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Old 16-02-2014, 06:50 PM
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Rod Burgess

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Caon Eos REbel Ti3 600D setup?

Hi, I was told to start a thread here about what I have planned with the use of my Canon 600D. I am purchasing a Comma Corrector for the camera as it is being used on a 254mm f3.9 Orion Astrograph (Newt. Reflector) and the manual recommends the use off, and from preliminary shots it does require this for a uncropped images as there are a lot funny looking stars at the edge of the photo's.. I am also purchasing a Orion 4 position 2" Motorised Filter Wheel and A range Of Filters LRGB Set And HA. I have already have a Moonlite Focuser with stepper operation and PC interface.
The Canon will only be used as a intermediate camera till I can afford some thing more dedicated.
The camera in unmodified and was wandering if there was any thing to look out for with the setup at the moment.
Thanks
Rod
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Old 16-02-2014, 08:59 PM
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hi Rodney,

I hope others will comment as well, I just wanted you to have all the facts clear before you spent your money.

Can you tell why you want to get the filter wheel and LRGB and Ha filters for the Canon 600d?
An unmodded dslr has an IR block glass in front of the sensor that blocks a significant part of the red spectrum. it also has a bayer matrix on the sensor that essentially has red, green, blue filters above each pixel.
so red light will only go through the pixels that have the red filter, blue through the blue and green through the green.
so of the 18million pixels on your sensor, only 1/4th will allow red, 1/4th allow blue and remaining green as the pixels are usually arranged in an RGGB square.
this should explain it.
http://en.wikipedia.org/wiki/Bayer_filter

therefore, using an LRGB filter will not give you true LRGB images as you'll have to extract each colour plane, that is separate RGB and then discard the rest. you'll be wasting a lot of time and effort this way.
LRGB filters are really designed for mono sensors.

same with the Ha filter. An unmodded dslr will block a lot of the Ha signal and since your dslr has a bayer matrix, you'll have to discard the G and B channels and the 18MP would drop down to 4.5MP as you can only use the R plane.
so you'll need to expose for a very long period to get any significant data and that introduces noise as your dslr is not cooled.

finally, the spacing.
most coma correctors need to have a very specific distance to the sensor.
the Baader mpcc which is a very common and effective corrector, requires 55mm to the sensor.
the dslr sensor to body is 45 mm so you're left with only 10mm. that will normally be taken up by the bayonet to T2 adaptor. so if you screw the coma corrector to the T adaptor, the distance would be perfect and you will have no coma and can use the full image FOV.
if you use a filter wheel, the distance becomes much more than 55mm and the corrector won't work.
you do have the option of using a rowe coma corrector or others that allow more than 55mm of back focus, but what i'm trying to advise is that the filter wheel with the dslr is very ineffective.
just trying to save you a lot of heartache as I've been down the road as well.

my suggestion.
get a coma corrector, and since you already have guiding, you can get some really good results with galaxies and nebulae even with an unmodded dslr.
then when you're ready for mono imaging, invest in a 2inch motorized 5 position wheel and an off axis guider with a cooled ccd. you need the 2inch as the light cone of your 10inch F3.9 is steep and you'll have vignetting.
so before you get into mono, experiment with the dslr and coma corrector.
I'd suggest you invest in a light pollution filter as well. the IDAS LPS P2 is a very good one and others tend to alter the colours a lot.

hope I've clarified things, I'm surprised that the vendor did not tell you all this.
any questions, just fire away. there are plenty more experienced members here glad to answer.

Cheers
Alistair
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Old 17-02-2014, 10:59 AM
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rodroger (Rodney)
Rod Burgess

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Quote:
Originally Posted by alistairsam View Post
hi Rodney,

I hope others will comment as well, I just wanted you to have all the facts clear before you spent your money.

