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Messages - noisejammer

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106
Hmm... no option to add more than one alternative?

I have a 1952 (?) Rollei TLR and a 1954(?) Agfa Super Silette RF and a couple of OM SLR's. I pick them up when I'm in the mood. They all work fine.

Even my phone camera gets it's day in the sun from time to time... it can do things than an SLR can't.

107
Lenses / Re: Wide angle lens advice and AF confirmation
« on: March 02, 2013, 09:22:38 AM »
I can't speak to the 24L but I own the 21 and 25mm Zeiss lenses and have used the TS-E 24 quite a bit.

You asked whether the ZE 25/2 is not up to the ZE 21/2.8.

In truth, they are very different lenses however I believe the 25/2 is at least it's optical equal. Bear in mind that the MTF plots show the lenses wide open and then stopped down two clicks. At f/4, the resolution of the 25 is the equal of the 21's resolution at f/5.6. Both lenses exhibit field curvature in the extreme corners and stopping down does not help much. Vignetting is similar - both lenses need to be stopped down to f/5.6 for this to go away.

The TS-E 24 is a very good lens indeed however it is bulky and (IMO) the focus mechanism is not up to the quality of the optics. Gearing on the tilt mechanism could be better too. All this said, it is a versatile lens that can double as a 34mm tilt-shift if you have a 1.4x tc. Note that it is optically slower which makes focusing through the view finder more difficult.

Focusing - With all MF lenses, I find that magnified live view and a Zacuto 3x Z-finder Pro allows me to achieve precise focus every time. The Z-finder can be installed on the camera using a Z-FRM and remain there. It looks odd but it works well for me. I use Magic Lantern albeit not as effectively as I might. The focus peaking does allow rapid checking of focus.

The distortion of the lenses is easily removed in post but be wary that this can cost you resolution. I'm experimenting with doing it as the last step in my processing.

Samples. You can take a look here... http://photography-on-the.net/forum/forumdisplay.php?f=107 . You should find hundreds of images from each lens to look at.

108
Lenses / Re: Will Canon step up to Zeiss with a 55mm 1.4L?
« on: February 21, 2013, 09:14:14 PM »
Would you be willing to drop $4k on a 55mm Canon lens?
Reading between the lines, that seems to be the expected price for the ZE beauty.

I already own 7 ZE lenses and this is way too rich for my blood.

109
Lenses / Re: Tilt Shift Lenses - Looking for Advice
« on: February 21, 2013, 01:07:19 PM »
I think I can comment on using a tc with a TS-E 17. My tests yielded an unexpected result.

I tested my TS-E 17 plus a 1.4x Mk III against my friends TS-E 24 II. I stopped both down to f/8 effective - in other words the 17 was stopped down to f/5.6 while the 24 was stopped down to f/8.  I used magnified live view to focus at the center of the frame, and then magnified live view to focus at 2/3 of the way out and in the corners.

My results
1. In the center there is no difference at all.
2. At the 2/3 position, there was no difference at all.
3. In the corners, the 17/1.4x combination was BETTER. If memory serves, point sources were rendered on half the pixels.
4. There was no difference in chromatic aberration between the two systems.
5. Focusing precisely enough to extract everything from this lens is extremely difficult - even magnified live view with a 3x loupe left me with some uncertainty.

Ok, so I've looked at the results on TDP.

Bryan and I disagree on our results however Bryan was shooting a flat calibration target. I refocused the lenses to eliminate the effect of focus curvature. My conclusion is that if was are shooting a brick wall, the 24 TS-E may well be sharper. If I was shooting something else, my results would depend entirely on how well the subject matches the focal curvature of the lens.

The other caveat is that I had exactly one 17mm, one 1.4x tc and one 24mm. I do not have any idea of whether this is representative or not. Nevertheless, I was convinced enough that I decided I did not need to purchase a 24 TS-E and picked up a 25/2 Zeiss instead.

Other thoughts
6. Using the TS-E 17 at f/8 is not an issue - if you are shooting a landscape, you are probably going to use f/8 to f/16 anyway.

7. Although I've found a way to use my Lee filters on my TS-E 17, this comes at the price of reduced shift before I hit vignetting. If memory serves, I can move the lens about 6 mm each way so that the effective image is about 48x24 mm (115 deg diagonal field of view) with the filters on. Fotodiox has a solution for this but I'm not willing to buy (or carry) yet another set of filters.

8. On reflection, I have not tried to see how the tc responds when the lens is exercised in shift. I'll try that when the lens comes back from Canon.

9. I strongly recommend you secure the adjustment knobs with a blob of nail polish / thread locker. Loosing one can be inconvenient... been there, done that.

10. Using the 17mm requires a lot of discipline. The front element is entirely unprotected and replacing it is expensive.

