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Messages - epsiloneri

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EOS Bodies / Re: EOS Bodies - The ultimate duo & why
« on: October 19, 2012, 02:51:03 PM »
While it may not be the best for the moon, I bet you get some amazing auroras.
If I lived in Canada that would be true, but in Europe you have to go even more north to see them regularly (although they show up here in Stockholm from time to time). I got a good display while visiting Yellowknife in Canada in 2009, however (50D, EF-S 10-22 f/3.5-4.5 USM @ 10mm/3.5, ISO 800, 15sec).

EOS Bodies / Re: EOS Bodies - The ultimate duo & why
« on: October 19, 2012, 11:24:54 AM »
Yes, I agree that the relatively softer image from 7D could very well be due to atmospheric distortion, since they were not simultaneous and due to the low altitude of the moon. This was in the summer, however, and from my location the moon did not rise much higher that night (I live on 59 deg northern latitude). If I find the time and a clear night I will repeat the experiment this winter with the moon much higher up (and a 5D3).

EOS Bodies / Re: do crop sensors really add reach?
« on: October 19, 2012, 02:32:58 AM »
Just adding my moon comparisons of 7D vs. 5D2+TC1.4x to the thread.

Lenses / Re: Canon should change name to Coma
« on: October 10, 2012, 12:54:35 PM »
I also use the EF 24/1.4L II for wide field astrophotography, and can confirm the unfortunate point-spread functions away from centre (in particular the wings, visible around saturated point sources). Below is an image from last year's Draconid shower (notice meteor hitting Bull's eye of Taurus!) with city scape in the foreground. This is a crop showing about 25% of the image area, but the aberrations are very visible in the citylights. f/1.4, 5 second, iso 100, 5D2.

Stopping down defies the purpose of having a fast lens; in astrophotography every additional photon is valuable. The Samyang looks interesting, in particular as missing AF is no issue for astrophotography. Thanks for sharing.

So now we can have L-bags as well! But where's the red ring?

I went back and put the RAW sharpness settings and unsharp masking to zero before converting the file to TIFF and: halos are gone.
You can also reduce the halos in unsharp mask by playing with the unsharp radius, e.g. making it much bigger removes background on a larger, smoother scale. You can increase the brilliance of the stars quite a bit by doing this (by reducing the sky haze), but have to take care to not introduce artefacts on large scales, e.g. foreground objects like the mountains in your case (or the dark lanes in the milky way). You can get around this by using masks etc, but I'm starting to get off topic.

Here is a image of the sun reflecting off a gazing globe.  Its a 100% crop, but no black ring.
The effect is more pronounced the greater the contrast (steep brightness gradient) and smaller the blown image, i.e. stars and hot pixels are ideal to produce dark halos. The sun in your image is more extended and bright also outside the saturated region, so sharpening shouldn't produce as easily visible halos.

This is a straight conversion from raw to jpg in LR 4, all the settings are nominal, no sharpening or NR.
Isn't sharpening applied when using nominal settings? (I'm not too familiar with LR4, but other software apply it by default) If you push sharpening using unsharp mask I'm sure you can produce a dark halo around the bright dot in the right hemisphere. Just to illustrate the effect. (looking closer at your image there actually seems to be a dark edge to the white spots [not the sun] - implying some sharpening may have actually taken place?)

But I also will take care next time and won't do 45 shots within 15 minutes!
I have taken long-exposure (30s) shots continously for hours (star trails!) without noticing any significant increase in noise, so I'm not sure this is a real problem. It should be very easy to find out though: do you notice a significant noise increase in your last image (when the sensor is "heated up") compared to your first image (with the sensor still at ambient) of that 15 min interval?

When i say it hasn't been processed and what is going on with images then it is still suggested i am lying and that it in fact has been sharpened, it bugs me a little.
I was commenting on Pedro's image. In your case it looks like hot pixels with demosaicing artefacts. Are the bright spots in your picture visible at the same pixel positions in other pictures taken at the same time with similar settings? There's always processing going on in producing images, it doesn't need to be the post-processing that introduces problems.

EOS Bodies / Re: 5D3 Problem black halos around stars in RAW files...hmm
« on: September 09, 2012, 02:57:21 PM »
I can't say but what about the fact that your points of light are ovals?
Since your question hasn't been addressed yet... the 'ovals' are due to motion blur.

Anyone out there having the same problems while doing night sky?
Yes, I happened to take a night shot with stars using a 5D3 yesterday, and I see this precise phenomenom for saturated stars when the default sharpening is used (just tested). When I turn sharpening off, the black halos disappear. I just tried it but am to lazy to produce screenshots for you... just try it yourself. Using unsharp mask as a "sharpening" filter is particularly good at producing black halos.

I agree with nubu. Looks like a postprocessing artefact (sharpening filter, NR).

Lenses / Re: A New EF 400 f/5.6L Before Photokina? [CR1]
« on: September 04, 2012, 02:48:34 AM »
Replacement lens that currently costs about same as 100-400.  At f/5.6 why would anyone want this lens?  Help me understand benefit over 100-400?   

Short answer: Image quality. Versatility. Weight. Pick two.

Longer answer: Different trade-offs; in general, there are many desirable properties of lenses (including those above + AF, price, etc) that cannot all be optimised at the same time, so you have to make trade-offs depending on your priorities. The 100-400 and 400/5.6 represent different choices (as does the 400/2.8 ). There is no single lens that is best at everything, even if not considering price.

I had two of these lenses and both were crap.
Thanks for contributing with your experience. Your review strikes me as a bit too emotional, exaggerating and contradicting with other reviews for me to take it seriously, in particular since this also is your first post and we haven't had a chance to gauge your experience, skills, language and general attitudes. I cannot say I've seen internet flooded with negative reviews of the lens. To measure barrel distortion you need to carefully align your paper wall with the sensor plane - they have to be absolutely parallel. This doesn't seem to be the case in your example photo, which looks as if tilted slightly downwards. Distortion has previously been measured to be very low, ~1% barrel at 24mm and 0.02% pincusion at 70mm, uniform across the frame. Very few issues with flare and ghosting, even when shooting into the light. Vignetting sure is a problem at f/2.8, but by f/5.6 it's down to half a stop in the corners, and is noticably better than Canon's current offering.
Good luck with your purchase of this lens....
Thanks, I probably will get it at some point, and then I will take care to evaluate the lens to check for any problems you mentioned. Maybe Tamron has problem with its QC, but at this point I cannot exclude user error.

You can only win here if you increase the exposure time. In total you have more noise compared to cropping or using a camera with smaller pixels, but you also have more photons if you increase the exposure time to overcompensate for that and increase DR and SNR after downscaling.
Yes, you got it right. The point is that you don't lose (much) light by using a TC, compared to cropping. Yes, the absolute noise increases, but the relative noise (noise relative to the signal) decreases as sqrt(number of photons), if photon dominated. To say that the noise increases can be confusing, since it gives the impression that to get the lowest noise images, you expose for as short time as possible. Ideally, a completely dark image has zero photon noise  ;)

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