Cannon EOS 700D

[NIGHTBOY]

Just been down to the local Currys and they're selling the 700d for £585 with a 55m lens.

Now I don't really know to much about cameras but I've been thinking of getting a dslr for a while now.

I would be using it with my 8'' dob (not ideal I know) but it would be more for planets than any deep space stuff. Of course I would be using it for daytime photography aswell.

I was hoping that anyone who has one of these or is just genrally 'in the know ' about cameras could shed some light...

I also looked at the 600d but I noticed the ISO speed on the 700d is 12800 compered to the 6400 of the 600d. I'm pretty sure this will produce a better image?????

Many thanks.

[Kal]

You have to remember that ISO isn't a the ideal way to get more light because you lose so much quality and gain so much more noise when shooting. The Canon 60Da - this is Canon's astrophotography DSLR - basically the same as a regular DSLR but the low-pass filter has been changed to allow it to pick up more of the infrared spectrum.

Here is an image I borrowed from somebodies Flickr that demonstrates the difference with noise levels (these were taken with a 7D, but you get the general idea.)

I can see that the 700D is rolling with the DIGIC5 image processor which is much better versus the DIGIC4 (600D & 60Da) when it comes to reducing image noise.

To sum up - if you wanted something specifically aimed toward astrophotography you could also save up a bit more and get the 60Da for around £800-£950 (depending where you get it). However there is absolutely nothing wrong with the 700D. I would say you made a great choice picking that out.

Also, once you get it - just remember that image quality will be much better when shooting on the lower ISO settings.

Feel free to ask me any questions regards to Canon DSLR's and I'll answer them and explain everything the best I can.

[Kal]

Forgot to address the part where you mention what you're shooting with it. DSLR should be fine for planets, you actually need to shoot with a shorter exposure time anyway to reveal the details versus DSO, Jupiter can be quite bright when shooting. Without any tracking DSO's may be beyond your reach because you're going to need to track objects over a few seconds (at least +15 seconds).

For example:

Jupiter - shot taken over 1/10th of a second at ISO 160

Jupiter - shot taken over 1/500th of a second at ISO 160

[dph1nm]

ISO is a bit of a red herring - it does not change the sensitivity of your camera to photons. So I wouldn't judge a DSLR for astro work on that alone. In the example given above from flickr, the high ISO shots are noiser purely and simply because they were taken with shorter exposure times. If the same exposure had been used for each ISO you would hardly be able to tell the difference.

NigelM

[NIGHTBOY]

That's great thanks Kal. I've literally just got it home and took a few shots on auto with it (lots to learn).

To begin with I'd just like to take some photos of the night sky with the camera itself so could to point me towards a few good settings as I'm sure it wont be a case of 'set to auto, point and shoot'!

[Kal]

ISO is a bit of a red herring - it does not change the sensitivity of your camera to photons. So I wouldn't judge a DSLR for astro work on that alone. In the example given above from flickr, the high ISO shots are noiser purely and simply because they were taken with shorter exposure times. If the same exposure had been used for each ISO you would hardly be able to tell the difference.

NigelM

Sorry if I got it wrong but all my photography knowledge comes from a basis of traditional photography where you are taught that to achieve the image you want you must balance the exposure, aperture and ISO. You are correct that he likely won't use the higher ISO settings the DIGIC5 image processor in the 700D is going to allow him to take higher ISO shots with less noise.

However, where you state.

If the same exposure had been used for each ISO you would hardly be able to tell the difference.

This just doesn't make sense to me, if your exposure time and aperture are fixed then each time you increase the ISO you're going to get a brighter image through the sensor becoming more sensitive to light, until it is so overexposed that all you get is white. Of course point out if I'm wrong here.

[NIGHTBOY]

Is there a free photoshop type jobby I can download for editing???

[Scubi]

Is there a free photoshop type jobby I can download for editing???

There is an open source package that goes by the unfortunate name GIMP (Gnu Image Manipulation Program) which I think is available for both PC and Mac.  It doesn't have all the bells and whistles of PS and is just as fiddly to get your head around but it is free!

http://www.gimp.org/

Chris

[stelios_t]

I have the 600d which I like a lot. The 700d is a bit better camera, but whether it's worth the price difference is another matter. The 60Da is very pricey, and many suggest just modding a camera if you're really into photographing nebulae. With a DOB, you are several pieces of equipment short, so I think that'd be overkill for you.

