127 Mak with a reducer

[bomberbaz]

Thinking about getting a 127 mak for a travel basis scope. Do not want a goto as i am enjoying star hopping when out with it but thing that puts me of the mak is the near F12 - 1500 Focal length makes it tricky to use manual. So I thought of adding a 0.5 reducer that can be screwed into the diagonal before inserting into the ota. This should then reduce FL to 750 at a litle under F6.

This makes the OTA more manageable for manual work and also my thinking is it will still be fine on a decent zoom ep.

Has anyone done similar with a mak and can anybody comment on any possible issues that I have overlooked.

TIA

Steve

[RT65CB-SWL]

Hi Steve,

I use my C6/SCT with a Celestron focal reducer mounted on my Giro or GP, as I too enjoy star hopping. I have not found any issues to date. Saying that, I am more of a lunar and planetary [visual] observer at the present time. 

[bomberbaz]

6 hours ago, Philip R said:

Hi Steve,

I use my C6/SCT with a Celestron focal reducer mounted on my Giro or GP, as I too enjoy star hopping. I have not found any issues to date. Saying that, I am more of a lunar and planetary [visual] observer at the present time. 

Thanks Philip. I think I will go down this track at some point in the future then. Thanks for the reply.

Steve

[astronymonkey]

Hi steve,

I too have a 127 mak for travel wnd find its a great scope. To be honest im a star hopper at heart but my mak is the first goto scope I have and I find it a great help. The main thing is the number of objects I can crqm into an hour outside with the scope meaning it doesnt eat into family time when away and the tracking means its great when showing others the sky.

As for your plans, ill be waiting to hear others thoughts but remember that the 127mak is a 1.25inch fitting and I wonder if adding a focal reducer would still allow it to come into focus. Am I right I  thinking that it woukd double the fov ?

 

Cheers

[bomberbaz]

3 minutes ago, astronymonkey said:

Hi steve,

I too have a 127 mak for travel wnd find its a great scope. To be honest im a star hopper at heart but my mak is the first goto scope I have and I find it a great help. The main thing is the number of objects I can crqm into an hour outside with the scope meaning it doesnt eat into family time when away and the tracking means its great when showing others the sky.

As for your plans, ill be waiting to hear others thoughts but remember that the 127mak is a 1.25inch fitting and I wonder if adding a focal reducer would still allow it to come into focus. Am I right I  thinking that it woukd double the fov ?

 

Cheers

you are indeed right and this is exactly what i would be aiming for. A 30mm plossl would give you around 2 DEGREES FOV and so making star hopping much easier. It might be a while before this happens but I think its on the cards now. 

[astronymonkey]

I use a 32mm plossl which is as low as you can go in this scooe apparently due to the field stop and although its a bit narrow its no worse than the widest filed in my big dob. I can fit the whole thing, Including a 7ah skywatcher power pack into a big toolbox from b&q with only the tripod left out so its great for camping trips and the box doubles as a seat.

cheers

[Ruud]

Hello Steve. A 1500 mm Mak with a 1.25" baffle tube has room for a 1.2° field: maximum tfov = 2* arctan ( (31.75/2) /1500 ) = 1.21 degrees. Unless the baffle tube is wider than 1.25" you will get vignetting beyond 1.2 degrees.

If you know the diameter (D) of the baffle tube you can calculate the maximum unvignetted true field: 
tfov = 2 * arctan ( (D / 2) / 1500 )

Vignetting does not become visible immediately, but at 2° I expect it would be obvious in a small Mak.

There's another consideration. Image quality might suffer from a reducer. An original Maksutov has quite a bit more field curvature than a Rutten-Maksutov so I think you'd need a reducer specifically designed for the type of Mak you'l get. There's not just field curvature, but also coma and astigmatism to consider, if you plan to use an image circle larger than the telescope was designed for. And there's the point whether or not you'll be able to reach focus with the eyepieces you plan to use.

I hope the reducer solution is a viable one. Maks are wonderful telescopes, but somewhat limited when it comes to wider views.

[bomberbaz]

17 hours ago, Ruud said:

Hello Steve. A 1500 mm Mak with a 1.25" baffle tube has room for a 1.2° field: maximum tfov = 2* arctan ( (31.75/2) /1500 ) = 1.21 degrees. Unless the baffle tube is wider than 1.25" you will get vignetting beyond 1.2 degrees.

If you know the diameter (D) of the baffle tube you can calculate the maximum unvignetted true field: 
tfov = 2 * arctan ( (D / 2) / 1500 )

Vignetting does not become visible immediately, but at 2° I expect it would be obvious in a small Mak.

There's another consideration. Image quality might suffer from a reducer. An original Maksutov has quite a bit more field curvature than a Rutten-Maksutov so I think you'd need a reducer specifically designed for the type of Mak you'l get. There's not just field curvature, but also coma and astigmatism to consider, if you plan to use an image circle larger than the telescope was designed for. And there's the point whether or not you'll be able to reach focus with the eyepieces you plan to use.

I hope the reducer solution is a viable one. Maks are wonderful telescopes, but somewhat limited when it comes to wider views.

To be honest the reducer is likely to be used only on very wide dso's and for star hopping/finding. I get that you are tinkering with light path quite a lot and this will cause some quality issues but with the aim of what i am trying to do which is a large increase in tfov, its something I can go with.

Beyond that I think I will manage with a simple zoom and the 30mm plossl as below.

30mm plossl and reducer x25 - 2 deg tfov (Finder/star hop)

30mm plossl no reducer x50 - 1.00

16mm zoom no reducer x94 - 0.53

12mm zoom no reducer x125 - 0.44

8mm zoom no reducer x188 - 0.32