23 replies to this topic

[GaryShaw]

Hi All:

 

I've been observing with a smallish Schmidt Newtonian which has been totally terrific for the astronomy that I'm doing. As with many of us though, I've developed an interest in having a bit more aperture but I haven't been able to find a larger one somewhere in the F-range I noted above.

 

Thank you for any suggestions to help me find one.

Gary

[jrcrilly]

Meade used to offer a 10" F/4 Schmidt-Newt. I doubt that they still do but there be some second hand ones out there. If you want faster optics, that 294 camera would work well on a Rowe-Ackerman like the 8" or 11" RASA.

[GaryShaw]

Thank you!
I’ll start looking.

[coopman]

There are numerous f/4 imaging newtonians available (no corrector plate to dew up on you), and I see that you have one of those already.  You'd need to use a coma corrector with them though. 

Try placing a wanted ad here in the classifieds and at astromart.com.  You might get lucky & find one.        

[coopman]

Several Meade 10" S/N scopes have been sold on Astromart this year, one as recently as last week.  Note that this OTA weighs approx. 45 pounds.  It's a beast!  

[coopman]

There are some very fast Newt. OTAs here but they aren't cheap:

https://www.teleskop...-corrector.html

[GaryShaw]

Thank you but I'm not seeing any fast Schmidt Newtonians there. That is what I am specifically looking for.

Gary

[junomike]

Meade SN 8" F4 and 10" F4 seem to be the only offerings (used).

 

Need to ask why it has to be a SN?

[GaryShaw]

Mike, I guess its a bit like religion, color and politics - personal preference.

Cheers,

Gary

[Jon Isaacs]

Mike, I guess its a bit like religion, color and politics - personal preference.

Cheers,

Gary

 

If you want to understand why SNs are uncommon, particularly in the larger sizes:

 

From a practical standpoint, Schmidt-Newtonians only correct about 1/2 the coma so compared to a standard Newtonian with a coma corrector, they're not well corrected. This would be worse at F/2.8-F/3.5 since coma is severe at these focal ratios. A Paracorr 2 full corrects the coma across a 46 mm field at F/3.5.. widest possible In a 2 inch format.

 

The corrector is fragile and prone to sewing up. It makes the scope heavy..

 

Jon

[coopman]

Jon meant "prone to dewing up".  

[stargazer193857]

Meade used to offer a 10" F/4 Schmidt-Newt. I doubt that they still do but there be some second hand ones out there. If you want faster optics, that 294 camera would work well on a Rowe-Ackerman like the 8" or 11" RASA.

That may have been the 10" f4 Schmidt newt I looked through with a 24mm ES 82 degree eyepiece at the Andromeda galaxy. Bright.

[stargazer193857]

If you want to understand why SNs are uncommon, particularly in the larger sizes:

From a practical standpoint, Schmidt-Newtonians only correct about 1/2 the coma so compared to a standard Newtonian with a coma corrector, they're not well corrected. This would be worse at F/2.8-F/3.5 since coma is severe at these focal ratios. A Paracorr 2 full corrects the coma across a 46 mm field at F/3.5.. widest possible In a 2 inch format.

The corrector is fragile and prone to sewing up. It makes the scope heavy..

Jon

And I thought mechanical load on the optical window and weight were the only issues. Thanks for telling me about the dew and coma.

I wonder how much coma an f5 achromat has compared to an f5 parabolic newt.

Edited by stargazer193857, 22 November 2020 - 09:33 PM.

[coopman]

A short focal length refractor will have spherical and chromatic aberrations.     

[Eddgie]

And I thought mechanical load on the optical window and weight were the only issues. Thanks for telling me about the dew and coma.

I wonder how much coma an f5 achromat has compared to an f5 parabolic newt.

An air spaced doublet should be coma free.  It would though have very pronounced field curvature, but that can be fixed with a flattener. These are among the worst telescopes I have ever owned and do not recommend them to anyone for anything when there are inexpensive ED scopes out there that can do everything better. 

 

Another option would be a used Televue Genesis SDF or later Televue 101 family of scopes.  Very flat field and well corrected for color.  

 

If you want to go faster, you can get imaging Newtonians down to f/2.8.

Edited by Eddgie, 23 November 2020 - 10:41 AM.

