October 24, 2014, 11:09:53 PM

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Messages - rs

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32
Because actually, the link for the C lens in Maximilian's post is wrong.
Yes, sorry! Link was wrong,  c&p error.
And I just looked at the links quickly on my phone. Well spotted.

33
Why do the mtf graphs of the two different lenses look identical?  :o

34
EOS-M / Re: AF speed 40/2.8 vs 85/1.8
« on: September 11, 2014, 05:20:57 PM »

A little surprised the 85/1.8 is quieter than the 40mm.... isn't the STM supposed to be a quiet motor?
STM lenses make a high pitch noise, almost similar to a loud version of baldy shielded processor noise leaking into amplifier circuitry. Nothing like the volume of micro motors of older cheap lenses. It's almost completely silent, and great for video work. USM motors are silent to all intents and purposes, although there is typically the noise of components other than the motor - the internals of the lens gliding over each other etc. And of course there's the fairly abrupt torque as the AF system start/stops to achieve its fast focus acquisition speed. This is no good when it comes to slow, smooth video AF requirements as the USM system will go through a constant start/stop sequence.

So - for video with DPAF, STM is significantly quieter and smoother (both for focus smoothness and torque/recoil you feel as you hold the lens), whereas USM is a little quieter and typically much faster for images.

35
Easy answer.

1. 7d and 500mm f/4 is 800mm equivalent and f/5.6 equivalent like DOF capabilities and rendering the fore/backgorund.

2. 5d iii and 500+1.4 is 700mm f/5.6 mm lens

Nearly - the 1.6x crop makes a 500/4 equivalent to a 800/6.4 lens vs a 700/5.6 on FF with a 1.4x TC

So in reality, the 800/5.6 behaves much like a 1280/9 on crop, vs an 1120/8 on FF and 1.4x TC.

I'd also argue that the supposed 7D2's AF system would be focusing at f5.6, vs the 5D3 at f8 - that should be an advantage, plus the FPS is nearly doubled. As stated, there's more than the theoretical 1.3 stops difference in S/N between the 5D3 and 7D1, so the gains of the faster lens are more than lost. But this is the unknown quantity of the 7D2 - who knows what it's S/N is?

You do not want 800 for crop. Your subject will be to far away and the air between the lens and the subject will blow your IQ. Believe me. Even 600 is to long for crop sensor.

Depends upon what size object you're focusing on. If it's as small as the lens can frame, you're only 6m away from the object - no issues there with the amount of air. If the humidity, pollution and heat haze levels are favourable, 100m could be perfectly fine. And other times getting closer simply isn't an option, so starting off with a competent lens/body can't hurt, even if the conditions aren't the best.

36
Lenses / Re: DXOMark Reviews Zeiss Otus 85mm f/1.4
« on: September 10, 2014, 01:17:44 PM »
Has anyone noticed that the 'true' max apertures as indicate by the Tstop is nowhere near the manufacturers claim? The Zeis is closer to a f1.8 lens than f1.4 and the rest fare no better....

T value is not aperture value, an f1.4 lens is a "true" f1.4 if the apparent aperture diameter is focal length divided by 1.4. The T value relates to actual light transmission and is pretty much irrelevant with TTL metering stills cameras.

Aperture value is always lower than T (transmission) value because however good the glass is you always lose some.
+1

Nothing is completely transparent - even the air inside the lens. And if you can see any reflections on any of the elements within the lens when peering through the end, that's light which hasn't made it through.

37
12mm for full fisheye coverage? Insane... 15mm is hella-wide as is with fisheye.
A typical fisheye at 15mm provides 180˚ coverage, corner to corner. Typically you can't get any wider than that without mechanical vignetting in the corners (as is the case with the 8-15 when zoomed below 14mm), or with a lens wider than 180˚ (some go up to about 185˚).

I believe the reason why this has a much shorter focal length is due to its projection - it is likely to be stereographic, which means it's much less obviously a fisheye. Most conventional fisheyes use a projection much closer to equidistant or equisolid, which tends to make the centre of the image bulge and the edges look all squashed. Stereographic looks much more natural. The centre is magnified much less, hence the typically shorter focal lengths to achieve the same angle of view.

http://en.wikipedia.org/wiki/Fisheye_lens

38
If this does have stereographic projection as I suspect, I might well be very interested in this lens. Obviously this is also dependant on its price and optical performance.

39
Photography Technique / Re: Benefits of IS in fast shutter speeds
« on: September 10, 2014, 11:13:46 AM »
And what about IS while shooting in 200 mm range handheld with shutter speeds 1/2000 and faster?
In some scenarios, it's a must - as highlighted in my above post. Although in typical handheld scenarios at that length and shutter speed, it's only there to stabilise the viewfinder a touch, making composing and getting the AF points on the subject slightly easier. However, if you really prefer not to use it at such speeds, just turn it off.

40
Photography Technique / Re: Benefits of IS in fast shutter speeds
« on: September 10, 2014, 08:23:08 AM »
As well as all the great advice given above, please remember the rule of shooting a shutter speed of 1/focal length is just a general guide - there are many variables that affect the outcome. For instance:

What is the pixel density of your body, and how big do you want to reproduce the image? (A 6mp image printed at 6x4 is much less demanding of sharpness than a future ~40mp body used to produce huge wall art)
How steady are you hands?
How steady is the platform you're shooting from? (I quite often shoot sports from small motorboats, and IS is a make or break feature for that)
Is there ever going to be any wind that could catch the lens/lens hood?

In other words, situations could exist where even 1/2000th won't give you the results you want for a 200mm lens without IS - ignoring the fact that you might not be able to frame, let alone get the AF point to lock onto the subject.

