PF Photography Thread

Borek

7.3 microradians, perhaps

Andy Resnick

The upper image appears brighter and more vivid- is that an aperture difference?

Good question- I'm not sure what the subtended angle is. Let's see: 800mm on a 35mm frame gives a total subtended angle of 2.5 degrees, and given the sensor format (6k x 4k, 7200 on the diagonal), each pixel subtends about 1.25 arcseconds (6 microradians). By my count, the 'fundamental' streak length is about 30 pixels, or 0.18 milliradians (0.6 arcminutes).

So there's a lot of room for improvement.

Andre

Curious, isn't? However, everything was identical, including the flash settings. Yet he colors are clearly different. Here are both orginal jpg's with EXIFs, slightly higher compressed to limit filesize.

http://dl.dropbox.com/u/22026080/70-300.jpg
http://dl.dropbox.com/u/22026080/100.jpg

d.smith292

I have some pretty cool photos on my blog at

http://www.broughttofocus.wordpress.com

and at my art gallery at

http://www.etsy.com/shop/dsmith292

Andy Resnick

I like the contrast in a lot of your B&W photos (like 'Lively squirrel' and 'Hidden content', for example)- do you use a filter to boost the contrast (like an O56), or just use a B&W mode on the camera?

d.smith292

No, actually I don't use filters at all. I am hoping one day to upgrade to a much better camera, but for now I'm using a Canon Powershot a520 and adjusting the contrast on my computer. Thank you for the complement. Oh and I always shoot my photos in color and change them to black and white later. I do this just in case the color version looks better in the end.

turbo

Hi, Andy. The moon is out, so a couple of minutes ago, I shot this. 1600 ISO to minimize atmospheric refraction and (human) shake. 100-400mm Canon L lens at full zoom, hand-held (no bracing of any kind) and cropped hard. I got a tad of color-noise at that ISO, so I converted the image to grayscale, since the Moon is a pretty white-gray place. Not the same quality that I could get with one of my APO refractors, but not bad for strolling (limping, actually) out onto the back deck and making a snapshot. The moon is a pretty featureless (low contrast) place when it is nearly full, but check near the lower limbs.

Andy Resnick

Nice!

I've been working with the 400mm lens today (and dodging raindrops)- with the teleconverter, the image is soft until I set the lens to f/8- then it's incredibly sharp (that is, an 800mm f/16 lens). Without the teleconverter, the image is much sharper always, and gets tack-sharp around f/4.

Consistently, any point-like 'sparkles' get rendered as short lines, always in the same orientation and length. This supports my idea of lens flap, but I won't know for sure until I can remotely trigger the shutter.

Andre

Another moonshot made around midnight last night. Hardware the 7D with the 70-300mm at full tele

Exposure manual trial and error, I ended up with this ISO 100 F6.7 Shutter 1/180

Raw processing: a tad more sharpening. contrast high tones priority and noise reduction off

100% size crop:






The glass keeps amazing me.

Borek

I planned to take a picture as well, but it was hazy. Seems like tonight can be better.

Gad

WOAHHHH
Amazing.

turbo

Same 4-15 image of the moon, but with smart sharpening in Photoshop. A bit grainy after sharpening.

Andy Resnick

The weather was highly cooperative this past weekend, and I was able to spend time sussing out the 400mm. There's definitely a 'sweet spot' to use the lens- in terms of shutter speed, either < 1/60s or >0.5s overcomes the mirror flap issue, and > f/5.6 gives tack-sharp images.

Here's the full moon last night, 100% (sorry, it's a bit over 650 pixels on a side): This was taken at 400mm, f/11, ISO 100, 1/80s



Looking carefully at the limb, you can see atmospheric effects- the atmospheric currents act like a lens, creating a 'mirage' kind of flicker. At 800mm, the effect is very pronounced (100% crop): 800mm, f/5.6, ISO 100, 1/80s:



It was pretty cool to watch through the lens, even though it limited the ultimate resolution.

I was able to get an acceptable image of Mizar (300% cropped image): 800mm, f/5.6, ISO 6400, 1/80 s:



I can tell it's a multiple, but perhaps not that it's a double binary. Atmospheric blurring is quite obvious here.

iBOOM

I really love the moon photos :O

turbo

They are the first real astrophotos that most amateurs could make during the age of photographic films. Sometimes, purists got wrapped up in trying to capture fainter and fainter stuff, so Moon photography fell out of favor, especially since the extra light would wash out faint details on long-exposure astrophos of galaxies, globulars, nebulae, etc. Now, technology allows photographers to take Moon shots as snapshots. That's a pretty good thing. The Moon is our closest neighbor and it changes from night to night. You don't have to set up a $$$$ telescope and accept washed-out astrophotos of faint objects on nights when the Moon is up. It took me probably 30 seconds total to grab a couple of snapshots.

Andy Resnick

It always feels good to solve a problem. Here's a 100% crop taken through the 800mm with a shutter speed of 1/6s (10-second delay) of the label on a nitrogen tank in the lab (from across the room):



The delay allows all transient vibrations to dampen out, but when the mirror comes up for exposure, the induced vibrations cause what you see above. 1/6s is about the worst-case scenario: long enough to really capture the vibration, and short enough to *only* capture an image while everything is moving. The workaround was to use either shutter speeds very fast or very slow- either using the lens wide-open with very high camera gains (ISO) to get the exposure time down, or use very high f/# to force long exposure times. Both introduce restrictions- long exposures mean the subject has to be motionless, while high ISO introduces a lot of noise and using the full aperture of the lens also maximizes the aberrations.

Adding the $9 remote shutter results in this image - again, 1/6s exposure, using the mirror lockup option and waiting 3 seconds between the mirror lock and exposure:



I don't think the improvement could be any more dramatic.

Andre

Nice work, Andy. I knew about that problem too and I use a remote as well, locking the mirror, using the life view mode. Etc.

Recently I changed studio work by using the laptop as remote 'wired' control. It also locks up the mirror, ad it stores the image, where it should go anyway, directky on the computer.