What are the Pros and Cons of Sensor Size and Resolution?

[PeterC65]

I'm new to EEVA and I'm trying to understand the pros and cons of small sensor / low resolution cameras VS large sensor / high resolution cameras.

I have an Altair GPCAM2 327C which has a 5.6mm x 3.1mm 2.1MP sensor with 2.9µm pixels and a Canon EOS 1100D which has a 22.2mm x 14.7mm 12MP sensor with 5.2µm pixels. I've mostly been using the Altair camera as its more convenient and I'm concerned about over use of the shutter on the DSLR (it isn't just used for astronomy).

It seems to me that a larger sensor with higher resolution gives me a wider field of view (for a given optical setup), and allows me to zoom digitally or use ROI (without pixilation) to get a similar image to the one I get from the Altair.

I like that I can get a wide field of view with the Canon camera for targets such as M31 and M45.

With the Altair I miss being able to easily change magnification by swapping eyepieces to zoom in on a target.

Is my understanding correct? Are there down sides to a large sensor / high resolution camera? Bear in mind I'm interested in EEVA rather than AP.

I've been considering the Altair Hypercam 269C which has a 20.5mm x 17.8mm 20.9MP sensor with 3.3µm pixels, so a similar sensor size to the existing Canon and similar pixel size to the existing Altair.

[Martin Meredith]

There are also small sensor / high resolution cameras e.g. my ASI 290 has a smaller FOV but higher resolution than my Lodestar.

Resolution isn't a property of the camera only -- you have to take into account the focal length of your scope.  A camera that looks like it is low-res with one scope might have sufficient resolution with a different scope. Have you checked out astronomy.tools CCD suitability calculator?

Assuming a suitable scope, then, re the specific question of any downsides of a large FOV / high resolution setup, I see a few, but none of them are necessarily game changers

(1) With a large FOV you're probably going to get some vignetting, which then leads you down the 'flats' route -- an additional complication in EEVA, though not necessarily difficult. 

(2) Large FOV tends to come with large megapixel count cameras, which take longer to transfer, longer to process and eat up more storage. This can be mitigated by using ROI, but not if you also want to digitally zoom. 

(3) Most DSOs don't benefit from large FOVs unless your main interest is in bright or dark nebulae, or some of the larger open clusters. For nearly all galaxies, PNs and globs, a small FOV is sufficient

(4) Cameras such as the small sensor guide cams (ASI 290/Ultrastar/Lodestar) tend not to have any issues with reaching focus on any scope, nor do they get in the way of the mount for certain scope models. This may or may not be an issue for you, but I mention it as a potential downside of large sensor cameras.

Bear in mind though that I'm a fan of small FOV sensors for EEVA, so long as the FOV is large enough to find enough stars to stack, platesolve put the DSO on the sensor in the first place. Others will have different views!

[PeterC65]

Thank @Martin Meredith for these useful comments.

I'm mainly using a 432/72mm APO for EEVA and with the Altair GPCAM2 327C the CCD suitability calculator is saying 1.38"/pixel without a Barlow / reducer which seems OK.

I expect I might get vignetting with the Canon camera or another large sensor camera if using 1.25" adaptors (my filters and Barlows / reducers are all 1.25") but I can use 2" adaptors to fit the camera to the APO.

The megapixel count could be an issue as my current laptop is 7 years old!

 

[pipnina]

I've been thinking about this a little myself.

Is it possible to use an IMX585 based camera with a 0.5x telecompressor in place of say an IMX571 to bridge the FOV gap somewhat, as cooling the cameras isn't so important these days and the IMX571 has a MASSIVE increase in cost to consider. £350 Vs £900 for OSC, and the ASI IMX571 costs almost £2000!

[PeterC65]

3 hours ago, pipnina said:

I've been thinking about this a little myself.

Is it possible to use an IMX585 based camera with a 0.5x telecompressor in place of say an IMX571 to bridge the FOV gap somewhat, as cooling the cameras isn't so important these days and the IMX571 has a MASSIVE increase in cost to consider. £350 Vs £900 for OSC, and the ASI IMX571 costs almost £2000!

