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  #1  
Old 02-12-2014, 05:03 PM
mbaddah (Mohammed)
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The 7D mark II is the best Canon DSLR for astrophotography.

According to the following:

http://www.clarkvision.com/reviews/e...on-canon-7dii/

Dramatic improvement from the previous generation that's for sure.
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Old 02-12-2014, 07:44 PM
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You might just have helped me make a decision
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Old 03-12-2014, 08:41 AM
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zenith (Tim)
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I just bought a Canon 6D, I decided to go with a full frame sensor. I Also considered the 7D mark II and also Nikon D750, as I really like the articulated screen and inbuilt flash.

Here are a couple of good websites showing noise in various situations.

http://www.imaging-resource.com/IMCOMP/COMPS01.HTM
http://www.brendandaveyphotography.com/?page_id=726
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Old 04-12-2014, 06:29 AM
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You also have to take into account that full frame has something like a 2 stop advantage over APS sized sensors merely from size of the sensor alone.

So images from both 6D and 7D2 side by side would be needed to make a more informed decision.

For example my Fuji XT1 (APSc) and Sony A7r show this difference. Both are very low noise. But 2 images at ISO6400 show the Sony as being many times brighter for the same lens/exposure. Its just real estate size of the sensor capturing more photons.

Greg.
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Old 04-12-2014, 10:22 AM
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Quote:
Originally Posted by gregbradley View Post
You also have to take into account that full frame has something like a 2 stop advantage over APS sized sensors merely from size of the sensor alone.
I'm struggling to understand why this would be

What happens when the object in question occupies roughly the same number of pixels on each chip?
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Old 04-12-2014, 10:28 AM
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pluto (Hugh)
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Quote:
Originally Posted by gregbradley View Post
Its just real estate size of the sensor capturing more photons.
Surely it's about pixel size and not sensor size. For example, a 8x8Ám pixel will collect the same amount of light whether it's part of an APS-C or a FF sensor.
In general APS-C sensors tend to have smaller pixels than FF sensors but that doesn't have to always be the case.
EDIT: for example the fuji x100 with an APS-C sized sensor has slightly larger pixels than a Canon 5DmkII. I'm sure there are many other, better, examples but this is one I know of.
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Old 04-12-2014, 12:11 PM
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Gotta agree with Dunk and Hugh - if it were down to sensor size most CCDs would be rubbish compared to dSLR sensors, but that clearly isn't so. The pixel size and structure is what matters.
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Old 04-12-2014, 12:15 PM
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DXOmark.com strongly disagrees with the noise/sensitivity analysis presented above.

According to them it's very much middle-of-the-pack.

EDIT: removed direct links to DBs as they don't want to load.
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  #9  
Old 04-12-2014, 07:46 PM
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Pixel size does come into it as well and can muddy up the comparisons for sure. But the basic here is the difference in surface size that is collecting light irregardless of pixel size. A full frame sensor is simply larger and therefore collects more light.

There is a Wikipedia article about this and modern sensors with more efficient circuitry have tended to minimise this difference in some instances but still there is usually a difference. Especially when pixel size is the same.

Full frame sensors often have larger pixels as well which also gives an advantage.

This article touches on it but the Wikipedia was very specific about sensor size giving a 2 stop advantage. If I can find it I will post it.

http://www.gizmag.com/camera-sensor-size-guide/26684/

I also agree his analysis may be flawed as I have not read any reports about the 7D2 having super low noise at high ISO rather what I have read is it is better than the 7D but not massively so in the noise department. Certainly it would be worth verifying from owners rather than racing out and buying one instead of a 6D and being disappointed later.

http://www.dpreview.com/forums/post/54846228

Greg.
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Old 04-12-2014, 08:04 PM
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I'm a bit confused.
Are you saying that, for example, a 5.4x5.4Ám pixel on a FF sensor will receive more photons than the same sized pixel on an APS-C sized sensor?
Or is there some connection between physical sensor size and QE or read noise?

Of course a larger sensor receives more light than a smaller sensor but that light is divided amongst its pixels, or photosites.

