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Astrophotography and Sketching >> DSLR & Digital Camera Astro Imaging & Processing

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mpgxsvcd
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Re: Best dslr new [Re: foste1cc]
      #5635266 - 01/21/13 04:05 PM

Quote:

i have up to a couple grand max at the moment. wasn't looking to spend it all right now. was hoping a used camera wouldn't go for more than 2 or $300. Although the mount you bring up is great advice! i think i should defiantly invest in a new one as well. I have a celestron SCT 8SE with the stock mount. Would this mount for sure need to be replaced? or is it good enough to get by for starting off astrophotography?




At F10 and over 2000mm you will have to guide unless you use a focal reducer. However, using a focal reducer with a large sensor camera usually leads to coma issues.

Also you wonít be able to take long exposures with that mount. You will get field rotation issues if you go for several minute exposures.

You would be much better off spending your money on a fast scope(Low F number) and a GEM instead of spending a bunch on the camera. Spending the money on guiding will help also although that isnít necessarily a requirement.


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mpgxsvcd
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Re: Best dslr new [Re: mpgxsvcd]
      #5635276 - 01/21/13 04:11 PM

If you are looking for a camera in the sub $300 range then look at the Panasonic G3 instead of the GH3.

The G3 really isn't anywhere near as good as the GH3 or most of the Canon's. However, they are dirt cheap on ebay($220-$280) and they can be modified easily.

http://www.ebay.com/sch/Digital-Cameras-/31388/i.html?_from=R40&_nkw=Pana...

The G3 offers up to 4 minute and 16 second exposures and it has the lossless video crop mode that is essential for most solar system objects.


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Alex McConahay
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Re: Best dslr new [Re: mmalik]
      #5635338 - 01/21/13 04:53 PM

As you pick from that list, be sure to get something with LiveView and one-cable connections. This means, avoid the older cameras.....

Alex


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Tonk
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Re: Best dslr new [Re: Alex McConahay]
      #5635380 - 01/21/13 05:15 PM

Quote:

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


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TopherTheME
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Re: Best dslr new [Re: Tonk]
      #5635568 - 01/21/13 07:18 PM

As a couple others have stated I think you should be putting more attention to getting a new mount and scope rather than focusing on the camera. The 8se will probably be rather frustrating for you to use and you will outgrow its AP capabilities rather quickly. As far as cheap cameras go, I think just about any good used DSLR under $300 would work fine for just starting out.

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jhkayakr
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Re: Best dslr new [Re: TopherTheME]
      #5635594 - 01/21/13 07:32 PM

I'm quite happy with my Canon 6D.

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mpgxsvcd
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Re: Best dslr new [Re: Tonk]
      #5635824 - 01/21/13 10:13 PM

Quote:

Quote:

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.


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TopherTheME
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Re: Best dslr new [Re: mpgxsvcd]
      #5635883 - 01/21/13 10:48 PM

Quote:

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.


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Ducky62
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Re: Best dslr new [Re: TopherTheME]
      #5635983 - 01/21/13 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.

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Tonk
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Re: Best dslr new [Re: Ducky62]
      #5636212 - 01/22/13 04:24 AM

Quote:

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.

Quote:

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


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Footbag
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Re: Best dslr new [Re: Tonk]
      #5636436 - 01/22/13 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.

Edited by Footbag (01/22/13 09:53 AM)


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mpgxsvcd
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Re: Best dslr new [Re: Tonk]
      #5636447 - 01/22/13 09:10 AM

Quote:

Quote:

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 ďunity gainĒ 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 isnít 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 isnít 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 wonít 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 donít 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 isnít helpful for his situation. If he tries to achieve the ideal parameters that you recommend with his current equipment he isnít 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 didnít see any recommendations from you that would help him at all.

Edited by mpgxsvcd (01/22/13 09:16 AM)


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mpgxsvcd
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Re: Best dslr new [Re: Footbag]
      #5636450 - 01/22/13 09:13 AM

Quote:

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.

Edited by mpgxsvcd (01/22/13 09:16 AM)


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Footbag
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Re: Best dslr new [Re: mpgxsvcd]
      #5636487 - 01/22/13 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.

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mpgxsvcd
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Re: Best dslr new [Re: Footbag]
      #5636535 - 01/22/13 10:03 AM

Quote:

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 isnít always as straight forward and isnít 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?


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Tonk
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Re: Best dslr new [Re: mpgxsvcd]
      #5636570 - 01/22/13 10:17 AM

Quote:

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????


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Tonk
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Re: Best dslr new [Re: Tonk]
      #5636605 - 01/22/13 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


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mpgxsvcd
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Re: Best dslr new [Re: Tonk]
      #5636639 - 01/22/13 10:56 AM Attachment (24 downloads)

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 donít 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.

Edited by mpgxsvcd (01/22/13 11:20 AM)


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mpgxsvcd
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Re: Best dslr new [Re: mpgxsvcd]
      #5636641 - 01/22/13 10:57 AM Attachment (28 downloads)

Stacked HDR image ISO 12,800

Edited by mpgxsvcd (01/22/13 10:57 AM)


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mpgxsvcd
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Re: Best dslr new [Re: Tonk]
      #5636650 - 01/22/13 11:05 AM

Quote:


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




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.


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