: Reply with quote

As noted above, adjusting on the fly is what I do for video (prior to pressing the record button.) Though for still photography using darkfield illumination, I would like to try HDR (if I can get my hands on some prepared samples / static subjects.) I think a darkfield HDR portrait of Daphnia could look awesome.
Back to top
View user's profile Send private message
Beatsy



Joined: 05 Jul 2013
Posts: 911
Location: Malvern, UK

PostPosted: Tue Nov 07, 2017 2:24 am    Post subject: Reply with quote

Overall dynamic range of a DF scene is usually much greater than in brightfield too. The Sony A9 has a handy "protect highlights" metering mode that works wonderfully for DF images. It generally yields a very dark image overall but the high dynamic range of the sensor allows you to pull the shadows up by miles in post processing too. A pretty expensive option, I know, but if you have the camera for other uses anyway it's a handy feature to have in the toolbox. I presume there are other cameras with this option...?
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    www.photomacrography.net Forum Index -> Beginners Micro All times are GMT - 7 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group