OSC versus Mono - Which is best? Time to find out! Any ideas?

[Tim]

We all know that the debate between OSC and Mono will run and run for ever as the answer depends on a range of individual answers.

What I am not looking for in this thread is personal ideas about which type of camera you prefer, rather for ideas on how to conduct a useful comparison between the two types, as the resulting comparison chart may help future CCD purchasers to make a more informed choice.

To that end I have just taken delivery (Thanks FLO ) of an Atik 460ex OSC, and can run direct comparison images with the 460ex Mono camera.

I will be conducting the test with a Skywatcher Esprit 150, which has impeccable colour correction, and should provide some meaningful results that will help with deciding between mono and colour.

So I would appreciate your thoughts as to how I (we) can conduct some imaging exercises that will yield objective results, that will highlight the strengths of each camera, the weaknesses, and their suitability for various applications.

For instance, I will be comparing a 20 minute exposure with Ha filter with both cameras.

If we can come up with a methodical, logical approach, I reckon we can establish a really useful reference point, based on empirical results, and not on personal whim or fancy.

The comparisons will be conducted from my home observatory in Coventry. There is bucketloads of light pollution, and my horizons are limited to E > SSW, roughly a quarter of the sky. Any DSO targets suggested should be rising above 20° around 22:30 if possible, although I would prefer to keep away from the horizon if possible because I wont have a decent LP filter to use with the OSC, unless somebody wants to lend me a 1.25" IDAS I also would like to conduct the tests over one or two nights, in the same lunar conditions.

Thanks in advance for your suggestions.

Tim

[Oblong]

Sounds like a really useful exercise, but I suspect that comparisons of monochromatic exposures (i.e. one filter) will end up with a clear winner.

It may be better to compare, say, 2 hours of LRGB with the mono camera (e.g. 6x10min L, 2x10min of each of RGB) with the equivalent exposure time on the OSC, using the same sub lengths (12x10min). Or even set yourself a time limit, because the OSC may allow you to get more exposure time in over the course of a session. I guess that for most people deciding between OSC and mono, the goal is to get the best possible image in a given time. You might even want to factor in the additional time one spends processing mono data (although few of us do this during precious clear nights).

[RobH]

Hi Tim,

Off the top of my head, a few ideas.....

Obviously you need to shoot the same targets at the same altitude in conditions that are as similar as possible so you'll need to be swapping cameras around.

For star colour there is M13, and you'd need to balance the subs between the OSC and mono, so, without thinking about it much, I'd guess a single 3 minute (for example) OSCexposure vs 3 x 1 minute mono RGB exposures would be a good place to start.

NB.....foregone conclusion really as the mono will win hands down, but it'll be good to see a side by side comparison, and then maybe see how much more time you need with the OSC to match the mono.

Also, how about an exposure of (x) length with the OSC with the colour data discarded, in other words, an OSC luminance, vs a mono luminance of the same exposure.

Cheers

Rob

[Davey-T]

To be really comparable wouldn't you need a dual imaging mount, but then you'd need someone to lend you another 150 Esprit and I'm still saving up

Dave

[AlistairHowie]

Talk to Olly - he did a similar comparison with his Atik 4000 OSC and Mono cams a few years ago for Astronomy Now.

[nmoushon]

My suggestion would be this: If you want as thorough a comparison as possible I would first make a list of several different types of object. A galaxy, dark/reflection/emission nebula and star cluster. Find a relatively bright and a faint of each object. Could be all in one frame or target like the Horse Head region that has strong dark, emission and reflection in the same region or M42 that is mostly a very bright target but has plenty of faint dust around it. Then I would take the same amount of time worth of data in RGB (not L) and the OSC. So 3x10min of RGB and 9x10min with OSC. And compare apples to apples. I think that is the fairest comparison because its color vs color. THEN you add the filters (Ha,OIII, Lum, etc.) and taken another 3x10min of Ha on each camera or 3x10min of L and addition 3x10min of OSC and add then to their respective stacks and compare again.

So you would have a list of pictures that (for example) show that just RGB vs OSC is actually pretty close to equal. But when you add Filter X (Ha, OII, Lum, etc.) that mono does out do OSC when it comes to this filter or mono only has a slight advantage over OSC with this filter.

