Quote:
Originally Posted by Peter Ward
Just a small point on "megapixels"
If you count an Astro-mono camera in the same way as a "terrestrial" camera you need to look at a terrestrial bayer matrix (RGGB) and realise the likes of Canon Nikon Pentax et. al. interpolate data and place it in non-sensing pixel locations.
With "normal" daylight scenes this causes no problems, but with point or spectrally narrow sources (eg Astronomy) you will lose information.
eg. a 24Mp Canon camera only has 6M red pixels.
Using the same concept then, a 16MP mono camera doing a LRGB shot actually has 64Mp of data, but you can't get it with "one shot"...you need four....
This data not only 16 bit, but spatially more highly resolved (ie you are not interpolating colour data) than a "24Mp" one shot camera.
Plus with a luminance (ie unfiltered) domain, with all other aspects being equal, your S/N will be better as well.
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Good point Peter
Quote:
Originally Posted by gregbradley
I take it you have a CDK scope from your screen name.
STX would be good in several ways. SBIG seems to have closed the gap whilst retaining the self guiding as well as adding several guiding options. SBIG is ahead of the other camera makers in this regard.
One issue though with a CDK as I was thinking of an STX6303 is that the chip is lower down in the STX body than Apogee or FLI. It is 40mm plus the faceplate plus the filter wheel is thicker at around 30mm.
Normally that would not be an issue but if you plan to use the CDK reducer it has very limited backfocus and ideally is setup around 45mm from memory. It still works further out but spot sizes get larger and F ratio increases.
I am not sure if there is an advantage to the 65mm filters. I think that is needed so the guide chip gets light but I wonder if it reduces vignetting.
Not sure.
I get vignetting on most scopes with the 16803 but not a lot on the TEC180. I get a lot on the CDK.
Greg.
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I want to use the focal reducer on the CDK and yes you are right the optimum back focus is 47mm this does not give me much to play with.
The filter wheel is 32mm add this to the STX of 40mm and this is way over optimum.
I was looking at the FLI specs today the Proline has a back focus of only 30.23mm and the filter wheel that carries the 65mm filters is only 15.24mm thick, this would fit nicely. But as you said no room for a OAG.
Also I heard today that FLI are going to do a MAC driver to run with the SKY X. It is only in the beta stage but it's better than nothing.
So it might come down to filter wheels and thickness.
Maybe I should get a different scope for wider field imaging and not bother with the focal reducer. I am very unsure which way to go at the moment. All of these cameras seem very good.
Greg what do you think is causing the vignetting? with a flat field of 52mm the 16803 chip should fit nicely into this.
Cheers
Phil