4" Refractor that can support wide field eye pieces.

[Deadlake]

For portability reasons I'd like a 4" refactor (Doublet or Tripet) that can support 2" eye pieces. I have at present a SD103S that I can use with APM 5, 13 and 17 mm XWA's by using them with a 1.25" fitting to a Baader T2 prism diagonal. However when trying to use the above EP's with a Baader 2" dielectric diagonal there is not enough infocus. A 2" Baader prism diagonal has an optical path of 100 mm, that saves 12 mm over the 2" dielectric optical path of 112 mm. This will not be enough, the issue is the scope.

I'm looking for a scope which will support the 20 mm APM XWA and an APM 30 UFF. These need a 2" diagonal. 

I suspect a Takahashi 100DL would have the same issue of not enough infocus either.

Is this correct?

The only option I've come up with is a LZOS 105 mm/F6.2, focuser will have the range to support the EP.

Any other ideas or options? I'd need to cut the tube for the SD103S to work.

 I like the Vixen SD103S however I like the wide field views more.  

 Interested in 100 mm scope, not smaller or bigger.

Also supported Bino's without a GPC would be good, back focus of around 220 mm.

Thanks

Edited June 3, 2021 by Deadlake

[Space Hopper]

Maybe a SW Esprit 100 ?

That should give you the wide field views you are after ?

[Deadlake]

27 minutes ago, Space Hopper said:

Maybe a SW Esprit 100 ?

That should give you the wide field views you are after ?

SW  Esprit 100 has a back focus of 183 mm, not enough.

What about your APM 105? 😃

Edited June 3, 2021 by Deadlake

[Stu]

The DL is longer focal length so would lose the widefield advantage. What about a DF or DC? You can remove the additional section from the focuser (or fit a Feathertouch!) so would be able to reach focus with a 2” diagonal.

This image is from a while back, but shows my Tak with a 30mm ES 82 degree in the DC using, I think, a Baader Zeiss 2” prism. Looks to be plenty of infocus available, there might even be an extension in there!

I could give it a go with a Televue Everbrite 2” and 31mm Nagler just to confirm it works?

[Deadlake]

@Stu Thats a good idea. Additional requirement is to have 220 mm of focus range to support Bino's as well without a GPC. 

A DF or DZ could do this if FT?

Cheaper then a LZOS, which will not be available until sometime in 2022...

[Stu]

6 minutes ago, Deadlake said:

@Stu Thats a good idea. Additional requirement is to have 220 mm of focus range to support Bino's as well without a GPC. 

A DF or DZ could do this if FT?

Cheaper then a LZOS, which will not be available until sometime in 2022...

Here you go:

so yes, the DC will work natively with binoviewers with either the front section of the focuser removed, or an FT.

[John]

I can bring my Ethos 21 and Nagler 31 to focus with my FC100-DL using a 2 inch diagonal. It's not the optimum wide field scope though because of the focal ratio. I have a Vixen ED102SS (F/6.5) which is my widefield frac. These eyepieces also come to focus in that with around 15mm of inwards focuser travel to spare.

 

[Deadlake]

11 minutes ago, John said:

I can bring my Ethos 21 and Nagler 31 to focus with my FC100-DL using a 2 inch diagonal. It's not the optimum wide field scope though because of the focal ratio. I have a Vixen ED102SS (F/6.5) which is my widefield frac. These eyepieces also come to focus in that with around 15mm of inwards focuser travel to spare.

 

Presume a wide field scope needs a F ratio faster than F7?

[John]

1 minute ago, Deadlake said:

Presume a wide field scope needs a F ratio faster than F7?

It depends how much true field you want.

3.5 - 4 degrees of true field will show the whole of the Veil Nebula. I get 3.8 degrees with the Vixen and the Nagler 31. Some folks like to go as far as 5 degrees so you need a faster scope for that - something around F/5.5 or faster ?

 

 

[Stu]

30 minutes ago, Deadlake said:

Presume a wide field scope needs a F ratio faster than F7?

It’s not really about focal ratio per se, more the actual focal length, although if just talking about a 4” scope then of course it is all related.

