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Using a 4" Schiefspiengler?

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#1 StarDusty

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Posted 20 January 2013 - 10:26 AM

I built a 4" Schiefspiegler as seen at:

http://www.clearskyo...-schiefspiegler

To-date I have used it mainly for webcamming doubles as documented at:

http://www.clearskyo...red-double-star

I really have not used it than much for visual double star observation. This is a 4" f/29 Schief.

Although I have completed the AL double star list using a 16" f/4.5 Newtonian a few years ago by stopping it down to a 6" diameter between the spider vanes for the tighter doubles, I can see I do not have the experience many in this forum have with visual observation of doubles.

Do you think my 4" Schief would work well for visual double star observation? I think the shortest eyepiece I have is a 6mm TMB.

#2 Ed Wiley

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Posted 20 January 2013 - 12:52 PM

Allen: If you can web-cam them the scope should be great for visual doubles. Were your measures calibrated for plate scale and orientation? (I did not read the material carefully...). If so, you should not only use it for visual double observation, you should publish your measures in an appropriate journal such as JDSO.

Good measures!

Ed

#3 StarDusty

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Posted 20 January 2013 - 04:15 PM

The closest double I have been able to image with the webcam was HR 8040, 20585+5028, STF2741AB at just under 2 arcseonds.

#4 WRAK

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Posted 20 January 2013 - 05:10 PM

It is certainly fascinating to handycraft your own scope - congratulations. Concerning the optical features of a Schief for observing double stars I am somewhat unsure - it seems to combine the disadvantage of a refractor for splitting close equal bright doubles with the disadvantages of a reflector like collimation, coma, thermal issues and so on.
Wilfried

#5 Ed Wiley

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Posted 20 January 2013 - 10:01 PM

Allen,

I am sure you have found the power of Reduce to analyze your data and 2" is very impressive. Have you tried the autocorrelation routines and reeling off 1000 frames at something like 30 milliseconds?

Ed

#6 StarDusty

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Posted 20 January 2013 - 11:09 PM

Yes I am using Reduc. It took a few weeks but I went back through all my avi files from two years back an ran them through Reduc.

#7 azure1961p

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Posted 21 January 2013 - 12:08 AM

I think it'd be a terrific system and particularly in unequal doubles.

Pete

#8 Rich (RLTYS)

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Posted 21 January 2013 - 06:33 AM

A 4" Schiefspiengler would work quite well on doubles. Go for it. :jump:

Rich (RLTYS)

#9 DAVIDG

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Posted 21 January 2013 - 03:08 PM

I've been using my 4.25" homemade Schief for years for visual double star observing and find it be one the very best opticals system for this type of work. You have unobstructed system so there are no diffraction spikes to hide one of the pair. The unobstructed system also gives a visually appealing round Airy disk with clean diffraction rings. You have a perfectly achromatic system so both visually and for imaging the star images are not increased in diameter by chromatic aberration which makes it easier to see and image a very tight split. The perfectly color corrected system also allows you to see the true colors of the pair, which too me is half the fun of double star viewing. You also have a long focal length so you can use longer focal length eyepieces to achieve high power. My favorite is a vintage 16.3mm Galoc for splitting doubles.

- Dave

#10 azure1961p

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Posted 21 January 2013 - 06:08 PM

Dave,
I knew a fellow who was actually building a Schiefspiegler but he mentioned that due to the optical configuration the Iry fisc would be slightly ovular. Not due to Astiatism or poor optics but apparently a product of tilted components or some such. He was never clear and I lost touch with the guy. Have you found the airy discs out of round at all?

Pete

#11 StarDusty

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Posted 21 January 2013 - 10:47 PM

One time I removed the front plate of my Schief to clean the secondary and I replaced the front plate without re-collimation of the scope. I imaged a bright double and the stars were ovalized a small amount. I re-collimated and the stars were no longer ovals. So no I do not believe a Schief makes stars oval.

#12 DAVIDG

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Posted 22 January 2013 - 11:20 AM

Dave,
I knew a fellow who was actually building a Schiefspiegler but he mentioned that due to the optical configuration the Iry fisc would be slightly ovular. Not due to Astiatism or poor optics but apparently a product of tilted components or some such. He was never clear and I lost touch with the guy. Have you found the airy discs out of round at all?

Pete


Pete,
I've been designing and building Schief for a number of years. Both by raytracing and by actual use, they produce perfectly round Airy disks when correctly built and collimated. My 4.25" won first place in the optical judging at Stellafane a few years ago, and it won't have been given any level of award if there was any hint of non round Airy disk.
Visually they are excellent in high resolution observing, and especially suited for double star work. Like I was saying since they have no chromatic aberration the color of the stars you see is true and for imaging the lack of chromatic aberrations produces smaller star images that allow better determination of seperation distants.

- Dave

#13 azure1961p

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Posted 22 January 2013 - 11:04 PM

That's good to hear. It's too bad these scopes are so rarefied. The owners swear by them across the board.

Methinks my old friend might not have investigated the causes thoroughly enough.

Pete






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