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#26 jhkayakr

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Posted 21 January 2013 - 07:32 PM

I'm quite happy with my Canon 6D.

#27 mpgxsvcd

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Posted 21 January 2013 - 10:13 PM

ISO 12,800 and actually usable up to ISO 25,600


Which is pointless for AP if this is over the unity gain of the camera - quoting the ISO nearest unity gain (1 photon => 1 ADU) would be useful


It isn't pointless if you are unable to guide and the camera can do in-camera stacking to remove the excess noise.

I am not saying that shooting at these ISOs is ideal for all situations. However, for the case of an ALT AZ mount like the OP has you would need as fast a scope as possible and the ability to shoot an extremely high ISO.

#28 TopherTheME

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Posted 21 January 2013 - 10:48 PM

It isn't pointless if you are unable to guide and the camera can do in-camera stacking to remove the excess noise.

I am not saying that shooting at these ISOs is ideal for all situations. However, for the case of an ALT AZ mount like the OP has you would need as fast a scope as possible and the ability to shoot an extremely high ISO.


+1. This would make a lot of sense for someone on a budget interested in AP.

#29 Ducky62

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Posted 21 January 2013 - 11:41 PM

I've been shopping for a dSLR primarily for non-astro use. I have no astrophotography experience but as a cheapskate the cheapest dSLR deals I've seen are a T2i refurb w/ kit lens direct from Canon for just under $300 (probably over with tax and shipping)and a new Pentax K-01 mirrorless w/40mm prime lens from Amazon for $315 shipped. Neither deal is available right now but might come up again. I ordered the Pentax which has the same sensor as the K-5 mentioned upthread and can mount almost any Pentax film camera lens. I am going to play around with the Pentax for astro use.Once again, I was just looking for a cheap good camera and not intending it for dedicated AP.

#30 Tonk

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Posted 22 January 2013 - 04:24 AM

It isn't pointless if you are unable to guide and the camera can do in-camera stacking to remove the excess noise.


I don't think you understand that once the ISO amplifier is converting the signal due to 1 photon to 1 digital unit then there are absolutely no gains to be made AT ALL going beyond this. All you are doing after this is wasting dynamic range within the digital storage and filling the gaps with random noise.

The other thing is the ISO amplifier has amplified the signal and the noise recorded by the sensor equally so the "excess" noise is a fallisy (bar the small amount of noise introduced by the amplifier) - so you still have the same signal/noise ratio.

ability to shoot an extremely high ISO.


ISO setting does not change the sensitivity of your camera - maybe this is the origin of your misunderstanding.

ISO is all about mapping an analogue signal into a range of digital values. Say we have a 4 bit camera (for arguments sake) that records 16 different brightness levels. Say we set the camera to a very high ISO that has the camera working at twice unity gain so 1 photon is converted to the value 2, 2 photons to the value 4. You will see that only half the digital space is actually filled (2, 4, 6, 8, 10, 12, 14, 16). Now we add our noise say at (+/- 1) level to peturb these values and we end up noting that all values 1 to 16 are now apparently present if we record values over the whole image.

Hence it is entirely dillusional that cranking up ISO beyond this point (unity gain) is actually any help.

Using the in-camera stacking feature this way is just patching over a mistake with the ISO selection - sorry.

Now in-camera stacking at unity gain and below IS a benefit and I'd buy into that. Sure that camera may be good - but its not because of the super high ISO


#31 Footbag

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Posted 22 January 2013 - 09:06 AM

Tonk is right about this. After unity gain, there is zero benefit in raising iso. In fact, if you are calibrating in post processing, it is introducing more noise and lessening dynamic range. You would be much better off shooting at unity gain, and selectively amplifying a post calibrated image in photoshop.

But, I can think of one place that high iso may be handy. If you have no intention of post processing, stacking or calibrating then you may choose to use it. Or if you are using a DSLR for video astronomy, it may be effective. The point is, your final image comes SOTC(straight out of the camera)

Otherwise, you are best imaging at unity gain for your camera, then doing your calibration, then doing your post processing.

#32 mpgxsvcd

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Posted 22 January 2013 - 09:10 AM

It isn't pointless if you are unable to guide and the camera can do in-camera stacking to remove the excess noise.


