Does size matter?

[Philip Benson]

...when it comes to pixel size?

For example with solar (or lunar) imaging, what difference does pixel size make?   I am looking at one camera which has a 2.4mp chip with 5.9um pixels and another which has a bigger 3.2mp chip but smaller 2.4um pixels.    

Which would be better?

[SkyBound]

The smaller pixels for planetary, as the objects are bright but small, larger pixels for dimmer larger objects, but the scope,being used on also comes into the equation, also if you use mono, then with the smaller pixels you can always bin 2x2 and double the pixel size, but you can't shrink them...!!

[Philip Benson]

That is very true.  For solar imaging I use  a Lunt LS152.   Binning is fine if the software allows.  Doesn't always seem to be the case.   I always use mono cameras.   I was pleasantly surprised that the smaller chip gives a much larger FOV.  On account of the pixel size I guess.

[SkyBound]

49 minutes ago, Philip Benson said:

That is very true.  For solar imaging I use  a Lunt LS152.   Binning is fine if the software allows.  Doesn't always seem to be the case.   I always use mono cameras.   I was pleasantly surprised that the smaller chip gives a much larger FOV.  On account of the pixel size I guess.

Hmmmm, that doesn't sound correct, the chip size determines the FOV and not pixel size, it makes no difference what pixels size it is to the FOV, if you have two cameras with identical chip size, but one with 6 micron pixels and the other with 3 micron, the FOV would be identical....!  but the resolution would be far better on the smaller pixels...

[ollypenrice]

1 hour ago, SkyBound said:

Hmmmm, that doesn't sound correct, the chip size determines the FOV and not pixel size, it makes no difference what pixels size it is to the FOV, if you have two cameras with identical chip size, but one with 6 micron pixels and the other with 3 micron, the FOV would be identical....!  but the resolution would be far better on the smaller pixels...

You're right.

The other difference with smaller pixels on the same size chip is that the final PC screen image is larger from the small pixel camera when viewed at full size simply because one camera pixel is given one screen pixel in both cases.

Regarding pixel scale, the key difference between 'lucky imaging' with fast frame cameras and long expoure deep sky imaging is that in 'lucky imaging' with fraction of a second subs you'll get some which have had great seeing and you select and use only those. You can, therefore, work at very long focal length and 'beat the seeing.' On long exposures you can't do this so it is sensible to match pixel size to focal length to get somewhere between about 0.8 arcsecs per pixel and about 3.5. Less than that and you'll be lucky to get good enough seeing and guiding and more than that will give you blocky stars. No two imagers will ever agree on where in the continuum it is best to be!

Olly

[Philip Benson]

4 hours ago, ollypenrice said:

Hmmmm, that doesn't sound correct, the chip size determines the FOV and not pixel size

I quite agree Olly and understand your confusion.   Since my new Altair camera (IMX174) chip has a smaller 2.4mp size compared with my Flea3 (IMX036) which has a larger 3.2mp resolution I was fully expecting the Altair camera to have a smaller FOV.  But it doesn't.  It is actually much larger.  In the X direction it has a 42' diameter allowing me to get the full width of the solar disk in frame at once with a B1800 BF.

I quite appreciate that pixel size alone shouldn't affect FOV size - that is why binning a CCD camera x2 or x3 provides greater sensitivity but doesn't alter the FOV.

[SkyBound]

Olly didn't say that, I did, so I think it may be you that is a little confused.....Olly just quoted me...

but it still stands that pixel size does NOT affect FOV in any way shape or form...., that is what Olly was agreeing with

if the FOV of the two cameras you mention, are different, then the chips are also different sizes....that much will be true..and so the reason for your dilemma, but if the chils are identical in size in both directions, then the FOV will also be identical through the same scope....

[SonnyE]

When I read the title to this, "Does size matter?" I was reminded of when we were going electrical troubleshooting in the offices.

When my partner said "Turn it on."

I at the Circuit Breaker Panel would call back to him, "Coming Hot." Meaning the circuit was being turned back on for him as a warning.

Up and down the hallway a chorus of giggles would come from the ladies in the offices....

I don't know know if size matters, but sometimes the verbiage does.

Me? Oh I stopped by to see what I could learn.

[ollypenrice]

I do wish that every single chip spec sheet, without exception, gave the width and height and diagonal in mm. We NEED this information! We can get the diagonal from Pythagoras but not the width and height from the diagonal. GRRRR.

Olly

[SkyBound]

47 minutes ago, ollypenrice said:

I do wish that every single chip spec sheet, without exception, gave the width and height and diagonal in mm. We NEED this information! We can get the diagonal from Pythagoras but not the width and height from the diagonal. GRRRR.

Olly

I totally agree, every time I look at buying a new CCD or CMOS camera, I look and sensor size, and it nearly always tells you the diagonal, but as Olly says, this is so frustrating and meaningless, as it's the XY sizes we really want, but I guess showing the diagonal always makes the chip initially sound bigger, maybe that's the logic behind it from a sales point of view..

[ollypenrice]

11 minutes ago, SkyBound said:

I totally agree, every time I look at buying a new CCD or CMOS camera, I look and sensor size, and it nearly always tells you the diagonal, but as Olly says, this is so frustrating and meaningless, as it's the XY sizes we really want, but I guess showing the diagonal always makes the chip initially sound bigger, maybe that's the logic behind it from a sales point of view..

There is a logic behind quoting the diagonal: you can compare it with the fully illuminated and corrected image circle of a lens or scope. The corrected circle must at least be as wide as the chip diagonal - but we still want the x-y dimensions.

Olly