Sorting new Maksutov issues...

[parallaxerr]

I've been lucky enough to get 1st, 2nd & 3rd light with my new Orion 150mm Maksutov this week. Had some great views of Jupiter so far when the seeing allowed, managing to catch both Io and Ganymede transit shadows and re-apperances on the limb

Optically, I am very impressed but I have identified a few small issues with the scope I wish to resolve:

1. The focuser is not great. There's a reasonable amount of mirror shift but more importantly a horrid little notch right around the point of focus. This is leading me to consider a crayford focuser.

2. Balance - it's already back end heavy with a 2" diagonal so adding a focuser will just make this worse. I am also considering a dovetail clamp mounted counterweight for the front.

3. There's a small floating donut shaped ghost reflection on bright objects - assuming it's the primary reflection.

 

Given that I am considering the focuser upgrade which will exacerbate the balance issues, a lighter diagonal may be in order.

 

Would a 1.25" prism diagonal (Tak) help with the reflection I am seeing, as the prisms are often touted to reduce scatter etc?

Edited August 23, 2021 by parallaxerr

[Louis D]

35 minutes ago, parallaxerr said:

3. There's a small floating donut shaped ghost reflection on bright objects - assuming it's the primary reflection.

That's usually caused by reflections off of the interior of the rear baffle tube.  Try putting flocking material in it.  Generally, just roll it up in a tube after cutting it to length and push it up in there without removing the sticky backing covering.  Friction will tend to keep it in place.

[parallaxerr]

4 minutes ago, Louis D said:

That's usually caused by reflections off of the interior of the rear baffle tube.  Try putting flocking material in it.  Generally, just roll it up in a tube after cutting it to length and push it up in there without removing the sticky backing covering.  Friction will tend to keep it in place.

Thanks Louis. As luck would have it, I recently ordered a fresh roll of flocking material, I'll try this tonight 👍

[Pixies]

Flocking the baffle tube shown here:

I did similar for a Mak90. I removed the backing and stuck it against the inside of the baffle tube, rather than letting it rest in place. I found the best way was to wrap it around a pencil, sticky-side out, and then press it against the inside of the baffle tube and run the pencil in the opposite direction that you rolled the flocking material, pushing outwards as you go. The FLO flock isn't too sticky and makes this easy. Didn't need much!

 

[parallaxerr]

3 minutes ago, Pixies said:

Flocking the baffle tube shown here:

I did similar for a Mak90. I removed the backing and stuck it against the inside of the baffle tube, rather than letting it rest in place. I found the best way was to wrap it around a pencil, sticky-side out, and then press it against the inside of the baffle tube and run the pencil in the opposite direction that you rolled the flocking material, pushing outwards as you go. The FLO flock isn't too sticky and makes this easy. Didn't need much!

 

That's great, thanks. Looks like the flocking offers a significant improvement in contrast too!

[Pixies]

13 minutes ago, parallaxerr said:

That's great, thanks. Looks like the flocking offers a significant improvement in contrast too!

I did it to remove that odd halo/ring that appeared to expand out when a bright star passed outside the field stop. I can;t say that I saw a difference with contrast for astronomical observing, though.

[johninderby]

The Baader prism comes with an eyepiece micro focuser for fine focusing.

https://www.rothervalleyoptics.co.uk/baader-prism-diagonal-t-2-90-with-focusing-eyepiece-holder-and-125-nosepiece.html

 

Another focuser option is using a 1.25” crayford focuser. Much lighter than a typical 2” add on focuser. Focuser isn’t too expensive but the SCT adaptor is a special order.

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p11734_TS-Optics-1-25----T2-Crayford-Focuser-for-Refractors--Cassegrains-----.html

 

 

Edited August 23, 2021 by johninderby

[parallaxerr]

Well John, you read my mind.....

I just flocked the baffle tube and did rather a good job, if I do say so myself. Removed the backing so it's stuck in there nice and straight and even.

I switched out the 2" diagonal for a 1.25" which has re-established a good balance, actually slightly front end heavy with the dew shield on.

More to your point John, I couldn't find stock of the baader, so I ordered the cheaper option of a ZWO microfocuser and 1.25" nose piece. Should look quite snazzy with the red Altair diagonal.

[johninderby]

Also did try the Svbony version of the microfocuser.which worked quite well.and had more travel than the Baader microfocuser.

Edited August 23, 2021 by johninderby

[Zermelo]

4 hours ago, johninderby said:

The Baader prism comes with an eyepiece micro focuser for fine focusing.

https://www.rothervalleyoptics.co.uk/baader-prism-diagonal-t-2-90-with-focusing-eyepiece-holder-and-125-nosepiece.html

That looks rather nice. I've been considering a dielectric diagonal for my Mak, and I already have a Baader helical focuser on my other scope, which works well.
Reviews suggest that the prism has slightly better contrast and less scatter than a dielectric, and CA problems shouldn't be an issue on a Mak. I can't see a transmission figure quoted, but should be comparable with a dielectric?
 

[johninderby]

There are two versions of the T2 prism. The cheaper standard and the Zeiss prism. Not a lot of difference performance wise but the Zeiss has a few mm more aperture. 

Suits longer focal lengths such as a mak and maybe a tiny bit better than the dielectric mirror diagonal.

I use one on my Classical Cassegrain 6” which has replaced my mak.

Edited August 23, 2021 by johninderby

[F15Rules]

10 hours ago, johninderby said:

There are two versions of the T2 prism. The cheaper standard and the Zeiss prism. Not a lot of difference performance wise but the Zeiss has a few mm more aperture. 

Yep, I have the standard Baader T2 prism which has 32mm clear aperture will work well with most 1.25" eyepieces. I use it regularly on my F8 Tak and contrast is superb👍.

I also use a  very good 2" dielectric for my big 2" Axiom LX eyepieces, and both seem to offer identical performance to my eyes.

Dave