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C8, Lodestar and FR's


Ain Soph Aur

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Hi folks. After all the awesome posts about the Lodestar X2 and LL, I opted in for both a X2-M and X2-C. I am planning on using my 8SE OTA a GSO low-profile crayford (1 inch drawtube travel, 3.4" minimum height) and  Celestron 6.3 and Meade 3.3 FR's. Can anyone offer any advice on the best method//spacers when using these FR's with the GSO focuser?

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Welcome to SGL and the Lodestar club.

Here is a formula that I use to calculate the spacing between the reducer and the camera sensor. They have both your reducers listed.

http://www.wilmslowastro.com/software/formulae.htm#FR

The spacing between the OTA back and the reducer will affect the primary mirror position to obtain focus. Moving the primary mirror in a SCT will change it's focal length some. To know what focal length you actually have in operation, it's best to check by plate solving or measuring the time it takes a star at the celestial equator to cross the camera FOV.

I don't have experience using an external focuser on my SCT's, but my understanding is that they usually don't have much focus range like the standard primary mirror does. I believe the recommendation is to use the mirror to get close and then use the Crayford for fine adjustment.

Hope this helps. I'm sure you are going to enjoy your Lodestars.

Don

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To attach SCT threaded focal reducers to my 2" visual back, I use the 2" barrel that I unscrew from my GSO 2" diagonal. This has SCT threads. This barrel can also be bought separately for example here http://agenaastro.com/gso-chrome-barrel.html

The Meade 3.3 reducer is somewhat sensitive to the spacing. It's best to stay close to the recommended 51mm distance between the rear flange of the reducer and the sensor. The sensor of the Lodestar is 12.5mm inwards from it front flange, exactly where the two pieces of its housing barrel connect.

The 6.3 reducer is very tolerant within a wide range of spacings. You can pick your favorite one using the formula in Don's post or set it experimentally to match your object.

You have a very nice setup, I wish you lots of fun with it!

Clear Skies!

--Dom

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Hi Don and Dom. Thank you both for your helpful replies. I am looking forward to a real 'first light' with the X2's Sunday evening, if the forecast holds up. I was able to get somewhat of a first light when the camera's arrived a few days back, but its was through extremely thin hazy clouds in which I was only able to make out Venus, Jupiter and 2-3 of the very brightest stars. Conditions so bad that I had trouble getting LL to stack.

Don, your results have been amazing and really inspired me to buy the X2's. I even picked up one of the Orion 50mm mini guide scopes that you have had such good results with to give that a try also. :) Until I work out extender tubes for the f/3.3 and 6.3 reducers, i will be experimenting with a C80ED and the mini guider.

Thanks guys!

Brandon

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Thanks, for the kind words, Brandon.

When I use the 50mm guider, I also use a narrow band Ha filter and only view emission nebulae. Unfortunately, the good NB Ha filters are expensive with the cheapest about $175. They are well worth the money though. If you don't use the filter, the star bloat with the mini guider is pretty bad. My Ha filter is an Orion 7nm.

Starting out with wider field views is a good idea. Your c80ed should work nicely. Finding things and tracking are less problematic. Once you get the hang of things, you can move on to longer FL's with your C8 SCT.

If questions pop up just post them here.

Don

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The Meade 3.3 reducer is somewhat sensitive to the spacing. It's best to stay close to the recommended 51mm distance between the rear flange of the reducer and the sensor. The sensor of the Lodestar is 12.5mm inwards from it front flange, exactly where the two pieces of its housing barrel connect.

I believe I have worked out the spacing issues with the Meade 3.3 reducer. I happened to have a low profile Baader SCT to T2 adapter that I attached to the reducer. I have ZWO filter wheel attached to the Baader adapter directly via the T2 thread, and screwed a Baader 1.25" Clickclock EP clamp onto the T-2 thread On the tip of the stock ZWO 1.25" EP adapter. I then measured 51mm from the reducer and noted how far to seat the X2 body into the EP. This will also work very well since the Baader 1.25" Clicklock also has a nice helical micro-focuser built it which will be perfect for fine focus!

