36 replies to this topic

[sharkmelley]

I have had my Canon EOS R full-frame mirrorless camera for a few weeks now, long enough to do a whole batch of technical testing.  So it's time for a review.

 

This is very much a technical review, so rather than describing the handling of the camera and its various features (which can all be found elsewhere) I am more concerned about the technical characteristics that will affect long exposure astrophotography. In many cases I will be comparing it to the Nikon Z6 which I also own and which has a recent Sony sensor.

 

This will be a fast ride, full of information, so strap yourself in and let's begin!

 

Introductory Comments

 

All my tests were done using a telescope or a (legacy) non-CPU lens. Since the lens (and telescope) is unrecognised by the camera firmware this means it is unable to make any hardcoded corrections.

 

For all tests, noise reduction, lens corrections and dual pixel mode were all switched off in the camera menus.

 

On the subject of dual pixels, the Canon EOS R mirrorless shares the same sensor as the Canon 5D mark iv DSLR, where every pixel is a dual pixel.

 

Since Canon's EOS Ra astro-camera is essentially the same camera but with different internal filtering (to enhance H-alpha sensitivity) I would expect my analysis to apply equally well to the (discontinued) EOS Ra.

 

Read Noise Gain etc.

 

I don't intend to duplicate Bill Claff's excellent work at PhotonsToPhotos because I obtain very similar figures:

• Read noise: https://www.photonst...14,Nikon Z 6_14
• DxOMark Derived Characteristics: https://www.photonst...14,Nikon Z 6_14

Regarding the DxOMark Derived Characteristics, note that Bill says that fitting the DXO data has its limitations, affecting estimates of gain, read noise, QE etc.

 

The read noise has the typical Canon characteristic of being constant for 3 consecutive ISOs. I would therefore stick to the main ISO values i.e. 100, 200, 400, 800, 1600, 3200 etc. and avoid the intermediate ones.

 

It's worth pointing out that the bias level at ISO 100 and ISO 200 is 512 which is different from the bias of 2048 at higher ISOs.

 

It can be seen from the PhotonsToPhotos that the Canon EOS R read noise is noticeably higher than the typical Sony sensor at the ISOs most likely to be used for astrophotography i.e. ISO 800/1600.  However, for long exposure RGB imaging the read noise is usually swamped by the noise of the background sky so read noise is not a concern.  On the other hand, low read noise might be important if short exposures are being used or if narrowband filters are being used.

 

 

Dark Current and Camera Self-Heating

 

My methodology for testing dark current and self-heating is to put the camera in a dark room at 20C ambient temperature and leave it to acclimatise for an hour or two.  I then switch the camera on and immediately run a couple of hours of consecutive 5 minute dark frames with the rear LCD folded out from the rear of the camera to allow heat dissipation.  By subtracting each frame from the previous one, the thermal noise can be calculated and ultimately converted into dark current.

 

Here's the result for a few cameras, measured in electrons per pixel per second:

 

 

However, a lot of the difference is caused by the size of the pixels, so I find it's more meaningful to display the graph in terms of electrons per square micron per second:

 

 

It can be seen that the EOS R has low dark current and remarkably low self-heating during an extended session of long exposures.  Remember also that during an actual imaging session the self-heating should be lower because the camera is thermally attached to a potentially heavy telescope and also the wind will be circulating the air around the camera body, both of which will have a cooling effect. 

 

However any time spent in live view will potentially heat the sensor quite rapidly so live view should be kept to an absolute minimum to prevent any heat building up.  Beware if you are controlling the camera from a laptop via USB because live view will be on continually. I therefore switch the tethered camera off unless actively focusing or framing the shot.

Edited by sharkmelley, 11 September 2021 - 04:55 PM.

[SandyHouTex]

That’s great to know.  Thanks Mark, and I look forward to your further testing.

[sharkmelley]

Banding and PDAF stripes

 

Horizontal banding problems are well known on many Canon cameras and they will often appear in the final stacked image.  I did a lot of testing of this on the Canon EOS R. The only banding I found was positioned randomly from one frame to the next in a sequence of exposures.  The amplitude of the banding was 1 ADU or less. Hence at typical astro-imaging ISOs 800/1600 the amplitude of the banding is buried in the read noise and stacking doesn't reveal it because the randomness causes it to cancel out.