Then I would take as many shots, with that camera the comes up short, as needed to come up to par with the camera that originally came out on top. This would show how much more time you would need to collect. If its not that much added time someone might find it worth shooting the extra subs so that they don't have to buy the extra equipment and mess with changing filters and such. Or it will show that you would need to (for example) double or triple your time to be par with the winning camera then its worth spending the extra money and effort on filter changes.

[Gina]

An interesting idea and some interesting thoughts there I agree that without a dual imaging rig, comparisons are difficult because conditions change and you would need to do repeated tests to statistically average out the sky conditions.

I think the most useful comparison would be with colour as that's more likely to show the least difference. But doing NB to show the greater difference first is OK - get that out of the way - as I see it there would be no contest.

As for colour I see two options :-

1. OSC v mono RGB
   
2. OSC v mono LRGB with the RGB binned 2x2
   

Option 1. should give the nearest results but I think option 2. would be more realistic as that is whet most people do for LRGB colour (or is it?) While you're at it a comparison between LRGB with RGB binned 2x2 and RGB unbinned would be interesting but it's not in the remit

[steppenwolf]

although I would prefer to keep away from the horizon if possible because I wont have a decent LP filter to use with the OSC, unless somebody wants to lend me a 1.25" IDAS

This is a cool endeavour, Tim as this is sooo subjective (and I am as guilty of this as anyone else!) but would it not be 'unfair' to use an LP filter with the OSC camera and not with the mono and filters camera?

Biggest problem that I foresee is not taking both sets of images at the same time as different nights give very different results.

I applaud the idea though as this question comes up again and again!

PS I like OSC

[RobH]

I don't see that you need a dual imaging rig at all. Simply be prepared to change cameras.

You don't need a huga amount of subs to do this shootout, so with a good clear night you could get it all done.

Nor do you need to worry about flats, so changing cameras isn't a problem. You're not trying to get another competition winner

Shooting everything quickly so the conditions are the same is the trick. Yes, with a dual rig this would be easier, and with small scopes that's quite easy, but 6 inch apo's don't grow on trees, and you'd probably be looking at 2 mounts also, with the associated setup time to take into account.

Cheers

Rob

[kirkster501]

Biggest problem that I foresee is not taking both sets of images at the same time as different nights give very different results.

Easy fix there Steve, get two Espirit and two mounts and laptops and run the two side by side I mean, we all have two mounts and scopes don't we..

[Sp@ce_d]

Hmm I'm also thinking a twin shooter is the only way to ensure a methodical approach to conditions, guiding etc. You'll really want to be collecting subs at the same time under identical conditions surely?

[steppenwolf]

I don't see that you need a dual imaging rig at all. Simply be prepared to change cameras.

Don't agree - conditions change throughout the night as well as from day to day - an empirical test requires matching test conditions for both runs. You could argue, of course, that the two 'matching' telescopes may actually differ from one another but any difference there would pale into insignificance against sky condition changes.

[RobH]

Don't agree - conditions change throughout the night as well as from day to day - an empirical test requires matching test conditions for both runs. You could argue, of course, that the two 'matching' telescopes may actually differ from one another but any difference there would pale into insignificance against sky condition changes.

To be strictly accurate, you're right of course, but I'd argue that in practice, and bearing in mind that we're talking about the rig that Tim is using, as long as you don't take too long, the conditions will often be near enough to get the sort of results that would be of interest.....but....you'd have to be quick in the sense of shooting the way I suggested, in other words, something like, for one example, 3 x shortish RGB subs, then a single OSC sub of 3 times the length of the mono's, changing the camera in between.

I'd guess that if you didn't take more than 30 minutes or so, and were shooting on a stable night near the zenith, conditions would be so close as to not affect the result in a significant manner.

For a truly accurate test, you would of course need 2 rigs, and you'd have to use photometry.

Cheers

Rob

[steppenwolf]

For a truly accurate test, you would of course need 2 rigs, and you'd have to use photometry.

Tee hee, Tim is going to have his work cut out for him here but all joking aside, it's a fascinating project and I am looking forward to seeing how it progresses!

[RobH]

Tee hee, Tim is going to have his work cut out for him here but all joking aside, it's a fascinating project and I am looking forward to seeing how it progresses!