After much research and deliberation, I decided that an IMX585 based camera would be the best compromise for an increased field of view at reasonable cost.

I was going to buy the ASI 585MC, but the spec changed, pushing the HCG switching point, and therefore the point of lowest read noise, up to a higher gain and therefore a lower full well and dynamic range. That put me off, given that I plan to use the camera for EEVA and really need a low read noise. So, I've bought a Player One Uranus-C which is also IMX585 based but seems to have a better spec, and certainly a lower HCG switching point, than the ZWO equivalent. It's currently in transit. It will be interesting to see what SharpCap makes of it when I do a sensor analysis.

A x0.5 reducer should give me the field of view that I currently get with the DSLR. I already have the Astro Essentials x0.5 reducer which does certainly widen the field of view, but it is quite cheap and cheerful, so I expect there is lots of distortion. I have been considering the better quality StellaMira x0.6 Reducer / Flattener but this would need an extension tube and the two together would be another £180 so I'll check the Astro Essentials x0.5 reducer again when the new camera arrives.

Comparing the Uranus-C with the GPCAM2 327C, they both have the same read noise and pixel size, and the only difference is the number of pixels and sensor size. So, I'm expecting the same performance but double the field of view. The Uranus-C is also supposed to have no amp glow which I sometimes notice with the GPCAM2 327C.

 

[Mike JW]

Hi Peter,

For what it is worth I use a cheap 0.5 reducer on most of the posts you see of mine, as does Bill (I think).

Mike

[PeterC65]

3 hours ago, Mike JW said:

Hi Peter,

For what it is worth I use a cheap 0.5 reducer on most of the posts you see of mine, as does Bill (I think).

Mike

That's good to know. The couple of times I've used the Astro Essentials reducer it's been fine. On targets like M45 I'm really just looking to see the space around the target so that it stands out, and then a bit of distorsion around the edges isn't a problem anyway.

[pipnina]

Are we talking about distortion from an 0.5x reducer in terms of barrel and pincussion, or in terms of abberations like spherical, coma, astigmatism, unflattening the field etc?

Barrel and pincussion can be corrected very easily in pixinsight. The others, not so much.

[PeterC65]

10 hours ago, pipnina said:

Are we talking about distortion from an 0.5x reducer in terms of barrel and pincussion, or in terms of abberations like spherical, coma, astigmatism, unflattening the field etc?

Barrel and pincussion can be corrected very easily in pixinsight. The others, not so much.

I'm talking about all forms of distortion.

I use my camera for EEVA rather than AP so post processing isn't a solution for me, but then I'm also not expecting a perfect image, just to be able to see (much) more than is possible with an eyepiece.

I bought the Astro Essentials x0.5 reducer because it was inexpensive, just as a punt. What concerns me is that there are very many reducers out there that are much more expensive and mostly scope specific and that makes me think that the reducer I have must have some serious limitations. So far I've only used it a couple of times and it seems to work fine, with perhaps some distortion in the shape of stars in the out edge of the field of view.

As I mentioned previously, even with a wider field of view the target will mostly be in the centre with clear space around it. I think this clear space enhances the view of the target, making star clusters stand out from the background sky for example. I expect the only issue will be with really big targets like M31 where the target does fill the available field of view.

My plan is to see how the new Uranus-C camera performs without a Barlow / reducer and with my current x2.25 Barlow and x0.5 reducer before deciding whether a more expensive reducer might be worthwhile.

 

[bosun21]

On 12/09/2022 at 19:02, PeterC65 said:

was going to buy the ASI 585MC, but the spec changed, pushing the HCG switching point, and therefore the point of lowest read noise, up to a higher gain

Have you seen this video Peter?

 

 

 

[PeterC65]

10 hours ago, bosun21 said:

Have you seen this video Peter?

Yes I've seen the video. I don't think it explains why ZWO made the change to the ASI585MC, and I think it leaves the Player One Uranus-C as the better of the two.