Re: [Utah-astronomy] Longer Focal Length Imaging
I have been experimenting with imaging at longer focal lengths using the SBIG STT-8300 with FW8G-STT, filter wheel with built-in-guider. I have been using the Mewlon 250 with the Astro-Physics .67 focal reducer. This gives a focal length of 2010 mm or 79.13 inches. At this focal length a guide scope is difficult to use without getting flexure. Using off-axis guiding is the most effective way. The new SBIG filter wheel intercepts some of the light with a small off-axis pick off mirror and passes it through a focal reducer before going to the separate built in guide camera bypassing the filters so you always guide with unfiltered light. This setup allows long guided exposures at relatively high magnification. On Saturday I took 9 - 15 minute luminances and 8 each 5 minute RGB images and combined them for the image of M 51 (see below link). Not one image had any star trailing, which I find quite amazing. The seeing was not very good which I think affected fine detail. http://www.slas.us/gallery2/main.php?g2_itemId=5755&g2_imageViewsIndex=1 Clear Skies, Don Colton
The stars are a tad bloated Don, but even so, that is an excellent image. Keep going, and well-done! On Tue, Jan 28, 2014 at 2:16 PM, Don J. Colton <djcolton@piol.com> wrote:
I have been experimenting with imaging at longer focal lengths using the SBIG STT-8300 with FW8G-STT, filter wheel with built-in-guider. I have been using the Mewlon 250 with the Astro-Physics .67 focal reducer. This gives a focal length of 2010 mm or 79.13 inches. At this focal length a guide scope is difficult to use without getting flexure. Using off-axis guiding is the most effective way. The new SBIG filter wheel intercepts some of the light with a small off-axis pick off mirror and passes it through a focal reducer before going to the separate built in guide camera bypassing the filters so you always guide with unfiltered light.
This setup allows long guided exposures at relatively high magnification. On Saturday I took 9 - 15 minute luminances and 8 each 5 minute RGB images and combined them for the image of M 51 (see below link). Not one image had any star trailing, which I find quite amazing. The seeing was not very good which I think affected fine detail.
http://www.slas.us/gallery2/main.php?g2_itemId=5755&g2_imageViewsIndex=1
I think the bloating was more a function of the seeing. I couldn't get as tight of focus as normal even with short exposures. Usually FWHM is about 2-3 on 6th mag stars but I was getting about 5 at best. -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Chuck Hards Sent: Tuesday, January 28, 2014 2:35 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Longer Focal Length Imaging The stars are a tad bloated Don, but even so, that is an excellent image. Keep going, and well-done! On Tue, Jan 28, 2014 at 2:16 PM, Don J. Colton <djcolton@piol.com> wrote:
I have been experimenting with imaging at longer focal lengths using the SBIG STT-8300 with FW8G-STT, filter wheel with built-in-guider. I have been using the Mewlon 250 with the Astro-Physics .67 focal reducer. This gives a focal length of 2010 mm or 79.13 inches. At this focal length a guide scope is difficult to use without getting flexure. Using off-axis guiding is the most effective way. The new SBIG filter wheel intercepts some of the light with a small off-axis pick off mirror and passes it through a focal reducer before going to the separate built in guide camera bypassing the filters so you always guide with unfiltered light.
This setup allows long guided exposures at relatively high magnification. On Saturday I took 9 - 15 minute luminances and 8 each 5 minute RGB images and combined them for the image of M 51 (see below link). Not one image had any star trailing, which I find quite amazing. The seeing was not very good which I think affected fine detail.
http://www.slas.us/gallery2/main.php?g2_itemId=5755&g2_imageViewsIndex =1
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Don, I would be proud and pleased as punch if I could get an image half as good. I agree, it is fun to look at the background galaxies as well. There looks to be a nice irregular in the lower left of the image, and a square galaxy just above M51. If that was my shot I'd frame it and put it above the fireplace. Thanks for posting.
I agree Don, and that's what I was alluding to. It's an excellent shot. Bloated stars are a sign of soft seeing. On Jan 28, 2014 5:14 PM, "Don J. Colton" <djcolton@piol.com> wrote:
I think the bloating was more a function of the seeing. I couldn't get as tight of focus as normal even with short exposures. Usually FWHM is about 2-3 on 6th mag stars but I was getting about 5 at best.
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Chuck Hards Sent: Tuesday, January 28, 2014 2:35 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Longer Focal Length Imaging
The stars are a tad bloated Don, but even so, that is an excellent image. Keep going, and well-done!
On Tue, Jan 28, 2014 at 2:16 PM, Don J. Colton <djcolton@piol.com> wrote:
I have been experimenting with imaging at longer focal lengths using the SBIG STT-8300 with FW8G-STT, filter wheel with built-in-guider. I have been using the Mewlon 250 with the Astro-Physics .67 focal reducer. This gives a focal length of 2010 mm or 79.13 inches. At this focal length a guide scope is difficult to use without getting flexure. Using off-axis guiding is the most effective way. The new SBIG filter wheel intercepts some of the light with a small off-axis pick off mirror and passes it through a focal reducer before going to the separate built in guide camera bypassing the filters so you always guide with unfiltered light.