I agree Steve. Combined with Olly's research on the same subject, it'll be a really useful set of results

Cheers

(Mono) Rob

[Davey-T]

Still think a dual setup would be easier, you don't neccessarily need a 150mm scope, be easier to borrow a couple of 80mm Apos.

Dave

[russellhq]

It may help if you set out a detailed hypothesis as that will help focus what you want to test. Or is this just a straight image quality tests? Are you just trying to show a) one camera makes a better image than the other OR b ) both cameras produce comparable images. If that's the case, then a simple agreement on the amount of data to capture for each camera should be enough to get started. The rest of the variables you should keep as similar as possible. e.g. obj position, time of capture, moon location, ambient temp, sensor temp, equipment, guiding etc...

Also, differences in sky conditions (unless drastically different) should be evened out after stacking. Maybe FWHM values of the stacked images will be able to help judge if sky conditions are going to have a significant effect?

What might happen is not enough clear sky time to allow you to make and RGB image from the mono!

[Tim]

Thanks for all your responses, (which I haven't read yet )

I tested the 460ex OSC last night. It doesn't fit to exactly the same place as the mono version, so to get the same framing there will be a bit of adjusting between shots to do, luckily on the Esprit refractor the focuser rotates, so I can simply mark the positions ans swap at will pretty much.

I'll put together a workflow sheet based on your suggestions and see if I can't come up with something useful.

Cheers

Tim

[Tim]

Well if somebody want to lend me a pair of matched APO's then so be it

BUT! They would need to be as well corrected as the Esprit, otherwise the mono will gain an advantage, and I'd like this to be a camera against camera test, with the scope playing as little a role as possible.

In practice of course many refractors dont have perfect colour correction, and that will need to be allowed for, but in the basic state of cam against cam, the stakes need to be fair.

[Tim]

Easy fix there Steve, get two Espirit and two mounts and laptops and run the two side by side I mean, we all have two mounts and scopes don't we..

Hmm, I have the capacity to run 2 rigs simultaneously, but would need another Esprit 150

[Tim]

So end results are all over the place, but i'm thinking that 60 mins of one against 60 minutes of the other, star colour from 30 mins of OSC and 3x10 mins of RGB,

The more ideas we get of one against the other to show off or discover the real differences in practical terms the better so please keep the suggestions coming.

I'll say from the outset that I prefer a mono camera. But I will also say that I find RGB subs tedious, boring, and a general drag, which is why I prefer narrowband. I've bought the OSC to see if I cant cheat and use the colour from that with Luminance from the Mono camera just for star colour, as I want to image narrowband targets with RGB stars.

[Gina]

I'll say from the outset that I prefer a mono camera. But I will also say that I find RGB subs tedious, boring, and a general drag, which is why I prefer narrowband. I've bought the OSC to see if I cant cheat and use the colour from that with Luminance from the Mono camera just for star colour, as I want to image narrowband targets with RGB stars.

Yes, I prefer a mono camera too but agree with you that RGB stars are better than Ha/OIII/SII stars, I've tried various things including combining Ha B and G to produce coloured stars in my Simeis 147 image. I considered using an OSC camera to add RGB - a DSLR - but an OSC CCD camera would clearly be better. It will be interesting to see how it goes with an OSC CCD compared with RGB from a mono camera. With a good apochromatic scope I think the difference could be minimal.

[Sp@ce_d]

One of the problems I've found using the CCD/DSLR twin shooter is the noise, especially the chromatic noise from the DSLR. So I'll be very interested in the outcome of this as I'm inclined to replace the DSLR with another mono CCD at this point in time.

[Gina]

I'm going for a second mono CCD - that will be more versatile.

[Uranium235]

One of the problems I've found using the CCD/DSLR twin shooter is the noise, especially the chromatic noise from the DSLR. So I'll be very interested in the outcome of this as I'm inclined to replace the DSLR with another mono CCD at this point in time.

Already done that mate, for the exact same reason. I found chromatic noise to be a bit of a pain to remove, no such problems with two mono cameras though.

With two mono cameras, you would be in a much more flexible position when it comes to narrowband imaging (which I prefer over RGB). Lets face it, we only ever seem to get clear sky when the moon is out thesedays!