I don't think you understand that once the ISO amplifier is converting the signal due to 1 photon to 1 digital unit then there are absolutely no gains to be made AT ALL going beyond this. All you are doing after this is wasting dynamic range within the digital storage and filling the gaps with random noise.

Now in-camera stacking at unity gain and below IS a benefit and I'd buy into that. Sure that camera may be good - but its not because of the super high ISO


What you said technically is absolutely correct. That is absolutely true that increasing ISO past the point you referred to as “unity gain” will decrease dynamic range and increase noise excessively. However, the stacking process in the GH3 reduces the noise significantly.

In addition that mode can compress the dynamic range of the scene by up to 6 stops. Now this isn’t a true 6 stop gain in dynamic range. It is a software solution that basically compresses the scenes dynamic range for up to 6 stops. It is not the ideal method. However, it is very affective when you have limitations on the shutter durations you can use.

And that is where you neglected to factor in every parameter that matters. In a perfect world cost is no issue so you can say that everyone should guide, and buy a rock solid mount, and have a fully corrected large scope.

In reality we have budgets and in order to stay in those budgets we have to make compromises. In this situation shutter duration is going to be his biggest limitation. He simply isn’t going to be able to track for very long without buying an entirely new setup.

The GH3 can give him a solution that will work with his current setup. It can do clean images at ISO 25,600 in seconds instead of minutes or stacks that take hours. Now they are not going to equal those hour long images because of the losses you mentioned. However, if he can get to 80%-90% of those images in 1/3rd the cost I would consider that a wise purchase.

The biggest issue right now is that most people in AP won’t dare to step outside the box and try something entirely different than what they are accustomed too. They stick with what they have been using for years and don’t dare to try an entirely new approach.

The solutions I recommended are not the best all-around solutions. They have many limitations. However, for his specific situation that is about the only thing in his budget that is going to give him the ability to do good solar system objects along with good DSO images without changing his mount and perhaps scope.

Although your technical explanation was correct it really isn’t helpful for his situation. If he tries to achieve the ideal parameters that you recommend with his current equipment he isn’t going to be satisfied with the results. In addition, buying new equipment may or may not fit within his budget.

All I did was recommend two solutions that could work within his budget. The GH3 could work with his current equipment and the G3 is cheap enough where he could buy a new mount and scope and still stay within his budget(Although a T2i would probably fit that scenario just as well).

I didn’t see any recommendations from you that would help him at all.

#33 mpgxsvcd

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Posted 22 January 2013 - 09:13 AM

Tonk is right about this. After unity gain, there is zero benefit in raising iso. In fact, if you are calibrating in post processing, it is introducing more noise and lessening dynamic range. You would be much better off shooting at unity gain, and selectively amplifying a post calibrated image in photoshop.

But, I can think of one place that high iso may be handy. If you have no intention of post processing, stacking or calibrating then you may choose to use it. Or if you are using a DSLR for video astronomy, it may be effective.

Otherwise, you are best imaging at unity gain for your camera, then doing your calibration, then doing your post processing.


If you have tracking errors or field rotation nothing in Photoshop is going to fix that. The point here is that you will trade a little noise and a little less dynamic range to resolve the limitations of your mount.

I never said that what it does is not a lossy process. However, it is the only camera that can do it in-camera so that makes it very useful for people that have mount limitations.

#34 Footbag

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Posted 22 January 2013 - 09:33 AM

You are missing the point. Nobody is suggesting lengthening the exposure and lowering the iso. Just lowering the iso. You can do all of the amplification in post processing. The key is to begin with the purest signal. This is what unity gain provides.

#35 mpgxsvcd

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Posted 22 January 2013 - 10:03 AM

You are missing the point. Nobody is suggesting lengthening the exposure and lowering the iso. Just lowering the iso. You can do all of the amplification in post processing. The key is to begin with the purest signal. This is what unity gain provides.


Yes that is correct unless at unity gain a portion of the signal(either the dark areas or bright areas are clipped). Then you would have to use multiple images in order to be able to lift or pull down those areas in post processing.

That post processing can either happen in-camera or on a computer. I was simply providing a solution that is simpler in the fact that it does that post processing in camera and does it well. Stacking images on a computer is easy and cheap. Stacking and combining multiple exposures with different durations isn’t always as straight forward and isn’t always free on a computer.

The solutions I suggested are not the end all be all. They are just one approach that puts most of the processing solution in the camera.

