Looking for diagonal adapter

[msacco]

Hi guys, looking to buy a diagonal adapter, and I wonder what would be a good choice, and how much difference does it make?

Since my country is extremely expensive, I'm going to buy in ebay/aliexpress, so looking for suggestions.

I'm not sure how much I wanna spend on it, as I'm not looking for something very expensive, but just something decent that will work properly and do the job.

This looks ok to me for example: https://www.aliexpress.com/item/OOTDTY-Telescope-Mirror-Erecting-1-25-90-Degrees-Zenith-Diagonal-Adapter-Positive-Prism-Optic-Astronomical-Eyepiece/32865889922.html?

Total price for this is 9.8$ including shipping, there are a few other options, some cheaper, some more expensive.

Any recommendations? Thanks!

[Cosmic Geoff]

Why do you want to buy a diagonal? If you have a telescope and a diagonal came with the kit, I doubt very much that a diagonal costing a mere $6.81 will perform any better.

Even if you buy a premium diagonal you will not necessarily see any improvement looking through the eyepiece. When I upgraded a basic diagonal to a Circle T I could not see any difference.  Even the cheap ones have adequate optical flatness. Pay more, and the improvements are in build quality, reflectivity and coating life.

If you don't have a diagonal or are replacing one that broke, the one you cite will probably do.

[msacco]

5 minutes ago, Cosmic Geoff said:

Why do you want to buy a diagonal? If you have a telescope and a diagonal came with the kit, I doubt very much that a diagonal costing a mere $6.81 will perform any better.

Even if you buy a premium diagonal you will not necessarily see any improvement looking through the eyepiece. When I upgraded a basic diagonal to a Circle T I could not see any difference.  Even the cheap ones have adequate optical flatness. Pay more, and the improvements are in build quality, reflectivity and coating life.

If you don't have a diagonal or are replacing one that broke, the one you cite will probably do.

I don't have a diagonal at all

So basically, just get the cheapest I could find?

[John]

What sort of telescope do you have ?

 

[msacco]

Just now, John said:

What sort of telescope do you have ?

 

Skywatcher 200p with EQ5 goto.

[Cosmic Geoff]

Isn't that a Newtonian? You can't use a diagonal with that! The added optical path length is just one reason.

[Cornelius Varley]

1 minute ago, msacco said:

Skywatcher 200p with EQ5 goto.

The telescope probably won't reach focus if you use a diagonal, reflectors aren't designed to be used with one.

[msacco]

Just now, Cosmic Geoff said:

Isn't that a Newtonian? You can't use a diagonal with that! The added optical path length is just one reason.

 

Just now, Cornelius Varley said:

The telescope probably won't reach focus if you use a diagonal, reflectors aren't designed to be used with one.

Really? What is the reason for that? Doesn't it simply mirrors whatever I receive in the eyepiece?

[Cornelius Varley]

The eyepiece needs to be a certain distance from the secondary to reach focus. If you place a diagonal in the holder the eyepiece will now be farther away from the secondary. Diagonals and reflectors don't work together.

[msacco]

5 minutes ago, Cornelius Varley said:

The eyepiece needs to be a certain distance from the secondary to reach focus. If you place a diagonal in the holder the eyepiece will now be farther away from the secondary. Diagonals and reflectors don't work together.

So hmm...is there anything similar I can use for a newtonian? ?

As you probably know sometimes the angle gets really uncomfortable to watch.

[Cosmic Geoff]

2 minutes ago, msacco said:

So hmm...is there anything similar I can use for a newtonian? ?

As you probably know sometimes the angle gets really uncomfortable to watch.

This is one reason I bought a SCT. ?

Failing that, you can rotate the tube in the tube rings to get the eyepiece in a better position (maybe difficult with an aligned GoTo).  And maybe use a step-up if the eyepiece is high.  The 8" Newtonian/equatorial mount combination is just not user-friendly.

[michael8554]

4 minutes ago, msacco said:

sometimes the angle gets really uncomfortable to watch.

One of the advantages of the Newtonian over the Refractor is that the focuser and eyepiece are usually in a comfortable position - you can rotate the scope in the securing rings until you're happy.

Michael 

[msacco]

5 minutes ago, Cosmic Geoff said:

This is one reason I bought a SCT. ?

Failing that, you can rotate the tube in the tube rings to get the eyepiece in a better position (maybe difficult with an aligned GoTo).  And maybe use a step-up if the eyepiece is high.  The 8" Newtonian/equatorial mount combination is just not user-friendly.

SCT = catadioptric?

As you already said, don't really think it's possible(or easy) to rotate the tube with an aligned GoTo. What does a step up means?

