Multiple Planet Images

[Peter B]

Some help and advice please.  I started my observing with a Skywatcher Startravel 102 refractor on an AZGTi Go-To mount and I really enjoy observing the night sky with that scope using the SynScan App on my mobile phone.   I've now bought a Bresser MC127 Maksutov, also on an AZGTi mount, as shown, and the other night I set both scopes up to compare them on Jupiter which was a beautiful target on a gin clear moonless night.  I was alarmed to find that the MC127 Mak showed what appeared to be three 'ghost' images of the planet which I've tried to illustrate in the attached sketch.  I've done a simple collimation check on the Mak using a bright LED torch and the defocussed pin point of light showed as concentric circles, so collimation on the Mak appears to be good.   So I should be most grateful for any advice as to why my Bresser MC127 appears to be giving me ghost images.    Thanks.

[TerryMcK]

Hi Peter. Have you tried the diagonal and eyepieces from the SkyWatcher on the Bresser. If it looks the same with them you can dismiss the eyepiece end being the problem.

I suspect that @Nightspore may have the answers though as he is purely visual.

[Peter B]

No I didn't try that but thanks for the advice, I'll try that at the next opportunity.

[Nightspore]

It sounds like a diagonal or eyepiece related problem. Synta Mak's often show a bright second diffraction ring, which is why they are unsuitable for splitting doubles IMO. If the Bresser diagonal is using an Amici prism it could produce multiple ghost images on certain bright objects. It could be a problem with internal baffling and/or the Gregory Spot, which may not have any bearing on collimation. I suspect the bright second diffraction ring on Synta Mak's is due to the Gregory Spot, I don't know for sure though.  Like Terry says; it's worth checking out the eyepiece and/or diagonal from the Bresser Mak on the ST102, just to check if it's them. 

 

BTW your ST102 seems to have an aftermarket focuser.

 

 

I've had three on mine, not including the stock focuser. After a GSO, which was a tad glitchy, I swapped the stock for a 'Sky-Watcher' (Long Perng).

 

 

Then finally a MoonLite.

 

 

The Long Perng is now on my 80ED Evostar.

 

[Peter B]

OK, got all that and thanks for the advice - much appreciated.  I'll check it all out next clear sky opportunity.

 

Yes, my ST102 has an aftermarket focuser.  You can just see the original focuser sitting on the windowsill in the picture.

[Nightspore]

1 hour ago, Peter B said:

OK, got all that and thanks for the advice - much appreciated.  I'll check it all out next clear sky opportunity.

 

Yes, my ST102 has an aftermarket focuser.  You can just see the original focuser sitting on the windowsill in the picture.

 

Hi Pete, I was just wondering what type of focuser you were using on your ST102.

[Peter B]

Hi......it's the Astro Essentials focuser.   I found the original focuser very difficult to use so I bit the bullet and fitted this one and I love it, well worth the investment.   I'm thinking of putting one on the Mak!

Edited January 13 by Peter B

[Nightspore]

2 hours ago, Peter B said:

Hi......it's the Astro Essentials focuser.   I found the original focuser very difficult to use so I bit the bullet and fitted this one and I love it, well worth the investment.   I'm thinking of putting one on the Mak!

 

Yeah, it's the same as mine. I'm pretty sure these are made by Long Perng, not totally unlike these. Some don't have holes for a finder shoe, which is a bit of a necessity for me.

 

 

I was initially worried that there was only one 1.25" adapter screw on the 2" adapter.

 

 

I soon fixed that though. I decided on a white finder shoe, as it seemed to match the Sky-Watcher colours.

 

 

The GSO I used originally had some rotation issues.

 

 

I wasn't over impressed by the stock focuser either.

 

 

It fitted the ST102 well. It's got a smoother focus and fine focus than the MoonLite IMO.

 

 

MoonLites are OK, well engineered, but the screws holding them into the OTA are basically Allen keys which are a slightly soft metal, which doesn't make them easy to tighten with an Allen key. Luckily they sit proud enough from the tube itself to be tightened with a pair of pliers.

 

 

I had a second MoonLite for the Evostar. Unfortunately it was a bit borked and also never seemed to sit well in the ED80's optical tube.

 

 

The Long Perng fits it like a glove though. The shorter drawtube of the Sky-Watcher/Long Perng doesn't give me any focusing issues as the ED80 is f/7.5. The MoonLite works fine on my f/4.9, ST102 however.

