Long Lens vs Telescope for Astrophotography

[Andy Lucy]

Not necessarily.....Leaving out the "pinhead" 1" and 2/3 sensors...(which are nearly worthless for AP unless you're shooting at f2), pixel size is nearly equal between most modern 4/3 , APS-c and FF cameras..

1-inch sensors nearly worthless for AP unless at f2?

This moon image was taken with a 1 inch sensor (Nikon J5) at f10 (8-inch SCT). Acquired using the 4K video mode and processed in AutoStakkert2! Seems OK to me.


Image Scale = 0.23 arcseconds / pixel

 

[Painter19]

Very cool image. I guess developments in sensor technology have already ,and probably will continue to make small sensors more sensitive with more useable resolution.

The Sony RX10 IV I’ve been using since February has a 1” sensor. It’s a fixed lens zoom with a 24-600mm equiv. focal length. In absolute terms it’s around 220mm at the long end.

I just mention the lens to say it’s not so long in astrophotography terms, but it’s sharp and bright (f4 is sharp at the long end), and the sensor seems to do quite well within the limits of the lens.

 

[Painter19]

FF sensors are 36mm X 22mm, while APS-C sensors are 22.4mm X 14.9 mm. The surface area of full-frame sensor is 2.4 X that of an APS-C.

FYI, FF is actually 36mm x 24mm. And what you quote above for APS-C is Canon's APS-C format. Sony APS-C sensors used in Sony, Nikon, Pentax and Fujifilm cameras are a little larger: about 23.5mm x 15.6mm.

There aren’t too many new APS-C sensor cameras with only 16 mp these days, though.

True, but it was just an example to illustrate a point. Context is everything.

Just another way to look at it:

My 24MP FF camera has about 6 micron pixel size.

My 24MP APS-C camera has about 4 micron pixel size.

Pixel size is what limit resolution given a perfect lens. Not image sensor size.

So my APS-C camera will outresolve my FF camera (1.5x linear and 2.25x by area). But my FF camera will capture a larger field of view given the same lens or telescope.

When using my FF camera in crop mode the pixel size is still 6 micron (the image sensor does not change by cropping away part of the image).

Plate scale is pretty close to 1 arc sec per pixel when using 4.8 micron pixels and 1000mm focal lenght. This is a linear measure and easy to scale.

To reach 1 arc sec resolution horisontally or vertical twice that focal lenght is needed (one pixel alone is unresolved). Pixels are square so if taking account for diagonal resolution, multiply the focal lenght by 2.8x.

Very interesting . Thanks. I’m new to this stuff and am trying to learn about arc secs. and pixel size, focal length and resolution. Alen K, and others have been stressing individual pixel size to me.

I just came across this article . I’m wondering what you guys think of it?

https://www.atik-cameras.com/news/rules-1-2-arc-second-per-pixel-and-when-to-break-them/

 

[swimswithtrout]

How much in -camera resampling was done to get the 20.8MP native resolution down to 8.5 MP 4K video.......

Most "planetary CMOS cams" are only 1/3" chips....



But that doesn't help the OP understand image scale.

 

[Tristimulus]

FF sensors are 36mm X 22mm, while APS-C sensors are 22.4mm X 14.9 mm. The surface area of full-frame sensor is 2.4 X that of an APS-C.

FYI, FF is actually 36mm x 24mm. And what you quote above for APS-C is Canon's APS-C format. Sony APS-C sensors used in Sony, Nikon, Pentax and Fujifilm cameras are a little larger: about 23.5mm x 15.6mm.

There aren’t too many new APS-C sensor cameras with only 16 mp these days, though.

True, but it was just an example to illustrate a point. Context is everything.

Just another way to look at it:

My 24MP FF camera has about 6 micron pixel size.

My 24MP APS-C camera has about 4 micron pixel size.

Pixel size is what limit resolution given a perfect lens. Not image sensor size.

So my APS-C camera will outresolve my FF camera (1.5x linear and 2.25x by area). But my FF camera will capture a larger field of view given the same lens or telescope.