Here's an objective comparison: http://snapsort.com/compare/Canon-Rebel-T5i-vs-Canon-T3i  (t3i is the 600d and t5i is the 700d)

For planets you'll be probably just taking videos and stacking them, as planets don't require sensitivity to light (they are bright). Don't know again how much luck you'll have, although software should be able to derotate the images (don't have direct experience, so ask some more on that point).

[lensman57]

I have the 600d which I like a lot. The 700d is a bit better camera, but whether it's worth the price difference is another matter. The 60Da is very pricey, and many suggest just modding a camera if you're really into photographing nebulae. With a DOB, you are several pieces of equipment short, so I think that'd be overkill for you.

Here's an objective comparison: http://snapsort.com/compare/Canon-Rebel-T5i-vs-Canon-T3i  (t3i is the 600d and t5i is the 700d)

For planets you'll be probably just taking videos and stacking them, as planets don't require sensitivity to light (they are bright). Don't know again how much luck you'll have, although software should be able to derotate the images (don't have direct experience, so ask some more on that point).

Hi,

It makes no sense to buy an expensive DSLR designed for terrestrial photography and then having it modded for astro work. In such case one is better off just paying up for something like a QHY8L which retails for not much more than most mid range DSLRs but at least it has active cooling and is made for purpose.  Canon 60da only differs from a standard 60d in just having a less aggressive IR cut filter, in tests it performed better than the standard camera but not as well as a fully modded 350d. For modding a DSLR, I think it is better to just get something like 1000d. 1100d or even a 450d, at least you could  pass it on to another buyer with not so much financial loss. I would urge you to read the article By Craig Stark, the author of Nebulasity and PHD, to gain an insight into what really goes on in the background of the DSLR even when you set the camera to take RAW data which we are all led to believe is unmolested but this is far from the truth.

Regards,

A.G

[Kal]

I would urge you to read the article By Craig Stark, the author of Nebulasity and PHD, to gain an insight into what really goes on in the background of the DSLR even when you set the camera to take RAW data which we are all led to believe is unmolested but this is far from the truth.

Regards,

A.G

Could you link me to the article you've mentioned? I'd search but I'm on my mobile.

Cheers!

[lensman57]

Could you link me to the article you've mentioned? I'd search but I'm on my mobile.

Cheers!

Hi,

It is a bit involved but it is worth the read.

Reagrds,

A.G

http://www.cloudynights.com/item.php?item_id=2786

[northwalesparry]

check out this weeks gadget show on ch5 cannon 700 tested . it gets 5Gs

[Astrosurf]

I have the 600D and it's wonderful. Look at Melsky's photos. I can't remember what he's called on Flickr. Ask him. He uses a 600D and his stuff is top-notch. But he does use a good-quality tracking mount and an Astrotrac.That makes a massive difference. But at least it shows you the quality of the camera and a possible comparison with the 700. Mel's is modded to let in IR. At least you'll have a cracking camera if you want to upgrade to a good tracking/guiding mount like the HEQ5 Pro.

There's this website about imaging with a dob though: http://www.iceinspace.com.au/63-201-0-0-1-0.html I don't know if  it'll be of any use to you.

Alexxx

[IanL]

This just doesn't make sense to me, if your exposure time and aperture are fixed then each time you increase the ISO you're going to get a brighter image through the sensor becoming more sensitive to light, until it is so overexposed that all you get is white. Of course point out if I'm wrong here.

Changing the ISO does not make the sensor more sensitive to light, that is where your confusion arises.

ISO numbers are a standardised system of measurement of film sensitivity from the pre-digital era, where they did indeed map to physical differences in the sensitivity of film emulsions to light.  The concept was carried forward to digital photography as a sales/marketing tool to sell to a customer base transitioning from film to digital photography, but it has no fundamental basis in the way digital sensors work.

A CMOS (or CCD) sensor has what is known as a Quantum Efficiency (QE) which is the percentage of incoming photons of light that are converted in to electrons that can be measured during read-out of the image.  A perfect sensor would have a QE of 100% at all wavelengths, but in reality all sensors have a QE that is much lower than this, and the QE will also vary by wavelength of light. A typical monochrome CCD sensor might have a QE of 40% at the blue end of the visible spectrum rising to perhaps 60 or 70% at the red and near infra-red end, whereas a typical (unmodified) DSLR sensor will have a QE of perhaps 40% for the pixels with the blue and green Bayer filters and maybe 30% for the red ones.

