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Danon

First mono camera

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Just now, Xplode said:

I would go with the ASI1600 or the QHY163, going for a 15 year old sensor like KAF8300 doesn't really make sense today.

They are very different cameras, and are used very differently, but both give excellent results, I would always go for CCD myself... personal choice.. :)

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Just now, WanderingEye said:

They are very different cameras, and are used very differently, but both give excellent results, I would always go for CCD myself... personal choice.. :)

I'm using a CCD myself, slow readouts and having to take long exposures because of the high readnoise are big drawbacks.
CMOS helps people with cheap mounts get better images because they can take short exposures, shorter exposures are easier on the guiding.
It's also easier to focus with CMOS because of the high framerate
CMOS + live stacking is also pretty amazing, especially if you got visitors :)

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12 minutes ago, Adam J said:

Not so, the number of photons arriving per pixel is purely determined by the f-ratio of the scope. A larger aperture at the same f-ratio will only give you more photons per arc-second^2 it will not give you more per pixel and that is what matters for signal to noise ratio. That happens because at fixed F-ratio as you increase aperture you increase focal length and as a result you reduce the image scale in terms of less arc seconds per pixel and so everything remains equal but you have less field of view and more ""magnification"" although the idea of magnification in terms of imaging is a false concept in itself.

Adam

Sorry if I wasn't clear.  Yes I know this, but was working on Danon's focal length aspirations of around 400mm to be able to the fit the targets of choice into the object.  Hence the suggestion of the RASA 8" which is a similar focal length.  I don't like the focal ratio 'myth' as it gives a false impression that you are gaining extra signal for the same aperture which is not what is happening - it's just how much you are spreading the light out by.  By simply binning the camera to a similar resolution for a larger aperture telescope (that has a base longer focal length) would give you the same effect as the same aperture but at a shorter focal length at the 1x1 pixel size.   

In this case an 200mm F2 would capture lots more photons than an 80mm F5 even though they are the same focal length.  You could get the same result by getting an 8"Edge F10 and binning by a, albeit, substantial amount.  The disadvantage in the latter is that your field of view is small.

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6 minutes ago, Whirlwind said:

Sorry if I wasn't clear.  Yes I know this, but was working on Danon's focal length aspirations of around 400mm to be able to the fit the targets of choice into the object.  Hence the suggestion of the RASA 8" which is a similar focal length.  I don't like the focal ratio 'myth' as it gives a false impression that you are gaining extra signal for the same aperture which is not what is happening - it's just how much you are spreading the light out by.  By simply binning the camera to a similar resolution for a larger aperture telescope (that has a base longer focal length) would give you the same effect as the same aperture but at a shorter focal length at the 1x1 pixel size.   

In this case an 200mm F2 would capture lots more photons than an 80mm F5 even though they are the same focal length.  You could get the same result by getting an 8"Edge F10 and binning by a, albeit, substantial amount.  The disadvantage in the latter is that your field of view is small.

Oh I understand :) and yes you are right, but I tend to think there is no Myth just people not understanding it correctly in the first place. As you say what you do get by using a focal reducer is more photons per pixel as you changed your image scale. As for binning...yes but you dont gain any field of view that way.

Personally I would not recommend a RASA for a beginner for multiple reasons.

Adam

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41 minutes ago, Xplode said:


CMOS helps people with cheap mounts get better images because they can take short exposures, shorter exposures are easier on the guiding.
I

I'd agree with whoever it was who pointed out that if you can guide for five minutes, you can guide for 10 minutes or half an hour.

CMOS is the obvious option for me because (a) I'm often cloud dodging and (b) my skyglow makes long exposures pointless as it dominates over read noise.

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18 minutes ago, Stub Mandrel said:

I'd agree with whoever it was who pointed out that if you can guide for five minutes, you can guide for 10 minutes or half an hour.

CMOS is the obvious option for me because (a) I'm often cloud dodging and (b) my skyglow makes long exposures pointless as it dominates over read noise.


Being able to guide for 5 min with nice round stars doesn't mean that one will be able to guide for 10min with the same nice round stars, flexure give a larger effect over time

There's also the higher chance of something happening for longer subs, wind, clouds etc can all ruin 1 10 min exposure, but if 10x1min were taken only 1 minute would be ruined.

Also there'sa big difference from 5 minutes to 10 sec which is possible for a CMOS setup, i've tried Sharpcap with 10 sec exposures which gives pretty good results, for most mounts it would be fine even without guiding.

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3 hours ago, Xplode said:


Being able to guide for 5 min with nice round stars doesn't mean that one will be able to guide for 10min with the same nice round stars, flexure give a larger effect over time

There's also the higher chance of something happening for longer subs, wind, clouds etc can all ruin 1 10 min exposure, but if 10x1min were taken only 1 minute would be ruined.

Also there'sa big difference from 5 minutes to 10 sec which is possible for a CMOS setup, i've tried Sharpcap with 10 sec exposures which gives pretty good results, for most mounts it would be fine even without guiding.

I think your setup has to be very sloppy before you will get flexure at over 2 arc seconds per pixel image scale with a 10min exposure. I certainly am not doing anything special with my guide scope and I have never encountered this problem.

Edited by Adam J

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17 hours ago, Xplode said:

Also there'sa big difference from 5 minutes to 10 sec which is possible for a CMOS setup, i've tried Sharpcap with 10 sec exposures which gives pretty good results, for most mounts it would be fine even without guiding.

I've managed to get usable images using 16 second subs in Sharpcap, even with OSC.

But it is worth going longer as CMOS does have some read noise!

I've found about 30 seconds to be the reliable limit for unguided subs, you can go longer but it's more dependent on mount performance (the odd glitch ruins frames) than PA accuracy (stars slowly become extended with longer runs).

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On 12/09/2019 at 19:52, Adam J said:

Oh I understand :) and yes you are right, but I tend to think there is no Myth just people not understanding it correctly in the first place. As you say what you do get by using a focal reducer is more photons per pixel as you changed your image scale. As for binning...yes but you dont gain any field of view that way.

Personally I would not recommend a RASA for a beginner for multiple reasons.

Adam

Adam you only get more photons per pixel as you now have a wider fov..

A higher f ratio scope at the same aperture has a shorter fl...it doesn't make the photons arrive any quicker 

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2 hours ago, newbie alert said:

A higher f ratio scope at the same aperture has a shorter fl...it doesn't make the photons arrive any quicker

The same focal lenght and larger aperature gives the same fov and it has larger field that gather photons. Probably that is what he's thinking?  

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5 hours ago, newbie alert said:

Adam you only get more photons per pixel as you now have a wider fov..

That's exactly what I said. 

""What you do get by using a focal reducer is more photons per pixel as you changed your image scale.""

Image scale being directly related to FOV for the same camera...

 

Edited by Adam J
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