The 31mm Nag shows about 3.4 degrees in the Tak FC100DC and about 5 degrees in the Genesis. The Tak is a little tight for the whole Veil at 740mm focal length, 3.6 or 3.8 is more comfortable, but the Genesis is fab for these objects at 500mm focal length. It is a petzval design so has a nice flat field, little or no field curvature.

[Deadlake]

30 minutes ago, Stu said:

It’s not really about focal ratio per se, more the actual focal length, although if just talking about a 4” scope then of course it is all related.

The 31mm Nag shows about 3.4 degrees in the Tak FC100DC and about 5 degrees in the Genesis. The Tak is a little tight for the whole Veil at 740mm focal length, 3.6 or 3.8 is more comfortable, but the Genesis is fab for these objects at 500mm focal length. It is a petzval design so has a nice flat field, little or no field curvature.

An NP101 did cross my mind as well..... Genesis no longer available.

An FSQ-106 from RO is around £4000, a little cheaper then the LZOS mark II  and you can actually buy.... 

Edited June 3, 2021 by Deadlake

[Highburymark]

1 hour ago, Deadlake said:

@Stu Thats a good idea. Additional requirement is to have 220 mm of focus range to support Bino's as well without a GPC. 

A DF or DZ could do this if FT?

Cheaper then a LZOS, which will not be available until sometime in 2022...

The DC is the only FC-100 to have that removable (green) section just in front of the focuser. Makes it really flexible for binoviewing and travel. I’ve never reattached mine after removing it years ago. 

[John]

1 hour ago, Stu said:

It’s not really about focal ratio per se, more the actual focal length, although if just talking about a 4” scope then of course it is all related....

 

Good point Stu. I was assuming that we were talking about ~4 inch scopes in my earlier post.

 

 

[Space Hopper]

4 hours ago, Deadlake said:

SW  Esprit 100 has a back focus of 183 mm, not enough.

What about your APM 105? 😃

The refractor in question is currently going modification.

Its current 2.5" focuser has a drawtube length of 90mm, and will allow focus with a bino sans GPC.

However, with the 2.6x gpc in place i run out of focus to where the focuser is fully racked out.

I can get it to focus by pulling the whole rig out and unseating it about 10mm or so but this is far from ideal.

I'd imagine a 2" diagonal and big 2" glass would be a similar situation, although i don't currently have any 2" eyepieces to test that.

The focuser on my scope has its limitations, so i'm upgrading it for something more robust ; not just for binoviewing, but for future imaging plans as well.

[Deadlake]

52 minutes ago, Space Hopper said:

The refractor in question is currently going modification.

Its current 2.5" focuser has a drawtube length of 90mm, and will allow focus with a bino sans GPC.

However, with the 2.6x gpc in place i run out of focus to where the focuser is fully racked out.

I can get it to focus by pulling the whole rig out and unseating it about 10mm or so but this is far from ideal.

I'd imagine a 2" diagonal and big 2" glass would be a similar situation, although i don't currently have any 2" eyepieces to test that.

The focuser on my scope has its limitations, so i'm upgrading it for something more robust ; not just for binoviewing, but for future imaging plans as well.

Are you saying get a FT for it?  😃 GPC aren't hat bad, needed for correcting the prims in the bino originally?

Is it the F6.2 or the F8?

Thanks

[vineyard]

This probably won't be v helpful b/c I don't think too many of them were ever made (maybe 100 odd based on a CN post), but fwiw I'm exceedingly happy w my TV102iis.  It's the BV friendly version so it can be used for mono (w a solid extension that comes w it), or native for BV.  Great for AP too (does need a flattener).  If you ever see one for sale, highly recommend snapping it up (no, that's not a precursor to listing mine  - not for sale!).

[Stu]

36 minutes ago, vineyard said:

This probably won't be v helpful b/c I don't think too many of them were ever made (maybe 100 odd based on a CN post), but fwiw I'm exceedingly happy w my TV102iis.  It's the BV friendly version so it can be used for mono (w a solid extension that comes w it), or native for BV.  Great for AP too (does need a flattener).  If you ever see one for sale, highly recommend snapping it up (no, that's not a precursor to listing mine  - not for sale!).

Very nice scopes, but more similar to the Tak DL or my FL102S at 880mm focal length. It won’t give the very wide fields of view possible with the shorter focal length scopes that I think Deadlake is looking for.