The lack of sensitivity at the red end is a problem for DSLRs as it blocks most of the useful Ha light from emission nebulae, but it can be improved by removing or changing the IR cut filter which is put on top of the whole sensor.  That IR cut filter is useful for daylight photographers as it produces more natural looking images out of the box, as well as avoiding problems due to out-of focus infra-red light falling on the sensor.  It is the bane of astro-imagers since it blocks most of the really important Ha wavelength, hence the  reason for Canon producing 60Da which is effectively factory modified with a different cut filter to improve red (and thus Ha) QE.  It is still not as high a QE as a typical mono CCD though.

The point is that each sensor pixel has a QE that was fixed at the point it was manufactured, and indeed the QE varies from pixel to pixel due to manufacturing imperfections.  That QE will be further reduced if you put a filter in front of it (whether that is an interchangeable filter for a mono CCD or the fixed Bayer pattern filter in a DSLR).  Strictly speaking, the QE of the sensor pixel is the same, but the effective QE reduces since the filter blocks some of the photons before they get to the sensor.  There is no setting on the camera which changes the underlying QE of the sensor elements. The same percentage of photons falling on the pixel will be converted to electrons regardless of any ISO or gain setting.

In the digital world, ISO is just a different way of expressing 'gain'.  Gain is simply the amount of amplification that is applied to the electrons in each pixel's electron well prior to converting the measured voltage to a number in the analog to digital convertor (ADC) on the sensor.  Increase the gain (amplification) and a bigger number comes out of the A/D converter, which results in a 'brighter' image on the screen.  The marketing and product development bods decided to map gain settings to the existing system of ISO numbers that their target market were already comfortable with as previously discussed.

Even so it is important to realise that whilst the gain settings are designed to mimic the sensitivity increments of film ISO numbers, there is no absolute fixed reference point.  One sensor's ISO 100 is not (necessarily) the same as another sensor's ISO 100 and in any case neither is a reflection of the true sensitivity of the sensor, just that 'brightness' of the resulting image is similar to that of using ISO 100 film.

That said, using some DSLR 'ISO' (gain) settings may produce a better signal to noise ratio than other 'ISO' settings.  The higher voltage coming out of the amplifier may result in less noise from the ADC; your mileage will vary depending on the camera model. 

Of course the marketing people realised that people always buy on the basis of the biggest numbers, so 'ISO wars' broke out.  Everyone wants a bigger speedboat than the neighbours, and they also want a camera that offers ISO 25600 instead of one that only goes up to ISO 3200 or ISO 6400!  In reality those really high ISOs are simply multiplication of the digital values after ADC.  The cut off between amplifier gain and digital multiplication is usually somewhere in the region of ISO 1600 or ISO 3200, again mileage will vary with model.  This latter process (for astro-imagers) is not generally useful since you can stretch the image histogram in post processing to achieve the same result and do it with far more control.  Indeed you may end up losing detail if you use a really high ISO setting since you can end up compressing different physical voltages to the same digital number unnecessarily.

If you look at an astronomical CCD camera, it does not have an ISO setting.  It will either have a factory-fixed gain setting to give the best signal-to-noise ratio, or a user configurable gain setting which will just be some range of numbers that makes sense to the camera/capture software creators (in which case you'll be expected to perform tests to figure out the best gain setting for your requirements).

Still not convinced?  If you look at your mobile phone, webcam or low-end digital camera it doesn't have an ISO setting even though it will have the same sort of CMOS or CCD sensor as a DSLR.  At best you'll have a brightness and contrast setting which are used to manipulate both the sensor gain and the histogram transfer function simultaneously in a way that is familiar to people who remember analogue TVs.   Again, contrast and brightness are just concepts carried over from the world of analogue TV for familiarity's sake (both in the webcam and digital TV worlds)!  Indeed with a typical mobile phone or point and shoot camera, the device itself will try to absolve you or all responsibility for gain and transfer functions by analysing the image and coming up with the best settings it can untouched by human hand.

As an astro-imager, really you need to focus on gain (through the imperfect medium of ISO numbers for DSLR users) and histogram transfer functions (in post-processing) to avoid misunderstanding what it is you are really doing when creating or processing an image.

[Kal]

As an astro-imager, really you need to focus on gain (through the imperfect medium of ISO numbers for DSLR users) and histogram transfer functions (in post-processing) to avoid misunderstanding what it is you are really doing when creating or processing an image.

Great post Ian, I had to re-read some of it a few times to understand but I get it. I always just accepted the ISO in digital was similar to the ISO from film.

[dph1nm]

I always just accepted the ISO in digital was similar to the ISO from film.

Not surprising, as terrestrial photography magazines keep pedaling the myth that ISO magically changes the sensitivity of your digital camera - they should know better really!

