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Meade f/6.3 Focal Reducer gives some very unexpected results

PostPosted: Sat Apr 01, 2017 12:12 am
by rtemen
I just purchased the Meade Reducer, and I was very disappointed in the results.
I trained my Celestron C11 on a reasonable star and took a picture before I installed the Reducer.
Then, without changing the scope's position, I installed the Reducer and took another picture.
WOW! there is now a very obvious 'light doughnut' in the center of the view.
Here is a side by side shot of the two pics.
Image

Does anyone have any ideas what this is all about?

Rich

Re: Meade f/6.3 Focal Reducer gives some very unexpected res

PostPosted: Sat Apr 01, 2017 9:41 am
by julianr
I am not sure that the exact same stretch is on both images but it looks like vignetting - have you dialed in the correct backfocus from the reducer? If you have then good flats should fix it

Sent from my SM-G900F using Xparent Skyblue Tapatalk 2

Re: Meade f/6.3 Focal Reducer gives some very unexpected res

PostPosted: Sat Apr 01, 2017 2:53 pm
by rtemen
julianr wrote:I am not sure that the exact same stretch is on both images but it looks like vignetting - have you dialed in the correct backfocus from the reducer? If you have then good flats should fix it

Sent from my SM-G900F using Xparent Skyblue Tapatalk 2


Please explain what it means:

have you dialed in the correct backfocus from the reducer?

I am not sure what this means.

Rich

Re: Meade f/6.3 Focal Reducer gives some very unexpected res

PostPosted: Sat Apr 01, 2017 3:08 pm
by carastro
All reducers have to have a correct spacing between the sensor of the camera to the lens of the reducer (some manufacturers give that space to the edge of the spacer, so you need to check the spacing on the reducer you bought.

This will make a lot of difference to the shape of stars in the corners of images.

When you use a focal reducer it also speeds up the optics so everything needs to be more accurate. But you can capture data much more quickly.

It definitely looks like vignetting, and this is normal for imaging, taking of flat fields and applying them in the stacking procedure will counteract this.

To my eye these photos don;t look like the same field of view even allowing for the reducer increasing the FOV, though that shouldn't make any difference to the results.

Carole

Re: Meade f/6.3 Focal Reducer gives some very unexpected res

PostPosted: Sat Apr 01, 2017 3:52 pm
by purgitoria
Basically what you need to work out is 2 things; firstly whether you have thew older or newer reducer as this will greatly affect what the spacing needs to be. You will then need to work out the backfocus of your camera, if you could let us know what camera setup you have we could help you work that out.
Once you know these values we have a starting point and can proceed as follows:
For the older reducer the backfocus was 100mm meaning you need to have a spacing of 100mm from the glass of the reducer to your camera sensor for the optimum image quality so in most cases this would require that you install some additional spacers/extension tubes to make up this quite large distance.
For the newer reducer the backfocus is 45mm from the glass of the reducer to the camera sensor and depending on exactly what camera setup you are using this may be more difficult to achieve if you have a filter whell attached to the camera but should still be achievable but may still require a small extension tube to get the correct distance. From what i recall Meade id at one point offer an adjustable T-thread adapter to allow fine tuning of the backfocus distance.

There is a long discussion topic on the yahoo group site if you are a member available here https://groups.yahoo.com/neo/groups/LX200GPS/conversations/topics/119127

Re: Meade f/6.3 Focal Reducer gives some very unexpected res

PostPosted: Sat Apr 01, 2017 8:27 pm
by rtemen
Here is the list of my equipment.

Celestron C11 OTA
Canon T3i (EOS 600D)
KoWI LMA-TM_EOS AP306 T-Ring
Various T-Ring Adapters
Meade Series 4000 f/6.3Focal Reducer/Field Flattener Multi Coated China

I don't now how to tell if I have the old or newer Reducer. Anyone know how to tell?

Rich

Re: Meade f/6.3 Focal Reducer gives some very unexpected res

PostPosted: Sat Apr 01, 2017 8:58 pm
by purgitoria
From what i recall the 4000 series reducer is the newer model which would give it an optimal backfocus distance of 45mm. The backfocus of your camera however without the T-Ring adapter added is already 44mm which means that once you add the T-Ring adapter you will probably be more than the optimal distance. I would suggest you first try correcting with flat frames as suggested by Carole or Julian to see what difference that make but if that does not provide optimal imaging quality then i would suggest swapping the Meade reducer for the Celestron F6.3 reducer which i think has a backfocus distance of 105mm and will allow you to install your camera, T-ring adapter and an additional 50mm spacer which should have you at the right spacing.

Re: Meade f/6.3 Focal Reducer gives some very unexpected res

PostPosted: Sat Apr 01, 2017 9:25 pm
by rtemen
Thanks for all of the information.
Do you know what the older model of the Meade unit was?
I have read online that meade used to make them in Japan, but then moved to China. The authors of this info were implying that the Japanese model worked better. Perhaps, the Japanese units were the 105mm???
How do we know for sure that the Celestron unit is 105mm?
I cannot find that level of technical info on their websites.
Sigh.
And then to top it off, it is Saturday, and neither company has any assistance until Monday.

Rich

Re: Meade f/6.3 Focal Reducer gives some very unexpected res

PostPosted: Sat Apr 01, 2017 10:07 pm
by purgitoria
The spacing information can be found here and came from the Celestron usergroup forum in the link found on this page but i am not a member so i cannot access the original documentation http://www.astrotarp.com/Focal_Reducer_Distance_to_Sensor_Page.html
I am not 100% sure on the Meade reducer but i think they just referred to it as the F6.3 reducer and it did not have the 4000 series demarcation on it, i think i may have one in a box somewhere i got with the 12" LX200 i bought many years ago as it was when they first released that series, i recall because mine has the original "R" suffix that they ended up getting taken to court for and ordered to remove from the product name so my reducer should be that old version. If in any doubt you should be able to reference the product number on the side of the reducer (if it is is on there or on the box) as the new version should have the #07545 product code and that will have the 45mm backfocus. Think i also have the 3.3 reducer that is no longer manufactured as well but it was never really very good for anything other than very small camera sensors due to the amount of comma it caused.
As i mentioned try first taking flats and calibrating the images as if you are close enough that may just be enough to correct the image.

Re: Meade f/6.3 Focal Reducer gives some very unexpected res

PostPosted: Sun Apr 02, 2017 10:05 am
by carastro
If you bought it from a retailer they should be able to tell you.

Carole