Some more experiments

During an outing yesterday, Buggato asked if I was going to chase any moon shots in the next few nights, and I shrugged and said, “Maybe.” I had some experiments to try, but the past several nights the humidity and haze were affecting things too much.

Going out after 11 PM, however, I saw the moon was showing as deep contrast as I’ve ever seen, evidence of a good clear night, so I said What the hell? and got out the tripod. One of the experiments was trying out the Tokina 2x teleconverter with the newer Tamron 150-600mm lens. A teleconverter is essentially a magnifier that goes between camera and lens, and will magnify the image by the specified amount while reducing the light by largely the same amount, so in this case, two stops darker. This is one of the problems with teleconverters, in that they not only eradicate any chance of autofocus in most cases because of this darkening, but they also reduce the light which increases the shutter speed and thus the opportunities for camera shake. To say nothing of the quality, which is often not optimal.

I’d obtained this one close to twenty years ago (certainly not one of the top-of-the-line models because those are ridiculously expensive,) and used it here and there, but it’s strictly tripod work, and with the old Sigma 170-500 lens the results were sporadic, to say the least – in most cases I was better off without it, especially for astrophotography. But it was worth a shot.

So below, the lens as-is, no converter, and you can see how distinct the contrast was last night.

waxing gibbous moon with Tamron 150-600 at 600mm
I take quite a few images of subjects like the moon, as I’ve said before, because precise focus is very hard to obtain, so it was pleasing to have the first frames bang on.

By the way, firmly-fixed tripod, mirror lock-up with at least a two-second delay, and a remote release were all used here. 1/160 second, f9 at ISO 250.

Now for the teleconverter test.

waxing gibbous moon with Tamron 150-600 at 600mm with Tokina 2x teleconverter
This time, the exposure was 1/40 second, f8 at ISO 250, which accounted for the light loss through the teleconverter nicely. And I’ll be damned if the resolution isn’t kicking it here, too; the initial views during editing had me pretty fired up. But of course, both of these are reduced for blog display and nowhere near full resolution, so let’s see those, side by side.

comparison of two images, with teleconverter and without but upsampled
The comparison here really is between the quality of the teleconverter and simply upsampling the original image without a teleconverter to see if it’s actually worth it. As you can see, the quality is damn near identical, even though the upper image is the original that has been expanded to twice its original size to compare directly. Actually, not quite twice, but a 91% increase rather than the promised 100% (2x,) but that’s a trivial quibble. There’s a faint greenish color cast from the converter in the bottom image, nothing to worry about, and a little loss of contrast, but again, not enough to cause me to tear my (remaining) hair out.

So if the quality is the same if I simply upsample the original in an editing program, why not just stick to that? And for astrophotography and various other uses, this may be just fine, but sometimes the image depends on what’s captured in the frame, and this especially holds true for video – cropping video footage is usually more hassle than it’s worth. But video is also rendered in lower resolution than still photos, so the teleconverter could probably produce even crappier results and still not be too noticeable. And so, while out there for a few minutes, I shot a brief video clip intended only to show how much the moon was moving (or the Earth was turning – you know, pedantism) in that time. The teleconverter made this much more distinct.

I saw the speck cross the frame while watching the LCD on the back of the camera and was pretty excited, let me tell you. Weeks earlier I’d seen much the same thing before I could trip the shutter, and figured I’d missed a satellite passing in front of the moon because, by my reasoning, for a bird to appear that small it would be moving much slower across the face. We now see I was playing Silly Buggers, because it clearly crosses quite quickly even when rendered as little more than a speck. And of course, were these birds, or bats? Not too many birds are out at night, but there are some, among them owls and nighthawks naturally; I can rule out the former I think, from the flight and flapping patterns, but not the latter. To be sure, I’d have to catch some closer to the camera for more detail. So it remains to be seen if I’m ever going to burn up the memory card in further attempts at this, but hey, three in one minute is encouraging at least.

Also illustrated rather handily with that clip is how much minor vibrations are magnified with telephoto lenses. At the beginning and end of the clip, all I did was reach up to the camera and press the button on the back to start/stop the video, and I wasn’t being heavy-handed. Seeing how long it takes for that to die down is convincing enough to use mirror lock-up and a nice delay, to eradicate the vibration from the mirror at least. Unfortunately, the corded remote release does not activate the video, but the infra-red one will, so, next time.

« [previous]
[next] »