At last i have progressed to off axis guiding the C9.25 with a sony nex5 , orion off axis guider and meade f6.3 reducer. Attached is a pic of eta carina made up of 10 x4min pictures @ iso400 stacked in DSS with darks, lights ,flats and biases (original picture is 14 Mp). must now practice the processing in PS.
philip
Last edited by 5ash; 12-04-2013 at 05:00 PM.
Reason: add
Nice job Philip. If you haven't already done so, I suggest that you
repeat the excercise at ISO 800 and 1600, plus perhaps shorten the exposures a bit to eliminate what seems to be a tiny amount of star
elongation. Hopefully the higher ISO will bring out a lot more nebulosity
without unduly affecting image quality. Looking forward to seeing the
results should you decide to try it.
raymo
Thanks Raymo . I think the stars in the centre of the field are quite round and perhaps some of those to one side show the effects of coma. I purposely exposed at iso400 to improve the dynamic range of colour and reduce noise . I will try at higher iso values to gain more nebulosity and layer mask to maintain the detail and exposure of the keyhole.
Regards philip
My apologies; upon closer inspection you are absolutely right; it does
seem to be a little bit of coma. I am still looking forward to
your next images.
raymo
I also get the same coma results with my 9.25", Meade reducer and 450d on the outer stars. I have been told using a Celestron reducer will fix this but I am not totaly sure.
I assume you took the image with the 350D? if so is there any chance you can post a phoyo of you image train. The only reason I ask is I to have a 9.25" and a Meade reducer and had to buy the snub nose T-Adapter from Bintel to get the camera as close to the reducer as possible to reach focus, the standard Celestron 936330-A left me to far away. I was looking at the off axis guider and my calculations showed me with this unit in my train I would again not read focus.
I assume you took the image with the 350D? if so is there any chance you can post a phoyo of you image train. The only reason I ask is I to have a 9.25" and a Meade reducer and had to buy the snub nose T-Adapter from Bintel to get the camera as close to the reducer as possible to reach focus, the standard Celestron 936330-A left me to far away. I was looking at the off axis guider and my calculations showed me with this unit in my train I would again not read focus.
Carl[/QUOTE]
Hi Carl,
No I did not use the 350D , was using the nex5 . However the T adapter for it is about 5x the thickness of the canon Eos t adapter.so I would assume the image train would be similar.i will try to take a picture of my image train with the nex5
I also get the same coma results with my 9.25", Meade reducer and 450d on the outer stars. I have been told using a Celestron reducer will fix this but I am not totaly sure.
I assume you took the image with the 350D? if so is there any chance you can post a phoyo of you image train. The only reason I ask is I to have a 9.25" and a Meade reducer and had to buy the snub nose T-Adapter from Bintel to get the camera as close to the reducer as possible to reach focus, the standard Celestron 936330-A left me to far away. I was looking at the off axis guider and my calculations showed me with this unit in my train I would again not read focus.
Carl
Hi Carl,
Here is a picture of the image train. You can see how big the T-adapter is for the nex5 , so I would think there would be no problem with the canon.
Regards philip
Ps it seems to have uploaded from my IPad upside down? Also the distance from the focal reducer to camera sensor is about 90mm
Last edited by 5ash; 13-04-2013 at 11:28 AM.
Reason: Comment
Thanks for taking the time to do that, it is very much appreciated. As I suspected, wont be buying an off axis guider, the 90mm will leave me short of focus. As you can see by the image below my camera has to be very close to the reducer I can probably only go another 10 mm at best.
Hi Carl ,
If you start from scratch with a low profile SCT female to male T thread adapter ,then off axis guider to female T -Thread ,to canon eos ring you should have plenty of room.The off axis guider comes with several T -thread extensions if needed.If my nex5 to T-thread adapter was not 40mm long and only about 10mm like your eos adapter I would have to use an extension tube to get the focal reducer at an adequate distance.I'm sure with the bits I have I could put my 350d in place of the nex5. Looking at your picture you seem to have a extension tube of similar dimensions to the off axis guider without its extension tubes.look at the off axis guider in my picture , it has none of the extension tubes in the image train.hope this helps .
Regards philip
Good point Philip, if my T-ring will mount directly on the back of the off axiz guider then I should still have enough back focus. If I still need a T-adapter on the back and then my T-ring I know I will be over.
What was your reasoning for using an OAG rather than a guidescope?
I'm sitting here not far from John Hunter with a C9.25, EQ6, QHY-5, 40D, etc., just trying to figure out which way to go for guiding .........of course, while we have this stupid weather I'm not going to have much chance of attempting imaging anyway. I'll probably have questions about your setup later on.
What was your reasoning for using an OAG rather than a guidescope?
I'm sitting here not far from John Hunter with a C9.25, EQ6, QHY-5, 40D, etc., just trying to figure out which way to go for guiding .........of course, while we have this stupid weather I'm not going to have much chance of attempting imaging anyway. I'll probably have questions about your setup later on.
Cheers,
Chris
Hi Chris ,
There were two reasons i chose off axis guiding , the most important of which was the small size of the opening in my observatory which meant both scopes would not necessarily be able to look through parts of the opening at the same time. secondly off axis guiding removes the problems of possible flexure between guide scope and imaging scope. only drawback seems to be finding guidestars in a more limited field of view. i have used both forms of guiding with my ED80 and had no problems but with the longer focal length of the C9.25 with focal reducer i suspect they would become obvious.
regards philip
.........of course, while we have this stupid weather I'm not going to have much chance of attempting imaging anyway
. I'll probably have questions about your setup later on.
