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Meade SN8" vs. New Refractor

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#1 forestc

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Posted 06 August 2014 - 09:57 PM

Alright folks, 

 

I've been scouring the web for the answer to my question, but I feel the only way to get a good answer is to ask the wonderful people of CN. I bought a Meade LXD-75 SN8 about 2 years ago (not knowing anything about what to buy) and since then have grown more and more fond of deep-sky astrophotography. I built my own observatory, upgraded to a moonlit focuses, got a modified camera and upgraded my mount to a Losmandy Gemini II. I still am disappointed with my photos though. My stars are never round on the edges, my telescope won't seem to stay collimated and I feel like my corrector plate is misaligned...

 

My question is this: I have a bit of money that I would like to sink into really getting myself setup for a few years of happy deep-sky astrophotography. I would like to get what I need to allow myself to get the beautiful images I keep seeing all of you posting. Would it be smart to upgrade my telescope? I was thinking of an ES102mm APO or maybe an ES80mm APO? Or the much cheaper ES152 Achromatic? 

 

I have about $1500 to $2000 to work with. Is this a smart upgrade, or should I spend the money trying to get my current telescope to work? I know the answer might just be that I need more time to practice, and I totally would understand that as well. It's just looking around on AstroBin there are very few images taken with a Meade SN8.

 

Thanks for all of your help! 

 

Forest



#2 jgraham

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Posted 06 August 2014 - 10:33 PM

Hmmm, I've been imaging with stock SN6s and SN8s for years and I absolutely love them! I've heard that you can improve the image quality of the SNs by adding a Paracorr. That should clean up the edges of the field. Any simple telescope (and a refractor doubet/triplet is a simple telescope) is going to have varying degrees of coma and field curvature. A refractor will require a field flatenner to get results better than what you are getting now with the SN8. I suspect that you'll be trading one set of issues for another. But that s not necessarily a bad thing.



#3 shawnhar

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Posted 06 August 2014 - 10:42 PM

"Round on the edges"...LOL, how much money you got? And what are your expectations?

  I imaged with a 10" SCT and a 6.3 focal reducer for a couple of years and lived with bad stars around the edge. I just borrowed a Meade SN6 and to me it's awesome...because...I went from .75 arcsec per pixel to 1.5 in resolution. I don't know what you consider bad, but APO's need a field flattener too.

 I think you should browse Astrobin and post some links of images you like, then folks can make suggestions.

(and PM me with what you are willing to sell the SN8 for, by the time you are ready, I might be interested in buying it from you. I would try to talk you into trading for my Meade 10" SCT, but that would be wrong, just plain wrong if you are looking for better stars :lol: )



#4 forestc

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Posted 06 August 2014 - 10:43 PM

Ok. Haha. Cancel my question. I just needed some reassurance. 


Edited by forestc, 06 August 2014 - 10:45 PM.


#5 jzeiders

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Posted 06 August 2014 - 11:36 PM

I have a Meade SN 8 and am currently working on getting it sorted. So far with an APS-C camera it looks quite good. No coma corrector used for this shot, but I did crop it. I also reduced the res down to 1920 to keep file size reasonable.

 

Here is a shot I made with the Meade 8" f/4 Sn;

 

http://s175.photobuc...html?sort=3&o=1

 

That is only a single exposure of 56 seconds a ISO 3200 with  Nikon D90. The D90 has a broadband low pass filter mod but that is all. The image is unguided, no darks, flats, bias, filters, etc. Neither is it a stack of sub exposures. One shot, one frame. I did post process in LR and photoshop to bring out what was there. Click on the magnifier icon at the lower right twice to blow up the image tp flu size. Your scope should be able to do as well or better.

 

The refractor will require lots of accessories, flatteners, correctors, etc. and the exposures will be much longer and require many more of them. Small refractors are deceiving, they look inexpensive and simple, then reality slowly creeps in, a field flattener here, a focal reducer there, oh, yeah, a auto guiding setup, better mount, it never ends.

 

If you really want a great small refractor for Ap, look at the cost of a basic Tak FSQ 106ED. Ouch!

 

Jack



#6 forestc

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Posted 07 August 2014 - 07:56 AM

Well, it seems like I was wrong. That's a beautiful image. Let me ask you all this then: what tools do you use to ensure that your SN telescope is properly aligned? Just a basic collimator, or is there something better?



#7 Madratter

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Posted 07 August 2014 - 09:00 AM

Those and the refractors you mentioned are such different instruments. What do you want to image?



#8 forestc

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Posted 07 August 2014 - 09:43 AM

I mostly would like to photograph DSO's. I really have no interest in solar, lunar or planetary imaging.  



#9 Madratter

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Posted 07 August 2014 - 09:46 AM

Yes, but what sort of DSOs. Imaging small galaxies requires very different equipment than imaging large nebula.



#10 forestc

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Posted 07 August 2014 - 09:55 AM

That's where I'm unsure. I really like the larger nebulas and some smaller galaxies. I'm not really interested in anything really small at this point though. 



