Celestron 8" RASA & ZWO ASI1600MM

[irtuk]

Dumb question here but, hey its a lot of money to spend so I want to ask, with scopes like this celestron RASA where the imaging gear is at the front of the scope, do all the wires and gizmo's not get in the way of the light and impact the image?

I am looking at getting a narrowband mono rig set up and, obviously I can see some incredible results on these forums from rigs but I would like to understand what you do with all the wires in setups like this.

Thanks

Ed

[Waldemar]

Hi Ed,

There are no dumb questions, just stupid answers...

If you choose the right camera with the same or smaller diameter as the central obstruction, only two wires are in the field of view.
When tied behind each other the effect is not really visible, especially not when they are a little bended, like bended spider vanes.
I would not use a DSRL camera, for they are quite an obstruction.

[wimvb]

There are several members on this forum who have a RASA (Göran Nilsson, @gorann gets excellent results with his), but they are best combined with an osc camera. Obviously, a filter wheel will be too much of an obstruction, so if you want to use it with a mono camera you will need a filter drawer and change filters manually.

Edited April 4, 2021 by wimvb

[fwm891]

19 hours ago, irtuk said:

Dumb question here but, hey its a lot of money to spend so I want to ask, with scopes like this celestron RASA where the imaging gear is at the front of the scope, do all the wires and gizmo's not get in the way of the light and impact the image?

I am looking at getting a narrowband mono rig set up and, obviously I can see some incredible results on these forums from rigs but I would like to understand what you do with all the wires in setups like this.

Thanks

Ed

Hi Ed, I have a RASA 8 and yes the wires/cables do need some attention in use. Generally it's best to curve the cables to avoid diffraction spikes which is easy enough to do.

I've not done any mono work with the RASA but your limitation is with the back focal distance with the RASA 8 either 25 or 29mm depending on where you measure from. There are filter draws that can be fitted allowing you to change filters manually which is quite simple. I use an ASI 533 Pro cooled OSC with my rasa and have now switch filters to a Baader UV/IR for broadband use and an IDAS NBZ for multi-narrowband captures.

I won't now go back to mono imaging I'm having a far more productive time with my OSC. While many will say OSC cameras can't produce the quality of a mono system (and I probably agree to some extent) what the cooled OSC and the RASA combination allows me to do is capture images far more quickly - which suits me given the poor weather the west of the UK has to live with.

A lens shield is a good idea with the RASA as the corrector plate sits right at the front.

https://www.astrobin.com/users/fwm891/

Hope that helps

[gorann]

1 hour ago, fwm891 said:

Hi Ed, I have a RASA 8 and yes the wires/cables do need some attention in use. Generally it's best to curve the cables to avoid diffraction spikes which is easy enough to do.

I've not done any mono work with the RASA but your limitation is with the back focal distance with the RASA 8 either 25 or 29mm depending on where you measure from. There are filter draws that can be fitted allowing you to change filters manually which is quite simple. I use an ASI 533 Pro cooled OSC with my rasa and have now switch filters to a Baader UV/IR for broadband use and an IDAS NBZ for multi-narrowband captures.

I won't now go back to mono imaging I'm having a far more productive time with my OSC. While many will say OSC cameras can't produce the quality of a mono system (and I probably agree to some extent) what the cooled OSC and the RASA combination allows me to do is capture images far more quickly - which suits me given the poor weather the west of the UK has to live with.

A lens shield is a good idea with the RASA as the corrector plate sits right at the front.

https://www.astrobin.com/users/fwm891/

Hope that helps

Ed: Yes I can highly recommend a RASA 8 but you really should use it with a cooled circular CMOS camera. The new OSCs from ZWO and QHY are not far behind a mono and will make life easier.

Francis: do you need to use an IR/UV filter for your OSC? My ASI OSCs (2600 and 071) have one built in

[fwm891]

33 minutes ago, gorann said:

Ed: Yes I can highly recommend a RASA 8 but you really should use it with a cooled circular CMOS camera. The new OSCs from ZWO and QHY are not far behind a mono and will make life easier.

Francis: do you need to use an IR/UV filter for your OSC? My ASI OSCs (2600 and 071) have one built in

Hi Goran, The ASI 533 only has an anti reflective coating on the chip cover glass and I've found that the UV/IR cut filter really reduces star bloat. Plus having removed the Celestron supplied protective filter it needs those 2mm of glass as part of it's optical train.

Francis

[tomato]

One other point I have noted with my RASA8 and a QHY268c, if you fit a dewshield it can impede the camera cooling, especially if the ambient temp is in double figures. It isn’t a big deal though, as the modern CMOS cameras with short exposure times don’t need to run much below zero degrees anyway.

In my experience the combination is a great way of obtaining decent colour images in a short space of time.

[irtuk]

Thanks everyone!

Currently I am using a D800E with a 102mm refractor but I, and critically the wife, are ready for an upgrade.

Ed.

 

[gorann]

3 hours ago, tomato said:

One other point I have noted with my RASA8 and a QHY268c, if you fit a dewshield it can impede the camera cooling, especially if the ambient temp is in double figures. It isn’t a big deal though, as the modern CMOS cameras with short exposure times don’t need to run much below zero degrees anyway.

In my experience the combination is a great way of obtaining decent colour images in a short space of time.

I can't remember when I last had double figure centigrees up here Steve, unless you put a minus in front - that I can well remember. In my case the heat from the camera in combination with a dew shield means that I never need a heater on the scope, not even at -15°C.

Edited April 4, 2021 by gorann

[wimvb]

14 hours ago, gorann said:

In my case the heat from the camera in combination with a dew shield means that I never need a heater on the scope, not even at -15°C.

I wonder if that combination can introduce heat currents and what effect these would have on star shapes, similar to heat currents in open tube telescopes such as Newtonians or RC.

[gorann]

3 minutes ago, wimvb said:

I wonder if that combination can introduce heat currents and what effect these would have on star shapes, similar to heat currents in open tube telescopes such as Newtonians or RC.

I also wondered about this but since I have not seen it mentioned anywhere I do not worry. It is also hard to test since the camera and its heat production and fan needs to be there. It could be that the fan in the camera mix the air so effectively that the currents are fast and nonsignificant. Maybe also currents in front of a mirror is worse than in front of a corrector lens.