When using my FF camera in crop mode the pixel size is still 6 micron (the image sensor does not change by cropping away part of the image).

Plate scale is pretty close to 1 arc sec per pixel when using 4.8 micron pixels and 1000mm focal lenght. This is a linear measure and easy to scale.

To reach 1 arc sec resolution horisontally or vertical twice that focal lenght is needed (one pixel alone is unresolved). Pixels are square so if taking account for diagonal resolution, multiply the focal lenght by 2.8x.

Very interesting . Thanks. I’m new to this stuff and am trying to learn about arc secs. and pixel size, focal length and resolution. Alen K, and others have been stressing individual pixel size to me.

I just came across this article . I’m wondering what you guys think of it?

https://www.atik-cameras.com/news/rules-1-2-arc-second-per-pixel-and-when-to-break-them/

The Atik gang is a bunch of very clever ones and this is solid down to earth advice.

You may calculate all day long, but when captuing at night you will see that the basic advice given here is pretty good.

At my location seeing is usually more like 3-4 arc seconds (that is how much the stars are blurred during a time exposure). So my location is sub optimal in this regard.

For the moon and planets recording sub arc second resolution is hard from most locations, and obviously longer focal lenghts and shorter exposures are needed.

My M51 image a bit above in this thread is recorded at 1.5 pixels per arc second (530mm focal lenght and 3.8 micron pixels).

 

[Painter19]

FF sensors are 36mm X 22mm, while APS-C sensors are 22.4mm X 14.9 mm. The surface area of full-frame sensor is 2.4 X that of an APS-C.

FYI, FF is actually 36mm x 24mm. And what you quote above for APS-C is Canon's APS-C format. Sony APS-C sensors used in Sony, Nikon, Pentax and Fujifilm cameras are a little larger: about 23.5mm x 15.6mm.

There aren’t too many new APS-C sensor cameras with only 16 mp these days, though.

True, but it was just an example to illustrate a point. Context is everything.

Just another way to look at it:

My 24MP FF camera has about 6 micron pixel size.

My 24MP APS-C camera has about 4 micron pixel size.

Pixel size is what limit resolution given a perfect lens. Not image sensor size.

So my APS-C camera will outresolve my FF camera (1.5x linear and 2.25x by area). But my FF camera will capture a larger field of view given the same lens or telescope.

When using my FF camera in crop mode the pixel size is still 6 micron (the image sensor does not change by cropping away part of the image).

Plate scale is pretty close to 1 arc sec per pixel when using 4.8 micron pixels and 1000mm focal lenght. This is a linear measure and easy to scale.

To reach 1 arc sec resolution horisontally or vertical twice that focal lenght is needed (one pixel alone is unresolved). Pixels are square so if taking account for diagonal resolution, multiply the focal lenght by 2.8x.

Very interesting . Thanks. I’m new to this stuff and am trying to learn about arc secs. and pixel size, focal length and resolution. Alen K, and others have been stressing individual pixel size to me.

I just came across this article . I’m wondering what you guys think of it?

https://www.atik-cameras.com/news/rules-1-2-arc-second-per-pixel-and-when-to-break-them/

The Atik gang is a bunch of very clever ones and this is solid down to earth advice.

You may calculate all day long, but when captuing at night you will see that the basic advice given here is pretty good.

At my location seeing is usually more like 3-4 arc seconds (that is how much the stars are blurred during a time exposure). So my location is sub optimal in this regard.

For the moon and planets recording sub arc second resolution is hard from most locations, and obviously longer focal lenghts and shorter exposures are needed.

My M51 image a bit above in this thread is recorded at 1.5 pixels per arc second (530mm focal lenght and 3.8 micron pixels).

Thanks for confirming the article. I went back and looked at your M51 image . It’s beautiful. I’m glad to start learning about pixel sizes and arc secs and focal length and how they relate to each other along with aperture to image resolution. Can i ask you what camera you used?