[vineyard]

8 minutes ago, Stu said:

Very nice scopes, but more similar to the Tak DL or my FL102S at 880mm focal length. It won’t give the very wide fields of view possible with the shorter focal length scopes that I think Deadlake is looking for.

Ah ofc, overlooked that.

(Am not a good judge of measuring FOV visually so, just in case one ever comes up, the manual says it can do 3 deg w a 55mm Plossl or 41mm Panoptic.  3.3deg possible w a 0.8x reducer for prime focus AP).

Good luck w the choice - that LZOS does look v nice but ouch re the price (there was a Baader 95/580 Travel Companion which sold recently here on SGL for c GBP3k)?

[Space Hopper]

9 hours ago, Deadlake said:

Are you saying get a FT for it?  😃 GPC aren't hat bad, needed for correcting the prims in the bino originally?

Is it the F6.2 or the F8?

Thanks

Yes a Feathertouch. In for a penny, in for a pound.

Yes, the GPC is definitely needed for high power, but not for low. With my 24mm @ 27x i can nicely frame M45 into the field of view.

My scope is the F6.2 version.

 

[Louis D]

If the focuser can accept a 3" diagonal, the 30mm ES-100 comes into play along with custom Siebert 3" observatory eyepieces.  Many refractors intended for astrophotography come with 3" or larger focusers, so there might be some options there if there is enough back focus, which there should be since they're intended to accept filter wheels, OAGs, and other gear in between the focuser and camera.

[Deadlake]

7 hours ago, Space Hopper said:

Yes a Feathertouch. In for a penny, in for a pound.

Yes, the GPC is definitely needed for high power, but not for low. With my 24mm @ 27x i can nicely frame M45 into the field of view.

My scope is the F6.2 version.

 

Interested to hear what the differences are between standard and uprated version. It’s not although I’ll be able to order one anytime soon, given the availability of lens cells…. Next year, however the FT and rube adds a thousand to the price…

In addition what it performs like once barlowed if possible. You can always add focal length but cannot take it away, without cutting the tube. 😃

I know Takahashi Q extender might be an option, works with AP scopes as well.

Edited June 4, 2021 by Deadlake

[Deadlake]

On 03/06/2021 at 10:16, John said:

I can bring my Ethos 21 and Nagler 31 to focus with my FC100-DL using a 2 inch diagonal. It's not the optimum wide field scope though because of the focal ratio. I have a Vixen ED102SS (F/6.5) which is my widefield frac. These eyepieces also come to focus in that with around 15mm of inwards focuser travel to spare.

 

What mount do you use with say a Ethos 21 and Vixen ED102SS (F/6.5)?

When I use my SD103S on a ScopeTech Zero with an APM XWA EP the scope will move any time I change an EP due to the larger then usual weight of the EP. 

[John]

31 minutes ago, Deadlake said:

What mount do you use with say a Ethos 21 and Vixen ED102SS (F/6.5)?

When I use my SD103S on a ScopeTech Zero with an APM XWA EP the scope will move any time I change an EP due to the larger then usual weight of the EP. 

I use either a Skytee II or the Giro Ercole.

The Ercole needs the axis lock to be used when switching heavy eyepieces. The Skytee II has enough "sticktion" in it's axis to handle the changeover without the need to lock the movement.

 

 

[Deadlake]

35 minutes ago, John said:

I use either a Skytee II or the Giro Ercole.

The Ercole needs the axis lock to be used when switching heavy eyepieces. The Skytee II has enough "sticktion" in it's axis to handle the changeover without the need to lock the movement.

 

 

Any idea what the modern day equivalent of the Vixen ED102SS (F/6.5) would be?

I'd imagine the weight would be similar to the SD103S.

[John]

34 minutes ago, Deadlake said:

Any idea what the modern day equivalent of the Vixen ED102SS (F/6.5) would be?

I'd imagine the weight would be similar to the SD103S.

The ED102SS weighs around 4kg with tube rings and a diagonal fitted.

Today's nearest equivalent is the 102mm F/7 FPL-53 doublet refractors of which there seem to be versions by Telescope Services, Altair, Technosky etc.