Not Your Everyday Banana

by Bart Arondson

submit your photo


Hall of Fame
View past winners from this year

Please participate in Meta
and help us grow.

134 reputation
8
bio website chroniclesofnojo.blogspot.com
location London, United Kingdom
age 35
visits member for 1 year, 7 months
seen May 10 at 16:05
Never* seen without a cup of coffee in hand, I enjoy programming scalable server-based software and working in distributed computing environments. *Ok, there was that one time...

Dec
25
comment What are the ideal settings to shoot Star Trails with a Nikon D90?
@JWalker: with a single 30 minute exposure, you risk clipping the highlights and losing the distinction between different luminosities of each star. With a stacked approach, you get to keep all that information. I successfully tried multiple exposures in the 6-8 second range, with the camera in a continuous drive shooting mode.
Dec
24
accepted Are there any consumer digital cameras with grayscale sensors?
Dec
24
comment Are there any consumer digital cameras with grayscale sensors?
By "grayscale" I mean that I intend the sensor to capture the brightness of the light, regardless of its wavelength. I am probably not using correct terminology here - feel free to correct me.
Dec
24
asked Are there any consumer digital cameras with grayscale sensors?
Dec
22
comment Can I intercept and interpret the autofocus signals sent to the lens?
I am concerned that the autofocus system requires a fully functioning lens (both electronically and optically) in order to trigger the signals one would be trying to reverse engineer.
Dec
22
comment Can I intercept and interpret the autofocus signals sent to the lens?
I did consider micro 4/3rds for its openness, but as you say it isn't free.
Dec
22
accepted Can I intercept and interpret the autofocus signals sent to the lens?
Dec
21
asked Can I intercept and interpret the autofocus signals sent to the lens?
Dec
16
awarded  Benefactor
Dec
16
accepted How to calculate the size of the image circle at infinity focus?
Dec
15
comment How to calculate the size of the image circle at infinity focus?
@jrista: No, I don't. If anything, I wondered if removing it would cause vignetting. But you've already answered that question, thanks!
Dec
15
comment How to nail focus for DSLR astrophotography?
+1 for the online generator link and suggestion to try making one yourself. All it took me was a craft knife, an A4 sheet of mounting cardboard and a side helping of patience; now my view is crystal clear. :)
Dec
14
comment How to calculate the size of the image circle at infinity focus?
@Olin: FWIW, I took the cheap webcam and pointed it at Jupiter (48.4 arcseconds tonight) expecting it to show up with a diameter of roughly 1.525mm on the image plane. No Barlow (no glass at all, in fact) just 1.7 degrees FOV and 650mm of focal length from a single parabolic mirror. Instead, the tiny 640px*480px (2.4mm*1.8mm) sensor registered it at 58 pixels in diameter when the formula predicted less than 41 pixels.
Dec
14
awarded  Commentator
Dec
14
comment How to calculate the size of the image circle at infinity focus?
@Olin: It can only be the Barlow. I'd been trying for the pure reflector approach but got caught out by my SLR's long flange focal distance. That's what forced the Barlow into the equation. Otherwise there's just one parabolic mirror (and a flat secondary). Finding another decent camera body that can mount on the telescope at prime focus would cost more than I'm willing to part with. I tore apart a cheap webcam (I can measure the sensor size) and stuffed it into the tube as a proof of concept but now it's cloudy outside and I don't have anything I can use as a measurable object.
Dec
14
comment How to calculate the size of the image circle at infinity focus?
The aperture may be nominally large, but it's still only f/10, which is smaller than the smallest aperture on most compact digital cameras (though granted it's still not a pinhole). If the approximation came within 5% of the observed figures I'd be happy, but I don't think that anything over 50% is useful.
Dec
14
comment How to calculate the size of the image circle at infinity focus?
@jrista, I wasn't trying to say that the Barlow lens reduced the image circle size, rather the opposite. I do understand your point of enlarging a smaller central portion of the image circle by 2x, but don't see why it's necessary to crop the field of view by 1/2 (surely you'd just add a 2x bigger CCD i.e. 4x area and you'd be back to capturing your original field of view?)
Dec
14
comment How to calculate the size of the image circle at infinity focus?
Another thing, @jrista's comment states that a Barlow lens doesn't affect image circle size. However, that would imply we must use the shorter focal length of 650mm in these formulas, which gives us an image circle small enough to cause vignetting on even my DX CCD (and I didn't see any, even when shooting in daylight).
Dec
13
comment How to calculate the size of the image circle at infinity focus?
OK, now that's the same formula that's in Wikipedia's angle-of-view entry (just rearranged). Celestron give 1.7 degrees as this scope's FOV in the specs, which when plugged into 2*TAN(a/2)*f gives me 38.6mm (a number smaller than the 35mm FX diagonal of 43.3mm, indicating vignetting on full frame CCDs). I tried shooting the moon with my own DX (23.6mmx15.8mm) and expected it to fill only 76% of the height but it was actually too big to capture completely. Somewhere, the formula and figures aren't matching reality.
Dec
13
revised How to calculate the size of the image circle at infinity focus?
try to clarify question asked (move follow up question out of main question)