I was messing around on Astronomy Tools FOV Calculator page this morning. I was interested to see one ZWO camera, the ASI 120MC-S has a pixel size of 3.75 microns. I was also interested to see the Panasonic GX8 I’m thinking about buying used has a pixel “pitch” of 3.33 microns. is that the same as pixel size?

Anyhow, do you have any thoughts about using a four-thirds camera like the 20mp Panasonic GX8 with a Celestron C5? Again they would be most often used from my LA apartment with occasional forays elsewhere with our Moon being my main subject. I still like the crop factor of a 4/3, and now there is the GX8 pixel size as a plus perhaps(?) I probably would also get into an astro camera and image stacking software later, as well.

 

[Andy Lucy]

That's a good point that 4K video resamples the data in the J5. The final output is actually 7.5MP frames - but this is not taken from the whole area of the sensor - the edges are cropped. It's not clear exactly what size the video file output pixels are - so the 0.23 arcsecs/pixel I quoted is too small - my guess it's probably around 0.3 arcsecs /pixel. In any event, with an 8-inch scope it's all a bit academic since the Dawes limit for the scope is 0.57 arcseconds.

I think the key point is that - in line with your earlier post - aperture is key for lunar and planetary imaging. I've taken lunar images with a high quality 300mm fl, f/4 (75mm aperture) lens on my J5 and the image quality is way short of that with a 2032 fl, f/10 (200mm aperture) scope on the same camera.

Regards,

Andy

 

[swimswithtrout]

I was messing around on Astronomy Tools FOV Calculator page this morning. I was interested to see one ZWO camera, the ASI 120MC-S has a pixel size of 3.75 microns. I was also interested to see the Panasonic GX8 I’m thinking about buying used has a pixel “pitch” of 3.33 microns. is that the same as pixel size?

Yes.... pixel pitch is the same as pixel size.....a 16MP Olympus OMD EM10 Mark II 4/3 camera has 3.74um pixels , the 61 Mp FF Sony A7IV has 3.76 um pixels...


The ZWO is a 1.2MP camera because it's only a 1/3" chip


So now that you are finally getting a grasp that "resolution" has nothing to do with chip size and is solely dependent on pixel size and fl, can we drop the long debunked myth of "Equivalent Focal Length" ?


Re: the GX8....There is a point of seriously diminishing returns as pixel size decreases. Smaller pixels are inherently more noisy, it takes a LOT of light to overcome the background noise. That's why I sarcastically said you could buy one of the Nikon "super-zooms" with a "2000mm equivalent" for the same cost as used GX8...a 16MP P900 has 1.34um pixels.......packed on a 2/3" chip......

 

[Painter19]

I was messing around on Astronomy Tools FOV Calculator page this morning. I was interested to see one ZWO camera, the ASI 120MC-S has a pixel size of 3.75 microns. I was also interested to see the Panasonic GX8 I’m thinking about buying used has a pixel “pitch” of 3.33 microns. is that the same as pixel size?

Yes.... pixel pitch is the same as pixel size.....a 16MP Olympus OMD EM10 Mark II 4/3 camera has 3.74um pixels , the 61 Mp FF Sony A7IV has 3.76 um pixels...

Thanks about pixel pitch/size. Woah!, surprised to see that pixel size on a FF sensor, but then 61 is a lot of them, and they have to fit .

The ZWO is a 1.2MP camera because it's only a 1/3" chip

What’s a chip - a sensor?

So now that you are finally getting a grasp that "resolution" has nothing to do with chip size and is solely dependent on pixel size and fl, can we drop the long debunked myth of "Equivalent Focal Length" ?

Well, maybe. i’m in possession of a morphing understanding. Still hard for me to envision how a crop from a larger sensor containing fewer receptor sites/ pixels than a sensor of the same area as that crop can have an equivalent resolution of detail, except maybe by allowing for the less crowded sites on the larger sensor crop receiving more light. It’s the idea that it’s the size of individual pixels, not how many of them are in a certain area, that determines resolution is still counter-intuitive for me. I’m sure it’s right now, and am trying to grasp it more fully, but it’s a work in progress.