110
Lenses / Re: Tripod collar for 200mm f/2.8 L?
« on: February 18, 2013, 05:15:33 PM »
There are plenty of options on fleabay... Search for an A(B) or A II (B) ring.  I saw some going for $6

111
Canon General / Re: Canon 1D X on the Street
« on: February 18, 2013, 12:14:50 PM »
I drag a 1d4, 5d2, 5 Zeiss lenses, a TS-E, 70-200/2.8 ii and a 400/4 DO pretty much everywhere I go including annual expeditions to Southern Africa. I take reasonable care but it's all insured for replacement. Apart from the deductible, theft would be a nuisance but I really don't stress at all.

112
Canon General / Re: Digital Rev!
« on: February 18, 2013, 12:04:49 PM »
I dealt with DR twice... The first time was fine, the second was the last. Basically, they took my money and didn't ship an expensive lens for more than a week. My emails went unanswered until the item was finally delivered at which point they wanted to know why I was tense.. I have no problem waiting for an item but BE HONEST if it's not in stock.

I looked around and discovered that there are several suppliers that are less expensive, more reliable and faster... The usual suspects... Aden, B&H, Adorama and 2filter....

113
Landscape / Re: Need some advice & guidance about night/astrophotography
« on: February 16, 2013, 08:54:00 AM »
Finding the Milky Way
I suppose the easiest way is to download a copy of Cartes du Ciel, or if you're willing to spend a couple of bucks, an app for your smartphone or tablet (assuming you have one.) I use Cartes to plan observing sessions and "The Night Sky" by iCandi on my mobile devices. Cartes is completely free and can be had from http://www.ap-i.net/skychart/start .

On photographing the Milky Way,
1. You really want to get to the darkest site you can find. The light from the MW is very faint and if there is any light polution, it will be overpowered. So... look for a place far from the maddening crowds.

2. Choose a clear, moonless night - the moon can wash out the MW too.

3. Try wind the ISO up to 1200 or 2400 - on a 5D2, these offer the same noise as 800 and 1600 ISO respectively and you can do some noise filtering later.

4. Use a wide angle lens because it will allow a longer exposure without visible smearing of the stars. This is dependent on the direction you're facing (as well as the pixel size and lens resolution) but a reasonable rule of thumb is 15-30 seconds with a 24 mm lens. If the focal length doubles, the exposure must half. I made the calc for a 5D2 - if the pixels get smaller than 6 microns, the exposure must get shorter too.

5. Select a lens that has no focal plane curvature when it's focused at infinity. Ideally it will be reasonably fast - say f/1.4 or so so that you can stop down to f/2 and improve the image quality and vignetting considerably. A manual focus lens (read Zeiss) is probably your very best bet.

6. Use a very stable tripod, mirror lock up and either a timer or cable release to start the exposure. I usually use sunlight white balance.

7. Turn off autofocus and use magnified live view to focus the image manually. Use a Zacuto 3x loupe if you can afford one. Finally, it's best to focus at about 1/3 to 1/2 of the way from the edge of the field because that tends to get most of the image reasonably sharp.

Ok - it may be bad form but I may as well make a plug for the Canon DSLR Digital Astrophotography group on Yahoo! We have something like 2300 active members. Full disclosure - I'm one of the moderators.

114
Lenses / Re: How do yall compose a shot using a fisheye lens?
« on: February 13, 2013, 01:47:30 AM »
I find that the "rule of thirds" is inappropriate for a fisheye. It's more a case of look through the viewfinder and see what works with the subject. Keeping your feet and fingers out of the frame can be harder than it sounds. Don't be afraid to experiment - take lots of images and trash the garbage.

I've found that getting very close to the subject can produce interesting perspective distortion.

115
Lenses / Re: Please help me.
« on: February 11, 2013, 04:02:48 PM »
The pixels of an APS-C camera are small so that photons are always at a premium. Because of this, I'm inclined to advise against the 10-22 and 8-16 offerings because they are very slow optically.

Similarly, I was fairly unimpressed with the way a 17-40 worked on my 7D, but it works very well indeed on a full frame camera. So temper your desire for an L lens with your long term aspirations.

When looking at lenses suited for the 60D, I'd say the Tokina 11-16/2.8 and the Canon 17-55/2.8 are about as good as you will get.

116
Lenses / Re: Considering the Zeiss 21
« on: February 10, 2013, 11:21:15 PM »
I own several ZE lenses and the 17 TS-E. I used to own the 17-40L.
My take is that the ZE 21/2.8 is a good lens, but I don't rate it as highly as several others in the Zeiss stable.
As for the ZE 18/3.5. You may need to be aware that it's very difficult to focus through the eyepiece (live view is fine.) It also suffers from a lot of edge fall off so that it only really reaches sensible levels at f/8 or f/11.
My suggestion would be to go for the 17-40 and exploit it's versatility. Maybe you can get a TS lens when it's appropriate. (Personally, I'd suggest the TS-E 17/4L because you can add a 1.4x tc and it works just fine at f/8.)


