65 minutes (13 x 5 minute subs) using the unmodded Canon 350D, Saxon 80ED, WO 0.8x reducer, using the IDAS LPS filter. Processed with Deep Sky Stacker and PS CS3.
Anyone got any clues why with the WO 0.8x reducer I am seeing this elongation so drastically? Do I have a spacing problem? I thought it was supposed to make this better!!! It's screwed right in to the t-ring adapter.
Great image, Robert. We have the same setup (pretty much) so I always look forward to your images.
I had the same problem with the WO 0.8x the other week - I think it's to do with a slight off-axis when screwing it into the focuser. I took more care the other night and in the raw frames (unprocessed so far) there doesn't appear to be the same warping on one side- although the corners are still elongated. I just think the WO 0.8x can't flatten the whole field.
But maybe try and take another image without it and see how well it does do.
I'll upload my raw frames from the other week and the other night to show the difference, make sure it's not in my head.
Rob,
I am not conversant with the W/O reducer, but suspect it will be a spacing discrepancy. Is there a published reducer to film/chip distance. If you ever buy Takahashi they has published "metal distances", and they need to be exact.
Maybe ask W/O what the actual required distance is.
Gary
The WO FF 0.8 distance is ~55mm. As the Canon EF mount is 44mm to sensor, that leaves 11mm for the t-ring to take up. The t-rings I have measured have been around 11mm, so it should be very close, unless you are doing something differently.
From the reading I have been doing on reducers lately, the image you posted is undercorrected. You could try tweaking the distance, but the smallest t-adapter spacers I have found are 7.5mm. Look for the Baader T2 7.5mm and 15mm spacers, I bought mine at OPT but there may be a domestic source.
The WO Flattener v2 and v3 are supposed to be targeted at differing focal lengths/apertures of scopes, so if you have the 2 you might want to try out the 3, or vice versa.
I have the the oldest type of WO reducer... quite a chunky number.
When I first configured it, I opened up the camera, flipped up the mirror and measured to the front of the t-ring. It was pretty close to 50mm from memory (which is apparently what it is supposed to be, but I can't find any official specs), and I just assumed the discrepancy was my measurement inaccuracy.
I'll have to re-measure everything, and see if I can spot the difference, and hope that adding a spacer (rather than having to move it in!) is an option.
To be honest, I'm a bit frustrated. When I didn't have the flattener, I never had the elongated stars in the corners (well, it wasn't obvious). -- Just went back to check older images - it was there, just not as obvious because of the choice of image. If anyone else has the same reducer, please let me know how it goes for you.
Last edited by turbo_pascale; 02-03-2008 at 10:09 AM.
High praise coming from you Mike. It's taken a few years to get one out worth looking at.... admittedly, became productive when the shed roll-off was installed. Lots of frustration and mistakes up until then (and no doubt many more)
Turbo
Quote:
Originally Posted by strongmanmike
Pretty nice image there Robo
The stars aren't too bad IMO.
Paul Mayo has been noticing similar problems with his new APO and reducer, if he reads this perhaps he might chime in?