I am not sure what ISO is the unity gain for the Canon cameras. I can only assume it is ISO 1600 since that is what ISO everyone uses. How many dark objects will get clipped at ISO 1600 with F10 or even F6.3 with a focal reducer and less than 1 minute exposures?

#36 Tonk

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Posted 22 January 2013 - 10:17 AM

I never said that what it does is not a lossy process. However, it is the only camera that can do it in-camera so that makes it very useful for people that have mount limitations.


I'm wondering what real advantage exists between in camera "stacking" and doing it in software where the options are vast. Does the camera support Entropy Weighted, Sigma Kappa, Median, Min/max excluded or just average?

Second no matter what guiding you are using any mis alignment that the mount has from polar alignment accumulates over time (even if the stars in each frame are guided OK).

So I'm doubtful that frame registeration is going to hold say across the 6 hour imaging runs which I like to do. How does this camera cope with that?

So I'd rather collect all my frames and calibrate, register and stack after the event. I doubt any camera has the where-with-all to know how to any of this.

Or am I misunderstanding and by "stacking" do you actually mean in-camera noise reduction with an automaticaly taken dark???? :question:

#37 Tonk

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Posted 22 January 2013 - 10:32 AM

The very little info I can find on this out in webland leads me to believe that its for HDR (high dynamic range) images - automagically take images at different exposures to compress into one - gets done for you.

Not sure how this helps with real stacking for DSO images other than a couple of the usual suspects like M42

#38 mpgxsvcd

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Posted 22 January 2013 - 10:56 AM

There are two modes on the GH3. One is an HDR mode that takes three separate images. The ISO is fixed but you can select up to ISO 25,600. You can also select whether it increases the duration by 1,2,or 3 stops up and down.

Now that is not all that this mode does. It also subtracts out the differences in noise from those three combined images. In addition it also has a setting to turn Aligning on or off.

I have no way of knowing what the algorithm is for this mode. It could be using anything. I don’t contend that this mode does better stacking than a computer could do. However, it does do a better job with it than any other camera since it stacks the images to reduce noise as well as doing the Aligning and HDR process.

This is the mode that I think would help the OP the most with objects that are dark and have something bright near them. Orion is the best example but even the Horse Head has a bright star next to it.

The other mode has some limitations that make it not as useful for the OP but could be very intriguing for someone who is guiding. This mode allows you to stack an infinite number of RAW images in camera.

You have two choices here. You can either have it stack the RAW images to increase exposure. It is basically just summing the exposures. Or you can have it stack the RAW images to reduce noise just like our software programs do. Again I have no idea what algorithm it uses.

The RAW stacking mode is limited to ISO 1600 or less. I presume this is because that is the unity gain point for the GH3 like the Canon cameras. However, I have no evidence that supports that assumption.

The RAW stacking mode does not align the images so like you said you could not have any tracking errors at all. Guiding would probably eliminate this issue.

Here is an example of a single 8 second ISO 12,800 RAW image and then the equivalent stacked in camera HDR image below that.

Attached Files



#39 mpgxsvcd

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Posted 22 January 2013 - 10:57 AM

Stacked HDR image ISO 12,800

Attached Files



#40 mpgxsvcd

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Posted 22 January 2013 - 11:05 AM

Or am I misunderstanding and by "stacking" do you actually mean in-camera noise reduction with an automatically taken dark???? :question:


No. In camera noise reduction dark frames is a completely separate option from any of the stacking modes on the GH3. You can do the dark frame subtraction in-camera with any of the stacking modes. However, they are both completely separate options and no I am not confusing them like your emoticon implies.

#41 mpgxsvcd

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Posted 22 January 2013 - 11:15 AM

Part of the problem is that you are expecting a novice user like the OP to want to get the absolute best image possible regardless of price. You may like to take “6 hour imaging runs” but I think that is a little optimistic for the OP and his current equipment.

Judging by your equipment list I don’t think any of those items will fit into the OP’s budget. Your scope alone exceeds his entire budget. The entire setup I suggested would come in under his budget.

However, for someone who is guiding the RAW stacking process could be very interesting. I don’t guide so I haven’t played with it as much for AP. However, I have tested it indoors with a single spot light pointing at the camera to simulate extreme dynamic range.

It can do some really interesting things since it will stack images from entirely different exposure durations. You can also use the mode that reduces noise to completely eliminate noise. However, noise really isn’t an issue at ISO 1600. I don’t start to notice it until about ISO 6400.