Can you tell why you want to get the filter wheel and LRGB and Ha filters for the Canon 600d?
An unmodded dslr has an IR block glass in front of the sensor that blocks a significant part of the red spectrum. it also has a bayer matrix on the sensor that essentially has red, green, blue filters above each pixel.
so red light will only go through the pixels that have the red filter, blue through the blue and green through the green.
so of the 18million pixels on your sensor, only 1/4th will allow red, 1/4th allow blue and remaining green as the pixels are usually arranged in an RGGB square.
this should explain it.
http://en.wikipedia.org/wiki/Bayer_filter

therefore, using an LRGB filter will not give you true LRGB images as you'll have to extract each colour plane, that is separate RGB and then discard the rest. you'll be wasting a lot of time and effort this way.
LRGB filters are really designed for mono sensors.

same with the Ha filter. An unmodded dslr will block a lot of the Ha signal and since your dslr has a bayer matrix, you'll have to discard the G and B channels and the 18MP would drop down to 4.5MP as you can only use the R plane.
so you'll need to expose for a very long period to get any significant data and that introduces noise as your dslr is not cooled.

finally, the spacing.
most coma correctors need to have a very specific distance to the sensor.
the Baader mpcc which is a very common and effective corrector, requires 55mm to the sensor.
the dslr sensor to body is 45 mm so you're left with only 10mm. that will normally be taken up by the bayonet to T2 adaptor. so if you screw the coma corrector to the T adaptor, the distance would be perfect and you will have no coma and can use the full image FOV.
if you use a filter wheel, the distance becomes much more than 55mm and the corrector won't work.
you do have the option of using a rowe coma corrector or others that allow more than 55mm of back focus, but what i'm trying to advise is that the filter wheel with the dslr is very ineffective.
just trying to save you a lot of heartache as I've been down the road as well.

my suggestion.
get a coma corrector, and since you already have guiding, you can get some really good results with galaxies and nebulae even with an unmodded dslr.
then when you're ready for mono imaging, invest in a 2inch motorized 5 position wheel and an off axis guider with a cooled ccd. you need the 2inch as the light cone of your 10inch F3.9 is steep and you'll have vignetting.
so before you get into mono, experiment with the dslr and coma corrector.
I'd suggest you invest in a light pollution filter as well. the IDAS LPS P2 is a very good one and others tend to alter the colours a lot.

hope I've clarified things, I'm surprised that the vendor did not tell you all this.
any questions, just fire away. there are plenty more experienced members here glad to answer.

Cheers
Alistair
Thanks Alistair, I know I did not have a lot back focus left, and was intending for the Comma corrector to go into the end of the T/Ring. Thanks for the info on The Canon's Bayer matrix problem, I had the same problem with the Meade DSI II Colour CCD in Colour Mode, it did the same thing as spitting the image into 1/4 values per colour. I ended up using ordinary viewing filters in mono mode but colours where very strange.

So even if the Canon is set to Mono and use filters, there is no benefit?
I got better performance when I did this with the Meade DSI, I just thought the same would apply.

I already have a 2" Orion Skyglow filter, that was the main reason for the filter wheel, to have enabled or not, I get tired of squaring the Camera up to the scope each time I change something.
I could still use the LRGB and HA with the Meade but I intend to use the Meade DSI for doing my drift alignment only, So I could wait until I choose a Decent CCD camera but still might get the filter wheel, still thinking about this one as all I might use it for now is the Orion Skyglow Filter (light pollution). Thanks again Alistair, you same me a lot of money I do not need to spend yet
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Old 17-02-2014, 11:16 AM
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alistairsam
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Quote:
Originally Posted by rodroger View Post
Thanks Alistair, I know I did not have a lot back focus left, and was intending for the Comma corrector to go into the end of the T/Ring. Thanks for the info on The Canon's Bayer matrix problem, I had the same problem with the Meade DSI II Colour CCD in Colour Mode, it did the same thing as spitting the image into 1/4 values per colour. I ended up using ordinary viewing filters in mono mode but colours where very strange.

So even if the Canon is set to Mono and use filters, there is no benefit?
I got better performance when I did this with the Meade DSI, I just thought the same would apply.

I already have a 2" Orion Skyglow filter, that was the main reason for the filter wheel, to have enabled or not, I get tired of squaring the Camera up to the scope each time I change something.
I could still use the LRGB and HA with the Meade but I intend to use the Meade DSI for doing my drift alignment only, So I could wait until I choose a Decent CCD camera but still might get the filter wheel, still thinking about this one as all I might use it for now is the Orion Skyglow Filter (light pollution). Thanks again Alistair, you same me a lot of money I do not need to spend yet
Hi Rodney,

All one shot colour cameras including the Meade DSI, Canon, Nikon, even webcams, colour autoguiders, planetary cams etc have a bayer matrix and will not benefit from LRGB filters.