Any other recommendations? Including accessories or just tips? ^^

1 minute ago, michael8554 said:

One of the advantages of the Newtonian over the Refractor is that the focuser and eyepiece are usually in a comfortable position - you can rotate the scope in the securing rings until you're happy.

Michael 

Yes, and no, as I said above, don't really think it's a good solution with a GoTo.

[John]

No reason that you can't rotate the tube in the rings as far as I can see. You could add a single tube ring (or any sort of ring as long as it fits the tube and is reasonably strong) to the scope, above the one that is nearest to the eyepiece. They you can keep the other 2 rings slightly loose and rotate the tube with the additional ring making sure that the scope does not slide through the other tube rings.

Your scope will perform optically as well or better than an 200mm SCT - seems a pity to change it.

This thread is all about dealing with this issue:

 

[msacco]

1 minute ago, John said:

No reason that you can't rotate the tube in the rings as far as I can see. You could add a single tube ring (or any sort of ring as long as it fits the tube and is reasonably strong) to the scope, above the one that is nearest to the eyepiece. They you can keep the other 2 rings slightly loose and rotate the tube with the additional ring making sure that the scope does not slide through the other tube rings.

Your scope will perform optically as well or better than an 200mm SCT - seems a pity to change it.

This thread is all about dealing with this issue:

 

Did I mention anything about replacing my 200p? ? Hell no, I love it.

Well, I guess I might give it a try next time I'm going out  Did you try doing that using a GoTo? And thanks for sharing the post!

[John]

5 minutes ago, msacco said:

Did I mention anything about replacing my 200p? ? Hell no, I love it.

Well, I guess I might give it a try next time I'm going out  Did you try doing that using a GoTo? And thanks for sharing the post!

Glad you intend to keep it

I don't use GOTO myself now but I have used it in the past and I can't see why rotating the tube in the rings would be a problem, as long as you don't disturb the alignment of the mount.

 

[msacco]

6 minutes ago, John said:

Glad you intend to keep it

I don't use GOTO myself now but I have used it in the past and I can't see why rotating the tube in the rings would be a problem, as long as you don't disturb the alignment of the mount.

 

Well, I believe I will plan on getting something bigger in the future, but that's rather far in the future.

Regarding the rotation, well from my very short experience, any slight movement to the mount, tube, finderscope, eyepiece etc really makes a rather huge difference. Even if I rotate the tube and move it 1 cm to some direction, I believe it will make a difference, and might even get the GoTo out of alignment.

But again, I won't know without trying, so that's about it.

[John]

When you rotate the tube, the scope rotates around it's optical axis but the optical axis does not move itself. The GOTO system is designed to point the optical axis at a target so this should not be affected by rotating the tube. Likewise the finder scope should be aligned with the optical axis of the main scope so should still be pointing accurately after the tube is rotated.

If you do it carefully (ie: without moving the scope in RA or DEC and without changing the polar alignment of the mount, the GOTO should be unaffected. I realise that this can be awkward in the dark but its either that or get used to some interesting contortions to reach the eyepiece or put the scope on an alt-azimuth mount

Fitting rings which allow for tube rotation is a popular modification with newtonians on equatorial mounts.

[msacco]

1 minute ago, John said:

When you rotate the tube, the scope rotates around it's optical axis but the optical axis does not move itself. The GOTO system is designed to point the optical axis at a target so this should not be affected by rotating the tube. Likewise the finder scope should be aligned with the optical axis of the main scope so should still be pointing accurately after the tube is rotated.

If you do it carefully (ie: without moving the scope in RA or DEC and without changing the polar alignment of the mount, the GOTO should be unaffected. I realise that this can be awkward in the dark but its either that or get used to some interesting contortions to reach the eyepiece or put the scope on an alt-azimuth mount

Fitting rings which allow for tube rotation is a popular modification with newtonians on equatorial mounts.

Yes I'm aware that theoretically if you rotate the tube on it's axis it shouldn't make a difference, what I'm saying is that I'm not sure how easy it's to do that

I'll try modifying my tube so I'll be able to achieve that easily. Thanks for the help!

[michael8554]

Yes I agree PA and Star Alignment will change if you rotate.

But you can always set up with the focuser in a compromise position ?

Step up = step stool or step ladder I'd guess ?

Michael 

[Gabby76]

Another trick with Newtonian on a EQ mount is to point the focuser straight up. 

The eyepiece will most times be in a decent viewing position. 

As John mentioned above, fitting rings makes spinning the tube easier but if the budget is tight then wooden embroidery hoops can be used as well and these are much cheaper than a new set of rings.