#42 Footbag

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Posted 22 January 2013 - 11:32 AM

Part of the problem is that you are expecting a novice user like the OP to want to get the absolute best image possible regardless of price.


The $300 camera you suggested is cheaper then the $300 camera I suggested? :question:

#43 mpgxsvcd

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Posted 22 January 2013 - 12:02 PM

Part of the problem is that you are expecting a novice user like the OP to want to get the absolute best image possible regardless of price.


The $300 camera you suggested is cheaper then the $300 camera I suggested? :question:


Yes the G3 is ($220-$280) like I said. That is cheaper than $300. Is it not? Significantly cheaper than $300 in my opinion.

#44 foste1cc

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Posted 22 January 2013 - 12:21 PM

Once again guys, thank you so much for all the information. Seems like i may have a bad setup for AP? I just bought my scope last year and haven't even got to do any AP with it yet, but i saw in the manual it said its good for AP. I have the celestron nexstar 8se SCT. Stock mount, i bought a f/10-f/6.3 focal reducer and the necessary trings and t adapters to hook up my buddies dslrs to my scope. I just would like to purchase my own dslr for a cheap price in hopes of starting out AP. So am i pretty much screwed for starting out AP with the setup i have now? Or is it good enough to at least get decent pictures to start out with?

Also- i plan on building my own wedge for this mount. I've looked up many videos and sites on how to to do it, and since i work in a machine shop i figured i have all the right tools and measuring devices to make an accurate wedge. So with a wedge attached to the setup i have now be ok for starting off AP? I was also looking into getting orions cheap auto guider/ star tracker for a couple hundred $.

Would a tracker and wedge make up for some of the disadvantages in AP in my setup? I dont have many add-ons to my scope so there's little weight on the mount besides the scope and camera. Basically im looking for a way or loop hole around all the disadvantages for my setup without buying a new scope or mount (for the time being that is..)

#45 Footbag

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Posted 22 January 2013 - 12:21 PM

The Canon XS and the G3 are both in the same price class. If you can find a used G3 in that price range, you can find a used XS just the same.

The OP originally asked what the "best" DSLR he could get for AP was. I advised him not to spend a lot on a high end camera as an entry level camera would do. Spending more on the mount and less on the camera is always good advice, and is something many newcomers don't full understand.

You seem to be advocating a camera based on a single convenience feature, which will lose it's usefulness once the user progresses beyond being a beginner.

#46 mpgxsvcd

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Posted 22 January 2013 - 01:07 PM

You seem to be advocating a camera based on a single convenience feature, which will lose it's usefulness once the user progresses beyond being a beginner.


I agree that the mount is most important, the scope is next, and the camera is a close third. However, that doesn’t mean that a convenience features don’t matter on a camera.

There is a lot more the GH3 can do than the things I have mentioned already. It is just that some of these things may or may not apply to the OP. He listed a broad term(DSO) for what he wanted to see. I would like to hear exactly what he is expecting to see.

Does he want to just see bright things like Orion’s Nebula, the clusters, WhirlPool, Ring….etc. Or does he want to be able to point his scope at whatever dark object he wants and see it right then and there?

Here are the reasons I bought the GH3 for AP. I value being able to point my scope at just about any reasonable object(About Mag 12 or less) anyone asks for and show them what it looks like in color in less than 3 minutes above everything else.

However, I also like being able to stack just a few images and get good results without spending hours on a single subject. I value quantity of objects over absolute quality. That doesn’t mean I don’t want quality. I just don’t want to spend and exorbitant amount of time eeking out the last few percent.

Here are the things that the GH3 can do that I have not found in any other single camera. If the OP is interested in these things then the GH3 might be worth looking at.

1. Being able to shoot at ISO 25,600 and not display exorbitant noise or overly aggressive noise reduction.

2. In camera RAW stacking including being able to stack images from different sections of space to create impossible shots like Orion’s passing in front of the moon. Simply a novelty I want to try.

3. HDMI output at 1080p @ 60 FPS with the ability to have all of the information icons on screen or not have them at the flip of a switch.

4. Wireless capabilities to stream a semi live view to a tablet or phone within wireless range. Also be able to instantly transfer images to the tablet or phone straight from the camera.

