First test of f6.3 Reducer on M20, M8, M17, M16, NGC 2070, NGC 253, NGC 5139

[wayne anderson]

Last Tuesday Night I tried the Meade f6.3 reducer for the first time with reasonably good results considering smoke was hanging around from local backyard fires; just 25 quick shots of each object a quick stack, process and crop.

I do seem to be getting considerable vignetting of the images; it is my understanding that by adding the flat frames this can be reduced in the stacking process as the flat frames show any vignetting (and they do) and this can be accounted for in stacking, however vignetting was still very apparent in all shots.

Would where I place the reducer in the optical path make a difference or is the camera censor size an issue or something else?

The reducer is attached onto the rear cell of the SCT, then the zero shift micro focuser. T adapter & ring then Camera. The Sony Nex-3 camera has a 14.2 MP CMOS Image Sensor with a size of 23.4 x15.6 mm

A little help or insight into this problem of vignetting would be appreciated, thanks.

All shots attached are:

25 X 25 sec Subs at ISO 1600
10 Darks
10 Flats
12 inch Meade LX200 (Alt/Az Mounted)
Sony Nex-3 Camera
Stacked in DSS

1. Triffid Nebula M20
2. Lagoon Nebula M8
3. Swan Nebula M17
4. Eagle Nebula M16
5. Tarantula Nebula NGC 2070
6. Sculptor Galaxy NGC 253
7. Omega Centauri NGC 5139

[blink138]

yes wayne i have found the same thing and the advice was flats, which i am yet to do
but you can see my posts a little further down on these threads with my new 60da
pat

[rmuhlack]

how did you take the flats?

In the past I have taken my flats at twilight. Aim the scope/lens away from the rising or setting sun, towards a neutral part of the sky. then fire away a bunch of shots on apeture priority. Might need to experiment with the exposure compensation so that the flats are not too exposed. (eg you might need to try -1/3 to -1). check the histogram of the flats so that its sitting about midway.

If you take bias/offset shots as well - ie fastest shutter speed you can with the lens cap ON (so like a dark), on the same ISO as the lights, darks and flats - then DSS will automatically scale the darks and use them to subtract from the flats, so that the flats are dark calibrated so they dont add further to the noise of the image. I usually try to work with about 50ish flats and bias frames, and 20-50 darks.

[rmuhlack]

great effort on those shots by the way, especially considering they were with an alt/az :thumbsup:

[Chris.B]

Very nice. I have a 6.3 reducer. Have not tried it out yet. Looks like I had better. Well done. I thought you would have had some rotation with 25sec in alt az, but apparantly not.

[Nico13]

Same here with the 6.3 and the vigneting on my 8" Meade with the same setup. I would also be interested in any help with that.
Nice shots by the way must have kept you busy :thumbsup:

[Garbz]

I've got vignetting with a 6.3 reducer and a Celestron C8 too, it's correctable with flats when I shoot in DX mode (Nikon's term for cropping at centre APS-C sized part of the sensor). When I shoot at the full 35mm I get completely uncorrectable vignetting.

Your results looks quite good. I'm experimenting at the moment with the spacing between the camera and the reducer. The spacing seems to make quite a difference in coma but I haven't quantified it yet.

Would you be able to share what your current film plane to reducer distance is? I'm not sure if the NEX has a film plane indicator on the body but if it doesn't can you provide the distance from the corrector to the mount on the camera? Currently the coma on my images with the reducer is quite bad: http://www.flickr.com/photos/10090242@N03/7813406612/in/photostream

[wayne anderson]

Thanks Pat, I added more flats in the stack and it does work just a little better.

Thanks Richard, I took your advice on using darks, flats and bias, I followed the instructions on the DSS help files for the flats this time by placing a white T-shirt over the front of scope and pointed it toward a dimable light source to get just the right amount of exposure, it made a small but noticable improvement to the final shot but there was still vignetting but not as bad as before.

Thanks Christopher, definitly try your reducer I found it was vastly better than without. With alt/az photos I found that the DSS software takes out the the rotation when processing but it does have limitations if you are shooting close to the zenith point rotation is more noticable and results in bloated stars in the final photo also if I go from 25sec exposure to 30sec there is also a little bloating of stars.

Hi Ken and Chris, I have been researching on several forums the use of Meade f6.3 reducer and optimal spacing I have not varified this with experimenting yet but I found it stated that the optimal spacing between the reducer and the chip is 110mm to 115mm mine just happens to be 115mm and the optimal spacing from the rear cell to the reducer seems to vary greatly depending on the individule scope, some posts have stated it to also be 110 to 115mm for the LX200gps models, this seems to make sense as the distance from the rear cell to the end of the zero image shift focuser is about 115mm. The instructions with the reducer states to attach the reducer to the rear cell SCT thread (this is what I have done) however the instruction with the scope state to attach the reducer to the end of the focuser with the SCT thread adapter that I don't seem to have.