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When I use the 50mm guider, I also use a narrow band Ha filter and only view emission nebulae. Unfortunately, the good NB Ha filters are expensive with the cheapest about $175. They are well worth the money though. If you don't use the filter, the star bloat with the mini guider is pretty bad. My Ha filter is an Orion 7nm.

I've had an eye out for a second hand Orion 7nm Ha for a few days now. I've seen quite a few of your 7nm captures using the X2 Color, how well does this filter work with the mono?

Brandon

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I've had an eye out for a second hand Orion 7nm Ha for a few days now. I've seen quite a few of your 7nm captures using the X2 Color, how well does this filter work with the mono?

Brandon

Brandon,

I think it works better with mono. Because of the Bayer mask on the color LS, the resolution is reduced. Ha is in the red part of the spectrum so the red channel is the only one passing readable signal. Theoretically, the resolution should be only a third of what mono is, but Dom has shown that using it with the color LS has produced some excellent results. It comes down to individual preference. I like both. Mono offers a purer image, but color is stunning and usually a better wow factor and more liked for outreach. You have the dilemma solved. You have both.

Here's a comparison of two captures I took recently of M16, one color, one mono. There are more mono captures here in my gallery.

Don

http://stargazerslounge.com/gallery/album/3415-narrowband-ha-and-lodestar

post-36930-0-85820500-1435968845.jpg

post-36930-0-17438600-1435968882.jpg

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It's best to stay close to the recommended 51mm distance between the rear flange of the reducer and the sensor.

Hi Dom. I am looking at the www.wilmslowastro.com calcluator linked above, and it looks like the spacing CCD-FR spacing for the C8 and Meade 3.3 should be 61mm? Was 51mm a typo?

Just want to make sure I am clear on this before I order a T-2 extension for use with the 6.3 FR using the setup I mentioned above.

Thank you for your patience!

Brandon

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Thanks, for the kind words, Brandon.

When I use the 50mm guider, I also use a narrow band Ha filter and only view emission nebulae. Unfortunately, the good NB Ha filters are expensive with the cheapest about $175. They are well worth the money though. If you don't use the filter, the star bloat with the mini guider is pretty bad.

Off topic. I just realized that after I obtain a Ha filter, I can throw the Orion Mini 50mm on a vixen dovetail and mount it on the NexStar alt-az mount for the ultimate 'grab and go' EAA viewing on any clear night, Moon or not. Many nights I don't have the time nor patience to deal with the CGEM DX. Add the Celestron Starsense and let it align itself while I am eating dinner, lol. The NexStar mount has been stored unused for a long time, I am now very glad that I didn't sell it!

I imagine that this wide-field combo with LL would be very forgiving on an alt-az mount.

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Off topic. I just realized that after I obtain a Ha filter, I can throw the Orion Mini 50mm on a vixen dovetail and mount it on the NexStar alt-az mount for the ultimate 'grab and go' EAA viewing on any clear night, Moon or not. Many nights I don't have the time nor patience to deal with the CGEM DX. Add the Celestron Starsense and let it align itself while I am eating dinner, lol. The NexStar mount has been stored unused for a long time, I am now very glad that I didn't sell it!

I imagine that this wide-field combo with LL would be very forgiving on an alt-az mount.

Absolutely!

I have a Meade LS8 that I probably wouldn't have bought knowing what I know now, but I use it to go up to The Mauna Kea Visitors Center as a grab and go with my 50mm mini mounted. Now I am working on mounting my 80ST to the scope. With Lodestar Live the stacking feature will allow you to take shorter exposure and will align them to compensate for field rotation with your alt-az. The only thing I don't use much anymore are my eyepieces.

Don

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Hi Dom. I am looking at the www.wilmslowastro.com calcluator linked above, and it looks like the spacing CCD-FR spacing for the C8 and Meade 3.3 should be 61mm? Was 51mm a typo?

Just want to make sure I am clear on this before I order a T-2 extension for use with the 6.3 FR using the setup I mentioned above.

Thank you for your patience!

