Colour..Mono...Colour...Mono...

[Shelster1973]

..the great debate lives on.

Not heading into the big bad (and silly expensive) world of CCD imaging just yet, am looking at getting a guide cam.

Will be going for the QHY5L-II but am trying to decide between colour or mono.

Have been doing some reading on it and most are coming out saying go mono for guiding, but am wondering if the £45 extra for that camera really justifies itself?

AT present am trying to save the pennies so the colour cam is looking the more desirable of the two.  Plus if I factor in that I can then use this for planetary / solar imaging without the need for forking out more on filters and wheels, it looks even better.

Think I am 90% decided on which one I am getting, just wonder what other peoples opinions are and if there is any feedback from users of both as to what they think / have experienced.

Cheers all

[DaveS]

For guiding th emono every time, and the filter array will just decrease sensitivity. You can still do colout planetary, just use a filter wheel and capture three stacks.

[cgarry]

Have been doing some reading on it and most are coming out saying go mono for guiding

It sounds like you have already had the correct answer but are planning to ignore it!

Cheers,

Chris

[Shelster1973]

Cheers for replies guys.

Chris, not planning to ignore it it is just that as I have said, pennies are tight at present so if I can happily guide with the colour and also use this for imaging without the filters and wheel needed then the £45 would be better used elsewhere.  Guess it is the joys of having moved into a new house...women have different priorities which are mostly soft and cushiony.

[cgarry]

Cheers for replies guys.

Chris, not planning to ignore it it is just that as I have said, pennies are tight at present so if I can happily guide with the colour and also use this for imaging without the filters and wheel needed then the £45 would be better used elsewhere.  Guess it is the joys of having moved into a new house...women have different priorities which are mostly soft and cushiony.

Sorry if my post sounded harsh, it sounded light hearted in my head before I posted it!

If you were planning to use an OAG instead of a guide scope then you need your guide camera to be as sensitive as possible and I think you will regret not getting a mono camera.  If you are using a guide scope then this is less of an issue as there are usually plenty of brighter guide stars available.

For planetary I think you are right and a colour camera would be best (and cheapest) for you.  I have both mono and colour planetary cameras and to be honest I mostly just use the colour camera unless the seeing is really good.

At the end of the day it is a compromise as you say.

Cheers,

Chris

[Shelster1973]

Chris

No worries, no offence taken on that one.

Guiding for me will be via guidescope, so sounds good there.  May move into OAG later on when we have all the necessary curtains and rugs and scatter cushions and bits and bobs sorted, so could look at getting a second mono one then.  By the time that comes around there will probably have been 2 more generations of the camera out and hopefully I will be able to get one 2nd hand fairly cheap, although I have seen that they do retain their value quite well.

[alexjj67]

I use a colour one on an st80 for guiding and have never failed to fine stars.

I wish I could say the same for planetary imaging. I have failed at that completely.

[alpal]

The Bayer Matrix on a colour camera will cause faulty guiding.

It has to be a mono camera for guiding.

[Shelster1973]

The Bayer Matrix on a colour camera will cause faulty guiding.

It has to be a mono camera for guiding.

Have never heard that before...seems a bit odd if it is the case as they sell the colour one for guiding.  Would be hit with loads of returns as 'unfit for purpose' if that was the case, plus am sure someone would have tried to sue for misadvertising and misselling by now

[Starflyer]

The Bayer Matrix on a colour camera will cause faulty guiding.

It has to be a mono camera for guiding.

I've never heard this before, do you have a citation / link to something that explains why?

[Starflyer]

If you're using a guidescope then a colour camera will be fine and you'll be able to have a dabble with planetary imaging in colour too.  If you move to an OAG then you may find that the QHY5 colour probably won't be sensitive enough, when I made the move I found the mono version just wasn't sensitive enough either and I had to move to a lodestar to get a choice of stars.

The mono QHY5 does come up regularly for £110 - £120 on Astro Buy and Sell.

[alpal]

I've never heard this before, do you have a citation / link to something that explains why?

Apart from the sensitivity being lower with a Bayer Matrix -

the colour of the star will cause the position of the star to change as the centroid jumps around

from one section of the 4 pixels to another section.

It would be worse used with an OAG at native focal length and long focal length imaging.

[NickK]

Apart from the sensitivity being lower with a Bayer Matrix -

the colour of the star will cause the position of the star to change as the centroid jumps around

from one section of the 4 pixels to another section.

It would be worse used with an OAG at native focal length and long focal length imaging.