That's how they produce colour images. by exposing 3 filters at the same time and combining them in the camera's hardware/software (generally speaking).

enabling mono mode in the canon or any colour camera will not help as the mono is a "pseudo mono" built from the RGB data that the camera has captured.
reason is that you cannot force blue light through the Bayer's R filter so blue will still fall only on blue pixels.

you can create a synthetic luminance by combining your RGB data and using that as "L", but doesn't make too much of a difference.

your best bet, get your coma corrector spacing correct, use the LP filter at the end of the coma corrector and you'll be fine. you've got all the other bits.
you have a good FOV, so don't waste that by cropping it without a coma corrector.
the choices are - Baader MPCC mark3, Baader RCC1, Televue Paracorr apart from others. all have different spacing requirements so remember the 45mm for your camera, then add the depth of all the bits you add in front of it.

As suggested, save the money on the filter wheel and filters till you get a mono ccd. you can easily drift align with the dsi as is without filters.

The 10inch F4 is a powerful scope and you should get very good results with the dslr if you capture darks, keep exposure below 6 to 8 mins (depending on ambient temperate), iso 800, capture flats even sky flats.

Cheers
Alistair
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  #5  
Old 18-02-2014, 12:53 PM
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Rod Burgess

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Quote:
Originally Posted by alistairsam View Post
Hi Rodney,

All one shot colour cameras including the Meade DSI, Canon, Nikon, even webcams, colour autoguiders, planetary cams etc have a bayer matrix and will not benefit from LRGB filters.

That's how they produce colour images. by exposing 3 filters at the same time and combining them in the camera's hardware/software (generally speaking).

enabling mono mode in the canon or any colour camera will not help as the mono is a "pseudo mono" built from the RGB data that the camera has captured.
reason is that you cannot force blue light through the Bayer's R filter so blue will still fall only on blue pixels.

you can create a synthetic luminance by combining your RGB data and using that as "L", but doesn't make too much of a difference.

your best bet, get your coma corrector spacing correct, use the LP filter at the end of the coma corrector and you'll be fine. you've got all the other bits.
you have a good FOV, so don't waste that by cropping it without a coma corrector.
the choices are - Baader MPCC mark3, Baader RCC1, Televue Paracorr apart from others. all have different spacing requirements so remember the 45mm for your camera, then add the depth of all the bits you add in front of it.

As suggested, save the money on the filter wheel and filters till you get a mono ccd. you can easily drift align with the dsi as is without filters.

The 10inch F4 is a powerful scope and you should get very good results with the dslr if you capture darks, keep exposure below 6 to 8 mins (depending on ambient temperate), iso 800, capture flats even sky flats.

Cheers
Alistair
Thanks Again Alistair,
I am a bit concerned you mentioned to keep the exposure below 8 minutes as my main interest is Galaxies and I found with the Meade DSI, which seems to be more sensitive than the Canon but lower resolution, I achieved excellent results at 10 minute exposure and with the a Light pollution Filter I generally used a 15 minute exposure with no problems????
Does the canon have problems at longer exposures, I did do one test at 10 minutes ISO 100, even thought the histogram was pushed further to the right it was comparable to what my Meade achieved and looks like it was a reasonable setting but I have not had any clear skies to fully test it out with a 10 minute exposure???
I have been creating a large dark library with Maxim DL for use and noticed with one exposure that I did have a dark for it shifted the histogram quite a bit to the left after subtraction.
Cheers
Rod
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Old 18-02-2014, 01:50 PM
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alistairsam
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hi,

Reason I mentioned 8 minutes is to keep noise and amp glow low.
try taking darks at iso 800 with your canon from 1min to 15mins. have a look at where you start seeing the amp glow which is a reddish glow in a corner and at which exposure you start seeing random colour noise, suggest trying this when the ambient temperature is below 20.
I'd suggest another set with iso 400 as well. with a lower iso, you can go longer at the loss of details.

the meade dsi is a ccd with a sony chip and would have lower noise than the dslr and from what i could find, the QE or quantum efficiency is above 60% for the mono. which DSI do you have?

the 8 minutes was only a suggestion, you'll need to experiment and see which length suits your imaging with acceptable noise.

general rule of thumb is that if the outside temp is low, that is below 20, then long exposures with an uncooled dslr is fine, so i'd suggest varying the length based on ambient temperature.

you could experiment with shorter exposures and higher iso or the reverse.
unless you try a number of combinations, its hard to speculate which is ideal as there are several variables.

