Eta Carina and Canon 40D - where's the red???

[Dennis]

Hello,

Well, the experimentation continues with the 40D and deep space work. Last night, I learned that using a DSLR on fainter DSO’s is very, very different in terms of exposure duration required, compared to the SBIG ST7 which has a much higher quantum efficiency and is cooled.

Here is an image of Eta Carina cropped from the full frame. Noticeably, the red stuff is missing as is most of the data! This is a combination of 3 x 5 minute sub frames.

Tak Mewlon 180 F12 with Tak Reducer/Flattener around F9.6 so it is still a sloooow system.
Canon 40D, 3 x 5 minute exposures at 400ASA.
Processed in ImagesPlus and CS3.

There is a definite price to pay when stepping up to larger sensors and colour, in cost, set up, capture and processing! I might just stick to DSO's brighter than mag 4! :lol:

Cheers

Dennis

[astroturf]

Hi Dennis

To my novice eye that looks spectacular even tho there's not much red - very encouraging
I'm about to embark on the 40d AP journey & if I can manage detailed shots like that I'll be well chuffed
At this stage I'm not prepared to modify my 40d both for financial reasons and the concern the camera may never be the same for general photography

Cheers
bryan

[skwinty]

Hi Dennis
A good looking image regardless. Your 40d is modded for Ha isnt it?
I would be interested in seeing the exif info on those pix.
I have now received my rings and will be ready to use the eq6 visually but not photographically as i have not received the 2" 50mm extension for achieving dslr prime focus. I must still lop off 5cm from the OTA.
I cant wait. Starting to get real irritated!!
Kind regards
Steve

[leon]

Dennis there sure isn't much red in there, and i find that strange as when i do a shot of eta carinae with my un-modded Canon 5D it is so red i usually have to minus on the saturation.

Leon

[EzyStyles]

nice going dennis. guiding seem spot on!

[Dennis]

Hah – you should see the full resolution originals.:whistle: The one above is a smaller, central crop masking the minor guiding defects!:lol:

Cheers

Dennis

[Dennis]

Hi Leon

I’m working at around F9.6 which is very slooow and hence I don’t catch as many photons as your nice faster Tak and Canon glass – maybe it’s just a question of sufficient data via longer exposures?

Or, is your glass suffering from bad CA in the red wavelengths!:whistle::lol:

Cheers

Dennis

[Dennis]

Hi Bryan

Thanks for the complements. Like you, I’m not going anywhere near having my 40D modded, as its primary purpose is happy snaps with the occasional night time outing on the brighter DSO’s

Cheers

Dennis



Hi Steve

No – the 40D is bog standard, no modifications. Ouch – lopping 50mm off the OTA doesn’t sound like too much fun, how will you do this?

I’ll see if I can convert the Exif data to a text string and post the results.

Cheers

Dennis

[leon]

Dennis, no mate, my glass as you put it is just fine. ;) thanks for asking :lol:

Leon :thumbsup:

[Dennis]

Dang! I should have read your signature more comprehensively before posting my cheeky reply!:lol::lol: It was written there, in pink, right in front of my nose eh! :thumbsup:

Cheers

Dennis

[Terry B]

I've found that the red is low also but don't just try the few bright objects. Most galaxies are not heavily into red nor GCs. There's plenty of objects to image that aren't going to be the same old same old.

[Garyh]

You have some nice detail there Dennis..
Have you tried stretching the red channel?
Yeah a fast system really helps esp with a unmodded camera as you are getting only 1/3 the Ha that you would get with a modded camera.
Still a lovely image.
cheers

[Dennis]

Hi Gary

Thanks for the feedback and suggestions. I did try stretching the red channel and a lot of noise loomed up within the shadows. As you say, the combination of the Canon filter and a slow f-ratio has compounded the problem.

My over reaction to the lack of red really stems from an unfair comparison between the results I get from using the cooled, more sensitive ST7 and the un modded 40D.

Cheers

Dennis

[RB]

You've done a good job there Dennis.


Perhaps try using 800ASA and maybe lowering the exposure time to 3 minutes but take more exposures to help increase your S/N ratio and allowing you a greater dynamic range to play with.

What are you using to guide with Dennis?

[Dennis]

Hi Andrew,

Thanks for the tips – I’ll give them a try the next time I get another clear window in this La Nina cycle.

I’m using a WO 66mm F6 Petval, the (original) Orion Deep Space Star Shoot colour camera and PHDGuiding. The OTA’s are mounted side-by-side using the WO saddle plates.

I balance on both sides of the mount, with the OTA’s first pointing horizontal and then vertical to help ensure a good balance. I also route the cables carefully and clip them to the EM200 body and then the respective saddle plate as I have noticed that cable drag can contribute to trailed stars.

Cheers

Dennis

[RB]

Great tip for all of us to keep in mind, thank you Dennis.

[richardo]

Hi Dennis,
nice image even though it is lacking a lot of red channel data.
But as mentioned by Gary, the Canon DSLR's have a 'low pass' filter across the ccd chip that prevents much of the IR light.
This prevents over saturating of the chip in the red channel for balanced terrestrial photos.
You can actually remove this filter permanently which is just what's needed for astro images and when you're wanting to take happy snaps/ terrestrial, there's a screw on IR filter with the same band pass you can buy to fit the Canon lens' directly to the front.
If you seriously thinking of using the Canon for astro imaging, it might be a good cheap option for the best of both worlds.
Here's a link that might help.
http://astro.ai-software.com/articles/mod_350D/mod_350D.html

Also try Steve Canistra's site for a good description on processing DSLR images.
http://www.starrywonders.com/


Rich

[Dennis]

Hey Andrew

I purchased a Canon EOS T2 Adaptor from our local shop, Photo Continental and when I fitted it, I noticed that once the bayonet flanges had fully engaged with the 40D body, I could still rotate the camera body on the T2 mount, just by a small twitch or two, CW and AC.

This is not good when the mount is auto guiding as the USB Cables and Power Cords could easily rotate the 40D body over long exposures. Just another source of potential flexure to chase down eh!

Photo Continental is an excellent photo retailer and the product was genuine Japanese product. Where do you get your EOS adapters from? Have you noticed any slop?

Cheers

Dennis

[RB]

No Dennis I notice no movement at all.
I bought mine years ago after I bought the 300D, I think it was from the local Camera House store but I don't remember how much it was back then.

I have seen them available from Bintel (https://www.bintelshop.com.au/Product.aspx?ID=5551) though.

EDIT: I just realised that you may have to tighten the lock screw on the inside of the adaptor ring, I'd be checking this first as it may not be tight enough to hold fast.
You'll need a small screwdriver, like a jewelers type.

[Dennis]

Thanks RB – I noticed that tiny grub screw and wondered what is was for, as all my Pentax PK adapters didn’t have one.:thumbsup:

Cheers

Dennis

[skwinty]

Hi Dennis
Will circumcise telescope as per IIS article "Modding a newtonian for DLSR photography"" by Alchemy.
Regards
Steve