Brandon

Brandon and Dom,

I'm in between you guys at 57mm. It's what I use with my Meade 3.3. I also think a good approach is to get a setup where the spacing can be varied to accommodate the SCT primary mirror position effects and provide for lesser focal reductions with shorter spacing. The Lodestar's 1.25" body makes it ideal to move it to varied positions. If you need more info on potential set ups, let me know.

Don

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Excellent confirmation!

I found the Orion Ha filter second hand, actually the entire Orion Ha, O-III and S-II 'Extra-Narrowband' 7nm set for a very nice price that I couldn't pass up. Not sure how the O-III and S-II will do for EAA, but with Paul's mention of plans for 'on the fly multi-spectral stacking and processing - EAA does the hubble pallette!" for the next LL release I have my hopes up!

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Brandon,

I am not sure. I remembered 51mm.

Now I looked up my notes and they say that the FR's focal length is 85mm, hence for 0.33 reduction the distance between the reducer and sensor should be 57mm. (85-0.33*85=57) But this distance should be measured from the focal plane of the reducer that is somewhere inside of the lens system. My notes say that the focal plane is 8.4mm from the camera-side outer surface (flange) of the reducer. 57mm minus 8.4mm is not quite 51mm but is close. It is within the tolerance that I meant by "staying close to the recommended distance".

The Meade documentation, that comes with the reducer recommends two configurations with various Meade spacers and adapters. One results in f/3.3 and the other results in f/3 focal ratio. This suggests that a 10% deviation one way or the other should be just fine.

I don't have the dimensions of the Meade adapters and spacers mentioned in the documentation. Even if I had, they wouldn't provide the exact dimensions, as they were meant to work for a Meade camera, that has long been out of production. We don't know the flange to sensor distance of this camera.

There are two conclusions from the above.

1. The issue of spacings is not an entirely accurate science. 10% deviation one way or the other should be just fine.

2. The best setup for the Lodestar is one, in which the camera is held in place by a 1.25" eyepiece holder. In that case the camera can always be slid in our out of the ep holder a little bit.

Sorry if all this sounds somewhat confusing. This is the state of these arts, one needs to be a bit relaxed...

Clear Skies!

--Dom

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Thanks for the additional details. Here is the setup I have come up with using bits out of astro toolbox:

C8 + Meade f/3.3 FR

Meade f/3.3 -> Baader SCT to T2 adapter -> ZWO Filter Wheel -> 20mm T Extension -> Baader 1.25" Click Lock EP Clamp
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Brandon,

That's a nice setup, especially with the filter wheel. Now that you have the filter set, you can try some of the things Dom has been doing with various filters and stacking. Hopefully, the filters are par focal, so you don't have to refocus.

Good luck and please post some results.

Don

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  • 2 weeks later...

I finally had a chance to get the C8 out last evening with LL and the Meade f/3.3 reducer. I ran a few of my images through astrometry.net this morning and found out I was a bit off with the FR/Camera spacing as the actual f/l was f/4.1. While I wasn't getting any noticeable major aberrations, I would like work on the spacing to fine tune the reduction to 3.3.

Do any of you guys know which way the sensor needs to adjusted to lower the focal ration to f/3.3, closer in or further away from the FR? 

Thanks!

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Brandon,

More spacing will increase the reduction from the 4.1 to your desired 3.3. You can use the calculator now that you know your FR for the spacing you have. What was your FOV from the Astrmetry.net?

Don

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From the bottom of the FR thread to the senser, ~ 56mm. The X2 is deeply mounted in the Baader click-lock adapter, so pulling it out 7mm won't be an issue. Now that I know which way to go, it shouldn't be an issue fine tuning with Astrometry.net!

IMG_1060(1).JPG

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Hi Don. Adding 7mm got me from f/4.1 to f/3.7 and I left it like that last night. Next session I will try 7mm more and see if I hit f/3.3. After I get this nailed down I am going to try a few sessions at the C8 native f/10 as I need to get the SCT collimated a bit better and see how it does with smaller scale objects.

One goal I have is to image all of the PN's for the Astronomy League Planetary Nebula award program.

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