Eta from the doghouse - the dogbowl shot

[multiweb (Marc)]

Originally Posted by h0ughy

http://www.myastroshop.com.au/produc...sp?id=MAS-016O would this be a better solution for my problem?

Well I got one on my ED80 and I reckon it's terrific.
Couple of pics here & here.

[h0ughy (David)]

Originally Posted by multiweb

Well I got one on my ED80 and I reckon it's terrific.
Couple of pics here & here.

how did you find it to adjust?

[multiweb (Marc)]

Originally Posted by h0ughy

how did you find it to adjust?

Very easy because it has an internal mechanism to adjust the glass distance so all you need is a 40mm spacer let's say then you can tweak the rest with the FF itself. Pretty cool. It also has a rotating thing so you can adjust the orientation of your camera. Make sure you secure it before imaging and don't let it hang like I did.

[rogerg (Roger)]

It's not bad houghy.

Once you get the 0.8 reducer "working" you might be in the same position as I am with the 0.8 vIII reducer on my M90: I now have stars curving in a circular way around the FOV, instead of in towards the center.

[JohnH]

Originally Posted by h0ughy

http://www.myastroshop.com.au/produc...sp?id=MAS-016O would this be a better solution for my problem?

David - it could be - I think there were some good reports of the Falt 4 with APOs and in particular 127mm units but I also think the FLAT4 is expensive and has been reported as not acting as an FR (if that is what you want) - or at least my memory tells me that - and I think there have been two versions produced just to confuse further.

I have also heard recommend the HOTECH unit:

http://www.hotechusa.com/category-s/4.htm

Again not an FR though.

In my case I want an FR more than flattening as I have a small CCD but to date I have not been able to find one that I can use with my setup of 127 - OAG - 1.25" FW - CCD.

This area really does seem to be a black art - even when I had my VC200L which had a custom made corrector and FR the FR made the images soft and the native fl made the fov samm and the res too high with a DSLR though the field was flat...

I guess the best is to match the CCD to the optic and let the tube do its thing at its designed fl if you can - of course that might mean you need more than one scope...

[Moon (James)]

I did a quick process.
Here is M8 with the ED127 and Astrotech 2" flattener from last weekend, taken through light cloud:
http://deepspaceplace.com/show.php?id=ngc6523b

And here is the same target & scope from last year without the flattener:
http://deepspaceplace.com/show.php?id=ngc6523

If you zoom in (click on the image), the corners look better in the one with the flattener. I think it's a good match for this scope. I also attached a CCD Inspector report.

James

[JohnH]

James, looks like a good match. A couple of questions though - what is the spacing required (CCD to lens) - have you simply screwed this into the t-ring? How much backfocus does it require? The image with the flatterer seems to have bigger, bluer halos around the bright stars - is that your experiance or is it simply because the images were not processed the same way?

[Moon (James)]

For the spacing, its really easy - it just screws into the Canon T-Ring. It doesn't seem to take up much back focus - it's not a problem on the ED127 anyway.
The images I took on the weekend were all taken through high cloud. This gave all the stars a nice halo. I also rushed the processing a bit.
James

[bmitchell82 (Brendan)]

its very interesting the CCD report as you have "inverted" correction that is the stars are becoming less corrected towards the center. remember Black is flat green is bad. with my 10" newtonian its nearly flat in the middle (as it should be) and curves slighty up at the edges but a site load better than without the coma corrector.

Can you take a series of 6 shots on a star field and then average them with ccd stack with and without the corrector that would be a better comparison to the proformance of the corrector.

[multiweb (Marc)]

I think it's because of M8 in the middle. You'll get the same readings if you shoot Omega Cent for example. To get a true reading you need to shoot a uniform starfield. Although his field is extremely flat. 11% is really good and his FWHM variation is also very small. I have seen graphs on FSQ106N that were worse than that with a 14% field curvature. So this is indeed an outstanding result for an ED127.