 

I found no evidence of any horizontal banding in any of my master bias, master dark and master flat files and not in any of my final ISO 1600 stacked images.

 

In addition I found no stripes or bands caused by the PDAF (phase detection auto-focus) pixels, which is well known problem on the Nikon Z6, for example.  This may be because every pixel on the EOS R is a dual pixel and so the sensor is homogeneous.

 

One annoying attribute of Sony full-frame sensors is the vertical "seam" down the centre of the sensor.  This leads to artefacts near the centre line on both the Sony A7S and Nikon Z6 that never calibrate properly.  I found no such evidence of a vertical discontinuity with the Canon EOS R.

 

 

Histograms, RGB Channel Scaling and Concentric Coloured Banding

 

The Canon EOS R appears to perform digital scaling (known as white balance pre-conditioning) to the colour channels, which leaves regularly spaced gaps in the histogram of the green and blue channels.
For instance, here's a histogram of a 5 minute dark frame at ISO 1600:

 

 

The red channel appears to be unaffected by the scaling which is different to Nikon where the green channel is untouched.  This scaling of the channels is verified by the calculation of gain (e/ADU) which shows a different gain for each channel.
However the scaling is relatively well behaved and my testing showed no evidence of concentric coloured banding of the type found on the Sony A7S, for instance.

 

The channel scaling is the cause of the oscillations seen in green and blue channels of the EOS R ISO 100 photon transfer curve:
https://www.photonst...htm#Canon EOS R

However these oscillations are small.  At higher ISOs these oscillations more or less completely disappear.

 

There was an earlier Cloudy Nights thread on the Canon EOS Ra which discussed concentric rings:
https://www.cloudyni...non-ra-testing/
Further analysis shows that these rings are not caused by the channel scaling.  It's possible that the cause is some kind of automatic lens correction applied to lenses recognised by the camera firmware but it's not something I am in a position to test and it therefore remains an open question.

 

There was a another type of concentric ring mentioned in that thread, caused by spikes in the red histogram.  I found similar spikes in the EOS R histogram of a flat frame at ISO 100, near the values 1750 and 2350:

 

 

When this flat frame was used to calibrate another flat frame, two concentric rings did appear in the red channel:

 

 

I really don't understand the cause of those spikes but the good news is that it's impossible to cause the associated rings to appear at ISO 800 and above.

Edited by sharkmelley, 11 September 2021 - 05:02 PM.

[sharkmelley]

Raw data filtering

 

Raw data filtering can cause a range of effects including:

• Damage to small tightly focused stars (i.e. "star-eater")
• Colour bias in small tightly focused stars - turning them green or magenta
• Ineffective calibration with master dark frames

It has already been noted that there exist some weird artefacts in the Canon EOS R histograms and here's another example:

 

 

Here the green and red channel histogram gaps have become a pattern of scallops.

 

Despite weird patterns in the histograms I found absolutely no evidence of Canon EOS R raw data filtering.  Raw data filtering generally caps outlier pixel values to prevent them causing obvious noise in an image.  It can be detected by comparing every pixel value against the maximum of their neighbours, which is a technique I developed in this thread:

https://www.cloudyni...ours/?p=8914661

 

Here is a plot from a Canon EOS R ISO1600 5min dark frame:

 

 

It looks perfect!  Note the strong vertical "arm".  These are isolated bright pixels that have not been capped to the values of their neighbours i.e. no evidence of data filtering.

 

I also performed a FFT (Fast Fourier Transform) of a dark frame and this showed no evidence of high frequency filtering.

 

In addition, unlike my Nikon Z6, my Nikon D5300 etc., the Canon EOS R master dark frame calibrates the light frames perfectly. Dark calibration is very effective and well worth doing on this camera.

Edited by sharkmelley, 11 September 2021 - 04:47 PM.

[sharkmelley]

Electronic Shutter

 

The Canon EOS R has an electronic (silent shutter) mode.  On some cameras this can compromise the bit depth of the data, giving 12 bits instead of 14 bits.  This is not the case on the Canon EOS R (nor the Nikon Z6).  It is therefore safe to use electronic shutter with no fear of loss of image quality or unwanted image artefacts.  Electronic shutter prevents wear and tear on the mechanical shutter and it also allows very accurate fast exposures e.g. for taking flat frames against a bright sky.