Guiding works by effectively attempting to guess the real position of the centre of the star based on a what looks like a hill. This assumes that the intensity received by each pixel is the same in relation to each of the other pixels around it (point 1).

A star has a certain emission spectrum.

As the star moves over the colours, the spectrum causes different levels of brightness based on the colour of the filter it's on. This causes the intensity to change in relationship to the other pixels (see point 1).. however it is possible to balance the intensity based on calibrating the CCD response curves (i.e. boosting green etc) but this relies on the spectrum of the stars to be the same (they're not hence you get different colours).

So it's not normally ideal for guiders to be a OSC for the reasons given above, although it is possible to use an OSC as a guider but it may cause inaccurate shifts in the star movement due to spectrum vs bayer matrix (even with calibration).

[ollypenrice]

Lots of assertions here that guiding with a colour camera won't work or won't work as well. This is not what I found. For many years I had two Atik 16ics, one mono and one colour, as guide cameras. The difference between them as guide cameras was, so far as I could tell, precisely zero. In the years that I've been imaging I have never failed to find a guide star in the first test sub, ever. Sure, theory says that the Bayer Matrix will rob some sensitivity and it will, but chucking a bucket of water over the cliffs at Bempton will raise the sea level but won't flood Newcastle.

I can't speak for other OSC cams for guiding but my experience was that it made not a jot of difference. I decided to try a colour cam out of curiosity with respect to imaging. I then tried a serious OSC CCD imaging cam as well but concluded, in the end, that for imaging it would be mono for me.

Olly

[ollypenrice]

I wouldn't advise anybody to try to learn imaging and Pixinsight at the same time. Learn to ride a unicycle, learn to juggle, but don't learn to juggle while taking your first spinal injuries on a unicycle...

lly

[NickK]

Lots of assertions here that guiding with a colour camera won't work or won't work as well. This is not what I found. For many years I had two Atik 16ics, one mono and one colour, as guide cameras. The difference between them as guide cameras was, so far as I could tell, precisely zero. In the years that I've been imaging I have never failed to find a guide star in the first test sub, ever. Sure, theory says that the Bayer Matrix will rob some sensitivity and it will, but chucking a bucket of water over the cliffs at Bempton will raise the sea level but won't flood Newcastle.

I can't speak for other OSC cams for guiding but my experience was that it made not a jot of difference. I decided to try a colour cam out of curiosity with respect to imaging. I then tried a serious OSC CCD imaging cam as well but concluded, in the end, that for imaging it would be mono for me.

Olly

Sometimes reality is stranger than.. well the logic and maths!

In the end, most mounts couldn't adjust for tenths of microns of movement anyway..

[ollypenrice]

Sometimes reality is stranger than.. well the logic and maths!

In the end, most mounts couldn't adjust for tenths of microns of movement anyway..

Sometimes reality is stranger than.. well the logic and maths!

In the end, most mounts couldn't adjust for tenths of microns of movement anyway..

Indeed. It's worth noting that Craig Stark recommends soft focus on guide stars anyway because it improves the reliability of the centroid calculation. Also I think micron scale corrections, even when possible, would be more in response to the seeing that to anything else. 

To be clear, I wouldn't recommend an OSC guide camera since I expect an extreme test probably would reveal them to be less sensitive, but if the sky's that bad you won't be keeping the data anyway. However, if you have other reasons for wanting one then I found them to present no disadvantage in practice.

Olly

[strutsinaction]

I wouldn't advise anybody to try to learn imaging and Pixinsight at the same time.

Nothing like a challenge. I'm doing precisely that (and have been for the past 5 months or so). And have developed a twitch. 

Regards

John

[ollypenrice]

I go into Photoshop for a detox!

Olly

[nightster]

I wouldn't advise anybody to try to learn imaging and Pixinsight at the same time. Learn to ride a unicycle, learn to juggle, but don't learn to juggle while taking your first spinal injuries on a unicycle...

lly

Anonymous man says, "Hello, I'm Jeff and I am an addict. "

AstroImaging Group says, "Hello Jeff."

I too am learning both Imaging and PI this year. But I have decided to start to understand PS better.

In a couple of weeks I will be adding a mono ccd, and all its learning curves, to the mix. Does moving to ccd pose any issues with the guidecam that I currently have? Or better said, will moving to ccd force me to make any other unforseen upgrades?

[ollypenrice]

Anonymous man says, "Hello, I'm Jeff and I am an addict. "

AstroImaging Group says, "Hello Jeff."