If you can guarantee you'll only ever use the lens in lab controlled conditions, you'll be fine without IS.

41
Lenses / Re: Samyang 12mm F2.8 Full Frame Fish Eye
« on: September 10, 2014, 07:49:00 AM »
Would the focal length of 12mm, vs the 15mm of other diagonal fisheyes, mean it uses a different projection? The linked page says nothing about that.
I'm guessing that unlike a normal fisheye such as the Canon offerings (current and previous), this will be like the 8mm APS-C (1.5x crop) Samyang fisheye which has a stereographic projection. 8mm x 1.5 is 12mm, so it's a good fit.

42
EOS Bodies / Re: 7DII full frame?
« on: September 08, 2014, 11:45:22 AM »
well last rumor heard from a good informed source close to canon told me.... canon will introduce exchangeable sensors.

there will be no phase detection AF anymore because it´s obsolete.
DPAF II is now faster and way better.

so maybe the 7D MK2 Standard comes with APS-C and the Edition model comes with a FF sensor.


btw: Doug confirmed it was a placeholder text.
Yeah, DPAF has definite speed advantages over standard phase detect AF for DSLR's, and that big mirror and shutter blocking out the light to the sensor where DPAF is situated at the time of acquiring focus doesn't matter at all  ::)

Are these sensors you talk about to be available in a user replaceable canister?

43
Technical Support / Re: Any way to extend a failing shutter's life time?
« on: September 06, 2014, 08:47:08 AM »
The speed the shutter curtains move at is the same at any shutter speed. It's just the timing between the opening and closing which alters. X sync is when the 2nd curtain starts to close when the 1st curtain has just finished opening.

Having said that, at very high shutter speeds, the physical gap between the two curtains is so small it's just a narrow slit which scrolls across the sensor. If any mechanical issues occur there, they're more likely to contact. I have no idea what sort of speeds would be more likely to cause an issue.

Low temperatures are more likely to cause sticking issues.

But why not just get the shutter serviced/replaced?

44
Business of Photography/Videography / Re: 4K, 5K, 6K and Up Video
« on: September 06, 2014, 04:35:29 AM »
These higher res displays look radically better!

Man that new Dell sounds amazing! Maybe I got the UP2414Q too soon!

I mean think about it, these displays are like getting INSTANT, FREE 8MP and 14MP 24" and 27" prints!
It looks so much better than regular HD monitors, that it is not even funny. My PA241W HD monitor looks so fuzzy now and pixellated it's got to go!

And some of the 4k video samples I've seen are pretty amazing. It's so much more like you are really there looking at something.
I fully agree - for stills, these displays with that DPI/PPI and size are getting to the point where there's no need for further improvement. It's just like a scaled up retina display. No longer are you tied to seeing pixelated images. Just everything appearing like a perfect print (if the viewing angles, colour gamut and all that are good enough).

However, I disagree about the need for 4k video (and beyond) with current frame rates. Video is usually shot with a 180' shutter - in other words 1/50th for PAL (25fps) or 1/60th for NTSC (30fps). Each frame of 4k footage is approx 8MP. How many images of moving scenes with a 1/50th shutter speed would resolve much more than 2MP? The background is typically not moving too much but out of focus, and the foreground will have motion blur. 4k (8MP) and 8k (32/33MP) are great - if the temporal resolution is there to match the spatial resolution. NHK have been playing about with 8k at 120fps (allowing for a natural looking 1/250th shutter), and that should be great.

Most 4k footage you see in showrooms uses a very clever trick - it all has minimal movement between frames - either a time-lapse with a fixed camera position, slow motion, or footage of a waterfall or some other scene which doesn't really move. In other words, with the slow frame rate they've cheated and found a way around the whole unnatural shutter speed while maximising resolution. However, watch any real life 4k footage and it'll fall apart. I remember when 1080p was a new thing - they were advertising it on standard def TV, and the footage always looked amazing. However, everything was always in slow motion to make the SD feed appear sharper.

For stills, these displays make perfect sense right now.

45
Third Party Manufacturers / Re: SIGMA 150-600!!
« on: September 05, 2014, 06:32:25 PM »
As for wanting constant f/5.6, I don't see that as important or even useful. Remember, the camera body tells the lens what aperture to use and the lens has to figure out how to do it.

Well every quant of light counts.

It´s not much but it´s still better.
And with that weight plus over the Tamron it would be a nice bonus.

But i guess there are reasons for not doing it. Who knows how much more it would weight than.

600/5.6 results in a 107mm clear aperture, same as 300/2.8. The filter size of both this lens and the 120-300 is 105mm. Therefore, the 120-300 f/2.8 can't reach 300mm or be f/2.8 at that focal length. I'm hoping that Sigma is honest about the focal length and aperture for this new lens. We'll see. FWIW, the Tamron uses 95mm filters, which is as small as possible for 600mm and f/6.3.

I really don't expect it to be as good as my 300 but I do expect it to be very good, probably better than the Tamron. More important is whether it can focus quickly and accurately enough to capture race cars and motorcycles. I don't expect to buy it before next spring since, by the time it'll likely be available, there will be snow on the ground around here. So there's lots of time for people to test it.
Most lenses aren't built to precise specifications produced by marketing departments - if a manufacturer decides they're going to enter the 300/2.8 market, why should it be 300.0000mm and have an aperture ratio if f2.80000? For a start off, f2.8 in itself is shorthand for the square root of 8. In other words 2.82827 if we round to 5 decimal places. Most engineering departments will work towards a general goal, but sticking to it 100% is a waste of money, engineering resources, and could result in additional optical compromises, not to mention increased weight, size and cost in the end product.

Just read the patents for new lenses. Not one of them reads as neat as the specs once they've been sterilised by the marketing department.

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