Re: the GX8....There is a point of seriously diminishing returns as pixel size decreases. Smaller pixels are inherently more noisy, it takes a LOT of light to overcome the background noise. That's why I sarcastically said you could buy one of the Nikon "super-zooms" with a "2000mm equivalent" for the same cost as used GX8...a 16MP P900 has 1.34um pixels.......packed on a 2/3" chip......

I am sometimes sarcastic, except when i’m being on my best behavior, like now. I take your point about the noise and light issues with too small pixels, though. Thanks.

 

[swimswithtrout]

. Still hard for me to envision how a crop from a larger sensor containing fewer receptor sites/ pixels than a sensor of the same area as that crop can have an equivalent resolution of detail, except maybe by allowing for the less crowded sites on the larger sensor crop receiving more light. It’s the idea that it’s the size of individual pixels, not how many of them are in a certain area, that determines resolution is still counter-intuitive for me. I’m sure it’s right now, and am trying to grasp it more fully, but it’s a work in progress.

Last time......Most every camera uses the same 3.75 to 3.92 um pixels...the only thing that changes is the field of view...not the resolution...Larger cameras have more pixels..... a 16 MP 4/3camera has the same pixel density as a 61 MP FF camera.....

I took this shot with my 1.2 MP guidecam, the exact same camera as the ZWO 120, but QHY branded....

 

[Painter19]

. Still hard for me to envision how a crop from a larger sensor containing fewer receptor sites/ pixels than a sensor of the same area as that crop can have an equivalent resolution of detail, except maybe by allowing for the less crowded sites on the larger sensor crop receiving more light. It’s the idea that it’s the size of individual pixels, not how many of them are in a certain area, that determines resolution is still counter-intuitive for me. I’m sure it’s right now, and am trying to grasp it more fully, but it’s a work in progress.

Last time......Most every camera uses the same 3.75 to 3.92 um pixels...the only thing that changes is the field of view...not the resolution...Larger cameras have more pixels..... a 16 MP 4/3camera has the same pixel density as a 61 MP FF camera.....

Strange. I seem to find FF and APS-C generally have fewer pixels per sq.mm than 4/3 or 1” sensors, and often have larger pixel size.

I took this shot with my 1.2 MP guidecam, the exact same camera as the ZWO 120, but QHY branded....

Terrific Image, really great! That’s very encouraging for me regarding astro cams.

 

[swimswithtrout]

. Still hard for me to envision how a crop from a larger sensor containing fewer receptor sites/ pixels than a sensor of the same area as that crop can have an equivalent resolution of detail, except maybe by allowing for the less crowded sites on the larger sensor crop receiving more light. It’s the idea that it’s the size of individual pixels, not how many of them are in a certain area, that determines resolution is still counter-intuitive for me. I’m sure it’s right now, and am trying to grasp it more fully, but it’s a work in progress.

Last time......Most every camera uses the same 3.75 to 3.92 um pixels...the only thing that changes is the field of view...not the resolution...Larger cameras have more pixels..... a 16 MP 4/3camera has the same pixel density as a 61 MP FF camera.....

Strange. I seem to find FF and APS-C generally have fewer pixels per sq.mm than 4/3 or 1” sensors, and often have larger pixel size.

https://www.digicamdb.com/specs/olympus_om-d-e-m10-ii/

https://www.digicamdb.com/specs/sony_a7r-iv/

I don't know if you're trolling or just too dense to understand this...

Again here you go....no telescope needed

Verifying…

 

[Painter19]

. Still hard for me to envision how a crop from a larger sensor containing fewer receptor sites/ pixels than a sensor of the same area as that crop can have an equivalent resolution of detail, except maybe by allowing for the less crowded sites on the larger sensor crop receiving more light. It’s the idea that it’s the size of individual pixels, not how many of them are in a certain area, that determines resolution is still counter-intuitive for me. I’m sure it’s right now, and am trying to grasp it more fully, but it’s a work in progress.

Last time......Most every camera uses the same 3.75 to 3.92 um pixels...the only thing that changes is the field of view...not the resolution...Larger cameras have more pixels..... a 16 MP 4/3camera has the same pixel density as a 61 MP FF camera.....