5. 18 megapixels not because I want that much resolution. Instead I want it for the great cropped video mode for solar system objects.

6. For my telescope something in the 4/3” chip size is ideal. That allows me to get a full moon and Andromeda in a single frame and still be able to see the smaller objects as well.

7. 1080p Video @ 60 Frames Per second. A must for solar system objects.

8. A crop sensor mode that will allow me to get the equivalent field of view of adding a 4x barlow for video and at least a 2x for stills. I want it to be able to do the lossless cropping in real time live view.

9. At least a 10x instant crop mode for accurate focusing.

10. Adjustable shutter duration from 1/4000 of a second through at least 1 hour.

11. Real-time live view with shutter durations up to 8 seconds for accurate centering of dark objects.

12. In camera HDR capabilities to simulate an increase of dynamic range from 12 stops to up to 18 stops.

13. A fully electronic first and second curtain shutter to completely eliminate all shutter vibrations.

14. A built-in and fully customizable intervalometer. That would allow me to select any shutter duration and interval that I wanted without using a computer.

15. A flip out large LCD screen and a built-in viewfinder.

16. Incredible battery life. At least be able to shoot continuous images all night long on a single charge.

17. Complete weather sealing for those hot and humid nights where dew forms on everything.

18. Ability to modify the filter to be full spectrum.

#47 Tonk

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Posted 22 January 2013 - 01:15 PM

Also- i plan on building my own wedge for this mount.


That would go a long way to sorting out the first issue.

I would add that with a wedge you might consider a mounting bracket to piggy back a camera with a regular lens. I.e. don't actually shoot through the scope - yet. Starting out widefield is a much better option at the beginning as tracking errors and such are much more forgiving. There are plaenty of widefield targets to keep you going for a couple of years at least

#48 LeCarl

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Posted 22 January 2013 - 10:45 PM

ah... new cam?

I paid my used camera:
my t2i last year 380$w/ship (sold for 420$)
my xs paid 170$ w/ship on ebay (sold 230$)
my 2 t3i for +-400$ each w/ship very used...

t3i genuine canon battery last 6h+ in summer
(2h on winter night at -20 and less)
Chinese battery cost 4-6$ and last 3/4 of the canon ones...

I have difficulty to think about buying brand new cam to open it and remove part, used is fine, astro object don't see scratch on body of the cams... mine have holes, cover removed, a lot of tripod scratch on it... metal tape

Physics say,
aps-c is way better than 4/3, and full is way better than aps-c

in cam processing??? why... it takes same time as separate anyway, then it save no time, it's better to have separate ones and can play with, fine details is in noise... (for camera)

Iso performance, Tonk say all truth, you must find the 1:1 ratio,... all about steps in ADC converter...

For me for DSO, to the deepest or not:
XSI minimum(found for 200-250$ used), t3i better(400-450 used), 6D seem wow, good big pixels microlens, 20mpx is more than enough... over-resolution, but can't find new used one, I leave time to develop software and filters...

xs and older cam is not as good... (need more skills for same good picture, yes, it mean you can do something with skills, but faster and easier is better, particularly for only 30-50$ more...) ;)

I never seen a real dead canon camera yet, try to find one on ebay haha! moisture and cold... remove the battery and dry, never have been problem for dslr, have fun...! :roflmao:
see: http://www.youtube.c...h?v=D1tTBncIsm8

#49 LeCarl

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Posted 22 January 2013 - 11:00 PM

I guess that Orion is a good valid target to test astromaterial?... it can be imaged in cellphone?! ;p

#50 nofxrx

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Posted 22 January 2013 - 11:14 PM

xs and older cam is not as good... (need more skills for same good picture, yes, it mean you can do something with skills, but faster and easier is better, particularly for only 30-50$ more...) ;)


But the XS is "newer" tech...I think you are talking about the XTi, which did not have LiveView and required a separate cable to shutter release...
I think you should have said/meant: "Anything older than the XS is not as good", meaning it does NOT include the XS in the statement...but; "XS and older" means the XS is included. And it shouldnt be..imo

XS has LiveView, no amp glow, is full controlled with a single USB, etc..
That is all we need for AP

Am I missing something?
Just trying to make sure no one gets the wrong impression about the "line" between 'old' tech and newer tech.. ;)

Only "negative" about the XS is the 12bit ADC...not a big deal at all imho


Cheers






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