Sensor spacing on colour vs mono setup

[edarter]

Hi, 

I've been given a tentative green light by 'the boss' to start looking at dedicated astro cameras. I've very aware of the colour vs mono debate and its a really hard call to make (for me) between the two. I was coming down on the side of colour (asi 294mc Pro) just because of the convenience and the fact it would be cheaper. Something else just occurred to me though and it would be good to understand this before making a final decision.

If I were to go with a mono camera I would obviously need a filter wheel. Presumably this adds length to the imaging train though? The reason for my concern is that I use a sw 130pds, an excellent little scope but one that already suffers from the focus tube protruding in to the ota. Would going mono make this protrusion worse? I'm not interested in cutting down focus tubes etc so this could be a major factor in my final decision. 

Thanks

Ed

[JSeaman]

Ed, 

I use the 300 PDS with a filter wheel and no problems. I was in your position a few years ago and chose OSC (QHY8L at the time) and within a year I went for a mono set up and never looked back. It is night and day better than colour imaging and your first go at Ha will confirm this I'm absolutely sure!

James

[david_taurus83]

What camera are you considering for mono? Are you using a coma corrector? If so, then you'll still need to space the camera back 55mm if that's the case, and the drawtube will come into focus in the same place.

[edarter]

Thanks both, tbh what sparked this off was seeing the asi1600, filter wheel and filters on the for sale part of this forum. I had pretty much made my mind up that I was going to get an ASI 294MC Pro then saw the above advertised. It set the brain cogs going on mono again but then I had the thought about focus tube intrusion etc. I currently use a baader mk3 CC and a Canon eos 600d. Can't see how adding a fw can do anything other than mean the focus tube needs to go in a bit to compensate, so I'm obviously not understanding part of the setup correctly! 🙂

[JSeaman]

I would say buy it and you won't regret it

[Adam J]

10 hours ago, edarter said:

Hi, 

I've been given a tentative green light by 'the boss' to start looking at dedicated astro cameras. I've very aware of the colour vs mono debate and its a really hard call to make (for me) between the two. I was coming down on the side of colour (asi 294mc Pro) just because of the convenience and the fact it would be cheaper. Something else just occurred to me though and it would be good to understand this before making a final decision.

If I were to go with a mono camera I would obviously need a filter wheel. Presumably this adds length to the imaging train though? The reason for my concern is that I use a sw 130pds, an excellent little scope but one that already suffers from the focus tube protruding in to the ota. Would going mono make this protrusion worse? I'm not interested in cutting down focus tubes etc so this could be a major factor in my final decision. 

Thanks

Ed

Get the ASI1600 you will not regret it, but for best results chop a little off the draw tube like I did. 

Here is an example image with your exact setup I took a couple of years back. 

Adam

 

 

 

[iapa]

On 22/04/2021 at 07:56, edarter said:

Hi, 

I've been given a tentative green light by 'the boss' to start looking at dedicated astro cameras. I've very aware of the colour vs mono debate and its a really hard call to make (for me) between the two. I was coming down on the side of colour (asi 294mc Pro) just because of the convenience and the fact it would be cheaper. Something else just occurred to me though and it would be good to understand this before making a final decision.

If I were to go with a mono camera I would obviously need a filter wheel. Presumably this adds length to the imaging train though? The reason for my concern is that I use a sw 130pds, an excellent little scope but one that already suffers from the focus tube protruding in to the ota. Would going mono make this protrusion worse? I'm not interested in cutting down focus tubes etc so this could be a major factor in my final decision. 

Thanks

Ed

You will need to provide c 55mm between the focuser and and the camera sensor.

The cameras you mention have 6.5mm from the front to the sensor.

leaving a space requirement of 48.5mm

Add in the filter wheel, reduces this to 28.5mm

Because you have filters in the optical path, you need to add 1/3 of the thickness of the filters. 

ASI filters are 7mm from memory - check that - so you need to ADD 7/3mm, call it 2mm

This leaves 30.5mm to be filled with a spacer.

BAADER do adjustable spacers, 20-29mm, and a different size range.

you may need an M42-M42 adapter which is normally 1mm

Not cutting required.

[newbie alert]

The difference between colour and mono is a Bayer matrix..that's it.

So both will focus at the same point,  backfocus distance is governed by the scopes light cone