piggybacked 'Newt' = Lensless Schmidt camera

[nytecam]

After earlier recollimating my quasi-Newt I've now converted it into a Lensless Schmidt camera [LSC] by adding a 90mm 'hole' at the mirror radius and images are much sharper. 

Await some decent clear and may be moonfree nights to do better than last night's tests on M57 etc.  More details on my SGL DIY forum post and http://home.freeuk.com/m.gavin/lscmg.htm      

[NickK]

Is the aperture smaller than the primary mirror?

[RobertI]

Fascinating stuff. Interesting project. Do you have any images comparing the standard setup (with the corrector lens in place) with the revised setup with the 'hole' and without the hole? No getting away from the fact that it is a sharp image.

[nytecam]

Thanks Nick & Rob for your interest - most queries are probably answered @ http://home.freeuk.com/m.gavin/lscmg.htm and my old article @ http://home.freeuk.com/m.gavin/schmidt_lens.htm

Here's a recent M27 in 60s exp via LSC

and 'Newt' - without aperture mask

showing the coma-free images via the LSC.  I'm doing a short YT vid on the recent work plus the few images I've captured so far. 

Rob - any option with glass corrector plate would be prohibitably expensive and against the principle of a made do and mend project

Might be worth checking Meade dealer's skip as these scopes rated v.poorly in their Jones-Bird incarnation.  

[nytecam]

Tweaked the aperture mask position and shot brief images last night [full moon+cirrus haze] using LL#0.10 - here's an x1.5 enlarged negative of Vega field [click image for full size !] that shows coma-free stars images to the edge that is very pleasing indeed - proof the 90mm aperture 'Lensless' option works. Results much superior to the raw quasi-Newt without aperture mask with coma like stars over most of the fov away from the centre.

Faint stars' mags added from Sloan DSS reference. No darks flats used in 1x15s exposure.

[RobertI]

What a result from such a simple modification. I realise of course that it's 'simplicity' belies the research, experimentation and expertise behind it all!

[nytecam]

What a result from such a simple modification. I realise of course that it's 'simplicity' belies the research, experimentation and expertise behind it all!

Thanks Rob - DavidG in the States @ http://www.cloudynights.com/topic/474788-lensless-schmidt-camera-updated/ has done some Oslo spot diagrams of star images from my LSC with 75mm and 90mm aperture masks and finds the images excellent and may resurrect his old Coulter LSC kit mirror from the 1970s for same.;-)

[nytecam]

Despite suggesting elsewhere to leave alone and just image I haven't. Yesterday I modded the aperture mask [see pics] from 90mm f/5 to 100mm f/4.5 to increase light throughput. Brief tests on Vega field was good - tight + round coma-free images to the edge.

Still amazed how a simple 'hole' so effectively sharpens stars images - when I remove the mask to the full 114mm 'naked' aperture coma is rampant. Await a really clear night for more tests and DSO imaging. ;-)

[Martin Meredith]

Despite suggesting elsewhere to leave alone and just image I haven't. Yesterday I modded the aperture mask [see pics] from 90mm f/5 to 100mm f/4.5 to increase light throughput. Brief tests on Vega field was good - tight + round coma-free images to the edge.

Still amazed how a simple 'hole' so effectively sharpens stars images - when I remove the mask to the full 114mm 'naked' aperture coma is rampant. Await a really clear night for more tests and DSO imaging. ;-)

It is amazing and presumably says something about how difficult it is to get the reflections from the outer regions of the primary to line up in focus with the remaining reflections for a fast mirror? I don't know anything about lensless Schmidt camera principles, but presumably when you change the mask diameter you also have to change the distance from the primary to get the desired effective focal length? I'm also wondering if one could combine the lensless Schmidt with a light occluder/dew shield.

cheers

Martin