This setup allows long guided exposures at relatively high magnification. On Saturday I took 9 - 15 minute luminances and 8 each 5 minute RGB images and combined them for the image of M 51 (see below link). Not one image had any star trailing, which I find quite amazing. The seeing was not very good which I think affected fine detail.
http://www.slas.us/gallery2/main.php?g2_itemId=5755&g2_imageViewsIndex =1
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Beautiful, Don -- I'd love an 8300. On Tuesday, January 28, 2014 7:38 PM, Chuck Hards <chuck.hards@gmail.com> wrote: I agree Don, and that's what I was alluding to. It's an excellent shot. Bloated stars are a sign of soft seeing. On Jan 28, 2014 5:14 PM, "Don J. Colton" <djcolton@piol.com> wrote:
I think the bloating was more a function of the seeing. I couldn't get as tight of focus as normal even with short exposures. Usually FWHM is about 2-3 on 6th mag stars but I was getting about 5 at best.
-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Chuck Hards Sent: Tuesday, January 28, 2014 2:35 PM To: Utah Astronomy Subject: Re: [Utah-astronomy] Longer Focal Length Imaging
The stars are a tad bloated Don, but even so, that is an excellent image. Keep going, and well-done!
On Tue, Jan 28, 2014 at 2:16 PM, Don J. Colton <djcolton@piol.com> wrote:
I have been experimenting with imaging at longer focal lengths using the SBIG STT-8300 with FW8G-STT, filter wheel with built-in-guider. I have been using the Mewlon 250 with the Astro-Physics .67 focal reducer. This gives a focal length of 2010 mm or 79.13 inches. At this focal length a guide scope is difficult to use without getting flexure. Using off-axis guiding is the most effective way. The new SBIG filter wheel intercepts some of the light with a small off-axis pick off mirror and passes it through a focal reducer before going to the separate built in guide camera bypassing the filters so you always guide with unfiltered light.
This setup allows long guided exposures at relatively high magnification. On Saturday I took 9 - 15 minute luminances and 8 each 5 minute RGB images and combined them for the image of M 51 (see below link). Not one image had any star trailing, which I find quite amazing. The seeing was not very good which I think affected fine detail.
http://www.slas.us/gallery2/main.php?g2_itemId=5755&g2_imageViewsIndex =1
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Very nice Don. On Jan 28, 2014 2:18 PM, "Don J. Colton" <djcolton@piol.com> wrote:
I have been experimenting with imaging at longer focal lengths using the SBIG STT-8300 with FW8G-STT, filter wheel with built-in-guider. I have been using the Mewlon 250 with the Astro-Physics .67 focal reducer. This gives a focal length of 2010 mm or 79.13 inches. At this focal length a guide scope is difficult to use without getting flexure. Using off-axis guiding is the most effective way. The new SBIG filter wheel intercepts some of the light with a small off-axis pick off mirror and passes it through a focal reducer before going to the separate built in guide camera bypassing the filters so you always guide with unfiltered light.
This setup allows long guided exposures at relatively high magnification. On Saturday I took 9 - 15 minute luminances and 8 each 5 minute RGB images and combined them for the image of M 51 (see below link). Not one image had any star trailing, which I find quite amazing. The seeing was not very good which I think affected fine detail.
http://www.slas.us/gallery2/main.php?g2_itemId=5755&g2_imageViewsIndex=1
Clear Skies,
Don Colton
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Getting galaxies at a decent scale is no small feat. Longer focal lengths require a rock of a mount- you won't get sharp images with a SCT on a wedged fork mount no matter how good the seeing. Remember Tyler's advice concerning mounts. The OAG is a great tool, I think you nailed it, Don. I have yet to try my old Lumicon OAG with my DSLR but it should work. I may have to come up with something else for my Starshoot camera. The current trend toward "mini" guide scopes minimizes the flexure concerns but at these plate scales I still worry about guiding accuracy. On Tue, Jan 28, 2014 at 2:16 PM, Don J. Colton <djcolton@piol.com> wrote:
I have been experimenting with imaging at longer focal lengths using the SBIG STT-8300 with FW8G-STT, filter wheel with built-in-guider. I have been using the Mewlon 250 with the Astro-Physics .67 focal reducer. This gives a focal length of 2010 mm or 79.13 inches. At this focal length a guide scope is difficult to use without getting flexure. Using off-axis guiding is the most effective way. The new SBIG filter wheel intercepts some of the light with a small off-axis pick off mirror and passes it through a focal reducer before going to the separate built in guide camera bypassing the filters so you always guide with unfiltered light.
This setup allows long guided exposures at relatively high magnification. On Saturday I took 9 - 15 minute luminances and 8 each 5 minute RGB images and combined them for the image of M 51 (see below link). Not one image had any star trailing, which I find quite amazing. The seeing was not very good which I think affected fine detail.
http://www.slas.us/gallery2/main.php?g2_itemId=5755&g2_imageViewsIndex=1
participants (6)
-
Brent Watson -
Chuck Hards -
Don J. Colton -
Joe Bauman -
Larry Holmes -
Siegfried Jachmann