 

However, beware that the slow scan speed of the electronic shutter (reported to be around 1/15sec) can cause horizontal banding with the fluctuating cycle of artificial lights.  This is one reason I use sky flats.

 

 

QE (Quantum Efficiency)

 

On a clear sunny day I was able to test the EOS R and Nikon Z6 on exactly the same DIY spectrometer (a cardboard tube with a razor blade slit, diffraction grating and built in lens) pointing at a white target illuminated by direct sunlight.

 

The pixel values are converted into electrons using the gain for that colour channel and then adjusted for pixel area so we are comparing like with like i.e. photons recorded per unit area of sensor.  Here is the result:

 

 

A note of caution is needed when interpreting this chart.  The chart cannot be used to compare the QE of the sensor at the blue end of the spectrum against the red end.  The blue channel climbs higher than the red simply due to the spectral composition of the daylight being reflected off the white (or whitish) surface the spectrometer was pointing at.  However, at any individual wavelength the chart can be used to compare the response of the Canon EOS R against the Sony sensor in the Nikon Z6.

 

The overall shape of the curves is very typical of the difference between Canon and Sony sensors. In the red channel it is clear that the EOS R has a lower H-alpha response than the Z6.  In fact it is around 80% of the Z6 response.  On the other hand, the EOS R has a higher response at the H-beta and OIII wavelengths than the Z6.  In all three colour channels the EOS R peaks at a lower level than the Z6 and overall the EOS R has a lower QE than the Z6.

 

One thing worth pointing out is that the lower H-alpha response does not necessarily mean the sensor is less sensitive but it could be caused by differences in the internal filter cut offs.

 

Bill Claff calculates some QE figures from the DxOMark data on PhotonsToPhotos.net and the difference I see between the EOS R and Z6 is broadly in line with what he calculates.  It is sometimes claimed that DSLR and Mirrorless cameras have lower QE than dedicated one-shot-colour astro-cameras by erroneously comparing PhotonsToPhotos QE figures against the figures quoted by the astro-camera suppliers.  But astro-camera suppliers are quoting peak response whereas the figures on PhotonsToPhotos are necessarily some kind of average over the green channel.

 

 

Sensor Linearity

 

The question here is the linearity of the sensor response to incoming light i.e. are the mean values recorded by the pixels directly proportional to the incoming light.

 

In common with many (or all) cameras the Canon EOS R does not have a completely linear response.  This is evidenced by taking two flats at different exposure lengths in quick succession and then dividing one by the other. Here is the result of dividing two EOS R (bias-subtracted) ISO 1600 sky flats  shot with different (electronic) shutter speeds:

 

 

Notice the overall colour variations from the centre out towards the edges. Obviously this image has been highly stretched in order to show the effect, so although it looks dramatic the actual non-linearity is less than 1%.  But 1% is enough to cause noticeable calibration difficulties when stretching the data to reveal faint structures for integration times of many hours.

 

Another possible effect is pixel crosstalk whose effect potentially differs across the sensor according to the angle of incidence of the primary rays. This is an effect I haven't fully investigated.

 

In any case the impact of non-linearity on calibration can be mitigated by taking flats with the same colour and intensity as the background night sky as described in this thread:
https://www.cloudyni...s-a-case-study/

Edited by sharkmelley, 11 September 2021 - 05:08 PM.

[sharkmelley]

Sample Images

 

Here are the threads showing the 2 EOS R images I have shot and processed so far:

• North America Nebula: https://www.cloudyni...th-canon-eos-r/
• Iris Nebula and surroundings: https://www.cloudyni...th-canon-eos-r/

The second image required a huge amount of stretching to bring out the faint dust in the neighbourhood of the Iris Nebula and therefore needed flats of the same colour and intensity as the background night sky.

 

 

Conclusion

 

I am very impressed by the Canon EOS R camera and expect it to become my camera of choice for imaging deep sky objects.

 

Despite the higher read noise and the lower QE of the Canon sensor used in the EOS R (compared with typical recent Sony sensors) I have found this camera gives me image data that are far easier to process than either the Nikon Z6 or Sony A7S, resulting in a higher quality final image.

 

I plan to keep it and perform a full spectrum modification in the near future.

 

Comments and questions are welcome!

Edited by sharkmelley, 11 September 2021 - 05:11 PM.

[galacticinsomnia]

Wowza !  That is an amazing amount of information. 
Thank you !!!!!!


Clear Skies !!

