Annoying Light Bloom
This weekend it was inevitable that some sort of insect would become trapped inside the house and subsequently die what with the hot weather and the windows being open. Sure enough, the first dead fly appeared on Saturday and inspired me to try some super macro photography but this time I wanted to try a slightly different technique that that I used last time. This time I wanted to try to use the distance of the lens away from the camera sensor to provide the magnification. I had an old Pringles tin which I cut the end off to form a subsitute bellows, affixed one end to my lens-less camera with sticky tape and wedged my macro lens in the other. After setting up I noticed that I was getting an odd light bloom inside the image. I thoguht that maybe the light was bouncing around inside the tube as the inside was still silvered so I improvise a dark material to line the inside of the tube (it was a black bin liner) and tried again after wrapping another bin liner around the join between the tube and the camera to cut out any possible light leak through the rough join.
Still I ended up with the bloom.
So I fugured maybe I just needed to do a better job of blackening the inside of the tube so today I purchased some matt black spray paint and coated the inside of the tube with that. I also invested in a daylight bulb to illuminate my subject better. After spraying, drying, rejoining it all together and wrapping a small rubbish tips worth of bin liners around the assembly I tried again.
I still have an odd light bloom. Cleaning all the lens faces doesn't get rid of it (I thought it might be condesation on the lens or something as the bulb when on was slighly heating my lens). Changing the angle of the lens to the subject doesn't get rid of it. I'm at somewhat of a loss now as to what to try next. It may just not be possible to get of it with the dodgy set-up I've produced currently.
Still, it's getting late now and I've run out of ideas. Here's the best shot of the set so far.
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Light bloom
What happens if you cover the lens to test where the light is coming from. Do you still get the bloom? If so, then there is still a leak in the Pringles tube. Can you tell from where the bloom occurs the direction of the leak or does the bloom move around, ie not always in the same area. If the bloom is gone when you cover the lens assembly, then the leak is from that assembly. I presume you've tried most of these suggestions already but it would help to eliminate the source of the bloom. Let us know.
Simple tests are the best
Funnily enough I hadn't tried the 'cover the lens up' test. So I just had a go. No real light leak showed which suggests that it's just a problem with image quality. I've currently got the macro lens reversed in the tube. I'll quickly try it with the lens the other way round. I have a sneaky feeling that won't work either.
Still no good
I turned the lens around and had a go but it still wasn't too good. It seems it's just an image quality drop-off that I'm not going to be able to do anything about which is annoying. The Pringles tube is perfectly sized to allow the macro lens to be wedged in the end without the need for lots of sticky tape to hold it in place.
If I play with the light curves, increase the contrast and run a noise reduction exercise on it I can get it looking 'better' but it's a lot of effort for what is still essentially a poor quality picture (see below). I think I've exhausted all my ideas for this set up now. I might try with two lenses again later and I'll keep the Pringles tube for now...
Fly image
That looks a lot better. Have you tried using the set up on another object to see if the "bloom" is a reflection from an iridescent part of the fly?
I haven't
but I don't think it's that. It's to consistent and the fly is not that iridescent. I'll try and play a bit more later in the week.