EDIT: regarding that dpreview link, its hardly a surprise that the 7DmkII has better high I SO performance that the original - the original 7D had the worst noise of any Canon camera I've ever used!
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Old 04-12-2014, 08:36 PM
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Assuming both have the same sized pixels and same lens the full frame sees a wider field of view and thus more light. Not assuming any difference in QE, noise and certainly no extra light for each pixel of the same size between the 2 sensors. There may be a connection with less photon noise as the larger area can capture more. Not 100% sure of that though as generally it simply means a wider field of view when using a full frame versus an APS, hence more light.

There has been a lot of discussion of this aspect on DPReview in the past. Especially in the Fujifilm forum as its an APSc based system and it promotes the marketing claim that its system matches full frame performance.

In practice the basic gain of a full frame sensor may be diminished by higher QE, lower noise of well designed APSc sensors. Although in Fuji's case as they use Sony sensors with a different colour filter array the performance difference is questionable.

For nightscapes I see a big difference in sensitivity of my Fuji APSc low noise images and full frame either from a Nikon D800e (since sold) or Sony A7r. Also complicated by the fact that because Fuji has its own filter array normal ISO calculations seem to be twisted and ISO3200 on a Fuji X camera is not ISO3200 in brightness of a Canon, Nikon or Sony. Sony in particular seems very bright for the same ISO of other cameras I have used.

In practical terms you can see this at work in the nightscape section here. The full frame images are generally much more pleasing,brighter, wider field of view and lower noise than the APS images. So at the end of the day generally speaking full frame dominates in the Nightscapes department. Probably also with DSLR images with a telescope.

Greg.
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  #12  
Old 04-12-2014, 08:42 PM
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zenith (Tim)
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Canon 7D Mark II pixel pitch 4.1 Ám.
Canon 6D
pixel pitch 6.5 Ám, or 58% larger.
http://www.astropix.com/HTML/I_ASTROP/COMPARE.HTM

I am only a beginner to astro-photogoraphy, but it seems logical that for the same sized image projected onto the two sensors, the 6D will have lower resolution but 58% more photons captured per pixel. As for the noise, that depends on sensor quality, reading the signal from the sensor, and random noise introduced by the electronics. The 7D Mark II is newer and includes the Dual DIGIC 6 processor which I would be expected to have superior noise suppression. That said, 58% is a significant difference in raw signal strength per pixel.

It would be really nice to see a side-by-side comparison of several astro images...and then wait for the 6D Mk II
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  #13  
Old 04-12-2014, 09:06 PM
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You're exactly right Tim.

Greg - I understand what you're saying, and I have plenty of experience shooting nightscapes and through a scope with both ff and aps cameras. You're comparing different sensors which have quite different technologies, like fuji xtrans vs standard bayer, and some are better than others. Evidently the performance isn't necessarily linked to the pixel size, I guess this is to be expected with such different technology used, but I really can't work out where the link between sensor size and extra light is coming from.

To be more clear let's consider a hypothetical test. It has to be hypothetical as I don't know of any cameras that have identical sensors but one in ff and one aps.
So we have two cameras sitting next to each other and each has an identical lens attached. One has a ff and one aps sensor, both sensors have the same size pixels and QE.
Let's say they're looking at a field with a tree in the centre. In both images the tree takes up exactly the same number of pixels but the ff camera sees more of the field either side of the tree.

If we crop the ff image to the same fov as the aps image then they should be identical.
So the extra light you say the ff sensor receives is really just extra fov?
The only inherent benefit I can see with the ff in terms of nightscape photography is that you can get a wider image for any given lens.

Now I know that in practice most of the ff cameras I've used have given better low light results than the aps cameras I've used but I'm pretty sure that was because of: a. The ff cameras were more expensive than the aps cameras and had more advanced sensors and processors etc. And b. They had larger pixels.
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Old 05-12-2014, 03:51 PM
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Merlin66 (Ken)
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http://www.clarkvision.com/galleries...v.h-b5x5s.html
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Old 05-12-2014, 04:46 PM
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Wow. Love that it picked up all that red nebulosity...can anyone say Ha?
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Old 05-12-2014, 05:05 PM
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Hi Hugh,

Yes I think that was basically my point. Although independent of pixel size which as you point out is a big difference there is total amount of light the sensor receives simply by its size. Full frame is 2.25 times the surface area of APSc. Yes FF usually have larger pixels but some don't like Sony Nex 5 (16mp) and Sony A7r (36mp). The A7r noise levels are way lower.

