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Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068
We have a Canon 20D, 300D, and D60. All work equally well. As for lenses, its not too important, although you want a fast lense (f/2.8 for example) Plus, these are for shooting in the dark for corona detection.
A good lense is a Canon 24-70mm f/2.8L which is about $1400 new i think, and the Canon 20D about $1300.00.
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
A Canon Rebel XT/350D will give comparable image quality to the 20D at a lower price. It has a lower build quality but if you don't plan to throw it around it will not matter much in this case.
If you don't need zoom you can get a better and brighter lens for a fraction of the price. Like the Canon EF 85 mm f/1.8 USM for $350. It would need less than half the exposure time.
In all cases get a quality tripod with a metal head that has no creep to ensure you get sharp pictures.
Banned on April 7, 2007 Registered Member #277
Joined: Fri Mar 03 2006, 10:15AM
Location: Florida
Posts: 157
With regard to seeking various methods of viewing corona, I found the below text on the web, I invite comment as to the usefulness of night vision devices to view Corona. CM
"As indicated by John Snell..... we have found there is no better way than to use image intensifiers (night vision devices) which clearly reveal the type of corona, its intensity and its exact position."
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068
I would claim that the 85mm f/1.8 is a better lense. It may be faster, but it would have to be stopped down several stops to get the same performance of the 24-70mm f/2.8L at f2.8.
Also, i think you need to figure out what your needs will be. Are you merely going to look at high voltage equipment nearby, or try to zoom in on a power line overhead which may be several hundred feet away.
Also, before choosing between standard Canon glass and "L" series glass, take a look at the spectral transfer characteristics to see which passes UV light more readily. The "L" series, which is usually made from ED type glass (or fluorite in some of their larger zooms) might attenuate more UV than the cheaper glass.
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
It may be faster, but it would have to be stopped down several stops to get the same performance of the 24-70mm f/2.8L at f2.8.
It can be turned on the head and said that the 24-70 mm is not capable of anything close to the performance of f/1.8.
In bright light and when photographing point sources, sharpness is important (for scientific purposes). When you photograph something you can't see at a wavelength where the distance scale is not correct you are not going to get pin sharp pictures. The faster lens will win all the time.
"As indicated by John Snell..... we have found there is no better way than to use image intensifiers (night vision devices) which clearly reveal the type of corona, its intensity and its exact position."
That may work very well and be quite cheap. I suspect that different types of image intensifiers have quite different sensitivity to light that is not IR.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
The CoronaCam can actually see faint corona in broad daylight. I believe it does that with a special filter on the UV camera that passes the corona wavelengths and blocks visible light. So the gain on this camera can be turned up very high, and the output from it is combined with an ordinary camera that shows the daylit scene.
Bjoern: I could just as easily argue that when photographing an unknown scene like that, a fast lens is bad because it doesn't have much depth of field
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
I could just as easily argue that when photographing an unknown scene like that, a fast lens is bad because it doesn't have much depth of field
You could try, but I read the first post where he says the distance is 130 feet and I know from experince that it is possible to get reasonable results at f/1.8 by setting the focus close to infinity at that distance using an 85 mm lens.
Another point is that 85 mm is a bit short for that distance, 200 mm might be a better choice.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
wrote ...
In bright light and when photographing point sources, sharpness is important (for scientific purposes). When you photograph something you can't see at a wavelength where the distance scale is not correct you are not going to get pin sharp pictures. The faster lens will win all the time.
Firstly, not so. If you are going to photograph at a distance (i.e. powerlines), you do not want a fast lense. At 85mm and f/1.8, the depth of field is going to be extremely shallow, and unless you are perfectly focused (again hard to do since you don't even know where the corona is) , that corona will not be captured. At close range, i would agree with you (i.e. hv cabinets where camera is several feet away), but for telephoto work (i.e. powerlines), you need a larger depth of field to be effective.
Secondly, you are not going to photography corona that can't be seen with a digital SLR. Both the spectral response of the internal bayer matrix filter, and the response of the actual camera glass is going to attenuate UV light too much to be of any use. The DSLRs should be used to visible corona only.
Registered Member #27
Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058
At 85mm and f/1.8, the depth of field is going to be extremely shallow
The depth of field is 50 feet at a distance of 130 deet, that is far from extremely shallow, it is good enough that setting the lens at infinity will give a picture that will be just about perfect. As I said, I have tried it. It is at close range the depth of field becomes a problem, it can even become shorter than 1 mm.
Secondly, you are not going to photography corona that can't be seen with a digital SLR. Both the spectral response of the internal bayer matrix filter, and the response of the actual camera glass is going to attenuate UV light too much to be of any use. The DSLRs should be used to visible corona only
I have not measured the amount of UV compared to the amountof visible so I don't know if there is 5 times more UV or 1000 times more. If it is less than 100 times then the UV will make no difference. I can say that further up the thread you made a point of comparing which glass were passing most UV before buying a lens.
Corona has a strong peak at 360 nm and many non UV lenses transmit a usable amount of light in the 350-400 nm range so it is not all gloom.
Banned on April 7, 2007 Registered Member #277
Joined: Fri Mar 03 2006, 10:15AM
Location: Florida
Posts: 157
As is my nature, I'm going to try the cheapest route available to me first. I have a friend who is a private investigator who owns a professional quality night-vision videocamera he uses for surveillance. He's going to allow me to borrow it to train on the wire 130 in the air to see if it can record any flashes of light during the night (if indeed any flashes of light exist). The problem I foresee is that if the camera records no corona flashes, will I assume no corona is being produced... or will I assume the camera simply isn't suited to see the corona. Decisions, decisions. CM
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Seeking to purchase CoronaCam