#11 shawnhar

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Posted 07 August 2014 - 11:53 AM

I think we need to establish what is "wrong" with the SN8 1st. I have recently borrowed a SN6 and think it's fantastic.

If you could post samples of the stars you are unhappy with, it will give us something to work with. Your version of unhappy could be wildly different than mine.

Here is a crop of the center of an image I too the other night and am still working on processing.

Attached File  center.jpg   168.79KB   1 downloads

 

 and here is the lower left corner, is this what you are seeing with the SN8 that is making you unhappy?>

Attached File  left corner.jpg   116.98KB   1 downloads



#12 shawnhar

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Posted 07 August 2014 - 11:53 AM

And here is the whole thing, looks great at this scale!

Attached File  800.jpg   178.14KB   1 downloads



#13 forestc

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Posted 07 August 2014 - 01:26 PM

Mine look very similar to that, except I seem to be getting coma even in the center of my frames? Here's an un-cropped .fit file from a few nights back. 



#14 shawnhar

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Posted 07 August 2014 - 02:05 PM

I think you should start with the collimation. It looks like you have some nice round stars just to the left and above the Dumbbell, and the further away from that spot, the worse they get. You will have some left over coma, the corrector plate doesn't get rid of all of it, but I would expect less than that.

 

 Being out of collimation will exaggerate the coma, but that almost looks like the focuser is tilted or something.

 I used a celestron combination tool to collimate and aligned like you would a regular newt, what tool are you using? You can also use live view and a bright star, just defocus a hair, just enough to see 4 or 5 diffraction rings. I zoom way in and use the laptop screen so I can see it and the collimation screws at the same time.

  - Good luck!



#15 shawnhar

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Posted 07 August 2014 - 02:10 PM

By the way, focuser sag/tilt or tilted optical path plagues lots of imagers no matter what gear you have, take a look at this image taken with the ES 102 apo you mentioned.http://www.astrobin.com/full/104040/0/



#16 forestc

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Posted 07 August 2014 - 02:41 PM

Thanks for the advice. That helps so much. I just have the simple Orion laser collimator.

 

Is there a way to align the focuser (or whatever is misaligned in the optical path) without just manual guess and check?



#17 jzeiders

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Posted 07 August 2014 - 03:29 PM

I use the cats eye three tool set. I have a variety of scopes so all of them come in handy.

 

Do his in the day time.

 

I start off with a sight tube to make sure the secondary is round and centered in the sight tube. There is a built in offset due to the f/4 system, so be aware of that. You can adjust the cats eye sight tube for your specific system. You want a small concentric black ring around the bright secondary, this makes it easier to see if it appears oblate or prolate. If that is the case the tilt and or rotation is off. I take the primary cell off and start by getting the secondary pointed to show the empty bottom of the tube.  If you need to adjust the rotation of the secondary, you just loosen, NOT remove the retaining ring on the front of the corrector and use the three heavy ribs under the collimating cap to twist it slightly. When you get it right retighten that ring. If you take it off or loosen too much your secondary will fall off. Be carefull. I got my 8" SN cheap because it appears a previous owner made this mistake. There is a scar on the primary and the front of the secondary is chipped, but as you see it works fairly well.

 

After that is squared away I back off the primary locks and adjusters so it sits square in the cell as a starting point. Now you reinstall the primary and screws.

 

With the primary back in the tube you can use a laser, calibrated, to fine tune the secondary by looking at where the spot hits the primary. I put it in the middle of the target ring for now by fine tuning the secondary. I only use a laser for coarse adjustments.

 

Now with a cheshire I adjust the primary to make the target ring and eyepiece hole in the cheshire concentric. This should put you fairly close. 

 

After this comes the tricky part. With the auto-collimator you are working with several reflections and attempting to stack them one on top of the others. this takes great care and many very small adjustments. The objective is to have them all aligned with the three collimating screws equally snug. It can be quite frustrating if working by yourself.

 

For final tweaks, I use an artificial star. In this case a highlight off a insulator on a power pole a few hundred yards away. Use the highlight just like a real star for final tweaks.

 

Hope this helps,

 

jack



#18 shawnhar

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Posted 07 August 2014 - 03:29 PM

So the problem is you might be changing it when you attach the camera. What I am doing and others do as well, is rotate the tube so the focuser is on the bottom, that relieves some of the torsional force.

 The laser is suspect big time, never trust a laser unless you have verified it is in collimation itself, they are notorious for being out. Additionally, that secondary is a royal pain because it's attached to the glass. The laser won't help you here, you need a sight tube to center the secondary under the focuser, that's why I use the combination tool, it does it all.

The best thing is a star, because that is your setup while you are imaging. Attach camera, point to semi bright star, use live view on the screen to zoom way in and see the diffraction rings, bam, no guessing, you wan the secondary done already though at that point.



#19 forestc

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Posted 07 August 2014 - 10:08 PM

Wow, thank you so much. Those descriptions really helped a lot. I just took a look at that Catseye collimator, I might need to get myself one of those.