 

All's well that ends well ...

 

 

Edited January 13 by Nightspore
I need a reason?

[Peter B]

Brilliant!   Like I said, I'm thinking of putting one on the Mak but I'm not sure if there is such a thing.  There are Crayford focusers for SCTs but none for MCTs that I can find.    I phoned FLO to ask and they told me the SCT Craford focusers will not fit on a Mak which I find a bit odd.  Do you know if the SCT attachment thread is unique to SCTs or is it a universal thread on Maks as well?

[Nightspore]

12 minutes ago, Peter B said:

Brilliant!   Like I said, I'm thinking of putting one on the Mak but I'm not sure if there is such a thing.  There are Crayford focusers for SCTs but none for MCTs that I can find.    I phoned FLO to ask and they told me the SCT Craford focusers will not fit on a Mak which I find a bit odd.  Do you know if the SCT attachment thread is unique to SCTs or is it a universal thread on Maks as well?

 

I think there are a lot of problems with compatibility trying to put Crayfords on Mak's. It's a bit specialist.

 

 

I use a diagonal with a helical for fine focus on my Mak's.

 

 

Makes life easier. Having said that the stock Synta Mak focusers are actually pretty decent.

Edited January 13 by Nightspore

[Peter B]

I'm conscious that I've dragged this way off topic, but I hope it's OK!  Could you please give me the details of your diagonal with the helical focuser.  Can I just make out Baader on the diagonal?

[Nightspore]

41 minutes ago, Peter B said:

I'm conscious that I've dragged this way off topic, but I hope it's OK!  Could you please give me the details of your diagonal with the helical focuser.  Can I just make out Baader on the diagonal?

 

It's a Baader but I'm not sure which one.

 

 

I tend to use the Mak's mainly for the Moon and some planets. So, I use the Zeiss Amici a lot for the Moon, a 1.25" BBHS normal Prism and a bog-standard Baader prism (nearest to camera above). Just to confuse things I also have a 1.25" BBHS mirror diagonal. Some also now have twistlocks. William Optics also sell a helical Amici.

 

Edited January 13 by Nightspore
bad spells

[Peter B]

Great!  Thanks very much for your help and advice.   I'm definitely on the case now for a fine focuser for my Mak.

[Nightspore]

2 hours ago, Peter B said:

Great!  Thanks very much for your help and advice.   I'm definitely on the case now for a fine focuser for my Mak.

 

You're welcome. Although I find the stock focusers on my Synta Mak's are usually perfectly adequate. It is nice to occasionally have the option of a touch of fine focus with the helical.

[Peter B]

Just to finish this thread off......after a bit of research I found that several Mak owners use the Baader T-2 prism star- diagonal with 5mm focusing eyepiece with excellent results.  So even though I haven't determined yet if my ghost images are diagonal/eyepiece related I've ordered the Baader T-2 anyway.   Thanks again for all the help and advice on this thread - much appreciated.

[Nightspore]

13 minutes ago, Peter B said:

Just to finish this thread off......after a bit of research I found that several Mak owners use the Baader T-2 prism star- diagonal with 5mm focusing eyepiece with excellent results.  So even though I haven't determined yet if my ghost images are diagonal/eyepiece related I've ordered the Baader T-2 anyway.   Thanks again for all the help and advice on this thread - much appreciated.

 

Yeah, it's a good choice.

 

 

It's quite modular.

 

 

While being well priced.

 

 

Shown above on my 102mm Mak. I think the multiple images were probably caused by an eyepiece fault.

[Peter B]

I nearly bought this one instead which FLO confirms will screw onto the back of the Bresser MC127 Mak, but it weighs in at nearly a Kilo so the scope would be ridiculously unbalanced even at the end of travel of the dovetail.  It's also £189!

[Nightspore]

16 minutes ago, Peter B said:

I nearly bought this one instead which FLO confirms will screw onto the back of the Bresser MC127 Mak, but it weighs in at nearly a Kilo so the scope would be ridiculously unbalanced even at the end of travel of the dovetail.  It's also £189!

 

Well, it looks nice enough, and in my experience these Long Perng focusers are very smooth. You also have a 2" adapter choice. I'm just not sure how useful that will be on a Mak though. There will undoubtedly be internal baffles so I don't see any real advantage in 2" EP's. For me, at least, Mak's are high mag, slow f-number scopes. So the diagonal/helical is probably the best alternative anyway.