[SandyHouTex]

Sample Images

 

Here are the threads showing the 2 EOS R images I have shot and processed so far:

• North America Nebula: https://www.cloudyni...th-canon-eos-r/
• Iris Nebula and surroundings: https://www.cloudyni...th-canon-eos-r/

The second image required a huge amount of stretching to bring out the faint dust in the neighbourhood of the Iris Nebula and therefore needed flats of the same colour and intensity as the background night sky.

 

 

Conclusion

 

I am very impressed by the Canon EOS R camera and expect it to become my camera of choice for imaging deep sky objects.

 

Despite the higher read noise and the lower QE of the Canon sensor used in the EOS R (compared with typical recent Sony sensors) I have found this camera gives me image data that are far easier to process than either the Nikon Z6 or Sony A7S, resulting in a higher quality final image.

 

I plan to keep it and perform a full spectrum modification in the near future.

 

Comments and questions are welcome!

I really appeciate all the work you put in in this.  I retire next year and plan to start doing some serious astro-imaging.  Your findings, and the fact that I have an Ra, should make it much easier to get good results.

 

You should write a book.

[skanker]

Thx for the detailed review! I will mod an R soon too 

CS Gernot

Edited by skanker, 13 September 2021 - 11:17 AM.

[Etendue645]

That looks like a great full frame camera to buy! Thanks for the technical analysis! I was looking into a Nikon Z6 but after reading this I think the Canon EOS R is a clear winner!

[AlemanSky]

Wow, that's an awesome review

I've followed your story that lead you to get a EOS R. Thank you for sharing every bit of it and preventing others from suffering the same fate.

I was also looking for a new cam. After this review Canon EOS R will be in my bag.

 

It's interesting to know which firmware version your camera has, since manufacturers can change some parameters with an update.

Edited by AlemanSky, 28 September 2021 - 04:18 PM.

[sharkmelley]

It's interesting to know which firmware version your camera has, since manufacturers can change some parameters with an update.

My EOS R is on firmware version 1.7.0 which I know is not the most recent version but the update to 1.8.0 does not appear to offer anything I need.

 

Mark

Edited by sharkmelley, 28 September 2021 - 04:26 PM.

[Astrofriend]

Hi,

I'm going to buy a new used camera. My old is the Canon 6D DSLR, but I want a shorter backfocus and my plan was to buy a used Canon RP, similar to the one in this thread.

 

But to my disiapointment I read this in the beginning of this thread:

 

"However any time spent in live view will potentially heat the sensor quite rapidly so live view should be kept to an absolute minimum to prevent any heat building up.  Beware if you are controlling the camera from a laptop via USB because live view will be on continually. I therefore switch the tethered camera off unless actively focusing or framing the shot."

 

What does it mean ? Is it impossible to shut of the liveview when tethering the camera to a computer ? If so the camera is useless and maybe all other mirrorless cameras too.

 

/Lars

[Ettu]

Hi,

I'm going to buy a new used camera. My old is the Canon 6D DSLR, but I want a shorter backfocus and my plan was to buy a used Canon RP, similar to the one in this thread.

 

But to my disiapointment I read this in the beginning of this thread:

 

"However any time spent in live view will potentially heat the sensor quite rapidly so live view should be kept to an absolute minimum to prevent any heat building up.  Beware if you are controlling the camera from a laptop via USB because live view will be on continually. I therefore switch the tethered camera off unless actively focusing or framing the shot."

 

What does it mean ? Is it impossible to shut of the liveview when tethering the camera to a computer ? If so the camera is useless and maybe all other mirrorless cameras too.

 

/Lars

Hi /Lars,

 

First - I want thank Mark for all the work he's done here, for the benefit of all of us.

You can count on, rely on, what he has to say.

 

So, THANK YOU MARK

 

I was going to follow up on Marks mention of the tethered chip heating problem.

Yes it's a problem as described. In fact in my experience, having it tethered and connected to and controlled, in my case by APT, raises the temp of the chip 10-12 deg C above ambient - just sitting there.

Note: I'm talking about the temp as recorded by the camera at the beginning of an exposure. - which I find to be a fairly good indicator of the heat noise recorded on the image.

I find anything over 20 deg becomes increasingly difficult to suppress in your image development routine. So without taking measures, you can easily have a chip running at 30C or more in a 20C ambient. As Mark said, dark frames are needed, and they have to be dynamically applied to each light frame, unless you can manage to keep them all at the same temp, and know what that is - pretty hard to do.