Strange. I seem to find FF and APS-C generally have fewer pixels per sq.mm than 4/3 or 1” sensors, and often have larger pixel size.

https://www.digicamdb.com/specs/olympus_om-d-e-m10-ii/

https://www.digicamdb.com/specs/sony_a7r-iv/

I don't know if you're trolling or just too dense to understand this

Those 2 links about 2 cameras do nothing to prove the general rule you were suggesting. that cameras with different-size sensors generally have the same number of pixels per sq mm. I am not trolling. I don’t know whether you’re trolling, or are too dense to understand that.

 

[swimswithtrout]

. Still hard for me to envision how a crop from a larger sensor containing fewer receptor sites/ pixels than a sensor of the same area as that crop can have an equivalent resolution of detail, except maybe by allowing for the less crowded sites on the larger sensor crop receiving more light. It’s the idea that it’s the size of individual pixels, not how many of them are in a certain area, that determines resolution is still counter-intuitive for me. I’m sure it’s right now, and am trying to grasp it more fully, but it’s a work in progress.

Last time......Most every camera uses the same 3.75 to 3.92 um pixels...the only thing that changes is the field of view...not the resolution...Larger cameras have more pixels..... a 16 MP 4/3camera has the same pixel density as a 61 MP FF camera.....

Strange. I seem to find FF and APS-C generally have fewer pixels per sq.mm than 4/3 or 1” sensors, and often have larger pixel size.

https://www.digicamdb.com/specs/olympus_om-d-e-m10-ii/

https://www.digicamdb.com/specs/sony_a7r-iv/

Those 2 links about 2 cameras do nothing to prove the general rule you were suggesting. that cameras with different-size sensors generally have the same number of pixels per sq mm.

??????????


Reread the links...the 4/3 camera has the same pixel density as the FF camera...Everyone here has told you the same thing..


You are either trolling, or have a severe reading problem...done..over and out....

 

[Painter19]

. Still hard for me to envision how a crop from a larger sensor containing fewer receptor sites/ pixels than a sensor of the same area as that crop can have an equivalent resolution of detail, except maybe by allowing for the less crowded sites on the larger sensor crop receiving more light. It’s the idea that it’s the size of individual pixels, not how many of them are in a certain area, that determines resolution is still counter-intuitive for me. I’m sure it’s right now, and am trying to grasp it more fully, but it’s a work in progress.

Last time......Most every camera uses the same 3.75 to 3.92 um pixels...the only thing that changes is the field of view...not the resolution...Larger cameras have more pixels..... a 16 MP 4/3camera has the same pixel density as a 61 MP FF camera.....

Strange. I seem to find FF and APS-C generally have fewer pixels per sq.mm than 4/3 or 1” sensors, and often have larger pixel size.

https://www.digicamdb.com/specs/olympus_om-d-e-m10-ii/

https://www.digicamdb.com/specs/sony_a7r-iv/

Those 2 links about 2 cameras do nothing to prove the general rule you were suggesting. that cameras with different-size sensors generally have the same number of pixels per sq mm.

You really can’t understand that giving the info on two cameras and their sensors and pixel density does not prove the general assertion that different sized camera sensors generally have the same pixel density?? Really? Over and out to you.

??????????

Reread the links...the 4/3 camera has the same pixel density as the FF camera...Everyone here has told you the same thing..

You are either trolling, or have a severe reading problem...done..over and out....

 

[Painter19]

. Still hard for me to envision how a crop from a larger sensor containing fewer receptor sites/ pixels than a sensor of the same area as that crop can have an equivalent resolution of detail, except maybe by allowing for the less crowded sites on the larger sensor crop receiving more light. It’s the idea that it’s the size of individual pixels, not how many of them are in a certain area, that determines resolution is still counter-intuitive for me. I’m sure it’s right now, and am trying to grasp it more fully, but it’s a work in progress.

Last time......Most every camera uses the same 3.75 to 3.92 um pixels...the only thing that changes is the field of view...not the resolution...Larger cameras have more pixels..... a 16 MP 4/3camera has the same pixel density as a 61 MP FF camera.....