I too am learning both Imaging and PI this year. But I have decided to start to understand PS better.

In a couple of weeks I will be adding a mono ccd, and all its learning curves, to the mix. Does moving to ccd pose any issues with the guidecam that I currently have? Or better said, will moving to ccd force me to make any other unforseen upgrades?

Perhaps this should be a new thread but I can't see why CCD should extend the spendiing beyond itself. You'll get cleaner and deeper data from a CCD making life easier rather than harder. I suppose you might be tempted by some costly Astrodon NB filters at some point...

Olly

[alpal]

Sometimes reality is stranger than.. well the logic and maths!

In the end, most mounts couldn't adjust for tenths of microns of movement anyway..

My Lodestar mono guide camera has 8.2 micron pixels.

The resolution of the camera is therefore not 1/10ths of microns but about 8 microns.

I image at 1220 mm focal length with an OAG & will change to 1000mm when my new  10" f4 Newt. arrives.

If it had a Bayer matrix the resolution would be at least 16 microns

as a Red or Blue star would be a minimum of 2 pixels away in the next Bayer matrix group of 4.

This could be improved by putting the guide cam a bit out of focus.

Good results with a OSC guide camera could be because of poor seeing.

I still maintain that with long focal length & good seeing a mono guide camera must be better

& would be measurable in a scientific experiment.

I don't think if you were a scientist in charge of a major Govt. observatory &

your reputation was on the line that you would choose an OSC  guide camera.

Amateurs can choose whatever pleases them & is within their budget.

cheers

Allan

[NickK]

My Lodestar mono guide camera has 8.2 micron pixels.

The resolution of the camera is therefore not 1/10ths of microns but about 8 microns.

I image at 1220 mm focal length with an OAG & will change to 1000mm when my new  10" f4 Newt. arrives.

If it had a Bayer matrix the resolution would be at least 16 microns

as a Red or Blue star would be a minimum of 2 pixels away in the next Bayer matrix group of 4.

This could be improved by putting the guide cam a bit out of focus.

Good results with a OSC guide camera could be because of poor seeing.

I still maintain that with long focal length & good seeing a mono guide camera must be better

& would be measurable in a scientific experiment.

I don't think if you were a scientist in charge of a major Govt. observatory &

your reputation was on the line that you would choose an OSC  guide camera.

Amateurs can choose whatever pleases them & is within their budget.

cheers

Allan

Yup - with a long focal length, then you'll want a mono - even from a sensitivity point of view (the higher the fl, the less starts you'll have and so making the most out of the different spectrum stars out there is desirable. No disputing there.

I normally work with the 10:1 ratio - so if you're measuring cm you need to be aware of millimeters. The same is true for mount encoding where it helps to be accurate by being able to measure 10th of the scale. However most programs will use a centroid and that gives them the interim measurement.

Olly's point is simply that the majority of imagers probably would not see a large difference in the final result.

[Shelster1973]

Quick update....in the end went with the colour versions as managed to snap one up from teh Classifieds on here...a perfect bit of alignment with me looking and then one coming up for sale.

Hopefully will arrive tomorrow and can then get it focused up.....apologies now for the next 6 weeks of clouds due to new purchase    

[ollypenrice]

My Lodestar mono guide camera has 8.2 micron pixels.

The resolution of the camera is therefore not 1/10ths of microns but about 8 microns.

I image at 1220 mm focal length with an OAG & will change to 1000mm when my new  10" f4 Newt. arrives.

If it had a Bayer matrix the resolution would be at least 16 microns

as a Red or Blue star would be a minimum of 2 pixels away in the next Bayer matrix group of 4.

This could be improved by putting the guide cam a bit out of focus.

Good results with a OSC guide camera could be because of poor seeing.

I still maintain that with long focal length & good seeing a mono guide camera must be better

& would be measurable in a scientific experiment.

I don't think if you were a scientist in charge of a major Govt. observatory &

your reputation was on the line that you would choose an OSC  guide camera.

Amateurs can choose whatever pleases them & is within their budget.

cheers

Allan

I agree that a that a scientist in charge of a large Govt observatory would and should go for a mono guide camera!  That wasn't the OP's question, though.

Your resolution would be 16 microns with an OSC? OK, but what does this resolution have to do with guide stars? The guider guides on a centroid calculation, not on a central pixel. If finding a central pixel were the name of the game how would we guide sub pixel and why would Craig Stark tell us to soft focus our guide stars?

Olly