I find readings below 10 deg relatively easy to deal with.

 

I bought the Canon Ra when it came out. I knew it was primarily going to be used for astrophotography, and I knew summertime would be a problem, so I had mmalic  put a cold finger in it. That basically brings a tethered chip to ambient to start with, and over a series of exposures, below ambient.

 

I don't know if any other vendor offers some sort of cooling option, but if I were going to get an R today and plan on using it mostly for astro, I'd send it to mmalic to get both mod's done at the same time.

https://mc2camera.com/

 

In the past, with other Canon cameras I've had, opening the display screen, and having a fan blowing on the back (I used a small attached 12vidc PC fan) was a significant help, but to my surprise it was of surprisingly little effect with the Ra. I believe it's been mentioned somewhere that the chip is relatively deep and layered away from the back surface

Edited by Ettu, 07 November 2022 - 12:48 PM.

[jgraham]

Interesting. I have always operated my EOS Ra remotely via Backyard EOS and I vaguely recall that there was a way to turn off the live view. Maybe not, I'll have to check. Regardless, the camera has been a solid performer for me.

[Astrofriend]

Yes, he must have spent a lot of time to cerate this fine report. Thanks a lot from me too ! This kind of information help all of us.

 

But it was sad to realize that the Canon EOS mirrorless camera get problem when connected to a computer for remote operating. There is a software that can be installed in some Canon cameras, Magic Lantern. But can't see that help to solve this problem.

 

https://magiclantern.fm/

 

So maybe best for me to keep the Canon 6D, at last I can turn off the live view in this camera. But I had liked the short backfocus of the Canon RP. My Canon 6D heats up a little bit even if the live view is turned off, it increase the internal temperature about 6 degree Celsius compare to the outdoor's temperature. My older Canon 5D (Mark I) increased the temperature by 3 degrees Celsius.

 

/Lars

[xonefs]

nevermind

Edited by xonefs, 18 November 2022 - 10:45 PM.

[xonefs]

So I'm used to shooting with sony sensors that are iso-invariant and then always shoot at one of the low base isos.

 

What isos are a good compromise on the eos r for deep sky?

[sharkmelley]

What isos are a good compromise on the eos r for deep sky?

The best ISO to use is determined not by the read noise and iso-invariance but by the need to avoid concentric rings appearing in the stacked image as discussed in post #3.

Hence ISO 800 and above must be used.  I typically use ISO 1600.

[jambi99]

The best ISO to use is determined not by the read noise and iso-invariance but by the need to avoid concentric rings appearing in the stacked image as discussed in post #3.

Hence ISO 800 and above must be used.  I typically use ISO 1600.

How is the amp glow on the EOS R?

[sharkmelley]

How is the amp glow on the EOS R?

Good question!

 

It's pretty much non-existent.  Here's an extremely stretched room temperature master dark created from ISO 600 two minute darks:

 

 

The background streaks are far more prominent than the amp glow.  I don't know the cause of the streaks.

 

Mark

[jambi99]

Good question!

 

It's pretty much non-existent.  Here's an extremely stretched room temperature master dark created from ISO 600 two minute darks:

 

EOSR_Masterdark.jpg

 

The background streaks are far more prominent than the amp glow.  I don't know the cause of the streaks.

 

Mark

Ok thanks. There is absolutely no way to turn-off liveview while tethering the camera from a computer?

[piaras]

Try covering the EVS. The sensor will turn off the screen. I have not tried it with the R as I have a RA. In the photos. One has the EVS uncovered and tethered to my laptop via Backyard EOS. The other shows covered by a piece of leather as that was close to hand. Even a paper towel works.

Pierre

 

Edited by piaras, 28 November 2022 - 06:17 PM.

[sharkmelley]

Ok thanks. There is absolutely no way to turn-off liveview while tethering the camera from a computer?

I finally worked out how to do this!

 

When the camera is tethered, the rear screen is permanently on (unless you have set your display options to use the viewfinder instead) and the rear screen never times out except when a long exposure is in progress.  However, the "INFO" button on the rear of the camera lets you cycle between what is displayed on the screen.  If you cycle through to the shooting menu then the liveview is switched off.

[jambi99]

Awsome! Thanks for your help.