Strange. I seem to find FF and APS-C generally have fewer pixels per sq.mm than 4/3 or 1” sensors, and often have larger pixel size.

https://www.digicamdb.com/specs/olympus_om-d-e-m10-ii/

https://www.digicamdb.com/specs/sony_a7r-iv/

Those 2 links about 2 cameras do nothing to prove the general rule you were suggesting. that cameras with different-size sensors generally have the same number of pixels per sq mm.

??????????

Reread the links...the 4/3 camera has the same pixel density as the FF camera...Everyone here has told you the same thing..

You are either trolling, or have a severe reading problem...done..over and out....

Do you really believe that giving the information on two cameras proves your general assertion that different-sized sensors generally have the same pixel density?? - Really?

You're either trolling, or have a severe logic problem. Over and out.

 

[Tristimulus]

. Still hard for me to envision how a crop from a larger sensor containing fewer receptor sites/ pixels than a sensor of the same area as that crop can have an equivalent resolution of detail, except maybe by allowing for the less crowded sites on the larger sensor crop receiving more light. It’s the idea that it’s the size of individual pixels, not how many of them are in a certain area, that determines resolution is still counter-intuitive for me. I’m sure it’s right now, and am trying to grasp it more fully, but it’s a work in progress.

Last time......Most every camera uses the same 3.75 to 3.92 um pixels...the only thing that changes is the field of view...not the resolution...Larger cameras have more pixels..... a 16 MP 4/3camera has the same pixel density as a 61 MP FF camera.....

Strange. I seem to find FF and APS-C generally have fewer pixels per sq.mm than 4/3 or 1” sensors, and often have larger pixel size.

https://www.digicamdb.com/specs/olympus_om-d-e-m10-ii/

https://www.digicamdb.com/specs/sony_a7r-iv/

Those 2 links about 2 cameras do nothing to prove the general rule you were suggesting. that cameras with different-size sensors generally have the same number of pixels per sq mm.

??????????

Reread the links...the 4/3 camera has the same pixel density as the FF camera...Everyone here has told you the same thing..

You are either trolling, or have a severe reading problem...done..over and out....

Do you really believe that giving the information on two cameras proves your general assertion that different-sized sensors generally have the same pixel density?? - Really?

You're either trolling, or have a severe logic problem. Over and out.

Astrophotography and pixel size and light collection and light density and a lot of other terms used are often confusing because the same words are used in different contexts. Most seems to need some time to grasp what this is all about, and others spread misinformation based on loss of context or comprehension.

Shutting off the dialog leads nowhere - trying to define what we are talking about is a better strategy.

To sum up (might be wrong) what has been said so far:

- resolution depends upon pixel size and focal lenght given a perfect lens

- larger sensors capture a larger field of view than smaller sensors given the same lens

- larger apertures (entrance pupils) collect more light than smaller ones

So for light colection the lens is the most important single factor.

Like to add that modern sensors use very efficient microlenses so larger or smaller pixels are less relevant (did not say not relevant) than in the early CCD days when fill factor was a big issue. The quantum effeciency of modern image sensors are pretty much similar (did not say equal).

Then: onward... ;-)

 

[Painter19]

. Still hard for me to envision how a crop from a larger sensor containing fewer receptor sites/ pixels than a sensor of the same area as that crop can have an equivalent resolution of detail, except maybe by allowing for the less crowded sites on the larger sensor crop receiving more light. It’s the idea that it’s the size of individual pixels, not how many of them are in a certain area, that determines resolution is still counter-intuitive for me. I’m sure it’s right now, and am trying to grasp it more fully, but it’s a work in progress.

Last time......Most every camera uses the same 3.75 to 3.92 um pixels...the only thing that changes is the field of view...not the resolution...Larger cameras have more pixels..... a 16 MP 4/3camera has the same pixel density as a 61 MP FF camera.....