Having said that, it is possible that the ability to do very high ISO is indicative of very low read noise, which would be a good thing for astro, but I don't think this is always the case. Often it just means that they have improved the in-camera processing of jpegs (not RAW) to artificially 'smooth away' the noise.

NigelM

[lensman57]

Great post Ian, I had to re-read some of it a few times to understand but I get it. I always just accepted the ISO in digital was similar to the ISO from film.

Film and Digital are fudametntally different from each other, there is no comparison what so ever.  The majority of film emulsions closely mimicked the response of the human eye to the visible spectrum, the classic S curve of exposure V density of the emulsion. CCDs have   linear response until saturation, that is the only quality in digital capture  that allows you to stretch the stack. ISO settings  are meaningless concepts so far as digital sensors are concerned.

A.G

[mikeknowle]

I have the 600D and it's wonderful. Look at Melsky's photos. I can't remember what he's called on Flickr. Ask him. He uses a 600D and his stuff is top-notch. But he does use a good-quality tracking mount and an Astrotrac.That makes a massive difference. But at least it shows you the quality of the camera and a possible comparison with the 700. Mel's is modded to let in IR. At least you'll have a cracking camera if you want to upgrade to a good tracking/guiding mount like the HEQ5 Pro.

There's this website about imaging with a dob though: http://www.iceinspace.com.au/63-201-0-0-1-0.html I don't know if  it'll be of any use to you.

Alexxx

Alex, what exactly do you use to connect your camera and scope? 2" extender tube maybe???

I have a 600D and a Skywatcher 300P, so pretty similar to you. I usually put the 600D on the back of my Meade OTA, but just fancied do a bit through the Dob. with it for fun.

For example, Jupiter looked good last night visually....so I fancied taking a few shots...

[Astrosurf]

I'm so sorry I never answered this! I use a Canon T-ring adaptor. I remove the entire EP holder assembly fom the scope's focusing tube. I then unscrew the EP holder from the flanged part that goes into the focusing tube. This flanged part can then screw onto to the T-ring. So it's camera>T-ring>flanged part. I then re-attach the whole thing to the focusing tube. HTH.

Alexxx

[rob0971]

Is there a free photoshop type jobby I can download for editing???

Apparently adobe Photoshop cs2 is free to download from adobe. It may not support your cameras raw files so a raw converter will be needed if shooting raw. I use lightroom, but the camera should come with a rudimentary raw converter/processing software CD. Convert it with this then process in PS.

[Rob63]

One annoying thing about the 700d is that it doesn't have the movie crop mode that earlier versions did.

This allowed you to use the center part of the sensor - in effect a digital zoom.

[satsumasalad]

One annoying thing about the 700d is that it doesn't have the movie crop mode that earlier versions did.

This allowed you to use the center part of the sensor - in effect a digital zoom.

Rob63, I have recently acquired a 700D myself, loving it, still exploring it but found a search icon when you use LiveView (I think it's called) - when you patch the viewfinder through to the touch screen.  That behaves remarkably like a digital zoom, but the few pix I took this way were not digitally zoomed.  So whether it's just to help you explore the image I don't know, if so it's a remarkably fiddly way of doing it.  Just as likely to be me having missed a critical step - not a keen user of digital zoom usually.

While I'm on, and in the hope that people are still following this, this might be a totally newbie question but when people above are talking about using DSLRs for astrophotography, do you mean using the camera "neat", eg on a tripod pointing to the sky, or have you hooked it up to your telescope somehow?

Would love to know

Satsuma

[toxic]

Is there a free photoshop type jobby I can download for editing???

yes there is adobe photoshop cs2 in fact all the cs2 software is free just register and down load the product,

the product key is to the right of each software package.and you can convert cr2 (raw files) to tiff with Digital Photo Professional which is on the canon eos cd.

[Cornelius Varley]

yes there is adobe photoshop cs2 in fact all the cs2 software is free just register and down load the product,

the product key is to the right of each software package.and you can convert cr2 (raw files) to tiff with Digital Photo Professional which is on the canon eos cd.

That is actually incorrect. The "free" version of CS2 is only available to registered users of Adobe CS2 and is was not intended to be given away to the general public

"On behalf of Adobe Systems Incorporated …

You have heard wrong! Adobe is absolutely not providing free copies of CS2!

What is true is that Adobe is terminating the activation servers for CS2 and that for existing licensed users of CS2 who need to reinstall their software, copies of CS2 that don’t require activation but do require valid serial numbers are available. (Special serial numbers are provided on the page for each product download.) See <http://forums.adobe.com/thread/1114930>.