Jump to content

NLCbanner2024.jpg.2478be509670e60c2d6efd04834b8b47.jpg

MN190 and a focal reducer

Catanonia

By Catanonia
in Imaging - Discussion

Recommended Posts

nightvision

nightvision

Posted
Posted

Just completed fitting of reducer inside EOS adapter. Fitted to 100ED, noted apparent vignetting through the viewfinder. Inward focus no longer seems to be a problem, focused on distant trees and I still had 65mm to spare.

Took some test images, very little vignetting on the image but shows on the flat. Result ED100-F9 now F6. :)

I don't have any before images (and I don't want to remove the reducer) but here are some after images and a flat showing the vignetting. I will try to set up a flat test object and see how good the focus is at the edges.

post-24562-133877564524_thumb.jpg

post-24562-133877564531_thumb.jpg

post-24562-133877564538_thumb.jpg

Link to comment
Share on other sites
  • Replies 71
  • Created
  • Last Reply
Catanonia

Catanonia

Posted
  • Author
Posted

Well update.

The extension rings arrived and it all fits together absolutely perfect.

Even unscrewed the reducer glass and turned it around in the housing so it should work correctly.

By my calculations, the reducer to chip distance is about 40mm. Need to measure precisely.

Some photos

Just need to clean everything, put it together and test on a star field now.

By calculations I should now have the MN190 down from 1000mm F5.3 to 750mm F3.9 with inward travel to focus of 13.9mm out of the 19mm I have spare

post-16631-133877564772_thumb.jpg

post-16631-133877564776_thumb.jpg

Link to comment
Share on other sites
nightvision

nightvision

Posted
Posted

That looks like it has worked out great, I am not familiar with the arrangement you have, did the reducer just fit inside the M54 extender which then split your FW nosepiece as in your drawing below but with reducer flip round the correct way?

It looks like you have solved the inward focus issues. :)

post-24562-133877564809_thumb.jpg

Link to comment
Share on other sites
Catanonia

Catanonia

Posted
  • Author
Posted

The reducer glass was flipped in its housing and screwed in backwards into the 2inch nose piece. The 2 inch nosepiece has M54 connectors to the filter wheel so yes the M54 extender just shrouded the whole assembly.

basically the reducer is sat inside of the M54 connections with the actual glass of it inside the filter wheel :)

Link to comment
Share on other sites
Catanonia

Catanonia

Posted
  • Author
Posted
That sounds very slick, can you get focus? I just tried my F5 300mm Newt and it gives F3.5 but I would need a very low profile focuser. Would only do this if I ever get round to building my guided dob project!

Can't until tell until nighttime as using a CCD camera.

Looks like some clear skies tonight for a test with and without the mod.

Fingers crossed, a 190mm F3.9 astrograph :) Vignetting is around the 29mm mark so will definately need flats to compensate, but should be great for galaxies etc in the 750mm focal lengh.

Lets hope the Antares glass does its job ok.

All cleaned assembled and ready to go :(

Link to comment
Share on other sites
Catanonia

Catanonia

Posted
  • Author
Posted

BAD NEWS...

Easily got focus and near the center of the FOV the stars were great, but 1/2 way across the chip they were badly distorted :)

Oh well, it was an elegant solution, but unfortunately it didn't work as planned.

Will post some images later.

Link to comment
Share on other sites
riklaunim

riklaunim

Posted
Posted

Got that effect too, but that was much stronger reduction factor. That's some sort of field curvature added by the reducer. Maybe you could try a f/6.4 SCT reducer/corrector? (or "Antares 2 inch 0.7x Focal Reducer" as description says it uses the same optics). Or refractor 0.8x field flattener? :)

Link to comment
Share on other sites
nightvision

nightvision

Posted
Posted

Completed a basic test of the reducer in a ED100 F9 refractor.

The degradation is noticeable at the edge.

'Starry Heavens' text is centre frame.

'Phases of the Moon' text is in the corner of the frame with no reducer and further towards the centre with the reducer.

Lower 2 images are with the reducer installed. It seems with the reducer installed the centre can look sharper.

The 'December 2005' text looks sharper with the reducer because it is closer to the centre of the image due to the image down scaling.

Conclusion: It's no way to deliver a larger field due to degradation of the new area but it does deliver a brighter sharp image over a smaller area of the CCD. The camera selected 1/250 with the Reducer and 1/125 without. So a smaller brighter sharp image area is possible and shorter exposure times. Not sure if this can be considered advantageous. I have shown in the final image what I think is the approximate usable area for imaging.

I don't think I'll be using it for imaging. It may well be going into my latest DIY guide scope. :)

post-24562-133877565837_thumb.jpg

post-24562-133877565846_thumb.jpg

post-24562-133877565854_thumb.jpg

post-24562-13387756586_thumb.jpg

post-24562-133877565867_thumb.jpg

Link to comment
Share on other sites
nightvision

nightvision

Posted
Posted

A question for the for those with imaging experience. Using this reducer effectively results in a sharp usable chip area of about 3mp from the 300D 6mp CCD and exposure times that are halved. This seems like something worthwhile especially if tracking or guiding becomes an issue with long exposures.

Have I got this correct? I can still see benefits from using this sort of device, they are not an increased usable FOV, they are not being able to use the whole CCD image but they are shorter exposure times and possibly easier focusing.

Link to comment
Share on other sites
Catanonia

Catanonia

Posted
  • Author
Posted

To be honest I wouldn't even consider it now for any type of imaging or even guiding due to the degradation.

See this link... This is where I got the inspiration for this thread from

POWERNEWT TELESCOPE

This uses exactly the same principle of a focal reducer in the focuser. However the one they use with this scope is specifically designed for the scope.

Link to comment
Share on other sites
Coco

Coco

Posted
Posted

Celestron are rumoured to be bringing out a reducer for the already flat Edge scopes, this should be worth a look at when it eventually arrives.. the Edge scopes are surly over due a reducer..

Link to comment
Share on other sites
Coco

Coco

Posted
Posted
To be honest I wouldn't even consider it now for any type of imaging or even guiding due to the degradation.

See this link... This is where I got the inspiration for this thread from

POWERNEWT TELESCOPE

This uses exactly the same principle of a focal reducer in the focuser. However the one they use with this scope is specifically designed for the scope.

PM Boren Simon.. Stargazers Lounge - View Profile: Boren

its his website...

Link to comment
Share on other sites
Catanonia

Catanonia

Posted
  • Author
Posted
It was worth a try, the powernewts I note dont have a front corrector already insitu unlike the SW 190.

Quite correct, they use the reducer in the focuser to reduce and correct the image to F2.8

This is probably the problem I have with the corrected image then reduced in the MN190 and hence all the curvature issues.

Link to comment
Share on other sites
  • 1 year later...
Catanonia

Catanonia

Posted
  • Author
Posted
Hi, i am italian.

I have MN190.

Am ende....we can reduce the focal length without distortion or not?

Old thread and no is the answer, well not easily or cost effectively. I ended up getting a powernewt.

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.