117
EOS Bodies / Re: Please Help a Brother understand
« on: February 09, 2013, 09:31:20 AM »
I think the 5D2 is good bang for buck, even though it's getting old. A nice one can be had for $1200-ish on POTN. If you have enough cash, the 6D has a very good centre AF point that is better than anything else that Canon offers.

The classic street focal length is a fast 35 mm but if you want to be a bit more discrete, a 135 mm allows you to get some separation from your subject. If you're looking for a 35 lens, the new Sigma 35/1.4 runs rings around everything else. Among 135's, it is the Canon 135L.

118
EOS Bodies / Re: Need seasoned advice - keep 5D Mark II or NO?
« on: February 09, 2013, 09:19:44 AM »
I'm something of a luddite - I figure that as long as my camera isn't the determining factor in my image quality, it doesn't need upgrading. Although I own a 1D4, my 5D2 gets far more use.

Beside this, after deducting the price of your 24-105 the 5D2 effectively cost you $1300... it isn't going to depreciate more than $300 over then next couple of years. Let's say you decide to upgrade then - you get the use of an excellent camera for 40 cents a day.... How can you go wrong? (I'm guessing here but I really expect the 6D and 5D3 to loose half their value over then next year or so - it happens when you buy things that are close to the bleeding edge.)

119
Canon General / Re: Why did you choose Canon?
« on: January 27, 2013, 09:29:46 PM »
I purchased a 40D several years ago with the intention of using it for astrophotography. Although Nikon had similar offerings, the wisdom was that Canon's in-camera processing was gentler which would mean faint stars were less likely to be nailed.

As things turned out, I only used the 40D for lunar shots - I bought a cooled CCD camera for faint object astrophotography. Of course, I bought a couple of lenses which more or less cemented the relationship and five years down the line, here I am.

It has occurred to me that the reason Nikon systems have better out-of-camera noise remains the same - Nikon is more aggressive with the in-camera processing.

120
EOS Bodies - For Stills / Re: Too much dynamic range?
« on: November 24, 2012, 11:31:32 AM »
...Let me add a twist: the ADC works linearly, but what you see is log

So, if you have a 14-bit ADC (you can count up to 16384)and can record 14 stops of DR, here is how those values will be distributed:

14th stop: 8192 to 16383
13th stop: 4096 to 8191
12th stop: 2048 to 4095
11th stop: 1024 to 2047
10th stop: 512 to 1023
9th stop: 256 to 511
8th stop: 128 to 255
7th stop: 64 to 127
6th stop: 32 to 63
5th stop: 16 to 31
4th stop: 8 to 15
3rd stop: 4 to 7
2nd stop: 2 to 3
1st stop: 0 to 1
...

This is incorrect - if you replaced "bit" with "stop" then it is correct (and it's then obvious why ETTR works too.)

It's easier to consider a 3- or 4-bit digitiser. Let's say it offers 4 bit resolution then the possible counts are 0000 through 1111. This translates to 2^4 or 16 levels. Written the way that Norman stated it, there would only be four distinct levels - this is incorrect (but I understand he meant there would be 16 levels.)

Some things appear to have been glossed over in the discussion. First, the ADC operates on a per-pixel basis.

I've read the DxO tests on various sensors. It is important to remember that the notional dynamic range is referred back to an 8 mp standard. This means that the D800's quoted 14 bits dynamic range is significantly less than 14 bits at a per-pixel level. The 36 mp > 8 mp conversion gains the sensor sqrt(4.5) = 2.1x notional improvement in dynamic range. The 2.1x is slightly more than 1 stop in quoted dynamic range. This means that the true per-pixel dynamic range is about 12.9 stops.

In order to read those 12.9 stops, the ADC needs a bit more resolution than the 13 bits required by the pixel. I'm quite surprised because the 14 bits in the ADC suggests that the entire detection chain has ~1 bit of noise.... It sounds improbable.

Photon shot noise has been commented on briefly. If we assume 13 bits dynamic range and (say) 10% quantum efficiency (pidooma), then the number of photons required to fill a pixel is 10 x 2^13 or 80k. Since shot noise varies with the square root of the number of photons, the pixel could have shot noise of up to 280 photons (rms).

Since 1 bit translates to 80k/8192 = 10 photons and we must have about 6 bits of photon noise at the upper end of the sensor's dynamic range. At the bottom end, the quantum efficiency sets the performance and there must be ~3 bits of noise.

Shot noise alone suggests that the true dynamic range of an image cannot be more than about 8-10 bits. It seems that the only way to improve on this is by greatly enhancing the sensor's quantum efficiency.

To answer the OP's question - photon noise alone suggests that there's not a whole lot of benefit to high resolution ADC. It does allow for more sophisticated noise filtering - presumably at the expense of resolution.

<---- physicst / astronomer

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