Eta from the doghouse - the dogbowl shot

[h0ughy]

Well i feel as thought it is the dogbowl shot with the curvature in the field. Still working on the 8" so i stuck with the 127Ed and the Wo 0.8 reducer. I really need to sort this out - somehow this must work? Anyway it is of 3 hours and 32 minutes duration of wasted effort from last night and this morning guiding and pushing the camera at 4 degrees and iso400 - and not using a LP filter the shots were 3minutes each.

so i did two versions processed in pixinsight and a tweak with special herbs and spices- not happy with either to be honest:shrug:

[leon]

Nothing wrong with that one Houghy, well done mate, stay with it.

Leon

[Vanda]

Great shots!

[duncan]

Hi David,
That bit of curvature gives it a 3D effect. I know you want rid of it so i'll not say anmore,Lol.
Looks good to me.
Cheers,
Duncan:)

[sheeny]

OK, a little bit of curvature, but it's far from a dog's breakfast!

Al.

[telecasterguru]

I can't see too much wrong with the image at all. I think it is a fine effort.

Frank

[gbeal]

Dog tucker indeed Huff, LOL.
What is the issue? There must be enough of you guys with this Gilman Special to have worked out what is needed to keep it all flat?? Surely?
In my case a while back with an 80mm triplet I used an MPCC, so if you have access to one of them, try that. Be prepared to try differing spacings, like Marc MultiWeb did.
A great project for the full moon period, instead of barking at it, LOL. Sorry couldn't help myself.
Gary

[iceman]

Getting there Dave, coming along nicely!

[JohnH]

David - which WO flattener are you using? I have a FLAT2 and 3 and find neither of them works very well on the 127 - in fact the Canon20D works better with no flattener in line.

I think there is under correction as your corner stars are

\ /
/ \


If I have this right this means the sensor needs to be further from the corrector - try a small spacer. If you get stars in the corners like this:

/ \
\ /

you are over corrected and you need to get closer unfortunately that is tricky to achieve with a DSLR.

How do your images look with no corrector in line? (BTW it is not a crime to crop a little if your field is not flat all the way to the corners)

Finally you may also get a better result by focusing on a star 1/2 way to the corner not one dead centre on the CCD as this will balance the focus better.

[multiweb]

As Gary pointed out you're going to have to try different spacing to find the sweet spot. If you can't then you'll need a different reducer/corrector. It's all part of the fun. Nothing wrong with that shot though. The center field looks great. You just need to tidy up the edges. :thumbsup:

[h0ughy]

John thanks for your reply - it is version 3 i have. The information is great - and i will have a try at the spacers. have a look at a sample image i have withought a spacer http://www.iceinspace.com.au/forum/showthread.php?t=59765

[h0ughy]

thanks Marc

[multiweb]

Do you have CCD Inspector? If not post a link to one raw sub and give us your sensor pixel size and the FL the picture was taken at. I'll send you back the graphs. Might help in checking what's off and you'll get there faster.

[h0ughy]

thanks Leon

Ta

thanks for the opinion

Sorta like Mydog

Frank i couldnt post a larger image due to file size - but it is bad

Valuable information and advice Gary ;) LOL

one day Mike , one day i will get there:rofl:

[h0ughy]

thanks - send you a PM

[Scorpius51]

If that's what Meaty Bites does for you David ... where's my bowl?

:thumbsup:

Cheers
John

[Moon]

I like the one with special herbs and spices.
I did some tests on the weekend (in between the clouds up at Heathcote) and I recon the Astro-Tech 2" field flattener is a perfect match for the ED127 and a DSLR. The images comes out very flat in CCD Inspector, and the spacing seems spot on when it is screwed directly into a canon t-ring.

It's cheap too.

http://www.astronomics.com/main/product.asp/catalog_name/Astronomics/category_name/7U1FFR2KKXEB8L34WN0HW6E3L3/product_id/AT2FF

James

[h0ughy]

can you post a pic

[Moon]

Sure. It might take me a few days to get my act togther (the images are still on the laptop, unprocessed)
James

[h0ughy]

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

[multiweb]

Well I got one on my ED80 and I reckon it's terrific. :thumbsup:
Couple of pics here (http://www.iceinspace.com.au/forum/showthread.php?t=59895)& here (http://www.iceinspace.com.au/forum/showthread.php?t=58785).

[h0ughy]

how did you find it to adjust?

[multiweb]

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. :P

[rogerg]

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. :rolleyes:

[JohnH]

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]

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]

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]

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]

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.