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another camera choice question

Anthonyexmouth

By Anthonyexmouth
in Discussions - Cameras

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Anthonyexmouth

Anthonyexmouth

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Will after a lot of consideration I don't think I'm rich enough or ready to make the jump to mono, with the zwo sale I'm now looking at the 183c and 294c . Leaning toward the 294 as although the calculation says it's slightly under sampling at my 490mm focal length I think I'm right in saying drizzle will make up for that and with the larger pixel scale it will smooth out any minor guiding errors. Am I right in this thinking? 

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vlaiv

vlaiv

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Do look here for my drizzle opinion:

It's simply easier to either go with proper sampling, or over sampling and then just bin. In most cases, under sampling will not be enough to fully exploit drizzle, nor system is precise enough to provide needed sub pixel displacements (they just end up being random in most if not all amateur setups).

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vlaiv

vlaiv

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Both of those are quite ok sampling rates. It will depend on your guiding/tracking and seeing conditions if you are going to under sample or not.

Even if you do, it will not be large under sampling.

Thing with OSC cameras is that you can't really calculate sampling rates like with mono cameras. This is because of "sparseness" of bayer matrix. Take for example red. You calculate that pixel scale is ~2"/px for 294. This is if you consider each pixel next to each other, so sampling will be every 2" - like 2", 4", 6", 8", ... If you look at bayer matrix and red pixel, you will not have 2"/px sampling. Although pixel size/scale is 2"/px, you are not sampling every pixel for red channel, so your samples of red channel will be 2", 4" (not red, so we don't count it), 6", 8" (not red again), .... or 2", 6", 10" ... this is 4"/px sampling.

Same goes for blue, and if we think of green as being green1 and green2 - they will also be sampling at 4"/px. Only difference between red, blue and greens is that you have two set of green samplings, so you increase number of subs that you acquire.

Even if you look at it like this, you still won't be too under sampled. I've found that 2"/px is just right for 80mm scope under average / good conditions.

Choose your camera based on intended targets. If you want to get in "closer" 183 will be better choice, but it will lack FOV. It will have nicer field as any FF/FR spacing issues will less impact 16mm imaging circle.

If you want to go wider - choose 294. 294 will also be better choice for future scope upgrades (like larger scopes and more focal length).

If you opt for 183, then think of it in terms of quarter pixel count, and use super pixel mode rather than regular debayering - 2748 x 1836. You can work with full resolution and use interpolating debayering, but that will just produce over sampled results (not so in 294 case).

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RolandKol

RolandKol

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Major Undersampling sample below :)

Check the "square like" stars, they are visible, but just a bit... Do not have original file in the office, I can drop one in from home.

But on another hand, - are they actually so visible? 

I presume, the undersampling was a Real issue in old CCD times, with the large pixel sizes and small resolution (1200x800)... Slight undersampling with resolution 5000x4000 at 4microns per pixel, should not be an issue in the final images.

 

(Image done with Samyang 135mm and Canon 1300D - bad seeing)

Untitled.png.6a58bf75230c69c294b10723c34f244b.png

 

Rosette Nebula [N2244]

 

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Z3roCool

Z3roCool

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I have been going betwen the ZWO 183MM and 1600MM for the last month and really cannot decide! Hope you have made your decision :D

I want to go for the 183 for its resolution and also AR coating but seeing images of the 1600MM always look so much cleaner, even with cheaper filters. Maybe just becasue there are so many more 1600's around there are more images to look at.

Good luck with your choice...I am sure I will still be making mine in another month! 

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Anthonyexmouth

Anthonyexmouth

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6 minutes ago, Z3roCool said:

I have been going betwen the ZWO 183MM and 1600MM for the last month and really cannot decide! Hope you have made your decision :D

I want to go for the 183 for its resolution and also AR coating but seeing images of the 1600MM always look so much cleaner, even with cheaper filters. Maybe just becasue there are so many more 1600's around there are more images to look at.

Good luck with your choice...I am sure I will still be making mine in another month! 

Think it's going to be the 294c for me. Make your mind up while the zwo Easter sale is on. 

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vlaiv

vlaiv

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1 hour ago, RolandKol said:

or maybe wait a bit for ZWO 16Bit cameras? :)

No need to go with higher bit count.

It might be good thing for day time use, to have massive FW capacity and hence higher bit count values, but for AP usage, more important aspect is lower read noise. Lower read noise allows for shorter exposures, and with short exposures, even bright stars won't saturate.

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