The QE of dslr's is not measured in the same way as mono CCD's from what I've read but the comparable value is in the 30% range compared to CCD's which are generally above 60%.

have a look at the dark frames here. the 600d and 450d are relatively low noise. these darks are at iso1600 though.
http://dslrmodifications.com/T3iReview/T3iReview.html

don't worry too much about length of exposures, depending on your skies, 5 to 10min subs but a lot of them will yield good results and for galaxies, you will need reasonably dark skies.

the other option is to look at one shot colour ccd's but i'd suggest taking it one step at a time, experiment with the dslr and then move on.

Cheers
Alistair
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Old 18-02-2014, 07:32 PM
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rodroger (Rodney)
Rod Burgess

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Quote:
Originally Posted by alistairsam View Post
hi,

Reason I mentioned 8 minutes is to keep noise and amp glow low.
try taking darks at iso 800 with your canon from 1min to 15mins. have a look at where you start seeing the amp glow which is a reddish glow in a corner and at which exposure you start seeing random colour noise, suggest trying this when the ambient temperature is below 20.
I'd suggest another set with iso 400 as well. with a lower iso, you can go longer at the loss of details.

the meade dsi is a ccd with a sony chip and would have lower noise than the dslr and from what i could find, the QE or quantum efficiency is above 60% for the mono. which DSI do you have?

the 8 minutes was only a suggestion, you'll need to experiment and see which length suits your imaging with acceptable noise.

general rule of thumb is that if the outside temp is low, that is below 20, then long exposures with an uncooled dslr is fine, so i'd suggest varying the length based on ambient temperature.

you could experiment with shorter exposures and higher iso or the reverse.
unless you try a number of combinations, its hard to speculate which is ideal as there are several variables.

The QE of dslr's is not measured in the same way as mono CCD's from what I've read but the comparable value is in the 30% range compared to CCD's which are generally above 60%.

have a look at the dark frames here. the 600d and 450d are relatively low noise. these darks are at iso1600 though.
http://dslrmodifications.com/T3iReview/T3iReview.html

don't worry too much about length of exposures, depending on your skies, 5 to 10min subs but a lot of them will yield good results and for galaxies, you will need reasonably dark skies.

the other option is to look at one shot colour ccd's but i'd suggest taking it one step at a time, experiment with the dslr and then move on.

Cheers
Alistair
Cool, thanks again Alistair, The Meade I have is the Meade DSI II Colour
Here are a couple of last shots with this Camera, created from Mono Frames and Mono frames with viewing Filters, all equal exposures. 10min Mono and 10 minute with filters. The first one was created from mono frames and RGB from the camera in colour mode, I did not use the split lum.

http://www.rodroger.com/images/Astro...x12_RGBx10.jpg

The Pavo group - 12 x 10 minutes Mono, 10 x RGB 10 minute colour Mode -Meade DSI Orion 254mm Astrograph

http://www.rodroger.com/images/Astro...a-p_Spikes.jpg

NGC7793 - 19 x 10 minute Mono, 7 of each RGB using ordinary viewing filters with DSI in Monochrome mode

http://www.rodroger.com/images/Astro...x10-600sec.jpg

This was again taken with the DSI, 16 x 10 minute mono, 10 of each RGB 10 minute using ordinary viewing filters (strange colours )

http://www.rodroger.com/images/Astro..._Gx30_Bx29.jpg
This was taken using 2 minute Mono and 2 minute RGB with camera in colour mode, again I did lot use the lum frames same as the one below. these last two I took while at Queenslands Astrofest 2013. all the others are taken out in my backyard in Suburban Redcliffe

http://www.rodroger.com/images/Astro...x16_RGBx32.jpg
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