Strange. I seem to find FF and APS-C generally have fewer pixels per sq.mm than 4/3 or 1” sensors, and often have larger pixel size.

https://www.digicamdb.com/specs/olympus_om-d-e-m10-ii/

https://www.digicamdb.com/specs/sony_a7r-iv/

Those 2 links about 2 cameras do nothing to prove the general rule you were suggesting. that cameras with different-size sensors generally have the same number of pixels per sq mm.

??????????

Reread the links...the 4/3 camera has the same pixel density as the FF camera...Everyone here has told you the same thing..

You are either trolling, or have a severe reading problem...done..over and out....

Do you really believe that giving the information on two cameras proves your general assertion that different-sized sensors generally have the same pixel density?? - Really?

You're either trolling, or have a severe logic problem. Over and out.

Astrophotography and pixel size and light collection and light density and a lot of other terms used are often confusing because the same words are used in different contexts. Most seems to need some time to grasp what this is all about, and others spread misinformation based on loss of context or comprehension.

Shutting off the dialog leads nowhere - trying to define what we are talking about is a better strategy.

To sum up (might be wrong) what has been said so far:

- resolution depends upon pixel size and focal lenght given a perfect lens

- larger sensors capture a larger field of view than smaller sensors given the same lens

- larger apertures (entrance pupils) collect more light than smaller ones

So for light colection the lens is the most important single factor.

Like to add that modern sensors use very efficient microlenses so larger or smaller pixels are less relevant (did not say not relevant) than in the early CCD days when fill factor was a big issue. The quantum effeciency of modern image sensors are pretty much similar (did not say equal).

Then: onward... ;-)

Yes, there’s a lot to wrap one's head around. Thanks. I appreciate that summary, and all the information from you and others here. Onward !

 

[DavidWright2010]

Astrophotography and pixel size and light collection and light density and a lot of other terms used are often confusing because the same words are used in different contexts. Most seems to need some time to grasp what this is all about, and others spread misinformation based on loss of context or comprehension.

Shutting off the dialog leads nowhere - trying to define what we are talking about is a better strategy.

I agree. We need to recognize that communication (information sent and received) can be difficult in this type of forum discussion - a little tolerance is sometimes needed.

Also, this forum ranges from a dozen or so extremely advanced users to newbies, and there may often be misperceptions about what a newbie knows.

To sum up (might be wrong) what has been said so far:

- resolution depends upon pixel size and focal lenght given a perfect lens

- larger sensors capture a larger field of view than smaller sensors given the same lens

- larger apertures (entrance pupils) collect more light than smaller ones

So for light colection the lens is the most important single factor.

Like to add that modern sensors use very efficient microlenses so larger or smaller pixels are less relevant (did not say not relevant) than in the early CCD days when fill factor was a big issue. The quantum effeciency of modern image sensors are pretty much similar (did not say equal).

Then: onward... ;-)

Let's also mention the 'pixels across the subject' that Alan (I think) mentioned.

I have 2 cameras for AP - both Pentax - the K-70 and the K-1. If what I want to image fits in the frame of the aps-c K-70, I will use that because it has smaller pixels (3.88 micron pixels) and I will therefore get more pixels across my object of interest. OTOH, if the object is bigger (like the Orion Loop), I would use the full frame K-1 (4.88 micron pixels) because each image will cover 2.3X the area of a K-70 image, albeit at a slightly lower resolution. (Of course, the lens would have to be able to cover the FF sensor with reasonable image quality)

David

 

[DavidWright2010]

Yes, there’s a lot to wrap one's head around. Thanks. I appreciate that summary, and all the information from you and others here. Onward !

Keep asking questions.

BTW, the extension tube for my C5 arrived yesterday and I was able to take some sample images (daytime, back yard). Yikes! There is no way my existing ball head will work. Even at a 1/500th sec exposure (and 12 sec delay) the images aren't sharp.

OTOH, if I just lay the cam + C5 on the dining room table and shoot through a window, images are much sharper.

I had previously ordered a more robust ball head - it arrives today. If it's better I can do a Moonshot tonight. If not, need to look into a gimbal or gear-head.

David