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Optimizing an 8" f4 and 8" f5 for Visual?

Beginner DIY ATM Reflector Visual Dob
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#26 topomountain

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Posted 06 October 2023 - 10:07 PM

ive done similar stuff on mine, in the process of putting my 8" f4 vixen in a hastings tube

 

you could also just slide the f4 primary and cell up into the f4.9 tube and test it to find where it comes to focus with an ep in it with no extension, just slide it up however many inches and use tape or any temp solution just lay it on a table sideways and eyeball the place to drill holes to mount the cell, not sure if your cell can slide in, some can, or you can modify it aor buy a used cell like an edmond or novak and they slide inside.  you can later cut the tube off at the bottom if it works.

 

you will also have less tube flex in the focuser if the focal plane is closer to the tube...

 

both these newts can improve by this process, you already showed you can figure this out with your sct reducers etc, same idea here.

 

the hastings tubes are not much btw

 

also as to the mirror quality, there is some variation but mostly they are pretty decent, its not a zambutto but it is a decent mirror most likely... my orion xt12i is an awesome mirror, i have had about 8 orion dobs and all were certainly useable and decent, 2 are really good, not like my vixen but still good, and the worst of them are not bad.... based on the ones i have seen anyway.


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#27 Echolight

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Posted 06 October 2023 - 11:04 PM

ive done similar stuff on mine, in the process of putting my 8" f4 vixen in a hastings tube

 

you could also just slide the f4 primary and cell up into the f4.9 tube and test it to find where it comes to focus with an ep in it with no extension, just slide it up however many inches and use tape or any temp solution just lay it on a table sideways and eyeball the place to drill holes to mount the cell, not sure if your cell can slide in, some can, or you can modify it aor buy a used cell like an edmond or novak and they slide inside.  you can later cut the tube off at the bottom if it works.

 

you will also have less tube flex in the focuser if the focal plane is closer to the tube...

 

both these newts can improve by this process, you already showed you can figure this out with your sct reducers etc, same idea here.

 

the hastings tubes are not much btw

 

also as to the mirror quality, there is some variation but mostly they are pretty decent, its not a zambutto but it is a decent mirror most likely... my orion xt12i is an awesome mirror, i have had about 8 orion dobs and all were certainly useable and decent, 2 are really good, not like my vixen but still good, and the worst of them are not bad.... based on the ones i have seen anyway.

Thanks for the tips.

 

I'll see if a cell can be slid up the tube.

 

Just from trying the fit of the rings, the f4.9 tube is quite a bit bigger than the f4 tube. The f4.9 rings are way too big for the f4 tube. 

So I would need to either use some washers on the outside of the f4 cell, or some spacers around the outside of the mirror if I put the f4 mirror in the f4.9 cell 

 

I did do a star test on both scopes last night.

 

The f4 had pinched optics. So I will have to take it apart and fix that. I had just been using it for low power richfield and never noticed. I've only had it for a very short time.

 

The f4.9 looked good after I collimated at high power on a star, other than some thermals. I need to get it cooled properly to really see how good it can get..

 

 

I'm thinking I should just order a new tube from Hastings. That sounds painless.


Edited by Echolight, 06 October 2023 - 11:36 PM.


#28 topomountain

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Posted 07 October 2023 - 10:33 AM


 

 

I'm thinking I should just order a new tube from Hastings. That sounds painless.

 

you may still consider playing with the f5 tube to get the measurements right before you drill out the hastings tube and turn tht tube intio a testing rig



#29 Echolight

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Posted 07 October 2023 - 08:42 PM

 

 

 

I'm thinking I should just order a new tube from Hastings. That sounds painless.

 

you may still consider playing with the f5 tube to get the measurements right before you drill out the hastings tube and turn tht tube intio a testing rig

 

How much lighter is a Hastings tube than a steel tube?

I almost would just as soon get a piece of scrap about six inches long and add it to the bottom of the f4 tube. Because I'm kinda liking the linear bearing focuser better than the low profile focuser on the f5. I don't think the GSO linear bearing focuser will fit on the Synta tube because of the giant hole.

 

With Moonlite and JMI gone. And no affordable high quality low profile focusers, I think I'll just add enough to get rid of the extension and use the lower half of the linear bearing focuser since all of my eyepieces focus within a half inch of each other. About 3.5 inches should do it.

If I find a real nice low profile focuser then I'll get a little bit longer full replacement tube from Hastings.

 

As for the f5, I found some 1.5 inch aluminum tube out in the shed. So am thinking of getting started on a three strut dob build.

Depending on how I do the UTA, I might either adapt an SCT Moonlite focuser that I have, or buy a super low and lightweight helical.

I think it'd look kinda crazy cool to have an 8 inch f5 with those big struts. And likely wouldn't have any trouble with sagging with the big tubing, and since it would only be about 40 inches long..

The tubing is a lot lighter weight than it looks. And it'd be easy to grab the top tube and carry it in one hand.


Edited by Echolight, 07 October 2023 - 08:49 PM.



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