I am at this moment experimenting with processing settings if I get a good result I will post it here with details.

Thanks everyone for your help, I will keep experimenting and researching.

[Garbz]

Interesting. From what I've heard the optimal spacing was 87mm. That said I've read more than once that there were two different mead reducers out there. Certainly I got quite bad coma with my 109mm t spacer I used to use. I'm going through the steps to figure this all out right now.

[wayne anderson]

Yes your right chris i have read reports varying from 44mm to115mm, the most common responses seem to be 87mm or 110mm to 115mm. So if you find the right one let me know, i have noticed no issue with coma with the setup i use but there is still vignetting.

[5ash]

Nice pictures , what settings do you use for white balance? Are you using an interval timer to take your pics?
Philip

[Gem]

Nice selection of objects! I have found my reducer has been great with my C9.25. Definitely a good purchase! :)

[wayne anderson]

Hi Phillip, i just left the white balance on auto, i might try other dettings next time, i used the cameras basic 10sec timer 5 shots setting and manually repeated after each cycle, your nex 5 will have the same options.

Yes Grant i agree the reducer is a good purchase well worth it.

[Garbz]

I'm getting there through my experiments. I did some analysis on the images today. I have no fancy software so I have been doing it by eye, but currently my results seem to indicate that the optimal range in my case lies somewhere between 87mm and 100mm. My best result so far is 93mm.

I intend to try 89mm, 90mm, 96mm, and 99mm if I ever see a clear sky at night again (stupid clouds).

[Nico13]

Thanks for the info on that Chris, the weather here seems to be on the improve after a very long bleak winter of cloud and I've manage a bit of time in the last couple of weeks allowing testing with my new guide camera and scope but have been imaging with the ED80.
With that info I will try some shots asap with the 8" and check my distances for a comparrison. :thumbsup:

Cheers

[ourkind]

Kick ass!! My favourite is all of them! Awesome :thumbsup::thumbsup::thumbsup:

[Terry B]

I have also just purchased one of these and searched for the correct distance. There are 2 versions. The old one had a longer fl so the distance was longer to the camera. I think they changed the focal length some 5 years ago.
Sccording to meade here http://www.meade.com/accessories/premium/index.html
the ideal distance is 45mm. This is quite hard to achieve if you have anything other than the camera in the way.

[Merlin66]

The "original" Meade/ Celestron X0.63 reducer was specifically designed for a distance between the rear rubber shoulder to the film plane of 110mm. (The doublet has a focal length of 240mm)
There is no restriction on the positioning of the reducer in the optical axis, generally it is mounted on the rear SCT thread of the mirror cell.

Some years ago there was a "dud" batch of these reducers ( with a far shorter focal length - they were similar to the x0.33 reducer focal length) and this gave rise to many discussion on many forums.

Two years ago there was talk that the reducer had indeed been changed to a shorter focal length. I have never seen one of these.
Interestingly, no one has commented on the Celestron version...this still seems to be the same as the original and still needs the 110mm spacing.
(If someone has a shorter focal length Meade x0.63 reducer I'd love to hear from them)

[wayne anderson]

Thanks for all that interesting history and facts about the f6.3 reducer and spacing it clears up a few things.
Interesting that the Meade site now states that the ideal distance is 45mm, with a little rearranging of the various adapters I have to connect the camera I will just manage to reduce the spacing to minimum of 85mm.
I can't reach the ideal 45mm spacing so I will try the 85mm spacing next time and see if it is better than the 115mm I have been using.

[Merlin66]

Wayne,
Double check the focal length of the reducer before committing....
Focus the sun's image and measure the distance. For a 45mm backfocus, this should be very close to 100mm....if you find the focal length around 240mm then the backfocus distance should be 110mm.

[Terry B]

Ken
I have just bought a new one to go on my new C11 (:D). I set it up last night with the LISA attached and it seems to work very well. No idea about the image quality as I'm not really interested in the quality of the off axis stars on the slit. It certainly produced a nice spectra of R71. I will take it off again and measure the fl.
The LISA has a focal distance of 41mm to the T thread. The adaptor I have is about 10mm long so about 51mm in total. It probably doesn't matter for spectroscopy.
Cheers

Terry

[Merlin66]

Terry,
Hmmmm "new C11".....
Did you buy the Meade or Celestron version of the reducer??
I'd certainly be interested to find out the focal length and also the reduction you get with your spacing....

[Terry B]

The meade version. It was about 1/2 the price.

[Terry B]

I measured the fl tonight of my new meade FR and it is almost exactly 200mm from the back of the flange.

[Merlin66]

Thanks Terry.
That's very close to the original....
The 45mm quoted seems either to be an error or the spacer required for a DSLR.