 

One more question: would it be worth it to purchase the Baader MPCC to further reduce the coma on the edges? Or would something like that actually make the problem worse?

 

Thanks in advance. 



#20 shawnhar

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Posted 07 August 2014 - 10:51 PM

The claim is -  "The MPCC has been tested and found to work well on Meade SN Schmidt-Newtonians."

I can't verify this, but that's what Agena says on their website...

 Since they don't make the SN's anymore, it might be hard to find examples of people using it.



#21 jzeiders

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Posted 07 August 2014 - 11:49 PM

I have the MPCC and he Meade Sn. Unfortunately we are currently under a blanket of smoke from various forrest fires around the state and a bunch of clouds that severely limit any ap testing. I'll make a note to try it next time I take the Sn out. May be a while though. Just a guess, it likely will be fine with a APS-C camera and perhaps less so with a full frame. I know the MPCC fared poorly with the coma of my f/4 Newtonian and a full frame, Nikon D800, camera. It was bad enough I don't use that combination any longer. The coma of the SN is significantly less though.

 

For comparison, here is a shot with the 8" f/4 Newtonian and the D800 with the MPCC of M31;

 

http://jzeiders.phot...0000MhtJtN17J7A

 

The center is fine but I had to crop it a bit. You can see the stars are getting funky about 3/4 out from the center.

 

The M8 image I posted above was a test shot without any corrector at all, the camera was attached to just a T-ring on a 2" tube inserted into the draw tube.

 

I also replaced the stock focuser with a moonlight, vastly better though a bit expensive. You get what you pay for in this case, the 2 speed moonlight is great!

 

Jack



#22 SKYGZR

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Posted 08 August 2014 - 12:00 AM

The claim is -  "The MPCC has been tested and found to work well on Meade SN Schmidt-Newtonians."

I can't verify this, but that's what Agena says on their website...

 Since they don't make the SN's anymore, it might be hard to find examples of people using it.

 

Attached are images taken w/ the SN8 & MPCC (they are cropped a bit), yet the MPCC works as "advertised". (Haven't used it "visually", so can't commet on that). The only issue I seem to have w/the SN8 is reflections on brighter objects (Like M45)..haven't taken the time to track the problem down. Not sure if it's off collimation a bit, or if I have a "back" reflection of some kind. By "back" reflection, I mean the brightness of a cluster of stars like M45, reflecting off the inside of the corrector plate, then hitting the backside of the secondary. The tube is flocked, and pretty much all surfaces have been "blackened", yet still have the issue. (Can't find a "sample image" right now, otherwise I'd post it for evaluation/crituqe.)

Attached Files



#23 forestc

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Posted 08 August 2014 - 08:11 AM

Perfect, it looks like a good investment as long as I don't expect miracles. Thanks you all. You have been such a big help! I can't wait until I can be on the other end of things and answer some of your questions. 



#24 Charlie B

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Posted 08 August 2014 - 04:51 PM

Alright folks, 

 

I've been scouring the web for the answer to my question, but I feel the only way to get a good answer is to ask the wonderful people of CN. I bought a Meade LXD-75 SN8 about 2 years ago (not knowing anything about what to buy) and since then have grown more and more fond of deep-sky astrophotography. I built my own observatory, upgraded to a moonlit focuses, got a modified camera and upgraded my mount to a Losmandy Gemini II. I still am disappointed with my photos though. My stars are never round on the edges, my telescope won't seem to stay collimated and I feel like my corrector plate is misaligned...

 

My question is this: I have a bit of money that I would like to sink into really getting myself setup for a few years of happy deep-sky astrophotography. I would like to get what I need to allow myself to get the beautiful images I keep seeing all of you posting. Would it be smart to upgrade my telescope? I was thinking of an ES102mm APO or maybe an ES80mm APO? Or the much cheaper ES152 Achromatic? 

 

I have about $1500 to $2000 to work with. Is this a smart upgrade, or should I spend the money trying to get my current telescope to work? I know the answer might just be that I need more time to practice, and I totally would understand that as well. It's just looking around on AstroBin there are very few images taken with a Meade SN8.

 

Thanks for all of your help! 

 

Forest

 

You have almost the same setup as I do.  Check out the observatory link.  I use an Orion laser collimator almost every time I image and have the Baader MPCC field flattener to use with the Canon camera.  I also have a SV115 T2 that I use for star parties.  Your current telescope should work very well, but there are a number of things that could cause problems (collimation being the first).  Do you use a laser collimator?

 

Regards,

 

Charlie B



#25 Charlie B

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Posted 08 August 2014 - 04:57 PM

Thanks for the advice. That helps so much. I just have the simple Orion laser collimator.

 

Is there a way to align the focuser (or whatever is misaligned in the optical path) without just manual guess and check?

 

Sorry!  I did not read all the messages before I posted.  I see you use the laser collimator that I do.  First I center the laser dot in the donut on the primary with the three secondary  adjustments.  I then use the primary mirror adjustments to center the laser dot in the collimator's bull's-eye.  The MPCC works great.

 

Regards,

 

Charlie B








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