[junomike]

If you want to understand why SNs are uncommon, particularly in the larger sizes:

 

From a practical standpoint, Schmidt-Newtonians only correct about 1/2 the coma so compared to a standard Newtonian with a coma corrector, they're not well corrected. This would be worse at F/2.8-F/3.5 since coma is severe at these focal ratios. A Paracorr 2 full corrects the coma across a 46 mm field at F/3.5.. widest possible In a 2 inch format.

 

The corrector is fragile and prone to sewing up. It makes the scope heavy..

 

Jon

Jon, I find that my Meade SN10 is better corrected using a Coma Corrector than a standard/conventional Newt.  Also, the Secondaary on my SW 12 Dews up as much as the Corrector on the SN10 however the big buzzkill for me on the SN is cooling.  Takes forever....

[KLWalsh]

Several Meade 10" S/N scopes have been sold on Astromart this year, one as recently as last week.  Note that this OTA weighs approx. 45 pounds.  It's a beast!  

No, an SN-10 is closer to 23 lbs. I have one and my CGEM easily handles it.

In terms of weight and balance, the corrector places the COG nicely near the middle of the tube, unlike a standard Newt that is primary-end heavy, with the eyepiece high above the saddle.

 

The Schmidt corrector fixes much, but not all, of the coma. For visual use, that’s usually adequate correction for moderately wide FOVs.

For AP a Baader MPCCIII corrects the coma for a full-frame sensor, but works best at a 49 mm flange distance instead of (the typical) 55 mm. If you have an APS-C or smaller sensor, you probably won’t need a coma corrector.

 

As with any Schmidt corrector it will collect dew. There are Dew-Not straps and Astro-Zap shields that fit the SN-10.
 

[jrcrilly]

No, an SN-10 is closer to 23 lbs. I have one and my CGEM easily handles it.

The poster may have been thinking of the 12" model. I have owned both, and the 12" is MUCH heavier than the 10".

[Jon Isaacs]

Jon, I find that my Meade SN10 is better corrected using a Coma Corrector than a standard/conventional Newt.  Also, the Secondaary on my SW 12 Dews up as much as the Corrector on the SN10 however the big buzzkill for me on the SN is cooling.  Takes forever....

 

 

That would be strange.  The Paracorr 2 fully corrects for coma at F/3.5... 

 

Jon

[rutherfordt]

The poster may have been thinking of the 12" model. I have owned both, and the 12" is MUCH heavier than the 10".

Jon,

 

I don't believe that there is a 12-inch one-- Meade only made them in 6, 8, and 10-inches.  You might be thinking of a Schmidt-Cassegrain instead of a Schmidt-Newtonian.

[jschner]

I saw the back and forth on the SN-10 weight,  just weighed the OTA with rings, 12" dovetail and Moonlight focuser. No finder or eyepiece and it was 38lbs. It's heavy. 

[Eddgie]

I saw the back and forth on the SN-10 weight,  just weighed the OTA with rings, 12" dovetail and Moonlight focuser. No finder or eyepiece and it was 38lbs. It's heavy. 

Not surprised.  A 10" f/5 Newtonian is usually about 35 lbs and I could not see for the life of me how the Meade 10" would weigh much less than this. 

 

There may be some other larger SNs out there, but the Meade is the only one I know of. 

 

I get someone wanting what they want, but something like the 10" Boren-Simon is likely a far better choice for imaging.  f/2.8 and very sharp.  Carbon Fiber tube so weight is around 30 lbs with rings.

 

So yeah, the Meade is the only SN I see come up for sale in the 10" size, and I have never seen a 12" SN.

 

Sub aperture correctors have made coma a thing of the past and if diffraction spikes are the worry, curved vane spiders will fix that.  No one really ever made SNs faster than f/3.6 that I know of and those were only available in 5.5".

[junomike]

I saw the back and forth on the SN-10 weight,  just weighed the OTA with rings, 12" dovetail and Moonlight focuser. No finder or eyepiece and it was 38lbs. It's heavy. 

Mine clocks in the same.  My AT12 F4 clocks in close to 50lbs......Not light when you get up in aperture.

[shark-bait]

I own an SN10 and it has fantastic optics. I do not use a coma corrector and it is a visually stunning scope. Weight is an issue for AP. My CGEM DX that has been Hypertuned handles it with an autoguider but it is taxed. I do not notice a lot of coma with a crop sensor nor visually with premium eye pieces. I also do not have dew issues on the corrector with an Astrozap metal dew shield. I really love that scope.