More flattener reducer questions....

[StargeezerTim]

Hi folks,

I have had an issue with large/out of focus stars on the edge of my images. I am using a Altair Astro 72 ED-R scope with a lightwave 0.8 reducer/flattener.

I recently replaced the flattener and have tried adding spacers. I have found that adding .6mm gives the sharpest image.

This is an example of a recent sub. Its not perfect but by working on the stars in post processing I find I can get a reasonable image. 

The stars at the outer edges are larger than those nearer the centre. I may well be able to improve further slightly with spacing but it seems that the outer stars are consistently larger than the rest. I have a couple of Q's.

1. I am thinking of trying a flattener without a reducer function. Does anyone know if flatteners without reducers are optically better than a flattener/reducer combined?

2. Any other suggestions for improving the result? As i said, with lots of processing I can get a fair image but it would be nice to not to have to do that!

3. Is there any free software that I could use to check the tilt etc of the image? I do have Max Selector but it only accepts FIT files. I can convert to FTS files in DSS it won't accept that. Again, if anyone has any ideas or solutions, I would be very grateful!

 

Sorry if this is a bit of a rambling post or lacks focus. I am OK about accepting that the quality of image I get is the best poss from the scope, and I am generally really happy with the scope, but if I can improve it, then I would be delighted!

Thank you...

edit... should say, I image with a DSLR (100D)

[libraryman]

Hi Tim, I can put any images through CCD inspector if you wish..

hth

Ray

[StargeezerTim]

On 11/10/2016 at 13:13, libraryman said:

Hi Tim, I can put any images through CCD inspector if you wish..

hth

Ray

Thanks Ray, that has been very helpful in sorting out how much added space is best for my setup.

I am still unsure whether you can expect better optics from a flattener as opposed to a flattener/reducer? I have been looking at the skywatcher or hotech flatteners but would hope to get some feedback from some stargazers before i commit.

 

 

[silios]

Hi Tim!

i'll hazard a guess here, since that jpeg has too small stars for my eyes even at full res
Something is a bit miss-alligned in your imaging train (i hope its not the primary optics -  objective tilt (miscollimation) but that could be easily ruled out by removing the flattener and taking an image ).
Most propable culprits would be the focuser and the flatener it self. I would check those firstly. Do you have some images of the whole image train?
That guess stems from the halo in your centre star having its largest part in the same corner as the bottom left out of focus stars.
I hope i'm making sense

 

BUT
the sensor on that 100D is quite big and to have it corrected to the edges is really tricky in my experience (actually not possible from what i have seen up to this day).
I am talking about sub-millimetre spacing adjustments required and to use techniques such as 2/3rds focusing (physchobilly and uranium have posts about that here).
Have a look at this thread for some very good advices i got from fellow SGL'ers https://stargazerslounge.com/topic/249588-sw-ed80-reducer-elongated-stars-problem/
The https://www.astronomics.com/astro-tech-2-inch-field-flattener-astro-tech-tmb-refractors_p17393.aspx has been used widely in many scopes (ED80 league) by fellow astronomers with great results (not with that big sensor such as yours KAF8300 size) but maybe someone with your specific scope can drop in and suggest something that matches your setup even better.

 

 

[StargeezerTim]

4 hours ago, silios said:

Hi Tim!

i'll hazard a guess here, since that jpeg has too small stars for my eyes even at full res
Something is a bit miss-alligned in your imaging train (i hope its not the primary optics -  objective tilt (miscollimation) but that could be easily ruled out by removing the flattener and taking an image ).
Most propable culprits would be the focuser and the flatener it self. I would check those firstly. Do you have some images of the whole image train?
That guess stems from the halo in your centre star having its largest part in the same corner as the bottom left out of focus stars.
I hope i'm 

BUT
the sensor on that 100D is quite big and to have it corrected to the edges is really tricky in my experience (actually not possible from what i have seen up to this day).
I am talking about sub-millimetre spacing adjustments required and to use techniques such as 2/3rds focusing (physchobilly and uranium have posts about that here).
Have a look at this thread for some very good advices i got from fellow SGL'ers https://stargazerslounge.com/topic/249588-sw-ed80-reducer-elongated-stars-problem/
The https://www.astronomics.com/astro-tech-2-inch-field-flattener-astro-tech-tmb-refractors_p17393.aspx has been used widely in many scopes (ED80 league) by fellow astronomers with great results (not with that big sensor such as yours KAF8300 size) but maybe someone with your specific scope can drop in and suggest something that matches your setup even better.

 

 

Thanks Silios,

I'm working on sub mm spacing at the moment. The Delrin spacers are actually too large. It looks like I need about .3 or .4 mm space added (home made cardboard cutouts will hopefully do the trick!). I'll also try the 2/3rds focusing technique. I do that on images I take with Lens but never really thought to try it with a scope. Just need some clear skies to carry on.

As you say, hopefully someone will be able to give some ideas about a decent flattener for my setup. I'd still like some thoughts on Flatteners vs Flattener/reducers. My hunch is that a flattener should work better that a flattener/reducer but I'm sure there are people here with great optical knowledge who could bear out or refute my hunch.

Cheers, Tim. 

[Jessun]

Hi!

The top image shows stars that are somewhat stretched towards the edges - like the moment before the 'jump to light speed'. That indicates that the reducer is too close still. But probably only by a smidge. It may well be that you are at the limit of what your optics can produce for that sensor size.

/Jesper

[StargeezerTim]

This is from last night with two thicknesses of card as spacers. It's probably about .4mm and is much better than .2 or .6mm. So much for a tolerance!

Anyway, I'm pleased with this, much easier to edit the stars and retain 98% of the FoV now .

I would still like to hear if anyone knows the optical qualities of Flatteners as opposed to Flattener/reducers (image wise...I know the F stays the same and longer subs are needed and smaller FoV). Cheers...