'Galaxy' scope for imaging.. choices

[900SL]

21 hours ago, vlaiv said:

I would think so.

Don't be afraid to bin, and also - do pay attention that you need larger aperture to hit certain pixel scale. I would not go below 1"/px, and even approaching that, you would need 8" or more.

6" is more suited for ~1.4-1.5"/px range as upper limit of sampling rate.

Can I bin a 533MM Pro? Mono camera, 3000 x 3000 pixels at bin 1, so 2x2 bin would bring this down to 1500x1500? With a 150mm F8 newtonian the pixel scale would be around 1.3"/px

With my 90mm f6 I can get 1.4 "/px, so presumably not a lot of point in binning to use the f8 newt at 1200mm?

[vlaiv]

Just now, 900SL said:

With my 90mm f6 I can get 1.4 "/px, so presumably not a lot of point in binning to use the f8 newt at 1200mm?

Point is faster system with 150 F/8.

Both setups will have roughly the same pixel scale 1.4"/px vs 1.3"/px - but 150mm will have much more light gathering surface over 90mm.

That and, if both scopes are of decent optical quality - 150mm will produce ever so slightly sharper image.

[900SL]

Thanks Vlaiv. I'm tempted to take a chance on the Bresser. I have a 10% off voucher, and it won't need a coma corrector. Might make a good lunar/planet/galaxy scope with my existing set up.  It's a long aluminium tube so focus might change a bit over the course of an evening..

[vlaiv]

2 minutes ago, 900SL said:

Thanks Vlaiv. I'm tempted to take a chance on the Bresser. I have a 10% off voucher, and it won't need a coma corrector. Might make a good lunar/planet/galaxy scope with my existing set up.  It's a long aluminium tube so focus might change a bit over the course of an evening..

That's 150mm F/8 newtonian right?

Aluminum has about thermal expansion of about 22um per meter Celsius. You have about a 1.2 meters, so you get something like 26um of expansion for every C.

F/8 system has critical focus zone of about 156um, so you should be good for about 3C change in temperature (give or take - it might be even a bit more, depending where you landed with original focus).

Slower scopes are harder to get knocked out of focus due to temperature change because critical focus zone grows as square of F/ratio.

Btw, Coma free zone of F/8 newtonian is about 5.7mm radius, so 11.4mm diameter circle. That is shy of 16mm diagonal of ASI533, but you'll likely not notice much coma to the edge of the sensor as it is very small at that F/ratio.