It may be clearer this way - full frame image compared to tiny sensor in an Iphone image. The iphone has small pixels but also a tiny sensor. Noise levels are nowhere near the full frame image.

Micro 4/3rds cameras have excellent IQ until light levels drop and then the biggest complaint I read is noise even at low ISO levels. Yes small pixels but there is the factor of size of the sensor collecting the total amount of light.

There is a very clear Wikipedia article about this that explains it way better than I am. I'll try to find it again.

I agree the above gets lost because of the different sized pixels, different efficiencies of sensors and the general rule that large pixels have less noise and deeper wells than small pixels and thus lower noise.

Another way of expressing it would be APS sensors will have to work much harder and be more efficient to keep up with a full frame sensor.

By the way the Xtrans and Sony A7r are both Sony Exmor sensors so the differences there are not as great as you would think. So in a way they are a good example. A better example is this one:
http://www.dpreview.com/reviews/imag...62535884370765

The Xtrans colour filter array does complicate things but basically its designed to allow no moire with no antialiasing filter and to reduce luminance noise both of which it does and hence the marketing claim that their APS sensor can match full frame (not entirely true but it does do a good job).

Greg.
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Old 05-12-2014, 05:17 PM
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I think we're basically saying the same thing

But when you say that a "full frame has something like a 2 stop advantage over APS sized sensors merely from size of the sensor alone" perhaps it would be more accurate to say that it has an advantage for any given FOV. For any given object, in the context of shooting through a scope, the advantage will always go to larger pixels (all other things being equal) and has nothing to do with sensor size.
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Old 05-12-2014, 05:27 PM
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Yes I think that is correct. Although with a telescope a small sensor has the same effect as increasing focal length. Use a small sensor on even a small aperture/short focal length scope and you get quite a magnified image.

For example the Sony 694 sensor on my CDK17 gives a highly magnified view compared to my 16803 camera on the same object. Much like a full frame camera that has a crop mode - you get an instant 1.6X zoom.

The interesting development to me in camera sensors is likely about to be released by Sony. An active pixel sensor that does not have a Bayer filter array, shoots in colour and somehow gets red, green and blue info of each pixel, has 24 stops of dynamic range at ISO5120 and low noise and capable of 16,000 frames per second. If all true it would be an unbelievable jump in sensor performance. I believe its not far away.

It potentially could be a huge advance for astrophotography. Low noise at high ISO being the unkown factor but likely to be good as the pixels can be very large due to not needing 4 pixels to make a colour pixel like in Bayer sensors.

Greg.
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Old 07-12-2014, 11:41 AM
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I have to admit to having wandered by the local camera shop and played with the 7D mk II.

My impression with the Canon (and Nikon) cameras at the prosumer end of the market is that they are lumpy old dinosaurs. Is that being unkind? But it is nearly 2015...

I was drawn like a moth the flame of the Sony alpha series and discovered a camera that was beginning to feel and act like something I would expect in an internet connected world, and was especially interested to discover that you can buy apps for it including star trails and time lapse software.

My dilemma though would be the choice between the A7R and A7S which are so different, and I just feel that the monster pixels of the A7S are a big price to pay for the increased sensitivity, on the other hand...
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Old 07-12-2014, 12:02 PM
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I am not ready for Sony. My expensive Sony television died long before its time, and my mate's play station did not work out of the box. It took him hours on the phone, and 3 months in total to have it replaced (with him footing all shipping costs). I have a Sony DVD player and it has every feature know to mankind, and all of them are executed poorly, including the only ones I really need: stop, play, pause, top-menu.
They will need to lift their quality and customer service before I shop with them again.
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